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SU‐G‐JeP2‐13: Spatial Accuracy Evaluation for Real‐Time MR Guided Radiation Therapy Using a Novel Large‐Field MRI Distortion Phantom
Author(s) -
Antolak A,
Bayouth J,
Bosca R,
Jackson E
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957033
Subject(s) - imaging phantom , nuclear medicine , distortion (music) , materials science , volume (thermodynamics) , cylinder , displacement (psychology) , biomedical engineering , physics , mathematics , geometry , medicine , psychology , amplifier , optoelectronics , cmos , quantum mechanics , psychotherapist
Purpose: Evaluate a large‐field MRI phantom for assessment of geometric distortion in whole‐body MRI for real‐time MR guided radiation therapy. Methods: A prototype CIRS large‐field MRI distortion phantom consisting of a PMMA cylinder (33 cm diameter, 30 cm length) containing a 3D‐printed orthogonal grid (3 mm diameter rods, 20 mm apart), was filled with 6 mM NiCl 2 and 30 mM NaCl solution. The phantom was scanned at 1.5T and 3.0T on a GE HDxt and Discovery MR750, respectively, and at 0.35T on a ViewRay system. Scans were obtained with and without 3D distortion correction to demonstrate the impact of such corrections. CT images were used as a reference standard for analysis of geometric distortion, as determined by a fully automated gradient‐search method developed in Matlab. Results: 1,116 grid points distributed throughout a cylindrical volume 28 cm in diameter and 16 cm in length were identified and analyzed. With 3D distortion correction, average/maximum displacements for the 1.5, 3.0, and 0.35T systems were 0.84/2.91, 1.00/2.97, and 0.95/2.37 mm, respectively. The percentage of points with less than (1.0, 1.5, 2.0 mm) total displacement were (73%, 92%, 97%), (54%, 85%, 97%), and (55%, 90%, 99%), respectively. A reduced scan volume of 20 × 20 × 10 cm 3 (representative of a head and neck scan volume) consisting of 420 points was also analyzed. In this volume, the percentage of points with less than (1.0, 1.5, 2.0 mm) total displacement were (90%, 99%, 100%), (63%, 95%, 100%), and (75%, 96%, 100%), respectively. Without 3D distortion correction, average/maximum displacements were 1.35/3.67, 1.67/4.46, and 1.51/3.89 mm, respectively. Conclusion: The prototype large‐field MRI distortion phantom and developed software provide a thorough assessment of 3D spatial distortions in MRI. The distortions measured were acceptable for RT applications, both for the high field strengths and the system configuration developed by ViewRay.