Pulmonary

Question 1

NM: perfusion vs ventilation tracers

Answer 1

perfusion: Tc99m MAA
ventilation: Xenon 133; Tc99 DTPA

Question 2

NM: perfusion study

Answer 2

Tc99m MAA which lodges in pulmonary capillary bed (particles 10-30 microm in size)

approximately 3-5 mCi Tc99 MAA administered which = 200-600K particles

can 1/2 dose if pts are kids, pregnant, mild pulmonary hypertension, known R->L shunt

particles break down in ~30 min

Question 3

relative contraindication to MAA

Answer 3

severe pulmonary hypertension, obstruction of few pulmonary capillaries can cause clinical worsening

Question 4

cause of clumping of MAA

Answer 4

MAA indadvertently drawn back into injection syringe; causing coagulation with pt blood

Question 5

R>L shunt on perfusion study

Answer 5

immediate renal/brain uptake after IV injection due to shunt

can quantify shunt fraction if seen in head

Question 6

differentiating between R>L and L>R shunt

Answer 6

R>L shunt: immediate brain uptake, no uptake in neck (thyroid)

L>R shunt: renal/brain uptake

Question 7

thyroid uptake in perfusion study

Answer 7

free pertecnetate taken up by thyroid

Question 8

Xe: 133 half life, gamma photons, critical organ

Answer 8

half life: 5.3 days (physical), biological (exhalation)

emission: 81 keV gamma, beta emitter

critical organ: trachea

Question 9

ventilation study protocol

Answer 9

imaged posteriorly to limit attenuation artifact

administered in negative pressure room to prevent accidental leakage; trapped air is disposed of through exhaust to atmosphere or trapped in charcoal

Question 10

Tc99 DTPA vs Xe 133

Answer 10

Xe 133 can be used for washin/washout imaging (shows COPD)

Tc99m is a technetium labeled aerosol; particles stay in place for 20-60 min (30 mCi administered)

easier to use; no need for exhaust systems, image in multiple projections/portable

Question 11

evaluation of PE in pregnancy

Answer 11

lower dose to maternal breast with perfusion scanning

Question 12

PIOPED II

Answer 12

high, intermediate, low, and very low probability

high: >2 large mismatched segmental defects without associated radiographic abnormality
intermediate: one large subsegmental mismatched perfusion defect (not clinically helpful, further imaging required)

low probability: single large/moderate matched VQ defect; absent perfusion fo entire lung, more than 3 small segmental lesions

very low probability: nonsegmental lesions

Question 13

triple match VQ scan

Answer 13

defect in perfusion, matched defect on ventilation, corresponding abnormality on chest radiograph in lower lung fields

intermediate probability

Question 14

stripe sign

Answer 14

thin line of MAA uptake between perfusion defect and adjacent pleural surface