A brief history of the development of transcranial tissue Doppler ultrasound

Abstract

This article documents the early development of the first transcranial Doppler (TCD)-based ultrasound system for continuous monitoring of brain tissue pulsations (BTPs). Transcranial tissue Doppler (TCTD) uses a lightweight, wearable single-element ultrasound probe to track tissue motion perpendicular to the skin's surface, providing tissue displacement estimates along a single beam line. Feasibility tests using an adapted TCD system confirmed that brain tissue motion data can be obtained from existing TCD hardware. Brain Tissue Velocimetry (Brain TV), a TCTD data acquisition system, was then developed to provide a lightweight and portable means of continuously recording TCTD data in real-time. Brain TV measurements are synchronized to a 3-lead electrocardiogram and can be recorded alongside other physiological measurements, such as blood pressure, heart rate and end-tidal carbon dioxide. We have shown that Brain TV is able to record BTPs from sample depths ranging from 22 to 80 mm below the probe's surface and from multiple positions on the head. Studies in healthy volunteers, stroke patients and ultrasound phantom brain models demonstrate how TCTD might provide insights into the relationships between physiological measurements and brain tissue motion and show promise for rapid clinical assessment and continuous monitoring of BTPs.

Keywords: brain tissue pulsation amplitude; brain tissue pulsations; transcranial doppler; transcranial tissue doppler; ultrasound.

Figure 1.

The Brain TV control unit. This captures brain tissue pulsation (BTP) recordings from two transducers and other physiological measurement data, including blood pressure (BP) and heart rate (HR), which are provided as inputs from an external device (e.g. Nihon Kohden Life Scope monitor, an OLG−3800 carbon dioxide monitor [Nihon Kohden, Japan], and a Finometer [Finapres Medical Systems B.V., Enschede, The Netherland]).

Figure 2.

The Brain tissue velocimetry (Brain TV) user interface with labelled controls.

Figure 3.

The Brain tissue velocimetry (Brain TV) data analysis graphical user interface (GUI). (a) saved Brain TV recordings, (b) recording file in use, (c) brain tissue pulsation (BTP) signals displayed to the user as a waterfall plot, (d) waveform data for end-tidal carbon dioxide (EtCO₂) and (e) the save data button.

Figure 4.

A schematic diagram to show the typical Brain tissue velocimetry (Brain TV) experimental setup. Participants may be seated (as shown) or lying supine or semi-supine (not shown).

Figure 5.

A Brain tissue velocimetry (Brain TV) recording is displayed in MATLAB; a waterfall plot is produced where the signal from adjacent depths is offset by 20 µm. Horizontal lines correspond to the depths in the brain from below the probe’s surface. Depth 1 is displayed as ~22 mm below the probe’s surface at the top (yellow) and depth 20 displayed as ~60 mm (blue). Vertical lines indicate the R-R interval for each cardiac cycle and are numbered at the top of the waterfall plot. A depiction of time-to-primary-peak (TtPP) and brain tissue pulsation (BTP) amplitude are given across the cardiac cycle.