الفهرس 
FUNCTIONAL ANATOMY OF THE BRAINOnly 14 pages are availabe for public view
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Abstract
PET is unique in its ability to create ”functional” im¬ages of blood flow or metabolic processes rather than the more conventional structural or anatomic images produced by x-ray examination, CT, MRI, and even SPECT.
PET provides metabolic information that has been documented to be useful in patient care. The properties of positron decay permit accurate imaging of the distribution of positron-emitting radiopharmaceuticals. The wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. PET is used for characterizing brain disorders such as head trauma, cerebrovascular diseases, brain tumors, epilepsy and Alzheimer disease. The major utilization of PET clinically is in oncology and consists of imaging the distribution of FDG)an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue(.
PET can play a complementary role to anatomical imaging by providing additional pathophysiological and clinical information. It can reveal areas of hypometabolism not associated with anatomical abnormalities, and it is able to detect more lesions than CT. MRI is especially sensitive for detecting small lesions because of its excellent spatial resolution. PET is important for evaluating brain injury especially in the chronic setting, it may correlate better with outcome and cognitive dysfunction compared to MRI or CT.
PET studies are important in detection of ischemic lesions that develops after head trauma and help to clarify the significance of ischemia both clinically and pathophy-siologically in these patients. It also can be used to diagnose patients with DAI in order to determine the extent of damage and prognosis. It helps delineate reversible and irreversible lesions in order to direct therapeutic interventions towards preventing further damage.
PET represents a unique methodology for examining the biochemical features of brain tumors and can therefore function as a translational bridge between invitro biologic discovery and clinical medicine. High sensitivity is reported for primary brain tumor detection with PET. Initial FDG-PET studies can identify elevated FDG uptake in primary brain tumors with good correlation of the grade of malignancy .
Studies reveal that FDG may differentiate recurrence from other therapy-related changes, demonstrating that tumoral FDG uptake lower than adjacent cortical tissue is associated with a longer survival time than observed in tumor FDG uptake higher than in the adjacent cortex.
In the early postoperative period, FDG-PET can be used to differentiate residual tumor tissue from postoperative surgical effects. It seems clear that a decline in tumor tissue uptake of FDG weeks or months after therapy is suggestive of a good response to treatment .After intensive irradiation or chemotherapy for malignant brain tumors, MRI is not able to distinguish tumor progression from radiation damage or necrosis. FDG uptake suggests the presence of viable brain tumor tissue when the uptake of FDG was high before therapy, while absence of FDG uptake suggests that necrosis may be present.
PET studies of epilepsy have been routinely restricted to the interictal state due to short half lives of PET radiotracer. However, in patients with very frequent seizure PET imaging is possible. It has been used extensively in the presurgical evaluation of patients with intractable partial complex epilepsy. The relation between the area of hypometabolism and the extent of surgical resection is needed for seizure control particularly in extratemporal foci. PET studies are also successful in differentiating AD from other forms of dementia.
In conclusion, PET represents a new step forward in the way scientists and doctors look at the brain and how it functions. Over this decade, PET will probably assume an increasing role in the evaluation and management of patients. The unique ability of PET to provide important physiologic information for diagnosing diseases and objectively monitoring the effects of therapy will be important in the practice of medicine.