Accelerated proton–echo-planar spectroscopy imaging (PEPSI) using GRAPPA with large-N phased-array coils

Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan.
Magnetic Resonance in Medicine (Impact Factor: 3.57). 05/2008; 59(5):989-98. DOI: 10.1002/mrm.21545
Source: PubMed


Parallel imaging has been demonstrated to reduce the encoding time of MR spectroscopic imaging (MRSI). Here we investigate up to 5-fold acceleration of 2D proton echo planar spectroscopic imaging (PEPSI) at 3T using generalized autocalibrating partial parallel acquisition (GRAPPA) with a 32-channel coil array, 1.5 cm(3) voxel size, TR/TE of 15/2000 ms, and 2.1 Hz spectral resolution. Compared to an 8-channel array, the smaller RF coil elements in this 32-channel array provided a 3.1-fold and 2.8-fold increase in signal-to-noise ratio (SNR) in the peripheral region and the central region, respectively, and more spatial modulated information. Comparison of sensitivity-encoding (SENSE) and GRAPPA reconstruction using an 8-channel array showed that both methods yielded similar quantitative metabolite measures (P > 0.1). Concentration values of N-acetyl-aspartate (NAA), total creatine (tCr), choline (Cho), myo-inositol (mI), and the sum of glutamate and glutamine (Glx) for both methods were consistent with previous studies. Using the 32-channel array coil the mean Cramer-Rao lower bounds (CRLB) were less than 8% for NAA, tCr, and Cho and less than 15% for mI and Glx at 2-fold acceleration. At 4-fold acceleration the mean CRLB for NAA, tCr, and Cho was less than 11%. In conclusion, the use of a 32-channel coil array and GRAPPA reconstruction can significantly reduce the measurement time for mapping brain metabolites.

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    • ", GRAPPA with EPSI [18] [19] and SENSE with spiral trajectories [20], have also been proposed for achieving an even faster scan time. However, the application of these fast techniques for clinical applications might need more evaluation for the SNR, volumetric coverage, possible artifacts and their impact on the metabolite levels and the disease extent definition. "
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