Comparison of Image Distortion between Three Magnetic Resonance Imaging Systems of Different Magnetic Field Strengths for Use in Stereotactic Irradiation of Brain

Abstract

In this study, we evaluated the image distortion of three magnetic resonance imaging (MRI) systems with magnetic field strengths of 0.4 T, 1.5 T and 3 T, during stereotactic irradiation of the brain. A quality assurance phantom for MRI image distortion in radiosurgery was used for these measurements of image distortion. Images were obtained from a 0.4-T MRI (APERTO Eterna, HITACHI), a 1.5-T MRI (Signa HDxt, GE Healthcare) and a 3-T MRI (Signa HDx 3.0 T, GE Healthcare) system. Imaging sequences for the 0.4-T and 3-T MRI were based on the 1.5-T MRI sequence used for stereotactic irradiation in the clinical setting. The same phantom was scanned using a computed tomography (CT) system (Aquilion L/B, Toshiba) as the standard. The results showed mean errors in the Z direction to be the least satisfactory of all the directions in all results. The mean error in the Z direction for 1.5-T MRI at －110 mm in the axial plane showed the largest error of 4.0 mm. The maximum errors for the 0.4-T and 3-T MRI were 1.7 mm and 2.8 mm, respectively. The errors in the plane were not uniform and did not show linearity, suggesting that simple distortion correction using outside markers is unlikely to be effective. The 0.4-T MRI showed the lowest image distortion of the three. However, other items, such as image noise, contrast and study duration need to be evaluated in MRI systems when applying frameless stereotactic irradiation.

Review of potential improvements using MRI in the radiotherapy workflow

“…Although higher field strength corresponds to a relatively higher geometrical distortion as demonstrated by Takemura et al [41], 3.0 T imaging units still are the best currently available and suitable machines for frameless image acquisition for stereotactic treatments. Geometrical and target localisation were investigated in depth on 3.0 T scanners by MacFadden [42]; Zhang et al [43] proposed an optimized protocol in 3.0 T acquisitions for stereotactic therapy, thus firmly establishing this field strength for RTP use, when available.…”