Accelerating volumetric cine MRI (VC-MRI) using undersampling for real-time 3D target localization/tracking in radiation therapy: a feasibility study

Abstract

Purpose To accelerate volumetric cine MRI (VC-MRI) using undersampled 2D-cine MRI to provide real-time 3D guidance for gating/target tracking in radiotherapy. Methods 4D-MRI is acquired during patient simulation. One phase of the prior 4D-MRI is selected as the prior images, designated as MRIprior. The on-board VC-MRI at each time-step is considered a deformation of the MRIprior. The deformation field map (DFM) is represented as a linear combination of the motion components extracted by Principal Component Analysis (PCA) from the prior 4D-MRI. The weighting coefficients of the motion components are solved by matching the corresponding 2D-slice of the VC-MRI with the on-board undersampled 2D-cine MRI acquired. Undersampled Cartesian and radial k-space acquisition strategies were investigated. The effects of k-space sampling percentage (SP) and distribution, tumor sizes and noise on the VC-MRI estimation were studied. The VC-MRI estimation was evaluated using XCAT simulation of lung cancer patients and data from liver cancer patients. Volume Percent Difference (VPD), Center of Mass Shift (COMS) of the tumor volumes and tumor tracking errors were calculated. Results For XCAT, VPD/COMS were 11.93±2.37%/0.90±0.27mm and 11.53±1.47%/0.85±0.20mm among all scenarios with Cartesian sampling (SP=10%) and radial sampling (21spokes, SP=5.2%), respectively. When tumor size decreased, higher sampling rate achieved more accurate VC-MRI than lower sampling rate. VC-MRI was robust against noise levels up to SNR=20. For patient data, the tumor tracking errors in Superior-Inferior (SI), Anterior-Posterior (AP) and Lateral (LAT) directions were 0.46±0.20mm, 0.56±0.17mm and 0.23±0.16mm, respectively, for Cartesian-based sampling with SP=20% and 0.60±0.19mm, 0.56±0.22mm and 0.42±0.15mm, respectively, for radial-based sampling with SP=8% (32 spokes). Conclusions It is feasible to estimate VC-MRI from a single undersampled on-board 2D cine MRI. Phantom and patient studies showed that the temporal resolution of VC-MRI can potentially be improved by 5–10 times using a 2D cine image acquired with 10–20% k-space sampling.

Beyond T2 and 3T: New MRI techniques for clinicians

“…A motion model may be constructed from 4D MR or CT images, which can be acquired before therapy and the image data binned according to a measurement of the breathing cycle. As model input, 2D realtime images can be used to estimate 3D motion [214][215][216][217][218][219], to overcome slow MR image acquisitions [220] or system latencies using filters [221,222] or artificial neural networks [223,224].…”

Technical Note: Real‐time 3D MRI in the presence of motion for MRI‐guided radiotherapy: 3D Dynamic keyhole imaging with super‐resolution

“…Respiratory‐related tumor motion can be detected using time‐resolved 4D MRI and cine MRI . Time‐resolved 4D MRI provides high‐spatial resolution 3D MRI datasets with multiple respiratory amplitudes/phases.…”

“…11,12 Respiratory-related tumor motion can be detected using time-resolved 4D MRI and cine MRI. [13][14][15][16] Time-resolved 4D MRI provides high-spatial resolution 3D MRI datasets with multiple respiratory amplitudes/phases. For example, in motion studies, iterative reconstruction techniques in 4D MRI improved image quality while reducing motion artifacts.…”

A Novel method to generate on‐board 4D MRI using prior 4D MRI and on‐board kV projections from a conventional LINAC for target localization in liver SBRT

“…Previously, deformable image registration (DIR) has been used in the clinic for contouring and dose accumulation in adaptive radiation therapy . Recently, we have developed DIR based optimization algorithms to estimate on‐board limited angle 4D CBCT and volumetric cine MRI, respectively, using prior images and on‐board data acquired within the same modality . A previous method was also developed to use deformable motion reconstruction using x‐ray imaging for proton beam therapy .…”

“…[14][15][16][17][18][19] Recently, we have developed DIR based optimization algorithms to estimate on-board limited angle 4D CBCT and volumetric cine MRI, respectively, using prior images and on-board data acquired within the same modality. 5,7,20,21 A previous method was also developed to use deformable motion reconstruction using x-ray imaging for proton beam therapy. [22][23][24] However, at present, no method has been developed to use DIR, prior images, and on-boardlimited kV projections from a conventional LINAC to generate on-board multimodality images to improve the soft tissue localization accuracy for SBRT treatment.…”