Non-linear Matching Pursuits and its apllication in bone mineral measurement

Weakening of the bones because of the progressive loss of bone mass is a potentially serious side effect of extended space flight and it is a disease that cannot make complete recovery after landing. The measurement, prevention and treatment of bone loss are indispensable for long-term space flight. Quantitative ultrasound (QUS) measurement is the only densitometry technologies of bone mineral density (BMD) that is non-radioactive and can be used in space flights. Speed of Sound (SOS) is a significant parameter in ultrasonic BMD measurement. To get precise SOS value, the thickness of bone and the time that sound passes through must be accurate. Frequently used methods to gauge delays, such as maximum value point, zero-crossing detector, and threshold detector, are not so precise and can easily be disturbed by noise. This article analyses the composing of the receiving signals, and proposes a method to extract valid signals and calculate the time difference using Matching Pursuits algorithm. Besides, to eliminate the influence of saturation property widely encountered in ultrasound receiving circuits, a non-linear Matching Pursuits algorithm is introduced and trends to be effective.