Characterization of tissue magnetic susceptibility‐induced distortions for MRIgRT

Abstract

The susceptibility distortions were quantified as a function of multiple parameters such as the χ inhomogeneity size and shape, the magnitude of B(0) and the readout gradient, and the orientation of B(0) with respect to the sample geometry. The analysis was performed for several anatomical sites and corresponding to two B(0) orientations as featured by MR-linac systems.

Converting from CT- to MRI-only-based target definition in radiotherapy of localized prostate cancer

“…The susceptibly artefact in the 1.5 T MRI scanner is typically within 1 mm with an imaging gradient strength of 5 mT/m [20]. The estimated mean registration uncertainty was 1.3 mm.…”

Spatial Precision in Magnetic Resonance Imaging–Guided Radiation Therapy: The Role of Geometric Distortion

“…Magnetic susceptibility is a bulk property of a medium that describes the medium's capacity to become magnetized when placed in an applied magnetic field (58). A magnetic field influences the orbital angular momentum of electrons and the spins of electrons and nuclei.…”

“…the median magnitude of the maximum systeminduced geometric distortion is 3.0 mm, while Stanescu et al(58) obtained median magnitudes of the maximum patient-dependent geometric distortion of 0.38 mm at 0.5 T and 2.42 mm at 3.0 T (Table 2). Linearly interpolating these values for patient-dependent distortion to 1.5 T, the field strength used in the prototype MR-guided linear accelerator (123), one obtains a median magnitude of the maximum patient-induced geometric distortion of 1.20 mm.…”

Anatomic and dosimetric changes in patients with head and neck cancer treated with an integrated MRI-tri-60Co teletherapy device

“…higher magnetic field suffers larger geometric distortion and increased gradient strength results in reduced geometric distortion. As shown by Stanescu et al, 30 the maximum distortion at nasal sinus air cavities is about 0.6 mm for a 0.5-T magnetic field with a gradient strength of 5 mTm 21 . 30 The VR MRI system has a smaller magnetic field (0.35 T) with a much higher gradient strength (18 mTm 21 ).…”

“…As shown by Stanescu et al, 30 the maximum distortion at nasal sinus air cavities is about 0.6 mm for a 0.5-T magnetic field with a gradient strength of 5 mTm 21 . 30 The VR MRI system has a smaller magnetic field (0.35 T) with a much higher gradient strength (18 mTm 21 ). 25 It is reasonable to believe that the magnetic susceptibility-induced geometric distortion for the MRI system used in the study is not a major concern for contouring.…”