| 摘要 |
PURPOSE:To surpass the restriction due to the relatrion between the measured maximum blood flow speed and depth and measure the Doppler frequency beyond the range of the Nyquist frequency by applying the second aliasing countermeasure. CONSTITUTION:The phase of the reflected wave signal obtained from a Doppler unit 70 in sequence is detected to obtain the phase vector consisting of an actual section and a virtual section, it is converted into digital by an A/D board via an operation amplifier 80 and executed by an MTI filter and speed arithmetic processing in a signal processing section constituted of a DSP board 100 and a computer 110. The phase of the reflected wave from a moving object obtained in sequence every time transmission is repeated is detected to obtain the phase vector, the phase difference vector is obtained from the difference of the phase difference vectors between the present packet and the next packet, the phase difference vector indicating the phase difference average value for each of the preset number of packets is obtained, the phase difference vector of the difference is obtained from the difference of the phase difference vector between the preset packet and the next packet, the angle DELTADELTAthetan of the phase difference of the difference is calculated, this is added to the phase difference obtained up to the present to determine the phase difference DELTAthetan+1 at the next time, and the blood flow speed is correctly detected beyond limitation. |
