Physical Basis of Spatial Distortions in Magnetic Resonance Images

Peter Jezzard 1 Introduction 425

University of Oxford 2 Review of Image Formation 425

2.1 Nuclear Relaxation Times T1, T2

3 Hardware Imperfections 427

3.1 Gradient Coil Linearity • 3.2 Static Field Inhomogeneity • 3.3 Radio-Frequency Coil Inhomogeneity

4 Effects of Motion 429

4.1 Pulsatile Flow Effects • 4.2 Respiratory Motion • 4.3 Cardiac Motion • 4.4 Bulk Motion

5 Chemical Shift Effects 431

5.1 Implications for Conventional MRI • 5.2 Implications for Ultrafast MRI

6 Imperfect MRI Pulse Sequences 432

6.1 Truncation Artifacts • 6.2 Non-Steady-State Effects • 6.3 Unwanted NMR Echoes •

6.4 Signal Aliasing

7 fMRI Artifacts 435

7.1 Echo Planar Imaging and Spiral Imaging Artifacts • 7.2 Physiological Noise Effects

8 Concluding Remarks 437

References 437

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