Alias subtraction more efficient than conventional zero-padding in the Fourier-based calculation of the susceptibility induced perturbation of the magnetic field in MR.
Forward calculation of the susceptibility induced field shift by Fourier-based procedures requires spatial zero-padding to prevent aliasing artifacts (periodic wrap-around). Padding with a factor of two gives accurate results, however, halves the maximal attainable resolution, and slows down the calculation, which may hamper the feasibility of real-time calculations. Herein is proposed to first perform the calculation at the original resolution--allowing aliasing-and to remove aliasing with an additional convolution in a lower resolution, to alleviate these restrictions regarding memory size and calculation speed, a procedure we termed "virtual" zero-padding. Virtual zero-padding was numerically and experimentally tested and validated with conventional zero-padding and the analytical solution (in the case of spheres) on several phantoms. A demonstration of the increased efficiency is given by implementing virtual zero-padding in a dynamic calculation procedure. The improved efficiency is expected to be relevant regarding the ongoing increase in spatial and temporal resolution in ultra-high-field MRI. Procedures are presented for circular convolution using the discrete Green's function and k-space filtering using the continuous Green's function.
Image Sciences Institute, University Medical Center Utrecht, The Netherlands.
Job G
JG
Bouwman
Chris J G
CJ
Bakker
D000465:Algorithms; D016477:Artifacts; D005583:Fourier Analysis; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013382:Subtraction Technique