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Purpose: To explore the high signal‐to‐noise ratio (SNR) efficiency of interleaved multishot 3D‐EPI with standard image reconstruction for fast and robust high‐resolution whole‐brain quantitative susceptibility (QSM) and R2∗$$ {R}_2^{\ast } $$ mapping at 7 and 3T. Methods: Single‐ and multi‐TE segmented 3D‐EPI is combined with conventional CAIPIRINHA undersampling for up to 72‐fold effective gradient echo (GRE) imaging acceleration. Across multiple averages, scan parameters are varied (e.g., dual‐polarity frequency‐encoding) to additionally correct for B0$$ {\mathrm{B}}_0 $$‐induced artifacts, geometric distortions and motion retrospectively. A comparison to established GRE protocols is made. Resolutions range from 1.4 mm isotropic (1 multi‐TE average in 36 s) up to 0.4 mm isotropic (2 single‐TE averages in approximately 6 min) with whole‐head coverage. Results: Only 1‐4 averages are needed for sufficient SNR with 3D‐EPI, depending on resolution and field strength. Fast scanning and small voxels together with retrospective corrections result in substantially reduced image artifacts, which improves susceptibility and R2∗$$ {R}_2^{\ast } $$ mapping. Additionally, much finer details are obtained in susceptibility‐weighted image projections through significantly reduced partial voluming. Conclusion: Using interleaved multishot 3D‐EPI, single‐TE and multi‐TE data can readily be acquired 10 times faster than with conventional, accelerated GRE imaging. Even 0.4 mm isotropic whole‐head QSM within 6 min becomes feasible at 7T. At 3T, motion‐robust 0.8 mm isotropic whole‐brain QSM and R2∗$$ {R}_2^{\ast } $$ mapping with no apparent distortion in less than 7 min becomes clinically feasible. Stronger gradient systems may allow for even higher effective acceleration rates through larger EPI factors while maintaining optimal contrast. [ABSTRACT FROM AUTHOR]

Purpose The aim of the study was to examine pH heterogeneity during fatigue induced by neuromuscular electrical stimulation (NMES) using phosphorus magnetic resonance spectroscopy (31P-MRS). It is hypothesized that three pH components would occur in the 31P-MRS during fatigue, representing three fiber types. Methods The medial gastrocnemius of eight subjects was stimulated within a 3-Tesla whole body MRI scanner. The maximal force during stimulation (Fstim) was examined by a pressure sensor. Phosphocreatine (PCr), adenosintriphosphate, inorganic phosphate (Pi), and the corresponding pH were estimated by a nonvolume-selective 31P-MRS using a small loop coil at rest and during fatigue. Results During fatigue, Fstim and PCr decreased to 27% and 33% of their initial levels, respectively. In all cases, the Pi peak increased when NMES was started and split into three different peaks. Based on the single Pi peaks during fatigue, an alkaline (6.76 ± 0.08), a medium (6.40 ± 0.06), and an acidic (6.09 ± 0.05) pH component were observed compared to the pH (7.02 ± 0.02) at rest. Conclusion It is suggested that NMES is able to induce pH heterogeneity in the medial gastrocnemius, and that the single Pi peaks represent the different muscle fiber types of the skeletal muscle. Magn Reson Med 77:2097-2106, 2017. © 2016 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Purpose To recover local phase contrast at the edges of the brain (e.g., cortex), where it is otherwise unavailable with the conventional form of the technique sophisticated harmonic artifact reduction for phase data (SHARP). Methods A harmonic potential field, such as the magnetic 'background' field, is an analytic field and can thus be represented by a convergent power series. Using SHARP to obtain an initial estimate of the harmonic background field over a reduced inner portion of the brain, a three-dimensional Taylor expansion was performed to extend field coverage to the brain edges. The method, called Extended-SHARP, was quantitatively assessed through a numerical field-forward simulation and qualitatively demonstrated in vivo. Results Using a typical spherical kernel (6 mm radius), Extended-SHARP recovered on average 26% more in vivo brain volume than SHARP. When applied to the numerical model, local field contrast around an otherwise lost edge source was recovered, with the resulting error comparable to that of conventional SHARP. Conclusion The lost field values near the edges of the brain can be recovered through an easily implemented adaptation to conventional SHARP. Magn Reson Med 73:851-856, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]