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Most of you have heard of MRI (magnetic resonance image) scans but these are not terribly helpful in making the diagnosis of Parkinson's disease or in assessing its progression. Neurologists will sometimes order an MRI scan or a CT scan to look for other causes of a patient's symptoms that might mimic PD.
Recently, we have begun to image the brain differently and look less at the anatomy- since there is nothing anatomically wrong with a PD patient's brain- and more at the neurochemistry of a patient's brain. The chemical changes that take place are largely due to a reduction in dopamine, one of the brain's neurotransmitters. There are two ways to image the brain and get a glimpse of the chemical changes that are taking place; namely, PET scans and SPECT scans. With these scanning techniques we have a new window into the workings of the brain.
PET (pos itron emission tomography) imaging begins wi th the injection of a metabolically active tracer, a biological molecule that carries with it a positronemitting isotope. Within minutes, the isotope accumulates in an area of the body for which the molecule has an affinity. The radioactive nuclei then decay by positron emission. PET scans provide three-dimensional color-coded images that are created based upon the detection of these positrons. PET scans can help identify certain biochemical abnormalities such as the dopamine deficiency in PD. Up until recently PET scanning has largely been a research tool because of the need for a cyclotron, a very complex and costly apparatus, to make the radioactive tracers. Within the next few weekss we will have routine access to a PET scan in Danbury.
Different radionuclides are used for SPECT imaging that emit a single photon rather than positron emission as in PET. SPECT imaging involves the rotation of a photon detector array around the body to acquire data from multiple angles. While it doesn't provide the same resolution as PET, SPECT is less expensive and more widely available.
Some of the most exciting research in PD takes advantage of these molecular neuroimaging techniques. The upcoming neuroprotective trial, which we wil l be conducting, will use SPECT to evaluate the effectiveness of the compound on modifying the rate of disease progression.
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