Flash MRI Images
Magnetic Resonance Spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei. This phenomenon and its origins are detailed in a separate section on nuclear magnetic resonance. The most important applications for the organic chemist are proton NMR and carbon-13 NMR spectroscopy. In principle, NMR is applicable to any nucleus possessing spin.
Initial NMR experiments were done by Rabi and co-workers in 1938. These efforts were acknowledged by the Nobel Prize in 1944. Later Purcell and Bloch (1952) first detected NMR signals from magnetic dipoles of nuclei when placed in an external magnetic field. The first NMR imaging was performed in 1970 on animals followed by human application developed by Dr. Damadian in 1980, who introduced the first commercial MRI scanner. Parallel to the introduction of magnetic resonance imaging (MRI) to clinical practice, initial in vivo brain spectroscopy studies were done in the early 1980s. Magnetic resonance spectroscopy (MRS) has rapidly progressed in its clinical utility and recognition. Today, MRS has become a significant no-invasive diagnostic tool and has gained wide clinical acceptability.
N-Acetyl Aspartate (NAA) is an amino acid found exclusively in neurons. It is regarded as a non-specific marker and is thought to be involved in Coenzyme A interactions and lipogenesis within the brain. It is a marker of neuronal viability. Normal NAA concentration is in the range of 8-9 mmol/kg in healthy adult brain. Concentrations are decreased in conditions leading to axonal injury or neuronal loss. NAA is also decreased in other conditions such as neoplasm, infarction, and inflammatory conditions such as multiple sclerosis. NAA peak is seen at 2.0 ppm (parts per million) on MR spectra.
The Choline (Cho) peak is a heterogeneous peak representing various choline-containing compounds such as acetylcholine, phosphocholine (lecithin), glycerophosphocholine, and various other intermediates of phospholipids metabolism. It is an indicator of cell density and cell wall turnover. Elevated levels are found tumors, especially malignant ones, and in certain demyelinating diseases. Choline resonance presents at 3.22 ppm. Studies have shown there is also a direct association between Cho and levels of Ki-67, a protein expressed in all phases of the cell cycle except GO that serves as a good marker for cellular proliferation. This observation makes Cho a reliable predictor of cellular activity in tumor tissue.
Creatine (Cr) is basically related to cell energy pathways. It is both the substrate and product of creatine kinase. Creatine reflects the energy potential available in brain tissue. Its concentration in normal brain remains very high and stable due to high metabolic energy needs of brain cells. Its peak is noticed at 3.0 ppm. Creatine-Choline ratios are an important indicator of disease states such as demyelization.
Lactate (Lac) is absent in normal brain tissue and its presence is indicative of anerobic glycolysis at the cellular level. Elevated levels are associated with ischemic conditions or metabolic disorders (where anerobic glycolysis predominates) but is also noted at the edges of large brain tumours. The peak is very sensitive to the technique employed and unless the correct echo time is employed, it may be artifactually suppressed. The spectral peak lies at 1:33 ppm. The peak is often inverted or bifid.
Lipid is also absent normally but can increase in tumors, infections or metabolic conditions. The peak is at 1.3 ppm and it overlaps with lactate peak.
Myo-inositol (Ins) is a naturally occurring sugar. It is the dominant peak in newborn brains and lies at 3.56/4.06 ppm. It is regarded as an astrocytic marker and is a possible marker for intracellular osmotic integrity. Its concentration is decreased in stroke, tumours, lymphoma and some low -grade malignancies.
Glutamate/Glutamine/GABA are neurotransmitters and act as markers for neuronal-glial interaction. Peaks lie at 2-2.5 and 3.4-3.7 ppm.
Spectroscopy Publication References
Mikulis DJ, Roberts TP Neuro MR: protocols. .J Magn Reson Imaging. Oct 2007;26(4):838-47.
Sajjad Z, Alam S. “Magnetic Resonance Spectroscopy IMRS): Basic Principles and applications in Focal Brain Lesions”. Pak J Neurol Sci. 2007; 2(1): 42-46.
Stadlbauer A, Gruber S, Nimsky C, Fahlbusch R, Hammen T, Buslei R,Tomandi B, Moser E, Ganslandt O. “Pre-Operative grading of gliomas by using metabolite quantification with High–Spatial–Resolution Proton MR Spectroscopic imaging. Radiology 2006; 238: 958-969.
Weybright P, Sundgren P, Maly P, Hassan D, Nan B, Rohrer, S, Junck L, “Differentiation between brain tumour recurrence and radiation injury using MR spectroscopy.” American Journal Roengenol 2005; 185:1471-1476.
Di Costanzo A, Trojsi F, Tosetti M, Giannatempo GM, Nemore F, Piccirillo M, Bonavita S, Tedeschi G, Scarabino T. “High-field proton MRS of human brain.” Journal Article. Review, European Journal of Radiology. Nov 2003;48(2):146-53.
Pillai J, Kwock L, “Brain magnetic resonance spectroscopy.“ In: Haaga, JR, Lanzieri CF, Gilkeson, RC. “CT and MR imaging of the whole body.” 2003;1:371-395.
Law M, Yang S, Wang H, Babb J, Johnson G, Cha S, Knopp E, Zagzag D, “Glioma grading: Sensitivity, specificity, and predictive value of perfusion MR imaging compared with conventional MR imaging.” AJNR. 2003; 24:1989-1998.
Galanaud D, Chinot O, Nicoli F, Confort-Gouny S, Fur Y, Barrie-Attarian M, Ranjeva J, Fuentes S, Viout, P. Figarella-Branger, D. Cozzone, P. “Use of proton magnetic resonance spectroscopy of the brain to differentiate gliomatosis cerebri from low-grade glioma.” J Neurosurg. 2003; 98: 269-276.
Moller-Hartmann W, Herminghaus S, Krings T, Marquardt G, Lanfermann H, Pilatus U, Zanella F, “Clinical application of proton magnetic resonance spectroscopy in the diagnosis of intracranial mass lesion.” Neuroradiology. 2002;44: 371-381.
Law M, Cha S, Knopp E, Johnson G, Arnett J, Litt A. “High-grade gliomas and solitary metastases: Differentiation by using perfusion and proton spectroscopic MR imaging.” Radiology. 2002; 222: 715-721.
Gupta R, Vastal D, Husain N, Chawla S, Prasad K, Roy R, Kumar R, Jha D, Husain M. “Differentiation of tuberculous from pyogenic brain abscesses with in vivo proton MR spectroscopy and magnetization transfer MR imaging. AJNR. 2001; 22: 1503-1509.
Kwock L. Localized MR spectroscopy: basic principles. Neuroimaging Clin N Am. Nov 1998;8(4):713-31.
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