Purpose Multi-echo spin-echo (MSE) transverse relaxometry mapping using multi-component models is used to study disease activity in neuromuscular disease by assessing the T-2 of the myocytic... Show morePurpose Multi-echo spin-echo (MSE) transverse relaxometry mapping using multi-component models is used to study disease activity in neuromuscular disease by assessing the T-2 of the myocytic component (T-2water). Current extended phase graph algorithms are not optimized for fat fractions above 50% and the effects of inaccuracies in the T-2fat calibration remain unexplored. Hence, we aimed to improve the performance of extended phase graph fitting methods over a large range of fat fractions, by including the slice-selection flip angle profile, a through-plane chemical-shift displacement correction, and optimized calibration of T-2fat.Methods Simulation experiments were used to study the influence of the slice flip-angle profile with chemical-shift and T-2fat estimations. Next, in vivo data from four neuromuscular disease cohorts were studied for different T-2fat calibration methods and T-2water estimations.Results Excluding slice flip-angle profiles or chemical-shift displacement resulted in a bias in T-2water up to 10 ms. Furthermore, a wrongly calibrated T-2fat caused a bias of up to 4 ms in T-2water. For the in vivo data, one-component calibration led to a lower T-2fat compared with a two-component method, and T-2water decreased with increasing fat fractions.Conclusion In vivo data showed a decline in T-2water for increasing fat fractions, which has important implications for clinical studies, especially in multicenter settings. We recommend using an extended phase graph-based model for fitting T-2water from MSE sequences with two-component T-2fat calibration. Moreover, we recommend including the slice flip-angle profile in the model with correction for through-plane chemical-shift displacements. Show less
Meyerspeer, M.; Boesch, C.; Cameron, D.; Dezortova, M.; Forbes, S.C.; Heerschap, A.; ... ; Experts Working Grp P MR 2020
Skeletal muscle phosphorus-31 P-31 MRS is the oldest MRS methodology to be applied to in vivo metabolic research. The technical requirements of P-31 MRS in skeletal muscle depend on the research... Show moreSkeletal muscle phosphorus-31 P-31 MRS is the oldest MRS methodology to be applied to in vivo metabolic research. The technical requirements of P-31 MRS in skeletal muscle depend on the research question, and to assess those questions requires understanding both the relevant muscle physiology, and how P-31 MRS methods can probe it. Here we consider basic signal-acquisition parameters related to radio frequency excitation, TR, TE, spectral resolution, shim and localisation. We make specific recommendations for studies of resting and exercising muscle, including magnetisation transfer, and for data processing. We summarise the metabolic information that can be quantitatively assessed with P-31 MRS, either measured directly or derived by calculations that depend on particular metabolic models, and we give advice on potential problems of interpretation. We give expected values and tolerable ranges for some measured quantities, and minimum requirements for reporting acquisition parameters and experimental results in publications. Reliable examination depends on a reproducible setup, standardised preconditioning of the subject, and careful control of potential difficulties, and we summarise some important considerations and potential confounders. Our recommendations include the quantification and standardisation of contraction intensity, and how best to account for heterogeneous muscle recruitment. We highlight some pitfalls in the assessment of mitochondrial function by analysis of phosphocreatine (PCr) recovery kinetics. Finally, we outline how complementary techniques (near-infrared spectroscopy, arterial spin labelling, BOLD and various other MRI and H-1 MRS measurements) can help in the physiological/metabolic interpretation of P-31 MRS studies by providing information about blood flow and oxygen delivery/utilisation. Our recommendations will assist in achieving the fullest possible reliable picture of muscle physiology and pathophysiology. Show less