Geometric accuracy of the MR imaging techniques in the presence of motion

Abstract

Magnetic Resonance Imaging (MRI) is increasingly being used for improving tumor delineation and tumor tracking in the presence of respiratory motion. The purpose of this work is to design and build an MR compatible motion platform and to use it for evaluating the geometric accuracy of MR imaging techniques during respiratory motion. The motion platform presented in this work is composed of a mobile base made up of a flat plate and four wheels. The mobile base is attached from one end and through a rigid rod to a synchrony motion table by Accuray® placed at the end of the MRI table and from the other end to an elastic rod. The geometric accuracy was measured by placing a control point‐based phantom on top of the mobile base.In‐house software module was used to automatically assess the geometric distortion. The blurring artifact was also assessed by measuring the Full Width Half Maximum (FWHM) of each control point. Our results were assessed for 50, 100, and 150 mm radial distances, with a mean geometric distortion during the superior–inferior motion of 0.27, 0.41, and 0.55 mm, respectively. Adding the anterior–posterior motion, the mean geometric distortions increased to 0.4, 0.6, and 0.8 mm. Blurring was observed during motion causing an increase in the FWHM of ≈30%. The platform presented in this work provides a valuable tool for the assessment of the geometric accuracy and blurring artifact for MR during motion. Although the main objective was to test the spatial accuracy of an MR system during motion, the modular aspect of the presented platform enables the use of any commercially available phantom for a full quality control of the MR system during motion.

Digital phantoms for evaluating the dosimetric Impact of MRI Geometric inaccuracy in SBRT planning for liver cancer in the presence of motion

“…The MR geometric distortion as well as blurring artifacts during motion presented in this study were measured and reported in our earlier study [36]. In that study, Axial, sagittal and coronal Cine MR slices acquisitions of an in-house motion phantom were compared with the CT images using our in-house developed software.…”

“…In this current work, we present a methodology for the development of digital phantoms used in order to investigate the dosimetric impact of MR system-related inaccuracy during motion on treatment plans in an MR-only workflow. MR distortion maps as well as blurring artifacts calculated in our previous work [36] were used to deform different type of digital phantoms. Dose plans were initially generated and optimized on the distorted datasets and then transferred to the original datasets to calculate new dose distributions and to study the MR geometric inaccuracy impact on dose-volume histograms (DVHs).…”

MRI-guidance for motion management in external beam radiotherapy: current status and future challenges

“…Moreover, it is also important to note that MRI suffers from geometrical distortion which could affect MRI-based dose calculation and organ motion quantification. This aspect was reviewed in Schmidt and Payne (2015) and, to our knowledge, just one publication has been reported dealing with moving organs (Torfeh et al 2018). Effects of geometrical distortion are outside the scope of this review but require additional evaluation on the accuracy of MRI for treatment guidance and protocols should be defined to account for these uncertainties.…”