Review Article
The Role of Imaging in Radiation Therapy Planning: Past, Present, and Future
Table 2
Sources of MR distortion, correction, and method for assessment.
| Level of distortion | Distortion source | Distortion correction | Assessment of residual distortion |
| System | Gradient nonlinearity | Gradient coil design (HW) Model-based corrections (SW) | Geometric fidelity phantoms and assessment tools | Static field (B0) inhomogeneity | Magnet design and static-field shims (HW) | B0-field map in phantoms |
| Patient | Static-field (B0) inhomogeneity | Gradient-shim coils (HW) Patient-specific B0 field correction (SW) | B0-field map in the patient | Transmit-field (B1) inhomogeneity | Multiple RF transmit channels (HW) Patient-specific B1 field correction (SW) | B1-field map in the patient |
| Sequence | Gradient switching (eddy currents) | Gradient preemphasis (HW/SW) Protocols with low gradient slew rates (SW) | Visual inspection |
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