A further decrease in FA was seen with higher-order correction in the unipolar sequence, since there were more substantial higher-order eddy currents in the unipolar sequence relative to the bipolar sequence. The MD was found to be more robust against eddy-currents compared to the FA in this isotropic phantom, since higher-order
correction did not result in significant changes in the MD in either the unipolar or bipolar sequence. Differing MD values between bipolar and unipolar buy Ruxolitinib sequences could have been because they were estimated at different TEs and result in different SNRs. In a truly isotropic phantom where FA is zero, noise results in an upward bias in the FA and a negative bias in the MD (due to an apparently
insufficient decay in the diffusion signal). In addition to noise, the positive bias in the measured FA could also have been caused by systemic errors including the calibration of the diffusion gradients, the possibility that the phantom did not truly have an FA of zero, or by the presence of mechanical find more motion. Although the same b-values were used for comparison between the unipolar and bipolar sequence, different waveforms resulting in different diffusion times could also have led to a different q-values, and hence, signal intensity. The use of minimum TEs in this study reflects how the sequences would be used in clinical practice. Comparison of eddy-current corrected images with affine image registration shows that eddy-current correction with phases from the field camera performs Florfenicol better than image registration. In the presence of higher-order eddy-current distortions, it was expected that affine image registration would leave residual misalignment artifacts. The ability to correct distortions with image registration will depend
on the anatomy of interest and the nature of the eddy-current distortions. The drawback of affine image registration is that even if the distortions can be aligned, the intensities may not be fully recovered. Image registration has been shown to be suboptimal for diffusion images that have significant contrast changes due to directional anisotropy [36] and [37]. Another disadvantage of image registration is SNR dependency. It was found that image registration performed better on diffusion images obtained at lower b-values than those at higher b-values where the SNR was low [38]. Eddy-current correction with the field camera is expected to perform well regardless of the SNR in the image. However, the drawback of eddy-current correction with the field camera is that extra hardware is required. It was found that performing the first step of the full iterative procedure (as described in Wilm et al. [20]), i.e., conjugate phase reconstruction, was adequate for removing bulk object shifts arising from higher-order terms.
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