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Zusammenfassung:
Purpose/Introduction: In whole-body MR/PET, the limitation of an MR-based axial field-of-view (FoV) due to B0 inhomogeneities and gradient nonlinearities
[1,2] may cause a truncation of the MR data and has therefore potential impact on the attenuation correction [3]. Furthermore, a large FoV may also be relevant in MR-based interventional applications, e.g. radiotherapy
and biopsy. Recently, the feasibility of an axial extension of the MR-based FoV using a gradient field that compensates the B0 inhomogeneities has been shown [4]. However, the optimal gradient strength is space-dependent and therefore does not achieve optimal distortion reduction in all slices. In this work we developed a multislice 2D spin-echo-based sequence that calculates and adapts the readout (RO) gradient for each slice position automatically and offers an extended FoV in multiple slices during one single scan.
Subjects and Methods: Distortions due to B0 inhomogeneities and gradient nonlinearities in 2DFT SE frequency encoding can be reduced by using an adapted space-dependent readout gradient:
GRO (x,y,z) = - δB0(x,y,z) / c(x,y,z), where δB0 is the B0 inhomogeneity and c is the relative error in the gradient field. Field deviations in the main magnetic field and the gradient field were quantified as described in [4]. A multislice 2D spin-echo-based sequence was developed to calculate and adapt the optimal
RO gradient strength and polarity for each slice position automatically (Fig. 1).
