Lung
Ventilation perfusion (VQ) lung scan is well established in evaluating PE. Advances shifting from 2D (ie. traditional planar) to 3D (ie. SPECT) techniques has increased the sensitivity & specificity resulting in less interobserver variation and better delineation of sub-segmental mismatched defects. At NMI we also adopt a binary reporting approach. While CTPA is also used in suspected PE, it is worth noting that in the PIOPED II study, the sensitivity was 83%, and 25% of patients failed to undergo CTPA because of abnormal renal function, contrast allergy or possible pregnancy.
Case 1
Indication: Dyspnoea
A 65 yr old man presented with gradual worsening dyspnoea over 2 months. Apart from a family history of thromboembolism, he did not have other risk factors for PE. CXR did not reveal any obvious abnormality. VQ scan (Fig. 1) was requested which showed multiple segmental perfusion mismatches (arrows) consistent with extensive PE.
Case 2
Indication: Suspected PE in Pregnancy
A 32-week pregnant woman developed tachycardia & dyspnoea, presented to her GP. Since the risk for PE is increased during pregnancy, VQ SPECT (Fig. 2) was requested which demonstrated normal lung perfusion excluding PE. VQ scan is preferred in pregnancy because of a high incidence of non-conclusive CTPA (due to artefact) & significantly higher radiation dose to the mother (especially breast tissue). The foetal dose is similar for both techniques. At NMI we utilise half-dose techniques for both ventilation & perfusion imaging.
