Steven P Allen1, Xue Feng1, Samuel W Fielden2, Craig H Meyer1,3. 1. Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia. 2. Department of Imaging Science and Innovation, Geisinger, Danville, Pennsylvania. 3. Department of Radiology & Medical Imaging, University of Virginia, Charlottesville, Virginia.
Abstract
PURPOSE: Images acquired with spiral k-space trajectories can suffer from off-resonance image blur. Previous work showed that averaging 2 images acquired with a retraced, in/out (RIO) trajectory self-corrects image blur so long as off-resonant spins accrue less than 1 half-cycle of relative phase over the readout. Practical scenarios frequently exceed this threshold. Here, we derive and characterize a more-robust off-resonance image blur correction method for RIO acquisitions. METHODS: Phantom and human volunteer data were acquired using a RIO trajectory with readout durations ranging from 4 to 60 ms. The resulting images were deblurred using 3 candidate methods: conventional linear correction of the component images; semiautomatic deblurring of the component images using an established minimized phase objective function; and semiautomatic deblurring of the average of the component images using a maximized energy objective function, derived below. Deblurring errors were estimated relative to images acquired with 4 ms readouts. RESULTS: All 3 methods converged to similar solutions in cases where less than 2 and 4 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<13 ms readout at 3T). Above this threshold, the linear and minimized phase methods introduced several errors. The maximized energy function provided accurate deblurring so long as less than 6 and 10 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<34 ms readout at 3T). CONCLUSION: The maximized energy objective function can accurately deblur RIO acquisitions over a wide spectrum of off resonance frequencies.
PURPOSE: Images acquired with spiral k-space trajectories can suffer from off-resonance image blur. Previous work showed that averaging 2 images acquired with a retraced, in/out (RIO) trajectory self-corrects image blur so long as off-resonant spins accrue less than 1 half-cycle of relative phase over the readout. Practical scenarios frequently exceed this threshold. Here, we derive and characterize a more-robust off-resonance image blur correction method for RIO acquisitions. METHODS: Phantom and human volunteer data were acquired using a RIO trajectory with readout durations ranging from 4 to 60 ms. The resulting images were deblurred using 3 candidate methods: conventional linear correction of the component images; semiautomatic deblurring of the component images using an established minimized phase objective function; and semiautomatic deblurring of the average of the component images using a maximized energy objective function, derived below. Deblurring errors were estimated relative to images acquired with 4 ms readouts. RESULTS:All 3 methods converged to similar solutions in cases where less than 2 and 4 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<13 ms readout at 3T). Above this threshold, the linear and minimized phase methods introduced several errors. The maximized energy function provided accurate deblurring so long as less than 6 and 10 cycles of phase accrued over the readout in in vivo and phantom images, respectively (<34 ms readout at 3T). CONCLUSION: The maximized energy objective function can accurately deblur RIO acquisitions over a wide spectrum of off resonance frequencies.
Authors: Bénédicte M A Delattre; Robin M Heidemann; Lindsey A Crowe; Jean-Paul Vallée; Jean-Noël Hyacinthe Journal: Magn Reson Imaging Date: 2010-04-21 Impact factor: 2.546
Authors: Steven P Allen; Francesco Prada; Zhiyuan Xu; Jeremy Gatesman; Xue Feng; Helen Sporkin; Yekaterina Gilbo; Sydney DeCleene; Kim Butts Pauly; Craig H Meyer Journal: Magn Reson Med Date: 2020-11-11 Impact factor: 3.737