| Intravascular ultrasound (IVUS) has proven to be a valuable clinical tool for obtaining high-resolution images from within the coronary arteries. Unfortunately, the technique has proven inadequate for accurately discriminating tissue types. In order to progress towards reliable tissue characterization, a state-of-the-art radio frequency system has been designed and implemented to capture digitized ultrasound data.; Models, theory, and simulations were initially used to compare several methods for measuring the parameter of attenuation and to derive the Cramer-Rao lower bound which predicts the minimum standard deviation of the estimated attenuation for a region of interest. The minimum standard deviation is found to be a function of the number of independent samples acquired from a region of interest. The theoretical predictions were subsequently compared against a time domain slope method specifically developed to measure the attenuation of in vitro blood. Using both 30 MHz and 40 MHz catheters, the measured attenuations were 2.1 and 2.7 dB/mm, respectively, with standard deviations verified by the estimation theory.; As a clinical demonstration of the usefulness of these techniques, radio frequency data were acquired from normal host aorta and immunologically rejected allograft aorta from in vivo monkeys. While no differences were perceived in the intravascular ultrasound images, the attenuation differed significantly (p < 0.001) and was 4.02 +/- 1.16 and 2.64 +/- 1.28 dB/mm in the host and allograft aorta, respectively. These results suggest that this technique will have application in determining atherosclerotic plaque composition.; Development of accurate three-dimensional images from conventional two-dimensional IVUS remains a challenge because the vessel or catheter curvature must somehow be measured. A general fast Fourier transform method of measuring relative scatterer motion has been proposed as a means of measuring this vessel curvature. The effects of scatterer velocity and transducer angle have been explored using simulations, in vitro blood experiments, and in vitro tissue experiments. Finally, a catheter-based device that employs these methods, along with a transducer mounted such that its angle varies as a function of catheter curvature, has been proposed to measure the catheter curvature. |
