Artifacts in MRI
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The document summarizes common artifacts seen in MRI imaging including wrap around artifacts caused by a small field of view, partial volume artifacts from thick slices, chemical shift misregistration from misaligned water and fat signals, and motion-induced ghosts from patient movement during scanning. It provides examples and explanations of each artifact type as well as potential corrections.
Artifacts in MRI
- 1. Artifacts in MRI BY Arun A Dr.Shaji’s MRI Perinthalmanna
- 2. Common Artifacts Wrap around Partial volume Chemical shift mis registration Chemical shift edge cancellation Truncation Motion induced ghost Zipper Corduroy appearance Susceptibility Cross excitation Sub optimal fat saturation Magic angle Eddy current Others
- 3. WRAPAROUND CAUSE FOV too small for body part CORRECTION Sample data sufficient for a larger FOV Use of local coil to reduce sensitivity of tissue outside image APPEARANCE Body parts extends beyond one edge of image and is projected at the opposite side Show Images
- 4. PARTIAL VOLUME CAUSE More than one tissue is included with in a voxel Usually because of thick slices CORRECTION Increase spatial resolution (particularly in the slice direction ) APPEARANCE Edge of structure contain tissues from two adjacent slices Show Images
- 5. CHEMICAL SHIFT MISREGISTRATION CAUSE Water and fat are misregistered relative to each other CORRECTION Increase sampling Bandwidth per pixel APPEARANCE Bright band on one slice dark band on other side of water structure surrounded fat along the frequency- encoded axis Show Images
- 6. CHEMICAL SHIFT EDGE CANCELLATION CAUSE Water and lipid signals in a voxel at fat – water interfaces destructively CORRECTION Use spin echo or In phase gradient echo technique Suppress lipid signal intensity APPEARANCE Black line at fat–water interfaces Show Images
- 7. TRUNCATION CAUSE Abrupt ,high contrast boundaries cannot be accurately represented by Fourier Transform CORRECTION Increase spatial resolution APPEARANCE Ring –down artifact at high contrast interfaces Show Images
- 8. MOTION INDUCED GHOST CAUSE Motion causes phases changes during signal sampling Or intensity changes b/w signals Both result in phase encoding errors CORRECTION Average multiple signals Complete image acquisition rapidly Trigger acquisitions so the image anatomy is constant from view to view Balance gradients to eliminate gradient moment Reduce signal of moving tissue APPEARANCE Repetitive patterned noise that resembles the source structure Repeated at regular intervals along phase encoding axis Show Images
- 9. ZIPPER CAUSE Nondecayed transverse magnetization RF feed through Or extraneous noise CORRECTION Improve spoiling of transverse magnetization Alternate polarity of excitation pulses Eliminate source of noise APPEARANCE Band of alternative white and black dots Show Images
- 10. CORDUROY APPEARANCE CAUSE Bad data points CORRECTION Increase sapling of k-space APPEARANCE Corduroy appearance across some images
- 11. SUSCEPTIBILITY CAUSE Magnetic field altered by heterogeneous magnetic properties in body part CORRECTION Eliminate source of heterogeneous susceptibility Maximize sampling bandwidth Minimize TE Refocus echoes APPEARANCE Signal loss Distortion Show Images
- 12. CROSS EXITATION CAUSE RF pulse targeted to one slice particularly excites an adjacent slice CORRECTION Use gap b/t slices in 2D multislice acquisitions Allow sufficient time for recovery b/w radial overlapping slice acquisitions APPEARANCE Reduced signal intensity
- 13. SUBOPTIMAL FAT SATURATION CAUSE Magnetic field heterogeneity causes the lipid resonance to vary within the field of view so the fat suppression RF pulse doesn't correspond to all lipid CORRECTION Improve magnetic field shimming Improve tuning of fat suppression pulse APPEARANCE increased signal intensity on lipid Possibly suppression of water signal
- 14. MAGIC ANGLE CAUSE T2 of oriented fibers depends on angle relative to magnetic field CORRECTION Use sufficiently long TE for structure to have long signal intensity regardless of angle APPEARANCE variable signal intensity on of tendons and other structures Show Images
- 15. EDDY CURRENT CAUSE Electrical currents caused by rapidly switching gradients CORRECTION Improve precision of gradient pulses Use eddy current compensation APPEARANCE Reduced peripheral signal intensity Show Images
- 16. OTHERS In homogeneity on fat sat Annefect Gradient amplifier failure Spike noise Spatial saturation Out of slice contamination
- 17. Wrap around NEXT IMAGE
- 18. wraparound
- 19. Partial volume 3 mm Partial volume 3 mm 10 mm A partial volume artifact is any artifact which is caused by the size of the image voxel.
- 20. Chemicals shift NEXT IMAGE
- 21. Chemicals shift
- 23. Motion
- 24. Metal object/susceptibility NEXT IMAGE
- 26. Eddy current Metal object/susceptibility
- 28. ZIPPER
- 32. In homogeneity on fat sat NEXT IMAGE Truncation
- 34. Gradient amplifier failure NEXT IMAGE
- 35. Spike noise NEXT IMAGE Annefect
- 36. Spike noise NEXT IMAGE Annefect
- 37. Spatial saturation NEXT IMAGE Annefect
- 38. Out of slice contamination