PET Scans

What is a Positron Emission Tomography (PET) scan? PET scans have been around for over two decades. A PET scan is like a CT or MRI scan and is an imaging technique that can be used to visualize various parts of the body. The main concern of this blog is related to PET images of the brain.

A mildly radioactive contrast must be administered to the patient before the scan. The radioactivity, as in other areas of nuclear medicine, is not dangerous to the subject. This radioactive “label” is generally hooked up to a molecule called glucose.

Glucose is a sugar and is the main energy supply of all cells in the body, especially those in the brain. Thus, a PET scan can measure increased or decreased metabolic activity. This is a dynamic process, unlike CT or MRI scans, which are static. PET scans have the capacity to measure what parts of the brain are active (using large amounts of glucose) or quiet (not much cellular activity).

PET scans are mainly used in treating patients with cancer. Cancer cells rapidly divide and grow consuming large amounts of glucose and “light up” on a scan. This is especially important in identifying hidden nests of cancer cells (metastatic disease).

However, it became obvious from the beginning of research on TBI (traumatic brain injury), and even mild TBI, that PET scans are valuable. Now, in emergency or acute situations, PET scans are generally not available. But in the chronic phase research, there has been significant progress. Where traditional CT and MRI scans are normal, PET scans frequently demonstrate a decrease in glucose metabolic activity in processing areas of the brain. The brain is slowed down compared to normal activity. These regions of “slow down” correlate with neurocognitive function where patients are actually tested by neuropsychologists. Regions of decreased brain activity, even in mild TBI, are related to real world behavior. This link is critical because research is always trying to verify if what’s happening to a person can be correlated to what’s happening in the brain. In this manner, new drugs can be tested to help reverse abnormalities in glucose metabolism and hopefully improve neurologic function. This is the main goal in TBI research.

PET scans are more expensive than standard CT or MRI scans and are not done at every hospital. But since they are important in cancer treatment, these scans are readily available and more PET scans of the brain for TBI are being done. One important observation is that a patient’s initial loss of consciousness or Glasgow Coma Rating (see previous blog) does not predict ultimate damage to the brain. As I have discussed previously, most traumatic brain injury is missed in the emergency room.

One must make a cost benefit analysis on performing PET scans on all TBI victims, as I’ve stated, PET scans are not cheap (usually $1,000-$3,000) a scan.
But missing these patients can have a profound economic and personal impact on their lives. The PET scan is one more very important tool in diagnosing TBI.

Steven H. Rauchman, M.D. is an eye physician and surgeon who has been in private practice for 30 years. He has served as a Traumatic Brain Injury (TBI) medical/legal expert for the last 6 years specializing in the area of personal injury and related traumatic brain injuries.

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