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Non-Invasive Technique Developed to Measure Brain Pressure

CT scan of the brain six days after acute stroke. (INR)

(Institute for Neurological Research)

Researchers at Massachusetts Institute of Technology, with colleagues in the U.S. and the U.K., have devised a non-invasive technique to measure intercranial pressure that builds up in cases of head trauma and brain tumors. Their findings are described in this week’s issue of the journal Science Translational Medicine (paid subscription required).

When head trauma or some brain tumors occur, pressure often builds up in the brain that can damage brain tissue or cut off blood supply to the brain. Monitoring pressure in the brain in these circumstances can help doctors determine the best treatment, but current procedures require drilling a hole through the skull, and as a result, it is done only in the most severely injured patients.

Researchers in MIT’s Research Laboratory of Electronics have developed a new technique based on a computer model of the way blood flows through the brain. The model lets researchers calculate brain pressure from the arterial blood pressure and an ultrasound measurement of the velocity of blood flow through the brain. Not only can these measurements be taken more easily and less invasively, they allow brain pressure to be measured over time, which can alert doctors of problems that emerge more slowly.

Faisal Kashif, a postdoctoral fellow in electrical engineering at MIT and first author of the paper, developed the computer model as part of his Ph.D. dissertation. The model relates arterial blood pressure and blood flow through the brain to pressure in the brain. This intercranial pressure — defined as difference in pressure between the blood entering the brain and pressure inside the brain — can be calculated from the flow and the pressure of blood entering the brain. The pressure of blood entering the brain is not directly measurable, so the MIT technique measures radial arterial pressure as a proxy, and adjusts the model to compensate for the difference in location.

Kashif and colleagues verified the accuracy of their technique using data collected several years ago by collaborator and co-author Marek Czosnyka at Cambridge University in the U.K., from 37 patients with traumatic brain injury. Czosnyka’s 35 hours of data include time-stamped measurements of radial arterial blood pressure and ultrasound blood flow velocity. The MIT team ran Czosnyka’s data through the model, which Czosnyka then compared to the invasive procedures.

The comparisons show the MIT results were somewhat less accurate than those obtained with the best invasive procedures, but comparable to other invasive procedures that are still in clinical use, and to some less invasive techniques that have been tried.

The next steps involve incorporating the technology into systems that are feasible for hospital staff to administer to patients and record over time. For example, peripheral arterial pressure that Kashif measured with a catheter can also be measured continuously and noninvasively by using a finger cuff like the arm cuff commonly used to measure blood pressure. The researchers are now investigating whether data obtained this way is accurate enough to use in their model. Vera Novak of Beth Israel Deaconess Medical Center in Boston, a co-author of the paper, is also now collaborating with doctors at the hospital to test this approach on patients in the neurosurgical intensive care unit.

Thomas Heldt, an MIT lab colleague and senior author of the paper, says that once the data collection and model are well-established, the team hopes to test different patient populations — such as athletes with concussions, or soldiers who have experienced explosions — to come up with ways to determine the extent of injury and determine if an athlete or soldier can return to the field.

Lab director and study co-author George Verghese cautions that this validation step is critical. “To convince people that this works, you need to build up more [data] than we currently have,” says Verghese. “Our hope is that once it’s been validated on additional sorts of patients, where you’re able to show that you can match what the invasive measurement is people will have confidence in starting to apply it to patients who are currently not getting monitored.”

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