TH‐EF‐BRA‐11: Feasibility of Super‐Resolution Time‐Resolved 4DMRI for Multi‐Breath Volumetric Motion Simulation in Radiotherapy Planning

Abstract

Purpose:To develop a novel super‐resolution time‐resolved 4DMRI technique to evaluate multi‐breath, irregular and complex organ motion without respiratory surrogate for radiotherapy planning.Methods:The super‐resolution time‐resolved (TR) 4DMRI approach combines a series of low‐resolution 3D cine MRI images acquired during free breathing (FB) with a high‐resolution breath‐hold (BH) 3DMRI via deformable image registration (DIR). Five volunteers participated in the study under an IRB‐approved protocol. The 3D cine images with voxel size of 5×5×5 mm3 at two volumes per second (2Hz) were acquired coronally using a T1 fast field echo sequence, half‐scan (0.8) acceleration, and SENSE (3) parallel imaging. Phase‐encoding was set in the lateral direction to minimize motion artifacts. The BH image with voxel size of 2×2×2 mm3 was acquired using the same sequence within 10 seconds. A demons‐based DIR program was employed to produce super‐resolution 2Hz 4DMRI. Registration quality was visually assessed using difference images between TR 4DMRI and 3D cine and quantitatively assessed using average voxel correlation. The fidelity of the 3D cine images was assessed using a gel phantom and a 1D motion platform by comparing mobile and static images.Results:Owing to voxel intensity similarity using the same MRI scanning sequence, accurate DIR between FB and BH images is achieved. The voxel correlations between 3D cine and TR 4DMRI are greater than 0.92 in all cases and the difference images illustrate minimal residual error with little systematic patterns. The 3D cine images of the mobile gel phantom preserve object geometry with minimal scanning artifacts.Conclusion:The super‐resolution time‐resolved 4DMRI technique has been achieved via DIR, providing a potential solution for multi‐breath motion assessment. Accurate DIR mapping has been achieved to map high‐resolution BH images to low‐resolution FB images, producing 2Hz volumetric high‐resolution 4DMRI. Further validation and improvement are still required prior to clinical applications.This study is in part supported by the NIH (U54CA137788/U54CA132378).