Pulmonary

Question 1

What radiotracer is used for perfusion?

Answer 1

Tc-99m MAA (macroaggregated albumin) - prepped by denaturing human serum albumin

Question 2

Pathway of Tc-99m in the circulation?

Answer 2

vein -> SVC -> PA -> Lung -> STOP

Question 3

Biologic half life of Tc-99m?

Answer 3

4 hours, fall apart and enter systemic circulation -> RE system

Question 4

2 radiotracers for ventilation scan?

Answer 4

Xe-133, Tc-99m DTPA

Question 5

Biologic half life of Xe-133?

Answer 5

30 seconds

Question 6

Why do you need to do the ventilation exam with first?

Answer 6

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

Question 7

What are the 3 phases of Xe-133 exam?

Answer 7

1) Wash in - single max inspiration and breath hold
2) Equilibrium - RA breathing and XE mix
3) Wash out - RA breathing

Question 8

What if Tc99m-MAA is seen in the brain?

Answer 8

R->L Shunt somewhere; ASD, VSD or Pulm AVN

Question 9

How big are particles of Tc99m-MAA

Answer 9

Bigger than capillaries (10 micrometers) but smaller than arterioles (150 micrometers) so 10-100

Question 10

When do you have to reduce particle amount of Tc99m-MAA? (4)

Answer 10

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

Question 11

Reduced particles = Reduced dose of Tc99m-MAA?

Answer 11

No, can get the full dose to fewer particles

Question 12

Multiple focal scattered hot spots of Tc99m-MAA?

Answer 12

“clumped MAA” = tech drew blood into syringe prior to exam

Question 13

Persistent Xe-133 activity during washout phase?

Answer 13

Air Trapping - COPD

Question 14

Accumulation of Xe-133 over RUQ?

Answer 14

Fatty infiltration of liver (Xe fat soluble)

Question 15

Washout time comparison between Xe-133 and Tc-99m DTPA? and advantage of this?

Answer 15

Slower wash out with Tc-99m DPA = can get multiple projections

Question 16

Where is activity of Xe-133 and Tc-99m DTPA?

Answer 16

Xe-133 homogenous in lungs

Tc-99m DTPA - “clumping” common in mouth, central airways and stomach (from swallowing)

Question 17

What is a quantitative perfusion done to evaluate?

Answer 17

Pre lung resection/transplant to make sure remaining lung can perform well enough

Question 18

Is quantification possible with Tc-99 DTPA aerosol?

Answer 18

NO - can do it with combined Xe + Tc MAA because Xe doesn’t interfere with Tc

Question 19

Tracer seen in thyroid or stomach on VQ? (2 reasons)

Answer 19

Free Tc, or R->L Shunt

Question 20

What needs to be seen to call R->L shunt on VQ?

Answer 20

Tracer in brain

Question 21

If you suspect shunt how do you alter scan?

Answer 21

Reduce number of particles (if normal is 500k, reduce to 100k for example)

Question 22

How do you alter scan for a patient with Pulm HTN?

Answer 22

Reduce particles

Question 23

Particle reduction = dose reduction?

Answer 23

No, full dose

Question 24

How do you alter scan for a neonate?

Answer 24

Particle reduction, down to 10-50k - don’t want to cause a PE

Question 25

Unilateral perfusion defect (whole lung) with no ventilation defect next step?

Answer 25

Get a CT/MRI; DDx Mass, fibrosing mediastinitis, central PE with MCC being central obstructing mass (bronchogenic carcinoma)

Question 26

Grade of unilateral whole lung perfusion defect with no ventilation defect?

Answer 26

Low probability

Question 27

What radiotracer is used for pulmonary infection imaging?

Answer 27

Gallium 67 scan

Question 28

What gives gallium and advantage over Indium WBC scan?

Answer 28

Can bind to neutrophil membranes even after cells are dead, helpful in chronic infection

Question 29

Brief: how is Ga67 produced?

Answer 29

Bombard Zn68 -> complexed with citric acid to make gallium citrate and decays (Half Life 3 days) via electron capture

Question 30

What are the 4 photopeaks (gamma ray emission energies) from the electron capture of Gallium Citrate?

Answer 30

93 keV (40%)
184 keV (20%)
300 keV (17%)
393 keV (5%)

Question 31

When are images taken in Ga67 scan?

Answer 31

Not sooner than 24 hours because background is too high

Question 32

What is the critical organ of a Ga67 scan?

Answer 32

Colon

Question 33

Normal localization of Ga67?

Answer 33

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

Question 34

Is gallium uptake specific?

Answer 34

No, can be seen with many things such as infxn, CHF, atelectasis, ARDS

Question 35

What do you use Gallium scan for in sarcoidosis?

Answer 35

Look for active dz, 90% sensitive for active disease with increased uptake in lungs; can also help guide bx and lavage

Question 36

What is the lambda sign on Gallium scan?

Answer 36

Nucs equivalent of 1-2-3- sign on CXR - increased uptake in bilateral hila, and right paratracheal lymph node

Question 37

What is the panda sign on Gallium scan? Seen in?

Answer 37

Prominent uptake in the nasopharyngeal region, parotid salivary gland, and lacrimal glands. Seen in sarcoid, sjorgren’s, and treated lymphoma.

Question 38

Noninfectious uses of Gallium scans? (2)

Answer 38

Early reaction to chemo/drugs

Monitor response to IPF therapy

Question 39

Immunosuppresed patient uses of Gallium scan? (3)

Answer 39

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

Question 40

Can GA pick up abdominal and pelvic infections? Malignant otitis media? and Spinal osteomyelitis?

Answer 40

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.