Perfusion SPECT in patients with suspected pulmonary embolism

Ventilation/perfusion tomography (V/PSPECT), with new interpretation criteria and newer tracers for ventilation imaging, has markedly improved the diagnostic yield in acute pulmonary embolism (PE). Here, we evaluated the diagnostic performance of perfusion SPECT (PSPECT) without ventilation imaging.

We studied 152 patients with clinically suspected PE who had been examined with both V/PSPECT and multidetector computed tomographic angiography (MD-CTA). The diagnosis or exclusion of PE was decided by the referring clinician based on both the V/PSPECT and/or MD-CTA findings in combination with the clinical findings. PSPECT images were retrospectively examined by a physician with experience in the interpretation of planar perfusion scans who was blinded to clinical, V/PSPECT and MD-CTA data. PSPECT images were interpreted without the aid of chest radiography. All the patients who were deemed to have PE were given anticoagulant therapy.

Of the 152 patients, 59 (39%) received a final diagnosis of PE, and 19 (32%) had associated cardiopulmonary diseases such as pneumonia, COPD, or left heart failure. PSPECT correctly identified 53 (90%) of the 59 patients with PE. The specificity was 88 of 93 (95%). None of the PSPECT images was rated nondiagnostic. PSPECT yielded an overall diagnostic accuracy of 93% (95% confidence interval, CI, 87-96%). At the observed PE prevalence of 39 %, the positive and negative predictive values of PSPECT were 91% (95% CI, 80-97%) and 94% (95% CI, 86-97%), respectively.

In managing critically ill patients, PSPECT might be a valid alternative to V/PSPECT or MD-CTA since it was able to identify most patients with PE with a low false-positive rate and no inconclusive results.