Theformationoffreeradicals（?）OHand（?）Hinanaturallyair-saturatedaqueoussolutionexposedtotherapeuticCWultrasoundatafrequencyof820kHzhasbeenconfirmedbyusingspintrapping5,5-dimethyl-1-pyrroline-1-oxide（DMPO）andelectronspinresonance（ESR）technique.Itissuggestedthattheseradicalsareformedduetothehightemperatureandpressureproducedbytheultrasonictransientcavitation.Thetransientcavitationthresholdisfoundat0.537-0.632W/cm2underasonicationtimeof3minutes.Withincreasingsoundintensitytheyieldoffreeradicals（?）OHraisesrapidlyattheintensityrangingfrom1—2W/cm2,andnolongerincreaseisobservedatabove3W/cm2.Thesoundintensity（I）dependenceoftheyieldof（?）OH（D）canbeapproximatelydescribedbyaregressionequation:D=8.1(I1/2-（Ic）1/2)1/2,whereIc=0.667W/cm2.UnderafixingsoundintensitytheyieldofOHincreasesmonotonouslywiththesonicationtime.
