ASA 125th Meeting Ottawa 1993 May

3aPA7. Use of continuous wave ultrasound for measurement of the dynamic response of soft tissue to facilitate diagnosis of disease.

Mardi C. Hastings

Lee E. Schroeder

Dept. of Mech. Eng., Ohio State Univ., 206 W. 18th Ave., Columbus, OH 43210

A noninvasive, noncontact ultrasonic system for measurement of amplitudes of vibration of soft tissue has been developed for operation in air. The measurement method, based on phase modulation of low power, continuous wave ultrasound, was originally developed by Rogers and Hastings [U.S. Patent No. 4,819,643 (11 April 1989)] to measure the frequency response of auditory organs in fish underwater. In this study, the technique was used to measure the response of corneas of enucleated bovine eye globes to acoustic excitation at audible frequencies in air. Data were recorded at different levels of intraocular pressure (IOP) which is routinely clinically measured to screen for glaucoma. A mathematical model for harmonic motion of the corneal shell was developed for correlation with empirical results. The stiffness and natural frequency of the thin corneal shell are functions of IOP; thus the data provide a noncontact measurement of this parameter. This ultrasonic measurement technique eliminates the problems associated with current contact tonometry methods which include maintaining sterility, abrading the corneal surface, and inherently altering the IOP. [Work supported by NSF Grant No. MSS 9058607.]