Intracoronary ultrasound imaging: intraobserver and interobserver variability of morphometric measurements.

Measurements of lumen and plaque dimensions by intracoronary ultrasound imaging are useful in assessing effects of intracoronary interventions and in quantifying plaque burden in transplant patients or during regression trials. However, these measurements are affected by inter- and intraobserver variability. In 87 patients, 120 intracoronary ultrasound images were obtained with a 4.3F, 30 MHz catheter. Morphometric measurements were performed two times by three independent observers using computerized planimetry. Intraobserver and interobserver agreement for qualitative parameters (presence of atherosclerotic plaque, calcified plaque, and residual nondiseased wall) was high (> 87%). For quantitative parameters measured directly in the images (lumen area, minimal and maximal lumen diameters, area within the internal elastic lamina, arc of calcium plaque) interobserver and intraobserver correlation between measurements was high (correlation coefficient r > 0.90) and differences between measurements were low (mean differences < 10%; SD < 20%). Measurement of the arc of nondiseased wall showed less interobserver correlation (r = 0.76 to 0.91), but percentages of difference between the measurements were low. Parameters derived from directly measured variables (plaque area, area stenosis, thickness, and eccentricity) showed slightly higher variability (correlations between measurements r = 0.78 to 0.91). SD for percentages of difference ranged between 20% and 30% (plaque area, area stenosis, and thickness) and systematic deviation between measurements (mean differences > 10%) occurred for plaque area. Thus most qualitative and quantitative measurements of lumen and plaque dimensions performed in intracoronary ultrasound images have low in intraobserver and interobserver variability; derived parameters may have slightly higher variability. Variability of morphometric measurements has to be considered, especially when serial ultrasound measurements are compared.