A full digital design of TCD ultrasound system using normal pulse and coded excitation

Abstract

Transcranial Doppler (TCD) ultrasound is commonly used in some departments to detect blood flow and emboli in the cerebral artery at the forefront of medical technology. Conventional TCD systems expose more and more disadvantages such as inadequate depth information, low sensitivity and poor accuracy in clinical diagnosis. In this study, a full digital design of TCD ultrasound system is introduced, in which raw radiofrequency (RF) is directly converted to digital data with an A/D converter. All signal processors such as digital I/Q demodulator can be achieved by utilizing digital signal processing (DSP) techniques. This design can solve the problems above. In particular, it offers a full-depth intracranial examination, which can be used to locate tran- scranial windows conveniently so as to make TCD analysis much easier even for an inexperienced person. Furthermore, coded excitation is allowed. In our experimental system, RF signals are collected in vitro from a flow phantom using a TCD system, which alternately transmitted 8 wavelengths normal pulse and 4 wavelengths pulse coded by 7-chip Barker code. The in vitro results are promising. Qualitatively the blood flow is easier to track using the pulse compressed signal. It is both feasible and beneficial to implement the full digital design in a TCD system.