ROLE OF MAGNETIC RESONANCE SPECTROSCOPY IN GRADING OF BRAIN GLIOMAS.

Dr. Rashida Nalwala 1 and Dr. Aarti Anand 2 . 1. Post-Graduate Resident, Department of Radiodiagnosis, Government Medical College & Hospital, Nagpur. 2. Professor and Head, Dept. of Radiodiagnosis, Govt. Medical College & Hospital, Nagpur. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 15 March 2019 Final Accepted: 17 April 2019 Published: May 2019


ISSN: 2320-5407
Int. J. Adv. Res. 7 (5), 546-550 547 used in clinical practice to predict the grade of the tumour and to aid clinical decision of when to intervene surgically. 1 One such advanced imaging technique is magnetic resonance spectroscopy (MRS) which analyses the metabolism of organs and cells, biochemical changes and quantitative analysis of compounds in humans. Various metabolites in brain tissue, such as N-acetyl aspartate (NAA), choline compounds (Cho), creatine and phosphocreatine (Cr), lactate and lipid, can be measured using proton MRS (1H-MRS). 2 The recent emphasis on the utilization of 1HMRS (coupled to routine MRI techniques) in the evaluation of tumors has arisen because it provides greater information concerning tumor activity and characterization of the tumor tissue than is possible with standard MRI techniques alone. 3 Conventional MR imaging provides important information regarding contrast enhancement, peritumoral edema, distant tumor foci, hemorrhage, necrosis and mass effect which are helpful in characterizing tumor aggressiveness and hence tumor grade. However, often a high-grade glioma may be mistaken for a low-grade glioma when it demonstrates minimal edema, no contrast material enhancement, no necrosis, and no mass effect. Therefore, accurate preoperative grading of gliomas and planning of adequate treatment strategies are often difficult with conventional MR imaging alone. The addition of complementary biochemical information, as provided by 1HMRS imaging, could lead to further advances in the determination of the tumor grade of gliomas.

Study Setting-Tertiary Care Hospital
Study Period-January 2015 to January 2017.
Sample Size-30 patients. All patients were subjected to MR imaging followed by multivoxel MR Spectroscopy.
Study Instrument-1.5 Tesla, Philips MR Achieva (Brain coil) Participant Selection-Inclusion criteria: 30 patients with gliomas evaluated on 1.5T Conventional MR imaging followed by multivoxel proton MR Spectroscopy

Exclusion criteria:
Patients with ferromagnetic implants, pacemakers and aneurysm clips. Claustrophobic patients.

Interpretation of images:
There are two types of spectroscopic imaging, namely, single-voxel and multivoxel MR spectroscopy. Single-voxel imaging involves the sampling of only one region of tissue. PRESS (point-resolved spectroscopy) and STEAM (stimulated echo acquisition mode) are the two types of sequences used for single-voxel spectroscopy. Multiple volume MR spectroscopy is also referred to chemical shift imaging (CSI). It is a method for obtaining spectroscopic information from multiple adjacent volumes over a large volume of interest. It is essentially similar to single-voxel spectroscopy except that the defined volume is normally a large slab.
CSI is better suited for evaluation of brain tumors because of their larger size and morphological and metabolic heterogeneity. It also allows for comparison and normalization of pathologic spectra to spectra in normal tissue. 4 Spectral patterns or specific metabolite intensities can be overlaid onto gray-scale MR images either to compare changes in spectra from adjacent voxels or to obtain a distribution pattern of a particular metabolite within the tissue 548 examined. NAA is a marker for neuronal density and viability and therefore is decreased in all disease processes in which there is death of the neurons or replacement of neurons by other cells. The NAA peak is assigned at 2.0 ppm and is the largest peak. The second largest peak is creatine. The peak is assigned at 3.03 ppm and serves as a marker for energy-dependent systems in the brain cells. The Cho peak is assigned at 3.2 ppm and reflects the metabolism of cellular membrane turnover and therefore is increased in all processes leading to hypercellularity. An abnormal peak of lactate is normally not found in the brain. It is assigned at 1.32 ppm and when detected indicates the presence of anerobic or nonoxidative metabolism, e.g. in necrosis.
Results:- 1. In present study of 30 patients, 14 were men (48%) and 16 were women (52%). Maximum 15 (50%) were in the age group of 31 to 40 years. 2. Out of 30 patients, 18 patients (60%) were diagnosed with high grade glioma and 12 patients (40%) with low grade glioma. 3. The mean Cho/Cr ratio and Cho/NAA ratio was higher in high grade gliomas ( Figure.1   LGGs using tumoural metabolite ratios including Cho/Cr, Cho/NAA and NAA/Cr. Although there was no significant difference in AUC between Cho/Cr and Cho/NAA groups, Cho/NAA ratio showed higher sensitivity and specificity than Cho/Cr ratio and NAA/Cr ratio. 3. Lactate was elevated in 77% of patients with HGG. The presence of lactate appears to correlate with higher grade of malignancy. (Figure.2) Martin Bulik, Radim Jancalek, Jiri Vanicek et all 7 in their study on potential of MR spectroscopy for assessment of glioma grading stated that malignant transformation of the glial tumors is accompanied by the presence of lactate and lipids in MR spectra of grade III but mainly grade IV gliomas.  Figure.2) 5. Low grade gliomas showed low levels of choline with no significant lactate and absence of lipids.

LESIONS
Bulik M, Jancalek R, Vanicek J, Skoch A et al 8 in their study concluded that low-grade gliomas are generally characterized by low level of choline and absence of lactate and lipids.

Conclusion:-
The mean Cho/Cr and Cho/NAA ratio was significantly elevated in high grade gliomas as compared to low grade gliomas. Higher ratios indicate increasing grade of malignancy. So it can be concluded that Cho/Cr and Cho/NAA can be used in grading of malignancies. It was not possible to differentiate between high grade and low grade gliomas on basis of NAA/Cr ratios. The presence of lactate and lipids correlate with higher grades of malignancy. MR Spectroscopy is a newer noninvasive modality which provides biochemical information about different tissues that cannot be obtained by conventional MRI. It complements MRI and is particularly useful when MRI findings are