Campbell-Walsh Urology, 11th Edition

PART I

Clinical Decision Making

2

Urinary Tract Imaging: Basic Principles of CT, MRI, and Plain Film

Basic Principles of CT, MRI, and Plain Film

Jay T. Bishoff; Art R. Rastinehad

Questions

  1. The measure of the potential adverse health effects of ionizing radiation in sieverts (Sv) is known as:
  2. radiation exposure.
  3. absorbed dose.
  4. equivalent dose.
  5. effective dose.
  6. relative radiation levels.
  7. The relative radiation level associated with abdominal computed tomography (CT) without and with contrast is:
  8. none.
  9. minimal, <0.1 mSv.
  10. low, 0.1-1.0 mSv.
  11. moderate, 1-10 mSv.
  12. high, 10-100 mSv.
  13. Bladder filling may precipitate autonomic dysreflexia in patients with a spinal cord injury above:
  14. S2.
  15. L4.
  16. T10.
  17. T12.
  18. T6.
  19. Radiation exposure diminishes as the square of the distance from the radiation source. An exposure of 9 mSv at 1 foot from the source would be how much at 3 feet from the source?
  20. 0.09 mSv
  21. 1 mSv
  22. 3 mSv
  23. 9 mSv
  24. 27 mSv
  25. Type 2 diabetics on oral metformin biguanide hyperglycemic therapy are at risk for biguanide lactic acidosis after exposure to intravascular radiological contrast media if they:
  26. discontinue metformin 48 hours before the study.
  27. have severe renal insufficiency and take metformin the day of the study.
  28. are given a saline injection while taking metformin.
  29. have normal kidney function and fail to stop metformin 48 hours before the study.
  30. decrease metformin dose and increase other antihyperglycemic agents on the day of the study.
  31. All of the following are true EXCEPT:
  32. Patients with a history of asthma are at greater risk of having an adverse reaction to contrast media.
  33. Severe allergic reactions are not dose dependent.
  34. Hyperosmolar contrast media are more likely to cause contrast reactions than are iso-osmolar agents.
  35. The mechanism of action associated with severe idiosyncratic anaphylactoid (IA) reactions is an immunoglobulin E (IgE) antibody reaction to the contrast media.
  36. Severe cardiac disease is a risk factor for an adverse reaction to contrast media.
  37. After rapidly assessing airway, breathing, and circulation, the medical treatment of choice for a severe, life-threatening adverse drug reaction following exposure to contrast media is:
  38. subcutaneous injection of epinephrine 0.5 mg of 1 : 10,000 epinephrine.
  39. intravenous injection of 100 mg of methylprednisone.
  40. 0.01 mg/kg of epinephrine (1 : 10,000 concentration), given intramuscularly in the lateral thigh.
  41. intravenous diphenhydramine, 50 mg.
  42. 0.01 mg/kg of epinephrine (1 : 1000 concentration), given intramuscularly in the lateral thigh.
  43. Which of the following is NOT a risk factor for developing contrast-induced nephropathy (CIN)?
  44. Type 2 diabetes mellitus
  45. Dehydration
  46. Hypertension
  47. Ventricular ejection fraction < 50%
  48. Chronic kidney disease (glomerular filtration rate [GFR] <60 mL/min)
  49. Nephrogenic systemic fibrosis (NSF) is:
  50. a rare genetic condition exacerbated by the use of gadolinium-based contrast medium (GBCM).
  51. immediately evident after exposure to gadolinium in 10% of exposed patients.
  52. fibrosis of the skin, subcutaneous tissue, and skeletal muscle seen in patients with chronic hypertension exposed to gadolinium contrast medium.
  53. not seen in patients with GFR > 60 mL/min/1.73 m2.
  54. mainly seen in dialysis patients exposed to gadolinium contrast medium.
  55. During a diuretic renal scintigraphy:
  56. the diuretic is administered approximately 2 minutes after peak activity is seen in the collecting system.
  57. a T1/2of greater than 14 minutes is consistent with obstruction.
  58. 99mTc-DMSA is the most sensitive for obstruction and determination of glomerular filtration rate.
  59. intestinal or gallbladder activity should never be seen with 99mTc-MAG3.
  60. a T1/2of less than 10 minutes is consistent with a nonobstructed system.
  61. Positron emission tomography (PET):
  62. has a higher diagnostic accuracy than CT for seminoma and nonseminoma testis cancer following chemotherapy.
  63. is sensitive and specific for detection of postchemotherapy teratoma.
  64. Can be used with high positive predictive value within 2 weeks of completion of chemotherapy for bulky lymph adenopathy.
  65. Has greater predictive value of primary disease in metastatic urothelial carcinoma than magnetic resonance imaging (MRI).
  66. Is able to detect local or systemic recurrence of prostate cancer in 74% of patients with prostate-specific antigen recurrence.
  67. What is the minimum estimated GFR for use of gadolinium-based contrast agents?
  68. Less than 30 mL/min/1.73 m2
  69. Greater than 50 mL/min/1.73 m2
  70. Greater than 35 mL/min/1.73 m2
  71. Greater than 30 mL/min/1.73 m2
  72. There are no restrictions with patients with renal insufficiency.
  73. In magnetic resonance (MR) images using T2-weighted sequences, fluid appears as:
  74. dark.
  75. bright.
  76. low signal.
  77. signal void.
  78. indeterminate.
  79. What lesions may have a high signal (bright) on T2-weighted MRI of the adrenal gland?
  80. Pheochromocytoma
  81. Metastasis
  82. Adrenal cortical carcinoma (ACC)
  83. None of the above
  84. All of the above
  85. MR chemical shift imaging for adrenal adenoma takes advantage of which of the following phenomena to aid in the diagnosis?
  86. Water and fat within the same voxels signals are canceled out in opposed-phase imaging.
  87. Opposed-phase imaging will exhibit a high signal (bright).
  88. Intracellular lipid content within an adenoma is low.
  89. Intravenous contrast is required.
  90. All of the above.
  91. Oncocytoma typically has been characterized by a central scar. Which other renal lesion may also exhibit a central scar on T2-weighted images?
  92. Clear cell carcinoma
  93. Angiomyolipoma
  94. Chromophobe carcinoma
  95. Transitional cell carcinoma
  96. No other renal masses exhibit a central scar.
  97. Which renal mass exhibits signal drop on opposed phase imaging?
  98. Papillary renal cell
  99. Chromophobe carcinoma
  100. Angiomyolipoma
  101. Clear cell carcinoma
  102. Transitional cell carcinoma
  103. What signal characteristics do kidney stones exhibit on MR urography?
  104. High signal on T2-weighted images
  105. Low signal on T2-weighted images
  106. Signal void
  107. High signal on T1-weighted images
  108. Low signal on T1-weighted images
  109. Multiparametric imaging of the prostate consists of anatomic and functional sequences. Match the correct pair.
  110. Anatomic : Diffusion-weighted imaging
  111. Functional : T1- and T2-weighted images
  112. Anatomic : Dynamic contrast enhanced sequences
  113. Functional : Apparent diffusion coefficient maps
  114. All of the above

Answers

  1. d. Effective dose.The distribution of energy absorption in the human body will be different based on the body part being imaged and a variety of other factors. The most important risk of radiation exposure from diagnostic imaging is the development of cancer. The effective dose is a quantity used to denote the radiation risk (expressed in sieverts) to a population of patients from an imaging study.
  2. e. High, 10-100 mSv.The average person living in the United States is exposed to 6.2 mSv of radiation per year from ambient sources, such as radon, cosmic rays, and medical procedures, which account for 36% of the annual radiation exposure (NCRP, 2012). The recommended occupational exposure limit to medical personnel is 50 mSv per year (NCRP, 2012). The effective dose from a three-phase CT of the abdomen and pelvis without and with contrast may be as high as 25 to 40 mSv.
  3. e. T6.Autonomic dysreflexia, also known as hyperreflexia, means an overactivity of the autonomic nervous system that can result in an abrupt onset of excessively high blood pressure. Persons at risk for this problem generally have injury levels above T5. Autonomic dysreflexia can develop suddenly, is potentially life threatening, and is considered a medical emergency. If not treated promptly and correctly, it may lead to seizures, stroke, and even death.
  4. b. 1 mSv.Maintaining the maximum practical distance from an active radiation source significantly decreases exposure to medical personnel.
  5. b. Have severe renal insufficiency and take metformin the day of the study.Patients with type 2 diabetes mellitus on metformin may have an accumulation of the drug after administering intravascular radiologic contrast medium (IRCM), resulting in biguanide lactic acidosis presenting with vomiting, diarrhea and somnolence. This condition is fatal in approximately 50% of cases (Wiholm, 1993).*Biguanide lactic acidosis is rare in patients with normal renal function. Consequently in patients with normal renal function and no known comorbidities, there is no need to discontinue metformin before IRCM use, nor is there a need to check creatinine following the imaging study.
  6. d. The mechanism of action associated with severe idiosyncratic anaphylactoid (IA) reactions is an IgE antibody reaction to the contrast media.The IA reactions are most concerning, because they are potentially fatal and can occur without any predictable or predisposing factors. Approximately 85% of IA reactions occur during or immediately after injection of IRCM and are more common in patients with a prior adverse drug reaction to contrast media; patients with asthma, diabetes, impaired renal function, or diminished cardiac function; and patients on beta-adrenergic blockers (Spring et al, 1997).
  7. e. 0.01 mg/kg of epinephrine (1:1,000 concentration) intramuscularly in the lateral thigh.Rapid administration of epinephrine is the treatment of choice for severe contrast reactions. Epinephrine can be administered intravenously (IV) 0.01 mg/kg body weight of 1 : 10,000 dilution or 0.1 mL/kg slowly into a running IV infusion of saline and can be repeated every 5 to 15 minutes as needed. If no IV access is available, the recommended intramuscular dose of epinephrine is 0.01 mg/kg of 1 : 1000 dilution (or 0.01 mL/kg to a maximum of 0.15 mg of 1 : 1000 if body weight is < 30 kg; 0.3 mg if weight is > 30 kg) injected intramuscularly in the lateral thigh.
  8. d. Ventricular ejection fraction < 50%.The most common patient-related risk factors for CIN are chronic kidney disease (CKD) (creatinine clearance < 60 mL/min), diabetes mellitus, dehydration, diuretic use, advanced age, congestive heart failure, age, hypertension, low hematocrit, and ventricular ejection fraction < 40%. The patients at highest risk for developing CIN are those with both diabetes andpreexisting renal insufficiency.
  9. d. Not seen in patients with GFR > 60 mL/min/1.73 m2. Patients with CKD but GRF > 30 mL/min/1.73 m2are considered to be at extremely low or no risk for developing NSF if a dose of GBCM of 0.1 mmol/kg or less is used. Patients with GFR > 60 mL/min/1.73 m2 do not appear to be at increased risk of developing NSF, and the current consensus is that all GBCM can be administered safely to these patients.
  10. a T1/2of less than 10 minutes is consistent with a nonobstructed system. Transit time throughout the collecting system in less than 10 minutes is consistent with a normal, nonobstructed collecting system. A T1/2 of 10-20 minutes shows mild to moderate delay and may be a mechanical obstruction. The patient's perception of pain after diuretic administration can be helpful for the treating urologist to consider when planning surgery in the patient with middle to moderate obstruction. A T1/2 of greater than 20 minutes is consistent with a high-grade obstruction.
  11. a. Has a higher diagnostic accuracy than CT for seminoma and nonseminoma testis cancer following chemotherapy.There are data on the use of PET/CT in testis cancer, where PET/CT was found to have a higher diagnostic accuracy than CT for staging and restaging in the assessment of a CT-visualized residual mass following chemotherapy for seminoma and nonseminomatous germ-cell tumors (Hain et al, 2000; Albers et al, 1999).
  12. d. Greater than 30 mL/min/1.73 m2. NSF occurs in patients with acute or chronic renal insufficiency with a GFR < 30 mL/min/1.73 m2.
  13. b. Bright.High signal on T2-weighted images. Fluid exhibits a low signal on T1-weighted images.
  14. e. All of the above.Traditional teaching reported the lightbulb sign to be consistent with pheochromocytoma. However, metastasis and ACC also have a high signal on T2-weighted images. Furthermore, Varghese and colleagues reported that 35% of pheochromocytomas demonstrated low T2 signal, contrary to conventional teaching. Therefore the conventional teaching of the “lightbulb sign” is incorrect.
  15. a. Water and fat within the same voxels signals are canceled out in opposed-phase imaging.MR chemical shift imaging (CSI) is performed on T1-weighted images. Opposed-phase imaging will demonstrate a low signal (dark) if fat and water occupy the same voxel. Adrenal adenomas have high intracytoplasmic fat. CSI is performed without the use of intravenous contrast.
  16. c. Chromophobe carcinoma.Chromophobe carcinoma exhibits a high signal on T2-weighted images.
  17. d. Clear cell carcinoma.Microscopic intracytoplasmic lipids have been found in 59% of clear cell carcinomas, which allows it to be differentiated from other renal cell carcinoma cell types.
  18. c. Signal void.Nephrolithiasis/calcification on MR imaging has no signal characteristics; therefore it appears as a void on imaging.
  19. d. Functional : Apparent diffusion coefficient maps.Multiparametric MRI refers to the use of anatomic sequences (T1-weighted images, T2 triplanar [axial, sagittal, and coronal] images) and functional sequences (diffusion-weighted imaging/apparent diffusion coefficient maps, dynamic contrast-enhanced MRI, spectroscopy). The combined approach has reported negative and positive predictive values to be greater than 90% in detecting prostate cancer.

Chapter review

  1. Absorbed dose for therapy is measured in units called gray (Gy); 1 rad = 0.01 Gy, or 1 centigray (cGy) = 1 rad.
  2. The amount of energy absorbed by a tissue for diagnostic purposes is referred to as the equivalent dose and is measured in sieverts (Sv). Exposure of the eyes and gonads to radiation has a more significant biologic impact than exposure of other parts of the body. The occupational safety limit is 50 mSv. Exposure time during fluoroscopy should be minimized by the use of short bursts of fluoroscopy; positioning the image intensifier as close to the patient as feasible substantially reduces scatter radiation.
  3. There are four basic types of iodinated contrast media: (1) ionic monomer, (2) nonionic monomer, (3) ionic dimer, (4) nonionic dimer.
  4. Idiosyncratic anaphylactoid reactions are potentially fatal, are not dose dependent, and are more common in patients with a history of adverse reactions to contrast media, those with asthma or diabetes, those with impaired renal and cardiac function, and those on β-adrenergic blockers.
  5. It is common to have nausea, flushing, pruritus, urticaria, headache, and occasionally emesis after administration of contrast media.
  6. Patients at high risk for adverse allergic reactions should be medicated with steroids, given 12 to 24 hours before the injection of contrast media, as well as antihistamines.
  7. For retrograde pyelography, it is useful to dilute contrast media by half with sterile saline, which facilitates identifying filling defects in the collecting system. There is a low risk of contrast reactions in patients in whom a retrograde or loopogram is performed.
  8. Metformin does not need to be held before contrast administration in a patient with normal renal function and no comorbidities.
  9. The risk of developing contrast induced nephropathy is increased in patients with decreased renal function (GFR < 60 mL/min), diabetes mellitus, dehydration, advanced age, congestive heart failure, liver disease, and cardiac ejection fraction less than 40%.
  10. TcDTPA is primarily filtered by the glomerulus. It is a good agent to assess renal function.
  11. Because TcDMSA is both filtered by the glomerulus and secreted by the proximal tubule, it localizes in the renal cortex and is a good agent for assessing cortical scarring and ectopic renal tissue.
  12. TcMAG3 is cleared mainly by tubular secretion; it has a limited ability to access renal function.
  13. A T1/2less than 10 minutes suggests an unobstructed system. A T1/2 greater than 20 minutes is consistent with renal obstruction.
  14. A positive bone scan is not specific for cancer. Moreover, the volume of cancer cannot be quantitated on bone scan. Patients with widely metastatic disease may have diffuse uptake (hyper scan) and no discrete lesions.
  15. Glucose, choline, and amino acids have been used as imaging agents for PET scans.
  16. 18F-fluorodeoxyglucose (FDG) is used as an imaging agent in PET scanning and takes advantage of the fact that tumors have increased glycolysis and decreased dephosphorylation. This scan is useful in testicular germ cell tumors, particularly seminomas, in determining residual viable tumor following chemotherapy.
  17. The Hounsfield units scale assigns a value of − 1000 Hounsfield units for air. Dense bone is assigned a value of + 1000 Hounsfield units, and water is assigned 0 Hounsfield units.
  18. With the exception of some indinavir stones, all renal and ureteral calculi may be detected by helical CT.
  19. The advantage of MRI is high-contrast resolution of soft tissue on T1-weighted images. Fluid has a low signal and appears dark on T1-weighted images; on T2-weighted images, fluid has a high signal and appears bright. Gadolinium increases the brightness of T1-weighted images. Hemorrhage within a cyst results in a high signal on T1-weighted images. MRI is the imaging modality of choice for patients with iodine contrast allergies.
  20. The risk of developing nephrogenic systemic fibrosis after gadolinium administration is increased in patients with GFRs below 30 mL/min.
  21. Adrenal adenomas have high lipid content and may be differentiated from adrenal cancers or metastatic disease by specialized CT or MRI scans.
  22. Thirty-five percent of pheochromocytomas do not enhance on T2-weighted images.
  23. MRI and CT are excellent imaging studies to determine the presence and extent of renal vein and vena cava tumor thrombus. Uptake of gadolinium by the thrombus on MRI differentiates tumor from bland (blood clot) thrombus.
  24. Prostate MRI coupled with an assessment of dynamic contrast uptake and washout increases the diagnostic accuracy for detecting cancer.
  25. MR spectroscopy for prostate cancer is based on decreased citrate levels and increased creatine and choline levels.
  26. Bladder filling in patients with spinal cord injuries higher than T6 may precipitate autonomic dysreflexia.
  27. Radiation exposure diminishes as the square of the distance from the radiation source.

* Sources referenced can be found in Campbell-Walsh Urology, 11th Edition, on the Expert Consult website.