Pulmonary Flashcards
What radiotracer is used for perfusion?
Tc-99m MAA (macroaggregated albumin) - prepped by denaturing human serum albumin
Pathway of Tc-99m in the circulation?
vein -> SVC -> PA -> Lung -> STOP
Biologic half life of Tc-99m?
4 hours, fall apart and enter systemic circulation -> RE system
2 radiotracers for ventilation scan?
Xe-133, Tc-99m DTPA
Biologic half life of Xe-133?
30 seconds
Why do you need to do the ventilation exam with first?
Low energy (80 keV) on Xe-133 and short half life. Tc-99m DTPA requires pt cooperation, breathing through a mouth guard and nose clamp
What are the 3 phases of Xe-133 exam?
1) Wash in - single max inspiration and breath hold
2) Equilibrium - RA breathing and XE mix
3) Wash out - RA breathing
What if Tc99m-MAA is seen in the brain?
R->L Shunt somewhere; ASD, VSD or Pulm AVN
How big are particles of Tc99m-MAA
Bigger than capillaries (10 micrometers) but smaller than arterioles (150 micrometers) so 10-100
When do you have to reduce particle amount of Tc99m-MAA? (4)
1) Don’t block more than 0.1% of capillaries, so anyone with one lung, children, etc.
2) Anyone with a R->L shunt because you cant block capillaries in brain
3) Pulmonary hypertension
4) Pregnancy
Reduced particles = Reduced dose of Tc99m-MAA?
No, can get the full dose to fewer particles
Multiple focal scattered hot spots of Tc99m-MAA?
“clumped MAA” = tech drew blood into syringe prior to exam
Persistent Xe-133 activity during washout phase?
Air Trapping - COPD
Accumulation of Xe-133 over RUQ?
Fatty infiltration of liver (Xe fat soluble)
Washout time comparison between Xe-133 and Tc-99m DTPA? and advantage of this?
Slower wash out with Tc-99m DPA = can get multiple projections
Where is activity of Xe-133 and Tc-99m DTPA?
Xe-133 homogenous in lungs
Tc-99m DTPA - “clumping” common in mouth, central airways and stomach (from swallowing)
What is a quantitative perfusion done to evaluate?
Pre lung resection/transplant to make sure remaining lung can perform well enough
Is quantification possible with Tc-99 DTPA aerosol?
NO - can do it with combined Xe + Tc MAA because Xe doesn’t interfere with Tc
Tracer seen in thyroid or stomach on VQ? (2 reasons)
Free Tc, or R->L Shunt
What needs to be seen to call R->L shunt on VQ?
Tracer in brain
If you suspect shunt how do you alter scan?
Reduce number of particles (if normal is 500k, reduce to 100k for example)
How do you alter scan for a patient with Pulm HTN?
Reduce particles
Particle reduction = dose reduction?
No, full dose
How do you alter scan for a neonate?
Particle reduction, down to 10-50k - don’t want to cause a PE
Unilateral perfusion defect (whole lung) with no ventilation defect next step?
Get a CT/MRI; DDx Mass, fibrosing mediastinitis, central PE with MCC being central obstructing mass (bronchogenic carcinoma)
Grade of unilateral whole lung perfusion defect with no ventilation defect?
Low probability
What radiotracer is used for pulmonary infection imaging?
Gallium 67 scan
What gives gallium and advantage over Indium WBC scan?
Can bind to neutrophil membranes even after cells are dead, helpful in chronic infection
Brief: how is Ga67 produced?
Bombard Zn68 -> complexed with citric acid to make gallium citrate and decays (Half Life 3 days) via electron capture
What are the 4 photopeaks (gamma ray emission energies) from the electron capture of Gallium Citrate?
93 keV (40%) 184 keV (20%) 300 keV (17%) 393 keV (5%)
When are images taken in Ga67 scan?
Not sooner than 24 hours because background is too high
What is the critical organ of a Ga67 scan?
Colon
Normal localization of Ga67?
Liver (highest), Bone marrow (poor man’s bone scan), spleen, salivary, lacrimal, breasts (lactating/pregnant).
Kidney + Bladder - Seen in first 24 with faint uptake in lungs
After 24 seen in bowel
Growth plates and thymus in children
Is gallium uptake specific?
No, can be seen with many things such as infxn, CHF, atelectasis, ARDS
What do you use Gallium scan for in sarcoidosis?
Look for active dz, 90% sensitive for active disease with increased uptake in lungs; can also help guide bx and lavage
What is the lambda sign on Gallium scan?
Nucs equivalent of 1-2-3- sign on CXR - increased uptake in bilateral hila, and right paratracheal lymph node
What is the panda sign on Gallium scan? Seen in?
Prominent uptake in the nasopharyngeal region, parotid salivary gland, and lacrimal glands. Seen in sarcoid, sjorgren’s, and treated lymphoma.
Noninfectious uses of Gallium scans? (2)
Early reaction to chemo/drugs
Monitor response to IPF therapy
Immunosuppresed patient uses of Gallium scan? (3)
Gallium HOT for PCP - diffuse bilateral pulm uptake
Gallium negative/Thallium positive for Kaposi sarcoma
Intense lobar configuration without parotid/nodal uptake for bacterial pneumonia
Can GA pick up abdominal and pelvic infections? Malignant otitis media? and Spinal osteomyelitis?
Yes - although In-111 WBC better than gallium for abd/pelvic infections
Yes, MOM is both gallium and bone scan (temporal bone) hot
Yes, it is superior to Indium WBC for spinal infection.
