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Geometry – Key Points
• 1. System or scanner-related: B0 inhomogeneity,
gradient non-linearities
– Correction: with grid phantom + image processing
software
– Issues of system drift, system upgrades…
• 2. Patient or device-induced: susceptibility or
chemical shift (fat)
– Correction: a) numerical sims (our approach) and exp by
acquiring additional image data with diff parameters (e.g.,
reversed gradient).
– Magnitude: a few mm depending on the interface, worst
for air-soft tissue.
– distortion ~ Gr/Bo; where Gr is the readout gradient
strength and B0 main magnetic field.
Issues mitigated by individual CT reference check!