Diagnostic Accuracy of offline lung perfusion SPECT/CT in Pulmonary Embolism

Background: Standard ventilation and perfusion(V/Q) scintigraphy uses planar images for the diagnosis of pulmonary embolism (PE). Availability of optimal radiopharmaceuticals for ventilation scan are limited in most nuclear medicine centers. To evaluate whether software based fusion of perfusion single photon emission CT(Q-SPECT) with non-contrast CT(NCCT) improves the diagnostic accuracy of the procedure, we want to compare this method with standard planar V/Q scans in patients at high risk for PE.Methods: Between 2016 and 2017, most patients referred for diagnosis of PE underwent lung planar aerosol V/Q scan, Q-SPECT and also chest NCCT. Offline fusion of perfusion SPECT on NCCT was done using dedicated software. Time interval between Q-SPECT and lung NCCT was not more than 2 days. All scans were reviewed retrospectively by two observers; planar scans were read with modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED II ( and Prospective Investigative Study of Pulmonary Embolism Diagnosis (PISA-PED) criteria. On offline Q-SPECT/CT, any wedge-shaped peripheral perfusion defect occupying > 50% of a segment without corresponding pulmonary parenchymal or pleural disease was considered to show PE. PE was excluded when there was a normal perfusion pattern or perfusion defects were caused by lung parenchymal abnormalities or were not arranged in accordance with the pulmonary vasculature. The final diagnosis was established with a composite reference standard that included ECG, ultrasound of lower-extremity veins, D-dimer levels, CT pulmonary angiography (when available), and clinical follow-up for at least 3 months.Results: Fifty-three patients with mean Wells’ score of 4.1 had sufficient follow-up; 11 patients were given a final diagnosis of PE, and 42 patients were given a final diagnosis of no PE. According to PIOPED II, 7 studies were graded as intermediate probability. Sensitivity and specificity for PE were 50% and 98%, respectively, based on PIOPED II criteria; 86% and 93%, respectively, based on PISA-PED criteria; and 91% and 94%, respectively, based on offline fused Q-SPECT and CT. Offline Q-SPECT/CT yielded a significantly higher diagnostic accuracy than planar (Q) (p < 0.001) and SPECT (Q) (p < 0.001) scans.Conclusions: Offline Q-SPECT/CT scan has a higher accuracy than planar aerosol V/Q imaging based on PIOPED II criteria and relative better accuracy than PISA-PED criteria in patients with high risk for PE.

Keywords:

Pulmonary thromboembolism , Perfusion , SPECT/CT , Offline fusion