Human fetal diagnostic ultrasound exposimetry system

Abstract

Significant improvements have been made to a unique human fetal diagnostic ultrasound exposimetry system which has been designed to measure acoustic pressure in situ with a 7-element linear array hydrophone during an obstetric ultrasound examination. The purpose of the exposimetry system is to develop a data base of fundamental ultrasound propagation properties for human tissue under in vivo conditions from which the ultrasound exposure, and possibly the ultrasound dose, can be estimated under normal clinical conditions. The basic system design allows for the obstetrician to record calibrated acoustic pressure waveforms in situ that have propagated through tissue layers under conditions in which both the diagnostic ultrasound transducer and the calibrated hydrophone are hand-held. The improvements have increased the reliability of the recorded acoustic pressure waveform and provided the new capability of recording the image from the diagnostic ultrasound system simultaneously with the acoustic pressure waveform. The RF acoustic pressure waveforms are digitized at 50 MHz and displayed on a monitor to provide direct visual feedback to the obstetrician. The recorded acoustic pressure waveform is based on a two-decision process. First, the pulse intensity integral (PII), a measure of energy in the pulse, is calculated for each acquired waveform and subsequent recorded waveforms must have a greater PII. Second, a correlation coefficient is calculated for each acquired waveform and must exceed a predetermined correlation coefficient to be recorded. At the same time an RF pressure waveform is acquired, the exposimetry system digitally records the image from the diagnostic ultrasound scanner. This image shows the location of the hydrophone and provides the basis for estimating the types and distances of tissue layers between the diagnostic ultrasound scanner and the hydrophone, thus providing a direct tie between the acoustic propagation path and the recorded calibrated waveform.