title: Measurement of the speed of sound in follicular fluid.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Medical Vision Laboratory, Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK. gooding@robots.ox.ac.uk
authors.forename: M J
authors.initials: MJ
authors.lastname: Gooding
authors.forename: D
authors.initials: D
authors.lastname: Barber
authors.forename: S H
authors.initials: SH
authors.lastname: Kennedy
authors.forename: J A
authors.initials: JA
authors.lastname: Noble
mesh_terms: D001707:Biopsy, Needle; D002138:Calibration; D005260:Female; D005307:Fertilization in Vitro; D015571:Follicular Fluid / Q000000981:diagnostic imaging*; D006801:Humans; D066298:In Vitro Techniques; D007247:Infertility, Female / Q000000981:diagnostic imaging*; D012016:Reference Values; D013696:Temperature; D014463:Ultrasonography / Q000379:methods / Q000592:standards*