METHOD FOR MEASURING INTRACRANIAL PRESSURE
Increased pressure inside the brain - the result of severe head injury, bleeding, tumors or other neurological problems - can be fatal.
That's why measuring intracranial pressure is critical in such cases. And yet, the invasive methods typically used for measurement carry a risk.
Now, a noninvasive method that uses standard magnetic resonance imaging technology readily available in today's hospitals is being developed by Noam Alperin, associate professor of medical physics in the department of radiology at the University of Illinois at Chicago College of Medicine, and collaborators in the departments of neurosurgery, ophthalmology, and mechanical engineering.
"The advantage of this measurement method is that it is safe and painless," said Alperin. "Furthermore, in many instances it indicates the cause of the abnormal pressure."
According to the National Institutes of Health, which is funding the research, Alperin's work represents a breakthrough that promises to have "significant clinical impact."
Instead of drilling into the skull or opening the spinal column, a physician can derive the intracranial pressure from a series of MRI images of blood and cerebral spinal fluid flow. (View animated examples of MRI images of blood and cerebral spinal fluid flow.)
The method, which is patented, relies on the fact that pressure in a closed system such as the cranium is directly related to volume. The change in intracranial blood volume that occurs naturally during each cardiac cycle is calculated from the difference between blood and cerebrospinal fluid flows into and out of the brain. This process can be visualized in a series of MRI images, repeated at short intervals, that are sensitive to motion.
"It's like perturbing a string on a guitar to find out how tight it is," Alperin said. "We are using the natural pulsatility of the blood flow to probe the 'tension' in the brain."
Tests to date on both baboons and humans show that measurements of intracranial pressure using this method compare favorably with those from the invasive tests.
The invasive tests are done by inserting a catheter into the brain or a needle into the lumbar spine, both of which carry a risk of further injury. Although a lumbar spine measurement is less traumatic, it is associated with increased risk of brain stem herniation, which can lead to death, especially in patients with an already elevated intracranial pressure.
Despite the risks, the tests are used because intracranial pressure is such an essential clinical parameter. In patients with head injuries, for example, studies have shown that if the pressure is monitored and managed, mortality rates drop from 50 percent to 30 percent.
Annually, over 1.5 million people in the United States alone suffer from neurological problems stemming from traumatic brain injuries, hydrocephalus, intracranial hemorrhages, tumors, and other disorders that are associated with abnormal intracranial pressure. These patients could benefit from this promising methodology.
For more information on the UIC College of Medicine, visit www.uic.edu/depts/mcam/
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