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Fig. 2 | BMC Musculoskeletal Disorders

Fig. 2

From: Repeatability assessment of sodium (23Na) MRI at 7.0 T in healthy human calf muscle and preliminary results on tissue sodium concentrations in subjects with Addison’s disease

Fig. 2

Flowchart diagram shows post-processing steps for in vivo 23Na-MRI data. The local transmitter B1+ field was mapped with a phase-sensitive method [20] and external B0 field inhomogeneity correction was achieved by generating a data set with two different echo times from 23Na data. B0 and B1+ measurements were performed on a cylindrical homogeneous phantom which filled the coil completely and was scanned under the same geometrical conditions as study participants. The correction factors derived from the phantom and were applied on in vivo data. The muscle segmentation mask for the reference compartments (red-gastrocnemius medialis, green-soleus, yellow-tibialis anterior, blue-other muscles) is created based a high-resolution 1H acquisition and co-registered to the 23Na images. The structural information was used in combination with a simulated point spread function (PSF) to calculate the corresponding region-spread functions (RSF) via convolution [25]. For the PSF simulation and relaxation correction of the 23Na data sets, we used values that we obtained in healthy subjects. Colored bars show distribution of calculated region-spread function values in arbitrary units (a.u.)

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