Photon-Counting CT Iodine Maps for Diagnosing Chronic Pulmonary Thromboembolism : A Pilot Study

OBJECTIVES The aim of this study was to evaluate the feasibility and efficacy of chronic pulmonary thromboembolism assessment using photon-counting detector computed tomography (PCD-CT) iodine maps of the lung parenchyma. MATERIALS AND METHODS This institutional review board-approved retrospective study included 83 subjects (49.4% male, aged 62.4 ± 13.4 years; 50.6% female, aged 59.9 ± 17.1 years) who underwent clinically indicated PCD-CT scan to rule out chronic thromboembolic pulmonary hypertension (CTEPH). Two blinded readers used iodine maps and corresponding sharp-kernel CT reconstructions in the lung window to evaluate perfusion defects and identify patients with chronic pulmonary thromboembolism (CTEPH, CTEPH overlap with other causes of pulmonary hypertension [PH], chronic thromboembolic disease [CTED]). No other clinical or imaging information was given. Discordance was resolved in a subsequent consensus read. The clinical diagnosis was reviewed in an interdisciplinary clinical setting. The accuracy, sensitivity, and specificity of radiologic evaluation and clinical diagnosis were calculated. RESULTS Of the 83 subjects included, 32 were diagnosed with CTEPH, CTEPH overlap, or CTED, 35 were diagnosed with PH caused by other pathologic mechanisms, 10 had no PH, and 6 had suffered previous acute pulmonary embolism, which resolved. The interreader agreement was good (Cohen κ = 0.74). The consensus reached high accuracy (0.88), sensitivity (0.94), and specificity (0.84), as well as good agreement with interdisciplinary clinical diagnosis (Cohen κ = 0.75). No cases with confirmed CTEPH as the primary cause of PH or CTED were missed. Patients with pulmonary arterial hypertension were most frequently rated false-positive. The mean effective dose (±standard deviation) was 1.3 (±0.76) mSv. CONCLUSIONS Accurate, sensitive, and specific diagnosis of pulmonary chronic thromboembolism at low radiation dose is possible using iodine maps reconstructed from PCD-CT scans.