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Transcranial Doppler (TCD)

Clinical Focus

Taking into account the facts that

  • embolism - particularly solid - into brain circulation is responsible for approximately 85% of the strokes and observed neurological complications in surgery and stenting procedures,

  • TCD is the sole technique permitting the depiction of emboli in the main brain arteries,

it is logical to base new neuroprotection strategies on the detection of emboli during procedures via TCD.
The ABMI products line is fully based on the transcranial Doppler (TCD) technology, to which we have added powerful software and expert systems in order to perform signal processing and provide the medical practitioners with the real-time information about the patient's condition.

TCD is a standard non-invasive ultrasound method to measure intracranial blood flow and embolization of the brain. TCD is a form of ultrasound in which high frequency sound waves bounce off or pass through body tissues. While most other types of ultrasonography create images of the tissue being studied, the results of TCD are audible sounds that the examiner can listen to, record, and analyze. At present, TCD analysis is performed by the clinician's ear - ABMI proposes automated analysis software and expert systems that advantageously replace such uncertain and variable human ear analysis.

TCD procedures are safe, non-invasive, and painless. TCD uses what is called the Doppler effect to measure the rate and direction of blood flow inside vessels. Just as a siren's pitch sounds higher when the siren moves toward us and lower as it moves away, ultrasound waves will change pitch, or frequency, as they bounce off the red blood cells moving with the blood flow. It is these pitch changes that produce audible sounds during the TCD exam.

TCD is carried-out using either one or two probes placed in contact with the skin. The examiner spreads a clear gel on the areas of the head where a probe will be placed. Usually, the probes are placed on the temples, on the basis of the skull at the back of the neck, or over closed eyelids. These locations offer the least amount of thick, protective bone, permitting sound waves to penetrate more readily. The examiner adjusts the probe position and orientation to direct the sound waves toward the blood vessels of interest.
A full TCD exam may last 30 minutes to 1 hours, and often longer in patients with disease. TCD is also often used during operations (mostly heart related operations) to monitor the anesthetized patient's cerebral blood vessels. Existing technology allows emboli detection with no (or little) processing of embolic signals and data analysis, and interpretation is done manually.

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