The reliability of bedside eye movement exams, which are often used to determine whether or not a comatose patient will recover, have high rates of misdiagnosis of vegetative states or minimally conscious states. Now, a new study suggests that positron emission tomography (PET) imaging could be used to learn whether comatose patients have a chance of recovery.

In the study, published in the Lancet, researchers studied 122 patients who were at the University Hospital of Liège, Belgium, between 2008 and 2012.

Forty-one of the study subjects were in a vegetative state. Because patients who are in a vegetative state for a year are considered to have no chance of recovering, it is considered grounds for medical treatment to be stopped.

Eighty-one patients in the study were classified as minimally conscious. These patients exhibit signs of responsiveness and awareness at times, and are considered to have better chances of recovering than patients who are in a vegetative state.

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Imaging Tests Find Miminal Consciousness

The researchers administered two tests: PET imaging, which measures the activities in the regions of the brain that are associated with consciousness, and magnetic resonance imaging (MRI), which monitors brain activity.

The imaging tests found minimal consciousness in 13 of the 41 vegetative patients. After a year, nine of the 13 had progressed into minimally conscious states or a higher level of consciousness, the researchers said. Overall, PET scans were a better measure than MRI scans, according to the researchers.

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PET Scan Shows Benefits

According to the researchers, PET scans are better at identifying conscious and unconscious patients. In fact, a third of the subjects who were diagnosed as behaviorally unresponsive using bedside tests were found to have some level of consciousness when assessed using PET scans.

According to study researcher Steven Laureys of the University of Liège, PET scans have the ability to detect processes in the brain that are not detected by bedside tests.

The researchers said that brain scans can provide valuable help to standard behavioral tests in identifying vegetative state patients who have the potential to recover.

In a written statement, the researchers said that PET scan could be used to complement bedside examinations and predict long-term recovery of patients with unresponsive wakefulness syndrome.

"Active MRI might also be useful for differential diagnosis, but seems to be less accurate," the researchers reported.

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What Does the Future Hold?

Pointing out that this type of PET scan is not widely available and not ready for routine use, the researchers cautioned that the test might show signs of awareness in people who turn out to have little or no chance of meaningful recovery.

“We shouldn’t give these families false hope,” Dr. Laureys said. “This is very difficult. But it’s just a very complex medical reality. Quantifying consciousness is tricky.”

Dr. Joseph J. Fins, the chief of the medical ethics division at Weill Cornell Medical College in New York, who was not involved in the study, told the New York Times that PET scans could help doctors resolve puzzling cases in which patients are unresponsive but have unexpectedly healthy-looking brains.

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