Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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The accuracy of metabolic quantification in MR spectroscopy is limited by the unknown radiofrequency field and T(1). To address both issues in proton ((1)H) MR spectroscopy, we obtained radiofrequency field-corrected T(1) maps of N-acetylaspartate, choline, and creatine in five healthy rhesus macaques at 3 T. ⋯ Their histograms from all 140 voxels in each animal were similar in position and shape, characterized by standard errors of the mean of the full width at half maximum divided by their means of better than 8%. Regional gray matter N-acetylaspartate, choline, and creatine T(1)s (1333 +/- 43, 1265 +/- 52, and 1131 +/- 28 ms) were 5-10% longer than white matter: 1188 +/- 34, 1201 +/- 24, and 1082 +/- 50 ms (statistically significant for the N-acetylaspartate only), all within 10% of the corresponding published values in the human brain.
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The use of proton resonance frequency shift-based magnetic resonance (MR) thermometry for interventional guidance on abdominal organs is hampered by the constant displacement of the target due to the respiratory cycle and the associated thermometry artifacts. Ideally, a suitable MR thermometry method should for this role achieve a subsecond temporal resolution while maintaining a precision comparable to those achieved on static organs while not introducing significant processing latencies. ⋯ The proposed MR thermometry method was evaluated for 5 min at a frame rate of 10 images/sec in the liver and the kidney of 11 healthy volunteers and achieved a precision of less than 2 degrees C in 70% of the pixels while delivering temperature and thermal dose maps on the fly. The ability to perform MR thermometry and dosimetry in vivo during a real intervention was demonstrated on a porcine kidney during a high-intensity focused ultrasound heating experiment.