SU-F-303-03: Auto-Alignment of 2D Cine Imaging Planes for Real-Time Motion Management During MRI-GRT

Abstract

Purpose: Spatial-temporal-contrast resolution tradeoffs preclude acquisition of real-time 3D MRI volumes for exception gating and target tracking. Consequently, acquisition of 2D imaging planes has been proposed. However, to minimize through-plane motion the orientation of the 2D imaging planes must be chosen appropriately. The goal of this work was to develop a methodology to auto-align 2D cine imaging planes for real-time cine imaging on MRI-gRT systems. Methods: Phase-resolved 4D MR images of a healthy volunteer set up in treatment position were acquired at 3T. Following offline reconstruction in MATLAB, the binned 4D MR images were transferred to MIM (MIM Software, Cleveland, OH). To simulate target, a contour of the right kidney was generated on the 0% phase image and then deformably propagated to the remaining nine respiratory phase images. Dynamic, 3D centroid motion of the kidney target was calculated at each respiratory phase. Principal component analysis was used to determine the eigenvectors of maximal kidney motion. Direction cosines required to orient a 2D cine imaging plane in the MR scanner coordinate system along the lines of maximal kidney motion were calculated. The direction cosines were applied on the MR scanner during acquisition of 2D cine images to capture kidney motion. Results: Deformable propagation of kidney contours across binned 4D MR images was possible. Kidney centroid motion ranged from 0.8mm, 5.5mm, and 14.5mm in the right/left, anterior/posterior, and superior/inferior dimensions, respectively. Direction cosines required to align 2D cine imaging planes were 75.7 and 12.3 degrees along the sagittal-coronal and sagittal-transverse planes. Conclusions: Auto-alignment of 2D cine imaging planes based on centroid motions derived from daily pre-treatment phase-resolved 4D MR images is a feasible approach for motion monitoring on MRI-gRT systems. Elekta Instruments, AB