Comparative evaluation of the polynomial and spline fitting methods for the B0 correction of CEST MRI data acquired from human brains

To compare the magnetization transfer ratio asymmetry (MTRasym) values calculated with polynomial and spline fitting methods for B0 correction of the full Z‐spectrum images, full Z‐spectrum data was obtained from 12 elderly healthy subjects by using a 3D segmented EPI sequence, as well as from 17 other subjects by using a 3D GRASE sequence with two different 3 T MRI systems. The full Z‐spectra were analyzed to map MTRasym with three different fitting methods, namely the 10th and 14th polynomial and spline methods, for B0 correction. The MTRasym values for each offset frequency were compared among the three fitting methods. For the 3D segmented EPI sequence, the MTRasym values significantly differed among the three fitting methods at 0.86, 2.14, 3.00, and 3.43 ppm offset frequencies. For the 3D GRASE sequence, the MTRasym values obtained by 14th polynomial and spline fitting methods significantly differed at arbitrary offset frequencies. The MTRasym values are sensitive to the fitting methods of B0 correction and to the type of acquisition sequence for the full Z‐spectrum. Therefore, an appropriate fitting method should be used to analyze the full Z‐spectrum obtained from the brain.