N. Hemmati - Department of Medical Radiation Engineering, Tehran Polytechnic University, TEHRAN Research Center of Science and Technology in Medicine (RCSTIM)
M. DJ. Abolhassani - Department of Medical Engineering, Tehran University of Medical Science, TEHRAN Research Center of Science and Technology in Medicine (RCSTIM)
A. Baradarani - Department of Medical Radiation Engineering, Tehran Polytechnic University
A. Montazer - TEHRAN Research Center of Science and Technology in Medicine (RCSTIM)

Nowadays different equipment is used to measure bone mineral density. The physics of these systems are based on the interaction between x-ray or ultrasound beams with bone. Ultrasound has been used to measure bone characteristics such as speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness. In order to construct an ultrasonic bone densitometry system, although complex but more acceptable immersion method has been implemented. Two transducers one as transmitter and another as receiver are employed. Using an A/D converter the received signal is converted to digital data and transfer to a PC via serial port for signal post processing. To achieve the best accuracy and reduce calculation errors, data acquisition can be performed up to 100 times for each test. At each burst, time interval between pulse transmission and reception is measured and by using the time of flight (TOF) technique and having heel width, the average speed of sound in bone can be calculated. SOS is proportional to tissue density and elasticity. In normal bones, SOS is higher than in cancellous and osteoporotic bones. The amount of attenuation in transmitted ultrasound beam can be calculated from received signal spectrum. Using FFT computation of transmitted and received signal and calculation the received signal spectrum to transmitted signal spectrum ratio within band width of 200KHz to 600KHz, variation of BUA against frequency can be drawn. The slope of this curve is proportional to the bone density. Software for display and process the obtained data, and to present the computed parameters, is developed using appropriate algorithms. For osteoporosis diagnosis, these parameters are compared to the one taken from statistical samples of the Iranian society.

speed of sound, broadband attenuation, DFT algorithm, bone stiffness, TOF technique