Abstract
Accurate and fast (1) H MR spectroscopic imaging (MRSI) water reference scans are important for absolute quantification of metabolites. However, the additional acquisition time required often precludes the water reference quantitation method for MRSI studies. Sensitivity encoding (SENSE) is a successful MR technique developed to reduce scan time. This study quantitatively assesses the accuracy of SENSE for water reference MRSI data acquisition, compared with the more commonly used reduced resolution technique. 2D MRSI water reference data were collected from a phantom and three volunteers at 3 Tesla for full acquisition (306 s); 2× reduced resolution (64 s) and SENSE R = 3 (56 s) scans. Water amplitudes were extracted using MRS quantitation software (TARQUIN). Intensity maps and Bland-Altman statistics were generated to assess the accuracy of the fast-MRSI techniques. The average mean and standard deviation of differences from the full acquisition were 2.1 ± 3.2% for SENSE and 10.3 ± 10.7% for the reduced resolution technique, demonstrating that SENSE acquisition is approximately three times more accurate than the reduced resolution technique. SENSE was shown to accurately reconstruct water reference data for the purposes of in vivo absolute metabolite quantification, offering significant improvement over the more commonly used reduced resolution technique.
Highlights
The two most popular types of Magnetic Resonance Spectroscopy (MRS) investigation are single voxel spectroscopy (SVS) and MR spectroscopic imaging (MRSI)
Before the comparison between the faster MRSI methods, a quantitative analysis between the full acquisition and full acquisition data were performed to validate the subsequent use of full acquisition (R 1⁄4 1) as a valid comparator data set
A 6 Â 6 voxel voxels within the PRESS box (VOI) was excited using PRESS (Fig. 1a) and water amplitude (Fig. 1b) maps were produced for all MRSI acquisition methods for both phantom and volunteer data
Summary
The two most popular types of MRS investigation are single voxel spectroscopy (SVS) and MR spectroscopic imaging (MRSI). MR spectroscopic imaging (MRSI) or chemical shift imaging (CSI) is a multivoxel technique which can spatially map metabolite information throughout a predefined volume [10] This technique is practically promising for the investigation of diseases such as brain tumors, where tumor heterogeneity [11] and diffuse margins [12] are commonly observed features, with significant clinical interest. Absolute quantitation is most commonly performed by referencing metabolite signal amplitudes to the signal obtained from water which acts as an internal standard [15,16,17] This method has been shown to be effective for SVS and can be routinely performed due to a minimal increase in scan time (
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