Background: The optimal cutoff value of fractional flow reserve (FFR) derived from coronary computed tomography angiography (FFR CT ) remains unclear. Methods: The current study population consisted of 93 patients with 139 vessels, who had suspected coronary artery disease by computed tomography angiography and underwent invasive FFR. We evaluated diagnostic performance of FFR CT according to different FFR CT cutoff values and FFR CT ranges with invasive FFR ≤0.80 as the reference standard. Results: In per-vessel analysis, median invasive FFR was 0.85 (interquartile range, 0.75–0.90), and 57 out of 139 vessels (41%) showed hemodynamically significant stenosis (≤0.80). Median FFR CT was 0.77 (interquartile range, 0.66–0.84; mean difference [invasive FFR-FFR CT ], 0.06±0.11). Per-vessel accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were 73%, 95%, 59%, 61%, and 94% for the cutoff value of FFR CT ≤0.80, 81%, 86%, 78%, 73%, and 89% for FFR CT ≤0.75, and 83%, 74%, 89%, 82%, and 83% for FFR CT ≤0.70, respectively. Per-vessel accuracy across the different ranges of FFR CT ≤0.60, 0.61 to 0.70, 0.71 to 0.80, 0.81 to 0.90, and >0.90 with the cutoff value of FFR CT ≤0.80 were 95%, 74%, 32%, 93%, and 100%, respectively. Setting a gray zone of FFR CT 0.71 to 0.80 provided high positive predictive value (82%; n=42/51) in the range of FFR CT ≤0.70 and high negative predictive value (94%; n=48/51) in FFR CT >0.80. Conclusions: This study suggested that referral to invasive coronary angiography should be considered individually in the range of FFR CT 0.71 to 0.80, whereas dichotomous decision could be made in FFR CT ≤0.70 and >0.80. Future prospective studies evaluating clinical outcomes are needed to establish optimal FFR CT -based diagnostic algorithm.

Purpose: Flexible positron emission tomography (fxPET) employing a non-local means reconstruction algorithm, was designed to fit existing magnetic resonance imaging (MRI) systems. We aimed to compare the qualitative and quantitative performance of fxPET among fxPET with MR-based attenuation correction (MRAC), fxPET with CT-based attenuation correction (CTAC) using CT as a part of WB PET/CT, and whole-body (WB) PET/CT. Procedures: Sixteen patients with suspected head and neck cancer underwent 2-deoxy-2-[ 18 F]fluoro-D-glucose WB PET/CT scans, followed by fxPET and 3T MRI scans. Phantom data were compared among the three datasets. For registration accuracy, we measured the distance between the center of the tumor determined by fxPET and that in MRI. We compared image quality, detection rates and quantitative values including maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG) and tumor-to-muscle ratio (TMR) among the three datasets. A Self-archived copy in Kyoto University Research Information Repository https://repository.kulib.kyoto-u.ac.jp Results:The phantom data in fxPET, except the percent contrast recoveries of 17-mm and 22-mm hot spheres, were inferior to those in WB PET/CT. The mean registration accuracy was 4.4 mm between fxPET using MRAC and MRI. The image quality was comparable between two fxPET datasets, but significantly inferior to WB PET/CT (p < 0.0001). In contrast, detection rates were comparable among the three datasets.SUVmax was significantly higher, and MTV and TLG were significantly lower in the two fxPET datasets compared with the WB PET/CT dataset (p < 0.005). There were no significant differences in SUVmax, MTV and TLG between the two fxPET datasets, or in TMR among the three datasets. All quantitative values had significantly positive correlations.Conclusions: Compared with WB PET/CT, the phantom data and image quality were inferior in fxPET. However, the results of the detection rates and quantitative values suggested the clinical feasibility of fxPET.