Nuclear Medicine Section

The following are True/False questions:

 

 

 

 

 

 

 

 

 

 

 

1.

 

1. F

2.  F

3.   T

4.  F

5. F

With the standard 5 mCi dose of technetium-99m-MAA (200,000-500,000 particles) approximately 0.1% of pulmonary arterioles are embolized. In the infant, the number of arterioles is not as great and the number of particles is therefore reduced to 100,000. In patients with pulmonary hypertension, who have thickening of the arterial walls and pruning of the vascular tree, the number of particles must also be reduced.

It is possible to detect shunts and calculate shunt index ratios for both L-R and R-L shunts. It is possible to detect shunts as small as 20%. A mathematical function called the gamma variate is used.  Activity is measured over the lungs including recirculation.

R-L shunts may be detected using Tc-99m labeled MAA. The ratio of tracer in the lung to the tracer gaining access to the systemic circulation provides a measure of severe shunting.

 

2.

 

1 T

2. F

3. T

4. F

5. F

Renin->Angiotensin l ->/(Captopril) Angiotensin 2 ->Aldosterone -> salt and water retention

 

3.

 

1 T

2. T   Morphine contracts the sphincter of Oddi, CCK contracts GB

3.  T

4.  F  over a few minutes.

Morphine is used as an alternative to delayed imaging which is used to ensure the dx of cholecystitis and non filling of the gallbladder. Morphine is used when there has been excretion into the bowel but no visualization of the gallbladder after 1 hour. Morphine increases the intraluminal pressure at the sphincter of Oddi. This results in preferential biliary flow via the cystic duct if it is patent.

Scintigraphic examination of pt with chronic cholecystitis is usually normal. Delayed gallbladder filling is seen in <5%.

Pancreatitis is thought to create a false positive examination.

Pancreatitis is only a relative contraindication. If there is a dilated common bile duct but there is excretion to the bowel, then giving morphine is not a problem. But if there is no excretion into the bowel and the CBD is dilated, if you give morphine, you can't exclude a CBD stone. In this case, to evaluate for excretion into the bowel, need to wait hours and take a delayed film.

 

4.

 

Answer:

1. true - modified in vivo aka in vivtro, or False for traditional in vivo.

RBC labeling -- In vivo method has a labeling efficiency of 75-80%. Stannous pyrophosphate is injected. Wait 10-20minutes. Inject Na pertechnetate.

Modified in vivo (aka in vivtro) labeling has an efficacy of 85-90%. Inject stannous pyrophosphate, wait 10-20 min, withdraw 5-8ml into a shielded syringe containing Tc-99m Na pertechnetate, gently mix syringe contents for 10minutes at room temperature and reinject.

In vitro has two forms both with 98% labeling efficiency. The Brookhaven method, mix heparainized whole blood with Sn 2+, Na citrate, dextrose, NaCl. Incubate 10 minutes, add EDTA, centrifuge. Withdraw 1.25ml of packed rbc and transfer to sterile vial containing 1-3ml Tc 99m pertechnetate. Incubate at room temp for 10 minutes.

The in vitro commercial labeling kit, add heparanized whole blood to stannous chloride and mix. Add Na hypochlorite and mix. Add Citric acid, Na citrate, dextrose and mix. Add Tc pertechnetate to reaction vial and mix. Allow to react for 20 minutes.

0.5-1.0 mg of stannous ion injected for modified in vivo labeling which is described above. However, in the initially described in vivo labeling, 3.4 mg of Stannous is injected and later Tc-99 was injected directly into the blood IV NOT into a syringe of withdrawn blood.

 

5.

 

Answer:

3. False

4. True

5. False

6. True

Persantine (dipyrimidole) is an inhibitor of adenosine deaminase. It allows accumulation of adenosine in the coronary bed. This allows detection of ischemia through creation of steal phenomenon, increasing coronary blood flow 3-5 times above resting levels.

Chest pain during persantine thallium is a non-specific symptom. Other side effects include: headache, dizziness, flushing, and nausea. Side effects may be treated with aminophylline.

The half-life of adenosine is measured in seconds.

 

6.

 

Answer:

7. true

8. false

9. true

Tc sestamibi is a member of the isonitriles. Tc 99m sestamibi diffuses passively out of the blood and localizes in the mitochondria on the basis of their negative electrical potentials. The extraction fraction in the coronary circulation is less than teboroxime or Tl-201. At rest flows, the extraction is 1/2 of Tl-201. The maximum extraction decreases with increasing flow. Sestamibi underestimates flow at very high flows and overestimates at low flows.

Uptake in the myocardium is rapid but is somewhat obscured by activity in the lung and liver in the time immediately after injection. Clearance t 1/2 of Tc-sestamibi is excess of 5 hours. Progressive clearance by lung and liver over 60-120 minutes improves imaging of heart. There is minimal recirculation or redistributions after initial uptake.

Diagnostic criteria for sestamibi are the same as with thallium. In normal, there should be no defects at rest or exercise. Prior MI's will demonstrate abnormalities. Areas of exercise induced ischemia will appear as defects on post stress studies and will normalize when tracer is reinjected at rest. Sestamibi has very little redistribution.

 

6a.

 

Answer:

10. false

11. false

12. true

13. true

14.  true

Thallium 201 planar imaging uses a low-energy, high resolution or general purpose, parallel hole collimator and a 20-25% window centered at 80 KeV. This 80 keV window encompasses the K-beta series of mercury-201 x-rays. Pt are imaged in the supine position. Obtain 35 degree LAO, 70 degree LAO, left lateral views for 10 minutes each. For rest redistribution studies, repeat the same views 2-4 hr later. Use a standard or large field of view camera. The larger the matrix size, the better the potential spatial resolution, but the longer the time to achieve adequate counting statistics. Most use 64x64 or 128x128,

For SPECT imaging, use general all purpose collimator and 10%window centered at 80 KeV. The matrix is 64x64 byte mode. the framing is 60 views/180 degree arc length from 45 degree RAO to 135 degree LPO for a single head camera.

Spatial resolution is degraded the farther the camera head is from the organ of interest. So noncircular orbits or body-contoured arc paths are desirable to keep the camera head as close to the body surface as possible.

Among low energy collimators, designs are optimized for either sensitivity or resolution. The thicker the collimator, the higher the spatial resolution and the lower the sensitivity.

A variable # of stations can be used as long as the imaging is done in 15 minutes. So 36 station w/ 20-40s each is 12-24minutes.

 

7.

 

Answer:

15. false

16. true

17. true

18 . ? true

19 . false

Ga-67 is cyclotron produced with a t 1/2 of 78hrs. The biological behavior is similar to that of ferric iron. After injection it dissociates and binds to transferrin in the blood. Adequate blood supply is primary requisite for localization. Ga is delivered via increase vascular permeability. Although bacterial uptake and binding to leukocytes occur, it is not the major mechanism of localization.

Ga is taken up by normal bone and there is increased uptake in reactive bone. False positive studies occur in pt with underlying bone disease, prior surgery, fracture, prostheses. To improve specificity, Ga is used w/ Tc-99 bone scan. In direct comparison studies with In-111 WBC, Ga is less accurate. However, Ga can be useful in dx disc space infections which often have an associated soft tissue component.

Although the use of labeled WBC has replaced many of the initial indications for Ga, the detection of interstitial and granulomatous pulmonary diseases remains an important role for Ga including pneumonia, lung abscess, TB, pneumoconiosies, PCP, IPF, sarcoid, ARDS, CMV. In-111 is not as good for pulmonary disease b/c can get uptake in atelectasis. There is lower sensitivity for WBC in TB and fungal disease.

When the intraabdominal dx remains uncertain when the site of infection can't be localized with clinical, CT or US, Ga helpful. In-111 WBC is preferable b/c the tracer is not cleared thru the intestines or kidneys and the study can be complete w/in 24hrs. in pt who have not had recent surgery, Ga-67 may be the most sensitive test to uncovering the source. If + surgery history, In-111 WBC is better.

Intraabdominal abscess-- Ga has disadvantage in that it takes too long. In-111 is preferable with overall sensitivity of 90% and specificity of 95%.

 

8.

 

Answer:

20. True

21. True

22. False

23. False

24. True

Typically both the ejection fraction and stroke volume images are obtained in the 45 degree LAO projection.

Dyskinetic segments of ventricle can be identified employing the paradox image. The paradox image is essentially an inverse stroke volume image in that the diastolic frame of the ventriculogram is subtracted from the systolic frame. With normal left ventricular activity, no areas of activity (positive values) should be identified in the region of the left ventricular wall. If there is abnormal wall motion, and the wall bulges out during systole, that bulge of activity is detected as an area of unsubtracted activity.

In a normal phase analysis, the contraction pattern is expected to follow a standard sequence: atrial contraction fills the ventricular chambers followed by contraction of the ventricles. Since the atria are filling when the ventricles are emptying and vice versa, they can be thought of as contracting with the phase difference of 180 degrees.

 

9.

 

Answer:

25. true

26. true

27. ??? true

28. true

With the traditional treadmill test, ischemia is detected by alterations in the electrolyte flux across ischemic membrane which result in ST depression. On scintigrams, there is decreased regional blood flow which is seen as a cold area.

Failure to achieve adequate exercise is the single most common reason for false negative results. Included in the reasons for failure to achieve adequate exercise is dysarrhythmia.

Actual anatomy of coronary circulation is variable in its details. The distribution of the major vessels is reasonably predictable. The LAD serves the septum and anterior left ventricular wall. The left circ serves the lateral and posterior walls. The RCA serves the RV, inferior wall, inferior septum.

Poor perfusion happens first and then results in ischemia which leads to EKG changes. So, scintigraphy is more sensitive than EKG in identifying ischemic changes. In arrthymia, although there are greater false positives in scintigraphy, it is still more sensitive than EKG especially in cases like A. fib. In LBBB, the septum contracts while the rest of the ventricle is in diastole, so decreased uptake is seen in this region and classically gives a false positive reading. With EKG abnormalities, if there is ST depression in certain leads, identifying the area of ischemia is less reliable than on scintigraphy.

 

10.

 

Answer:

30. true

31. ??? false

32. false

33.

Uptake in bone by Tc-99m MDP is rapid and uptake by 2-6hrs after the injection represents approximately 50% of injected dose. In practice, most imaging begins by 2-3hrs post administration.

Mechanism of tracer localization is less well understood for phosphate substances. It is felt that adsorption is primarily to the mineral phase of bone with little binding to the organic phase. Uptake is higher in amorphous calcium phosphate than mature hydroxyapatite. This helps explain the avidity of tracer for areas of increase osteogenesis.

In Resnick, the mechanism of MDP is also not well understood. But it suggests that MDP may be able to diffuse across the bone capillary wall. The phosphate compound may chemiabsorb at kink and dislocation sites on the surface of the HA crystal. Sites of rapid bone turnover, are associated with large mineral surface that is available for exchange and chemisorption. It has also been proposed that such binding predominates at the organic matrix, particularly in the immature collagen.

 

11.

 

Answer:

34. False

35. False

36. False

37. True

38. False

- The dose of Tc-99m-SC is usually 0.5-3 mCi.

- fluids exhibit exponential emptying with a "half-life" of 30 minutes

- solids exhibit a linear curve with a "half-life" of 90 minutes. Solids are more sensitive for detecting abnormality.

- Caloric content and meal size affect the emptying time - lipids reduce the rate of emptying of both solids and liquids

 

12.

 

Answer:

39. ?false( pancreatitis is only a relative contraindication)

40. false

41. ???true

42. true

43. ?false

Morphine is used as an alternative to delayed imaging which is used to ensure the dx of cholecystitis and non filling of the gallbladder. Morphine is used when there has been excretion into the bowel but no visualization of the gallbladder. Morphine increases the intraluminal pressure at the sphincter of Oddi. This results in preferential biliary flow via the cystic duct if it is patent.

Scintigraphic examination of pt with chronic cholecystitis is usually normal. Delayed gallbladder filling is seen in <5%.

Pancreatitis is thought to create a false positive examination.

Pancreatitis is only a relative contraindication. If there is a dilated common bile duct, but there is excretion to the bowel, then giving morphine is not a problem. But if there is no excretion into the bowel and the CBD is dilated, if you give morphine, you can't exclude a CBD stone. In this case, to evaluate for excretion into the bowel, need to wait hours and take a delayed film.

 

13.

 

Answer:

44. True

45. False

46. True

47. False

48. True

49. prob true

Since Propylthiouracil blocks the organification of iodine, patients on PTU cannot be treated with I-131. A patient should be off PTU for at least 2 weeks prior to I-131 administration. While it is not desirable, if must Rx pt on PTU, increase dose by 25%.

Beta-blockers are often used for control of hyperthyroid symptoms. There is no interference with I-131 therapy.

Multinodular goiter is only treated if it is toxic. Toxic nodular goiter is called Plummerís disease. It is particularly resistant to radioactive iodine therapy and frequently requires doses 2 to 3 times larger than those applicable in diffuse toxic goiter (Graveís disease).

I-131 is only for treatment of functioning thyroid carcinoma, toxic nodular goiter (Plummer disease - dose = 20-30 mCi), or in a patient who is toxic from Graveís disease (dose = 8-15 mCi).  Administered doses are frequently selected at the higher end of the dose range if the patients are severely hyperthyroid or have large glands or significant cardiac disease aggravated by their thyrotoxic state. Note that he does not indicate a requirement to increase the dose, so answer the question as you see fit. A large gland does require an increased dose. Also, want to make sure that in pt w/ heart disease that the hyperthyroidism is cured, therefore curing the heart disease, so prob need to give a higher dose of I-131.

Patients can become transiently hyperthyroid following I-131 therapy ("thyroid storm"). However, this is rare and cardiac symptoms can be treated with beta-blockers, etc.

Pt with toxic nodules are generally thought to be more difficult to treat with radioiodine than pt with goiter because the tissue is relatively radioresistant.

 

14.

 

Answer:

50. False

51. True

52. True

53. False

54. False

55. True?

Well-differentiated papillary, follicular, and mixed carcinomas represent about 75% of all primary thyroid malignancies. Well-differentiated papillary carcinoma tends to metastasize to local neck lymph nodes, whereas follicular lesions tend to hematogenously metastasize with a predilection for the lungs and skeleton. Medullary and anaplastic carcinomas are less common and rarely concentrate I-131; therefore, iodine imaging is not useful for following these patients or in a therapeutic capacity.

I-131, not I-125 is used for imaging thyroid tissue or metastases anywhere but the anterior neck, including the substernal region.

The photopeak of I-123 is 159 keV and the photopeak of Tc-99m is 140 keV.

Discordant nodules are hot on Tc-99m but cold on iodine imaging. Some of these prove to be cancer so hot nodules on Tc-99m should be further evaluated with iodine imaging. Imaging with iodine would obviate the problem of discordant nodules.

The dose to the thyroid is lowest with

Tc-99m pertechnetate (2 rad = 0.12-0.20 rad/mCi X 5-10 mCi per exam)

I-123 (8 rad = 11-20 rad/mCi X 100-400 microCi per exam)

I-131 (80 rad = 1100-1600 rad/mCi X 30-50 microCi per exam). Therefore, the dose of I-131 is around 80 rads.

Chances of malignancy:

- patient with a cold nodule and prior head and neck radiation = 40%

- patient with a cold nodule with no history of head and neck radiation = 20%

- hot nodule = <1%

- discordant nodule = 78%

Other Factors Tending toward Malignant:

- young patients

- males

- hard lesion

- no shrinkage on thyroid hormone

- family history of thyroid carcinoma

 

15.

 

Answer:

56. True

57. False

58. True

59. False if really exact

60. True- obscures the inferior LV

Thallium is an analog of the potassium ion - it is delivered to capillary beds by regional blood flow and is actively pumped into viable cells by the Na/K adenosine triphosphate pump.

The first pass extraction of Thallium is about 90% and the plasma half-life is 10 minutes. Only 3-5% of thallium activity localizes in the heart.

The flow rate for normal/abnormal is about 2:1. Animal studies have shown that at maximum exercise, 50% stenosis is generally sufficient to consistently present as a defect.

Photopeaks of Tl-201 are 69 keV thru 81 keV (98%).

Activity in the RV is best visualized on a 30-45 degree LAO view. It is often seen normally during the stress portion of the exam. Its absence, or a defect that later redistributes, should be regarded as suspicious for ischemia. During the redistribution study phase, RV activity is usually too minimal to be visualized in normal individuals. When there is RV activity on a rest-only study, it suggests RV hypertrophy or an increased RV workload, such as pulmonary hypertension.

The right and left chamber sizes are roughly equal by scintigraphy. The ratio of lung to heart activity is usually 30%. A value of 50% or greater is abnormal, and suggests left ventricular dysfunction on the basis of coronary artery disease.

Liver or spleen activity overlying the inferior wall of the left ventricle, especially on the redistribution images, may produce a relative increase in activity in the inferior wall, with the resultant appearance of reversible redistribution on exercise studies and the reverse effect noted on dipyridamole studies suggesting inferior wall myocardial ischemia.

 

16.

 

Answer:

61. True

62. False

63. False

64. True

65. False

Cobalt-57 is used for extrinsic field uniformity (with collimator).

A point source of 200-400 microCi Tc-99m is used for intrinsic field uniformity (without collimator).

Uniformity tests are done daily.

For extrinsic field uniformity testing, most labs use a phantom filled with uniform solution of Tc-99m or permanent disk source of uniformly distributed Cobalt-57.

A bar phantom is used for resolution.

 

17.

 

Answer:

66. false- greater than 3x

67. False

68. False

69. False

Pledget activity/serum activity ratio >1.5 indicates CSF rhinorrhea (leak). ratio greater than 3:1, nasal to plasma., is considered positive.

Plasma = Serum + Fibrinogen

Imaging should be done at 1-3 hours initially because most leaks occur near basilar cisterns and this is usually when radioactivity arrives there. This also lets you check the adequacy of injection into the subarachnoid space. Measure approximately 4hrs later.

The agent of choice is Indium-111 labeled DTPA. Tc-99m compounds are of little use in adult CSF imaging because of their short half life.

Patients should be imaged in whatever position provokes the rhinorrhea.

The scintigraphic evaluation of CSF leaks always includes an imaging study and may also include a cotton pledget radioassay (i.e., well-counter measurement) if there is rhinorrhea or otorrhea. CSF leaks are detected by appearance of intrathecally administered radiotracer in a location outside the neural axis. Locations may include the nose, ears, eyes, pharynx and stomach or gut after swallowing of radiotracer. The pledget study is positive if the pledgets contain radioactivity in a ratio of 3:1 counts/gram of fluid vs. counts/gram of serum. The pledgets are usually placed in the nose and ears after the LP, removed and counted every 12 to 24 hours. Imaging should take place routinely as in cisternography at 2-6 hours, 24 hours and 48 hours as needed. In addition, an abdominal image should be obtained to detect swallowed activity.
 

18.

 

Answer:

70. True

71. true

72. True

73. False

74. False

It is more difficult to interpret a high probability scan in a patient with prior PE. This is assuming that there are no prior studies or that the prior study was abnormal. Only about 50% of patients less than 40 y/o revert to a normal V/Q scan after a PE. A normal scan is unlikely after a PE in a patient older than 60 y/o, underlying lung disease, or a PE-caused infarct. PIOPED is designed to look at patients who have not had a prior PE but can still extrapolate findings to patients with prior PE (i.e., 2 new large defects is high probability). A high probability scan in a patient with prior PE has a 74% positive predictive value - in patients without prior PE the positive predictive value is 91%.

More than 80% of patients with high probability V/Q scan have a PE. (20-79% of patients with intermediate probability and <20% of patients with low probability) Therefore, an intermediate probability scan is not worthless, especially if there is a very high or very low clinical suspicion. PIOPED data varied the probability based on clinical suspicion.

Xe-127 has a photopeak of 203 keV, and therefore can be used after Tc-99m-MAA. Xe-133 must be performed before the perfusion scan.

 

19.

 

Answer:

75. True

A CXR abnormality doesnít preclude doing a V/Q scan. One can have V/Q mismatches in areas where there is no CXR abnormality, thus giving intermediate or high probability depending on the number and size of the defects.

 

20

 

Answer:

76. False

77. False

78. False

A Low Energy All Purpose collimator is a parallel hole collimator, so it is not sensitive to lateral decentering.

The pinhole collimator is less sensitive to tracer activity but has better resolution and therefore has greater sensitivity for detecting disease.

I-131 is high energy so needs a high energy collimator with thick septa.

A low energy collimator is designed to be used with radionuclides whose emissions are up to 150 keV; it is used for technetium-99m and thallium-201. A medium-energy collimator is designed for radionuclides with emissions of up to 400 keV; it is used for I-131 and indium-111.

 

21

 

Answer:

79. True

80. False

81. False

82. False

Gallium is more sensitive than CXR for evaluation of PCP. Gallium often shows diffuse activity bilaterally when the CXR is normal. However, Gallium-67 is nonspecific and there are numerous other causes of increased lung activity (bleomycin toxicity, miliary TB, XRT, ....). The Gallium scan will return to normal only after the PCP has been completely treated.

Uptake in the hila in a patient with AIDS is more suggestive of MAI or TB. In a patient who does not have AIDS, this pattern can be seen with sarcoid, lymphoma, etc. Similarly, uptake in abdominal lymph nodes can be seen with MAI, but also with many other entities, especially lymphoma.

With Indium-111 scanning, diffuse lung activity corresponds to disease in only 10% of cases. One in six normal patients have increased pulmonary localization of Indium-111-labeled WBCs, for reasons which are not clear.

 

22

 

Answer:

83. False

84. False

85. False

86. False

87 False

Thin layer chromatography is used to check for radiochemical impurity. To check for free TcO4-, the agent is typically acetone, since this will cause free technetium to migrate and most labeled compounds will remain stationary (including Tc-99m-MAA, colloid, and microspheres).

Macroaggregated albumin particle size may be evaluated by using a hemocytometer slide.

USP limit for radiochemical purity is 95% for TcO4-, 92% for TcSC and 92% for all other Technetium-labeled compounds.

With the standard 5 mCi dose of technetium-99m-MAA (200,000-500,000 particles) approximately 0.1% of pulmonary arterioles are embolized. In the infant, the number of arterioles is not as great and the number of particles is therefore reduced to 100,000. In patients with pulmonary hypertension, who have thickening of the arterial walls and pruning of the vascular tree, the number of particles must also be reduced.

 

23

 

Answer:

88. False

89. False?

90. True

91. False

92. False

In a patient with a known malignancy, a single bone lesion on bone scan has a 54% chance of being a metastasis . Pain at the site of a bone lesion increases the likelihood of tumor being present. Half of the solitary metastases discovered by bone scan will not be evident on plain film.

At least in 1995, bone scan is frequently used in preoperative staging of patients with prostate cancer, looking for occult metastases (MR may eventually take over this role). It is more sensitive than plain films for detecting nearly all metastases. There needs to be 50% cortical loss to see metastases on plain film versus 2% for some tumors on bone scan.

Renal cell carcinoma is one tumor that may give photopenic metastases, reflecting the low metabolic activity and bone turnover, but they can show areas of increased activity. Bone scanning is relatively insensitive for bone metastases in metastatic renal cell carcinoma, with a true positive rate of 50% or less. However, the metastases usually are clinically apparent.

Prostate metastases always show increased activity reflecting their osteoblastic nature.

A positive bone scan in any patient with previously unsuspected diffuse metastases will obviously change prognosis.

Flare refers to worsening of a patients bone scan in the period immediately following chemotherapy reflecting healing of metastases. This can be seen as early as 3 weeks following treatment and as late as 6 months after treatment, so donít recommend a bone scan during this period because you canít tell the difference between better and worse!

 

24

 

Answer:

93. True

94. False

95. False

96. False

97. False

Total body imaging is usually done to find metastases - the dose is 2-5 mCi I-131. Scanning is frequently performed beyond 24 hours (usually 48-72 hours) because it demonstrates more lesions. The long half-life (8.1 days) allows this. Medullary and anaplastic carcinomas do not take up iodine. You can get bowel activity of I-131 (via salivary secretions) but it usually does not interfere, particularly on >24 hour delayed images

Guidelines:

- off of T4 for 6-8 weeks

- off of T3 for 3 weeks

- off of PTU for 2 weeks

- not have had water soluble iodinated contrast for 4 weeks

Stunning of the thyroid is the real reason why activity is limited. At >2mCi stunning can happen. It most commonly occurs after 5-10 mCi I 131, most marked at 24 hr. This finding is pretty recent-- 1995-96.

 

25

 

Answer:

103. False

104. False (if the collimator doesnít get larger, making thinner septae gives a larger hole diameter, and possibly greater septal penetration)

105. True

106. True

Resolution of a scintillation camera is comprised of intrinsic resolution of the camera (Ri) and resolution of the collimator (Rc). Overall resolution is the square root of Ri squared + Rc squared.

Resolution of the collimator is inversely proportional to d (F + L + c)/L where:

d = hole diameter

F = distance of the source from the collimator face

L = length of the collimator

c = thickness of the crystal

Intrinsic resolution of the camera cannot be changed by the operator.

Note that in general resolution and sensitivity are inversely proportional - increasing the sensitivity will decrease the resolution and vice versa.

Pinhole collimators have extremely high resolution at the expense of sensitivity (very few photons get through) and distortion of images arising from photons arising from different planes.

 

26

 

Answer:

107. False

108. False

109. False

110. False

In patients with Alzheimer disease, brain scans typically reveal bitemporoparietal defects. Accompanying bifrontal decreased activity has also been described. Sensitivities of 80-90% have been reported using either hexamethylpropylene amine oxime (HMPAO) or iodoamphetamine (IMP). "Alzheimerís disease may be differentiated from other causes of senile dementia by the characteristic bilateral decrease in regional cerebral blood flow in the parietotemporal cortex with preservation of uptake in the sensory-motor cortex, basal ganglia, visual cortex, and cerebellum." Alzheimers has a predilection for the temporal and parietal lobes.

Pick disease is a form of dementia which is clinically similar to Alzheimer disease. The hallmark is severe atrophy of the anterior portion of both frontal lobes. With SPECT imaging, bifrontal defects are seen, accompanied by volume loss. Progressive supranuclear palsy may also demonstrate similar findings.

AIDS encephalopathy is due to infection of the brain by the HIV virus, and does not indicate an opportunistic infection. Multiple, small cortical defects are seen using SPECT imaging with either IMP or HMPAO. The pattern is not distinguishable from multiinfarct dementia.

 

27.  

 

Answer:

111. False

112. False

113. False

114. False

If there are no perfusion defects or if perfusion defects are substantially smaller than radiographic abnormality then the scan is low probability.

If there are large unmatched V/Q abnormalities, a scan can be called high probability in a patient with COPD.

The fissure sign represents pleural fluid in fissures - it is unrelated to COPD.

The stripe sign refers to a margin of radioactivity between a perfusion defect and the pleural surface of the lung. The significance of this finding is that this indicates that the perfusion defect is likely due to parenchymal abnormality rather than PE.

Revised PIOPED criteria:

- intermediate prob. ------> 1 large + 1 segmental defect

- high probability ---------> greater than or equal to 2 large or 1 large and greater than or equal to 2 moderate or greater than or equal to 4 moderate segmental defects

 

28

 

Answer:

115. True

116. False

117. True

118. True

119. False

Neuroblastomas do and Wilms donít take up bone scan agents.

Chemotherapeutic agents which may cause increased uptake in the kidney on bone scan: doxorubicin, vincristine, cyclophosphamide.

 

29.  

 

Answer:

120. True

121. False

122. True

123. False

124. False

Iodine scans require approximately 2 weeks off of propylthiouracil (PTU). PTU blocks Iodine organification in the gland, but will not affect the Tc-99m-pertechnetate scan. Although a technetium pertechnetate scan can be completely done in 2 hours, an iodine uptake can be done in 2 hours. Technetium pertechnetate is given IV and iodine is given po.

If there is a hot nodule on the pertechnetate examination, then an iodine scan should be done ----> 2-3% will be cold (i.e., carcinoma). If the lesion was hot on a previous iodine scan, technetium pertechnetate will not add any information.

I-131 treatment should only be based on I-123 or I-131 uptakes.

 

30.  

 

Answer:

125. True

126. False

127. True

128. True

Imaging is done immediately after ingestion.

Sulfur colloid or indium may be used.

Calculations are done with a geometric mean of the anterior and posterior counts to correct for attenuation; however, if this choice is not given, anterior scanning is better than posterior scanning.

 

31.

 

Answer:

129. false

 

32. 

 

Answer:

130. False

You canít do equilibrium or washout with Krypton (because of short half-life of 13 seconds) to measure air trapping. The photopeak is 191 keV.

 

33. 

 

Answer:

131. False

132. False

133. False

134. False

135. True

Any room is OK, Xenon needs a special room. Xenon requires collection of exhaled gas and outside ventilation (under strict regulation) or trapping in charcoal until counts decay to background.

Tc-99m DTPA ventilation scans are done with aerosol. Approximately 30 mCi/ 2 ml is injected into the nebulizer. Initial images are obtained for 200,000 counts (or 3 minutes) with the patient in the erect position. Other views may be obtained. The nebulizer may be connected to an endotracheal tube. Because perfusion imaging is also performed using a Tc-99m agent, a 3-5 times count rate differential must be used when using Tc-99m aerosol to prevent interference of the two radiopharmaceuticals. Of course, the order doesnít matter as long as the second examination has the greater number of counts.

With Xe-133, images are usually only obtained in one projection and are performed before the perfusion study.

The Xenon-133 study consists of three phases. First, a single-breath image is obtained, followed by 4 minutes of rebreathing (ending with a 300,000-count image), and 6 minutes of washout images. The lung fields should return to baseline after 3 minutes of washout.

Only 7% of ventilation abnormalities are seen on the first-breath study alone. Overall, 64% of all ventilatory abnormalities are seen on first-breath images. On the washout images, there is a 94% sensitivity for ventilatory abnormalities at 1 minute, accompanied by only a 62% specificity. At 3 minutes, the sensitivity decreases to 83%, but the specificity improves to 85%.

Usually, only posterior images of the lung are obtained on Xenon studies. For this reason, anterior defects are sometimes poorly appreciated.

 

34.

 

Answer:

136. True

137. False

138. False ???

139. True

140. True

 

35.

 

Answer:

141. True (??? False)

142. True

143. false

144. True

145. False

Ejection Fraction (EF) = (end diastolic - end systolic)/(end diastolic - background)

Normal EF is >55%.

If the left atrium or ascending aorta is inappropriately included in measurement of end systolic counts, EF will be falsely lowered (ED will measure inaccurately high). If end systolic counts are undermeasured, this will falsely elevate EF. Under measurement or failure to include background counts in the denominator will increase it, thus falsely lowering the EF.

Diastolic dysfunction may precede abnormalities of systolic function (EF). Diastolic function may be evaluated by first pass imaging/time activity curves by measuring peak filling rates. Peak filling rates are decreased with diastolic dysfunction secondary to decreased compliance of the LV.

 

36.

 

Answer:

146. true

147. ?true

148. ???true

149. ??? true

150. ???true

One of the advantages of SPECT is that the volume of image data is collected simultaneously. Planar radionuclide imaging suffers a limitation in the loss of object contrast from background activity-- the radioactivity underlying and overlying an object is superimposed on the object. For thallium -201 it is desirable to keep total imaging time below 10minutes because of internal redistribution. So for 180 degree arc is used for single head cameras. Multihead cameras get info in a shorter time.

For planar imaging, get three views for ten minutes each.

Two artifacts in imaging the ventricle is overlying soft tissue from the breast in women and the interposition of the diaphragm between the gamma camera and the heart on the left lateral view with the pt supine.

 

37.

 

Answer:

151. True

152. True

153. False

154. prob. True

Hemangiomas typically demonstrate hypoperfusion on the angiographic phase, followed by relative increase in activity in the liver lesion as compared to the normal liver tissue in delayed images. It has been suggested that a 2-hour delayed scan may improve specificity.

With technetium-labeled RBCs imaging should be done at 1-3 hours, as there may be decreased visualization of the hemangioma at >4 hours. Decreased flow in early imaging is essential for diagnosis, increased flow important later.

In vivo tagging involves injecting 2 mg of stannous pyrophosphate intravenously. After 10-20 minutes, 20 mCi of technetium-99m pertechnetate is injected. This results in 60-70% labeling. The in vitro method of labeling is preferred (labeling efficiency approximately 95%). The labeling efficiency of the in vivo method is approximately 80% - this would decrease sensitivity - itís up to you to decide if that is "significant."

 

38.

 

Answer:

155. True

156. probably True

157. True

158. True

The technetium agents = Sestamibi or Teboroxime

At rest, the extraction fraction of Sestamibi in the coronary circulation is about 1/2 that of thallium.

Sestamibi does not redistribute (myocardial clearance half-life of Tl-201 is approximately 5-10 minutes while that of Sestamibi is greater than 5 hours) - therefore image Tl-201 5 minutes after injection and image Sestamibi 30-90 minutes after injection .

Sestamibi has only a slight redistribution. (Teboroxime does not redistribute at all.) The lack of redistribution of Sestamibi means that 2 injections must be done - one at rest and one at stress. Since thallium redistributes, in theory, you only need one injection for both stress and rest. However, two injections are routinely employed to improve detection of reversible defects.

 

39.

 

Answer:

159. True

160. True

161. False

Multiple gated acquisition.

Atrial fibrillation does degrade the quality of the scan. Each R-R interval is divided into 16-32 segments and data is sorted into these segments. An irregular rhythm can severely degrade images.

A first pass study is more accurate for RVEF than MUGA. The right ventricle is not reliably separated from the right atrium and left ventricle on equilibrium studies.

An inappropriately small systolic ROI does not cause an artifactually low EF, actually it causes and artifactually high EF.

 

40.

 

Answer:

162. False

163. false

164. True

165. true

Data on single photon emission computed tomography (SPECT) is obtained volumetrically which permits multiple tomographic slices to be obtained simultaneously with registration of the data between planes. Image reconstruction for PET is the same principle as SPECT.

 

41.

 

Answer:

172. False

173. False

174. True

175. False

Daily: peaking, constancy or uniformity (before first clinical case using point source)

Weekly: spatial resolution and linearity; SPECT - center of rotation shift test, uniformity

Monthly: collimator uniformity

Yearly: accuracy (+/- 5%)

Upon installation and after every repair: geometric efficiency

 

42.

 

Answer:

176. True

177. True

Parathyroid scintigraphy is usually a combination of pertechnetate and thallium imaging. A pertechnetate (thyroid) scan is subtracted from a thallium (both thyroid and parathyroid) scan to reveal parathyroid activity alone, although the pathology is evident in most cases without subtraction. False positives in parathyroid scintigraphy include thyroid carcinoma, goiter, and lymphoma (all accumulate thallium but not pertechnetate).

In subtraction imaging, the thallium is avidly taken up in the thyroid and parathyroid tissue, while Tc-99m is only accumulated in thyroid tissue. Pitfalls of this technique include, inhomogenous uptake in a multinodular goiter, or follicular adenoma. Primary mets can take up Thallium and give a false positive. Pt motion can also give misregistration.

 

43.

 

Answer:

178. False

179. true

180. False

181. True

182. True

183. True???

Valid reasons for stopping the test are: angina, EKG change (ST segment depression of 5 mm in asymptomatic patients, and 3 mm ST depression in patients with angina), exhaustion, or hypotension. 

Pt request

inability to continue due to fatigue, dyspnea, faintness

chest pain

syncope, blurred vision

pallor, diaphoresis

ataxia,

claudication

V. tachy

atrial tachy/fib

2nd/3rd degree heart block

S-T depression >3mm

decreased systolic pressure

increase in systolic >240mmHg or

diastolic > 120mmHg

The LAD supplies the septum.

 

44.

 

Answer:

184. False

185. False

186. False

187. True

Normal resting ejection fraction should be greater than or equal to 55% and should rise by at least 5% with exercise (except in young females and in patients with high baseline ejection fractions - in this case the EF should increase by at least 3%).

 

Nuclear Medicine

Select the single best answer

 

45.

 

1 F

3

4

5 T

 

46.

 

Answer: 2

 

47.

 

Answer: c. 100-200 mCi

Doses are 100 mCi for thyroid only, 150 mCi for lymph node metastases, and 200 mCi for diffuse metastases. Repeated doses up to 1 Ci may be required.

 

48.

 

Answer: b

In the in vivo rbc labeling, the pertechnetate diffuses across the rbc membrane where it is reduced by the stannous ion. The Tc-99m label binds to the beta chain of the hemoglobin.

 

49.

 

Answer: a. has greater sensitivity than angiography

Nuclear medicine scintigraphy with sulfur colloid for GI bleeding can detect bleeding at rates of 0.05-0.12 cc/minute which approximately 1/10th the rate at which angiography can reliably detect bleeding.

There is too much background activity from accumulating activity in the liver and spleen to allow sulfur colloid imaging to be useful in the upper GI tract.

Sulfur colloid scanning is a one-shot deal with useful images being obtained for approximately 30-45 minutes after the injection. Labeled red blood cells can be used to image the patient in a delayed fashion for intermittent bleeds.

 

50.

 

Answer: c. metastatic breast cancer

Most metastases are space-occupying (therefore, decreased activity) lesions on liver-spleen scan. In a 40 y/o female breast cancer is more likely than colon cancer.

Focal nodular hyperplasia frequently is indistinguishable from liver on L-S scan but also can have increased uptake.

Adenomas are usually photopenic but can have normal activity (they don't contain Kupffer cells) - also, this is not a common lesion - breast metastases are more likely.

Budd-Chiari syndrome (hepatic vein thromboses) may occur secondary to tumor invasion or hypercoagulation syndromes, but frequently the etiology is undetermined. It presents as an enlarged, tender liver accompanied by ascites. It causes increased activity in the caudate lobe (or decreased activity everywhere) secondary to its direct IVC drainage.

SVC obstruction can cause increased activity in the quadrate lobe if injection is done in either arm.

Aluminum clumps cause focal increased activity.

 

51.

 

Answer: c

Radiopharmaceutical used in bone imaging included Strontium-85. Strontium is an analogue of Ca and is an avid bone seeker. The limitation includes the higher gamma photon energy and long t 1/2 resulting in high radiation dose. Strontium- 87 has a short t1/2 and decays by isomeric transition and has more favorable energy. The beta emitter Strontium -89 has been used for therapy of skeletal malignancy in the Rx of bone pain.

 

52.

 

Answer:

a. false

b. false

c. false

d. false

The dx of brain death is a clinical determination. The criteria defined include, deep coma with total abscence of brain stem reflexes or spontaneous respiration, reversible causes such as drug intoxication, metabolic problems, hypothermia must be excluded. The cause of brain dysfunction must be diagnosed and the clinical finding of brain death must be present for a defined period of time (6-24hr).

Confirmatory tests can increase the certainty, but the dx is primarily clinical. EEG, and radionuclide studies just evaluate the cortex not the brain stem. In the setting of barbituate toxemia, hypothermia, the EEG may be flat even though recovery is possible.

Scintigraphy is not affected by drug intoxication, hypothermia. Abnormal radionuclide angiogram is more specific than EEG for brain death.

Dx findings of brain death include the lack of intraarterial flow and no visualization of major venous sinuses. Often the "hot nose" sign is seen in dx of brain death. Can occasionally see faint visualization of sagittal or transverse sinus in absence of cranial perfusion.

Tc-99m HMPAO is used for cerebral perfusion imaging. In brain death, HMPAO shows no cerebral perfusion. It is advantageous because can evaluate on bolus flow images or on delayed images. therefore, it is not dependent on a good bolus needed for flow imaging. The distribution of HMPAO is proportional to the regional cerebral blood flow. By 10 minutes there is rapid 15% washout of brain activity.

 

53.

 

Answer:

a. false

b. false

c. false

d. true if mean to periphery of parenchyma

The stripe sign refers to a margin of radioactivity between a perfusion defect and the pleural surface. PE should extend all the way to the pleura. If stripe sign, suggest parenchymal abnormality such as pulmonary hemorrhage or other fluid accumulation other than PE.

Pleural effusions attenuate the signal. If the pt is upright, can get fluid in the fissure causing a curvilinear perfusion defect. If subpulmonic effusion, can potentially miss the presence of an effusion.

 

54.

 

Answer:

a. true

b. false

c. ?false

d. ?true

e. true

It is possible to detect shunts and calculate shunt index ratios for both L-R and R-L shunts. It is possible to detect shunts as small as 20%. A mathematical function called the gamma variate is used.  Activity is measured over the lungs including recirculation.

R-L shunts may be detected using Tc-99m labeled MAA. The ratio of tracer in the lung to the tracer gaining access to the systemic circulation provides a measure of severe shunting.

 

55.

 

Answer: b

A small perfusion defect is < 25% of the segment. So if there are five small defects, this is <125% of the lungs. In order to be high prob, two or more large defects must be seen or any combo of defects equivalent-- a large defect is >75%, so is > 150%. So , 5 small segmental perfusion defects is in the Intermediate category-- difficult to categorize in low or high prob.

PA-gram should be performed w/in 24 hours of the acute episode but with time, the thrombus fragments and relocates peripherally. If arteriography is delayed >24hrs, should really focus with magnified images on peripheral branches. Usually if PA-gram is performed w/in 24-48hrs, its sufficient for ID PE. An intermediate prob V/Q scan leads to Impedance Plethysmography (IPG) or US. If IPG is positive, treat. If negative IPG, don't treat if low clinical suspicion OR treat, if high clinical suspicion. This pt is a high clinical suspicion.

 

56.

 

Answer: a. 5

The dose calibrator should be tested daily. Calibration of the circuits should be done with 100-200 microCi of cesium 137 (662 keV) (which is similar in energy to Mo-99) and 2-5 mCi of cobalt 57 (122 keV) (which is similar in energy to technetium 99m). After decay corrections are made the observed activity should agree with the actual calibration source activity by +/-5%.

 

57.

 

Answer: d. metastatic breast cancer

Metastatic colon cancer and osteosarcoma may contain Ca++ and thus may show increased activity on Tc-99m-MDP.

Aluminum and air can cause clumping and focal areas of increased activity.

Metastatic breast cancer is more likely to cause a photopenic defect because its metastases rarely calcify. (However, this may not be true for treated breast mets!) Breast carcinoma metastases may pick up bone tracer, and widespread cholangiocarcinoma is another cause of this scintigraphic appearance.

Focal nodular hyperplasia frequently is indistinguishable from liver on L-S scan but also can have increased uptake.

Hepatitis on L-S scan can show a heterogeneous appearance.

 

58.

 

Answer: b

 

59.

 

Answer: b

Causes of a superscan with decreased renal uptake include metastatic disease, metabolic bone disease (hyperthyroidism, primary hyperparathyroidism, renal osteodystrophy, osteomalacia, hypervitaminosis D), myelofibrosis.

Scintigraphy doesn't have a role in osteoporosis. Can ID insufficiency fractures.

 

60.

 

Answer: a. delayed, decreased uptake in the right kidney

Captopril prevents the effect of angiotensin II on efferent arteriole vasoconstrictors. This results in decreased glomerular flow, decreased urine output, and decreased renal function. Renal blood flow may increase after captopril and may be one reason why there is slow uptake (and therefore slow increase in activity) - the glomerulus has less time to "see" the tracer on each pass. There is also decrease in peak activity and retention of activity by the kidney.

 

61.

 

Answer: a. useful for following antibiotic treated osteomyelitis

Gallium, not indium, is useful for following antibiotic-treated osteomyelitis. Antibiotic therapy is a cause for false negative indium scan.

 

62.

 

Answer: e. aluminum contamination

Dehydration is a common cause of increased renal uptake. Chemotherapy (cyclophosphamide, vincristine, doxorubicin), XRT, and nephrocalcinosis are less common causes of increased renal uptake. Blood aluminum is a rare cause of artifactual increased uptake in the kidneys.

Focal increase:

- common: urinary tract obstruction, normal variant

- uncommon: metastatic calcification (breast, poorly differentiated lymphocytic lymphoma), radiation therapy to kidney

- rare: renal carcinoma, renal metastases from lung carcinoma

Diffuse increase:

- common: urinary tract obstruction, unknown

- uncommon: metastatic calcification, malignant (transitional cell carcinoma of bladder, malignant melanoma), benign (hyperparathyroidism), chemotherapy (cyclophosphamide, vincristine, doxorubicin), thalassemia major

- rare: multiple myeloma, crossed renal ectopia, administration of sodium diatrizoate after the injection of Tc-99m-phosphate compound, paroxysmal nocturnal hemoglobinuria, acute pyelonephritis

 

63.

 

Answer: b. gangrenous cholecystitis

The rim sign is seen in 20% of patients with acute cholecystitis - 40% of these patients have gangrene or perforation. The sign is not associated with chronic cholecystitis or ascending cholangitis.

 

64.

 

Answer: b. 5-10%

This corresponds to a low probability V/Q scan, making the likelihood of PE<20%. High prob is >80% chance PE, Intermediate is 20-80%.

 

65.

 

Answer: d. normal first and second phases, hot on third

Shin splints represent a chronic traction periostitis at the posterior tibial muscle insertion. They usually present as a flat/linear area of increased activity in the posteromedial and anterolateral cortex of the tibia. Perfusion and blood pool images are normal. Treatment is rest and antiinflammatories.

Stress fracture presents as a fusiform focus of increased activity.

A bone scan is more sensitive than a radiograph for the diagnosis of both shin splints and stress fractures, and often becomes positive earlier in the course of disease.

 

66.

 

Answer: d. adrenal aldosteronoma

MIBG is used to scan adrenal medullary hyperplasia or tumors or other neuroendocrine tumors (APUDomas). These include adrenergic tumors (pheochromocytomas, neuroblastoma, ganglioneuromas, ganglioneuroblastoma, and paragangliomas), carcinoids, islet cell tumors, and medullary carcinoma of the thyroid. MIBG is structurally similar to norepinephrine and is taken up into presynaptic receptors. The senstivity for detection of pheochromocytoma is between 79% and 89%.

I131-NP-59 (iodocholesterol) is used to image adrenal cortical tumors

67.

 

Answer: a. morphine (and maybe c)

When you donít see the gallbladder after 30-45 minutes, morphine is given to cause contraction of sphincter of Oddi which refluxes DISIDA into the patent (normal) cystic duct and into the normal gall bladder. This raises the sensitivity to 95% for detecting acute cholecystitis.

Often, by the time you give morphine (dose is 0.04 mg/kg up to 4 mg), most of the DISIDA is gone, so you may need to reinject the patient.

 

68.

 

Answer: c. subacute thyroiditis

Subacute thyroiditis typically presents with symptoms of hyperthyroidism and increased T3 and T4 but very low thyroid uptake. It usually follows a viral illness - typically measles, mumps, rubella, coxsackie, or influenza. It presents with a tender gland, adenopathy, hyperthyroidism, thyromegaly, and can be painful.. None of the other choices listed are painful.

Hashimoto thyroiditis is characterized by autoantibodies to thyroid tissue and thyromegaly. It may be accompanied by hyperthyroidism, hypothyroidism, or normal thyroid function. A thyroid scan may reveal uniform increase uptake, a multinodular goiter, or diffusely poor uptake. Occasionally it may be difficult to distinguish from Grave disease.

Suppurative thyroiditis results from bacterial infection and is rare.

While iodinated contrast may lower subsequent levels of thyroid uptake, by 8 weeks after the CT scan it should not be <1%. We typically wait about 3 months after contrast-enhanced CT before doing an uptake measurement to assure that there is no effect from iodinated contrast.

The following drugs can affect the radioiodine uptake examination. Also given is minimum length that the drug must be withheld before uptake can give accurate results:

1. PTU - 7-10 days

2. T3 - 2 weeks

3. T4 - 6 weeks

4. water soluble iodinated contrast - 4-8 weeks

5. Pantopaque - many years

 

69.

 

Answer: b. low probability

PIOPED- modified

Hi prob- >80%

two or more large mismatched segmental defects w/o x-ray abnormality

any combo of smaller defects equal to above

Intermediate prob- 20-80%

one moderate defect w/ nl CXR

one large and one moderate mismatch w/ nl CXR

not low or hi prob

Low prob <20%

nonsegmental defects

any perfusion defects w/ larger CXR abnormality

matched V/Q defects

Nl

no perfusion defects

If the defects are in the lower lobes-- triple match, it is intermediate probability.

 

70.

 

Answer: a. Nocardia or c. Cryptococcus

PCP, CMV, and lymphoma take up Gallium-67 in the lungs. Granulomatous processes like miliary TB and histoplasmosis; therefore one would assume that Cryptococcus would also be positive. Given that Nocardia can be acute and suppurative, it is probably the right answer. A reference in Thrall that pulmonary Nocardia is hot on Gallium-67 - so ?is the answer Cryptococcus?"

 

71.

 

Answer: d. be performed

The nuclear medicine people say that the study should be performed as Tc-99m-MDP will not cross the placenta (free technetium will cross the placenta). Regardless ---> as a general rule of thumb: the medical condition of the pregnant woman dictates the need for radiographic studies --- if she needs it, do it, regardless of fetal age.

The effects of irradiation during pregnancy are related to the age of gestation. This can be divided into three stages:

1. preimplanation - through the ninth post-conception day. The principal result of irradiation is high incidence of prenatal death. Growth retardation is not observed and if the embryo survives, it grows normally in utero and afterwards.

2. organogenesis - in the ninth through forty-second day. During this stage, a great variety of congenital anomalies of a structural nature appear as a consequence of irradiation. The embryonic cells are in a differentiating stage and are particularly sensitive. Embryos exposed during early organogenesis also exhibit the greatest intrauterine growth retardation.

3. the fetal stage - corresponds to six weeks to term in the human. Irradiation during this period leads to fewer obvious structural abnormalities. Functional disabilities can occur, and are much more difficult to identify. It has been suggested that growth disorders and possibly a lowering of subsequent intelligence could result.

These guidelines are based on experience conducted on pregnant mice and rats. A dose of 200 rads during the organogenesis period results in abnormalities in virtually 100% of offspring, the lowest doses at which an excess of anomalies was reported was between 18 and 25 rads.

The effect of radionuclides on the developing embryo or fetus has not been studied as extensively as the consequences of externally administered X-rays. Biological effects depend on many factors including chemical form of the isotope, type and energy of the radiation emitted and whether or not the compounds containing the radioactivity crossed the placenta. There is justification for carefully avoiding the use of radioactive isotopes of iodine in pregnancy since organic iodine crosses the placenta and is taken up by fetal thyroid from the 10th week onward. Technetium-99m is much less hazardous since it has a shorter half-life and does not emit beta rays.

In the presented case, the woman in question is seven months pregnant which is beyond the organogenesis period. The estimated absorbed dose to embryo/fetus for technetium-99m phosphonate is 0.040 rads/mCi, It would be unlikely that the fetal absorbed dose from a technetium-99m radiopharmaceutical would exceed 0.5 rads. Based on this data, it would seem that a bone scan would probably not harm the fetus. However, after considering the consequences of a positive result (that the patient would either get chemotherapy or radiation which would definitely harm the fetus), the question is ... what difference would it make? Is the clinician going to treat a metastatic lesion and in so doing possibly harm the fetus?

Of course, the most appropriate first study would be a plain film with shielding of the fetus. If this was positive, then no further studies involving diagnostic radiation need be performed.

 

72.

 

Answer: b. Gallium-67 scan

 

73.

 

Answer: a. low

 

74.

 

Answer: a. portal hypertension or d. intrahepatic shunting  could it be b . hepatocellular dysfunction

In a liver-spleen scan with Tc-99m sulfur colloid, increased sulfur colloid concentration by the spleen and bone marrow compared with the liver ("colloid shift") may be found in patients with diseases that cause derangement of hepatic function and/or portal hypertension. Among diffuse hepatocellular diseases, hepatic cirrhosis is the most common abnormality presenting in this fashion.

The mechanisms governing colloid shift have variously been attributed to:

1) the consequences of portal hypertension with shunting of colloid-laden blood away from the liver to the spleen and bone marrow and/or

2) a decrease in the number or functional capability of hepatic Kupffer cells, thereby decreasing liver clearance of sulfur colloid.

In various liver diseases, either or both of these principles may play a role. However, the observation that alleviation of portal hypertension does not necessarily result in a return to normal radiocolloid distribution has led some investigators to postulate that intrahepatic shunting, not portal hypertension per se, plays the major role in producing the phenomenon of colloid shift, especially in cirrhotic patients. Such shunting would allow portal blood to bypass hepatic sinusoids, making more colloid available to the spleen and bone marrow.

 

75.

 

Answer: a. chronic renal failure with renal osteodystrophy

Hyperparathyroidism or renal failure may cause localized activity in the GI tract (particularly the stomach) as well as the lungs. Both may also cause a superscan.

Causes of a superscan include: metastatic disease from breast or prostate carcinoma and metabolic bone disease (osteomalacia, hyperparathyroidism, and renal osteodystrophy).

 

76.

 

Answer: b. intermediate probability

 

77.

 

Answer: a. lung

 

78.

 

Answer: e. hibernating myocardium

Hibernating myocardium refers to severe, chronically ischemic tissue that is viable but appears cold on thallium imaging and nonfunctional on echocardiography. PET imaging will demonstrate increased F18-labeled-FDG uptake.

Stunned myocardium is myocardium in the distribution of an acutely ischemic area -- this may not survive. Stunned myocardium usually will take up thallium.

Ammonia is a marker for myocardial perfusion-- look like thallium perfusion scans. FDG is a marker for glucose uptake. In areas of ischemia, metabolism is switched to glucose. Necrotic tissue does not demonstrate FDG uptake. In early studies, tissue that showed decreased perfusion but had FDG uptake, showed improved function after reperfusion surgery. Ischemic myocardium acute or chronic has decreased or no NH3 perfusion, but + FDG.

 

79.

 

Answer: c. pyelonephritis

ATN and cyclosporin toxicity typically present with preservation of renal perfusion but poor excretion of radiotracer. However, cyclosporin toxicity, hyperacute and chronic rejection, and ureteral or renal artery occlusion may all have diminished perfusion and function.

ATN, cyclosporin toxicity (similar scintigraphic appearance to ATN), obstruction, and renal artery stenosis S/P captopril will all show increasing MAG-3 activity.

Pyelonephritis results in defects of MAG-3 uptake. These can be wedge-shaped.

 

80.

 

Answer: probably b. detection of breakthrough molybdenum - this probably was an incompletely remembered matching question.

Photopeak testing is used to assess Mo-99 breakthrough in generator eluate. (Mo-99 has gamma rays at approximately 740 keV, Tc-99m at approximately 140 keV.) The NRC limit is 0.15 microCi Mo-99 per mCi Tc-99m. It is measured by putting a sample of the generator eluate in a lead shield ("pig") and placing it in a well counter. The technetium-99m photons are attenuated by the shield, but the higher-energy molybdenum-99 photons penetrate the shield and are counted.

Saline chromatography is used to detect other reduction states of Tc-99m in the eluate besides the desired +7 valence state (TcO4-).

Aluminum breakthrough is caused by leaching of aluminum from the generatorís elution column. When excess aluminum accumulates, it results in the formation of large particles, or colloid, which are then taken up by the liver. If used in the preparation of sulfur colloid, the particles that form may be large enough to be deposited in the lungs. Testing is done with colorimetric spot testing with Aurin tricarboxylic acid (rosolic acid paper). The limit is 10 micrograms per ml of eluate.

 

81.

 

Answer: c. 1-3 days

A positive scan may occur within 10-12 hours, but scans become increasingly positive until approximately 72 hours. they may revert to negative within 10 days to 2 weeks. A negative scan between 12 and 24 hours does not exclude acute MI and should be repeated.

 

82.

 

Answer: d. ejection fraction of 25% on MUGA scan

In general, Tc-99m-pyrophosphate imaging appears to predict morbidity and mortality by confirming the direct relationship between infarct size and the likelihood of acute complications. Extensive local infarcts (doughnut pattern) or an enlarging infarct give poor prognosis. If the scan is positive for more than three months this indicates increased risk of future ischemic event. However, to obtain maximum predictive benefit, the pyrophosphate imaging should be done at 24-72 hours after the symptoms.

Abnormally increased thallium uptake in the lungs correlates anatomically with multiple vessel coronary artery disease or single vessel disease involving either a dominant left circumflex artery of high-grade proximal LAD lesion - and clinically with increased morbidity and mortality.

 

Answer: d. ejection fraction of 25% on MUGA scan (changed 9/14/95 after conversation with Ian who spoke with cardiac nucs people.)

 

83.

 

Answer: e. donut sign

Scrotal imaging is usually performed with 10-20 mCi of technetium-99m-pertechnetate. Dynamic (2 second) images will reveal increased perfusion in cases of infection or tumor. The donut sign is due to absent flow within the testicle with surrounding dartos hyperemia giving a "bullís eye" or "donut" sign. This sign is not pathognomonic and can be seen with abscess, hematoma, reactive hydrocele, and occasionally a necrotic tumor. Other signs would include normal nuclear medicine angiogram or "nubbin sign" which is a bump of activity extending medially from the iliac artery due to reactive flow in the spermatic cord and abrupt termination.

In acute torsion, there should be normal or decreased activity during the flow phase, and a photon-deficient area on the delayed scans.

 

84.

 

Answer: c. decreased activity at L3

Following XRT, there is an initial (first few weeks) increase in activity in the portal. If >2000 rads have been given, there is a subsequent decrease in activity within 2-3 months. This persists for at least 12 months.

The answer to the above question assumed that the entire L-spine was not in the radiation portal.

 

 

85.

 

Answer: d. normal

There are no nuclear medicine findings with torsion of the appendix of the testicle. The clinical symptom is acute pain

.

86.

 

Answer: b. sarcoid

Diffuse pulmonary activity during a sulfur-colloid liver-spleen scan occurs with patients receiving estrogen therapy. This may be caused by a release of totipotential cells from the bone marrow, which travel to the lungs and assume the role of phagocytes, which trap the radiopharmaceutical. The differential diagnosis of increased lung activity on a sulfur-colloid scan includes cirrhosis, aluminum breakthrough, collagen vascular disease, Hunter syndrome, histiocytosis X, and widespread pulmonary metastases.

 

 

Nuclear Medicine Questions

The following are matching questions:

 

87.

 

1 a

2 b

 

88.

 

1a

2 b

3 d

 

89.

 

1 c

2  a

3  a

d and e don't exist

 

90.

 

1 b

2  a

 

91.

 

Answer:

1. a

2. c

Folllicular thyroid ca has the capacity to concentrate radioiodine. Mixed papillary-follicular can also take up radioiodine. Medullary ca doesn't concentrate radioiodine and aren't detected with scintigraphy. Radioactive iodine is useful in Rx of differentiated thyroid ca. It is not useful for Rx anaplastic and medullary tumors.

Multiple endocrine neoplasia syndrome is associated with medullary ca. Follicular ca usually undergoes early hematogenous spread and the pt may present with distant mets. Papillary usually spreads via nodes.

 

92.

 

Answers:

3. c

4. a

5. b

6. e

IV injection of 0.5-1.0 mg of stannous ion in the form of "cold" stannous pyrophosphate is done first. After allowing the ion to equilibrate in the blood for 20 minutes, approximately 20 mCi of Tc-99m pertechnetate is injected. Stannous chloride reduces technetium (TcO4-) to its active form (Tc4+) after it has crossed the red cell membrane. The Tc-99m then binds to the beta-chain of the hemoglobin molecule - thus, the red cell is labeled!

Technetium dioxide (TcO2) is an insoluble impurity

EDTA is a chelating agent and presumably binds excess alumina

 

 

93.

 

Answers:

7. a

8. b

9. e

10. a and b

11. f

Heat damaged RBCs are used for spleen scan.

 

94.

 

Answers:

12. d

13. b

14. a

15. d

MAG 3 and I131 Hippuran are used to assess renal blood flow and tubular secretion. MAG 3, like Hippuran, is 90% removed/pass and can be used to assess renal function down to 3% of normal.

DMSA binds to sulfhydryl groups of the proximal convoluted tubule and is a cortical agent (13% bound to the cortex)

DTPA is filtered only.

 

95.

 

Answers:

16. d

17. b

18. c

Like osteoid osteoma, osteoblastoma is hot on all three phases of bone scan. (Remember, size >2 cm = osteoblastoma)

Most benign and malignant bone tumors show increased activity on Tc-99m-MDP. A NOF is usually warm or hot on the third phase but does not show increased activity on the first two phases. (No benign tumors except osteoid osteoma do.)

Neuroblastoma may be hot or cold (60% of its metastases are hot).

Remember "MR. NEAT" as the differential of tumors that can be cold on bone scan:

M = myeloma, or medullary carcinoma of the thyroid

R = renal cell, reticulum cell

N = neuroblastoma

E = EG

A = anaplastic

T = thyroid

 

96.

 

Answers:

19. a

20. d

The spleen is the critical organ for In-111 WBCís since this is the site of degradation.

For Thallium-201, the route of excretion is the kidneys. As a rule, any tracer whose primary route of excretion is the kidneys has the bladder as a critical organ because there is more tracer there for longer. In this case, the manual states that the kidney is the critical organ - I donít know why.

Colon is the critical organ for Gallium-67.

Spleen is the critical organ for Tc-99m-SC.

 

97.

 

Answers:

21. c

22. a

23. e

Diaphragmatic creep due to post-exercise respiratory motion can mimic a reversible inferior wall defect which is indistinguishable from inferior ischemia.

A left bundle branch block may cause a reversible septal defect.

Breast attenuation can mimic a fixed lateral wall defect.

The apex is normally the thinnest part of the myocardium - this may mimic an infarct.

 

 

98.

 

Answer:

24.prob b

25. c

At least 50% stenosis is needed to generate a perfusion defect on stress images.

% for rest images

Coronary stenosis up to 90% may not be associated with any observable perfusion abnormality or Sx under baseline or resting conditions... most labs consider a coronary stenosis of 70% or greater as significant, based on the rapid fall off of flow reserve augmentation ability above this level.

 

99.

 

Answer:

26. a

27. b

Pentagastrin is used in a Meckelís scan to increase excretion of the gastric mucosa, therefore increasing uptake by 30%. Pretreatment with Cimetidine (Tagamet) for 48 hours before scanning blocks release, but not uptake, of Tc-99m-pertechnetate from any gastric mucosa present in a Meckel diverticulum. Glucagon, administered just before the exam, will decrease bowel motility and result in pooling of pertechnetate, thereby improving the chances of visualization.

 

100.

 

Answer:

28. GFR

29. GFR

30. ERPF (although GFR is also affected)

It appears that glomerular function is more sensitive to ureteral obstruction than is tubular secretion; however, once tubular changes occur, they take longer to reverse than do glomerular abnormalities.

In those patients with acute tubular necrosis, the vascular perfusion is usually quite well preserved and tubular clearance demonstrated by the renogram is comparatively poor.

With renal artery stenosis, the renin-angiotensin system tends to maintain GFR.

DTPA is used to approximate GFR; whereas, MAG3 or I-131 Hippuran is used to approximate the ERPF.

101.

 

Answer:

31. b

32. a

33. a

34. a

35. c

Hot nodules almost always represent hyperfunctioning adenomas of which up to 50% are autonomous.

While the overwhelming majority of cold nodules are benign, 15-25% prove to be malignant. Thyroid carcinoma appears as a cold nodule on imaging with I-123 or I-131. The likelihood of a cold nodule representing carcinoma significantly increases if the patient is a young female or male of any age.

A small number of hot nodules on the technetium-99m pertechnetate images have proven to be cold on iodine imaging and some of these represent carcinoma. These nodules have been described as discordant nodules and on the iodine images are cold.

 

102.

 

Answer:

36. b (or d )

37. c

Acute ureteral obstruction can be most effectively diagnosed with DTPA (or MAG-3, which is gaining increasing use). If you see collecting system fullness, then give Lasix. This is the basis for 2 phase diuresis renography

Phase 1: routine DTPA study

Phase 2: give Lasix if obstruction, or functional obstruction, is suspected.

A cortical agent, such as DMSA or glucoheptonate, can be used to diagnose normal cortical tissue such as is found in a column of Bertin.

DTPA - perfusion, GFR, obstructive uropathy, VCUR

Tc glucoheptonate- collecting system t=30min, renal parenchyma t=1-2hr

DMSA - functioning cortical mass, eg Bertin

Hippuran - renal tubular function/ ERPF

Mag 3- replaced heptonate and hippuran - renal plasma flow

 

103.

 

Answers:

38. c

39. a

40. b

DMSA concentrates in the renal cortex with 42% of the dose remaining in the cortex at 6 hours. It localizes by binding to sulfhydryl groups in the proximal renal tubules. The dose is 1-5 mCi and the critical organ is the kidney.

Iodine-131 Hippuran is 80% excreted by tubular secretion and 20% by glomerular filtration. The dose is 200-400 microCi (150 microCi per kidney). Time-activity curves are generated from the imaging data and clearance measurements reflect the effective renal plasma flow (ERPF).

MAG3 Tc-99m is also cleared by tubular extraction (therefore, can also be used to measure ERPF). MAG3-Tc-99m is the preferred agent for imaging patients with renal failure because of its high extraction rate.

DTPA is useful for both evaluation of renal perfusion as well as renal and urinary tract imaging. 90% of DTPA is filtered by simple exchange or diffusion into urine by glomerular filtration. A small amount (5-10%) is plasma bound; therefore, use of this agent to determine the GFR slightly underestimates the actual value. The dose is 10-20 mCi and the critical organ is the bladder.

 

104.

 

Answer:

41. c

42. b

43. d

Beta emitters include Mo-99, I-131, Xe-133 which are all produced in nuclear reactor.

Naturally occurring radionuclides have long t1/2 and have no use in nuclear med. These include uranium, actinium, thorium, radium, radon.

A radionuclide generator such has Mo-99/Tc-99 is used frequently. The Tc-99 is eluted off the generator with saline.

 

105.

Answers:

44. a

45. b

46. d

47. c