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Strategies for shimming the breast
Nimrod Maril1, Christopher M Collins, Robert L Greenman
1Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
Magnetic Resonance in Medicine
|October 12, 2005
Summary
Static magnetic field inhomogeneity in the human breast causes MRI artifacts. First-order shimming and spatial saturation pulses effectively correct these field variations, improving image quality.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Biomedical Engineering
- Medical Physics
Background:
- Static magnetic field inhomogeneity is a known issue in human breast imaging.
- This inhomogeneity degrades Magnetic Resonance Spectroscopy (MRS) and MRI data quality, causing artifacts like line broadening, frequency shifts, intensity loss, and spatial errors.
Purpose of the Study:
- To quantify regional variations in static magnetic field homogeneity in the human breast at 3 Tesla (T).
- To evaluate strategies for correcting these inhomogeneities, including shimming and spatial saturation pulses.
Main Methods:
- Measured static magnetic field at 3 T in human breast central planes using phase maps and multivoxel MRS.
- Assessed the impact of first-order and high-order shimming, and spatial saturation pulses on field homogeneity.
Main Results:
- The static magnetic field was primarily linear, showing a 300 Hz reduction from nipple to chest wall.
- First-order shimming reduced inhomogeneity by 65%.
- A combination of spatial saturation pulses and first-order shimming proved more effective than high-order shimming alone.
Conclusions:
- The study quantifies breast magnetic field inhomogeneity and demonstrates effective correction strategies.
- The combined approach of spatial saturation pulses and first-order shimming offers a practical solution for clinical scanners lacking advanced shimming capabilities, especially in the presence of fat.