ANTHEM: anatomically tailored hexagonal MRI.
OBJECTIVE
This study aimed to investigate the use of anatomically tailored hexagonal sampling for scan-time and error reduction in MRI.


METHODS
Anatomically tailored hexagonal MRI (ANTHEM), a method that combines hexagonal sampling with specific symmetry in anatomical geometry, is proposed. By using hexagonal sampling, aliasing artifacts are moved to regions where, due to the nature of the anatomy, aliasing is inconsequential. This can be used to either reduce scan time while maintaining spatial resolution or reduce residual errors in speedup techniques like UNFOLD and k-t BLAST/SENSE, which undersample k-space and unwrap fold-over artifacts during reconstruction. Computer simulations as well as phantom and volunteer studies were used to validate the theory. A simplified reconstruction algorithm for hexagonally sampled and subsampled k-space data was also used.


RESULTS
A reduction in sampling density of 13.4% and 25% in each hexagonally sampled dimension was achieved for spherical and conical geometries without aliasing or reduction in spatial resolution. Optimal subsampling schemes that can be utilized by UNFOLD and k-t BLAST/SENSE were derived using hexagonal subsampling, which resulted in maximal, isotropic dispersal of the aliases. In combination with UNFOLD, ANTHEM was shown to move residual aliasing artifacts to the corners of the field of view, yielding reduced artifacts in CINE reconstructions.


CONCLUSIONS
ANTHEM was successful in reducing acquisition time in conventional MRI and in reducing errors in UNFOLD imaging.
Saranathan
Manojkumar
M
Department of Electrical Engineering, Indian Institute of Science, Bangalore 560012, Karnataka, India. manojk@ee.iisc.ernet.in
Ramanan
Venkat
V
Gulati
Rakesh
R
Venkatesan
Ramesh
R
D000465:Algorithms; D016477:Artifacts; D003198:Computer Simulation; D006257:Head / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity