History
Sonomicrometry was originally applied in the study of cardiac function in research animals by Dean Franklin in 1956, and was quickly adopted by biologists working inMechanism
The primary criteria for making sonomicrometer measurements is that the intervening space or material between the crystals must be capable of ultrasonic sound conduction in the frequency range of 100 kHz to at least several MHz. This typically means that the crystals must operate in or on a medium composed of fluids, gels, soft solids and some hard solids, and this includes biological tissues (blood, muscle, fat, etc.). The measurement of distance between crystals becomes problematic or ceases completely if air gaps or solid objects intervene between the crystals. Sonomicrometer measurements are only accurate when the medium surrounding the crystals or the object the crystals are measuring has a uniform speed of sound. In biological settings, almost all tissues have a speed of sound in the range of 1550 to 1600 meters per second, which is satisfactorily uniform to give accurate measurements to within 3% to 4%, and more typically to within 1%. A sonomicrometer device measures distance by performing a timing measurement of the sound transmitted by one crystal and received by one (or more) adjacent crystals. The ability to resolve small differences in this transit-time (or "time-of-flight") directly correlates with the ability to resolve small changes in the distances between crystals. The first generation of sonomicrometer devices were analog devices that integrated the time-of-flight as a voltage ramp function. Their resolution was a function of the slope of the ramp and the electrical noise of system components. Those systems output the length measurements as an analog voltage. The second generation of sonomicrometer devices were digital—they measure time-of-flight by incrementing high-speed digital counters. Typically these are 12 to 16-bit counters operating from 32 to 128 MHz. A digital system will output length measurements in form of a digital number (the time-of-flight count value). Because of their digital nature, the resolution can be exactly specified as a function of counter clock frequency. For example, when making measurements in biological tissue at body temperature (velocity = 1,590 m/s), a digital sonomicrometer operating with a clock speed of 128 MHz will have a spatial resolution of 12 micrometres.Applications
Sonomicrometry is often used in studies of animal physiology where precise distances at high temporal resolution are needed, particularly when such distances are not externally measurable. Sonomicrometry crystals are most commonly implanted within skeletal or cardiac muscle tissue to track length changes during an activity (heartbeat, flapping a wing, chewing, etc.). However, they can be very useful for tracking movement of entire structures which are not visible but immersed in fluid, such as the bones in the mouth of a fish during feeding.References
*{{cite journal , last1=Sarazan , first1=R. Dustan , last2=Schweitz , first2=Karl T. R. , year=2009 , title=Standing on the shoulders of giants: Dean Franklin and his remarkable contributions to physiological measurements in animals , journal= Adv Physiol Educ , volume=33 , issue=3 , pages=144–156 , doi=10.1152/advan.90208.2008 , pmid=19745039 , s2cid=15287605 Metrology