Nucs Flashcards
1
Q
keV of PET photons
A
511 keV
2
Q
How do glucose and FDG get into the cell?
A
Glut 1/3 transporters.
Phosporylated by hexokinase.
3
Q
What enzyme phosphorylates FDG?
A
Hexokinase
4
Q
What is the half life of F-18?
A
110 minutes
5
Q
How do you calculate SUV?
A
(ROI activity x body weight)/administered activity
6
Q
Factors that can affect SUV
A
Specific equipment, time elapsed since administration of FDG, amount of tracer extravasation, muscle uptake, glucose and insulin levels at time of injection, etc.
Can’t diagnose or exclude maliganncy using SUV alone.
7
Q
What is considered “mild”, “moderate”, and “intense” uptake?
A
Ratio of background liver, cerebellum, or basal ganglia with a region of interest.
“Mild” - <20%
“Moderate” - 20-60%
“Intense” - >60%
8
Q
What is FDG uptake in both normal and pathological tissues dependent on?
A
Serum glucose and insulin levels.
Elevated insulin will cause increased muscle uptake and decreased sensitivity for detecting mildly PET-avid lesions.
Should be NPO for 4 hours to reach basal insulin levels.
Blood glucose should be below 200, preferably below 150.
After injection - rest in quiet room for 60 minutes.
9
Q
How long should a patient fast before PET?
What should glucose be?
A
Fast for 4 hours
Blood glucose should be <200, preferably below 150.
10
Q
What changes can Metformin cause on PET?
A
Increase colonic, and to a lesser extent, small bowel FDG uptake.
11
Q
Is small cell lung cancer evaluated with PET?
A
No. Considered metastatic at diagnosis.
12
Q
Size threshold for PET evaluation of pulmonary nodules?
A
8mm.
13
Q
What kind of lung cancer will give a false negative on PET?
A
Bronchioloalveolar cell carcinoma or carcinoid may not be metabolically active.
14
Q
What can give a false positive on PET evaluation of a pulmonary nodule?
A
Active granulomatous disease (including TB) may take up FDG.
Can’t diagnose a nodule as benign or malignant based on SUV.
15
Q
How long is a follow-up PET delayed after treatment?
A
2 (colon cancer) to 4 (head and neck) months due to flare phenomenon of increased FDG uptake in the peritreatment period.
16
Q
What types of thyroid cancer won’t take up radioiodine, but may be FDG avid?
A
Undifferentiated or medullary thyroid cancers.
Used in clinical setting of rising thyroglobulin level with negative whole-body radioiodine scans.
17
Q
In which types of lymphoma is PET used?
In which types is it not used?
A
Used in Hodgkin and non-Hodgkin lymphoma.
Some low-grade lymphomas, such as small lymphocytic and mantle cell, tend to be less FDG avid.
18
Q
In esophageal cancer, after initial neoadjuvant treatment, a decrease in FDG avidity by ___ suggests a favorable prognosis
A
at least 30%.
Those who do not show a decrease in SUV values can potentially be spared ineffective chemotherapy regimens.
19
Q
In what cancers does PET-CT play a limited role?
A
HCC - only 50% can be imaged due to high levels of phosphatase, which dephosphorylates FDG and allows it to diffuse out of cells.
RCC and bladder cancer - only 50% of RCCs are FDG-avid, although can detect metastatic disease. Ureteral or bladder lesions are limited to detect due to surrounding high urine FDG uptake.
Prostate Cancer - FDG PET not used. Carbon-11 choline PET has been FDA approved.
20
Q
What about HCC makes it difficult to detect with PET?
A
High levels of phosphatase - which dephosphorylates FDG and allows it to diffuse out of cells.
21
Q
New PET agent FDA approved for prostate cancer?
A
Carbon-11 choline
22
Q
What questions should be asked when a perfusion abnormality is seen in nuclear cardiology?
A
Is it reversible? - Or is it fixed at both stress and rest?
How large is it? - Small, medium, or large?
How severe is it? - Mild (subendocardial), moderate, or severe (transmural)?
Where is it? - In which coronary artery territory?
Are there any associated abnormalities- Right ventricular uptake, ischemic dilation, or wall motion abnormalities?
23
Q
What two components does a perfusion test have in nuclear cardiology?
A
Element of stress and method of imaging.
24
Q
What are the different types of stressing in cardiology?
A
Physical (treadmill), pharmacologic-adrenergic (dobutamine), or pharmacologic-vasodilatory (dipyridamole or adenosine)
25
What is the pharmacologic-adrenergic cardiac stressing agent?
Dobutamine
26
What are the pharmacologic-vasodilatory agents?
Dipyridamole or Adenosine
27
What are the clinical applications of myocardial perfusion imaging?
Evaluation of acute chest pain
Evaluation of hemodynamic significance of coronary stenosis - even with stenosis seen on angio or CT, with a normal nuclear cardiac perfusion exam, have a relatively low risk for cardiac events.
Risk stratification after MI
Preoperative risk assessment for noncardiac surgery
Evaluation of viability prior to revascularization therapy
Evaluation of myocardial revascularization status post CABG.
28
Annual rate of cardiac event with a normal myocardial perfusion exam among patients with high pretest likelihood of CAD?
0.6%
29
Findings on myocardial perfusion imaging that would classify a patient as high risk
Significant per-infarct ischemia
Defect in a different vascular territory - suggesting multi-vessel disease
Significant lung uptake - suggesting LV dysfunction
LV aneurysm
```
Low EF (less than 40% seen) on GSPECT
EF = (EDC - ESC)/(EDC - BC)
BC = background counts
```
30
How is EF calculated on cardiac GSPECT?
EF = (EDC - ESC)/(EDC - BC)
BC = background counts
31
Hypoperfused myocardium that is viable?
Hibernating myocardium
32
How is cardiac viability performed?
Rest-redistribution thallium-201 perfusion imaging or F-18 FDG PET.
PET is the gold standard for evaluation of myocardial viability, although unlike thallium, FDG-PET does not evaluate perfusion
33
What is the gold standard for evaluation of myocardial viability?
F-18 FDG PET
But does not evaluate perfusion like FDG-PET.
34
What agents are used for pure cardiac perfusion static SPECT?
Tc-99m sestamibi, rubidium-82 PET, or N-13 ammonia PET
Cannot distinguish between hibernating myocardium or scar. Both appear as a fixed (present on both stress and rest images) myocardial perfusion defect.
Evaluation of gated SPECT (GSPECT) functional data can suggest either hibernating myocardium or scar. Normal or nearly normal wall motion and wall thickening in the area of the perfusion defect suggests viability (hibernating myocardium), while a large defect with abnormal wall motion suggest scar.
35
What is a "mismatch" and "match" on perfusion and viability cardiac studies?
Mismatch - region of perfusion defect takes up FDG - is viable and may benefit from an intervention
Match - FDG PET match of a photopenic region corresponding to the perfusion defect is consistent with non-viable scar, and best treatment is medical therapy only.
36
What are the radionuclides used in Nuclear Cardiology?
Thallium-201
Technetium-99m sestamibi (Cardiolite)
Rubidium-82
Nitrogen-13 Ammonia
F-18 FDG
37
What is Thallium-201?
Cyclotron-produced radionuclide with half-life of 73 hours. Decays by electron capture and emits characteristic x-rays of 69-81 keV. - Relatively low energy x-rays increase attenuation artifact from chest wall soft tissues. Necessary to administer low doses due its long half-life, with resultant lower count densities.
Acts as a potssium analog - crossing into the cell via actie transport through the ATP-dependent Na-K transmembrane pump. Myocardial uptake is directly proportional to perfusion.
A 50% stenosis will generally produce a perfusion defect upon maximal exercise.
Thallium undergoes redistribution with simultaneous cellular washout and re-extraction of blood-pool radiotracer. Since ischemic myocardium progressively extract thallium but washes out more slowly than normal myocardium, post-redistribution images will therefore show normalization of defects in ischemic but viable myocardium. In contrast, a scar will show a persistent defect.
38
Half life of Thallium-201?
73 hours
39
Disadvantages of Thallium-201?
Half-life of 73 hours and decays by electron capture and emits characteristic x-rays of 69-81 keV.
Low energy increases attenuation from chest wall soft tissues.
Have to administer fairly low doses due to its long half-life, with resultant lower count densities.
40
How does Thallium-201 work in cardiac imaging?
Acts like a potassium analog, crossing into the cell via active transport through ATP-dependent Na-K transmembrane pump.
Myocardial uptake is proportional to perfusion.
41
How much stenosis will produce a perfusion defect with Thallium-201 upon maximal exercise?
50% stenosis
42
What cardiac radionuclide undergoes redistribution?
Thallium-201
Simultaneous cellular washout and re-extraction of blood-pool radiotracer. Since ischemic myocardium progressively extract thallium but washes out more slowly than normal myocardium, post-redistribution images will therefore show normalization of defects in ischemic but viable myocardium. In contrast, a scar will show a persistent defect.
43
What does redistribution of Thallium-201 mean in cardiac imaging?
Simultaneous cellular washout and re-extraction of blood-pool radiotracer. Since ischemic myocardium progressively extract thallium but washes out more slowly than normal myocardium, post-redistribution images will therefore show normalization of defects in ischemic but viable myocardium. In contrast, a scar will show a persistent defect.
44
What is Rubidium-82
A positron-emitting PET perfusion agent that is generated from Strontium-82.
Short half life of 76 seconds allows high doses to be administered, but can't use exercise stress. Pharmacologic stress is used instead.
Acts as a potassium analog, similar to thallium.
45
What is precursor to Rubidium-82?
Strontium-82
46
What is the half-life of Rubidium-82?
76 seconds
Can use high doses, but can't use exercise stress.
47
Pros and cons of Rubidium-82?
Perfusion agent.
Short half life of 76 seconds - can use high doses, but can't use exercise stress.
48
Rubidium-82 is a ____ cardiac agent?
Perfusion
49
How is Rubidium-82 used in cardiac imaging?
Potassium analog similar to Thallium-201.
50
What is Nitrogen-13 Ammonia?
Positron-emitting PET perfusion agent (like rubidium-82) with half life of 10 minutes. Unlike rubidum-82, N-13 is cyclotron produced (must be on site)
Has excellent imaging characteristics. N-13 positrons have low kinetic energy and don't travel very far in the tissue before annihilating, which allows relatively high resolution. Short half life = give higher counts. Can't use exercise stress
51
What are the cardiac PET perfusion agents?
Rubidum-82 and N-13 Ammonia
52
What is the function of F-18 FDG in cardiac?
Viability, not perfusion.
Correlate with the sestamibi perfusion study to evaluate viability.
53
How are the cardiac radionuclide agents produced
Thallium-201 = cyclotron-produced
Technetium-99m sestamibi = Moly generator
Rubidum-82 = Strontium-82 generator
Nitrogen-13 Ammonia = cyclotron-produced
F-18 FDG = cyclotron-produced
54
Patient preparation prior to exercise cardiac stress?
NPO for 6 hours to decrease splanchnic blood flow - decrease liver and bowel uptake.
Calcium channel blockers and beta-blockers should be held to allow the patient to reach target HR.
85% of 220 - age
55
How does Dipyridamole work for a cardiac stress?
Pharmacologic Vasodilator
Dipyridamole is an adenosine deaminase inhibitor that allows endogenous adenosine to accumulate - a potent vasodilator, increasing coronary blood flow.
Does not increase cardiac work or O2 demand.
Caffeine and theophylline reverse the effects of dipyradmole and must be held for 24 hours.
Antidote is aminophylline (100-200 mg) - has short half life.
56
Antidote for Dipyridamole cardiac stress?
Aminophylline (100-200 mg)
Caffeine and theophylline must be held for 24 hours
57
What is Regadenoson?
Adenosine receptor agonist with a 2-3 min half-life. Easier to administer than adenosine with a convenient universal-dose IV injection.
58
How does Dobutamine work in a cardiac stress?
B1 agonist - increases myocardial oxygen demand.
Usually reserved for when adenosine is contraindicated (severe asthma, COPD, or recent caffeine).
59
Protocol of a single-day Tc-99m sestamibi perfusion study?
Rest images first obtained after 8-10 mCi Tc-99m sestamibi.
Stress images obtained after additional 20-30 mCi Tc-99m sestamibi administered during peak exercise, or administration of pharmacologic stress.
Imaging does 30 min after injection to allow liver activity to clear. B/c no redistribtion, imaging can be delayed after tracer administration.
Gated SPECT images show wall motion at time of imaging, while perfusion images show perfusion at time of injection.
60
Difference between Gated SPECT and perfusion images with Tc-99m sestamibi perfusion study?
Gated SPECT images show wall motion at time of imaging.
Perfusion images show perfusion at time of injection.
61
What are the perfusion agents used for cardiac PET?
Rubidium-82 and N-13 ammonia.
Shorter half-life = higher activity with lower dose.
For quantification of myocardial blood flow, N-13 is preferred as rubidium has a lower extraction fraction.
62
Which cardiac PET perfusion agent is better for quantification of myocardial blood flow?
N-13 - has a higher extraction fraction than Rubidium.
63
How is an exercise thallium test imaged?
B/c thallium undergoes redistribution, imaging is performed immediately post-exercise and approximately 3-4 hours later once redistribution has occurred.
Uncommonly used b/c of long 73 hour half life and resultant high patient dose.
64
How to determine if a perfusion defect on stress images is small, medium, or large?
Small (1-2 segments)
Medium (3-4 segments)
Large (5 or more segments)
65
What is dilation of the left ventricle during rest called and what does it imply?
Transient ischemic dilation (TID)
Implies three-vessel diesease, even if there is no focal defect.
66
What are the 3 reconsruction axes and how are they cut?
SA - Short axis - "donut" - apex to base
VLA - Vertical long axis - "U-shaped" pointing to teh left - Septum to free lateral wall
HLA - Horizontal long axis - "U-shaped" pointing down - inferior wall to anterior wall
67
How many coronary segments are there?
17
68
What are the radiotracers used for thyroid imaging?
I-131
I-123
Tc-99m pertechnetate
69
What are the characteristics of I-131?
Emits both beta particles and 364 keV gamma photons (used for imaging)
Half life of 8 days.
Generator produced
70
What is the keV of gamma photons of I-131?
364 keV
71
What is the half life of I-131?
8 days
72
How is I-131 produced?
Generator
73
What are the characteristics of I-123?
Decays by electron capture and produces 159 keV gamma photons.
Half life of 13 hours.
Expensive. Produced by cyclotron.
Excellent for thyroid imaging. Can image in high detail and obtain thryroid uptake values.
74
What is the keV of gamma photons of I-123?
159 keV
75
What is the half life of I-123?
13 hours
76
How is I-123 produced?
Cyclotron
77
What is the keV of Tc-99m pertechnetate?
140 keV gamma photon.
78
What are the characteristics of Tc-99m pertechnetate?
Emits 140 keV gamma photon.
Half life of 6 hours.
Not trapped by the thryoid, unlike iodine, and released into the blood pool. Thyroid uptake is not routinely quantified due to rapid washout, but does provide excellent images of the thyroid gland.
Not specifically localized to the thryoid, high background counts are typical. Salivary gland activity.
Administered IV- iodine is orally.
Tc-99m pertechnetate is preferred over I-123 when patient has received recent IV contrast - iodine in contrast blocks thyroid uptake of additional iodine.
79
Fetal iodine is take up beginning when in gestation?
12 weeks
80
I-131 in pregnancy
I-131 contraindicated.
| Must stop breastfeeding.
81
I-123 in breast feeding
Resumed 2-3 days after administration
82
Tc-99m in breastfeeding
Resume 12-24 hours after administration
83
Indications for thyroid NM study (I-123 or Tc-99m pertechnetate)
```
Ectopic thyroid
Thyroid nodule
Graves Disease
Hashimoto Thyroiditis
Subacute thyroiditis
```
84
Functional thyroid tissue in an ovarian teratoma
Struma ovarii
85
Risk of malignancy in a cold nodule?
20%
Although MC cause is a colloid cyst.
86
What is a warm thyroid nodule?
Usually represents a cold nodule with overlapping thyroid tissue
Requires further investigation such as biopsy if oblique views are indeterminate.
87
What is a discordant thyroid nodule?
"Hot" on Tc-99m and "cold" on I-123.
Maintained ability to uptake Technetium but unable to trap iodine. Biopsy is usually recommended.
88
What are normal 6 and 24 hours thyroid uptakes?
Normal 6 hour: 6-18%
Normal 24 hour: 10-30%
89
Can you determine which radiotracer was given on a thyroid scan of Graves disease?
No.
Thyroid uptake can be so strong that the salivary glands are often not seen, causing similar appearance with either radiotracer.
90
When is I-131 therapy usually done after thyroidectomy?
1-2 months
91
What is the goal TSH for I-131 therapy?
TSH of 30-50
92
How is dosing determined for I-131 thrapy?
Dependent on oncologic risk
Low risk (tumor <1.5 cm, no invasion of thyroid capsule): <30 mCi
High risk: 10-200 mCi
93
The presence of what precludes the ability to monitor thyroglobulin levels?
Anti-thyroglobulin antibodies
94
Contraindications to I-131 therapy?
Pregnancy, lactation, and inability to comply with radiation safety guidelines
95
Radiotracer used in parathyroid imaging?
Tc-99m sestamibi
Parathyroid tissue does not take up Tc-99m pertechnetate, which can be administered in indeterminate cases.
96
What can be given for indeterminate parathyroid cases? Why?
Tc-99m pertechnetate- not taken up by parathyroid tissue.
97
What radiotracer is used for Liver-Spleen imaging?
Tc-99m Sulfur Colloid
98
How to Tc-99m Sulfur Colloid work?
Taken up by reticuloendothelial cells - found in liver, spleen, and bone marrow. Also take up by Kupffer cells in liver.
80-90% take up by liver. Most of the remainder by the spleen, and small amount in the bone marrow (not normally seen at typical windowing levels).
99
What is the biological half life of Sulfur Colloid?
2-3 minutes due to rapid clearance.
Physical half life is 6 hours.
100
Causes of focal decreased hepatic uptake on sulfur colloid scan?
MC is hepatic cyst - may be difficult to distinguish focal decreased uptake from a photopenic defect if lesion is small.
Most hepatic masses cause focal decreased radiocolloid uptake, including HCC, adenoma, and abscess.
Focal decreased uptake should raise concern for HCC in patient with any risk factors for HCC such as cirrhosis or chronic hepatitis.
101
Causes of focal increased hepatic uptake on sulfur colloid scan?
FNH can hyperconcentrate radiocolloid.
Regenerating nodule in a cirrhotic liver can cause focal increased sulfur colloid uptake.
Budd-Chiari syndrome can lead to increased uptake in the caudate lobe in the later stage of disease.
102
What is Colloid Shift?
Increased sulfur colloid accumulation within the spleen and bone marrow.
Suggests liver dysfunction, most commonly due to cirrhosis.
103
What causes diffuse pulmonary uptake on a sulfur colloid scan?
```
Nonspecific, but can be seen in:
Cirrhosis
COPD with superimposed infection
Langerhand cell histiocytosis
High serum aluminum (either due to antacids or excess aluminum in the colloid preparation).
```
104
Findings of FNH in nuclear medicine scans
Variable appearance on sulfur colloid scan.
Most commonly, indistinguishable from background liver on sulfur colloid scan due to Kupffer cells within the FNH.
Can have increased uptake due to hypervascularity and Kupffer sulfur colloid uptake.
In 1/3, there is insufficient colloid concentration and FNH may appear as a photopenic defect.
In contrast, a hepatic adenoma does not contain Kupffer cells and will consistently cause a cold defect.
On HIDA scan, FNH contains biliary ductules, so it should be positive on HIDA.
105
Tests to confirm presence of intrapancreatic spleen
Sulfur Colloid or Tc-99m damaged RBC study.
106
How is labeling of RBCs with Tc-99m done?
In vitro by mixing 1-3 mL of anticoagulated blood with stannous chloride and an oxidizing agent.
Tc-99m is added and has a labeling efficiency of 95%. Takes 20 min.
In vivo technique provides much noisier images due to worse labeling efficiency and resultant free pertechnetate, and therefore uncommonly performed.
107
Another option besides Tc-99m RBCs with GI bleeding
Sulfur colloid can be used in GI bleeding. Does not require much preparation time, but has rapid blood clearance and has a vascular half life of 2-3 minutes.
108
Flow that can be detected in a GI bleed with NM vs angiography?
Tagged RBC = 0.2 ml/min
Angio = 1 ml/min
109
Radiotracer used for Meckel diverticulum?
Tc-99m pertechnetate - localizes to gastric mucosa.
110
What is a Meckel Diverticulum?
Remnant of embryological omphalomesenteric duct, most commonly located in the distal ileum.
10-60% of Meckel diverticula contain ectopic gastric mucosa - may result in mucosal damage and GI bleeding.
111
Percentage of Meckel diverticula that contain gastric mucosa?
10-60%
112
Other findings that can be positive on Meckel scan?
Appendicitis and intussusception - causes more diffuse, regional uptake due to hyperemia.
113
Radiotracers used for HIDA imaging?
Tc-99m-iminodiacetic acid (IDA) analogs are used to image the biliary system.
Disofenin - used with bilirubin levels as high as 20 mg/dL and has 90% hepatic uptake.
Mebrofenin - used with bilirubin levels as high as 30 mg/dL and has an even higher 98% hepatic uptake.
Both actively transported into hepatocytes but are not conjugated.
114
Two radiotracers used for HIDA imaging and differences between them?
Both actively transported into hepatocytes but are not conjugated.
Disofenin - used with bilirubin levels as high as 20 mg/dL and has 90% hepatic uptake.
Mebrofenin - used with bilirubin levels as high as 30 mg/dL and has an even higher 98% hepatic uptake.
115
Mechanism of radiotracers for HIDA imaging
Both actively transported into hepatocytes but are not conjugated.
116
What is the protocol for HIDA imaging?
NPO for 6 hours, but must have eaten within 24 hours.
If NPO for >24 hours, then CCK infusion (0.02 microg/kg in slow infusion) to empty GB before radiotracer. Wait 2 hours after CCK to begin exam.
Dynamic imaging of RUQ begins immediately after injection. See GB = no acute cholecystitis.
No GB by 1 hour, morphine is given (0.04 mg/kg, up to 4 mg max) and image for 30 min.
Morphine only given if tracer is visualized in the small bowel, otherwise, potential risk of worsening a potential CBD obstruction. Nonvisualization is not specific for CBD obstruction.
If morphine allergy, can image for total of 4 hours.
117
What is infusion of CCK for HIDA?
0.02 microg/kg in slow infusion
118
Dose of morphine for HIDA?
0.04 mg/kg, up to 4 mg max
119
Alternative to morphine in HIDA if allergy?
Image for total of 4 hours.
120
False positive HIDA can be due to:
Recent meal (w/in 4 hours) or prolonged fasting (greater than 24 hours)
Administration of CCK immediately prior to the eam, which can cause persistent sphincter of Oddi relaxation
TPN
Pancreatitis
Severe illness
Chronic cholecystitis
Cholangiocarcinoma of the cystic duct
121
False negative HIDA can be due to:
Acalculous cholecystitis with a patent cystic duct
Duodenal diverticulum simulating the GB; however, a lateral view would differentiate.
Biliary cyst simulating the GB
122
What finding is suggestive of chronic cholecystitis?
Low GB EF.
<35% suggests chronic cholecystitis.
123
What GBEF suggests chronic cholecystitis?
<35%
124
Radiotracers used in pulmonary imaging?
Tc-99m-MAA (perfusion)
Xenon-133 (ventilation)
Tc-99m DTPA (ventilation)
125
What is Tc-99m-MAA?
Macro-aggregate albumin (MAA) is particulate radiopharmaceutical that lodges in the pulmonary capillary bed - used to evaluate pulmonary perfusion. Most particles are between 10 and 30 micrometers in size.
3-5 mCi Tc-99m MAA administered, comprising between 200,000 and 600,000 particles. Fragments begin to break down in approximately 30 minutes.
In children, pregnant patients, patients with mild pulm HTN, and patients with known R-to-L shunt, the dose can be halved to approximately 100K particles.
Relative contraindication to MAA is severe pulm HTN, as obstruction of even a few pulm capillaries can cause clinical worsening.
Clumping can be seen with MAA is inadvertently drawn back into the injection syringe, causing coagulation with the patient's blood.
126
Size of MAA particles?
10 to 30 micrometers in size
127
Dose and number of particles administered of MAA?
3 to 5 mCi Tc-99m MAA
200,000 to 600,000 particles.
128
Relative contraindication to MAA administration?
Severe pulmonary hypertension - obstruction of even a few pulmonary capillaries can cause clinical worsening.
129
What happens with MAA administration with a R-to-L shunt?
Causes immediate renal and brain uptake after IV injection.
MAA may be able to quantify the shunt fraction in these patients.
Renal uptake can also be seen in free pertechnetate, but evaluation of head and neck can differentiate free pertechnetate from a R-to-L shunt. Free pertechnetate is taken up by the thyroid, but not the brain. A R-to-L shunt, in contrast, demonstrates immediate brain uptake and no significant uptake in the neck.
130
How can you tell a R-to-L shunt vs free pertechnetate in MAA study?
R-to-L shunt causes immediate renal and brain uptake after IV injection.
Renal uptake can also be seen in free pertechnetate, but evaluation of head and neck can differentiate free pertechnetate from a R-to-L shunt. Free pertechnetate is taken up by the thyroid, but not the brain. A R-to-L shunt, in contrast, demonstrates immediate brain uptake and no significant uptake in the neck.
131
What is Xenon-133?
Used for ventilation pulmonary studies.
Inhaled gas with a physical half-life of 5.3 days, which emits 81 keV gamma photons and is also a beta-emitter. Critical organ is the tracha. Biological half life is very short b/c vast majority is exhaled. Can give high doses.
Imaged posteriorly to avoid breast artifacts - low keV is easily attenuated by soft tissue. Washin-washout imaging can be performed to evaluate for air trapping, which is seen in COPD.
132
What is the physical half life of Xenon-133?
5.3 days
133
keV of Xenon-133 gamma photons?
81 keV also a beta emitter. Need posterior imaging - avoid breast artifacts due to attenuation.
Biological half life is short b/c vast majority exhaled.
134
What is Tc-99m DTPA
Used for ventilation - aerosol.
Does not allow for washin-washout imaging. Once inhaled, remain in place for 20-60 minutes. 30 mCi is typically administered.
Compared to Xenon, DTPA has greater ease of use - can do multiple projections, no need for exhaust systems, and ability to use portably.
135
What is high probability finding of PE?
Two or more large (>75% of a segment) mismatched segmental defects w/o associated radiographic abnormality.
97% specific - 88% PPP
136
What is a large defect on a V/Q study?
>75% of a segment
137
What is intermediate probability finding of PE?
One large segmental mismatched perfusion defect
A triple match in the lower lung is intermediate probability - defect on perfusion, matched defect on ventilation, and a corresponding abnormality on CXR.
138
A triple match in the lower lung is what probability of PE?
Intermediate
139
What is a low probability finding of PE?
Single large or moderate matched VQ defect
Other low probability findings include absent perfusion of an entire lung, or more than three small segmental lesions.
Negative predictive value of 84%
140
What is very low probability finding of PE?
Nonsegmental lesions
Stripe sign peripheral to a perfusion defect is very low probability.
Solitary triple-matched defect in the mid-upper lung is very low probability.
141
Triple match defect in the mid-upper lung is what probability of PE?
Very low
142
Probability of PE of triple match lesion in lower lung vs mid-upper lung?
Lower lung = intermediate probability
Mid-upper lung = very low probability
143
Radiotracer used for MSK imaging?
Tc-99m MDP - diphosphate.
Rapid renal excretion is normal. Diffuse soft tissue uptake can be seen in renal failure
144
What is a three-phase bone scan?
Radionuclide angiogram (flow) evaluates blood flow, with images take every few seconds. Increased flow suggests hyperemia.
Blood pool evaluates extracellular distribution immediately following the blood flow phase.
Standard delayed (skeletal) images are performed approximately 3 hours after injection.
145
Patterns of low probability of metastatic disease (in a patient with known malignancy)
Single focus of uptake in a rib is thought to represent malignancy only ~10% of the time.
Uptake in similar locations in two adjacent ribs is almost always due to trauma
Multiple adjacent photopenic bony lesions are unlikely to be metastases, but may represent infarction, avascular necrosis, or sequela of radiation therapy.
146
Patterns of high probability of metastatic disease (in a patient with known malignancy)
Single sternal lesion in a patient with breast cancer is due to metastases ~80% of the time.
Multifocal areas of increased activity in nonadjacent ribs are suspicious for metastases.
A single photopenic lesion in patients with a known malignancy (especially neuroblastoma, RCC, and thyroid cancer) is due to metastases 80% of the time.
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Increased uptake in the brain or heart on a bone scan
May be due to recent infarction
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Increased uptake in a pleural effusion or ascites on bone scan
Malignant pleural effusion and ascites
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What is the clue to a bone superscan?
Nonvisualization (or very faint visualization) of the kidneys.
Renal failure may also cause lack of visualization of the kidneys, although the typical diffuse soft tissue uptake seen in renal failure helps distinguish renal failure from a superscan.
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Difference between renal failure and a superscan on a bone scan?
Nonvisualization of the kidneys
Diffuse soft tissue uptake is seen in renal failure.
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What does osteosarcoma look like on a bone scan?
Markedly increased uptake, often with increased uptake in the entire limb.
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What does Ewing sarcoma look like on bone scan?
Intense homogeneous activity. May be positive on all three phases of a three-phase bone scan, mimicking osteomyelitis.
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What bone tumor is positive on all three phases of a three-phase bone scan, mimicking osteomyelitis?
Ewing Sarcoma
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What does a osteoid osteoma look like on a bone scan?
Vascular central nidus, demonstrates intense activity.
Double density sign describes an intense focus of uptake corresponding to the nidus, surrounded by relatively increaed uptake representing hyperemia.
DDx of a double density sign - osteoid osteoma, Brodie abscess, less likely stress fracture.
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What is a double density sign on bone scan?
Double density sign describes an intense focus of uptake corresponding to the nidus, surrounded by relatively increaed uptake representing hyperemia.
DDx of a double density sign - osteoid osteoma, Brodie abscess, less likely stress fracture.
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What is the DDx of a double density sign on bone scan?
Double density sign describes an intense focus of uptake corresponding to the nidus, surrounded by relatively increaed uptake representing hyperemia.
DDx of a double density sign - osteoid osteoma, Brodie abscess, less likely stress fracture.
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What is normal to see in prosthesis evaluation on bone scan?
Normal to see activity surrounding the prosthesis up to 12 months in a cemented prosthesis.
In a noncemented prosthesis - activity may remain increased up to 2 years as bony in growth continues.
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What findings are seen on bone scan evaluation of a hip prosthesis to suggest loosening?
Focal activity at the lesser trochanter (which acts as a fulcrum site) and distal femoral prosthetic tip seen >1 year for cemented or >2 years for non-cemented prosthesis suggests loosening.
Generalized increase in radiotracer activity around the prosthesis may suggest osteomyelitis.
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What findings are seen on bone scan evaluation of a hip prosthesis to suggest loosening?
Generalized increase in radiotracer activity around the prosthesis may suggest osteomyelitis.
Focal activity at the lesser trochanter (which acts as a fulcrum site) and distal femoral prosthetic tip seen >1 year for cemented or >2 years for non-cemented prosthesis suggests loosening.
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Mild to moderate activity that is limited to the greater trochanter/intertrochanteric region is often due to __?
Heterotopic ossification
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A negative three-phase bone scan is very specific for osteomyelitis in the presence of what?
Normal radiograph - confirming no fracture
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What can increase the specificity of a bone scan for osteomyelitis in the presence of an underlying abnormality, such as fracture or prosthesis?
WBC imaging (In-111 or Tc-99m labeled WBCs).
Focal WBC activity in a region of devoid of colloid marrow activity is suggestive of osteomyelitis.
Galium-67 scan also increases specificity for osteomyelitis if the gallium uptake exceeds the bone scan uptake in the area of concern.
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Positive three phase bone scan on both sides of the joint
Septic arthritis.
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Increased skeletal activity in two adjacent vertebral bodies on bone scan
Discitis
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Increased parallel lines of activity along the cortex of long bones on a bone scan
Hypertrophic pulmonary osteoarthropathy
Long bone diaphyseal periosteal reaction due to pulmonary disease, MC caused by lung cancer.
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Findings of AVN on bone scan
Initially shows decreased radiotracer activity in the affected region, followed by a hyperemic phase with increased uptake
SPECT imaging of AVN (especially in the hips) will often show a rim of increased uptake with central photopenia, thought to represent revascularization progressing from outside in.
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What is spontaneous osteonecrosis of the knee (SONK)?
Cause of atraumatic knee pain in the elderly.
Typically appears as intensely increased radiotracer activity in the medial femoral condyle.
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What are the three phases of Paget's Disease and how do they appear on bone scan?
Lytic (early)- typically positive on bone scan and often negative on radiography
Mixed- abnormal on bone scan and radiography.
Sclerotic- persistent radiographic changes, but bone scan activity may subside.
Can get malignant degeneration to osteosarcoma - focal cold lesion should raise concern for necrosis in a region of malignant degeneration, although may be best appreciated by evaluating serial studies.
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What is complex regional pain syndrome and what does it look like on bone scan?
AKA- regional sympathetic dystrophy
Causes persistent pain, tenderness, and swelling often due to minor trauma.
Bone scan shows diffusely increased juxta-articular activity in multiple small joints of the hand or foot on delayed (skeletal) images. Blood pool and soft tissue phase uptake is variable, but most commonly both phases are increased.
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What are the radiotracers used for Kidney imaging?
Tc-99m DTPA - Glomerular agent
Tc-99m MAG3 - Tubular agent
Tc-99m DMSA
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How does Tc-99m DTPA work for kidney imaging?
Glomerular agent
Can measure GFR and evaluate renal perfusion
Excreted by glomerular filtration. 20% extracted by the glomerulus into the tubules with each pass. Identical extraction fraction as inulin, which is used to measure GFR exactly.
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What can Tc-99m DTPA measure for kidney function?
Glomerular agent
GFR and evaluate renal function
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Mechanism of Tc-99m DTPA in kidney imaging
Glomerular agent
Excreted by glomerular filtration. 20% extracted by the glomerulus into the tubules with each pass. Identical extraction fraction as inulin, which is used to measure GFR exactly.
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Which kidney imaging agent is identical to inulin?
Tc-99m DTPA - which is used to measure GFR.
Glomerular agent
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How does Tc-99m MAG3 work for kidney imaging?
Tubular agent
MAG3 is filtered and excreted by the tubules. Greater than 50% is extracted by the glomerulus into the tubules with each pass. MAG3 is cleared predominantly by the proximal tubules with minimal filtration. Higher extraction fraction than DTPA, which provides better images in patients with renal insufficiency or obstruction.
Can estimate renal plasma flow and evaluate renal perfusion, but MAG3 cannot measure GFR.
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Mechanism of Tc-99m MAG3 in kidney imaging.
Tubular agent
Filtered and excreted by the tubules. Greater than 50% is extracted by the glomerulus into the tubules with each pass. Cleared predominantly by the proximal tubules with minimal filtration.
Higher extraction fraction than DTPA, which provides better images in patients with renal insufficiency or obstruction.
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Which kidney imaging agent is better for imaging patients with renal insufficiency or obstruction?
Tc-99m MAG3 - Tubular agent - higher extraction fraction than DTPA,
Filtered and excreted by the tubules. Greater than 50% is extracted by the glomerulus into the tubules with each pass. Cleared predominantly by the proximal tubules with minimal filtration.
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What can be measured with the kidney imaging agents?
DTPA - Glomerular agent - measure GFR exactly
MAG3 - Tubular agent - Estimate renal plasma flow and evaluate renal perfusion - cannot measure GFR.
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Which renal agent can measure GFR?
DTPA - Glomerular agent
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Difference in mechanism between DTPA and MAG3?
DTPA - Glomerular agent - excreted by glomerular filtration - about 20% extracted into the tubules with each pass. Identical to extraction fraction as inulin - used to measure GFR exactly.
MAG3 - Tubular agent - filtered and excreted by the tubules. Greater than 50% is extracted by the glomerulus into the tubules with each pass. Cleared predominantly by the proximal tubules with minimal filtration. Higher extraction fraction than DTPA, which provides better images in patients with renal insufficiency or obstruction.
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Mechanism of Tc-99m DMSA in renal imaging
Specialized cortical agent - bound to renal tubules, which allows anatomic imaging of the cortex.
Only renal tracer where SPECT imaging is performed.
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What is a renogram in kidney imaging?
Time-activity curve that provides a graphical representation of renal uptake and excretion.
10 mCi Tc-99m MAG3 (most commonly) or DTPA is administered.
Three phases: flow phase (sharp upslope), cortical function phase (defined peak), and clearance phase (rapid excretion).
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Three phases of a renogram in kidney imaging?
```
Flow phase (sharp upslope)
Cortical function phase (defined peak)
Clearance phase (rapid excretion)
```
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A slow upstroke of the flow phase of a renogram suggests
Decreased perfusion
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A delayed cortical uptake peak on a renogram suggests
Decreased renal function
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Radiotracer commonly used for ACE inhibitor renogram
MAG3 - much less commonly DTPA.
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What to do if patient already on ACEI prior to an ACE inhibitor renogram?
Stop for 48 hours to 1 week prior to the exam.
Need IV access in case fluid resuscitation is needed for hypotension.
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How is MAG3 affected with decreased GFR?
Tubular agent - uptake and excretion are generally preserved even with a reduced GFR, but further decrease in GFR results in decreased urine production and decreased washout of secreted agent from collecting system.
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What are the positive criteria for a MAG3 ACE inhibitor renogram?
<40% uptake by one kidney at 2-3 minutes
Difference in cortical activity by 20%
Delay in time to peak activity of more than 2 minutes (compared to pre ACE inhibitor)
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How is DTPA affected by decreased GFR?
Unlike MAG3, decreased GFR causes diminished uptake and excretion of DTPA.
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What is the purpose of a diurectic renogram?
If hydronephrosis is present, a diuretic renogram can distingush between obstruction and a nonobstructive cause of collecting system.
Both renal function and urodynamics are evaluated.
Radiotracer is Tc-99m MAG3, much less commonly Tc-99m DTPA.
40 mg IV Lasix usually given at about 20 min. Higher dose may be needed in patients with renal insufficiency.
After Lasix, a fixed mechanical obstruction will show no change in the renogram curve. However, in causes of non-obstructive hydronephrosis, the additional pressure of the diuresed kidney will open up the collecting system and allow drainage of radiotracer from the kidney.
After Lasix, clearance time of <10 is normal, 10-20 minutes is borderline, and >20 minutes suggests obstruction.
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What do you look for in a diuretic renogram to suggest obstruction?
Clearance time.
Clearance time of <10 is normal, 10-20 minutes is borderline, and >20 minutes suggests obstruction.
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What does a positive study for pyelonephritis on DMSA look like?
Focal cortical defect, multifocal cortical defects, or diffusely decreased radiotracer.
194
What is radionuclide cystography used for?
Most sensitive test for evaluation of pediatric reflux - less radiation exposure than voiding cystourethrogram.
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Radiotracers used for radionuclide cystography?
Variable
Tc-99m pertechnetate, Tc-99m DTPA, and Tc-99m sulfur colloid work well.
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What is the grading of reflux on radionuclide cystography?
Minimal (RNC grade I): Reflux is confined to the ureter
Moderate (RNC grade II): Reflux extends superiorly to the pelvicalyceal system.
Severe (RNC grade III): Severe reflux causing a tortuous ureter and/or dilated intrarenal system.
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What is I-123 MIBG used for?
Image for pheochromocytoma in adults and neuroblastoma in children.
Lesser extent, take up by carcinoid, medullary thyroid carcinoma, and paraganglioma.
I-123 can be used for therapy of neuroblastoma in children
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What is the normal distribution of I-123 MIBG?
Areas of sympathetic innervation - salivary glands, heart, thyroid (although this is typically blocked with Lugol's solution to reduced thyroid dosimetry), liver, kidney, and bladder.
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What is Indium-111 pentetreotide (Octreoscan) used for?
Primarily used to image carcinoid
Analog of octreotide used to detect tumors with somatostatin receptors, including amine precursor uptake and decarboxylation (APUD) tumors
200
Characteristics of Indium-111 pentetrotide (Octreoscan)
Cyclotron-produced
Decays by electron capture
Emits two photons at 173 and 247 keV.
Half life of 67 hours
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How does Indium-111 pentreotide (Octreoscan) work?
Analog of octreotide used to detect tumors with somatostatin receptors, including amine precursor uptake and decarboxylation (APUD) tumors
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Uses for Indium-111 pentreotide (Octreoscan)
MC for evaluation of carcinoid or islet cell tumors.
Good for imaging gastrinoma, with relatively reduced sensitivity for insulinoma.
Although uncommonly performed, glomus tumors of the head and neck (extra-adrenal pheochromocytomas are seen better with indium-111 petreotide compared to MBG
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Normal distribution of uptake for Indium-111 pentreotide (Octreoscan)
Intense renal and splenic uptake, with slightly less hepatic uptake.
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What radiotracer showes intense renal and splenic uptake with less hepatic uptake?
Indium-111 pentreotide (Octreoscan)
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Why is MIBG a better imaging agent for pheochromocytoma than In-111 pentreotide?
Intense renal uptake with In-11 pentreotide may obscure an adrenal lesion.
Pentreotide can be considered as a second line agent for pheochromocytoma if the MIBG scan is negative.
For extra-adrenal pheochromocytoma (i.e., paraganglioma or glomus tumor), MIBG and pentreotide are roughly equivalent.
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What is the first line imaging agent for adrenal pheochromocytoma?
MIBG - Intense renal uptake with In-11 pentreotide may obscure an adrenal lesion.
Pentreotide can be considered as a second line agent for pheochromocytoma if the MIBG scan is negative.
For extra-adrenal pheochromocytoma (i.e., paraganglioma or glomus tumor), MIBG and pentreotide are roughly equivalent.
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Half life of Indium-111 pentetrotide (Octreoscan)?
67 hours
208
KeV of Indium-111 pentetrotide (Octreoscan) photons?
Emits two photons at 173 and 247 keV.
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How is Indium-111 pentetrotide (Octreoscan) produced?
Cyclotron
210
Characteristics of Gallium-67
Cyclotron-produced
Decays by electron capture
Half-life of 78 hours
Emits multiple gamma rays at 93, 184, 296, and 388 keV (90, 190, 290, and 390 keV).
Binds to transferrin, which is found in infection, inflammation, and neoplasm.
Normal distribution - High activity in bowel and colon, and less in liver, skull, bone marrow, and salivary glands. Use is limited in the abdomen due to high bowel and liver activity.
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How is Gallium-67 produced?
Cyclotron
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What is the half-life of Gallium-67?
78 hours
213
KeV of Gallium-67 gamma rays
93, 184, 296, and 388 keV (90, 190, 290, and 390 keV).
214
Normal distribution of Gallium-67
Normal distribution - High activity in bowel and colon, and less in liver, skull, bone marrow, and salivary glands. Use is limited in the abdomen due to high bowel and liver activity.
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DDx of pulmonary uptake in Gallium-67 scan
Pneumocystis pneumonia, idiopathic pulmonary fibrosis, sarcoidosis, lymphangitic carcinomatosis, miliary tuberculosis, and fungal infection.
216
How do Gallium scans work?
Binds to transferrin - found in infection, inflammation, and neoplasm.
Largely replaced by PET-CT.
217
What is the panda sign seen in Gallium scans?
Increased uptake of gallium in the nasopharynx, parotid glands, and lacrimal glands due to inflammation, resembling the dark markings on a panda's face - classically due to sarcoidosis.
Not specific for sarcoidosis, but strongly suggested when the lambda sign is also seen (bilateral hilar and right paratracheal adenopathy).
DDx of panda sign includes Sjogren syndrome, lymphoma after irradiation, and AIDS.
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Characteristics of Thallium-201
Cyclotron-produced
Decays by electron capture
Produces low-energy characteristic X-rays of 69-81 keV
Half-life of 73 hours
Normal distribution of thallium - prominent uptake in the kidneys, heart, liver, thyroid, and bowel.
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How is Thallium-201 produced?
Cyclotron
220
KeV of Thallium-201 electrons?
Low-energy characteristic X-rays of 69-81 keV
221
Half life of Thallium-201?
73 hours
222
Normal distribution of Thallium-201?
Prominent uptake in the kidneys, heart, liver, thyroid, and bowel.
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How has Thallium-201 been historically used?
Historically used in combination with a gallium scan to distinguish between Kaposi sarcoma, lymphoma, and TB in immunocompromised patients.
Also used in myocardial imaging.
Infrequently used due to long half-life and resultant high radiation exposure.
224
What is the normal distribution of Indium-111 labeled WBCs?
Spleen > Liver >> Bone marrow
Infection imaging with indium-111 WBC scan is performed at 24 hours
225
What is the key advantage of Indium-111 WBCs compared to Gallium?
Lack of bowel activity with Indium-111 compared to Gallium - allows evaluation of abdominal or bowel infection/inflammation.
Disadvantages compared to Gallium: tedious labeling procedure, higher radiation dose, and less accuracy in diagnosing spinal osteomyelitis.
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Disadvantages of Indium-111 WBCs compared to Gallium?
Disadvantages compared to Gallium: tedious labeling procedure, higher radiation dose, and less accuracy in diagnosing spinal osteomyelitis.
Advantage: Lack of bowel activity with Indium-111 compared to Gallium - allows evaluation of abdominal or bowel infection/inflammation.
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Advantages of Indium-111 WBC scan compared to Tc-99m HMPAO?
In-111: absence of interfering bowel and renal activity, ability to perform delayed imaging, and ability to perform simultaneous Tc-99m sulfur colloid or Tc-99m MDP bone scan.
Combined approaches are very helpful for evaluation of osteomyelitis in the setting of a baseline abnormal bone scan (e.g. prosthesis evaluation)
228
What labels are used for WBC scans?
Indium-111
| Tc-99m HMPAO
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Advantages of WBC scan with Tc-99m HMPAO compared to Indium-111
Tc-99m has shorter half life, allows higher administered activity, better counts, lower absorbed dose, and ability to perform earlier imaging - often preferred in children.
Major disadvantage of HMPAO - physiologic uptake w/in the GI and GU tracts due to unbound HMPAO complexes, which limits bowel evaluation.
Renal activity occurs early, while bowel activity is seen after 1-2 hours. Delayed imaging is less practical with Tc-99m due to shorter half life.
230
Major disadvantage of WBC scan with Tc-99m HMPAO compared to Indium-111
Major disadvantage of HMPAO - physiologic uptake w/in the GI and GU tracts due to unbound HMPAO complexes, which limits bowel evaluation.
Renal activity occurs early, while bowel activity is seen after 1-2 hours. Delayed imaging is less practical with Tc-99m due to shorter half life.
Advantage: Tc-99m has shorter half life, allows higher administered activity, better counts, lower absorbed dose, and ability to perform earlier imaging - often preferred in children.
231
Focal Gallium uptake in the liver
HCC
HCC is extremely unlike of gallium uptake is diminished.
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What are the uses of combined Gallium and Thallium imaging?
Kaposi Sarcoma - Thallium avid, but does not take up gallium. KaT (Kaposi is Thallium avid).
Tuberculosis and atypical mycobacteria take up Gallium but not Thallium. TuG (Tuberculosis is Gallium avid)
Lymphoma takes up both Gallium and Thallium. Lymphoma likes both.
233
Kaposi Sarcoma in Gallium and Thallium imaging?
Kaposi Sarcoma - Thallium avid, but does not take up gallium. KaT (Kaposi is Thallium avid).
234
Tuberculosis and atypical mycobacteria in Gallium and Thallium imaging?
Tuberculosis and atypical mycobacteria take up Gallium but not Thallium. TuG (Tuberculosis is Gallium avid)
235
Lymphoma in Gallium and Thallium imaging?
Lymphoma takes up both Gallium and Thallium. Lymphoma likes both.
236
When is the only time a positive triple-phase bone scan is specific for osteomyelitis?
When the radiograph is normal. If an underlying abnormality, gallium or WBC scan can increase specificity.
Gallium imaging can increase specificity of a positive bone scan, especially for vertebral osteomyelitis and discitis.
A WBC scan (typically with Indium-111) can increase specificity in evaluation of an infected orthoopedic prosthesis, when scanning in conjunction with Tc-99m sulfur colloid.
237
What can be done in addition to a positive bone scan to increase the specificity for vertebral osteomyelitis and discitis?
Gallium
238
What tracer is used for evaluation of carcinoid tumor?
Indium-111
239
Where are physiologic "hot spots" in Octreoscan that can decrease specificity?
Pituitary, thyroid, liver, spleen, urinary tract, or bowel.
Can get false positives with inflammation, Graves disease, and sarcoidosis - thought to be due to octreotide receptors expressed in activated lymphocytes.
240
What radiotracers are used in cerebrovascular imaging?
Tc-99m DTPA and Tc-99m HMPAO/Tc-99m ECD
241
What is Tc-99m DTPA?
Used in cerebrovascular imaging - has a transient perfusion agent. No uptake w/in the brain parenchyma as it does not cross the BBB.
242
How are Tc-99m HMPAO/Tc-99m ECD used in cerebrovascular imaging?
Both are perfusion agents that cross the BBB.
ECD is enzymatically modified in the cell - only taken up by living cells.
HMPAO simply needs to be protonated to be trapped- marker for perfusion.
ECD is generally preferred for brain imaging. Compared to HMPAO, ECD has more rapid blood pool clearance, better shelf life, more accurate characterization of perfusion, and is only take up by living cells.
Both are used for SPECT imaging.
243
Difference between Tc-99m HMPAO/Tc-99m ECD in cerebrovascular imaging.
Both are perfusion agents that cross the BBB.
ECD is enzymatically modified in the cell - only taken up by living cells.
HMPAO simply needs to be protonated to be trapped- marker for perfusion.
ECD is generally preferred for brain imaging. Compared to HMPAO, ECD has more rapid blood pool clearance, better shelf life, more accurate characterization of perfusion, and is only take up by living cells.
Both are used for SPECT imaging.
244
How is brain death imaging performed?
Planar imaging with either Tc-99m pertechnetate or Tc-99m DTPA.
SPECT may be performed with either HMPAO or ECD-labeled Tc-99m.
245
How is seizure imaging performed?
Seizure foci are hypermetabolic during a seizure (ictal imaging), and hypometabolic between seizures (inter-ictal imaging).
Neither Tc-99m HMPAO nor ECD undergo redistribution. Either can be injected during the seizure or up to 30 seconds after the end of the seizure.
246
What does Alzheimer disease look like on dementia imaging?
Symmetrically decreased SPECT tracer in the posterior temporal and parietal lobes.
247
What does Lewy body dementia look like on dementia imaging?
Similar to Alzheimer (posterior temporal and parietal lobes), but also involves the occipital calcarine cortex.
248
What does Pick disease look like on dementia imaging?
Decreased uptake in the frontal lobes and anterior portion of the temporal lobes.
249
Radiotracer used for brain tumor imaging?
Thallium-201 generally accumulates in malignant gliomas and not in post-treatment granulation tissue (Thallium is not taken up by radiation necrosis).
Thallium-201 uptake requires a living cell and BBB disruption.
Degree of thallium-201 uptake can be graded in comparison to the scalp activity:
2x scalp = high
Can also do Dual-phase F-18 FDG PET
250
How is Dual-phase PET used in brain tumor imaging?
Early and delayed imaging to evaluate a region of suspected tumor recurrence versus radiation necrosis.
PET scanning performed at 1 and 4 hours.
251
What is crossed cerebellar diaschisis?
Presence of a supratentorial lesion (seen in tumors, stroke, and trauma), where the cerebellar hemisphere contralateral to the lesion shows decreased radiotracer uptake.
Thought to be due to interruption of corticopontine-cerebellar pathways.
