超声血流流速描记器的临床应用 Ⅰ.定向式流速描记器的原理及液流测定的条件研究

CLINICAL APPLICATION OF THE ULTRASONIC BLOOD VELOCITY RECORDER I. PRINCIPLES OF THE DIRECTIONAL VELOCITY RECORDER AND STUDIES OF THE CONDITION NECESSARY TO MEASURE FLUID FLOW

基于运动物体对入射超声频率所产生的反射频率改变的多普勒效应原理,可测定血管搏动及血管内血流的大体情况,但不能定出血流的方向。为取出血流流速的准确数据及定出流速的方向(矢量),制成配套多普勒流速描记器。

The"back scattered"echo produced by the incident ultrasound on the praticles of the moving blood has been described.According to the"back scattered"effect,the blood flow produces a frequency shift between the incident and reflected ultrasound.Since the"back scattered"effect is a random phenomenon and the velocities of various blood particles in the vessel are different,the frequency shift△f is distributed in a narrow band of the frequency spectrum.The directional Doppler velocity recorder can offer two facilities:(1)It is often exactly and conveniently to show the value of frequency shift which is proportional to the blood velocity;(2)It can usually indicate the vector of the blood flow.The phase discriminator compares the phase of frequency output with the phase shift network and the received signal with the radio frequency amplifier.Phase preceded by the phase shift network causes the output from channel A;the output indicates the vector of blood flow towards the probe.Phase lagged behind the phase shift network causes the output from channel B;such an output often indicates the vector of blood flow away from the probe.These outputs from channels A and B through each zero-crossing detector and the cross-locking circuit,form the vector differentiation and give the velocity reading.Experimental studies of the necessary conditions for detecting fluid flow had been carried out.When the degased water passed through the polyethylene tube,no deflection of the velocity curve was noticed.On the other hand,when water containing talcum powder passed through the plastic tube,the velocity curve was recorded according.A velocity curve of a dog’s aortic arch flow could be observed clearly.The technical and theoretical errors of the machine were discussed.