PS82. Measurement of Carotid Plaque Volume by 3D Ultrasound

As investigations into nonsurgical treatment for atherosclerosis expand, the measurement of plaque regression and progression has become an important end point to study. Carotid plaque progression does not occur in only one or two dimensions. Therefore measurements of plaque volume are more sensitive to change than are traditional estimates of stenosis severity or cross-sectional area. Three-dimensional (3D) ultrasound (US) may allow monitoring of plaque volume changes but has not been used routinely due to the cumbersome motorized units required to drive transducers. We investigated the reliability of plaque volume measurement by a novel freehand 3D US system that can be applied in a clinical environment. Ten patients with carotid stenosis underwent 3D US imaging using a linear transducer integrated with a magnetic position tracker. Plaque boundaries were outlined in serial cross-sectional images 1 mm apart. Plaque volumes were measured by 4 observers and repeated by them 4 weeks later. This allowed measurement of interobserver and intraobserver variability of six pairs of observations. We measured Bland-Altman statistics, intraclass correlation, coefficient of reliability, and the minimum detectable plaque volume change. The mean plaque volume of carotid lesions in the study was 1276.8 mm3 (range, 620.6-1956.3 mm3). Bland-Altman plots demonstrated low interobserver and intraobserver variability; variability of volume measurements as a function of mean volume was 10.8%. Reliability, quantified by the intraclass correlation coefficient was 85.5%. The least detectable change in plaque volume was 21.1% (range, 14.1%-27.6%). Carotid plaque volume can be measured accurately and reliably with this novel 3D ultrasound technique. The volumetric change that must be observed to establish with 95% confidence that a plaque has undergone growth or regression is ∼20%.