Impact of analyzing less image frames per segment for radiofrequency-based volumetric intravascular ultrasound measurements in mild-to-moderate coronary atherosclerosis

Abstract

Volumetric radiofrequency-based intravascular ultrasound (RF–IVUS) data of coronary segments are increasingly used as endpoints in serial trials of novel anti-atherosclerotic therapies. In a relatively time-consuming process, vessel and lumen contours are defined; these contours are first automatically detected, then visually checked, and finally (in most cases) manually edited to generate reliable volumetric data of vessel geometry and plaque composition. Reduction in number of cross-sectional images for volumetric analysis could save analysis time but may also increase measurement variability of volumetric data. To assess whether a 50% reduction in number of frames per segment (every second frame) alters the reproducibility of volumetric measurements, we performed repeated RF–IVUS analyses of 15 coronary segments with mild-to-moderate atherosclerosis (20.2 ± 0.2 mm-long segments with 46 ± 13% plaque burden). Volumes were calculated based on a total of 731 image frames. Reducing the number of cross-sectional image frames for volumetric measurements saved analysis time (38 ± 9 vs. 68 ± 17 min/segment; P < 0.0001) and resulted for only a few parameters in (borderline) significant but mild differences versus measurements based on all frames (fibrous volume, P < 0.05; necrotic-core volume, P = 0.07). Compared to the intra-observer variability, there was a mild increase in measurement variability for most geometrical and compositional volumetric RF–IVUS parameters. In RF–IVUS studies of mild-to-moderate coronary disease, analyzing less image frames saved analysis time, left most volumetric parameters greatly unaffected, and resulted in a no more than mild increase in measurement variability of volumetric data.

Impact of analyzing fewer image frames per segment during offline volumetric radiofrequency-based intravascular ultrasound measurements of target lesions prior to percutaneous coronary interventions

“…This may be partly explained by the fact that a mild absolute difference between repeatedly detected contours may affect volumetric data in larger plaques to a lower extent compared to the smaller plaques studied in our previous report [19]. In addition, the assessment of significant coronary lesions is inherently associated with a somewhat lower IVUS image quality because of reduced flow due to luminal obstruction by the IVUS catheter, more direct contact between IVUS catheter and plaque, and the presence of somewhat more calcium compared to segments with mild-to-moderate disease that may explain the higher intra-observer variability [(standard deviation of mean difference divided by mean measurement) × 100]: <22% in present study versus <7% in mild disease [19]. …”

“…Similar to other studies that assessed the reproducibility of (RF-)IVUS, we did not include very tortuous and severely calcified vessels that could have led to a non-uniform pullback speed and/or inability to reliably detect the external vessel contour [17, 19–21]. Accordingly, measurement reproducibility could be lower in unselected cases with extensive calcification or vessel tortuousity.…”

“…Accordingly, measurement reproducibility could be lower in unselected cases with extensive calcification or vessel tortuousity. The number of coronary segments and the segment length studied was limited, but similar to previous studies on IVUS reproducibility [4, 17, 19–21]. We did not address potential variability between IVUS catheters, pullbacks, different pullback speeds, or pullback devices because our study was focused on the assessment of reducing the number of image frames for volumetric RF-IVUS analyses.…”

“…The trapezium method is derived from the Simpson’s rule method, but takes the accurate distances between adjacent image frames into account [18, 19]. The pcVH software program uses this method to calculate volumes from the cross-sectional area data.…”

Clinical validation of a novel software for quantitative analysis of coronary intravascular ultrasound

“…The non-ECG-gated image acquisition limited the accuracy of automatic border detection due to systolic-diastolic image artifacts and the 'saw tooth' appearance of the IVUS pullback. Frame skipping presumably did not add to the decreased reproducibility, as it is known from radiofrequency IVUS that it is source to only minor increase in measurement variability [19]. Despite the shortcoming in analysis approach, there was reasonable agreement in volumetric measurements with ICC N 0.93.…”