الفهرس 
AIM OF THE WORKOnly 14 pages are availabe for public view
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Abstract
Magnetic resonance spectroscopy has proven to be an important complementary examination for accurate diagnosis of suspicious brain lesions and saves the patient unnecessary biopsy taking regarding the ability of spectroscopy to non invasively monitor metabolic processes in living systems; it provides an attractive method of tissue characterization for the radiologist and clinicians. MR spectroscopy does not produce images but gives results in graphs. But recently, customized software programs can give us “the spectroscopic images” by displaying the level of metabolites as zones of different colors. Proton MR Spectroscopy of the brain detects resonance peaks of brain metabolites such as Choline, Creatine, NAA, Myoinositol, Glutamate, and lactate. Regarding the technique, the positioning of the voxel is very important to be placed within the viable component of the lesion. The alteration of the voxel position is avoided by minimizing the patient’s movement during the examination. Multi-voxel technique is much more preferred than the single one as it takes less time, covers the side of the lesion, areas outside of the lesion (which is beneficial in assessing infiltrating high grade glial neoplasms) and can evaluate very small lesions avoiding contamination of the voxel by the surrounding normal brain parenchyma, CSF or fat which may occur with single voxel technique. Regarding the interpretation, proton spectroscopy at intermediate echo times remains the technique of choice for most important questions in brain tumor evaluation. Using an echo time of 135 ms, has an additional advantage in that the lactate peak at 1.33 ppm is inverted and can be more easily discriminated from a lipid resonance in the same range. The important metabolites to be commented in the long TE are Cho, NAA, Cr and sometimes the MI, as well as, lipid/lactate peaks, however, it is better to comment on MI and lipid/lactate peaks in the short one. Other metabolites seen on short TE are alanine (mainly seen in meningioma), succinate, aspartate, acetate and others (seen in abscesses) and Glx seen in non neoplastic lesions. The intermediate TE is done to detect the inversion of the lipid/lactate peaks which denotes lactate, yet if it shows no inversion, so the peak is composed only of lipids and the presence of lipids indicates necrosis while lactate indicates a high grade neoplasm. Alanine is seen inverted in the intermediate TE as well. The long TE is done on the contra lateral side for comparison of the ratios. As for brain neoplasms, proton MR spectra obtained from them typically show: 1) decreased NAA as a marker for neuronal integrity,2) diminished Creatine, involved in cellular energetic and osmotic balance and 3) increased Choline, involved in cell membrane turnover. Lactate and mobile lipids could be evident in aggressive tumors reflecting increased anaerobic metabolism and cellular necrosis respectively. With higher WHO tumors grading, gliomas exhibit significantly increased Choline and Lipid formation. The important ratios to be calculated are: -Cho/NAA ratio within the lesion “n. =0.79 (0.56-1.2)”. -Cho/Cr both within the lesion and normal side “n. =1.14 (0.86-1.59)”. both ratios are seen elevated in the neoplastic lesions. -NAA/Cr ratio is not sensitive or specific value “n.1.39 (0.64-2.0)”. -MI/Cr ratio is important in tumoral grading when the suggesting diagnosis of the lesion is a neoplastic process. Proton MR Spectroscopy gives additional information to MRI in differentiating recurrent gliomas from radiation necrosis. As tumor recurrence show increased Choline peak and increased Cho/Cr ratio. While radiation necrosis shows abscent or depressed Choline peak. In conclusion, MR spectroscopy provides information about physiologic & metabolic status of the tissue and plays an important diagnostic and prognostic role in diagnosis, management and follows up of different intra-cranial SOLs.