Poblador Rodriguez, E; Moser, P; Dymerska, B; Robinson, S; Schmitt, B; van der Kouwe, A; Gruber, S; ... Bogner, W; + view all Poblador Rodriguez, E; Moser, P; Dymerska, B; Robinson, S; Schmitt, B; van der Kouwe, A; Gruber, S; Trattnig, S; Bogner, W; - view fewer (2019) A comparison of static and dynamic ∆B0 mapping methods for correction of CEST MRI in the presence of temporal B0 field variations. Magnetic Resonance in Medicine 10.1002/mrm.27750. (In press).

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Abstract

Purpose: To assess the performance, in the presence of scanner instabilities, of three dynamic correction methods which integrate ∆B 0 mapping into the chemical exchange saturation transfer (CEST) measurement and three established static ∆B 0 -correction approaches. Methods: A homogeneous phantom and five healthy volunteers were scanned with a CEST sequence at 7 T. The in vivo measurements were performed twice: first with unaltered system frequency and again applying frequency shifts during the CEST acquisition. In all cases, retrospective voxel-wise ∆B 0 -correction was performed using one intrinsic and two extrinsic [prescans with dual-echo gradient-echo and water saturation shift referencing (WASSR)] static approaches. These were compared with two intrinsic [using phase data directly generated by single-echo or double-echo GRE (gradient-echo) CEST readout (CEST-GRE-2TE)] and one extrinsic [phase from interleaved dual-echo EPI (echo planar imaging) navigator (NAV-EPI-2TE)] dynamic ∆B 0 -correction approaches [allowing correction of each Z-spectral point before magnetization transfer ratio asymmetry (MTR asym) analysis]. Results: All three dynamic methods successfully mapped the induced drift. The intrinsic approaches were affected by the CEST labeling near water (∆ω < |0.3| ppm). The MTR asym contrast was distorted by the frequency drift in the brain by up to 0.21%/Hz when static ∆B 0 -corrections were applied, whereas the dynamic ∆B 0 corrections reduced this to <0.01%/Hz without the need of external scans. The CEST-GRE-2TE and NAV-EPI-2TE resulted in highly consistent MTR asym values with/without drift for all subjects. Conclusion: Reliable correction of scanner instabilities is essential to establish clinical CEST MRI. The three dynamic approaches presented improved the ∆B 0 -correction performance significantly in the presence of frequency drift compared to established static methods. Among them, the self-corrected CEST-GRE-2TE was the most accurate and straightforward to implement.

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