title: Is your system calibrated? MRI gradient system calibration for pre-clinical, high-resolution imaging.
abstract: High-field, pre-clinical MRI systems are widely used to characterise tissue structure and volume in small animals, using high resolution imaging. Both applications rely heavily on the consistent, accurate calibration of imaging gradients, yet such calibrations are typically only performed during maintenance sessions by equipment manufacturers, and potentially with acceptance limits that are inadequate for phenotyping. To overcome this difficulty, we present a protocol for gradient calibration quality assurance testing, based on a 3D-printed, open source, structural phantom that can be customised to the dimensions of individual scanners and RF coils. In trials on a 9.4 T system, the gradient scaling errors were reduced by an order of magnitude, and displacements of greater than 100 µm, caused by gradient non-linearity, were corrected using a post-processing technique. The step-by-step protocol can be integrated into routine pre-clinical MRI quality assurance to measure and correct for these errors. We suggest that this type of quality assurance is essential for robust pre-clinical MRI experiments that rely on accurate imaging gradients, including small animal phenotyping and diffusion MR.
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: O'Callaghan
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: Jack
authors.initials: J
authors.lastname: Wells
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom; UCL Centre for Medical Image Computing, London, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Richardson
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: Holly
authors.initials: H
authors.lastname: Holmes
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: Yichao
authors.initials: Y
authors.lastname: Yu
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Walker-Samuel
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom; UCL Centre for Medical Image Computing, London, United Kingdom.
authors.forename: Bernard
authors.initials: B
authors.lastname: Siow
authors.affiliation: UCL Centre for Advanced Biomedical Imaging, Division of Medicine, London, United Kingdom.
authors.forename: Mark F
authors.initials: MF
authors.lastname: Lythgoe
mesh_terms: D002138:Calibration; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging