TH‐EF‐BRA‐08: A Novel Technique for Estimating Volumetric Cine MRI (VC‐MRI) From Multi‐Slice Sparsely Sampled Cine Images Using Motion Modeling and Free Form Deformation

Abstract

Purpose:To develop a technique to estimate on‐board VC‐MRI using multi‐slice sparsely‐sampled cine images, patient prior 4D‐MRI, motion‐modeling and free‐form deformation for real‐time 3D target verification of lung radiotherapy.Methods:A previous method has been developed to generate on‐board VC‐MRI by deforming prior MRI images based on a motion model(MM) extracted from prior 4D‐MRI and a single‐slice on‐board 2D‐cine image. In this study, free‐form deformation(FD) was introduced to correct for errors in the MM when large anatomical changes exist. Multiple‐slice sparsely‐sampled on‐board 2D‐cine images located within the target are used to improve both the estimation accuracy and temporal resolution of VC‐MRI. The on‐board 2D‐cine MRIs are acquired at 20–30frames/s by sampling only 10% of the k‐space on Cartesian grid, with 85% of that taken at the central k‐space. The method was evaluated using XCAT(computerized patient model) simulation of lung cancer patients with various anatomical and respirational changes from prior 4D‐MRI to onboard volume. The accuracy was evaluated using Volume‐Percent‐Difference(VPD) and Center‐of‐Mass‐Shift(COMS) of the estimated tumor volume. Effects of region‐of‐interest(ROI) selection, 2D‐cine slice orientation, slice number and slice location on the estimation accuracy were evaluated.Results:VCMRI estimated using 10 sparsely‐sampled sagittal 2D‐cine MRIs achieved VPD/COMS of 9.07±3.54%/0.45±0.53mm among all scenarios based on estimation with ROI_MM‐ROI_FD. The FD optimization improved estimation significantly for scenarios with anatomical changes. Using ROI‐FD achieved better estimation than global‐FD. Changing the multi‐slice orientation to axial, coronal, and axial/sagittal orthogonal reduced the accuracy of VCMRI to VPD/COMS of 19.47±15.74%/1.57±2.54mm, 20.70±9.97%/2.34±0.92mm, and 16.02±13.79%/0.60±0.82mm, respectively. Reducing the number of cines to 8 enhanced temporal resolution of VC‐MRI by 25% while maintaining the estimation accuracy. Estimation using slices sampled uniformly through the tumor achieved better accuracy than slices sampled non‐uniformly.Conclusions:Preliminary studies showed that it is feasible to generate VC‐MRI from multi‐slice sparsely‐sampled 2D‐cine images for real‐time 3D‐target verification.This work was supported by the National Institutes of Health under Grant No. R01‐CA184173 and a research grant from Varian Medical Systems.