CTC Nucs Flashcards
Hot spleen should make you think
Octreotide and WBC Scans
Sulfur colloid will have tracer in the spleen, but not as much as the liver.
Cardiac activity with MIBG
Will see it with I-123 not with I-131
High count study with no bones + liver + dark spleen + dark kidneys?
Octreotide
Images should be cleaner b/c of high counts.
Difference between Tc and In WBC scans
Both will have hot spleens. Tc will have higher count and will look cleaner.
Tc WBC have to image at 4 and 24 hours. At 4 hours you get lung uptake. At 24 hours, the lungs are clearing up, but you start getting bowel uptake
Tc WBC = Renal and GI
In WBC = No Renal and No GI.
How do you prepare MDP?
Kit which has MDP and stannous ion. Add free pertechnetate and the stannous ion reduces it so it will bind the MDP.
Don’t have enough stannous ion (or get air into the vial or syringe - that can cause oxidation) you might get free Tc (salivary gland, thyroid, stomach uptake).
Inject tracer (15-25 mCi) wait 2-4 hours to let tracer clear from soft tissues.
How do you tell the difference between an F-18 vs Tc-MDP bone scan vs PET-FDG with marrow stimulation?
Tc-MDP will have bone and kidney uptake. Will be blurry and fuzzy.
F-18 will be high resolution and look like a MIP PET
FDG-PET with bone stimulation will look similar to F-18, but will have BRAIN uptake
F-18 not commonly done b/c expensive.
Highest doses in MDP and F-18 bone scans?
MDP = bone
F-18 = Bladder
What is normal uptake on a bone scan? What factors will affect tracer uptake?
Normal: Bone, kidney, bladder, breasts (esp in young women), soft tissues - low levels, epiphyses in kids
Factors: OsteoBLASTIC activity, blood flow.
Marked uptake of skull sutures on bone scan?
Renal osteodystrophy
Normal to see some persistent visualization of skull sutures.
Increased renal cortex activity in bone scan?
Supposed to see renal activity, but when renal cortex is hotter than the adjacent lumbar spine, think hemachromatosis.
Diffuse renal activity - seen in setting of chemotherapy, but can be seen with urinary obstruction.
Diffuse renal uptake on a bone scan?
Seen in setting of chemotherapy, but can be seen with urinary obstruction
Increased renal cortex uptake can be seen with hemachromatosis - more than adjacent lumbar spine.
Causes of liver uptake on bone scan?
Too much Aluminum contamination in the Tc
Cancer - either hepatoma or mets
Amyloidosis
Liver necrosis
Cause of diffusely decreased skeletal uptake?
Free Tc
Bisphosphonate therapy
What is Flair Phenomenon with bone scans?
Bone scan with good response to therapy will mimic a bad response.
Increased radiotracer uptake (both in number and size of lesions) seen 2 weeks to 3 months after treatment.
Lesion will be more sclerotic on plain film if flair.
Will improve after 3 months.
Best bone tracer to use for neuroblastoma mets?
I-123 or I-131 MIBG
How can Pagets be shown on bone scan?
Super hot enlarged femur
Super hot enlarged pelvis
Super hot skull
Expanded hot “entire” vertebral body - BOTH vertebral body and posterior elements.
Metabolic superscan - from widespread Pagets.
What causes a metabolic superscan on bone scan?
hyperPTH
How can Fibrous Dysplasia be shown on a bone scan?
Super hot mandible
Leg that looks similar to Pagets
Lesions that are hot on bone scan?
Fibrous Dysplasia Giant Cell Tumor Aneurysmal Bone Cyst Osteoblastoma Osteoid Osteoma
Cold: Bone cyst without fracture
Variable: Hemangioma and multiple hereditary exostosis.
Why do you image heterotopic ossification on bone scan?
See if it’s “mature” or not. If active it has a higher rate of recurrence if resected.
How can you tell the difference between metabolic and malignant superscans?
Skull will be asymmetrically hot on a metabolic superscan.
Metabolic: hyperPTH, renal osteodystrophy, Pagets, or severe thyrotoxicosis.
What to do for “equivocal lesions” on bone scan?
Plain film. If no lesion = MORE suspicious for mets = MRI.
Bone scan with increased uptake on flow and blood pool with periarticular uptake on delayed phase?
Reflex Sympathetic Dystrophy
Often involves the entire extremity
What is the fourth phase of a bone scan?
Sometimes done in diabetics due to reduced peripheral blood flow - may help distinguish between bone and delayed soft tissue clearance.
When should you consider Tc99 HMPAO instead of In-WBC for infection?
Kids - Tc99 will have a lower absorbed dose and shorter imaging time
Small parts- Tc99m does better in hands and feet.
Disadvantages of Tc99 HMPAO
Shorter half life -6 hrs- limits delayed imaging
Normal GI and GB activity which would obscure injection in those areas.
Tracers used for V/Q ventilation?
Xenon 133 -
Physical half life of 5.3 days, biological half life is 30 seconds - only can do one view.
Low energy (80 keV) - NEED TO DO FIRST
3 phases: 1. Wash in (single max inspiration and breath hold). 2. Equilibrium (breathing room air and xenon mix). 3. Wash out (breathing normal air).
Tc-99m -
Requires patient cooperation. Must do first.
When doing V/Q, what must be done first?
Ventilation must be first.
V/Q Tc99 MAA tracer in brain
Shunt - ASD, VSD, or pulmonary AVM.
How big are Tc99 MAA tracer particles?
10-100 micrometers
Capillary is about 10 micrometers. Need to stay in lung, so can’t be smaller than that. Don’t want too big so they block arterioles.
Reduce particle amount if you have fewer capillaries (children or 1 lung), if they have a R-L shunt (stroke), and pulm HTN.
Reducing particles does NOT reduce dose - just added to fewer particles.
Multiple focal scattered hot spots in lungs?
Clumped MAA - tech draws blood into the syringe prior to injection
What causes multiple focal scattered hot spots in the lungs on MAA perfusion?
Clumped MAA - tech draws blood into the syringe prior to injection.
Persistent pulmonary activity during washout of Xenon ventilation?
Air trapping - COPD
Accumulation of Xenon tracer over the RUQ during ventilation?
Fatty infiltration of liver - xenon is fat soluble.
What is the classification of a triple match in the lower lung fields on V/Q?
Intermediate
What is a Reverse Mismatch on V/Q?
Normal perfusion with abnormal ventilation - MC atelectasis.
Can be pleural effusion, pneumonia, cardiometaly, and partial bronchial obstruction.
What is Stripe Sign on V/Q?
Zone of normally preserved peripheral lung.
PE is peripherally based, makes PE unlikely, considered very low probability.
Cause of Solitary Lobar or Solitary Whole Lung Perfusion Defects
Hilar mass, hypoplastic pulmonary artery, or mediastinal fibrosis - uncommon for PE
MC cause of unilateral whole lung perfusion defect with normal ventilation?
Lung cancer.
How do pleural effusions fit in V/Q scans?
Small effusion causing matched defects = intermediate prob
Large effusion = low prob
Triple matched defects in the lower lobe (caused by any size effusion) = intermediate
*Triple matched defects in the middle and upper lobe = low probability
When to f/u high probability scan?
Do f/u in 3 months for new baseline.
What are quantitative lung perfusion scans done for?
Evaluate prior to lung resection or prior to transplant.
Quant is NOT possible if you use Tc99 DTPA aerosol. Can do it with combined Xe + Tc99 MAA b/c the Xe will not interfere with the Tc.
How does Gallium work?
Works like iron- binds to lactoferrin and concentrates in areas of inflammation, infection, and rapid cell division. Not very specific for infection or tumor.
Produced in cyclotron via bombardment of Zn68 and complexed with citrate to make Gallium Citrate. Half life of 3 days (78 hours).
Decays by electron capture - 4 photopeaks - 90, 190, 300, 390.
Do images at 24 hours b/c background is too high.
Target organ is the colon.
Liver, bone marrow, spleen, salivary glands, lacrimal glands, breast (if lactating or pregnant)
Characteristics of Gallium
Works like iron- binds to lactoferrin and concentrates in areas of inflammation, infection, and rapid cell division. Not very specific for infection or tumor.
Produced in cyclotron via bombardment of Zn68 and complexed with citrate to make Gallium Citrate. Half life of 3 days (78 hours).
Decays by electron capture - 4 photopeaks - 90, 190, 300, 390.
Do images at 24 hours b/c background is too high.
Target organ is the colon.
Liver, bone marrow, spleen, salivary glands, lacrimal glands, breast (if lactating or pregnant)
Non-infectious things Gallium can be used for?
Show early drug reaction from chemotherapy (Bleomycin) or other drugs (Amiodarone)
Elevated in IPF and can be used to monitor response to therapy.
What can Gallium be used for in immunocompromised patients?
PCP = Gallium hot - diffuse bilateral pulmonary uptake
Kaposi Sarcoma = Gallium negative, Thallium Positive
Bacterial Pneumonia = Intense lobar configuration w/o parotid or nodal uptake
Use In-111 WBC or Gallium with abdominal and pelvic infection?
In-111 WBC is superior.
Gallium has normal GI uptake
Use In-111 WBC or Gallium for spinal osteo?
Gallium
What are the two types of thyroid imaging?
Trapping - Transported into the gland - I-123, I-131, and Tc99 all do this
Organification - Analog is oxidized by thyroid peroxidase and bound to tyrosyl moiety. 123 and 131 do this. Tc does not and slowly washes out of the gland.
Pros and cons of I-131, I-123, and Tc-99m for thyroid imaging
I-131:
Pro: Cheap
Con: Long half life (8 days) and high energy (364 keV) = crappy images with 1/2 inch crystal. Ideal for therapy, not routine imaging. Contraindicated in kids and pregnant women.
I-123:
Pro: Shorter half life (13 hours) and ideal energy (159). Decays via electron capture = prettier images.
Con: Costs more
Tc-99m:
Trapped, but not organified. Background levels are higher b/c only 1-5% is taken up by thyroid.
Choose Tc over Iodine when recent thyroid blocker on board or iodinated contrast
When would you choose Tc-99m over an iodine agent for thyroid imaging?
Had a recent thyroid blocker
Recent iodinated contrast.
Rules for breast feeding after thyroid imaging
Tc-99m: Resume in 12-24 hours
I-123: Resume in 2-3 days
I-131: Should not breast feed (not getting pregnant for 6-12 months).
How is an iodine uptake test done?
Give 5 mCi of I-131 or 10-20 mCi of I-123.
4-6 hours and 24 hours
Normals are 6-18% (4-6 hours) and 10-30% at 24 hours.
Correction for background is done for measurements prior to 24 hours.
Factors affecting uptake:
Renal function (increases stable iodine pool, reduces numbers)
Dietary Iodine - variable and controvercial
Medications - thyroid blockers, nitrates, IV contrast, Amiodarone
What factors can affect a thyroid uptake scan?
Factors affecting uptake:
Renal function (increases stable iodine pool, reduces numbers)
Dietary Iodine - variable and controvercial
Medications - thyroid blockers, nitrates, IV contrast, Amiodarone
What causes increased and decreased uptake on a thyroid scan?
Increased: Graves Early Hashimoto Rebound after abrupt withdrawl of antithyroid meds Dietary Iodine Deficiency
Decreased:
Primary or secondary causes of hypothyroidism
Renal Failure
Medications - thyroid blockers, nitrates, IV contrast, amiodarone
Dietary iodine overload
What is Plummer Disease?
Multi-nodular Toxic Goiter
Elderly woman with weight loss, anxiety, insomnia, and tachycardia.
Gland is heterogeneous, with uptake that is only moderately elevated. Nodules will be hot on the background of a cold gland.
How to tell the difference between a Toxic multi-nodular goiter vs a Non-toxic multi-nodular goiter?
Toxic goiter will have hot nodules on a background of cold thyroid.
Non-toxic will have warm/hot nodules on a normal background of the thyroid.
Graves = high uptake (70%), homogeneous
Toxic Multi-nodular goiter = uptake medium high: 40s, heterogeneous.
What is Hashimotos?
MC cause of goitrous hypothyroidism. Autoimmune disease that causes hyper first then hypothyroidism second as the gland burns out later. Usually hypo when its seen.
Increased risk of primary thyroid lymphoma.
Associated with Ab to thyroid peroxidase (TPO) and antithyroglobulin.
Hypothyroid = Inhomogeneous gland with focal cold areas.
Hyperthyroid (acute) = Looks like Graves.
Difference between Subacute Thyroiditis and Graves?
Both can have low TSH, high T3, and high T4.
Subacute thyroiditis will have low %RAU.
What kinds of nodules are more likely to be cancer?
Cold nodules when compared to functional (warm) nodules.
Most are cold and therefore most are benign (colloid, cysts, etc..). Colds nodules in a multi-nodular goiter are even less likely to be cancer compared to a single cold nodule.
What is a discordant nodule?
Hot on Tc99 but COLD on I-123.
B/c some cancers can maintain their ability to trap, but lose the ability to organify = can’t be benign until you show that it’s also hot on I-123.
What causes a thyroid that takes up Tc, but NOT Iodine on 24 hour imaging?
Congential enzyme deficiency that inhibits organification
Drug like PTU that blocks organification.
If just an iodine thyroid with low uptake on 24 hours, this is de Quervains, or a burned out Hashimotos.
MC subtype of thyroid cancer?
Papillary is popular. - does well with surgery plus I-131.
Medullary thyroid (MEN 2a and 2b) does not do well with I-131. Occasionally (10%) take up Octreotide - cold on thyroid scan.
Things that make you treatment resistant for I-131?
Medullary subtype CA - will not take up tracer
History of prior I-131- easy gland has been killed off
History of Methamazole treatment -even if years ago.
