Role of imaging end points in atherosclerosis trials: focus on intravascular ultrasound

A Dual-Mode Imaging Catheter for Intravascular Ultrasound Application

Both the morphological anatomy and functional parameters such as flow speed of the artery provide valuable information for the evaluation of cardiovascular diseases. Direct measurement of the arterial wall can be achieved by intravascular optical/ultrasound imaging methods, and however, no functional data are acquired with these methods. Fractional flow reserve and Doppler wire have been used to assess the blood flow information, but do not provide cross-sectional images of the artery. This paper is the first to design and fabricate a dual-mode imaging catheter that contains a forward-looking ultrasonic transducer and a side-looking ultrasonic transducer together in one catheter. This dual-mode catheter not only provides morphological information about the artery, but also a precise measurement of functional flow. The data indicate that the proposed catheter can be used to acquire multiple parameters of the artery with a one-time procedure. This novel one-catheter approach could be used for the functional diagnosis of atherosclerotic arteries.

Delineation of atherosclerotic plaque using subharmonic imaging filtering techniques and a commercial intravascular ultrasound system

The ability to delineate atherosclerotic plaque from the surrounding tissue using custom-developed subharmonic imaging (SHI) digital filtering techniques was investigated in vivo using a commercially available system. Atherosclerosis was induced in the aorta of two Watanabe Heritable Hyperlipidemic rabbits following which injections of an ultrasound contrast agent (UCA) Definity (Lantheus Medical Imaging, N Billerica, Massachusetts) were administered. Imaging was performed using a Galaxy intravascular ultrasound (IVUS) scanner (Boston Scientific, Natick, Massachusetts) equipped with an Atlantis® SR Pro Imaging Catheter (Boston Scientific). Four preliminary band-pass filters were designed to isolate the subharmonic signal (from surrounding tissue) and applied to the radio-frequency (RF) data. Preliminary filter performances were compared in terms of vessel-tissue contrast-to-tissue ratio (CTR) and visual examination. Based on preliminary results, a subharmonic adaptive filter and a stopband (SB) filter were designed and applied to the RF data. Images were classified as fundamental, SHI, and SB. Four readers performed qualitative analysis of 168 randomly selected images (across all three imaging modes). The images were scored for overall image quality, image noise, plaque visualization, and vessel lumen visualization. A Wilcoxon signed-rank test was used to compare the scores followed by intraclass correlation (ICC) evaluation. Quantitative analysis was performed by calculating the CTRs for the vessel-to-plaque and vessel-to-tissue (compared using a paired student's t test). Qualitative analysis showed SHI and SB to have significantly less image noise relative to the fundamental mode (p < 0.001). Fundamental mode scored significantly higher than SHI and SB for the remaining three categories. ICC showed mixed results among reader evaluation for delineation of plaque. However, quantitatively, SHI produced the best vessel-plaque CTR.