TRANSCRANIAL DOPPLER DEPTHS SIMULATOR

Thus, no one expects that the microemboli signals extend to the areas outside the signals of the arteries (Figures 6 and 7).

The other issue that can help in the differentiation of microemboli signals from artifacts is that microemboli are limited to the borders of the arteries. Listen carefully to these audios and try to differentiate the microembolus from artifact just by their sounds. This sound can be quite obvious with large microemboli, but can be much more subtle with smaller emboli.įurther, a microembolus produces a very soft sound but the sound of artifacts is coarse and much louder. Listen carefully and try to familiarize your ears with the chirping sound it causes. This reflects the movement of the emboli in relation to the Doppler probe over time. When M-mode recording is available, passage of the microemboli from deep to shallow depths (as the emboli moves distally through the vessel) may appear as a linear slightly slanted streak across multiple depths and produces diagonal signal in M-mode. This appears visually as a vertical linear bright signal within the Doppler spectrogram, and is often referred to as a high-intensity transient signal (HITS). When a microembolus passes through the insonated artery, a sharp “chirp” like sound is heard as the ultrasound energy reflects off the embolic material.

įor successful detection of microemboli signals, both spectral waveform and M-mode should be closely examined. Cavitation, which refers to the formation of bubbles from gas dissolved in the blood, is though to be responsible for development of gaseous microemboli. In contrast, in patients with mechanical prosthetic cardiac valves, gaseous microemboli are more common. Particles of thrombus and atheroma originating from vascular or cardiac sources are examples of solid emboli and generally considered as the main cause of cerebral ischemic events. According to their composition, emboli can be divided into two main subtypes i.e. Cerebral microemboli can be detected in various medical conditions such as atherosclerotic carotid disease, cardiovascular diseases, and cardiovascular invasive interventions and surgeries. Herein, we want to briefly explain different types of microemboli with special focus on their clinical significance. TCD is a promising tool for detection of microemboli and can be used in clinical practice to guide additional diagnostic and therapeutic decisions. High intensity transient signals in TCD either reflect gaseous or solid microemboli, or artifact. Now let’s watch some normal TCD recordings. Can you take a guess at which arteries these are? Characteristics of the vessels, such as depth, direction of flow and mean velocity can help you identify specific vessels. In the video following, the examiner is insonating through the temporal widnow and changes the depth of interest from the shallowest levels to the deepest possible levels, passing over at least 4 different vessels. Typically, therefore, a vessel which appears red in M-mode will have velocity values plotted above the baseline X-axis and a vessel which appears blue will be plotted under the X-axis. Blood flowing toward the TCD probe will have a positive velocity, and blood flowing away from the probe will have a negative velocity (this can be toggled back and forth on most TCD machines, however). The Y axis displays blood flow velocity over the specific depth of interest. Similar to M-mode, in the spectral plot X axis denotes the function of time. Here’s an example of an M-mode image (Figure 1): For color flow Doppler, red indicates blood flowing towards the probe and blue blood flowing away from the probe. In M-mode, the X axis denotes the function of time and the Y axis refers to the depth at which a signal is insonated. Most modern TCD devices will display two main types of visual information – 1) M-mode, which shows the depths at which a Doppler signal is present, and 2) the spectral plot, or waveform, which displays blood flow velocity at a single particular location. To begin, it may be useful to review the screen output of a typical TCD device.

TRANSCRANIAL DOPPLER DEPTHS SIMULATOR

If you are unfamiliar with TCD, a TCD simulator teaching tool developed by one of the originators of TCD technology is available online and may be useful ( ). This training module is designed to introduce the basic concepts involved in detection of microemboli using Transcranial Doppler (TCD). NIH StrokeNet Fellow – University of Pennsylvania

Transcranial doppler depths