The diagnostic value of PET metabolism imaging in patients with traumatic brain injury
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Background: Structural imaging (MRT/CT) is usually used as the first method to diagnose the presence or absence of traumatic brain injury (TBI). However, some studies show that in some cases abnormalities are missed when using structural imaging. The question arises whether the use of functional imaging techniques has additional value at all. For the functional imaging techniques, Single Positron Emission Computerized Tomography (SPECT) and Positron Emission Tomography (PET), the accuracy of detecting TBI by SPECT imaging has already been examined, of PET it has not. This thesis covers an evaluation of a possible role of PET-imaging in the diagnosis and possible clinical outcome of traumatic brain injury. The first study contains a literature review to evaluate the accuracy role of PET-imaging in the diagnosis of TBI. In a second section, a study is performed to determine a possible clinical value of PET-imaging in tracing a correlation between hypo glucose metabolic activity in specific brain areas and cognitive impairments. Methods: In the first study a literature search was performed with the use of the databases Psychinfo and Pubmed to identify relevant studies for assessing the accuracy of the PET scanning technique. The imaging method should identify abnormalities in TBI patients, however without missing abnormalities, and nor suggesting abnormalities where they are not; i.e. the method should be accurate. The second study: in a retrospective study eight patients with mild TBI were tested in the chronic phase of TBI. Neuropsychological assessments were examined and regional cerebral glucose metabolism at rest was measured with Fluordeoxyglucose-PET to find possible correlations. Results: 25 studies, out of an evaluation of 45 studies proved to be relevant and showed that PET-imaging is superior to structural imaging with a sensitivity of 97% for PET-imaging, against 44% for structural imaging. Despite this superiority in sensitivity of detecting TBI, previous studies suggest that PET-imaging has no predictive value with regard to the development of, and recovery from TBI. This suggestion may not be valid as the used studies showed a large heterogeneity in methods applied and in patients’ characteristics. Insufficient information was available on the effects of tracer used, time elapsed between injury and imaging, method of comparison between abnormal and normal tissue areas, degree of severity of TBI and age of the patient. The main outcome of the second study is that all the patients in the investigated group that had been tested showed at least one abnormal hypo-glucose metabolism in the frontal region, the parietal region or the subcortical regions. No abnormalities were found in other regions, such as the cingulate cortex. Due to the small number of participants, a correlation analysis gave no significant results. Conclusion: To determine the best method for detecting abnormalities as well as the predictive value of PET imaging prospective, repeated and simultaneously taken structural and functional imaging need to be compared. Although in the second study a clear distinction was made with regard to mild TBI, the chronic phase of injury and the used method of combining brain regions into larger domains the number of data was too small to conduct a correlation analysis. Further research with a larger sample size and with the use of a standardized method and no difference in method and patient characteristics is essential.