Dr. Zsolt Garami, medical director of the vascular ultrasound lab at Houston Methodist Hospital, puts it very straightforward: Transcranial Doppler (TCD) is one of the least understood, rarely utilized and potentially most valuable tools available for monitoring brain circulation.

THE PROBLEM

TCD was introduced by Aaslid in 1982. Thanks to the addition of power M-mode Doppler (PMD) in 2000, TCD can detect not only the presence of blood flow, but also its depth, direction and resistance (DDR), he explained.

"TCD provides great sensitivity in detecting foreign particles, known as emboli, as small as 40 microns in diameter present in the blood cell stream," he said. "As a noninvasive, safe and cost-effective method for evaluating cerebrovascular circulation, TCD is the 'stethoscope for the brain.'"

Emboli detected on TCD are referred to as HITS (high-intensity transient signals) and the TCD machine provides both a visual and auditory signal of their presence. Emboli traveling up the carotid system pass from deep in the brain, generating unique sound and images.

"Even with all its benefits, TCD is underutilized as it requires a trained sonographer to perform an exam," Garami noted. "In addition, interpretation of the captured signal is not taught in school, leaving only experienced physicians able to understand the value of the data provided by the detailed waveform images."

PROPOSAL

NovaSignal is a medical technology and data company that offers NovaGuide, a cerebrovascular monitoring system.

The company worked to attack TCD's primary shortcomings. The fully automated, robotic NovaGuide minimizes the need for a trained sonographer, and its AI algorithms assist with the reading of the captured waveforms.

"We have long waited for changes to come to Transcranial Doppler, and we are excited about the opportunity to see the technology continue to expand."

Dr. Zsolt Garami, Houston Methodist Hospital

"The robotic probe pods automatically identify the acoustic window in the temple that allows for the pulsed Doppler ultrasound to view blood flow in the brain," Garami explained. "This acoustic window varies from individual to individual, leading to variability in manual exams, even when performed by well-trained sonographers.

"NovaGuide eases that burden by automatically identifying the signal," he continued. "Furthermore, once the signal is acquired, NovaSignal has introduced novel AI algorithms to further aid in the interpretation of the cerebral blood flow velocity waveforms."

MEETING THE CHALLENGE

NovaGuide opens the opportunity for "green" medical staff, nurses without any TCD training or experience, to learn and use the robotic TCD system in just a few hours, Garami reported.

"With four billable clinical codes assigned to TCD, NovaGuide is economically suitable for big academic hospitals as well as small practices," he noted. "Specifically, for those centers with TCD experience, NovaGuide provides an automated solution to ease the clinical burden of longer exams. Additionally, if the site does not have the expertise required, NovaGuide provides access with just a few hours of training.

"TCD's sensitivity in detecting emboli presents an advantage for PFO tests where agitated air is deliberately injected into a systemic vein and shown passing into the cerebral circulation via the hole in the heart," he added. 

"Without the hole, the air would be filtered out by the lungs. We are currently conducting a research trial with NovaGuide to prove that this indirect diagnostic mode is the most sensitive test for PFO – and not as uncomfortable as swallowing a tube in sedation for the cardiac ultrasound."

At Houston Methodist Hospital, NovaGuide exports clinical reports to the PACS system for easy viewing and interpretation of the final reports.

RESULTS

There have been several clinical scenarios at the hospital where NovaGuide has provided concrete clinical evidence to help support the management of patients. A few specific examples revolve around the use within the operating theater for cardiac procedures.

"It has been well established that embolization occurs during a variety of cardiac procedures and the use of TCD can inform on how to change clinical practice to reduce these perioperative emboli and reduce stroke risk," Garami explained. 

"Multiple protection filters were developed to clean the blood flow from these materials. TCD helps to test these and, even early in development, to decide which could be more effective to use.

"I believe this technology has the ability to improve outcomes of those procedures, as it is the only tool able to provide real-time information about embolization during manipulation of the procedure," he continued. 

"In addition to emboli monitoring, we are currently using the system to assess and compare pre- and post-procedure cerebral hemodynamics to ensure the operation has accomplished the necessary clinical impact by restoring improved cerebral blood flow."

This can be done in real time at the bedside, before the patient is removed from the operating room.

"In addition to the operating room, the use of the NovaGuide has applications in the recovery room, intensive care unit and on the floor, as it provides bedside hemodynamic monitoring, a distinct advantage when compared to 'static' radiological images like CT, MRI, DSA, etc.," Garami said.

"Within these environments, TCD has many well-accepted clinical uses: vasospasm detection after intracranial bleeding, detecting large vessel occlusion in stroke/TIAs, detection of intracranial stenoses, PFO bubble test ... The list can be endless to utilize this technology."

ADVICE FOR OTHERS

TCD provides unique access to monitoring of cerebral hemodynamics in the large arteries of the brain and the ability to monitor emboli events. The technology is a noninvasive, safe and cost-effective method for evaluating cerebrovascular circulation, and complements existing "static" imaging, Garami advised.

"Unfortunately, the technology has been limited due to the difficulty in signal acquisition leading to some negative opinions by nonusers," he noted: "'I do not want to know about this emboli; it has no clinical manifestations,' or, 'The results are user-dependent and cannot be trusted.'

"The obvious retort is, 'Explain to me what kind of emboli do good when going up into the brain? Do you know what is going on in your brain?'

"We have long waited for changes to come to TCD, and we are excited about the opportunity to see the technology continue to expand," he concluded.

Twitter: @SiwickiHealthIT
Email the writer: bsiwicki@himss.org
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