Quantitative SENSE-MRSI of the human brain

Abstract

Purpose To develop a method for estimating metabolite concentrations using phased-array coils and sensitivity-encoded (SENSE) magnetic resonance spectroscopic images (MRSI) of the human brain. Materials and Methods The method is based on the phantom replacement technique and uses receive coil sensitivity maps and body-coil loading factors to account for receive B1 inhomogeneity and variable coil loading, respectively. Corrections for cerebrospinal fluid content from the MRSI voxel were also applied, and the total protocol scan time was less than 15 min. The method was applied to 10 normal human volunteers using a multislice 2D-MRSI sequence at 3 T, and seven different brain regions were quantified. Results N-Acetyl aspartate (NAA) concentrations varied from 9.7 to 14.7 mM, creatine (Cr) varied from 6.6 to 10.6 mM and choline (Cho) varied from 1.6 to 3.0 mM, in good general agreement with prior literature values. Conclusions Quantitative SENSE-MRSI of the human brain is routinely possible using an adapted phantom-replacement technique. The method may also be applied to other MRSI techniques, including conventional phase encoding, with phased-array receiver coils, provided that coil sensitivity profiles can be measured.

Constrained Source Space MR Spectroscopy: Multiple Voxels, No Gradient Readout

“…4,5 To reduce spectroscopic scan times, various "parallel imaging" approaches have been applied to reduce the amount of k-space data acquired. These techniques exploit the spatial sensitivity of individual elements in multichannel receiver coils [6][7][8][9] and can substantially reduce scan times. The spatial limitations of SVS are well recognized; it is usually the case that SVS spectra are required at more than one location, either to compare spectra from diseased and normal tissue or in the case of multifocal disease.…”

Proton magnetic resonance spectroscopy of skeletal muscle: A comparison of two quantitation techniques

“…However, care has to be taken to ensure that appropriate lipid content correction factors are used, and that the transmit B 1 levels are as homogeneous as possible (or determined using B 1 mapping). The methods described here are feasible for routine MRS of the MSK system, and should be readily applicable to MRS of other organ systems throughout the body, as well as for use with MR spectroscopic imaging [9]. …”

“…In addition, phased-array receiver coils are increasingly being used for MSK MRS, and quantitation methods designed for use with single-channel transmit-receive coils (e.g. [8]) require further modifications for use with phased-array coils [9]. …”

“…The advantages of this method include the lack of need for additional patient scan time, the known reference concentration, and the absence of potentially deleterious magnetic susceptibility effects [8]. Nevertheless, despite its advantages, the method remains sensitive to B 1 inhomogeneity and variable radiofrequency coil loading [9]. For transmit-receive coils, the coil loading can be estimated, and corrected for, using the reciprocity theorem [8], and this may be extended for use with receive-only phased array coils by comparing the relative sensitivities of each element of the receive array to that of the transmit coil [9, 16, 17].…”

Characterization of Peripheral Nerve Sheath Tumors with 3T Proton MR Spectroscopy

“…To account for the different radiofrequency coil loading between the phantom and in vivo, the water signal was also recorded (without suppression, 16 averages) from the localized volume by use of transmit body coil receive and phased-array receive, as described previously. 25,26 No lipid suppression was applied. Shimming up to second order was performed to optimize the field homogeneity by a physicist with 8 years of experience.…”