In Vivo Magnetic Resonance Spectroscopy - Data Acquisition

Data Acquisition

Acquiring an MRS scan is very similar to that of MRI with a few additional steps preceding data acquisition. These steps include: 1.) Shimming the magnetic field: this step is taken to correct for the inhomogeneity of the magnetic field by tuning different pulses in the x, y, and z directions. This step usually automated but can be performed manually 2.) Suppressing the water signal: because water molecules contain hydrogen, and the relative concentration of water to metabolite is about 10,000:1, the water signal must be suppressed or the metabolite peaks will not be discernible in the spectra. This is achieved by adding water suppression pulses. 3.) Choosing Spectroscopic Technique: requires proper planning of what you need to measure a. Single Voxel Spectroscopy (SVS): has spatial resolution of 1-8cm3, time efficient technique, data can be used quantitatively b. Chemical Shift Imaging (CSI): is a multi voxel technique that allows for measurement of larger volumes of tissue that can be divided into smaller voxels during the processing period c. Magnetic Resonance Spectroscopic Imaging (MRSI): is a 2-dimensional CSI technique that requires longer acquisition and processing time.

The more common MRI is used to detect H2O molecules in the brain, however MRS is used to probe other molecules that are common to tumors by comparing MRS spectra with known “fingerprint” spectra.