High frequency ultrasound vascular tissue characterization

A 50-MHz ultrasound backscatter microscope was designed to measure the backscatter of artery samples and the attenuation of artery samples and blood at high frequencies. Large differences in scattering were found between measurements made in the direction along the axis of the artery (axial) and radially out from the center of the artery (radial). Scattering (at 50 MHz) in the media of carotid arteries increased from 0.003 (Steradian (Sr)-mm)^-1 (axial) to 0.4 (Sr-mm)^-1 (radial). Scattering was found to be higher in elastic arteries (carotid) than in the muscular arteries (femoral). In the media, the average scatter (radial direction, 50 MHz) varied from 0.002 (Sr-mm)^-1 in muscular arteries to 0.4 (Sr-mm)^-1 in elastic arteries. The average attenuation in the artery wall increased from 4 dB/mm at 30 MHz to 10 dB/mm at 60 MHz. In blood, attenuation increased from 1.6 dB/mm to 5 dB/mm over the same frequency range. The relevance of these results to clinical imaging is discussed