Apparent diffusion coefficients of 31P metabolites in the human calf muscle at 7 T

Abstract

Purpose In this study, we aimed to measure the apparent diffusion coefficients (ADCs) of major phosphorous metabolites in the human calf muscle at 7 T with a diffusion-weighted (DW)-STEAM sequence. Methods A DW-STEAM sequence with bipolar gradients was implemented at 7 T, and DW MR spectra were acquired in three orthogonal directions in the human calf muscle of six healthy volunteers (TE/TM/TR = 15 ms/750 ms/5 s) at three b-values (0, 800, and 1200 s/mm2). Frequency and phase alignments were applied prior to spectral averaging. Averaged DW MR spectra were analyzed with LCModel, and ADCs of 31P metabolites were estimated. Results Four metabolites (phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi) and glycerol phosphorylcholine (GPC)) were quantified at all b-values with mean CRLBs below 10%. The ADC values of PCr, ATP, Pi, and GPC were (0.24 ± 0.02, 0.15 ± 0.04, 0.43 ± 0.14, 0.40 ± 0.09) × 10–3 mm2/s, respectively. Conclusion The ADCs of four 31P metabolites were successfully measured in the human calf muscle at 7 T, among which those of ATP, Pi and GPC were reported for the first time in humans. This study paves the way to investigate 31P metabolite diffusion properties in health and disease on the clinical MR scanner.

Longitudinal diffusion barriers imposed by myofilaments and mitochondria in murine cardiac myocytes

“…The latter study ( de Graaf et al, 2000 ) employed fibers with low mitochondrial content and showed that “instantaneous” ATP diffusion occurs with no restriction at all, while diffusion over long distances becomes restricted by ∼60%, with apparent boundaries occurring with 15–22 µm separations. For human calf muscle, a coefficient of 1.5 × 10 −6 cm 2 /s was recently reported using 31 P metabolites ( Huang et al, 2023 ). Relevant to these results, a molecular model of diffusion within myofilaments with lattice spacings of 16.5 or 18.3 nm predicted that ATP diffusibility would be decreased by 40% with respect to diffusion in free water ( Kekenes-Huskey et al, 2013 ).…”

Scaling the mountains: what lies above 7 Tesla magnetic resonance?

“…This makes RF technology established for 1 H MR at 7 T very well suited to be adapted and fine-tuned for hetero-nuclear MR at 14 T or 20 T. Leveraging this advantage, MR at 14 T or 20 T is conceptually appealing to improve our understanding of ion homeostasis and energy metabolism in vivo in humans, as outlined in [43]. For example, the sensitivity gain at 20 T is expected to reduce scan times for 31 P and 23 Na by a factor of 8-10 versus approaches outlined in this Special Issue for 7 T [44]. Implications of these gains in sensitivity and speed include the promise of sodium MR of the heart with a sub-millimetre spatial resolution in 5-10 min scan time, and the potential for probing cardiac metabolism with 31 P MR spectroscopy in clinically acceptable examination times.…”