A small-aperture, prototype ultrasonic imaging system, typical of the size necessary to be embedded in a catheter, was developed to evaluate the feasibility of intravascular ultrasonic imaging catheters (UICs). The evaluation included in vitro imaging of postmortem samples of human femoral and iliac arteries with the UIC prototype and a high-resolution magnetic resonance (MR) proton imager. Excellent correlations between results from the UIC images, MR images, and tissue specimens were demonstrated. Although the current prototype is too large to be useful in examination of smaller vessels such as coronary arteries, the signal-to-noise ratio and resolution obtained indicate that imaging with intravascular UICs is feasible and may have significant diagnostic value.