In vitro heating of human fetal vertebra by pulsed diagnostic ultrasound

The temperature rise generated at the surface of unperfused human fetal ver tebrae in vitro by an ultrasound beam with characteristics typical of those used in pulsed Doppler examinations has been measured. The bone samples we re from fetuses that ranged in age from 14 to 39 weeks, dating from the las t menstrual period. The samples were embedded in agar gel and the temperatu re rise at their surface was measured using a 50-mm diameter K-type thermoc ouple, The power in the ultrasound beam was 50 +/- 2 mW and the -6 dB diame ter was 2.9 mm, The temperature rise at 295 s ranged from 0.6 degrees C in the youngest sample to 1.8 degrees C in the oldest. Approximately 70% of th e temperature rise occurred in the first min. (C) 1999 World Federation for Ultrasound in Medicine & Biology.