Temperature corrected speed of sound for use in soft tissue imaging.
It has recently been suggested that values for the speed of sound in tissues currently reported in the literature are higher than those presently in use in diagnostic ultrasound. The purpose of this note is to indicate that the newer data under criticism was obtained at body temperature (and higher), whereas speed of sound in tissue data currently in use by medical physicists appear to be based on measurements made at room temperature. If a positive ultrasound temperature coefficient for soft tissue is used to extrapolate the data from body to room temperature, it can be seen that the extrapolation falls within the region of the bulk of room temperature measurements. Fortunately, most applications in which speed of sound data in tissue is used involves partial paths through lipidous tissue. Since the speed of sound in lipidous tissue is relatively lower at body temperature (liquid has a negative temperature coefficient) than is the speed of sound in soft tissue, the mean speed is lower than that obtained in soft tissue alone and room temperature values are probably justified. However, medical physicists should be careful to use body temperature data for soft tissue when the insonified region is composed mainly of soft tissue.