Magnetic Resonance Imaging: Single Coil Sensitivity Mapping and Correction using Spatial Harmonics

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Magnetic Resonance Imaging Single Coil
Sensitivity Mapping and Correction using Spatial
Harmonics
Eric Peterson and Ryan Lipscomb ECE
533 12/15/2006
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Outline

• Motivation
• Inhomogeneous coil sensitivity
• Theory
• Methods
• Spatial Harmonics
• Results

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Motivation
Flexible Torso Coil from Toshiba
Sensitivity profile of a circular phantom using
two coils (top and left)
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Motivation

• Due to the inhomogeneous and varying sensitivity
  of the vest coil the images vary

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Theory
Image degradation model
Spatial Harmonics equation
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Methods

• Parallel imaging uses spatial harmonics to define
  the coil sensitivity map
• Use low frequency spatial harmonics to define the
  sensitivity map
• Filter the image and the sensitivity map
• Invert the sensitivity map and apply it to the
  image

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Image Input
Find noise threshold with a user defined ROI
Key
Split noise and signal portions of the image
Original image
Crop
Crop
Noise only portions of the original image
FFT
Signal only portions of the original image
Select number of harmonics
IFFT
Sensitivity map
Invert and set minimum gain to 1
Inverse sensitivity map
Attenuate inverse map using a user defined
triangular filter
Corrected Image
Multiply the inverse map to the image to get the
corrected image
Normalize the means of the original and corrected
images
Output Corrected Image with Noise
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Results
Corrected
Original
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Results
Corrected
Original
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Results
Absolute difference between ADC images before and
after correction
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Conclusion

• This method does a good job of intensity
  normalization
• Preserves high frequency data
• The major limitation is due by high frequency
  components of the lung such as trachea

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References

• Bydder M, Larkman DJ, Hajnal JV. Generalized
  SMASH imaging. Magn Reson Med 200247160-170
• Sodickson DK, Manning WJ. Simultaneous
  acquisition of spatial harmonics (SMASH) fast
  imaging with radiofrequency coil arrays. Magn
  Reson Med 199738591-603
• Griswold MA, Jakob PM, Heidemann RM, Nittka M,
  Jellus V, Wang J, Kiefer B, Haase A. Generalized
  Autocalibrating Partially Parallel Acquisitions
  (GRAPPA). Magn Reson Med 2002471202-1210
• Chen XJ, Moller HE, Chawla MS, Cofer GP, Driehuys
  B, Hedlund LW, Johnson GA. Spatially Resolved
  Measurements of Hyperpolarized Gas Properties in
  the Lung In Vivo. Part I Diffusion Coefficient.
  Magn Reson Med 199942721728