Magnetic Resonance Spectroscopy

Magnetic Resonance Spectroscopy

Magnetic resonance spectroscopy (MP-spectroscopy) allows non-invasive information about brain metabolism. 1H-MR proton spectroscopy is based on a “chemical shift” – a change in the resonance frequency of the protons that make up different chemical compounds. This term was introduced by N. Ramsey in 1951 to refer to the differences between the frequencies of individual spectral peaks. The unit of measurement for a “chemical shift” is ppm (parts per million). We present the main metabolites and their corresponding chemical shift values, the peaks of which are determined in vivo in the proton MR spectrum:

NAA-N-acetylaspartate (2.0 ppm);
Cho-Mixin (3.2 points);
creatine (3.03 and 3.94 ppm);
ml – myinositol (3.56 ppm);
Glx-glutamate and glutamine (2.1-2.5 ppm);
lac – lactate (1.32 ppm);
The lipid complex (0.8-1.2 ppm).

Magnetic Resonance Spectroscopy, Currently, two main methods of MP-spectroscopy are used—single voxel and multi-shift (chemical arc imaging) MP-spectroscopy—a one-time detection of spectra from several brain regions. In practice, it is now beginning to include an MP-based multinuclear spectrum based on the MP signal from cores of phosphorous, carbon and some other compounds.

Magnetic Resonance Spectroscopy, For single-site 1H-MR spectroscopy, only one site (brain voxel) is selected for analysis. Analyzing the composition of the frequencies in the recorded spectrum of this voxel, the distribution of some metabolites on the chemical shift scale (ppm) is obtained. The ratio between the metabolic peaks of the spectrum, the decrease or the increase in the peak of individual spectral peaks allows for a non-invasive assessment of biochemical processes occurring in tissues.

Magnetic Resonance Spectroscopy, Using multi-pixel MP-multi-pixel spectroscopy, the MP spectrum of several voxels is obtained simultaneously, and the spectra of individual sections in the study area can be compared. Processing the data from multi-shot MP spectroscopy makes it possible to generate a parametric cut-off map, in which the concentration of the metabolite is marked with color, and visualize the distribution of metabolites in the cut, i.e. to obtain a chemical transformation-weighted image.

Magnetic Resonance Spectroscopy, Clinical application of MR spectroscopy. MP-band spectroscopy is now widely used to evaluate various brain volumetric formations. MP-spectral data does not allow to predict with certainty the histological type of a tumor, however, most researchers agree that tumor processes are generally characterized by low NAA/Cr ratio, increased Cho/Cr ratios and, in some cases, the appearance of a lactate peak. In most of the proton studies MR spectroscopy was used in the differential diagnosis of astrocytomas, ependymoma and primitive neuroepithelial neoplasms, presumably determining the type of cancerous tissue.

Magnetic Resonance Spectroscopy, In clinical practice, it is important to use protocol spectroscopy in the postoperative period for the diagnosis of persistent tumor growth, tumor relapse or radiation necrosis. In complex cases, 1H-MR spectroscopy becomes a useful additional method in differential diagnosis along with the acquisition of perfusion-weighted images. In the spectrum of radioactive necrosis, a characteristic feature is the presence of the so-called dead peak, an extensive lactate-lipid complex in the range of 0.5-1.8 ppm against the background of a complete reduction of the peaks of other metabolites.

Magnetic Resonance Spectroscopy, Another aspect of using IR spectroscopy – differentiation of newly diagnosed primary and secondary lesions, their differentiation and their infectious demielinizuyuschimi processes. Most revealing are the results of diagnosing brain abscesses using weighted images. The spectrum of abscesses in patients without the main metabolite peaks marked the appearance of a lipid-lactate peak with complex peaks and specific for abscess content, such as acetate and succinate (products of anaerobic decomposition of bacteria) and the amino acid valine and lysine (the result of proteolysis).

The literature also extensively examines the information content of MR spectroscopy in epilepsy, in the assessment of metabolic and white matter disorders of degenerative brain diseases in children with traumatic brain injury, cerebral ischemia and other diseases.

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