Lange Review Ultrasonography Examination, 4th Edition

Answers and Explanations

At the end of each explained answer, there is a number combination in parentheses. The first number identifies the reference source; the second number or set of numbers indicates the page or pages on which the relevant information can be found.

1. (D) The acronym DICOM stands for digital imaging and communication in medicine, which are the standards for distributing and viewing all kinds of medical images and files. This is the universal standard protocol that allows digital information to be compatible with all medical manufacturing equipment. (2:148)

2. (E) An ultrasound pulse takes up physical space in length and therefore is referred to as spatial pulse length. Spatial pulse length is defined as the product of the number of cycles in the pulse and its wavelength. This is generally shorter for higher frequencies since the wavelength is shorter. (2:25)

3. (E) Axial resolution, also called longitudinal, range, or depth resolution, is determined by the wavelength, damping, and frequency. Axial resolution improves with increased frequency. Damping (backing) material causes the number of cycles per pulse to decrease, thus improving axial resolution. (2:76–81; 24:41)

4. (B) Lateral resolution is defined as having the ability to distinguish between two structures that are in a plane that is perpendicular to sound path and is improved by reducing the beam diameter by focusing with acoustic lens or acoustic mirrors or using higher frequency transducer. (2:79; 24:45)

5. (C) The beam of an unfocused transducer diverges in the Fraunhofer zone. (1:351)

6. (C) Reverberation artifacts are present when two or more strong reflectors are located within the beam with decreasing intensity. Reverberation artifacts occur between the face of the transducer and a specular reflector. (2:263; 20:598)

7. (A) The acronym ALARA denotes “as low as reasonably achievable.” This principle was implemented to reduce the risk while obtaining diagnostic images. Minimize scanning time when possible, increase the gain and decrease the power output, use the highest frequency transducer when possible, and use a focus transducer. (2:322; 18:231)

8. (B) The grating side lobes are reduced by apodization, subdicing, and harmonic imaging. (2:105; 18:190)

9. (A) Coded excitation uses digitally coded pulses to provide good penetration and high resolution at the same time. It also improves signal-to-noise ratio, axial resolution, and contrast resolution. (2:92)

10. (B) Patient identification errors have a significant negative impact on patient safety. Return the patient to the ward for appropriate identification and tagging. (19:97)

11. (A, B, C, D, E) All rods must be used to check registration accuracy. (18:21; 21:282–283)

12. (A) See Fig. 1–24 and Table 1–3, Study Guide. (18:21; 21:282–283)

13. (B) See Fig. 1–24 and Table 1–3, Study Guide. (18:21; 21:282–283)

14. (D) See Fig. 1–24 and Table 1–3, Study Guide. (18:21; 21:282–283)

15. (C or E) See Fig. 1–24 and Table 1–3, Study Guide. (18:21; 21:282–283)

16. (C) Decreasing the spatial pulse length improves axial resolution. Axial resolution is equal to one-half of the spatial pulse length. (2:25)

17. (B) A rule of thumb approximating the attenuation coefficient of a reflected echo in soft tissue is 0.5 dB/cm/MHz. Thus, the attenuation coefficient will be one-half the operating frequency.

Image

18. (B) Improper axial (along-the-beam) position (2:43–44)

19. (D) Weakly attenuating structures (2:277)

20. (A) Directly proportional to the velocity of the reflector (2:170–171)

21. (A) The frame rate is between 15 and 30 frames per second (fps). Color Doppler has a slower frame rate, about 15 fps. Note: The scan converter in most modern systems turns the scanning frame rate (which is the subject of this question) into a display frame rate (or video frame rate), which is usually faster (30 video fps). This is done by displaying the same scan frame more than once if the scan frame is less than video rate. CRT television monitors have an image rate of 30 fps using 525 horizontal lines. Most ultrasound departments today use LCD flat-panel display using 60 fps and a resolution of 720 pixels to 1,080 pixels. (1:363; 2:143)

22. (E) Use a certified language line (19:41)

23. (B) Smaller beam diameter. Intensity is defined as power per unit beam area; as the beam area decreases, the intensity increases. (18:135)

24. (C) Increased by four times. Intensity equals the square of the amplitude. (2:28)

25. (A) Increased with tissue thickness. Attenuation is the product of the attenuation coefficient and path length. Attenuation is associated with frequency tissue characteristic, and depth. High frequency has high attenuation and poor penetration. Tissues such as bone and air have high attenuation when compared to water. (2:22)

26. (A) The matching layer is located between the active element and the skin. Both the matching layer and the acoustic gel reduce the reflection of ultrasound at the surface. The matching layer is chosen to be at a value approximately equal to the mean of impedances of the material on either side of it. (2:59; 18:190)

27. (D) After confirming that the patient name and medical record number are correct, an additional confirmation is the date of birth. (19:96–97)

28. (D) Use approved disinfectant (16:130–135)

29. (B) Depends on crystal thickness. Thickness equals one-half the wavelength. (2:55–56)

30. (C) The time taken to complete one cycle (one wavelength) (2:20; 18:20)

31. (D) Ratio of smallest to largest power level (18:257–262)

32. (E) Picture archiving and communications systems (PACS) provides the ability of digital images to be transmitted over the internet or viewed on workstations. This is not be confused with Digital Imaging and Communication in Medicine (DICOM), which is a standard to permit communication of information between manufacturers. (2:145–148)

33. (B) Increases the maximum depth that can be imaged (20:209; 18:51)

34. (C) Are not confirmed below 100 mW/cm2 SPTA for unfocused beam and are not confirmed below 1 W/cm2 (1,000 mW/cm2) SPTA for focused beam (2:325)

35. (B) The patient has the right to consent to or refuse any treatment by the hospital. A patient can revoke an uninformed consent at any time. (19:181)

36. (A) The first step is to introduce yourself to the patient with your employment ID and title visible. The second step is to be sure you have the right patient. The third step is to explain the ultrasound procedure to the patient. (8:70)

37. (E) The transvaginal transducer should be disinfected and covered with a probe cover after each patient. (16:130–135)

38. (D) Reduce the transmit power. The ALARA principle also suggests minimizing scanning time when possible, increasing the gain, and using the highest frequency transducer when possible. (2:322; 18:231)

39. (A) A mathematical process in which a waveform is multiplied by time-shift versions of itself. (2:188; 10:15)

40. (A) Stable cavitation occurs when the oscillation of the microbubbles does not collapse. (2:328; 20:622)

41. (D) The least likely possible potential ultrasound bioef-fect is high-frequency transducers. Low-frequency transducers have a higher potential for bioeffects. (2:394)

42. (A) Harmonic frequency sound waves are derived from nonlinear or asymmetrical wave propagation. (2:105–108; 20:664–665)

43. (D) Propagation speed is determined by the tissue medium. Different tissue media have different propagation speeds. The speed is highest in solids and lowest in gases. The average propagation speed in soft tissue is 1,540 m/s. (2:20; 20:96–97)

44. (C) The prefix “giga” denotes 1,000,000,000 or 109, which is a unit of measurement in the metric system. (18:6)

45. (C) Twenty-five percent. The reflection coefficient (R) is equal to

Image

where Z1 and Z2 are the acoustic impedances of each material. (1:366)

46. (A) Higher frequency transducers usually produce shorter spatial pulse lengths and thus improve axial resolution. (2:76–81)

47. (A) Longitudinal wave. In this type of wave, the motion in which the particle displaces in the medium is parallel to the direction of wave propagation. Transverse waves is the particle displacement perpendicular to the direction of wave propagation. (2:18; 10:153; 20:82–83)

48. (A) 0.3 mm (18:33)

Image

49. (D) The difference in specific acoustic impedances. The fraction of sound reflected at an interface (r) is given by

Image

where z1 and Z2 are the acoustic impedances of the boundary material. (2:37–38; 8:16)

50. (A) Image

51. (B) There are two conditions in which refraction occurs. First is an oblique incidence and the second is when the propagation speeds of the two media are different. Refraction is described by Snell’s law, which relates the incident angle (θi) to the transmitted angle (θt) to the relative velocities of the two media making up the interface. (2:39; 18:89–99)

Image

52. (D) Equal to the product of density and velocity for longitudinal waves (2:36–37; 20:153)

53. (E) The speeds of ultrasound in soft tissue are 1,540 m/s, 154,000 cm/s, 1.54 mm/μs, 0.154 cm/μs, or one mile per second. (2:20; 18:35)

54. (B) 8.0 cm. To change millimeters (mm) into centimeters (cm), move the decimal point one space to the left, and to change centimeters to millimeters, move the decimal point one space to the right. Recall that 10 mm = 1 cm. (18:5; 20:40)

55. (B) There are two conditions in which reflection occurs. First is a normal incidence and the second is a difference in acoustic impedances. (18:93)

56. (E) Ultrasound transducers convert mechanical energy to electrical energy and electrical energy to mechanical energy. (10:154)

57. (C) The medium (tissue) through which the sound is being transmitted and the mode of vibration determines the propagation speed. The speed is not affected by frequency. Ultrasound travels faster in solids and slower in gases. (18:34; 20:96)

58. (C) No change. The velocity of sound propagation depends on the material through which it is being transmitted and is independent of frequency. (18:34; 20:96)

59. (A) Refraction (2:38–39)

60. (A) Using a higher-frequency transducer. The near-zone length (x) is given by

Image

where r is the radius of the transducer, and λ is the wavelength. Thus, a longer near-zone length is achieved by increasing the transducer diameter or increasing the frequency. (2:140)

61. (A) 0.75 mm. The wavelength can be determined by using the following equation:

Image

Image

Image

62. (B) Impedance

Image

63. (A) Doppler-shift formula (2:270–273)

64. (C) Huygens (10:71)

65. (B) Tenfold difference in intensity or power (2:30–33)

66. (B) Threshold, negative, or reject level (1:376)

67. (B) Compression (2:108)

68. (A) A-mode is amplitude modulation that is a graphical presentation of an upward displacement along a baseline. The upward displacement is the vertical axis (y-axis) representing the amplitude of the echo, and the horizontal axis (x-axis) represents depth. A-mode is a one-dimensional scan, which is obsolete on modern ultrasound imaging. (10:11; 18:157)

69. (D) Relaxation processes are modes by which ultrasound may be attenuated in passing through a material. Suppression or threshold is another name for rejection. (2:79–85; 18:229)

70. (B) Digital scan converter (3:31)

71. (A) The fraction of time that pulsed ultrasound is actually on is the duty factor. (2:25; 18:58)

72. (D) Sensitivity (18:360)

73. (B) Linear array transducers produce a rectangular image. (Sector scanners produce a pie-shaped image.) (2:55)

74. (B) Magnitude of the voltage spike applied to the transducer by the pulser (18:214)

75. (D) Thermal index (TI) and mechanical index (MI) (2:326–327; 18:372–375)

76. (C) Quality factor, or Q factor, is equal to the operating frequency divided by the bandwidth. (1:36)

77. (E) Grating lobes result from multielement structures of transducer arrays. Side lobes are similar to grating lobes but are created by mechanical or single element transducers. (1:189; 20:69)

78. (D) Pulse duration (18:47)

79. (B) 1029, 10–6, 10–3, 10–2, (18:6)

80. (C) Specular reflection occurs when the ultrasound strikes a large, smooth mirror-like surface, which is angle dependent and relative to the wavelength of the wave. (20:148)

81. (B) Schlieren technique of measurement (1:362)

82. (D) Reverberation (2:263)

83. (B) Enhancement (2:277)

84. (B) Using a larger diameter transducer. The dispersion angle in the far field (θ) is given as: sin θ = 1.22 λd, where λ is the wavelength, and d is the diameter of the transducer. The angle can be reduced by using either a larger transducer or a higher frequency (smaller wavelength). (1:364)

85. (B) Spatial pulse length (2:64)

Image

86. (B) Quality factor (Q factor)

Image

where f0 is the central resonance frequency and (f2f1) is the frequency bandwidth. (1:360; 2:53)

87. (E) Vector array is the name applied to the type of transducer technology that converts the image format from a linear array (rectangular) to trapezoidal-shaped image. (2:73; 20:272–279)

88. (E) Ultrasound resistant to propagate and the speed in which it travels depends on the density, elasticity, and temperature of the medium (tissue type). Ultrasound travels with least resistance in fluid with low viscosity. Urine has lower viscosity than blood. (2:20–22, 160)

89. (A) Dynamic range (10:48)

90. (D) Ultrasound waves are longitudinal waves, compressional, and mechanical waves. (2:18)

91. (B) Axial resolution (18:355)

92. (C) Scan C (18:356)

93. (A) Dead zone (18:355)

94. (D) The AIUM test object is filled with a mixture of alcohol, an algae inhibitor, and water, which allows the propagation speed to approximate the speed of sound in soft tissue (1,540 m/s). (18:355)

95. (C) Horizontal caliper check (18:355–356)

96. (B) Lateral resolution (18:356)

97. (E) Attenuation, echogenicity, solid and cystic mass, gray scale, and scattering characteristics cannot be evaluated by the AIUM test object. These characteristics can best be evaluated by the tissue equivalent phantom. (18:356–357)

98. (D) Registration (18:356)

99. (E) When using the AIUM test object, the output power, time gain compensation (TGC), reject, transducer frequency, and focus should be kept constant for comparisons. (2:306–307)

100. (A) There are two types of cavitation: stable and transient. Transient cavitation results in a violent collapse of microbubbles, which can cause localized temperature elevations as high as 10,000 degrees Kelvin. (20:90, 646–647)

101. (D) Lead zirconate titanate, barium titanate, lithium sulfate, lead metaniobate, and ammonium dihydrogen phosphate are not natural. (2:55; 18:117)

102. (C) Air. Cork, rubber, epoxy resin, and tungsten powder in araldite are good acoustic insulators. Water and air are not suitable acoustic insulators for pulse ultrasound transducers. Most transducers used in therapeutic or continuous-wave Doppler ultrasound do not use backing material. (18:121; 20:81–85)

103. (C) The intensities for continuous wave are equal (SATA = SATP and SPTA = SPTP). (24:125)

104. (A) Infrasound (subsonic) is below the limit of human hearing with a frequency less than 20 Hz. (20:111)

105. (B) Ultrasound has a frequency above 20,000 Hz. (20:111)

106. (B) Audible sound range from 20 Hz to 20,000 Hz (20:111)

107. (B) The electromagnetic spectrum is a large family of electromagnetic waves. Light, x-rays, and infrared, and ultraviolet rays are among its spectrum; ultrasound is not. (1:1–3)

108. (D) Hertz (Hz) is the internationally accepted term for cycles per second (cps). (2:18; 20:93)

109. (C) A 90° interrogation with a vessel will possible yield no Doppler shift because the cosine for 90° is zero. (24:74)

110. (E) All of the answers given are correct. (2:55; 20:234)

111. (D) Increase or decrease depending on the polarity applied (20:234–237)

112. (D) 1 mega = 1 million. Therefore, 5 MHz = 5 million cycles per second or 5 million Hz. (18:21–22)

113. (G) The damping material reduces pulse duration and spatial pulse length and, as a result, improves axial resolution. (2:57–58)

114. (A) Velocity of ultrasound transmitted through a medium depends on the properties of the medium: (1) temperature, (2) elasticity, and (3) density. The speed of ultrasound varies with temperature. However, temperature/velocity in human soft tissue can usually be ignored because body temperature is usually constant within a narrow range, for example, 94°F (low) to 106°F (high). The velocity of ultrasound in soft tissue at 37°C or 98.6°F (core body temperature) is 1,540 m/s. (3:3; 20:114–121)

115. (C) Period is the time it takes to complete a single cycle. The distance it takes for one cycle to occur is a wavelength. (3:3; 20:201)

116. (A) Particle motion is parallel to (or in the same direction of) the axis of wave propagation (20:83–88)

117. (C) Particle motion is perpendicular to the axis of wave propagation (20:83–88)

118. (B) Compression (2:17)

119. (E) Rarefactions (2:17)

120. (C) All gunshot or stab injuries, child abuse, or fraud are reportable without consent from the patient. The request for patient medical records warrants an authorization signed by the patient. (19:64)

121. (F) both A and C (18:112)

122. (F) both B and D (18:149)

123128. See Fig. 1–8 in the Study Guide. (1:367; 2:98)

129. (B) Far gain (2:99–100)

130. (A) The unit for circumference is millimeter (mm) or centimeter (cm). The unit for area is square centimeter (cm2), and the unit for volume is cubic centimeter (cm3). (18:5)

131. (B) Apodization is used with array transducers to decrease the grating lobes. The grating lobes are reduced by different high voltages that excited the elements. (20:1004)

132. (A) The ring down or dead zone is evaluated by scanning the group of targets located at the top of the phantom close to the transducer. (18:355)

133. (E) Axial resolution is evaluated by scanning the group of targets located parallel to the ultrasound beam main axis. (18:355)

134. (C) Lateral resolution is evaluated by scanning the group of targets located perpendicular to the ultrasound beam main axis. (18:355)

135. (E) Deeper imaging decreases frame rate and results in a decrease in temporal resolution. (2:139–140; 18:196)

136. (B) An increase in aperture or frequency will increase the near-zone length. If the aperture size is increased, the resolution will decrease. Aperture refers to the size of the transducer surface. (2:74; 20:253)

137. (D) Subdicing is a technique of dividing the transducer elements into smaller elements, and as a result, the grating lobe artifact is reduced. (18:341)

138. (D) Continuous-wave (CW) Doppler transducers emit sound waves constantly and therefore do not need a backing material. However, when a backing material is required, air is used to allow much more energy into a forward direction toward the patient. This is due to the acoustical impedance mismatch between air and the piezoelectric crystal. (24:40)

139. (C) Fast Fourier transform (FFT) uses a mathematical technique to make the conversion from Doppler shift information into visual spectral analysis. (24:77)

140. (D) Harmonic frequency is twice the fundamental frequency. Harmonic frequency produces harmonic imaging, which is a new advancement in diagnostic ultrasound. There are currently two types of harmonic imaging: tissue harmonics and contrast harmonics. Tissue harmonics are created by reflections from tissue that are twice the transmitted frequency (fundamental frequency). Harmonic imaging improves the image quality and eliminates the grating lobe artifacts. Contrast agents are taken orally or by injection. The microbubbles acts as harmonic oscillator and contrast enhanced echo signals giving higher harmonics. (2:105; 18:263–264)

141. (E) If frequency increases, the wavelength decreases. (2:20)

142. (A) If frequency decreases, the wavelength increases. (2:20)

143. (A) As frequency increases, the penetration decreases. (2:25–26)

144. (B) As frequency increases, the resolution increases. (2:20–27)

145. (A) Higher frequency transmits shorter pulse and narrower beam width. (2:79)

146. (F) Air and barium sulfate (BaSO4). The contrast material used for intravenous pyelogram (IVP) and blood does not prevent the propagation of ultrasound. (18:35; 20:121)

147. (E) A coupling medium is a liquid medium placed between the transducer and the skin to eliminate air gap. Air has a reflection coefficient approaching 100%, which results in almost zero transmission. Water or saline can also be used, but they dry out faster than gel. (2:60)

148. (A) The progressive weakening of the sound beam as it travels. Attenuation occurs because of (1) absorption, (2) reflection, and (3) scatter. Barium sulfate and air impair ultrasound transmissions. (2:32–33)

149. (C) When crystals are subjected to pressure resulting in an electrical charge on their surfaces, it is called a piezoelectric effect. (18:117)

150. (B) When crystals are subjected to electrical impulse and generate ultrasound as a result, it is called a reverse piezoelectric effect. (18:117)

151. (B) Attenuation is the amount of energy lost per unit of depth into the tissue. The parameter used to express the energy loss is the decibel (dB). Attenuation coefficient is directly related to frequency. The parameter used to express attenuation coefficient is 0.5 dB/cm/MHz. (24:29)

152. (C) Waves carry energy from one place to another through a medium. (19:13–14)

153. (A) A mechanical (longitudinal) wave causes particles to oscillate in the direction of the wave propagation. (20:83–84)

154. (C) Wavelength is the distance between two identical points on the waveform. (2:19)

155. (A) Ultrasonic waves are mechanical, longitudinal, and compressional waves that require a medium for propagation. (20:83–84)

156. (B) Acoustic impedance is defined as the density of tissue × the speed of sound in tissue (Z = pc). (2:35)

157. (C) The black region in the middle of the color map is the base line and wall filter and represent no Doppler flow. (18:312)

158. (E) Ultrasound is above 20,000 cycles per second (Hz) and is above the audible range of sound. However, in the clinical settings, ultrasound transducers are in the megahertz range. (1–20 MHz). (20:111)

159. (D) The equation for period is

Image

(14:2; 18:22)

160. (D) The direction of the returning echo is related to the beam angle. The more perpendicular the beam gets to an organ interface, the greater the portion of the reflected echo that will be received by the transducer. (2:35–36)

161. (A) A decibel is the ratio of two sound intensities, highest to lowest (or vice versa). (10:39)

162. (C) Azimuthal is another name for lateral resolution. (18:112)

163. (B) The femur is a bone that has the highest sound velocity because of its stiffness. (2:35)

164. (E) No significant biologic effects have been proved in mammals exposed using a focused transducer below 1 W/cm2 or 100 mW/cm2 spatial peak temporal average (SPTA) for unfocused transducers. (2:334; 20:658)

165. (B) Coded excitation provides good penetration and high resolution while at the same time also improves axial resolution, contrast resolution, and signal-to-noise ratio. (2:92; 10:28)

166. (D) SATA has the lowest intensity because the intensity is averaged over the whole beam profile (SA), and over the whole duration of exposure (TA). (2:30)

167. (B) The beam uniformity ratio is defined as the spatial peak intensity (measured at the beam center) divided by the spatial average intensity (the average intensity across the beam). (2:29–30)

168. (C) The duty factor is the fraction of time the transducer is emitting sound. In a pulsed echo system, it is normally less than 1%. (2:25)

169. (D) Axial resolution is defined as one-half the spatial pulse length. Therefore, the shorter the spatial pulse length, the better the axial resolution. (18:111)

170. (C) Propagation speed (mm/μs); f= frequency (cycle/s) and λ wavelength (mm) (24:8)

171. (D) Attenuation of an ultrasound beam can occur by divergence of a beam, scattering, and reflection. It can also occur by absorption. (18:296)

172. (A) Attenuation coefficient of sound is determined by knowing dB/cm/MHz and then multiplying that quantity by the frequency expressed in MHz. (2:32–33)

173. (B) Transducer Q factor (quality factor) is equal to the operating frequency divided by the bandwidth. Therefore, if the transducer Q factor is low, the bandwidth is wide. (18:123)

174. (A) Axial resolution can be improved by shortening pulse length, increasing damping, and a higher-frequency transducer. (18:111–116)

175. (B) Axial resolution is primarily affected by spatial pulse length. Because the spatial pulse length is the product of wavelength, reducing the wavelength or increasing the frequency will affect axial resolution. (2:76–81; 18:111–116)

176. (D) Increasing transducer frequency will improve both lateral and axial resolution but decrease depth of penetration. (2:76–81; 18:111–116)

177. (C) Range resolution is another name for axial resolution. (18:148)

178. (B) The duty factor is the fraction of time that sound is being emitted from the transducer. In continuous wave, the sound is being emitted 100% of the time. (2:25)

179. (A) The arrow (B) points to blood cells moving toward the transducer. (18:312)

180. (D) Acoustic impedance is calculated as Z = p × c and measured with units of rayls. The average soft tissue impedance is 1,630,000 rayls. (18:86; 20:170)

181. (C) Constant depth mode (C-mode). Its application is pulsed-wave Doppler. (20:369–370)

182. (A) The height of the vertical spike corresponds to the strength of the echo received by the transducer (y-axes). (18:157)

183. (B) The arrow (C) points to blood cells moving away from the transducer. (18:312)

184. (A) The correct equation for calculating reflection percentage is

Image

(31:14–15)

185. (D) The reflection coefficient between water and air interface is 100%. Air prevents the sound from entering the body. It is for this reason that a coupling gel is necessary. (20:144–152)

186. (B) Beyond the critical angle, 100% of the sound beam is reflected and 0% is transmitted. (20:153)

187. (A) Rayleigh scattering occurs when the particle size is smaller than a wavelength (for ultrasound typically in the 1-mm range). (20:149)

188. (D) The least likely way to decrease the dead zone (main bang) is to increase pulse length. The dead zone is decreased with high frequency, short pulse length, and increasing the output power and acoustic standoff pad. (18:355)

189. (C) Power is defined as the rate at which work is done or energy is transferred (energy per unit time). (2:269)

190. (A) Lateral resolution is the minimum separation between two reflectors perpendicular to the sound path. (2:76–81)

191. (D) In most soft tissues, the attenuation coefficient increases directly with frequency. As frequency is increased, the attenuation coefficient increases, thereby limiting depth of perception. (2:32–33)

192. (A) Absorption is the conversion of ultrasound energy into heat. Absorption, scattering, and reflection are all factors of attenuation. (2:32–33)

193. (D) The rule of thumb for attenuation in soft tissue is 0.5 dB/cm/MHz. Therefore, an ultrasound beam of 1 MHz frequency will lose 0.5 dB of amplitude for every centimeter traveled. (2:32–33)

194. (C) Reverberation produces false echoes. (2:263)

195. (D) The acoustic impedance mismatch between fat and muscle is small; therefore, approximately 90% of the sound beam is transmitted. (20:174)

196. (D) Huygens’s principle states that all points on a wave-front can be considered as a source for secondary spherical wavelets. (20:269)

197. (B) Enhancement is the “burst of sound” visualized posterior to weak attenuations. (2:277)

198. (A) Half-value layer (HVL–sometimes called half-intensity depth) is defined as the thickness of tissue that reduces the beam intensity by one-half. (10:70)

199. (D) Propagation speed error. The ultrasound machine assumes a speed of 1,540 m/s. If the sound passes through a medium of a different velocity, the result is an error in the range equation. (2:267)

200. (B) The range equation explains the distance to the reflector, which is equal to one-half of the propagation speed × the pulse round-trip time. (2:338)

201. (A) For a specular reflector, the angle of incidence is equal to the angle of reflection. This type of reflection occurs from a surface, which is larger than the wavelength. (20:148)

202. (C) Propagation speed is determined by the medium. The transducer determines amplitude, period, intensity, and frequency. (20:120–121)

203. (D) Acoustic variables include density, pressure, temperature, particle motion, and distance. (18:12)

204. (E) Acoustic parameters include frequency, power, intensity, period, amplitude, wavelength, and propagation speed. (18:12)

205. (C) Continuous-wave Doppler requires two active elements mounted side by side. One element transmits and the other receives the echoes. (18:303)

206. (D) Reynold’s number is a dimensionless index that indicates the likelihood of turbulence to occur. (20:767)

207. (A) A is correct, with the propagation velocity in this order respectively: 331 m/s, 1,450 m/s, 1,585 m/s, and 4,080 m/s. (18:35)

208. (C) Backscatter is increased by increasing frequency and increasing heterogeneous media. (2:39)

209. (A) Critical angle is the angle at which sound is totally reflected and none is transmitted. (10:37)

210. (D) The pulse repetition frequency (PRF) is the number of pulses occurring per second. The PRF is inversely proportional to the pulse repetition period. The PRF and depth of view are inversely related and the PRF is equal to the number of scan lines per second. (18:55; 24:9)

211. (D) The duty factor is the fraction of time that the transducer is emitting a pulse. It is unitless. (18:58)

212. (A) The attenuation coefficient is the attenuation per unit length of sound travel. Its typical value is 3 dB/cm, for 6 MHz sound in soft tissue (0.5 dB/cm/MHz × 6 MHz = 3 dB/cm). (2:32–33)

213. (B) Normal incidence is also known as orthogonal, perpendicular, right angle, or 90°. At normal incidence, sound may be reflected or transmitted in various degrees. (2:36; 18:89)

214. (A) The difference (mismatch) of acoustic impedance between two media is what determines how much energy will be transmitted or reflected. (20:170)

215. (A) Acoustic impedance is equal to the product of the density of a substance and the velocity of sound. The propagation speed in solids is higher than that in liquids, and the propagation speed in gas is low. The increase in propagation speed is caused by increasing stiffness of the media, not by the density. (2:36)

216. (A) According to Snell’s law,

Image

the transmission angle is proportional to the incidence angle times the medium 2 propagation speed divided by the medium 1 propagation speed. (2:39)

217. (C) The depth of the interface is 3 cm. Ultrasound equipment is programmed at 1.54 mm/μs, and because the average speed in soft tissue is known, the depth and time can be calculated using the following equation:

Image

This equation is called range equation.

     Another method is using the 13-μs rule. This rule states that for every 13 μs of transmitted time, the reflected interface is 1 cm depth; therefore, 26 μs is 2 cm2 depth and 39 μs is 3 cm depth. (18:106)

218. (D) The mirror image artifact duplicates a structure on the other side of a strong curved reflector, e.g., the diaphragm and pleura. (2:265)

219. (C) The comet tail is a bright tapering trail of echoes just distal to a strongly reflecting structure. The greater the acoustic impedance mismatch, the greater the possibility of this artifact to occur. (5:7)

220. (C) The acoustic impedance mismatch between tissue and gas is very great; therefore, it may produce the comet tail artifact. (5:7)

221. (C) Aliasing occurs when the Doppler shift frequency exceeds one-half of the pulse repetition frequency (PRF). This is known as Nyquist limit. (2:340)

222. (D) By increasing damping, one also increases the bandwidth. Bandwidth is the range of frequency involved in a pulse. (2:57–58)

223. (E) All of the above (2:340)

224. (C) Using the range equation 13-μs rule, 4 × 13 = 52 μs. Therefore, the depth is 4 cm for 52 μs (18:106)

225. (A) An ultrasound transducer generally can resolve reflectors along the sound path better than it can resolve those perpendicular to it. (2:76–81)

226. (D) The number of electrical pulses produced per second is typically 1,000 Hz. (2:22–23)

227. (B) The most common artifact in Doppler ultrasound is aliasing. (2:340)

228. (B) With a typical PRF of 1,000 Hz, each pulse-receive interval is 1 ms (1,000 μs) long. Because an average pulse is 1 μs long, this leaves 999 μs for receiving. 999/1,000 is 99.9%. (9:190)

229. (C) Frequency equals velocity divided by wavelength. Because velocity is standard at 1,540 m/s, doubling the frequency will result in decreasing the wavelength by one-half. (2:45)

230. (A) Real-time transducers display two formats: sector and rectangular. The linear-sequenced array transducer displays a rectangular format. (2:66–73)

231. (C) Z is the acoustic impedance; p is the material density; and c is the propagation speed. Z (rayls) = p (kg/m) × c (m/s). (25:28)

232. (A) Lead zirconate titanate (PZT) is a ceramic material with piezoelectric properties. It is most commonly used in transducers because of its greater efficiency and sensitivity. (20:236)

233. (E) The pulse travels to the interface and back to the transducer, the total time for the distance travel is 39 μs. Using the 13 μs rule, 3 × 13 = 39 μs; therefore, the depth of the reflector is 3 cm. The total distance traveled is 2 × 3 = 6 cm. (18:106)

234. (C) The total round-trip time in human tissue for reflected echo at a depth of 2 cm is 26 μs. (18:106)

235. (A) Pulse repetition frequency (PRF) is the number of pulses emitted per second. (2:22–23)

236. (D) The pulser produces the electric voltage pulses; this, in turn, drives the transducer to emit ultrasound pulses. It also tells both the memory and the receiver when the ultrasound pulses were produced. (2:22–23)

237. (C) Shadowing is a useful artifact that helps with diagnosis. The ultrasound beam striking a highly reflective or highly attenuating structure causes this artifact. (2:267)

238. (D) PRF 18 kHz = 9 Nyquist limit (2:281)

239. (A) Lateral resolution is dependent on beam diameter, which varies with distance from the transducer. (2:76–81)

240. (C) A period is the time it takes for one full cycle to occur. (20:93)

241. (B) Half-intensity depth decreases with increasing frequency. As frequency increases, the wavelength decreases both axial and lateral resolution. (2:76–81)

242. (C) Redirection of a portion of the sound beam from a boundary (3:5)

243. (C) 7 MHz. The transmitted frequency is called the fundamental frequency. The second harmonic frequency is twice the fundamental frequency. (18:263)

244. (A) Bit is an acronym for binary digit and represents the basic digital unit for storing data in the main computer memory. (7:8.1)

245. (A) Eight bits equal 1 byte. A bit is a unit of data in binary notation and assumes one of two states: “on” representing the number 1, or “off” representing the number 0. (7:136)

246. (D) The purpose of using an acoustic lens on transducers is to narrow the ultrasound beam, which improves lateral resolution. (18:151)

247. (A) The needle or membrane hydrophone is used to measure pressure amplitude, wavelength, intensity, and pulse repetition frequency (2:319)

248. (C) Viscosity is measured in units of poise or kilograms per meter-second (kg/m-s). (2:160)

249. (C) The speed of ultrasound is dependent on bone, muscle, soft tissue, and fat, which make up the medium. The speed is not dependent on the range of frequency or output power. If stiffness increases, speed increases, and if density increases, speed decreases. (18:35–37)

250. (D) The resistance to flow offered by a fluid in motion is called viscosity. (2:160–161)

251. (C) Autocorrelation is the mathematical process commonly used to detect Doppler shifts in color Doppler instruments. (2:188)

252. (C) A decrease in frequency or transducer aperture size will decrease the near-zone length (Fresnel zone). (18:140)

253. (D) Water has the lowest viscosity. (2:160; 18:280)

254. (C) While the symbol k represents kilo or 1,000 in metric, in computer terminology K = 1,024. Then, the amount that can be stored in memory is 128 × 1,024 × 8 bits = 1,048,576 bits, referred to as 1 megabit. (7:8.1–8.17)

255. (B) Harmonics frequencies are created when structures undergo nonlinear oscillations. These nonlinear vibrations can occur both in tissue as well as with microbub-bles used as contrast agents. Harmonics frequencies are multiples of the fundamental frequency, e.g., twice that of the fundamental frequency. (2:41, 105–108; 18:263, 266)

256. (A) Frequency compounding reduces speckle and as a result, improves image contrast. (20:366)

257. (A) The unit for acoustic pressure is pascal (Pa). (18:12)

258. (E) The horizontal (or x-axis) on the M-mode display represents time. (18:161)

259. (C) 7 MHz. Diagnostic ultrasound transducers used in the clinical setting range from 2.5 MHz to 10 MHz. Ultrasound frequencies in the kilohertz range are not useful in diagnostic range. (18:21)

260. (B) The ratio of the minimum to maximum signal amplitude that can be applied to a device without producing distortion is called dynamic range. (10:48)

261. (C) The vertical (y-axis) on the M-mode display represents depth of the reflector. (18:161)

262. (B) Two: off or on. “Off” represented by the number 0. “On” represented by the number 1. (20:62)

263. (B) Two (0 or 1) (20:62)

264. (E) The number 30 is represented by 011110. To convert from decimal to binary, repeatedly divide by two and note the remainder.

Image

265. (D) The binary system, which is used in digital scan converter memory, is based on the powers of two. For four bits, 24 (2 × 2 × 2 × 2) or 16 different gray levels can be represented. Another way of looking at this is to list all possible states:

Image

There are 16 possible unique states. (2:121–123)

266. (B) Digital memory, where the electronic components are either on (1) or off (0), is based on the binary number system. We can say that the number of discrete levels possible, N, is equal to 2 raised to the power of that number of bits. N = 2n. Therefore, to make 64 shades of gray would require 26 bit memory.

Image

267. (B) The acoustic output with potential for producing cavitational effects in tissue is characterized by the mechanical index (MI). Cavitation is classified as either stable or transient. (2:328; 18:374–375)

268. (C) The receiver processes echoes detected by the transducer. These echoes may be amplified (gain), compensated for depth (TGC), compressed (to fit into the dynamic range of the system), and rejected (eliminating low-level signals). (18:291)

269. (D) The greater the pulse amplitude (electronic voltage applied to the transducer), the greater the amplitude of the ultrasound pulse provided by the transducer. (2:57; 20:234–235)

270. (B) The pulser produces electric voltage pulses that drive the transducer and serve to synchronize the receiver so that the arrival time of returning echoes can be accurately determined. (20:234–235)

271. (D) Components of a pulse-echo system include the pulser that produces the electrical pulse, which drives the transducer. For each reflection received from the tissue by the transducer, an electrical voltage is produced that goes to the receiver, where it is processed for display. Information on transducer position and orientation is delivered to the image memory. Electric information from the memory drives the display. (18:221–213)

272. (B) Transducers may be focused by using a curved piezoelectric transducer element (internal focusing) or by using an acoustic lens. (18:151–152)

273. (E) Quality factor (Q factor) is equal to the operating frequency divided by the bandwidth and is unitless. (2:26–27)

274. (E) Reduction in echoes from a region distal to an attenuating structure (2:267)

275. (G) An increase in echoes from a region distal to a weakly attenuating structure or tissue (2:277)

276. (A) A structure that is echo-free; not necessarily cystic unless there is good through transmission. A solid mass can be anechoic but will not have good through transmission. (19:922)

277. (D) An echo that does not correspond to the real target (20:593)

278. (I) A structure that possesses echoes (10:50)

279. (H) Echoes of higher amplitude than the normal surrounding tissues (10:72)

280. (B) Echoes of lower amplitude than the normal surrounding tissues (10:72)

281. (C) The surface forming the boundary between two media having different acoustic impedances (19:4)

282. (A and F) A structure without echoes and with low absorption; not necessarily cystic unless there is good through transmission. Sonolucent is a misnomer for anechoic. (10:132)

283. (E) Air. There are numerable backing materials used for damping. Pulse-echo transducer backing materials are: (1) epoxy resin, (2) tungsten, (3) cork, and (4) rubber. Continuous-wave Doppler transducers have little or no backing materials. (2:57; 18:304)

284. (C) Aliasing (18:319–310)

285. (C) Brightness of pixel (18:161)

286. (C) For ultrasound to propagate a medium, it must be composed of particles of matter. A vacuum is a space empty of matter; therefore, ultrasound cannot travel in a vacuum. (8:13)

287. (B) Wavelength (6:5)

288. (A) Period (18:20)

289. (B) Hertz (Hz) represents cycles per second (cps). Therefore, 20 cps = 20 Hz. (6:5)

290. (C) 1 MHz (6:5)

291. (B) Mechanical transducers have only one crystal, so this will result in total image loss. (18:12)

292. (A) A-mode is a shortened form of amplitude mode. This mode is presented graphically with vertical spikes arising from a horizontal baseline. The height of the vertical spikes represents the amplitude of the deflected echo. (18:157–161)

293. (B) B-mode is a shortened form of brightness modulation. This mode presents a two-dimensional image of internal body structures displayed as dots. The brightness of the dots is proportional to the amplitude of the echo. B-mode display is employed in all two-dimensional images, static or real-time. (18:157–161)

294. (D) M-mode is short for time-motion modulation. This mode is a graphic display of movement of reflecting structures related to time. M-mode is used almost exclusively in echocardiography. (18:157–161)

295. (D) A long dead zone may indicate a detached backing material. The use of a high-frequency transducer or a short pulse duration will typically decrease the dead zone. (18:361)

296. (E) The frame rate in ultrasound is determined by image depth and the speed of sound in the medium. (18:194)

297. (A) Doppler signals and velocities cannot be measured with perpendicular incidence (90°). (18:300)

298. (C) The technique used to visualize the dead zone is acoustic standoff. (18:361)

299. (C) The intensity of the ultrasound beam depends on the beam diameter. Intensity is defined as the beam power divided by the beam cross-sectional area. (2:27–28)

300. (C) Huygens principle (20:369)

301. (A) The fraction of time that a pulsed ultrasound is actually producing ultrasound is called the duty factor.

Image

302. (C) Real-time ultrasound instrumentation is classified as phased, linear, annular, and vector. (2:66–74; 20:278–279; 25:55)

303. (B) The speed at which ultrasound propagates within a medium depends primarily on the compressibility of the medium. (2:20–22)

304. (C) The reverberation artifact occurs when two or more reflections are present along the path of the beam. This gives rise to multiple reflections, which will appear behind one another at intervals equal to the separation of the real reflectors. (3:40; 2:263)

305. (C) Gain is the ratio of electric power. Gain governs the electric compensation for tissue attenuation and is expressed in decibels (dB). (2:94; 9:89)

306. (C) Multipath reverberation artifacts result from sound reflected from a highly curved specular surface when the echo takes an indirect path back to the transducer. (18:345)

307. (A) Doppler shift artifacts are called clutter. Clutter is eliminated by wall filters. (18:320)

308. (B) Echo signals that are in analog format as they emerge from the receiver are transferred to a digital format by an analog-to-digital (A-D) converter. Preprocessing then produces the best possible digital representation of the analog signal. (2:101)

309. (D) By increasing frequency (MHz) (f) and/or transducer diameter (mm), the near-zone length (mm) is increased, as shown in the equation:

Image

310. (B) Mass divided by volume (2:17)

311. (H) Progression or travel (2:20)

312. (D) Number of cycles per unit time (2:18–19)

313. (A) Rate at which work is done (10:105)

314. (G) The percentage of time the system is transmitting a pulse (2:25)

315. (F) Range of frequencies contained in the ultrasound pulse (2:26–27)

316. (E) Density multiplied by sound propagation speed (2:35–36)

317. (C) Conversion of sound to heat (2:38–39)

318. (I) Operating frequency divided by bandwidth (2:27)

319. (J) Power divided by area (2:27–28)

320. (B) The damping material reduces spatial pulse length, efficiency, and sensitivity. (2:57–58)

321. (C) Gain is electric compensation for tissue attenuation. (20:326)

322. (A) Spectral analysis allows the determination of the frequency spectrum of a signal. (6:16)

323. (B) The output power is a knob on the ultrasound equipment that is used to increase or decrease the brightness of the entire image; increasing the power output improves the signal-to-noise ratio, and increasing this output also increases patient exposure with potential bioeffect concerns. (18:232)

324. (C) Gray-scale resolution is the ability of a gray-scale display to distinguish between echoes of slightly different amplitudes or intensities. The first step in this problem is to figure out how many shades of gray are contained in a 5-bit digital system. The total number of shades of gray is 32 (25 = 32). The next step is to divide the dynamic range (42 dB) by the number of levels. This will give the number of decibels per level. 42 dB ÷ 32 gray levels = 1.3 dB/gray level. (2:109–121)

325. (B)

Image

However, 0.1 seconds is only the time to reach the echo source. The time of the round-trip must be calculated by multiplying by 2. Round-trip distance = 15.4 m × 2 = 30.8 m. (4:2)

326. (B) An edge artifact. Edge shadowing results from refraction and reflection of the ultrasound beam on a rounded surface, for example, the fetal skull. (13:42)

327. (A) A split image artifact (ghost artifact) may produce duplication or triplication of an image, resulting in ultrasound beam refraction at a muscle-fat interface. (11:29–34; 12:49–52)

328. (A) Multipath, mirror image, and side lobe artifacts are most likely to produce a pseudomass. A comet tail artifact is least likely. (13:27–43)

329. (A) Split image artifact is more noticeable in athletic and mesomorphic habitus patients. (12:49–52)

330. (C) Split image artifact (ghost artifact) is not caused by a gas bubble. The most likely cause is refraction of the sound beam at a muscle-fat interface. The artifact is more evident at an interface between subcutaneous fat and abdominal muscle or between rectus muscles and fat in the pelvis. The artifact can also be produced by an abdominal scar or superficial abdominal skin keloids. (11:29–34; 12:49–52)

331. (C) The most likely cause of beam thickness artifact is partial volume effect. This type of artifact occurs most often when the ultrasound beam interacts with a cyst or other fluid-filled structures. (13:27–45)

332. (C) Beam thickness artifacts depend on beam angulation, not gravity. Therefore, if an image of the gallbladder has what appears to be sludge, a change in the patient’s position relative to the beam could differentiate pseudo-sludge caused by artifact from layering of biliary sludge. (13:27–45)

333. (D) Side lobe artifacts are weaker than the primary beam. (13:27–45; 25:180)

334. (B) Shotgun pellets and metallic surgical clips produce a trail of dense continuous echoes. Bone, gas, calcifications, and gallstones produce a distal acoustic shadow. (13:27–45)

335. (A) The most common type of artifact observed in patients with shotgun pellets or metallic surgical clips are comet tail artifacts. This type of reverberation artifact is characterized by a trail of dense continuous echoes distal to a strongly reflecting structure. (10:30; 14:225–230)

336. (D) A ring-down artifact is characterized sonographically as high-amplitude parallel lines occurring at regular intervals distal to a reflecting interface. This type of artifact is commonly associated with bowel gas. (15:21–28)

337. (A) It is possible to calculate the displacement in split images by using Snell’s law. (11:29–34)

338. (C) The first large vertical reflection at the start of the A-mode is called “main bang,” or transducer artifact. (3:26–27)

339. (C) Annular-array real-time uses a combination of mechanical and electronic devices. The annular array is used for dynamic focusing; the mechanical part for beam steering. (2:66–74; 20:261–272)

340. (A) A decrease in the amplitude of the returning echo and also a decrease in the amount of transmitted sound: these result in a fade-away picture. The combination of the coupling medium and matching layers enables passage and return of echoes from the body to the transducer. (3:52; 2:60)

341. (A) Spatial compounding (24:94).

342. (C) M-mode stands for time-motion modulation. This mode displays a graphic representation of motion of reflecting surfaces. It is used primarily in echocardiography. (3:44)

343. (A) B-mode stands for brightness modulation. This mode displays a two-dimensional view of internal body structures in cross section or sagittal section. The images, displayed as dots on the monitor, result from interaction between ultrasound and tissues. The brightness of the dots is proportional to the amplitude of the echo. Realtime equipment uses B-mode. (3:44; 18:159)

344. (B) A-mode stands for amplitude modulation. This mode displays a graphic representation of vertically reflected echoes arising from a horizontal baseline. The height of the vertical reflection is proportional to the amplitude of the echo, and the distance from one vertical reflection to the next represents the distance from one interface to another. A-mode is one-dimensional. The horizontal baseline is the x-axis and the vertical reflection represents the y-axis. (3:26, 44; 18:157)

345. (B) The effects of ultrasound on human soft tissue are called bioeffects, or biologic effects. (2:319; 20:622)

346. (E) The speed of ultrasound in soft tissue is 1,540 meters per second (1,540 m/s), 1.54 millimeters per microsecond (1.54 mm/μs), 0.154 cm/μs, or one mile per second. (2:20; 18:35)

347. (C) Slope

348. (B) Delay

349. (D) Far gain

350. (A) Near gain (6:299–318; 18:224)

351. (C) Progressive weakening of the sound beam as it travels through a medium (2:30)

352. (F) A new imaging technique used to assess tissue stiffness. This is based on a well-established principle that malignant tissue is stiffer than benign tissue (25:92)

353. (G) Binary digit (2:121–123)

354. (B) The production and behavior of microbubbles within a medium (2:328–330)

355. (D) A liquid placed between the transducer and the skin (2:41)

356. (H) A method of reducing pulse duration by mechanical or electrical means (2:57–58)

357. (E) The number of intensity levels between black and white (2:118)

358. (J) Plastic material used in front of the transducer face to reduce the reflection at the transducer surface (2:59–60)

359. (A) Picture element (2:112–113)

360. (I) Single-frame imaging (2:218–220)

361. (D) W/cm2 (6:242)

362. (A) Spatial compounding (24:94)

363. (C) Spatial peak temporal average (2:29–32)

364. (B) kg/m3 (2:20–23)

365. (D) m/s (2:20)

366. (F) Hz (2:18)

367. (E) Joule (J) (2:261; 20:1009)

368. (A) W/cm2 (2:29–32)

369. (C) Wavelength can be expressed in millimeter (mm) or meter (m). One millimeter is one thousandth of a meter (0.001 m). (2:20; 18:32)

370. (G) dB (2:30–31)

371. (B) 0.002 W/cm2–0.5 W/cm2 SPTA (6:250)

372. (A) 0.5 W/cm2–2.0 W/cm2 SPTA (6:250)

373. (C) Under normal intensity ranges, diagnostic ultrasound is atraumatic, nontoxic, noninvasive, and nonionizing. It is nonionizing because the intensity in diagnostic ultrasound range is not sufficient to eject an electron from an atom. (10:26)

374. (D) Heat. However, at the diagnostic intensity range, the heat produced has no known effect. (10:26)

375. (A) The production and behavior of gas bubbles (micro-bubbles) is called cavitation. Cavitation occurs when dissolved gases grow into microbubbles during the negative pressure phase of ultrasound wave propagation. There are two types of cavitation, stable and transient. Stable cavitation is a phenomenon in which microbubbles are formed and persist in a diameter with the passing pressure variations of the ultrasound wave. In transient cavitation, the microbubbles continue to grow in size until they collapse, producing shock waves. (2:320–330)

376. (D) There are two types of cavitation, stable and transient. Stable cavitation is a phenomenon in which micro-bubbles are formed and persist. In transient cavitation, the microbubbles continue to grow in size until they collapse. (2:320–330)

377. (A) Doppler (2:6)

378. (A) When an interface is smooth, or “mirror-like,” or larger than the wavelength, it is called a specular reflector. When the ultrasound beam strikes a specular reflector, the angle of reflection can be a critical factor when performing sonograms. The maximum amount of reflected echo occurs when the transducer is perpendicular to the interface. (3:6, 12)

379. (B) When an interface is smaller than the wavelength, usually less than 3 mm, it is called a nonspecular reflector. Nonspecular reflectors are not beam-angle dependent. (3:6, 12)

380. (B) Spatial average temporal average (6:242; 18:71)

381. (C) Spatial peak pulse average (6:242; 18:71)

382. (A) Because Doppler instruments are used for moving structures, A-mode imaging does not apply. The Doppler instrument employs pulsed or continuous waves. The frequency ranges from 20 cps to 20,000 cps, which is amplified by a loudspeaker; thus, the resulting sound is audible. (18:294)

383. (A) 5 MHz, short-focus. The choice of focal zone depends on what structure is to be imaged. The choice of transducer frequency depends on the amount of penetration and/or resolution needed. High-frequency transducers display good axial resolution but reduced tissue penetration. For superficial structures, a high-frequency transducer is most useful; for deep structures, low frequency is most useful. (2:82)

384. (B) 3 MHz, long-focus. See explanation for Question 383. (2:82)

385. (A) Pixel is short for picture element. (3:32)

386. (A) Under normal circumstances, and depending on the lighting conditions, the human eye can distinguish as many as 16 shades of gray. The human eye can differentiate more color shades than gray shade. Current ultrasound systems can produce 256 shades of color, which is beyond the levels of the human lens under normal conditions. (2:129; 3:32)

387. (A) 512 × 512 × 8-bit deep with 256 shades (2:112)

388. (C) “Aliasing” results when the velocity exceeds the pulse repetition frequency (PRF). Aliasing is an artifact seen in pulse Doppler ultrasound. Aliasing never emerges with continuous-wave Doppler. (18:309)

389. (C) Continuous-wave Doppler does not have time-gain compensation. (18:303)

390. (A) As ultrasound propagates through body tissue, it undergoes attenuation, which is the progressive weakening of the sound wave as it travels. The causes of attenuation are:

1. absorption

2. reflection

3. scattering

When the sound wave is absorbed, it is then converted to heat. The heat generated from absorption is mostly removed by conduction. Cavitation does not occur at normal intensity levels. (3:5, 28; 8:74)

391. (E) One of the major disadvantages of continuous-wave Doppler is range ambiguity. (24:75)

392. (A) Turbulence is most likely to occur with a larger diameter, higher velocity, and lower viscosity. Anemia is a decrease in the amount of red blood cells causing the blood to have a decrease in viscosity. Therefore, a low hematocrit or acute anemia is related to lower viscosity. Polycythemia is an increase in the number of red blood cells causing the blood to have an increase in viscosity. (24:66–68)

393. (C) Decreasing the Doppler shift, increasing the pulse repetition frequency (PRF), adjusting the spectral baseline, or using a lower frequency can be used to decrease the likelihood of aliasing. (24:76)

394. (B) Temporal resolution is increased by shallow imaging, high frame rate, narrow sector, and low-line density. (18:205; 20:218)

395. (A) Aliasing is most likely to occur with high-frequency transducers, low pulse repetition frequency (PRF), and faster blood velocity. Aliasing does not occur in continuous-wave Doppler. (18:307)

396. (A) Digital memory can be visualized as squares on a checkerboard in which echoes are stored in a square corresponding to the location of the scanning plane. (2:109–113)

397. (A) Echo-free (18:330)

398. (B) Echogenic (18:330)

399. (C) Impedance cannot be measured by a hydrophone. (2:319)

400. (B) The hydrophone is made up of piezoelectric transducer elements and a membrane made of polyvinylidene fluoride (PVDF). (2:315–319)

401. (C) When ultrasound was applied for 2–3 minutes on laboratory animals, the results were growth retardation and hemorrhage. These effects were observed in laboratory animals, not humans, and with continuous-wave ultrasound. (6:251)

402. (C) Refraction is least likely associated with attenuation. Refraction is the bending of the sound beam as it crosses an acoustic impedance mismatch. (2:30; 3:5)

403. (B) Conversion of sound to heat (3:5)

404. (A) The spreading out of an ultrasound beam is referred to as diffraction. (3:5; 9:48)

405. (D) Redirection of the sound beam in several directions (2:215; 3:5; 9:60)

406. (C) The transducer’s piezoelectric ceramic is heat sensitive and should not be subjected to excessive heat sterilization because the crystal in the transducer housing could become depolarized and loses it piezoelectric properties. Transducers are made up of a variety of materials, including plastic, crystals, bounding seals, steel, or metal casing, but they are not all constructed alike. A disinfectant that is safe for some transducers may be destructive to others. The recommended method for sterilizing transducers is available from the manufacturer’s user manual or from the manufacturer’s technical support department.
Any product used on transducers against the manufacturer instructions or precautionary measures could result in damage to the transducer and loss of the transducer warranty. (16:130–131)

407. (A) An acoustic window is a pathway through which the sound beam travels without interference. Examples are the liver and urinary bladder. (22:77)

408. (A) The decimal number 10 may also be represented by the binary number 1010. (2:96)

409. (E) The lowest intensity measurements used in diagnostic ultrasound is SATA. (18:71)

410. (B) The intensity used in diagnostic ultrasound to measure the potential biological effects in mammalian tissue is SPTA. (18:71)

411. (A) All images of transverse scans should be viewed from the patient’s feet, in supine or prone positions. (22:86)

412. (B) In longitudinal (sagittal) scans, the images are presented with the patient’s head to the left of the image and feet to the right of the image in both supine and prone positions. (22:86)

413. (C) Within the receiver, a number of signal-processing functions take place: amplification, compensation, demodulation, compression, and rejection. (2:84)

414. (B) Because the particles in ultrasound waves oscillate in the same direction of wave propagation, no plane is defined. Therefore, ultrasound waves cannot be polarized. (2:17–18; 20:81–86)

415. (D) Quartz is the transducer crystal most likely to be employed. (2:55; 20:234–236)

416. (E) All of the above (2:55; 20:234–236)

417. (E) The sound beam from a linear phased-array transducer is electronically transmitted in outward direction to produce a sector shape image. (18:167–168; 24:47; 25:51)

418. (D) Two hundred fifty-six (256), or the number 2 raised to the power of 8 (the number of bits per memory element): 256 = 28(2:116–123)

419. (D) The highest intensity measurements used in diagnostic ultrasound are SPTP. (18:71)

420. (E) Both ultrasound and fluoroscopy evaluate moving structures in movie-like appearance. However, ultrasound is nonionizing because its intensity is insufficient to eject an electron from the atom. Fluoroscopy is ionizing and results in potential biologic effects. X-ray fluoroscopy is produced in vacuum tubes, which is a space without matter. Ultrasound needs matter in order to propagate. (8:13; 20:83)

421. (A) The contrast media used for roentgenographic oral cholecystogram (x-ray of the gall bladder) and nous pyelogram (x-rays of the kidneys) do not obscure the propagation of ultrasound. Barium sulfate (BaSO4) for upper gastrointestinal examination obscures the propagation of ultrasound. (8:13)

422. (I) A device used to focus sound beams (2:65)

423. (C) Picture element (2:112, 116)

424. (D) Pie shaped (2:68)

425. (F) A device that changes sound waves into visible light patterns acoustic-optics (Schlieren). (18:367)

426. (B) The portion of the sound beam outside of the main beam (18:189)

427. (H) Imaginary surface passing through particles of the same vibration as an ultrasound wave (2:209–217)

428. (A) Unit of impedance (2:35–36)

429. (G) The ratio between the angle of incidence and the refraction (2:39)

430. (E) A change in frequency as a result of reflector motion between the transducer and the reflector (2:6)

431. (B) The lateral resolution is defined as being equal to the beam diameter. (2:76–79)

432. (D) Perspex, aluminum, and polystyrene can be used to make acoustic lenses. Ethylene oxide is a gas, not a material used for lenses. (20:249–250)

433. (C) Both ultrasound and light can be focused and defocused by mirrors and lenses. (18:151–153)

434. (A) 0.77–0.15 mm (2–10 MHz transducer) (2:19)

435. (C) Individual cells cannot be identified because they are smaller than the wavelength used in the medium. Advancement in ultrasound allows depiction of nerve. This new methodology uses ultrasound to aid in nerve blocks. (2:322)

436. (D) Mass per unit volume (18:13)

437. (E) The longer the distance traveled, the greater the absorption. Absorption increases with increased frequency, and the amount of frictional force encountered by the propagating sound wave (viscosity) determines the amount of absorption. Absorption in the body also tends to increase in collagen content. (18:82; 20:642)

438. (D) There are no confirmed biologic effects on human tissue exposed to intensities used in the diagnostic range below 100 m/Wcm2. However, laboratory experiments on pregnant mice with intensities far greater than that used in the diagnostic range resulted in growth retardation in the offspring of the mice. (2:333; 6:251)

439. (C) Pregnant mice exposed to continuous-wave ultrasound, for 2–3 minutes, experienced hemorrhage, neu-rocranial damage, and growth retardation. (2:325)

440. (B) A combination of low frequency and high intensity is most likely to cause cavitation resulting in tissue damage. (6:250)

441. (H) Living human tissue (18:369)

442. (E) Tissue cultures in a test tube (18:369)

443. (F) A method of analyzing a waveform (2:229)

444. (G) The property of a medium characterized by energy distortion in the medium and irreversibly converted to heat (10:157)

445. (B) Elimination of small amplitude echo (10:120)

446. (C) A process of acoustic energy absorption (10:120)

447. (A) An in vivo phenomenon characterized by erythro-cytes within small vessels stopping the flow and collecting in the low-pressure regions of the standing wave field (2:3–12)

448. (D) Energy transported per unit time (10:10)

449. (F) All of the statements are false or unconfirmed at the present time. Experimental studies were conducted on pregnant mice, not pregnant women. The intensity, frequency, and exposure time were far greater than those used in a diagnostic setting. Continuous ultrasound was used in many of the experiments. (2:319–329)

450. (E) At present, there are no known exposure injuries in humans in the clinical setting. Injuries have been reported only in laboratory animals. (2:319–329)

451. (A) No distinction. All real-time scans are B-scans, and both static and real-time instruments employ B-mode. (13:44–45)

452. (D) The word transonic implies a region uninhibited to the propagation of ultrasound. An echo-free (anechoic) region does not guarantee the region to be transonic. For example, a homogenous solid mass can be echo-free but not transonic. Conversely, a region can exhibit echoes and be transonic. (10:152)

453. (B) Real-time is also referred to as dynamic imaging. A-mode and M-mode are also real-time modes. A static imaging cannot be changed or moved. (10:171)

454. (A) The TGC is composed of near gain, delay, slope, knee, and far gain. (22:58–61)

455. (A) The range of pulse repetition frequencies used in diagnostic ultrasound is 4–15 kHz. (2:89)

456. (C) Wavelength, cycles. The spatial pulse length (SPL) is defined as the product of the wavelength multiplied by the number of cycles in a pulse. (17:61)

457. (B) A-mode and M-mode (2:143; 18:157–161)

458. (B) Spatial compounding is a sequential averaging of frames that view anatomy from different angles. This creates multiple images over time and organizes them to create one image. Frequency compounding is a combination of echo data from the same location but different frequencies. (2:114; 10:65, 135)

459. (C) Ultrasound and x-rays are inaudible. Doppler instruments employ an audio mode (20–20,000 Hz). (18:22, 294)

460. (C) Continuous-wave mode. Continuous-wave mode requires two crystals, one for transmitting and the other for receiving. (18:303)

461. (A) Ring-down (dead zone) (20:708–709)

462. (B) Vertical measurement calibration (20:708–709)

463. (C) Axial-lateral resolution (20:708–709)

464. (D) Horizontal measurement calibration (20:708–709)

465. (B) 0.2–400 mW/cm2 (2:172–173)

466. (A) Higher frequency than the incident frequency (2:172)

467. (B) Lower frequency than the incident frequency (2:172)

468. (C) Bidirectional (2:128)

469. (A) Doppler color has faster velocities that are represented by lighter color or hue (2:186)

470. (B) Control used to suppress or increase echoes in the near field (18:224)

471. (A) Control used to suppress or increase echoes in the far field (18:224)

472. (D) Control the upward incline of the TGC. Used to display an even texture throughout an organ (18:224)

473. (C) Control used to delay the start of the slope (18:224)

474. (E) Controls the point where the slope ends (18:224)

475. (B) Bandwidth is the range of frequencies contained in an ultrasound pulse. (2:26)

476. (A) The Q factor is unitless. (2:27)

477. (B) The urine-filled bladder is characterized by sharp posterior walls and distal acoustic enhancement. The enhancement is associated with low attenuation. Solid and calcified masses demonstrate a different phenomenon, distal attenuation, the degree of which is determined by the attenuating properties of the mass. (8:11–12)

478. (C) Surgical clips, calcified masses, gallstones, or any high reflective or attenuating structure can produce an acoustic shadow. This results from failure of the sound beam to pass through the object. The urinary bladder, gallbladder, and any fluid-filled structure will demonstrate acoustic enhancement. In some circumstances, both acoustic enhancement and acoustic shadowing can be seen, for example, a gallbladder with stones. (8:11–12)

479. (B) Pooling not related to the sonographic descriptions of blood flow. Blood is classified into five different flow characteristics (1) plug flow, (2) parabolic flow, (3) laminar flow, (4) disturbed flow, and (5) turbulence flow. (2:162–163)

480. (C) When the beam strikes a vessel at a 30° angle. Doppler angle is the angle between the direction of propagation of the ultrasound beam and the direction of flow. Unlike real-time imaging of the abdominal organs in which the best images are obtained when the ultrasound beam has a perpendicular incidence, Doppler has minimum shift at 90° (perpendicular) incidence, and a maximum shift when the transducer is oriented parallel to the direction of flow, even though parallel transducer orientation is not possible in most cases. Doppler application employs a Doppler angle of 30°-60° with respect to the vessel. (18:299–300)

481. (B) 20 dB (18:75–76)

Image

(34:3)

482. (D) Time-gain compensation (TGC) (18:224)

483. (D) Refraction, propagation speed. Refraction occurs in oblique incident and if the propagation speed is different between the two media. (18:99)

484. (A) Better axial resolution. Axial resolution is related to the length of the pulse. The shorter the pulse, the better the axial resolution. (2:76–81)

485. (A) 0.25 mW/cm2. The reflection fraction R: (1:366)

Image

486. (B) Frequency and diameter. Near-zone length (NZL) is the same as the Fresnel zone:

Image

where D is diameter transducer (cm), and × is wavelength (cm). (2:63–65)

487. (D) The element thickness. The operating frequency is determined by the element thickness, the thinner the element the higher the frequency.

Image

488. (B) Refraction does not occur with normal incidence or when the propagation speed of the two media is the same. Refraction is described by Snell’s law, which relates the incident angle (Φ1) and the transmitted angle (Φ1) to the relative velocities of the two media.

Image

When there is normal incidence, Φ1 = 0, and the sound will only change velocity and will not be bent. (18:99)

489. (C) 1.54 mm/μs or 1,540 m/s (18:35)

490. (C) 1.0%

Image

(2:25)

491. (D) The amount of acoustic exposure is determined by the intensity of the ultrasound beam and the amount of examination time. (24:126)

492. (C) Tissue attenuation. Tissue attenuation increases and penetration decreases with increased frequency. (2:32–33)

493. (C) 3.5 dB

Image

The attenuation coefficient in dB/cm is by a rule of thumb equal to one-half the frequency in MHz; i.e., at 3.5 MHz, the attenuation coefficient is 1.75 dB/cm. (2:32–33)

494. (D) Propagation speed (2:20–22)

495. (A) Maximum velocity occur within the stenosis. (18:282)

496. (D) 70%

100% = percentage reflected + percentage transmitted (2:36)

497. (D) Turbulent flow is possible when blood flow exceeds of Reynolds number of 2,000. (2:163)

498. (C) Distance, velocity, and time

Image

(2:338)

499. (C) Reynolds number (2:163)

500. (C) 90°

Image

where V = velocity of blood flow; f, transducer frequency; C, velocity of sound. Because cos 90° is 0, the Doppler shift frequency is 0. (2:172)

501. (C) Turbulence is a non-laminar flow, with flow in randomized and in multiple directions. Turbulence flow occurs beyond (distal) the obstruction in a stenotic blood vessel. (2:163)

502. (A) The ratio of the maximum to the minimum intensity that can be processed. (18:257)

503. (B) If the thermal paper printer is not working, the first step is to check for a jam in the printer. (18:251)

504. (A) Compensates for attenuation effects (2:100–101)

505. (D) Computer memory (2:101–103)

506. (D) An increase in the peak rarefactional pressure could result in inertial cavitation. Mechanical index (MI) indicates the likelihood of cavitation. (2:329, 357; 20:1012)

507. (B) Weakly attenuating structures (2:30)

508. (D) Ultrasound depth penetration is inversely related to frequency. As frequency increases, penetration decreases. (2:25–26)

509. (E) Lateral resolution is affected by beam diameter, aperture, acoustic lens, focal zone, and frequency. Higher frequencies improve both axial and lateral resolution. (18:148–153)

510. (B) Increased frame rate. If the line density is kept constant, then the number of lines per image will decrease, making the time required per image smaller. (18:194–195)

511. (D) Line D. The transducer is placed on top of the tissue-equivalent phantom. The ultrasound beam is perpendicular to the group of nylon lines horizontal to the axis of the sound beam. This group is used to evaluate horizontal distance accuracy. (20:708–709)

512. (B) The transducer is placed on top of the tissue-equivalent phantom. The ultrasound beam is parallel to the group of nylon lines vertical to the axis of the sound beam. This group is used to evaluate range accuracy or vertical depth calibration. (18:362)

513. (D) The advantages of continuous-wave include the ability to measure very high velocities, higher frequency, no aliasing, and no Nyquist limit. The disadvantage is range ambiguity. (18:303–309)

514. (C) 15 dB. For every change of 3 dB, the intensity will change by a factor of 2. (2:30–32)

515. (C) Decreases the maximum depth imaged. The pulse repetition period (PRP) is the length of time allowed to collect echoes for each image line; a short PRP means less image depth. (18:52)

516. (E) The AIUM 100-mm test object is not used to evaluate attenuation, scattering, echo-texture, gray scale, and cystic and solid mass. (18:355–356)

517. (A) All ultrasound regardless of frequency travels at the same propagation speed if traveling in the same medium. It is the medium that determines the speed of ultrasound. Ultrasound travels faster in solids and slower in gases. Fast medium has long wavelength and slow medium has short wavelength. (18:34–35)

518. (A) Lateral resolution (18:189)

519. (D) Spatial compound imaging is a technique that improves the image quality with scan lines directed in multiple directions created over time and then averaged together to create one image. The benefits of compound imaging are the reduction of reverberation and shadowing and to visualized structures hidden beneath high attenuation. (20:366; 25:92)

520. (E) All ultrasound regardless of frequency travels at the same propagation speed if traveling in the same medium. It is the medium that determines the speed of ultrasound. Ultrasound travels faster in solids and slower in gases. Fast medium has long wavelength and slow medium has short wavelength. Gas and air in the lungs are slow medium and therefore have a short wavelength. (18:34–35)

521. (B) Sensitivity (18:360)

522. (A) Thermal and cavitation. Thermal or heating effects are normally unmeasurable with diagnostic instruments. Further cavitation is also unlikely at current diagnostic levels. Cavitation refers to the growth and behavior of gas bubbles produced in tissue by ultrasound. (2:327–328)

523. (B) Frequency and transducer diameter. High frequencies and/or large diameter transducers produce long near-zone (Fresnel zone) lengths. (2:62–63)

524. (B) No evidence of independently confirmed biological effects in mammalian below SPTA 100 mW/cm2 (20:643)

525. (C) Highest at the focal zone. This is true because the intensity is equal to the power/beam area, and the beam area is smallest at the focal zone. (2:62–63)

526. (B) 0.3 mm (2:19)

Image

(2:8)

527. (C) Two times smaller. A 3-dB attenuation change would correspond to a factor-of-2 reduction; that is, one-half. For each decrease in intensity of 3 dB, the intensity is decreased by one-half. Thus, for 6-dB attenuation, the intensity is decreased by one-fourth. (1:356)

528. (B) Linear-phased array is commonly called phased array. Linear-phased array has a sector-shaped image and linear sequential array is a rectangular image. (2:68; 18:185)

529. (A) A wide band of frequencies centered at 5 MHz (1:360)

530. (D) Thickness, resonance frequency. Specifically, thickness equals one-half wavelength, where wavelength is velocity divided by frequency. (1:358)

531. (A) Increased damping, sensitivity. Increased damping does improve axial resolution by making the spatial pulse length shorter; however, the result is to make the transducer less sensitive to small echoes. (1:360)

532. (A) Piezoelectric (2:55–57)

533. (C) Matching. Usually a matching layer is added to the front surface of the transducer acoustic impedance intermediate between the impedance of the transducer and that of soft tissue. (1:370)

534. (E) RAID is an acronym for redundant array of independent disks. RAID is an alternative to a large storage system that requires speedy data transfer rate and security. The main archive device for PACS server is RAID. (23:97)

535. (A) Highly attenuating structures (2:30)

536. (B) Occur with multiple strong reflectors. Reverberation artifacts are present when two or more strong reflectors are located in the beam. One of these may be the transducer itself. The sound, in essence, gets trapped between these reflectors. Reverberation artifacts are displayed as equally spaced echoes often seen in fluid-filled mass. (2:263)

537. (A) Good axial resolution. A large bandwidth is equivalent to a short spatial pulse length. (1:360)

538. (A) Fraunhofer zone. The far zone is also known as the Fraunhofer zone; this is the region from the focus and extending to beam diversion. (18:135)

539. (D) With normal incidence of the ultrasound beam. At oblique incidence, a sound beam will be bent if there is a change in propagation speed across the boundary. With normal incidence, however, the beam will either slow down or speed up, but will not bend. (18:99)

540. (C) The pulser voltage spike. The larger the applied voltage, the greater the deformation of the crystal and, consequently, the amplitude of the pressure wave produced. However, a larger crystal (same thickness) experiencing the same voltage will produce more acoustic energy. (18:212–213)

541. (B) The reflecting surface is large and smooth with respect to the wavelength. Reflectors whose boundaries are smooth relative to the wavelength behave as mirrors and reflect all frequencies equally. Small reflectors (diffuse or nonspecular) scatter the sound in all directions and show a frequency dependence. (18:79)

542. (C) Snell’s law (2:39)

543. (A) Annular phased array has multiple ring-shaped elements. (18:176)

544. (A) 90–100%. Because the acoustic impedance of gas is so much smaller than that of soft tissue, there is almost 100% of the energy reflected. (1:366)

545. (E) 1–10%

Image

where R is the percentage of beam reflected. (1:366)

546. (B) Focal zone can be moved to the skin surface. The acoustic standoff (waterpath) is normally positioned between the transducer and the patient skin to allow visualization of superficial structures. Superficial structures are sometimes difficult to image due to the dead zone. High-frequency transducer and acoustic standoff are used to image structures in the dead zone. (18:361)

547. (D) Longitudinal compression waves. Longitudinal implies that the variation in the pressure occurs in the direction of propagation. This is opposed to a transverse wave, where variations occur perpendicular to the propagation. Transverse waves can occur in bone. (2:18; 20:83)

548. (A) Shorter wavelength and less penetration. The wavelength is inversely related to the frequency, and the attenuation is directly related to frequency.

Image

where f is the frequency in MHz. (2:18–21)

549. (A) Ring-down time. A long ring-down time is undesirable. It increases the spatial pulse length and, thus, decreases axial resolution. (1:360)

550. (B) Electronically focus in two dimensions rather than one. An annular phased array can be focused dynamically in two dimensions. A linear array can be focused dynamically only in the plane of the array. In the slice-thickness direction, perpendicular to the array plane, focusing is achieved by shaping the transducer elements or by acoustic lens. This is often referred to as double focusing. (18:176–180)

551. (C) Gas, muscle, bone. This ordering proceeds along increasing stiffness or lack of compressibility. Therefore, gas is slow, with an increasing order to the fastest, which is bone. (18:35)

552. (A) Resolution, penetration. At low frequencies, the axial resolution becomes unacceptable (<1 MHz), whereas at high frequencies, the depth of penetration in the body becomes prohibitively small (10 MHz). (18:21–22)

553. (B). Engineering notation, also known as scientific notation, is a shorthand way of writing very large or very small numbers. The first step is to put a decimal after the first digit and drop the zeroes. For the given number 125,000,000,000, the coefficient is 1.25. To find the exponent, count the number of places from the decimal to the end of the number. This should be 11 places. The number 125,000,000,000 is written 1.25 × 1011(18:6)

554. (B) SPTP is always equal to or greater than SPTA. SPTP refers to spatial peak-temporal peak, and SPTA refers to spatial peak-temporal average. In all cases, peak values will be at least as great as the average values by definition. For continuous-wave ultrasound, there is no variation of the intensity in time, and peak values will be equal. (2:28–30)

555. (C) A hydrophone. A hydrophone is a small piezoelectric crystal that is moved in front of a transducer in a manner so that the beam pattern is mapped. A radiation force balance is used to quantify the total beam power. Other phantoms can be used to give qualitative estimates of beam profiles. (2:315, 319)

556. (E) When the direction of flow is perpendicular, 90°, to the sound beam, the velocity and cosine are zero. (18:300)

557. (B) Schlieren method. Schlieren photography gives a two-dimensional photograph of the beam pressure profile. (1:362)

558. (D) Time. Pulse duration is equal to the period of a wave times the number of waves in a pulse, usually microseconds in length. (18:47–48)

559. (C) Nyquist frequency is one-half of the pulse repetition frequency (PRF). The PRF given was 2,000 Hz; therefore, the Nyquist frequency is 1 kHz (1,000 Hz). (18:306–309)

560. (B) W/cm2. SPTA refers to intensity, which is power (watts) per unit beam area (cm2). (2:29)

561. (C) Curie point. Crystals heated above the Curie point lose their piezoelectric property. The Curie point for quartz is 573°C and for PZT is 328°C. (1:358)

562. (C) Increase ninefold. I = A2 = (3) =9, where Í is intensity, and A is amplitude. (1:388)

563. (A) Increasing the output power improves the signal-to-noise ratio. Increasing the receiver gain amplification does not change the signal-to-noise ratio. (18:231)

564. (D) Velocity, unchanged. The velocity is essentially independent of frequency and is rather dependent upon the physical properties of the medium. (18:34)

565. (B) Electronic time-delay pulsing. The delay pulsing of the array elements can be used to form a wavefront directed at different angles. Pulsing can also be used to focus the beam at different depths. (18:167)

566. (A) Is made possible by array-based systems. Dynamic focusing is possible only with array-based systems because it is necessary to monitor individually echoes received from each location. (2:66–67)

567. (A) Amplification of the receiver voltage (18:231)

568. (C) 1.54 mm. The velocity of ultrasound in soft tissues is 1.54 mm/μs. (2:35)

569. (A) Ring-down artifact. The arrow points to a ring-down artifact produced most probably by gas bubbles resulting in a tail of reverberation echoes. (15:21–28)

570. (A) Rods for measuring dead zone (ring-down). The small open arrowheads point to a rod group used in measurement of the transducer dead zone. (6:261–276)

571. (B) A simulated solid lesion (6:261–276)

572. (C) A simulated cyst (6:261–276)

573. (D). The thickness of active element. The frequency of the transducer is determined by the thickness of the active element and the speed of sound in the active element. (18:126–127)

574. (D) Most contrast agents contain gas-filled microbubbles that are stabilized by protein or lipid shell. The earliest agents used air-filled bubbles. More recently, perfluoro-carbon gas is used. (2:41)

575. (B) Perfluorocarbon (2:41)

576. (B) As the pulse repetition frequency (PRF) increases the depth of view decreases. (18:55)

577. (E) Acoustic clutter and ghosting artifact can be eliminated with wall filter. Clutter results from tissue, heart wall, or vessel wall motion. (2:297; 18:320; 20:545–547)

578. (B) Speckle is a form of acoustic noise that appears in close proximity to the transducer as random variation signal giving the impression of tissue texture but not corresponding to true anatomic tissue. (18:347; 20:168)

579. (D) All of the above. Color-flow images can be used to position a single-point, pulsed-Doppler, sample volume, as is the case with more conventional duplex imaging. (30:1241)

580. (C) Stationary tissue in gray-scale and moving tissues in color. All moving tissues in a color-flow imaging can produce color. Thus, stationary tissues are in gray scale, whereas moving tissues, including blood, are in color. (28:236)

581. (A) A form of color-flow imaging. Color-flow imaging includes both Doppler and non-Doppler forms of imaging. (28:236; 30:1241; 34:27)

582. (C) To all waves coming from a moving wave source. The Doppler effect happens to all waves coming from a moving source, regardless of propagating velocity or power levels. (37:172)

583. (B) The closing velocity between transducer and tissue, carrier frequency, and ultrasound propagation velocity. The Doppler equation looks like the following:

Image

where f0 is the carrier frequency, c is the propagation velocity, and θ is the Doppler angle. V cos θ is the closing velocity between the transducer and moving tissue. (37:173)

584. (D) Place a sample volume in the major streamline or jet and set the angle correction parallel to the streamline. Because the color pattern shows the location of the major streamline or jet, calculating velocity requires correction relative to the flow geometry, not the vessel. (37:195)

585. (B) One wavelength or less. This is necessary for textural information to reach the display in a digital scan converter. (32:654)

586. (C) One wavelength or more but less than 1 mm. Digital sampling for vascular flow information requires such an interval because larger intervals cannot show the flow patterns within the vessel. (28:236)

587. (C) The product of transmit and receive focusing. The effective beam width results from the mathematical product of both functions. (36:620; 38:155)

588. (A) True. The sample volume and flow interact in a manner that depends on the geometry of the sample volume. (33:9)

589. (C) The average Doppler shift frequency. At each sample site, the color-flow system determines the average Doppler shift frequency. (28:236)

590. (B) False. At each sample site, the system determines the average Doppler shift frequency. The display is then either these average frequencies or, in some cases, the calculated closing velocity. This velocity is the rate at which the flow is approaching or moving away from the transducer along the line of sight. (28:236)

591. (D) The relationship between the amplitudes and frequencies of the Doppler signals. The system will then avoid coloring strong slow-moving echo sources (tissue) but still color moderately fast weak echo sources (blood). (39:647)

592. (B) The vessel is open, but the blood velocity is too low to complete the image. As the vessel curves away from the beam, the Doppler frequencies become too low to be portrayed. The completeness of a color-flow image depends on the velocity of the blood flow and the Doppler angle. (27:19, 44)

593. (D) The smaller vessels do not reflect ultrasound as well as the larger vessels do. Every living cell in the body is no more than two cell layers away from a red blood cell. The smaller vessels, however, are not sufficiently echogenic and vanish from the color display first because of their small echo signals. (34:7)

594. (D) 1, 2, and 3. Color provides information about the existence of flow, its location in the image, its location in the anatomy, the direction of the flow relative to the transducer, the direction of flow within the vessel, the flow pattern within the vessel, and the pulsatility of the flow. It does not indicate the velocity of the flow. (30:1245)

595. (D) Changes in echo signal phase. As with all directional Doppler systems, color-flow systems detect the existence of motion with a change in echo signal phase. By measuring the direction of the phase change, the system shows whether the direction of motion is toward or away from the transducer. (33:34)

596. (B) Knowing the position of the scan plane on the patient’s body. The expected flow pattern in any vessel comes from knowing how the scan plane is positioned on the patient. For example, the patient’s head is always placed on the image left in long axis scans, and the patient’s right side is on the image left in cross-sectional scans. (37:407)

597. (D) Different colors (hues) or different levels of saturation (purity). The average frequency within each Doppler sample site is portrayed as a change in either color saturation (purity or whiteness) or hue (color). The object is to use the color to show flow patterns within the vessel lumen or heart chambers. (27:44)

598. (C) Changes in color hue. The variance in Doppler frequencies can be shown with a change in hue, such as green tones with increasing variance. (9:27; 28:236)

599. (A) Changes in color. Cardiac systems change color hues (frequencies) along red and blue lines to show changes in Doppler shift frequencies. Broadening frequencies in a sample site become shades of green. (27:44)

600. (B) False. Because only one frequency can come to the screen for each Doppler image pixel, all current systems use some estimate of the mean frequency. (28:236)

601. (B) False. Because color uses the average frequency at each location, the maximum systolic frequency will always be greater than the mean value. (28:236; 34:27; 35:591)

602. (A) True. Because synchronous signal processing uses the same echo signal for both Doppler and gray-scale signal processing, the frequency must be the same. (28:236)

603. (B) False. Asynchronous signal processing can, and often does, use different frequencies for the gray-scale image and the Doppler image. For example, it could image at 5.0 MHz and have a Doppler carrier of 3.0 MHz. (28:236)

604. (A) A Doppler angle significantly less than 90° to typical blood flow. All Doppler imaging requires a Doppler angle. In asynchronous systems that do not use a wedge, the angle comes from beam steering. (37:173)

605. (D) A Doppler angle between the typical flow patterns in vessels. Synchronous systems that keep the beams perpendicular to the transducer array (angiodynography) use a mechanical wedge to obtain the Doppler angle to the flow pattern of the vessel. (28:236; 34:27)

606. (D) Blood reflectivity is about 40–60 dB below that of soft tissue. The fact that blood reflectivity is about 1/100th to 1/1,000th that of soft tissues translates into reflectivities that are much lower than those of soft tissues. (33:18)

607. (A) True. Because the reflectivity of blood is low, many color-flow systems improve color penetration by greatly increasing the power of the transmitted Doppler output. (28:236)

608. (B) False. Synchronous signal-processing systems are limited by the power levels of the common transmitter used for both gray-scale imaging and Doppler imaging. As a result, imaging with and without Doppler produces similar power levels. (9:27; 28:236)

609. (A) True. The single-point spectrum requires the ultrasound beam to linger over its position longer than is the case in either real-time gray-scale imaging or color-flow imaging. (9:27; 28:236)

610. (A) Decrease. Color-flow imaging requires dwelling on each line of sight for as few as four pulse-listen cycles to as many as 32 pulse-listen cycles. Various systems have different dwell times. The typical end result is a reduction in image frame rate for color-flow imaging. (28:236)

611. (A) True. Real-time color-flow imaging of the heart requires relatively high frame rates. In general, Doppler requires dwelling on each line of sight for some period of time. In addition, each Doppler sample site requires processing time to extract the average Doppler shift frequency. Restoring suitable cardiac frame rates requires decreasing the number of color-flow lines of sight and the number of samples along each line. (9:27; 37:17)

612. (B) False. Cardiac color-flow imaging does not work well for vascular imaging because the Doppler sampling intervals are too large. Imaging the heart also involves a problem with reflectivities, not with tissue attenuation. (27:236)

613. (B) False. Doppler sampling for vascular imaging may be well below intervals of 1 mm. In contrast, sampling for echocardiography may be at intervals of several millimeters or more. (27:17)

614. (B) The ultrasound beams are always moving. This is the case because mechanical systems lack a special motor that could move the beam in small steps. Because Doppler signal processing is keyed to relative movement and the beam is always moving, color does not work well in mechanical systems. (27:17)

615. (A) 1 and 2. The linear phased array and the phased linear array have stationary ultrasound beams at each line of sight in the scanning plane. Both arrays also have increased grating lobes with beam steering. They do not have three-dimensional dynamic focusing or apertures necessarily of the same size. (2:21; 34:27)

616. (B) The linear array scan. The linear array with a rectangular scanning field is the geometry used for vascular imaging. The sector-scanning geometry makes reading color ambiguous in the straighter segments of a vessel. (27:44)

617. (D) A combination of A and C. Color-flow imaging of the heart uses the phased-array sector scan and the curved-linear array sector scan. These scanheads permit cardiac imaging from intercostal and subcostal windows. (27:41)

618. (B) 9 cm/s. Lowering the Doppler carrier frequency means that the same Doppler shift frequency requires a higher velocity to be just visible. (38:280)

619. (B) False. Like all pulsed Doppler systems, color systems will alias when the Doppler frequencies exceed the PRF sampling limit. (33:37)

620. (C) Decreasing the carrier frequency. This moves all Doppler frequencies downward and may bring the high aliasing frequencies below the aliasing limit. (37:192)

621. (D) Range ambiguity. High frame rates (high PRF) and high output power permit structures from outside the field of view to enter the image as a range ambiguity artifact. (39:83)

622. (B) False. The large fields of view for abdominal imaging slow the frame rate. In addition, vessel anatomy goes in all directions. Sorting out arteries and veins requires the spectrum to determine pulsatility. (35:591)

623. (D) A or B. In vascular color-flow imaging, turbulence appears as broken streamlines. The image then takes on a mottled appearance either in color or in color saturation. (36:591)

624. (D) A mottled green region. In color-flow echocardiog-raphy, the sampling intervals are too large to show turbulence. As a result, the system determines the spectral variance at each sampling site and expresses increased turbulence (increased variance) with increasing tones of green. (27:12)

625. (B) It encodes the power spectrum of the Doppler signal into color. Power Doppler looks at only the amplitudes of the Doppler signals in the I and Q channels. (40:13)

626. (C) It does not show the directionality of vessel flow. Power Doppler uses only the amplitudes of the signals in the I and Q channels. Without phase information, power Doppler cannot show the direction of flow. (41:14)

627. (A) Want to show tissue perfusion. Power Doppler will show wherever the system detects Doppler signal amplitudes. Thus, the color will distribute according to this signal map for both arteries and veins. (41:16)

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