Techniques for the assessment of the imaging characteristics of intravascular ultrasound scanners

Methods of assessing the imaging characteristics of intravascular ultrasound systems are described and applied to an HP Sonos 3000 system imaging at 12, 20 and 30 MHz. The presence of geometrical image distortion associated with bending of the catheter was detected by imaging silk filaments positioned at 45 degrees around a circle. Distortion was clearly present indicating that it is likely to occur in clinical studies. Resolution measurements (-12 dB) were made from images of 30 microns Nylon. The axial resolution did not change with depth and was in the range 150-400 microns. The lateral resolution increased linearly with depth for all frequencies, with values in the range 0.9-1.7 mm at a depth of 5 mm. High frequency catheter transducers therefore generate ultrasound with beamshapes similar to those expected from the familiar performance of devices in the 2-10 MHz range. Penetration measurements were made with material known to be tissue equivalent at 3-7 MHz. The penetration depth varied from 4.5 to 14 mm depending on catheter and frequency. There is a need for the manufacture of tissue equivalent materials for use in the frequency range 20-30 MHz, and also for the design of phantoms based on these materials for the measurement of contrast-detail performance and penetration depth.