TECHNIQUES FOR THE ASSESSMENT OF THE IMAGING CHARACTERISTICS OF INTRAVASCULAR ULTRASOUND SCANNERS

Methods of assessing the imaging characteristics of intravascular ultr asound systems are described and applied to an HP Sonos 3000 system im aging at 12, 20 and 30 MHz. The presence of geometrical image distorti on associated with bending of the catheter was detected by imaging sil k filaments positioned at 45 degrees around a circle. Distortion was c learly present indicating that it is likely to occur in clinical studi es. Resolution measurements (-12 dB) were made from images of 30 mu m Nylon. The axial resolution did not change with depth and was in the r ange 150-400 mu m. The lateral resolution increased linearly with dept h 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 ultras ound with beamshapes similar to those expected from the familiar perfo rmance of devices in the 2-10 MHz range. Penetration measurements were made with material known to be tissue equivalent at 3-7 MHz. The pene tration depth varied from 4.5 to 14 mm depending on catheter and frequ ency. There is a need for the manufacture of tissue equivalent materia ls for use in the frequency range 20-30 MHz, and also for the design o f phantoms based on these materials for the measurement of contrast-de tail performance and penetration depth.