ESTRO 2020 Abstract book

S442 ESTRO 2020

OC-0712 Improvement of respiratory motion monitoring using SENSE and Compressed SENSE for MR- guided RT Y. Ho 1 , O.L. Wong 1 , J. Yuan 1 , Y. Zhou 1 , K.Y. Cheung 1 , S.K. Yu 1 1 Hong Kong Sanatorium & Hospital, Medical Physics & Research Department, Hong Kong, Hong Kong SAR China Purpose or Objective Orthogonal-cine MRI based on balanced steady-state free precession (b-SSFP) sequence is utilized in MR-guided radiotherapy as an organ motion monitoring (MM) tool. High temporal resolution would compromise image quality (IQ) in real-time MM. SENSE acceleration (P) and recently developed Compressed SENSE acceleration (CS) techniques allow fast imaging based on parallel imaging in image domain and data sparsity in k-space respectively. In this study, task-based IQ (TIQ) and perceived IQ (PIQ) were assessed to explore improvement of respiratory MM protocol using P and CS acceleration techniques. Material and Methods 9 sets of free breathing abdominal cine MRI with 300 dynamics were acquired for each of 5 healthy adult volunteers on a 1.5T MR-simulator in axial and coronal planes. Reference images were based on the vendor- default b-SSFP sequence in a 1.5 T MR-Linac without P or CS applied (TR/TE = 2.9/1.45 ms, FOV = 400 × 424 mm 2 , acquisition voxel size = 3 x 3 x 5 mm 3 , 1.2 fps). P images and CS images were acquired separately with acceleration factors 2 (2.2 fps), 3 (3.3 fps), 4 (4.2 fps) and 5 (5.1 fps) applied. All image sets were rated by 3 MRI specialists in a single-blinded randomised fashion using fixed-point scale (1 - 5: totally unacceptable – totally acceptable). TIQ scores were rated based on organ edge sharpness and anatomical details visibility for the task of motion monitoring. PIQ scores were rated based on IQ aspects including noise level, banding artefact, motion artefact and saturation artefact. P and CS scores were compared using two-sample t -test. Interrater reliability was calculated by intraclass correlation coefficient (ICC) using ICC(3, k ) model defined by Shrout and Fleiss. Results The mean scores for TIQ and PIQ for the reference, P and CS image sets were reported in Table 1. TIQ and PIQ scores decreased monotonically as P or CS factors increased. The results suggested that acceleration factor up to 3 may be used without having unacceptable TIQ for the defined MM tasks as compared to the reference sequence, in which the frame rate could be increased by up to 2.8 times yielding higher temporal resolution. A severe degradation on TIQ and PIQ was observed when P or CS factors 5 was applied. In this qualitative IQ assessment, no statistically significant difference was found on the TIQ and PIQ scores between P and CS techniques ( p = 0.128) at 0.05 level of significance. ICC of TIQ scores for organ edge sharpness and anatomical details visibility were 0.76 (95% CI: 0.67- 0.84) and 0.84 (95% CI: 0.78-0.89) respectively, indicated a moderate to good interrater reliability. ICC of PIQ scores ranged from 0.38 to 0.92.

Conclusion Using SENSE and Compressed SENSE acceleration techniques, improvement in shortening the dynamic scan time can be achieved for rapid morphological imaging with acceptable task-oriented image quality as compared to the vendor-default motion monitoring MR sequence in the MR- Linac.