Science

Ultrasound imaging is now routinely used in a variety of clinical settings, including obstetrics and gynecology, cardiology, urology and cancer detection. There is also a growing use for ultrasound as a rapid imaging technique for diagnosis in emergency rooms. The main advantage of ultrasound is that structures inside the body can be observed without using ionizing radiation. Ultrasound can also be done much faster than x-rays or other radiographic techniques providing images in real-time. It is a non-invasive technique requiring no needles or injections. Furthermore, for standard diagnostic ultrasound imaging, there are no harmful effects on humans.

Ultrasound imaging works by using high frequency sound waves and their echoes to obtain images inside the human body. A transducer probe is used to generate the sound pulses and transmit them into the body. The sound waves travel into the body and are strongly reflected at interfaces between different types of tissue such as fat and muscle, or muscle and bone. At each interface a fraction of the sound wave is reflected and the rest transmitted through the interface to penetrate further into the tissue. This process occurs at each interface and by recording the reflected sound wave echoes an image can be produced. The recorded signal is converted to tissue thickness by measuring the time it takes the signal to reach the interface and multiplying the time by the sound speed through tissue (for fat sound speed is approximately 1400 m/sec, for muscle it is 1600 m/sec). In typical two dimensional ultrasound imaging, millions of sound pulses and echoes are sent and received each second to build the image.

The BodyMetrix™ devices use the same technology to collect information about the tissue structure along one ray (one-dimensional imaging). When the BodyMetrix™ device is applied to the skin inaudible, high frequency sound waves are directed into the body. To overcome reflections of the sound waves at the air layer between the skin and the transducer probe, a water based gel is applied onto the probe before contacting the skin. The reflected sound wave echoes are received by the transducer probe and produce a signal such as the one shown here for the measurement on a male thigh. By analyzing the recorded signal, the distance from the probe to the various tissue interfaces can be calculated and this information can be used to determine body composition.

For example, the BodyMetrix measurement shown here indicates the fat-muscle interface is seen at position 7.1 mm, the Muscle bone interface is at position 28 mm. Bone has a very high reflectivity for ultrasound and it is impossible to image beyond this boundary. The additional peaks observed in the signal are caused by other interfaces within the tissue. In many cases the muscle region comprises of multiple muscles which can cause a sequence of peaks to appear. Similarly fat can include fibrous tissue that can also produce secondary peaks.