Campbell-Walsh Urology, 11th Edition

PART I

Clinical Decision Making

3

Urinary Tract Imaging: Basic Principles of Urologic Ultrasound

Basic Principles of Urologic Ultrasound

Bruce R. Gilbert; Pat F. Fulgham

Questions

  1. The maximum excursion of a wave above and below the baseline is known as its:
  2. wavelength.
  3. frequency.
  4. period.
  5. cycle.
  6. amplitude.
  7. The artifact that occurs when an ultrasound wave strikes an interface at a critical angle and is refracted with limited reflection is:
  8. a reverberation artifact.
  9. an increased through-transmission artifact.
  10. an edging artifact.
  11. a comet-tail artifact.
  12. an aliasing artifact.
  13. Which ultrasound mode allows for detection and characterization of the velocity and direction of motion?
  14. Harmonic scanning
  15. Color Doppler
  16. Power Doppler
  17. Spatial compounding
  18. Gray-scale ultrasonography
  19. If the kidney is less echogenic than the liver, it is described as:
  20. hyperechoic.
  21. hypoechoic.
  22. isoechoic.
  23. anechoic.
  24. echogenic.
  25. The sonographic hallmark of testicular torsion is:
  26. the "blue dot" sign.
  27. epididymal edema.
  28. paratesticular fluid.
  29. increased epididymal blood flow.
  30. absence of intratesticular blood flow.
  31. Ultrasound waves are examples of:
  32. radio waves.
  33. mechanical waves.
  34. electromagnetic waves.
  35. ionizing radiation.
  36. light waves.
  37. The most important determinant of axial resolution is:
  38. impedance.
  39. speed of propagation.
  40. acoustic power.
  41. frequency.
  42. number of foci.
  43. Increasing frequency results in a loss of:
  44. absorption.
  45. axial resolution.
  46. lateral resolution.
  47. depth of penetration.
  48. mechanical index.
  49. When sound waves encounter the interface between two tissues with large differences in impedance, the waves are:
  50. increased in frequency.
  51. decreased in frequency.
  52. reflected.
  53. refracted.
  54. reverberated.
  55. When a tissue appears darker than the surrounding tissue on ultrasound, it is said to be relatively:
  56. hypoechoic.
  57. hyperechoic.
  58. hypodense.
  59. isoechoic.
  60. anechoic.
  61. The focal zone represents the area of best:
  62. lateral resolution.
  63. axial resolution.
  64. echogenicity.
  65. blood flow.
  66. tissue penetration.
  67. Increasing the gain has the effect of:
  68. increasing amplitude of the sound waves.
  69. increasing acoustic power.
  70. increasing thermal index.
  71. increasing mechanical index.
  72. increasing transducer sensitivity.
  73. One way to improve the visualization of deep structures is to:
  74. increase the frequency.
  75. decrease the frequency.
  76. increase the wave velocity.
  77. decrease the gain.
  78. use Doppler flow.
  79. The best frequency for performing external renal ultrasound in most adults is:
  80. 3.5 to 5 MHz.
  81. 6 to 10 MHz.
  82. 7.5 MHz.
  83. 10 to 12 MHz.
  84. none of the above.
  85. A simple cyst of the kidney would NOT display which of the following characteristics?
  86. Bright back wall
  87. Increased through transmission
  88. Anechoic interior
  89. Edging artifact
  90. Hyperechoic internal nodule
  91. Which of the following is correct?
  92. Measuring bladder volume requires three-dimensional scanning.
  93. A nearly empty bladder is desirable for bladder scanning.
  94. A curved array transducer is preferred for bladder ultrasound in most patients.
  95. Ureteroceles are usually poorly visualized because the membrane is thin.
  96. Bladder ultrasound is a sensitive screening exam for suspected bladder tumors.
  97. Which of the following are evaluable by transabdominal bladder ultrasound?
  98. Urine volume
  99. Bladder wall characteristics
  100. Stones or diverticulum
  101. Dilated ureters
  102. All of the above
  103. Scrotal ultrasound for the evaluation of possible testicular torsion may include all of the following but must include:
  104. B-mode ultrasound.
  105. multiple scrotal views.
  106. Doppler flow studies.
  107. simultaneous bilateral views.
  108. harmonic scanning.
  109. The most important limitation of ultrasound in attempting to characterize complex renal cysts as benign or malignant is:
  110. refraction.
  111. inability to evaluate enhancement.
  112. lack of axial resolution.
  113. increased through transmission with artifact.
  114. reverberation artifact.
  115. A complete transrectal ultrasound of the prostate should include an evaluation of:
  116. the rectal wall.
  117. the seminal vesicles and ejaculatory ducts.
  118. the bladder.
  119. prostate.
  120. all of the above.
  121. Which of the following would NOT typically be visible in a sagittal midline prostate ultrasound?
  122. Middle lobe of the prostate
  123. Central zone
  124. Ejaculatory duct
  125. Tip of the right seminal vesicle
  126. Apex of the prostate
  127. Characteristics of prostate cancer as demonstrated on transrectal ultrasound of the prostate may include:
  128. hypoechogenicity.
  129. hyperechogenicity.
  130. prostate asymmetry.
  131. increased vascularity.
  132. all of the above.
  133. The single most important determinant of patient safety in ultrasound use is:
  134. multifrequency probes.
  135. good documentation.
  136. an informed operator.
  137. periodic equipment inspection.
  138. Doppler capability.
  139. The disinfection level protocol required for transrectal ultrasound probes following needle biopsy is:
  140. low.
  141. moderate.
  142. high.
  143. critical.
  144. none of the above.
  145. For patient safety it is preferable to maximize ____ and limit ____:
  146. acoustic power, exam duration
  147. acoustic power, gain
  148. gain, acoustic power
  149. gain, use of cine function
  150. images, description

Answers

  1. e. Amplitude.In ultrasound physics it is crucial to understand the concept of amplitude. The amplitude of an ultrasound wave represents its relative energy state, and it is the amplitude of the returning sound wave that determines the pixel brightness to be displayed on a monitor during real-time gray-scale imaging.
  2. c. An edging artifact. Echo reflection is the primary mechanism whereby sound waves are returned to a transducer. It is important to understand how the angle of insonation affects the reflection and refraction of sound waves. There is a critical angle at which waves will travel along an interface rather than being returned to the probe. When this angle is encountered, it provides a dark or hypoechoic "shadow" called an edging artifact. A reverberation artifact is caused by multiple transits of a sound wave between the transducer and the reflecting object. Increased through-transmission artifact is caused by decreased attenuation of sound waves as they travel through a fluid-filled structure. Comet tail artifact is a special form of reverberation artifact and occurs when highly refractive objects, such as calcific or crystalline objects, are interrogated. Aliasing artifact is seen with Doppler ultrasonography.
  3. b. Color Doppler.Doppler ultrasonography is important for evaluating motion and flow. The critical difference between color Doppler and power Doppler is that color Doppler is able to evaluate both flow velocity and direction. Power Doppler evaluates integrated amplitude of the returning sound waves. Although gray-scale ultrasonography does permit the evaluation of motion, it does not permit the characterization of velocity or direction. Harmonic scanning and spatial compounding are modes that allow the selective evaluation of, or combination of, reflected frequencies in ways that improve image quality.
  4. b. Hypoechoic.In describing ultrasound images, it is important to use correct terminology. Descriptive terms involving echogenicity are relative terms. A hyperechoic or hypoechoic structure is being described in relation to the echogenicity of a reference standard. In most cases, the reference standard is the liver. In the adult, the normal kidney is hypoechoic relative to the normal liver in approximately 75% of patients.
  5. e. Absence of intratesticular blood flow. The absence of intratesticular blood flow is the classic sonographic finding in testicular torsion. However, there are many documented cases of some preserved intratesticular blood flow even in cases with significant torsion.Therefore testicular torsion remains a clinical diagnosis. Epididymal edema, paratesticular fluid, and increased epididymal blood flow may be seen with testicular torsion but may also be seen with other clinical conditions. The blue dot sign is a classic physical finding in torsion of the appendix testis.
  6. b. Mechanical waves.Mechanical waves are represented graphically as a sine wave alternating between a positive and negative direction from the baseline.
  7. d. Frequency.Axial resolution is directly dependent on the frequency of sound waves. The higher the sound wave's frequency, the better the axial resolution.
  8. d. Depth of penetration.The optimal ultrasound image requires trade-offs between resolution and depth of penetration. High-frequency transducers of 6 to 10 MHz may be used to image structures near the surface of the body (e.g., testis, pediatric kidney) with excellent resolution. However, deeper structures (e.g., right kidney, bladder) require lower frequencies of 3.5 to 5 MHz to penetrate. Such images will have poorer axial resolution.
  9. c. Reflected.The shape and size of the object and the angle at which the advancing wave strikes the object are critical determinants of the amount of energy reflected. The amount of energy reflected from an interface is also influenced by the impedance of the two tissues at the interface. Impedance is a property that is influenced by tissue stiffness and density. The difference in impedance allows an appreciation of interfaces between different types of tissue.
  10. a. Hypoechoic.The liver is usually used as a benchmark for echogenicity. A hypoechoic area is described as darker and black on B-mode ultrasound.
  11. a. Lateral resolution.Lateral resolution refers to the ability to identify separately objects that are equidistant from the transducer. Lateral resolution is a function of the focused width of the ultrasound beam and is a characteristic of the transducer. The location of the narrowest beam width can be adjusted by the user. The more focused the beam, the better the lateral resolution at that location. Thus image quality can be enhanced by locating the narrowest beam width (focus or focal zone) at the depth of the object or tissue of interest
  12. e. Increasing transducer sensitivity.Gain is a control mechanism for varying the sensitivity of the transducer to returning ultrasound waves.
  13. b. Decrease the frequency.The optimal ultrasound image requires trade-offs between resolution and depth of penetration. High-frequency transducers of 6 to 10 MHz may be used to image structures near the surface of the body (e.g., testis, pediatric kidney) with excellent resolution. However, deeper structures (e.g., right kidney, bladder) require lower frequencies of 3.5 to 5 MHz to penetrate. Such images will have poorer axial resolution.
  14. a. 3.5 to 5 MHz.Deeper structures (e.g., right kidney, bladder) require lower frequencies of 3.5 to 5 MHz to penetrate.
  15. e. Hyperechoic internal nodule.A simple cyst is an example of a structure that is well circumscribed, with an anechoic interior and through transmission.
  16. c. A curved array transducer is preferred for bladder ultrasound in most patients.A curved array transducer is of lower frequency (3.5 to 6 MHz) and provides greater depth of penetration however with less axial resolution. It is most often the transducer of choice for imaging the kidney and urinary bladder.
  17. e. All of the above.Urine volume, bladder wall characteristics, the presence of calculi or diverticulum, and the presence of dilated ureters just outside the bladder are all evaluable by transabdominal bladder ultrasound.
  18. c. Doppler flow studies.Caution should be used when interpreting Doppler flow studies in the evaluation of suspected testicular torsion. The hallmark of testicular torsion is the absence of intratesticular blood flow. Paratesticular flow in epididymal collaterals may appear within hours of torsion. Comparison with the contralateral testis should be performed to ensure that the technical attributes of the study are adequate to demonstrate intratesticular blood flow.
  19. b. Inability to evaluate enhancement.Unlike CT, presently ultrasound cannot evaluate enhancement. However, use of Doppler and elastography might aid in evaluation.
  20. e. All of the above.When evaluating the prostate, surrounding structures need to be accessed. Rectal lesions, including cancer, dilated seminal vesicles, and/or ejaculatory ducts as well as bladder pathology should all be evaluated for a complete examination.
  21. d. Tip of the right seminal vesicle.In a midline sagittal view, the tips of the seminal vesicles are not normally visualized on ultrasound. A lateral projection, however, must be obtained to allow measurement of the length of each seminal vesicle.
  22. e. All of the above.Although excellent resolution and tissue characteristics are possible with transrectal ultrasound, a diagnosis of prostate cancer often cannot be made with ultrasound alone.
  23. c. An informed operator.The ALARA principle (“as low as reasonably achievable”) is intended to limit the total energy imparted to the patient during an examination. This can be accomplished by (1) keeping power outputs low, (2) using appropriate scanning modes, (3) limiting examination times, (4) adjusting focus and frequency, and (5) using the cine function during documentation. All of these are dependent on an informed sonographer.
  24. d. Critical.Any time body fluids or tissues come in contact with an ultrasound transducer, critical or high-level disinfection protocols must be strictly adhered to.
  25. c. Gain, acoustic power.Unlike gain, which refers to amplification of the acoustic signal returning to the transducer, acoustic power is the amount of acoustic energy applied to the tissue. The biologic effects of ultrasound in terms of power are in the milliwatt range. High levels generate heat and cavitation, which might result in tissue damage.

Chapter review

  1. One cycle per second is known as 1 hertz (Hz). High- frequency ultrasonic transducers of 6 to 10 MHz are used to image structures near the surface. Deeper structures require lower frequencies of 3.5 to 5 MHz. Axial resolution improves with increasing frequency, and depth of penetration decreases with increasing frequency.
  2. Resistive index is the peak velocity minus the end-diastolic velocity over the peak systolic velocity. This is measured using the color flow Doppler with spectral display and is used to characterize renal artery stenosis, ureteral obstruction, and penile arterial insufficiency.
  3. By convention, the liver is used as a benchmark for echogenicity. Tissues with a high water content are generally hypoechoic; tissues with a high fat content appear hyperechoic.
  4. By convention, the cephalad aspect of the structure is to the left of the image.
  5. Ultrasonography may produce injury due to mechanical effects caused by cavitation or by heat generation.
  6. Color Doppler evaluates velocity and direction of motion. Blue usually indicates motion away from the transducer, red indicates motion toward the transducer—the colors DO NOT signify arterial and venous flow.
  7. Sonoelastography evaluates tissue elasticity. Less elastic tissues within a soft tissue organ, such as the prostate, are thought to be pathologic.
  8. Contrast agents used in ultrasound are generally compounds containing microbubbles that create strong echoes.
  9. The central band of echoes in the kidney is hyperechoic and represents renal hilar fat, blood vessels, and the collecting system.
  10. Ultrasound measurements of bladder volume have an error of 10% to 20%.
  11. Ultrasound is very helpful in defining the extent of corporal fibrosis in urethral stricture disease.
  12. Doppler ultrasound is useful in quantization of penile blood flow. It is also useful in helping to diagnose testicular torsion by evaluating testicular blood flow. It is not diagnostic of vasculogenic impotence in the former case or testicular torsion in the latter.