Measurement of the speed of sound in follicular fluid.
Gooding MJ., Barber D., Kennedy SH., Noble JA.
BACKGROUND: Measurement of ovarian follicles by ultrasound is common practice in fertility treatment. However, the effect of the speed of sound is not taken into account. We present results from a study aimed at measuring this. METHODS: The speed of sound was measured in samples of follicular fluid aspirated from patients undergoing fertility treatment. The transmitted and received pulses from a single element ultrasound transducer were recorded using a digital oscilloscope for a pulse passed through a sample of the fluid. The distance over which the pulse travelled was known from calibration with pure water. Variation with temperature was investigated in the range 25-45 degrees C. Dependence on ultrasound frequency, patient and time from aspiration were also investigated. RESULTS: The speed of sound in follicular fluid was found to be 1550+/-3 m/s at 37.3 degrees C using 5.0 MHz ultrasound. The speed varied from 1528+/-3 m/s at 24.8 degrees C to 1561+/-3 m/s at 44.8 degrees C. Variation with patient, time and frequency were not detected. CONCLUSION: The speed of sound in follicular fluid at body temperature is 1550 m/s. This small difference from the speed assumed by the ultrasound machine corresponds to the systematic bias in volume measurement evident in previously published results.