VQ scans

Severe pulmonary HTN where blockade of lung capillaries may acutely exacerbate the condition
Right-to-left shunts, take care with these, but advers effects on coronary or cerebral circulations have rarely been observed
- Can easily detect by immediate presence of renal activity best seen on posterior to lateral views and can be confirmed by demonstration of activity in the brain

Shouldn’t be injected through a filtered needle or a Swan
If drawing blood into syringe to confirm needle location, should not delay injecting or clots can form and will have clinically insignificant but radiolabeled clots

≥2 large mismatched V/Q segmental defects

All other findings

Nonsegmental
Q defect < CXR lesion
- If perfusion defect is substantially smaller than the corresponding radiographic abnormality, the probability of PE is very low (an infarction logically shouldn’t be bigger than the perfusion defect)
Solitary matched V/Q/CXR defect (≤1 segment) in mid or upper lung
- AKA “triple match”
- Evidence that triple match lower lobe, where blood flow is greater, more commonly represents PE thus making a lower lobe triple match intermediate probability
1-3 small segmental defects
Matched V/Q defects in ≥2 zones of one lung, regionally normal CXR
Stripe sign
Solitary large pleural effusion
Normal
No perfusion defects

Thin line/stripe of activity representing perfused lung tissue between a perfusion defect and adjacent pleural surface
With emboli, perfusion defect should go all the way to pleura
Most commonly due to emphysema

Lobar or whole-lung defects are unusual presentations for PE
- Consider hilar masses, mediastinal fibrosis, and hypoplastic pulmonary artery
Severe, diffuse COPD may lead to nondiagnostic V/Q
Triple matches in upper or mid zones are very low probability while lower zones is intermediate probability

Radiology Notes