Hemorrhage in murine fetuses exposed to pulsed ultrasound

In the late-gestation fetal mouse, exposure to piezoelectric lithotripter f ields at amplitudes < 1 MPa produced hemorrhages in tissues near developing bone, such as the head and limbs. This study was undertaken to determine i f exposure to pulsed ultrasound at diagnostic frequencies produces similar hemorrhages in the late-gestation fetal mouse. On the 18th day of gestation , fetal mice were exposed in utero to pulsed ultrasound with a 10-mu s puls e duration and 100-Hz pulse repetition frequency for a total exposure durat ion of 3 min. Hemorrhages occurred most often to the developing fetal head. At 1.2 MHz, a threshold for hemorrhage to the fetal head was determined at positive exposure pressures of similar to 4 MPa and corresponding negative pressures of similar to 2.5 MPa. The threshold increased with at least the first power of frequency. (C) 1999 World Federation for Ultrasound in Medi cine & Biology.