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Purpose: The transmit field B1+ at 3 T in brain affects the spatial uniformity and contrast of most image acquisitions. Here, B1+ spatial variation in brain at 3 T is characterized in a large healthy population. Methods: Bloch‐Siegert B1+ maps were acquired at 3 T from 385 healthy subjects aged 5–90 years on a single MRI system. After transforming all B1+ maps to a standard brain atlas space, region‐of‐interest analysis was performed, and intersubject voxel‐wise coefficient of variation was calculated across the whole brain. The B1+ variability due to age and brain size was studied separately in males and females, along with B1+ variability due to nonideal transmit calibration. Results: The voxel‐based mean coefficient of variation was 4.0% across all subjects, and the difference in B1+ between central (left thalamus) and outer regions (left frontal gray matter) was 24.2% ± 2.3%. The least intersubject variability occurred in central regions, whereas regions toward brain edges increased markedly in variation. The B1+ variability with age was mostly attributed to lifespan changes in CSF volume (which alters brain conductivity) and head orientation. Larger brain size correlated with more B1+ inhomogeneity (p <.001). Varying head position and anatomy resulted in an inaccurate transmit calibration. Conclusion: In standard atlas space, intersubject B1+ variability at 3 T was relatively small in a large population aged 5–90 years. The B1+ varied with age‐related changes of CSF volume and head orientation, as well as differences in brain size and transmit calibration. [ABSTRACT FROM AUTHOR]

A new 1H-MRS filtering strategy for selective measurement of glycine (Gly) in human brain in vivo at 3.0T is proposed. Investigation of multiple refocusing following a 90° excitation pulse indicated that triple refocusing is most effective for suppression of the strongly coupled resonances of myo-inositol (mI) at the Gly 3.55-ppm resonance. The echo times of the triple refocusing were optimized, with numerical analysis of the filtering performance, as {TE1, TE2, TE3} = {67, 62, 69} ms. Compared with the 90°-acquired mI signal the mI suppression ratios of the filter were 170 and 1000, in terms of peak amplitude and area, respectively, between 3.51 and 3.59 ppm. From LCModel analyses, using density-matrix calculated spectra as basis functions, the concentration of Gly in parieto-occipital cortex of healthy adults was estimated to be 0.5 ± 0.1 mM (mean ± SD, n = 6), with reference to creatine at 8 mM. Magn Reson Med, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Purpose: The transmit field B 1 + at 3 T in brain affects the spatial uniformity and contrast of most image acquisitions. Here, B 1 + spatial variation in brain at 3 T is characterized in a large healthy population., Methods: Bloch-Siegert B 1 + maps were acquired at 3 T from 385 healthy subjects aged 5-90 years on a single MRI system. After transforming all B 1 + maps to a standard brain atlas space, region-of-interest analysis was performed, and intersubject voxel-wise coefficient of variation was calculated across the whole brain. The B 1 + variability due to age and brain size was studied separately in males and females, along with B 1 + variability due to nonideal transmit calibration., Results: The voxel-based mean coefficient of variation was 4.0% across all subjects, and the difference in B 1 + between central (left thalamus) and outer regions (left frontal gray matter) was 24.2% ± 2.3%. The least intersubject variability occurred in central regions, whereas regions toward brain edges increased markedly in variation. The B 1 + variability with age was mostly attributed to lifespan changes in CSF volume (which alters brain conductivity) and head orientation. Larger brain size correlated with more B 1 + inhomogeneity (p < .001). Varying head position and anatomy resulted in an inaccurate transmit calibration., Conclusion: In standard atlas space, intersubject B 1 + variability at 3 T was relatively small in a large population aged 5-90 years. The B 1 + varied with age-related changes of CSF volume and head orientation, as well as differences in brain size and transmit calibration., (© 2021 International Society for Magnetic Resonance in Medicine.)