Independent and incremental value of ventilation/perfusion PET/CT and CT pulmonary angiography for pulmonary embolism diagnosis: results of the PECAN pilot study

Purpose This pilot study assessed the independent and incremental value of 68 Ga-V/Q PET/CT as compared with CT pulmonary angiography (CTPA) for the management of cancer patients with suspected acute pulmonary embolism (PE). Methods All 24 cancer patients with suspected acute PE prospectively recruited underwent both 68 Ga-V/Q PET/CT and CTPA within 24 h. PET/CT was acquired after inhalation of Galligas prepared using a Technegas generator and administration of 68 Ga-macroaggregated albumin. Initially, PET/CT and CTPA scans were read independently with the reader blinded to the results of the other imaging study. CTPA and PET/CT were then coregistered and reviewed by consensus between a radiologist and nuclear medicine physician. The therapeutic management was established by the managing physician based on all available data. Results The diagnostic conclusion was concordantly negative in 18 patients (75%). Of the six discordant diagnoses on independent reading, combined interpretation of V/Q PET/CTPA enabled a consensus conclusion in two patients, excluding PE in one and confirming PE in the other, similar to the initial diagnostic conclusion of the V/Q PET/CT. Of the remaining four patients, three had a single subsegmental thrombus on CTPA but a negative V/Q PET/CT scan, and two of these did not receive long-term anticoagulation and did not have a venous thromboembolic event during a 3-year follow-up period. The third patient, along with a patient with a positive V/Q PET/CT scan but a negative CTPA scan, presented with acute complications preventing any conclusions with regard to the appropriateness of the V/Q PET/CT results in the management of PE. Overall, V/Q PET had an impact on management in four patients (17%). Conclusion In this pilot study, we demonstrated the feasibility and potential utility of V/Q PET/CT for the management of patients with suspected PE. V/Q PET/CT may be of particular relevance in patients with equivocal findings or isolated subsegmental findings on CTPA, adding further discriminatory information to allow important decision-making regarding the use or withholding of anticoagulation. Given the other advantages of V/Q PET/CT (reduced acquisition time, low radiation dose), and with the increasing availability of 68 Ga generators, PET/CT is a potential replacement for V/Q SPECT/CT imaging.