title: Four dimensional magnetic resonance imaging with retrospective k-space reordering: a feasibility study.
abstract: OBJECTIVE
  Current four dimensional magnetic resonance imaging (4D-MRI) techniques lack sufficient temporal/spatial resolution and consistent tumor contrast. To overcome these limitations, this study presents the development and initial evaluation of a new strategy for 4D-MRI which is based on retrospective k-space reordering.
  
  
  METHODS
  We simulated a k-space reordered 4D-MRI on a 4D digital extended cardiac-torso (XCAT) human phantom. A 2D echo planar imaging MRI sequence [frame rate (F) = 0.448 Hz; image resolution (R) = 256 × 256; number of k-space segments (NKS) = 4] with sequential image acquisition mode was assumed for the simulation. Image quality of the simulated "4D-MRI" acquired from the XCAT phantom was qualitatively evaluated, and tumor motion trajectories were compared to input signals. In particular, mean absolute amplitude differences (D) and cross correlation coefficients (CC) were calculated. Furthermore, to evaluate the data sufficient condition for the new 4D-MRI technique, a comprehensive simulation study was performed using 30 cancer patients' respiratory profiles to study the relationships between data completeness (Cp) and a number of impacting factors: the number of repeated scans (NR), number of slices (NS), number of respiratory phase bins (NP), NKS, F, R, and initial respiratory phase at image acquisition (P0). As a proof-of-concept, we implemented the proposed k-space reordering 4D-MRI technique on a T2-weighted fast spin echo MR sequence and tested it on a healthy volunteer.
  
  
  RESULTS
  The simulated 4D-MRI acquired from the XCAT phantom matched closely to the original XCAT images. Tumor motion trajectories measured from the simulated 4D-MRI matched well with input signals (D = 0.83 and 0.83 mm, and CC = 0.998 and 0.992 in superior-inferior and anterior-posterior directions, respectively). The relationship between Cp and NR was found best represented by an exponential function (CP=1001-e(-0.18NR) , when NS = 30, NP = 6). At a CP value of 95%, the relative error in tumor volume was 0.66%, indicating that NR at a CP value of 95% (NR,95%) is sufficient. It was found that NR,95% is approximately linearly proportional to NP (r = 0.99), and nearly independent of all other factors. The 4D-MRI images of the healthy volunteer clearly demonstrated respiratory motion in the diaphragm region with minimal motion induced noise or aliasing.
  
  
  CONCLUSIONS
  It is feasible to generate respiratory correlated 4D-MRI by retrospectively reordering k-space based on respiratory phase. This new technology may lead to the next generation 4D-MRI with high spatiotemporal resolution and optimal tumor contrast, holding great promises to improve the motion management in radiotherapy of mobile cancers.
authors: Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710.
authors: Yilin
authors: Y
authors: Liu
authors: Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710.
authors: Fang-Fang
authors: FF
authors: Yin
authors: Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710 and Brain Imaging and Analysis Center, Duke University Medical Center, Box 2737, Hock Plaza, Durham, North Carolina 27710.
authors: Nan-kuei
authors: NK
authors: Chen
authors: Brain Imaging and Analysis Center, Duke University Medical Center, Box 2737, Hock Plaza, Durham, North Carolina 27710.
authors: Mei-Lan
authors: ML
authors: Chu
authors: Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710.
authors: Jing
authors: J
authors: Cai
mesh_terms: D005240:Feasibility Studies; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012189:Retrospective Studies
references: NMR Biomed. 2002 Apr;15(2):174-83
references: 11870913
references: Med Phys. 2003 Jun;30(6):1254-63
references: 12852551
references: Semin Radiat Oncol. 2004 Jan;14(1):81-90
references: 14752736
references: Phys Med Biol. 2004 May 21;49(10):2053-67
references: 15214541
references: Int J Radiat Oncol Biol Phys. 2004 Nov 1;60(3):933-41
references: 15465212
references: Radiology. 1993 Nov;189(2):411-6
references: 8210368
references: Med Phys. 2005 Apr;32(4):874-89
references: 15895570
references: Int J Radiat Oncol Biol Phys. 2006 Mar 1;64(3):799-803
references: 16298498
references: Phys Med Biol. 2006 Sep 7;51(17):4147-69
references: 16912374
references: Med Phys. 2007 Oct;34(10):4041-63
references: 17985650
references: Magn Reson Med. 2008 Jul;60(1):146-57
references: 18581355
references: AJR Am J Roentgenol. 2009 Jun;192(6 Suppl):S83-93 (Quiz S94-7)
references: 19458102
references: Radiother Oncol. 2009 Jun;91(3):449-54
references: 19394712
references: Med Phys. 2009 Nov;36(11):5000-6
references: 19994509
references: Radiol Med. 2010 Apr;115(3):467-82
references: 20077045
references: Med Phys. 2010 Sep;37(9):4902-15
references: 20964209
references: Med Phys. 2011 Mar;38(3):1359-65
references: 21520846
references: Med Phys. 2011 Dec;38(12):6384-94
references: 22149822
references: Magn Reson Med. 2012 Sep;68(3):741-50
references: 22190255
references: Z Med Phys. 2012 Dec;22(4):258-71
references: 22784929
references: Int J Radiat Oncol Biol Phys. 2013 May 1;86(1):198-204
references: 23414769
references: Med Phys. 2013 May;40(5):051909
references: 23635279
references: Int J Radiat Oncol Biol Phys. 2014 Mar 15;88(4):907-12
references: 24444759
references: Magn Reson Med. 2014 Jun;71(6):2172-9
references: 23900942