Arterial tissue characterization by intravascular ultrasound radio frequency signal analysis

Intravascular ultrasound imaging devices have been successfully used to provide anatomical information other than the arterial lumen contour. However, limited information is available regarding the quantitative capability of this technique in arterial tissue characterization. The purpose of this study was to investigate this aspect of intravascular ultrasound through an analysis of radio frequency echo signals.;The characteristics of the intravascular ultrasound device were determined empirically and compared to those of conventional ultrasound devices. Reflection measurements from an acrylic block revealed a high variance characteristic of small aperture phase-sensitive transducers. This variance could be partially overcome by either phase correction or spatial averaging. When a rough surface of the same reflector was interrogated, an order of magnitude increase in the variance was observed even after phase correction. This variance could only be attributed to the scattering characteristics of the surface profile. Thus, the mean and variance, along with the angular dependency, of the echo signal energy provided a means for tissue characterization.;A theoretical model of the arterial tissue consisting of both deterministic and random structures was proposed. Ultrasonic parameters were predicted based on statistical communication principles. The coherent and incoherent backscatter power from arterial specimens were analyzed and compared to theoretical predictions. Results demonstrated that atheromatous plaques composed primarily of fibrous tissue have a lower coherent backscatter power than other atheroma types. The performance of the incoherent backscatter power as a tissue characterization parameter was found to be unsatisfactory.;A technique for the high resolution deconvolution of echo signals was demonstrated using an autoregressive model of the tissue impulse response. The success of the autoregressive method was shown to depend on a favorable geometrical relationship between the transducer and the arterial wall. By comparing a number of impulse response functions obtained from the same tissue region, an estimation of the underlying structure can be obtained.;Quantitative tissue parameters can be superimposed as a parametric image on current two-dimensional vascular ultrasound images. The information obtained from these images will facilitate the determination of atheroma components and the selection and evaluation of interventional procedures.