In V/Q SPECT does Concurrent Low Dose CT Improve Diagnostic Accuracy?
Objectives : Hybrid SPECT/CT technology allows CT scans to be performed concurrently with V/Q SPECT. Whether this is of clinical benefit is unknown. The aim of this study was to determine whether the addition of a low dose CT scan can improve the diagnostic accuracy of V/Q scintigraphy in the assessment of suspected PE.
Methods : We evaluated a total of 48 patients with suspected PE in whom the final diagnosis could be confidently determined. Patients were selected at random and all had a low dose chest CT scan (30-50mAs) immediately following a V/Q SPECT scan (Technegas ventilation, Tc-99m MAA perfusion) using a hybrid scanner (Philips). Studies were reported blindly by 2 (or 3 if there was disagreement) experienced Nuclear Medicine physicians who initially viewed the V/Q SPECT study followed by the perfusion SPECT images coregistered to the CT scan using Hermes Multimodality fusion software.
Results : Of the 16 patients (33%) with PE, V/Q SPECT was positive in 15 (94%). Of the 32 patients (67%) without PE, 6 (19%) V/Q SPECT scans were reported as PE positive. Of these, 3 (50%), were correctly reclassified as PE negative after viewing the SPECT/CT images.
Conclusions : The addition of low dose CT to V/Q SPECT improves diagnostic accuracy by reducing false positive scan results (by 50% in this series). VQ SPECT/CT can characterise the cause of non-embolic mismatched perfusion abnormalities in some patients.