Agreement between SPECT V/Q scan and CT angiography in patients with high clinical suspicion of PE

Abstract

To track agreement between single positron emission computed tomography (SPECT) V/Q and CT angiography in patients with high clinical suspicion of pulmonary embolism (PE). If significant agreement occurs, a case could be made for more frequent use of chest radiography followed by SPECT V/Q scanning given its lower risk profile. Diagnosis of PE can be difficult. CT pulmonary angiography (CTA) is the preferred initial test, but may be indeterminate, is a significant source of ionizing radiation, and is contraindicated in renal insufficiency. SPECT ventilation/perfusion imaging (V/Q) is therefore preferred in certain patients. Two thousand nine hundred and twenty patients admitted to a tertiary care hospital in New York City were screened and 100 consecutive high-risk patients who required both CTA and V/Q for an initial indeterminate or negative imaging test despite a high pre-test probability were identified. The agreement between these tests was evaluated. There was no significant agreement between CTA and V/Q when positive, negative and indeterminate results were included (K=0.18, SE=0.09, p=0.051). However, in the presence of a positive finding on either test, there was substantial agreement between the two (K=0.62, SE=0.27, p=0.02). In 30 cases in which CTA was indeterminate, V/Q was diagnostic 93% of the time. In 12 cases in which V/Q was indeterminate, CTA was diagnostic 83% of the time and negative in 100% of those cases. In the presence of an indeterminate CTA in patients with high clinical suspicion of PE, SPECT V/Q often provides a diagnosis.