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Purpose To implement an accelerated MR-acquisition method allowing to map T 2 ∗ relaxation and absolute concentration of sodium within skeletal muscles at 3T. Methods A fast-UTE-2D density-weighted concentric-ring-trajectory 23 Na-MRSI technique was used to acquire 64 time points of FID with a spectral bandwidth of 312.5 Hz with an in-plane resolution of 2.5 × 2.5 mm2 in ~15 min. The fast-relaxing 23 Na signal was localized with a single-shot, inversion-recovery-based, non-echo (SIRENE) outer volume suppression (OVS) method. The sequence was verified using simulation and phantom studies before implementing it in human calf muscles. To evaluate the 2D-SIRENE-MRSI (UTE = 0.55 ms) imaging performance, it was compared to a 3D-MRI (UTE = 0.3 ms) sequence. Both data sets were acquired within 2 same-day sessions to assess repeatability. The T 2 ∗ values were fitted voxel-by-voxel using a biexponential model for the 2D-MRSI data. Finally, intra-subject coefficients of variation (CV) were estimated. Results The MRSI-FID data allowed us to map the fast and slow components of T 2 ∗ in the calf muscles. The spatial distributions of 23 Na concentration for both MRSI and 3D-MRI acquisitions were significantly correlated (P T 2 Fast ∗ in muscles was 0.7 ± 0.1 ms (contribution fraction = 37%), whereas T 2 Slow ∗ was 13.2 ± 0.2 ms (63%). The mean absolute muscle 23 Na concentration calculated from the T 2 ∗ -corrected data was 28.6 ± 3.3 mM. Conclusion The proposed MRSI technique is a reliable technique to map sodium's absolute concentration and T 2 ∗ within a clinically acceptable scan time at 3T.

Purpose To provide a rapid, noninvasive fat-water separation technique that allows producing quantitative maps of particular lipid components. Methods The calf muscles in 5 healthy adolescents (age 12-16 years; body mass index = 20 ± 3 kg/m2 ) were scanned by two different fat fraction measurement methods. A density-weighted concentric-ring trajectory metabolite-cycling MRSI technique was implemented to collect data with a nominal resolution of 0.25 mL within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data. Results The proposed MRSI technique provided individual fat fraction maps for eight musculoskeletal lipid components identified by LCModel analysis (IMC/L [CH3 ], EMCL [CH3 ], IMC/L [CH2 ]n , EMC/L [CH2 ]n , IMC/L [CH2 -CH], EMC/L [CH2 -CH], IMC/L [-CH=CH-], and EMC/L [-CH=CH-]) with mean structural similarity indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively, compared with the maps generated by the used Dixon method. Further analysis of voxels with zero structural similarity demonstrated an increased sensitivity of fat fraction lipid maps from the data acquired using this MRSI technique over the standard Dixon technique. The lipid spatial distribution over calf muscles was consistent with previously published findings in adults. Conclusion This MRSI technique can be a useful tool when individual lipid fat fraction maps are desired within a clinically acceptable time and with a nominal spatial resolution of 0.25 mL.

A reliable and practical renal-lipid quantification and imaging method is needed. Here, the feasibility of an accelerated MRSI method to map renal fat fractions (FF) at 3T and its repeatability were investigated. A 2D density-weighted concentric-ring-trajectory MRSI was used to accelerate acquiring 48×48 voxels (each of 0.25 ml spatial-resolution) without respiratory navigation implementations. The data was collected over 512 complex-FID timepoints with a 1250 Hz spectral bandwidth. The MRSI sequence was designed with a metabolite-cycling technique for lipid-water separation. The in vivo repeatability performance of the sequence was assessed by conducting a test-reposition-retest study within healthy subjects. The coefficient of variation (CV) in the estimated FF from the test-retest measurements showed a high degree of repeatability of the MRSI-FF (CV= 4.3 ±2.5%). Additionally, the matching level of spectral signature within the same anatomical region was also investigated, and their intrasubject repeatability was also high, with a small standard deviation (8.1 ±6.4%). The MRSI acquisition duration was ~3 minutes only. The proposed MRSI technique can be a reliable technique to quantify and map renal metabolites within a clinically acceptable scan time at 3T that supports the future application of this technique for the non-invasive characterization of heterogeneous renal diseases and tumors.

PurposeTo implement an accelerated MR-acquisition method allowing to map sodium T2* relaxation and absolute concentration within skeletal muscles at 3T.MethodsA fast-2D density-weighted concentric-ring-trajectory 23Na-MRSI technique was used to acquire 64 time-points of FID with a spectral bandwidth of 312.5 Hz from a 2.5 x 2.5 mm2 in-plane resolution within about 15 minutes. The fast relaxing 23Na signal was localized with a single-shot, inversion-recovery based, non-echo (SIRENE) OVS method. The sequence was verified using simulation and phantom studies before implementing it in human calf muscles. Within two same-day sessions, 2D-SIRENE-MRSI (UTE = 0.55 ms) and 3D-MRI (UTE = 0.3 ms) data were acquired. The T2* values were fitted voxel-by-voxel using a bi-exponential model for the 2D-MRSI data. Within-subject coefficients of variation were estimated for both acquisition methods.ResultsThe MRSI-FID data allowed for fast and slow T2* mapping of the calf muscles in vivo with minimal sensitivity reduction. The spatial-distributions of 23Na concentration for both in vivo MRSI and 3D-MRI acquisitions were significantly correlated (r = 0.7, P in calf muscles was 0.7 ± 0.1 (contribution fraction = 37%), while was 13.2 ± 0.2 ms (63%). The mean absolute muscle 23Na concentration calculated from the T2*-corrected data was 28.6 ± 3.3 mM.ConclusionThe proposed MRSI technique is a reliable technique to map sodium’s absolute concentration and T2* within a clinically acceptable scan time at 3T.

PURPOSE: To implement an accelerated MR-acquisition method allowing to map T(2)* relaxation and absolute concentration of sodium within skeletal muscles at 3T. METHODS: A fast-UTE-2D density-weighted concentric-ring-trajectory (23)Na-MRSI technique was used to acquire 64 time-points of FID with a spectral bandwidth of 312.5 Hz with an in-plane resolution of 2.5 × 2.5 mm(2) in about 15 minutes. The fast-relaxing (23)Na signal was localized with a single-shot, inversion-recovery based, non-echo (SIRENE) OVS method. The sequence was verified using simulation and phantom studies before implementing it in human-calf muscles. To evaluate the 2D-SIRENE-MRSI (UTE = 0.55 ms) imaging performance, it was compared to a 3D-MRI (UTE = 0.3 ms) sequence. Both datasets were acquired within two same-day sessions to assess repeatability. The T(2)* values were fitted voxel-by-voxel using a bi-exponential model for the 2D-MRSI data. Finally, intra-subject coefficients of variation (CV) were estimated. RESULTS: The MRSI-FID data allowed us to map the fast and slow components of T(2)* in the calf muscles. The spatial-distributions of (23)Na concentration for both MRSI and 3D-MRI acquisitions were significantly correlated (P

PurposeTo provide a rapid, non-invasive fat quantification technique capable of producing separate lipid component maps.MethodsThe calf muscles in 5 healthy adolescents (age 12-16 years; BMI = 20 ± 3 Kg/m2) were scanned by two different fat fraction (FF) quantification methods. A high-resolution, density-weighted concentric ring trajectory (DW-CRT) metabolite cycling (MC) magnetic resonance spectroscopic imaging (MRSI) technique was implemented to collect data with 0.25 mL resolution within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity (SSIM) analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data.ResultsThe proposed MRSI technique provided individual FF maps for eight musculoskeletal lipids identified by LCModel analysis (L09, L11, L13, L15, L21, L23, L53, and L55) with mean SSIM indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively compared to that of Dixon’s FF map. Further analysis of voxels with zero SSIM demonstrated an increased sensitivity of FF lipid maps from data acquired using this MRSI technique over the standard Dixon technique. The trend of lipid spatial distribution over calf muscles was consistent with previously published findings in adults.ConclusionThe advantages of this MRSI technique make it a useful tool when individual lipid FF maps are desired within a short scanning time.