Advantages of Autonomous TCD

What Is TCD?

TCD is a noninvasive and painless ultrasound method that uses sound waves to evaluate blood flow in and around the brain. There is no special contrast or radiation involved in the test. During the TCD exam, high frequency sound waves are transmitted through the tissues of the skull. These sound waves reflect off blood cells moving within the blood vessels, allowing the TCD system to measure the rate and direction of blood flow in the main cerebral arteries known as the Circle of Willis. While most forms of ultrasonography deliver images of the tissue studied, TCD delivers audible sounds that can be heard, recorded, and examined.

Why Is TCD Used?

Physicians recommend this highly accurate and sensitive test for patients with stroke or stroke-like symptoms. It is used to diagnose of a wide range of conditions affecting blood flow to, and within, the brain.

91% sensitive1 in detecting vasospasm after SAH

Detection and evaluation of cerebral vasospasm after spontaneous or traumatic subarachnoid hemorrhage.

Intraoperative monitoring

Intraoperative and perioperative monitoring of intracranial flow velocity and hemodynamic patterns during carotid endarterectomy, carotid stenting, or other high-risk surgeries.

Real-time emboli detection

Detection of free-floating particles in the bloodstream, known as emboli, which are a significant source of stroke risk.

Vasomotor reactivity

Assessment of vasomotor reactivity to determine if the small vessels that regulate blood flow to the brain are working properly.

96% sensitive2 in detecting vascular shunting

Assessment of right to left shunting through a bubble study.

Benefits Of TCD

There are five CPT codes covering TCD testing

Why Isn’t TCD More Broadly Used?

Similar to other ultrasound-based tests, TCD uses sound waves to evaluate structures inside the body, in this case the blood flow in the brain.  However, the brain is protected by the skull and ultrasound waves cannot easily pass-through bone.  TCD testing requires the operator to be able to find the transtemporal window (thin part of the bone in the skull) that will allow the ultrasound waves to penetrate the skull and find the blood vessels that need to be evaluated. Finding this window is one of the most difficult parts of the exam. It is unique to this form of ultrasound, resulting in a high learning curve compared to other ultrasound tests.

<5% of U.S. ultrasound personnel are trained to do TCD exams3

Because of the lack of TCD-trained healthcare professionals, many hospitals are not able to provide TCD testing for their patients.

The NovaSignal Platform Makes Complex TCD Assessments Easy to Perform

The NovaGuide Intelligent Ultrasound is an FDA cleared, AI-driven, robotic TCD system. Any healthcare practitioner can be taught how to set up the system and perform the exam. Offering secure, cloud-based access to exam data, NovaGuide View allows clinical specialists to view exam images and videos, add interpretations, and complete reports.

How Does NovaGuide Work?

The NovaGuide system autonomously finds the temporal window. Once the transtemporal window is identified, an algorithm finds and locks onto the strongest cerebral blood flow signal. The algorithm was designed to mimic the search of a TCD sonographer, but responds to real-time data rather than being a fixed search pattern. The signal acquisition time and signal accuracy of NovaGuide has been shown to be comparable to an expert TCD sonographer.4

Autonomous temporal window discovery and signal optimization

This can only be done with a 5 degree of freedom (DOF) system. Semi-automated solutions cannot perform this mapping.

Through thousands of cases and with the world’s largest cerebral blood flow data set, NovaSignal has been able to map the temporal bone for locations of signal acquisition.

Want to Learn More About Autonomous TCD? 

Download Increasing Exam Accuracy and Efficiency through AI-Driven, Robotic TCD Ultrasound to discover how the autonomous, robotic NovaGuide Intelligent Ultrasound broadens access to TCD for hospitals with no expertise, while also increasing exam accuracy and efficiency.



  1. Kumar G, Shahripour RB, Harrigan MR. Vasospasm on transcranial Doppler is predictive of delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage: A systematic review and meta-analysis. J Neurosurg. 2016;124(5):1257-1264. doi:10.3171/2015.4.JNS15428
  2. Katsanos, A. H., Psaltopoulou, T., Sergentanis, T. N., Frogoudaki, A., Vrettou, A., Ikonomidis, I., … Alexandrov, A. V. (2016). Transcranial Doppler versus Transthoracic Echocardiography for the Detection of Patent Foramen Ovale in Patients with Cryptogenic Cerebral Ischemia: A Systematic Review and Diagnostic Test Accuracy Meta-analysis. 625–635.
  3. Internal analysis based on industry data.
  4. O’Brien M, Ranjbaran M, Nie Z, Scheidt M, Radhakrishnan S, Hamilton R. Fully Automated, Robotic Controlled Transcranial Doppler Ultrasound (TCD) Middle Cerebral Artery (MCA) Insonation. In: 24th Meeting of the European Society of Neurosonology and Cerebral Hemodynamics. Linz, Austria; 2019.
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