Double quantum filtered 23Na 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 B0 in combination with B1 inhomogeneities alter the DQF‐MA signal intensity. We showed that, in the presence of B0 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 B0 = 3 T with a nominal spatial resolution of 12 × 12 × 36 mm3 within an acquisition time of TAcq < 10 min, and compared with spin density weighted (DW), as well as triple quantum filtration (TQF) 23Na 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 B0 and B1 inhomogeneities should be considered when interpreting DQF‐MA images.

ontrast-weighted images are commonly acquired in MRI, where one tissue-related parameter usually dominates the contrast, such as T1 or T2 weighting. Relative contrast differences across one image indicate different underlying tissue parameters, but this requires several sequences with different contrast weighting for a final diagnosis. These weighted contrasts provide only qualitative information, which limits the ability of qualitative MRI to depict mostly morphologic abnormalities. Pathologic conditions that alter tissue characteristics on a global or diffuse scale may be missed (1). Instead of indirectly visualizing tissue characteristics by using weighted contrasts, quantitative MRI attempts to directly measure them. Thereby, quantitative MRI could facilitate identification of physiologic changes that do not manifest themselves in morphologic changes or could help detect diffuse tissue changes (eg, in liver [2] and cardiac fibrosis [3]) that remain undetected by using qualitative MRI. It can provide more specific information than does qualitative MRI for characterizing pathologic conditions, such as multiple sclerosis (4) or brain tumors (5). Furthermore, quantitative MRI can be used to assess treatment response (6) or can aid in cases where no side comparison can be performed, such as hippocampal sclerosis (7). With quantitative MRI, diseases can be detected before gross morphologic

Background Studies on intravoxel incoherent motion (IVIM) imaging are carried out with different acquisition protocols. Purpose To investigate the dependence of IVIM parameters on the B0 field strength when using a bi‐ or triexponential model. Study Type Prospective. Study Population 20 healthy volunteers (age: 19–28 years). Field Strength/Sequence Volunteers were examined at two field strengths (1.5 and 3T). Diffusion‐weighted images of the abdomen were acquired at 24 b‐values ranging from 0.2 to 500 s/mm2. Assessment ROIs were manually drawn in the liver. Data were fitted with a bi‐ and a triexponential IVIM model. The resulting parameters were compared between both field strengths. Statistical Tests One‐way analysis of variance (ANOVA) and Kruskal–Wallis test were used to test the obtained IVIM parameters for a significant field strength dependency. Results At b‐values below 6 s/mm2, the triexponential model provided better agreement with the data than the biexponential model. The average tissue diffusivity was D = 1.22/1.00 μm2/msec at 1.5/3T. The average pseudodiffusion coefficients for the biexponential model were D* = 308/260 μm2/msec at 1.5/3T; and for the triexponential model D1* = 81.3/65.9 μm2/msec, D2* = 2453/2333 μm2/msec at 1.5/3T. The average perfusion fractions for the biexponential model were f = 0.286/0.303 at 1.5/3T; and for the triexponential model f1 = 0.161/0.174 and f2 = 0.152/0.159 at 1.5/3T. A significant B0 dependence was only found for the biexponential pseudodiffusion coefficient (ANOVA/KW P = 0.037/0.0453) and tissue diffusivity (ANOVA/KW: P < 0.001). Data Conclusion Our experimental results suggest that triexponential pseudodiffusion coefficients and perfusion fractions obtained at different field strengths could be compared across different studies using different B0. However, it is recommended to take the field strength into account when comparing tissue diffusivities or using the biexponential IVIM model. Considering published values for oxygenation‐dependent transversal relaxation times of blood, it is unlikely that the two blood compartments of the triexponential model represent venous and arterial blood. Level of Evidence: 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:1883–1892.

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