title: Correction of geometric distortion in Propeller echo planar imaging using a modified reversed gradient approach.
abstract: OBJECTIVE
  This study investigates the application of a modified reversed gradient algorithm to the Propeller-EPI imaging method (periodically rotated overlapping parallel lines with enhanced reconstruction based on echo-planar imaging readout) for corrections of geometric distortions due to the EPI readout.
  
  
  METHODS
  Propeller-EPI acquisition was executed with 360-degree rotational coverage of the k-space, from which the image pairs with opposite phase-encoding gradient polarities were extracted for reversed gradient geometric and intensity corrections. The spatial displacements obtained on a pixel-by-pixel basis were fitted using a two-dimensional polynomial followed by low-pass filtering to assure correction reliability in low-signal regions. Single-shot EPI images were obtained on a phantom, whereas high spatial resolution T2-weighted and diffusion tensor Propeller-EPI data were acquired in vivo from healthy subjects at 3.0 Tesla, to demonstrate the effectiveness of the proposed algorithm.
  
  
  RESULTS
  Phantom images show success of the smoothed displacement map concept in providing improvements of the geometric corrections at low-signal regions. Human brain images demonstrate prominently superior reconstruction quality of Propeller-EPI images with modified reversed gradient corrections as compared with those obtained without corrections, as evidenced from verification against the distortion-free fast spin-echo images at the same level.
  
  
  CONCLUSIONS
  The modified reversed gradient method is an effective approach to obtain high-resolution Propeller-EPI images with substantially reduced artifacts.
authors: Brain Imaging and Analysis Center, Duke University Medical Center, Durham, North Carolina, USA; ; Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan;
authors: Hing-Chiu
authors: HC
authors: Chang
authors: Tzu-Chao
authors: TC
authors: Chuang
authors: Yi-Ru
authors: YR
authors: Lin
authors: Fu-Nien
authors: FN
authors: Wang
authors: Teng-Yi
authors: TY
authors: Huang
authors: Hsiao-Wen
authors: HW
authors: Chung
keywords: Correction of geometric distortion; Propeller-EPI imaging; modified reversed gradient approach
references: Med Phys. 2012 Aug;39(8):4896-902
references: 22894416
references: Quant Imaging Med Surg. 2011 Dec;1(1):11-6
references: 23256049
references: Magn Reson Med. 1999 Sep;42(3):585-90
references: 10467304
references: Invest Radiol. 2006 Oct;41(10):769-75
references: 16971801
references: Magn Reson Imaging. 2000 Jul;18(6):681-7
references: 10930777
references: J Magn Reson Imaging. 2012 Jun;35(6):1312-21
references: 22241685
references: Magn Reson Med. 2005 Nov;54(5):1232-40
references: 16206142
references: Radiology. 2009 Oct;253(1):144-52
references: 19789257
references: J Magn Reson Imaging. 2004 Apr;19(4):499-507
references: 15065175
references: Invest Radiol. 2009 Oct;44(10):656-61
references: 19724235
references: Magn Reson Med. 1999 Nov;42(5):963-9
references: 10542356
references: IEEE Trans Med Imaging. 1992;11(3):319-29
references: 18222873
references: Magn Reson Med. 2013 Mar 1;69(3):793-802
references: 22592941
references: Magn Reson Med. 2006 Dec;56(6):1352-8
references: 17051531
references: AJNR Am J Neuroradiol. 2003 May;24(5):794-8
references: 12748073
references: Quant Imaging Med Surg. 2012 Dec;2(4):254-65
references: 23289085
references: NMR Biomed. 2010 Aug;23(7):794-802
references: 20222149
references: AJR Am J Roentgenol. 2011 Aug;197(2):W307-13
references: 21785057
references: Magn Reson Imaging. 2011 Jun;29(5):712-6
references: 21531103
references: Magn Reson Med. 1999 Nov;42(5):952-62
references: 10542355
references: Magn Reson Med. 2006 Jun;55(6):1298-307
references: 16676335
references: Magn Reson Med. 2012 Jul;68(1):140-51
references: 22144227
references: Magn Reson Med. 1998 Feb;39(2):328-30
references: 9469719
references: Magn Reson Med. 2002 Jan;47(1):42-52
references: 11754441