A wearable Transcranial Doppler ultrasound phased array system

Abstract

Transcranial Doppler (TCD) sonography is a specialized ultrasound technique that enables measurement of blood ow velocity from the basal intracerebral vessels. Use of TCD sonography is highly compelling as a diagnostic modality due to its safety in prolonged studies, high temporal resolution, and relative portability. Although TCD methods have been clinically indicated in a variety of cerebrovascular diagnostic applications, general acceptance by the medical community has been impeded by several critical deficiencies { including the need for a highly-trained TCD operator, operator dependent measurement results, and severe patient movement restrictions. This thesis seeks to mitigate such limitations through the development of a compact, wearable TCD ultrasound system, permitting untethered cerebrovascular monitoring with limited operator interaction. The prototype system incorporates a custom two-dimensional transducer array and multi-channel transceiver electronics, thereby facilitating acoustic focusing via phased array operation. Algorithmic vessel search and tracking further reduce operator dependencies by expediting vessel localization, systematizing vessel identification, and dynamically adapting to relative vessel position. Additionally, focal correction methods are presented, which improve acoustic beamformation capabilities in the presence of tissue inhomogeneities. Validation of the prototype hardware and embedded signal processing implementations under flow phantom and human subject testing yields high correlation with accepted velocimetry methods. Vessel search and tracking functionality are also verified experimentally. Circuit integration is explored to further reduce instrumentation dimensions and power consumption.