Double quantum filtered ²³Na MRI with magic angle excitation of human skeletal muscle in the presence of B₀ and B₁ inhomogeneities

Double quantum filtered 23 Na MRI with magic angle excitation (DQF‐MA) can be used to selectively detect sodium ions located within anisotropic structures such as muscle fibers. It might therefore be a promising tool to analyze the microscopic environment of sodium ions, for example in the context of osmotically neutral sodium retention. However, DQF‐MA imaging is challenging due to various signal dependences, on both measurement parameters and external influences. The aim of this work was to examine how B 0 in combination with B 1 inhomogeneities alter the DQF‐MA signal intensity. We showed that, in the presence of B 0 inhomogeneities, flip angle schemes with only one 54.7° pulse can be favorable compared with the classical 90°‐54.7°‐54.7° scheme. DQF‐MA images of the human lower leg were acquired at B 0 = 3 T with a nominal spatial resolution of 12 × 12 × 36 mm 3 within an acquisition time of T Acq < 10 min, and compared with spin density weighted (DW), as well as triple quantum filtration (TQF) 23 Na images. We found mean normalized signal‐to‐noise ratios of TQF/DW = 13.7 ± 2.3% (tibialis anterior), 11.9 ± 2.3% (soleus) and 11.4 ± 2.2% (gastrocnemius medialis), as well as DQF‐MA/DW = 4.7 ± 1.1% (tibialis anterior), 3.3 ± 0.73% (soleus) and 3.4 ± 0.6% (gastrocnemius medialis). These ratios might serve as additional measures in future clinical studies of sodium retention within human skeletal muscle. However, the influence of B 0 and B 1 inhomogeneities should be considered when interpreting DQF‐MA images.