Comparison of 3 Diagnostic Strategies of PE: Planar V/Q Scan, CTPA, and V/Q SPECT.

Current diagnostic strategies rely on the sequential use of pretest clinical probability, Ddimer test, and chest imaging. Two chest imaging modalities have been validated for PE diagnostic exclusion: Computed Tomography Pulmonary Angiography (CTPA) and planar V/Q scan. Main limitations of planar V/Q are the high proportion of non-conclusive results, therefore requiring additional testing and more complex diagnostic algorithms. Main limitations of CTPA are its higher radiation dose and contraindications (renal failure).

In a randomized trial that compared strategies based on CTPA and on planar V/Q scan, a 30% increase in the rate of PE diagnoses was found in the arm using CTPA, raising the hypothesis of over-diagnosing and over-treating PE when using CTPA.

V/Q Single Photon Emission CT (SPECT) is a new method of scintigraphic acquisition that has been reported to improve the diagnostic performances of the test, which could reduce the number of non-conclusive tests and allow simplified diagnostic algorithms.

The investigators hypothesize that a strategy based on V/Q SPECT could be an alternative to the two usual approaches responding rightly to the two mains issues and combining the advantages of CTPA (simplified diagnostic approach) and planar V/Q (no overdiagnosis, lower radiation exposure, no contraindication).

Although a recent survey showed that up to 70% of nuclear medicine centers perform SPECT rather than planar imaging for diagnosing PE, a diagnostic management outcome study, in which diagnostic decision would be made on the basis of a standardized algorithm based on the V/Q SPECT is lacking. Such a study needs to be conducted to ensure that the safety of diagnostic exclusion using a V/Q SPECT based strategy is non-inferior to that of previously validated strategies, and to verify that the use of V/Q SPECT does not lead to over-diagnosis.