LUNG DAMAGE ASSESSMENT FROM EXPOSURE TO PULSED-WAVE ULTRASOUND IN THERABBIT, MOUSE, AND PIG

The principal motivation of the study was to assess experimentally the question: ''Is the MI (Mechanical Index) an equivalent or better indi cator of nonthermal bioeffect risk than I-SPPA.3 (derated spatial peak , pulse average intensity)?''. To evaluate this question, the experime ntal design consisted of a reproducible biological effect in order to provide a quantitative assessment of the effect. The specific biologic al effect used was lung damage and the species chosen was the rabbit. This work was initiated, in part, by a study [1] in which lung hemorrh age was observed in 7-week old C3H mice for diagnostic-type, pulsed-wa ve ultrasound exposures, and, therefore, 6- to 7-week old C3H mice wer e used in this study as positive controls. Forty-seven adult New Zeala nd White male rabbits were exposed to a wide range of ultrasound ampli tude conditions at center frequencies of 3 and 6 MHz with all temporal exposure variables held constant. A calibrated, commercial diagnostic ultrasound system was used as the ultrasound source with output level s exceeding, in some cases, permissible FDA levels. The MI was shown t o be at least an equivalent, and in some cases, a better indicator of rabbit lung damage than either the I-SPPA.3 or p(r.3) (derated peak ra refactional pressure), thus answering the posed question positively. F urther, in situ exposure conditions were estimated at the lung pleural surface (PS); the estimated in situ I-SPPA.PS and p(r.PS) exposure co nditions tracked lung damage no better than I-SPPA.3 and p(r.3), respe ctively, whereas the estimated in situ MI(PS) exposure condition was a slightly poorer predictor of lung damage than MI. Finally, the lungs of six adult crossbred pigs were exposed at the highest amplitude expo sure levels permitted by the diagnostic ultrasound system (to prevent probe damage) at both frequencies; no lung damage was observed which s uggests the possibility of a species dependency biological effect.