Parkside Magnetic Resonance Center - Technology

MR Spectroscopy

MRI Spectroscopy is used to detect the chemistry of an area of the brain. This advanced imaging technique is used to enhance traditional MRI images to further investigate an area of abnormality as identified on a routine MRI scan. It can be used to differentiate radiation necrosis from recurrent tumor. It is also valuable in evaluating multiple sclerosis. No gadolinium is injected in this exam.

MRI Spectroscopy divides the images from an MRI into a grid and determines the magnetic resonance spectrum for each box in the grid. Certain tumors display a characteristic spectroscopic “fingerprint,” allowing the boxes containing tumor to be distinguished from those containing normal tissue, even when the appearance on MRI is similar. The “spectrum” is a graph derived from non-aqueous molecules based on their discrete radio-frequency signal, which is shifted away (chemical shift) from the water signal the MRI uses. A high peak means that the molecule at that RF location exists in greater concentration than an adjacent low peak. To be precise, it is the area under the peak that is relevant. Applying appropriate calibrations, the concentration of a given metabolite is calculated from the peak area. The peak locations correspond to specific molecules such as glucose, creatine, lactate, etc., however peaks from non-identical molecules may overlap.

Metabolite ratios for different tissue types (***).

Regarding the brain, three of the main metabolites of interest are: 1) Choline (Cho) a neurotransmitter that is increased in tumors. 2) N-Acetyl Aspartate (NAA) a neuronal metabolite that is decreased in tumors (**). 3) Creatine (Cr), a brain metabolite.

It has been revealed that the Cho to Cr and Cho to NAA ratios are generally highest in recurrent tumor, followed by RIN and finally normal appearing white matter (***).

Sources:
Advanced Radiology Consultants, Park Ridge; Virginia Commonwealth University, Department of Radiation Oncology; Colorado Springs Imaging, Colorado Springs; Lars Ewell, Russell Hamilton, 11/27/05, Diffusion Weighted MRI and Magnetic Resonance Spectroscopy to Differentiate Radiation Necrosis and Recurrent Disease in Gliomas

** Haacke, Brown, Thompson and Venkatesan, “Magnetic Resonance Imaging,” 1999, John Wiley and Sons, Inc., New York, New York.

*** Weybright et al., “MR Spectroscopy in the Evaluation of Recurrent Contrast-Enhancing Lesions in the Posterior Fossa After Tumor Treatment,” Neuroradiology, 46, 541-549, 2004.