BROAD-BAND MEASUREMENTS OF THE ATTENUATION COEFFICIENT AND BACKSCATTER COEFFICIENT FOR SUSPENSIONS - A POTENTIAL CALIBRATION TOOL

Tissue characterization would be facilitated by improved methods of ca libration with which to make absolute measurements of the backscatter and attenuation of tissue or contrast agents, In this paper, the use o f polystyrene microspheres is examined as a potential broadband in vit ro calibration tool by employing an experimental system designed to ch aracterize ultrasonic contrast agents. The frequency-dependent attenua tion coefficient and backscatter coefficient were measured for a serie s of microsphere size distributions with a broadband ultrasound system using a custom-built specimen chamber and a novel suspension mixing t echnique. The measurements were used in a broadband reduction method t o yield the backscatter coefficient. The range of ka spanned in this s tudy is from ka = 0.5 to ka = 12. The broadband nature of the pulses p ermitted simultaneous measurement of different regimes of scattering o f the microspheres (specifically, the transition region from Rayleigh to short-wavelength asymptotic scattering). Experimental results were compared with corresponding theoretical predictions for the attenuatio n and backscatter of solid elastic spheres in liquid and yielded good quantitative agreement. Discussion of some possible applications of th is technique to the fields of tissue characterization and contrast is presented. (C) 1997 Acoustical Society of America.