Nuclear Medicine Flashcards
What is the differential diagnosis for a superscan?
How do a metastatic and metabolic superscan tend to look different?
Intense symmetric activity in the bones with diminished renal and soft tissue activity on a Tc99m diphosphonate bone scan. Metastatic disease tends to affect the axial and proximal appendicular skeleton because mets preferentially involve red marrow, whereas metabolic affects the entire skeleton.
Causes:
Diffuse metastatic disease (prostate, breast, TCC, multiple myeloma, lymphoma).
Metabolic bone diseases: Renal osteodystrophy, hyperparathyroidism (often secondary), osteomalacia.
Myelofibrosis / myelosclerosis, mastocytosis, wide spread Paget’s disease
What are the main differential diagnoses for hyperthyroidism and how do they look on I-123 scan?
Graves disease- most common. Markedly elevated I123 uptake (often 60-80%, normal 10-30% at 24 hours). Most likely to visualize the pyramidal lobe.
Subacute thyroiditis- very low uptake (<3%). If focal, can simulate a cold nodule.
Toxic nodular goiter- hot nodules (adenomas), rest of thyroid suppressed. Can have moderately increased thyroid uptake values.
Rarely, transient Graves-like hyperthroidism in Hashimoto disease (normally hypothyroid).
How is I-131 ablation dose determined (?for benign conditions?) ?
Customized based on gland weight and the 24 hour iodine uptake. Typical = 6-30 mCi.
I-131 dose = (weight x 100 microCi) / RAIU
Radiopharmaceutical for a bone scan and dose?
Energy?
T1/2?
Critical organ?
20 mCi Tc-99m MDP (methylene diphosphonate) injected intravenously.
140 kEv gamma rays.
6 hours.
Bladder.
Diagnosis?
Differential?
Alzheimer’s dementia. Symmetric decreased FDG-PET or Tc99m SPECT uptake in the posterior temporal and parietal lobes, posterior cingulate cortex. Sparing of the occipital lobes, basal ganglia, and cerebellum. May involve the frontal lobes late.
VS:
Lewy body dementia: similar appearance, but more pronounced occipital involvement. Also, has decreased basal ganglia uptake on 18F-DOPA scan.
Multi-infarct dementia / AIDS-associated dementia: multiple asymmetric cortical defects, can also involve the basal ganglia.
Pick disease: anterior frontal and temporal hypoperfusion / hypometabolism.
What does hybernating myocardium look like on imaging?
How can it be differentiated from infarction?
A result of severly decreased coronary perfusion, but not to the point of causing infarction.
Results in a regional wall motion defect and fixed perfusion defect at rest and with stress.
Hybernating myocardium will have normal uptake with delayed redistribution imaging on SPECT (with THALLIUM 201, which redistributes to intact cell membranes), whereas infarct will still be low. Also, hybernating myocardium with have normal to increased uptake on FDG-PET and infarct will be down.
Radiotracer for a joint scan?
Source?
Photopeak?
T1/2?
Critical Organ?
Radiotracer- Tc-99m pertechnetate. Binds to albumin, is taken up by inflamed joints because of increased blood flow.
Usual adult dose- 20 mCi
Source- Mo-99 generator
Photopeak- 140 kEv
T1/2- 6 hours
Method of decay- Isomeric transition
Critical Organ- Stomach
Radiotracer for a bone marrow scan?
Photopeak?
T1/2?
Critical organ?
Radiotracer- Tc-99m sulfur colloid. Activity in liver, spleen, bone marrow.
Usual adult dose- 15 mCi
Source- Mo-99 generator
Photopeak- 140 kEv
T1/2- 6 hours
Method of decay- Isomeric transition
Critical Organ- Liver
Radiotracer for a WBC scan?
Photopeak?
T1/2?
Critical organ?
Radiotracer- In-111 labeled white blood cells. Image after 24 hours. Spleen > liver, bone.
Usual adult dose- 300-500 µCi
Source- Cyclotron
Photopeak- 174, 247 kEv
T1/2- 67 hours
Method of decay- Electron Capture
Critical Organ- Spleen
Radiotracer for a gastric emptying study?
Esophageal reflux?
Gastric accomidation?
Meckel’s scan?
Colonic transit?
Biliary scan?
Gastric emptying/small bowel/esophageal refux: Tc-99m sulfur colloid.
Gastric accomidation/Meckel’s scan: Tc-99m sodium pertechnetate.
Colonic transit: Indium-111 glucose.
Biliary scan: Tc-99m disofenin.
Radiotracer used for an octreoscan?
Photopeak?
T1/2?
Critical organ?
Uses?
Radiotracer: In-111 pentetreotide. Pentetreotide is a somatostatin analog. See physiologic spleen > liver, kiney, and soft tissue activity. No normal bone.
Usual adult dose- 5-6 mCi
Source- Cyclotron
Photopeak- 174, 247kEv
T1/2- 67 hours
Method of decay- Electron Capture
Critical Organ- Spleen
Uses: localization of somatostatin-rich tumors such as: carcinoid, islet cell, gastrinoma, pheochromocytoma, small cell lung cancer, medullary thyroid carcinoma, neuroblastoma.
Radiotracer used for an mIBG scan?
Photopeak?
T1/2?
Critical organ?
Uses?
Radiotracer- I-123 mIBG
Usual adult dose- 10 mCi
Source- Cyclotron
Photopeak- 159 kEv
T1/2- 13 hours
Method of decay- Electron Capture
Critical Organ- Thyroid (block pre injection with a cold iodine source such as potassium iodide)
Uses- mIBG is a norepinephrine analog (inject over 20-30 seconds due to risk for precipitating a hypertensive crisis). Pheochromocytoma, neuroblastoma, medullary thyroid carcinoma, paraganglioma, carcinoid.
Radiotracer for a thyroid uptake or whole body thyroid scan?
Source?
Photopeak?
T1/2?
Critical organ?
Radiotracer- I-123 sodium iodide
Usual adult dose- 1 mCi
Source- Cyclotron
Photopeak- 159 kEv
T1/2- 13 hours
Method of decay- Electron Capture
Critical Organ- Thyroid
Radiotracers used for a V/Q scan?
Ventilation: Radiotracer: Xe-133 gas, Dose: 20 mCi, Source: U-235 fission, Photopeak: 81 kEv, T1/2: __5.3 days, Decay: Beta decay, Critical organ: Lung.
Perfusion: Radiotracer: Tc-99m MAA, Dose: 4 mCi, Source: Mo-99 generator, Photopeak: 140 kEv, T1/2: 6 hours, Decay: Isomeric transition, Critical organ: Lung.
What are the consequences of elevated insulin levels during a PET scan (from recent meal or recent insulin injection)?
What are the consequences of elevated glucose levels?
Elevated insulin levels- drives FDG into skeletal muscle. Patients should fast at least 4-6 hours and avoid short-acting insulin for 2-4 hours.
Elevated glucose levels (above 150-200 mg/dL)- compete with FDG and cause decreased tumor uptake via competitive inhibition.
What is the most common tumor that is avid on a gallium scan? How does it work?
What activity do you look for on a gallium scan?
Gallium67 is a nonspecific neoplasm and infection/inflammation imaging agent (mostly replaced by PET for tumors). Iron analogue.
Lymphoma- most common tumor (Hodgkin and non). Also: melanoma, sarcoma (except Kaposi), HCC, lung. Sarcoid also commonly gallium-avid. Can be used for fever of unknown origin, diskitis/osteomyelitis.
See physiologic liver, spleen, colon, bone, and lacrimal gland uptake.
What percentage of Meckel’s contain gastric mucosa?
Finding on a Meckel’s scan?
What are some false positives on a Meckel’s scan?
20%
Look for focus of activity that appears at the same time as the stomach on a Tc99m pertechnetate scan. Typically RLQ.
False positives: other foci of ectopic gastric mucosa (duplication cysts). Should be able to differentiate other false positives based on timing of visualization, but can see: activity in congenital renal anomalies, vascular anomalies (aneurysm), bowel inflammation.
What does RUQ uptake on delayed ventilation images during a V/Q scan indicate?
Fatty liver. The Xe133 crosses the alveolar membrane and is distributed by the blood. It is lipophilic, and will accumulate in fatty livers.
According to the PIOPED criteria, what is low probability for PE?
<20% probability for PE.
- Small perfusion defects (matched or mismatched).
- Matched moderate or large perfusion defects.
- Perfusion defects (matched or mismatched) smaller than a corresponding radiographic abnormality.
How does PIOPED define small, medium, and large defects?
Small - 0-25% of a pulmonary segment.
Medium- 25-75%.
Large: 75-100%.
What are the imaging findings of acute cholecystitis?
Acalculus cholecystitis?
Chronic cholecystitis?
Acute calc- Nonfilling of the gallbladder on HIDA scan, even after delay/morphine. “Rim sign-“ rim of increased activity in hepatocytes adjacent to the inflamed GB fossa a sign of more advanced cholecystitis.
Acute acalc- Same, usually critically ill patients.
Chronic- <35% GB ejection fraction with CCK.
No biliary excretion of tracer by 1 hour indicates global hepatocyte dysfunction or CBD obstruction.
Note- patients should be fasting for >4 hours to avoid false positives due to GB contraction. But fasting > 24 hours can also cause false + due to thick bile (pretreat with CCK, slowly injected).
Differential diagnosis for regional decreased renal parenchymal uptake on Tc99m DMSA scan?
How does DMSA image the kidneys?
Acute pyelonephritis. (CT/MRI- decreased parenchymal perfusion or increased retention- striated nephrogram, US- regionally decreased perfusion on Doppler).
Chronic regional scarring- usually more focal and peripheral. May be associated with volume loss.
Renal tumor- more focal and masslike.
Tc99m-DMSA localizes to the kidneys via cortical tubular binding. Binds intensely to the renal parenchymal cortex, not the medulla or collecting system.
What is MIBG?
How does an MIBG scan look different than an octreotide scan? I131 WB scan?
A guanethidine analogue that accumulates in catecholamine-producing neuroendocrine tumors. Most commonly neuroblastoma in kids, pheochromocytoma in adults. Normal salivary, hepatic, enteric, and myocardial uptake. No bone activity.
Octreotide scan would show normal spleen and renal cortical uptake, no cardiac uptake (MIBG preferred to octreotide for adrenal neuroendocrine tumors b/c of renal activity in octreotide). I131 would not show cardiac activity.
Whole body scan without normal skeletal uptake… what could it be?
MIBG, octreoscan, or I131WB.
Diagnosis?
Cause?
Differential?
Hypertrophic osteoarthropathy.
Can be primary (rare, pachydermoperiostosis) or secondary (HPOA, secondary to tumors involving the pleura or inflammatory pleural disease. Can also be secondary to inflammatory GI/liver disease- IBD, celiac, PBC). Also get clubbing of fingers/toes, skin thickening, painful joints. May regress after underlying disease treated.
Shin splints (confined to mid-distal tibia), venous stasis (typically below the knees).
What is the most common nuclear medicine test in a patient with elevated PTH and serum calcium (suspected primary hyperparathyroidism)?
Tc99m-MIBI early and delayed imaging. Tracer binds to increased mitochondria in abnormal parathyroid glands. Tracer also binds to normal thyroid early; it washes out of the thyroid late but persists in abnormal parathyroids.
More sensitive for parathyroid adenoma than hyperplasia.
Note- MIBI is a nonspecific tracer. Focal uptake can represent parathyroid adenoma, parathyroid carcinoma, thyroid adenoma, thyroid carcinoma, mets, lymphoma, or infection/inflammation. Clinical history important.
What nuclear medicine test would be best to diagnose a dedifferentiated thyroid carcinoma recurrence (clinically, you see rising thyroglobulin)?
Diagnose medullary thyroid cancer?
Dedifferentiated thyroid carcinoma may not be I131 avid, but would be seen on PET/CT. (although these sometimes still respond to high dose I131 therapy) Low-grade papillary and follicular cancers, on the other hand, may be non-FDG avid, but radioiodine-avid.
Medullary thyroid cancer is also not iodine avid, but can be seen with octreotide or MIBG.
Note: TSH levels should be > 30 microU/mL before doing any studies. Can pre-treat with Thyrogen instead to avoid hypothyroid state if necessary, but will not be quite as sensitive.
What will be seen when there is free pertechnetate in studies with Tc99m?
How are red blood cells tagged?
Immediate uptake in the stomach, salivary glands, and thyroid.
2 strep process. 1) Provide an intercellular reducing agent (cold tin) then 2) introduce Tc99m to bind to hemoglobin. These steps can each be performed in a test tube (in vitro) or in vivo. Test tube provides better labeling efficiency.
Diagnosis?
Radiotracer?
Brain death (hot nose sign due to preferential ECA flow and no ICA flow). Note - can see some venous activity in the transverse or sagittal sinus due to scalp collaterals, even when no ICA flow.
Can use almost any tracer labeled with Tc99m. HMPAO and ECD (Neurolite) are brain-specific, allowing delayed imaging to ensure no cerebral flow. Other agents (pertechnetate, DTPA, glucoheptonate) can be used for dynamic angiographic images.
Diagnosis?
Tracer? Normal exam?
MRI findings?
Which type is most likely to benefit from shunting?
Obstructive communicating hydrocephalus (NPH is a subtype of this but can’t distinguish w/o LP).
This is an indium-111 DTPA scan. Normally, should see migration over the convexities by 24 hours, no later than 48 hours, and should never see activity in the ventricles.
MRI may help for defining who will respond to shunting. Look for CSF flow void in the cerebral aqueduct and 3rd ventricles, and ventricular dilation out of proportion to sulcal atrophy.
Type 4 benefits from shunting. This is based on the cisternogram- poor clearance and persistent ventricular activity.
Differential diagnosis?
Granulocyte colony stimulating factor (G-CSF) therapy, post chemotherapy, erythropoietin therapy.
Myelodysplatstic syndromes, beta thalassemia, chronic myeloid leukemia (CML), interleukins in pyrexic states, cytokines in tumours, diffuse marrow metastases (less likely), severe anemia (hyperplastic marrow).
Scan? When do you get the images?
Diagnosis?
Gallium scan (iron analogue, nonspecific uptake in some tumors esp lymphoma and melanoma, and active inflammation). Do delayed images (48-72 hours) because there is some initial renal and lung uptake that can be normal, but normal activity should clear out within the first 24 hours.
Diagnosis: Sarcoid. (“Lambda sign” = due to symmetric mediastinal and hilar uptake. “Panda sign” = due to involvement of the lacrimal, parotid, and salivary glands)
Other considerations would be lypmhoma, other infectious process.
Diagnosis?
Hypercalcemia.
Diffuse uptake in stomach, lungs, myocardium, and renal parenchyma.
Painful thyroid in a hyperthyroid patient. Diagnosis?
Same but nonpainful… differential?
Subacute thyroiditis. Markedly decreased thyroid radioiodine uptake (normal 10-30% at 24 hours). Most common subtype is DeQuervain (granulomatous), also includes postpartum. Self-limited.
Painless etiologies of hyperthyroidism with low thyroid uptake include thyrotoxicosis factitia, struma ovarii, and iodine or amiodarone induced thyrotoxicosis.
Primary or secondary hypothyroidism would also have low uptake, but these patients would present with hypothyroid.
How is the appearance of PE and microembolic disease (tumor, fat, talc, small-vessel vasculitis) different on Tc99m-MAA perfusion scan?
PE- multiple mismatched, wedge-shaped segmental and subsegmental perfusion defects.
Microembolic disease: multiple linear mismatched perfusion defects outlining the periphery of segments. “Segmental contouring” or “contour mapping” sign. See pic below.
Diagnosis?
Presentation?
Appearance on CT?
Lingual thyroid- failure of descent of the embryologic thyroid anlage from the posterior tongue.
Often hypothyroid. May present with obstruction to breathing or swallowing with larger lesions. Other (rare) locations for thyroid ectopy- submandibular glands, trachea, cervical lymph nodes.
On unenhanced CT, it will be higher attenuation because it is iodine-rich. Keep in mind that any disease that can affeect the normal thyroid can affect a lingual thyroid, so you can get ca here. Also, avoid biopsy because of risk for hemorrhage and precipitation of thyroid storm.
Diagnosis?
Appearance on MRI? 3 phase bone scan?
Complex regional pain syndrome (Reflex sympathetic dystrophy).
CT/plain film: periarticular osteopenia. MRI can demonstrate soft-tissue edema and enhancement, skin thickening, and muscle atrophy. Bone scan will demonstrate increased blood flow, blood pool, and delayed phase periarticular uptake. In the chronic “burned-out” phase, all 3 stages can be down.
