1416

View Abstract / View Presentation

Stabilization of bias field on 3D MPRAGE at 7T with dielectric pads and 3D-based B1+ scaling

Giske Opheim¹, Vincent O. Boer², Esben Thade Petersen^2,3, Martin Prener¹, Olaf B. Paulson^1,4, and Jan Ole Pedersen⁵
¹Neurobiology Research Unit, Dept. of Neurology, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark, ²Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Hvidovre, Denmark, ³Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs. Lyngby, Denmark, ⁴Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark, ⁵Philips Healhtcare, Copenhagen, Denmark

The coefficient of variation (CV) of bias fields varied significantly between three different B1+ control approaches. A combination of large pads and 3D-based RF gain optimization yielded the smallest variations of CV, indicating increased stability.

Figure 1:

Two images to the left: Examples of B₁⁺ maps after 2D and 3D RF gain optimization from the same subject. The 2D gain optimization for this subject caused B₁⁺ of 160% in the center of the brain. The 3D optimization caused B₁⁺ of 140% (yellow arrows). The green arrows indicate lateral area typically presenting B₁-induced inhomogeneity whose severity vary particularly with head size and placement of dielectric pads.

Two right images: Example of a bias field corrected 3D MPRAGE image and the computed bias field. The red arrows demonstrates 40% MPRAGE magnitude variations.

Figure 2:

Plots showing variability of CV across the slices in the individual brainmasks for group 1 (black, n=48), group 2 (blue, n=29) and group 3 (red, n=18). The slice-indexing is feet-head, i.e. high numbers corresponds to the top of the head.