Stand-alone performance of a computer-assisted detection prototype for detection of acute pulmonary embolism: a multi-institutional comparison

Objective: To assess whether the performance of a computer-assisted detection (CAD) algorithm for acute pulmonary embolism (PE) differs in pulmonary CT angiographies acquired at various institutions. Methods: In this retrospective study, we included 40 consecutive scans with and 40 without PE from 3 institutions (n=240) using 64-slice scanners made by different manufacturers (General Electric; Philips; Siemens). CAD markers were classified as true or false positive (FP) using independent evaluation by two readers and consultation of a third chest radiologist in discordant cases. Image quality parameters were subjectively scored using 4/5-point scales. Image noise and vascular enhancement were measured. Statistical analysis was done to correlate image quality of the three institutions with CAD stand-alone performance. Results: Patient groups were comparable with respect to age (p=0.22), accompanying lung disease (p=0.12) and inpatient/outpatient ratio (p=0.67). The sensitivity was 100\% (34/34), 97\% (37/38) and 92\% (33/36), and the specificity was 18\% (8/44), 15\% (6/41) and 13\% (5/39). Neither significantly differed between the institutions (p=0.21 and p=0.820, respectively). The mean number of FP findings (4.5, 6.2 and 3.7) significantly varied (p=0.02 and p=0.03), but median numbers (2, 3 and 3) were comparable. Image quality parameters were significantly associated with the number of FP findings (p<0.05) but not with sensitivity. After correcting for noise and vascular enhancement, the number of FPs did not significantly differ between the three institutions (p=0.43). Conclusions: CAD stand-alone performance is independent of scanner type but strongly related to image quality and thus scanning protocols.