Photon-Counting Detector CT Iodine Maps Versus SPECT/CT

Objectives The aim of this study was to compare the accuracy of photon-counting detector computed tomography (PCD-CT) iodine maps of the lung parenchyma with perfusion scintigraphy for detection and extent estimation of pulmonary perfusion defects. Materials and Methods This institutional review board–approved retrospective study included 26 subjects (11 male, aged 57.2 ± 15.8 years; 15 female, aged 55.2 ± 15.7 years) who underwent clinically indicated PCD-CT and perfusion SPECT/CT to assess for chronic thromboembolic pulmonary hypertension (CTEPH). Two blinded radiologists used CT iodine maps and corresponding sharp-kernel CT reconstructions in lung window to evaluate presence and extent of lobar perfusion defects and detect patients with CTEPH (or CTEPH overlap with other causes of PH). Accordingly, 2 blinded nuclear medicine physicians/radiologists evaluated perfusion SPECT/CT scans. The clinical diagnosis was reviewed in an interdisciplinary clinical setting. Quantitative analyses were calculated for both modalities. Perfusion defect estimation was compared with right heart catheter measurements. Results Of the 26 subjects included, 10 were diagnosed with CTEPH or CTEPH overlap, 12 were diagnosed with PH associated with other pathologic mechanisms, 3 had no PH, and 1 had previous acute pulmonary embolism, which resolved. Radiation dose was greatly reduced for PCD-CT compared with SPECT/CT (1.19 [±0.33] mSv; 6.34 [±1.68] mSv, respectively, P < 0.001). Both PCD-CT readers (R1, R2) showed a trend toward higher accuracy, sensitivity, and specificity for CTEPH diagnosis compared with the scintigraphy consensus (SC) (accuracy: R1 0.85, R2 0.88, SC 0.73; sensitivity: R1 0.90, R2 0.90, SC 0.80; specificity: R1 0.81, R2 0.88, SC 0.69), although there was no significant difference observed ( P > 0.688). There was good to excellent agreement between both PCD-CT readers for perfusion defect estimation. Moderate intermodality agreement was observed for CTEPH diagnosis certainty and perfusion defect estimation. The quantitative evaluation showed strong to excellent correlation between PCD-CT and SPECT/CT relative perfusion. There was a significant moderate correlation between PCD-CT perfusion defect estimations and mean pulmonary artery pressure (R1: r = 0.49, P = 0.020; R2: r = 0.49, P = 0.021), pulmonary vascular resistance (R1: r = 0.60, P = 0.003; R2: r = 0.52, P = 0.013), and cardiac index (R1: r = −0.45, P = 0.042). Conclusions PCD-CT iodine maps allow for accurate CTEPH detection and are comparable to perfusion SPECT/CT with good quantitative correlation, but only moderate qualitative agreement, at greatly reduced radiation dose. Furthermore, visual PCD-CT perfusion defect extent was associated with prognostic right heart catheter measurements.