biostudies-literatureEsmaeili MAustrian Science Fund FWFUS National Institutes of Health through the National Cancer InstituteNCI NIH HHSHelse Sør-Øst RHF1237-1250https://www.ebi.ac.uk/biostudies/studies/S-EPMC8717862biostudies-literatureUnknown53(4)<h4>Background</h4>Metabolic imaging using proton magnetic resonance spectroscopic imaging (MRSI) has increased the sensitivity and spectral resolution at field strengths of ≥7T. Compared to the conventional Cartesian-based spectroscopic imaging, spiral trajectories enable faster data collection, promising the clinical translation of whole-brain MRSI. Technical considerations at 7T, however, lead to a suboptimal sampling efficiency for the spiral-out (SO) acquisitions, as a significant portion of the trajectory consists of rewinders.<h4>Purpose</h4>To develop and implement a spiral-out-in (SOI) trajectory for sampling of whole-brain MRSI at 7T. We hypothesized that SOI will improve the signal-to-noise ratio (SNR) of metabolite maps due to a more efficient acquisition.<h4>Study type</h4>Prospective.<h4>Subjects/phantom</h4>Five healthy volunteers (28-38 years, three females) and a phantom.<h4>Field strength/sequence</h4>Navigated adiabatic spin-echo spiral 3D MRSI at 7T.<h4>Assessment</h4>A 3D stack of SOI trajectories was incorporated into an adiabatic spin-echo MRSI sequence with real-time motion and shim correction. Metabolite spectral fitting, SNR, and Cramér-Rao lower bound (CRLB) were obtained. We compared the signal intensity and CRLB of three metabolites of tNAA, tCr, and tCho. Peak SNR (PSNR), structure similarity index (SSIM), and signal-to-artifact ratio were evaluated on water maps.<h4>Statistical tests</h4>The nonparametric Mann-Whitney U-test was used for statistical testing.<h4>Results</h4>Compared to SO, the SOI trajectory: 1) increased the k-space sampling efficiency by 23%; 2) is less demanding for the gradient hardware, requiring 36% lower G_max and 26% lower S_max ; 3) increased PSNR of water maps by 4.94 dB (P = 0.0006); 4) resulted in a 29% higher SNR (P = 0.003) and lower CRLB by 26-35% (P = 0.02, tNAA), 35-55% (P = 0.03, tCr), and 22-23% (P = 0.04, tCho), which increased the number of well-fitted voxels (eg, for tCr by 11%, P = 0.03). SOI did not significantly change the signal-to-artifact ratio and SSIM (P = 0.65) compared to SO.<h4>Data conclusion</h4>SOI provided more efficient MRSI at 7T compared to SO, which improved the data quality and metabolite quantification.<h4>Level of evidence</h4>1 TECHNICAL EFFICACY STAGE: 2.Journal of magnetic resonance imaging : JMRIWhole-Slab 3D MR Spectroscopic Imaging of the Human Brain With Spiral-Out-In Sampling at 7T.PMC87178622018047J 4124R01 CA211080P 307011R01CA211080J 4124‐N36Moser PAndronesi OCEsmaeili MStrasser BBogner WWang ZfalseWhole-Slab 3D MR Spectroscopic Imaging of the Human Brain With Spiral-Out-In Sampling at 7T.<h4>Background</h4>Metabolic imaging using proton magnetic resonance spectroscopic imaging (MRSI) has increased the sensitivity and spectral resolution at field strengths of ≥7T. Compared to the conventional Cartesian-based spectroscopic imaging, spiral trajectories enable faster data collection, promising the clinical translation of whole-brain MRSI. Technical considerations at 7T, however, lead to a suboptimal sampling efficiency for the spiral-out (SO) acquisitions, as a significant portion of the trajectory consists of rewinders.<h4>Purpose</h4>To develop and implement a spiral-out-in (SOI) trajectory for sampling of whole-brain MRSI at 7T. We hypothesized that SOI will improve the signal-to-noise ratio (SNR) of metabolite maps due to a more efficient acquisition.<h4>Study type</h4>Prospective.<h4>Subjects/phantom</h4>Five healthy volunteers (28-38 years, three females) and a phantom.<h4>Field strength/sequence</h4>Navigated adiabatic spin-echo spiral 3D MRSI at 7T.<h4>Assessment</h4>A 3D stack of SOI trajectories was incorporated into an adiabatic spin-echo MRSI sequence with real-time motion and shim correction. Metabolite spectral fitting, SNR, and Cramér-Rao lower bound (CRLB) were obtained. We compared the signal intensity and CRLB of three metabolites of tNAA, tCr, and tCho. Peak SNR (PSNR), structure similarity index (SSIM), and signal-to-artifact ratio were evaluated on water maps.<h4>Statistical tests</h4>The nonparametric Mann-Whitney U-test was used for statistical testing.<h4>Results</h4>Compared to SO, the SOI trajectory: 1) increased the k-space sampling efficiency by 23%; 2) is less demanding for the gradient hardware, requiring 36% lower G_max and 26% lower S_max ; 3) increased PSNR of water maps by 4.94 dB (P = 0.0006); 4) resulted in a 29% higher SNR (P = 0.003) and lower CRLB by 26-35% (P = 0.02, tNAA), 35-55% (P = 0.03, tCr), and 22-23% (P = 0.04, tCho), which increased the number of well-fitted voxels (eg, for tCr by 11%, P = 0.03). SOI did not significantly change the signal-to-artifact ratio and SSIM (P = 0.65) compared to SO.<h4>Data conclusion</h4>SOI provided more efficient MRSI at 7T compared to SO, which improved the data quality and metabolite quantification.<h4>Level of evidence</h4>1 TECHNICAL EFFICACY STAGE: 2.2021-01-01T00:00:00Z2021 Apr2025-04-25T22:30:15.395Z2025-04-06T09:03:51.342ZS-EPMC87178623317983610.1002/jmri.27437