title: Four-dimensional diffusion-weighted MR imaging (4D-DWI): a feasibility study.
abstract: OBJECTIVE
  Diffusion-weighted Magnetic Resonance Imaging (DWI) has been shown to be a powerful tool for cancer detection with high tumor-to-tissue contrast. This study aims to investigate the feasibility of developing a four-dimensional DWI technique (4D-DWI) for imaging respiratory motion for radiation therapy applications.
  
  
  METHODS
  Image acquisition was performed by repeatedly imaging a volume of interest (VOI) using an interleaved multislice single-shot echo-planar imaging (EPI) 2D-DWI sequence in the axial plane. Each 2D-DWI image was acquired with an intermediately low b-value (b = 500 s/mm2) and with diffusion-encoding gradients in x, y, and z diffusion directions. Respiratory motion was simultaneously recorded using a respiratory bellow, and the synchronized respiratory signal was used to retrospectively sort the 2D images to generate 4D-DWI. Cine MRI using steady-state free precession was also acquired as a motion reference. As a preliminary feasibility study, this technique was implemented on a 4D digital human phantom (XCAT) with a simulated pancreas tumor. The respiratory motion of the phantom was controlled by regular sinusoidal motion profile. 4D-DWI tumor motion trajectories were extracted and compared with the input breathing curve. The mean absolute amplitude differences (D) were calculated in superior-inferior (SI) direction and anterior-posterior (AP) direction. The technique was then evaluated on two healthy volunteers. Finally, the effects of 4D-DWI on apparent diffusion coefficient (ADC) measurements were investigated for hypothetical heterogeneous tumors via simulations.
  
  
  RESULTS
  Tumor trajectories extracted from XCAT 4D-DWI were consistent with the input signal: the average D value was 1.9 mm (SI) and 0.4 mm (AP). The average D value was 2.6 mm (SI) and 1.7 mm (AP) for the two healthy volunteers.
  
  
  CONCLUSIONS
  A 4D-DWI technique has been developed and evaluated on digital phantom and human subjects. 4D-DWI can lead to more accurate respiratory motion measurement. This has a great potential to improve the visualization and delineation of cancer tumors for radiotherapy.
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, NC, 27710, USA.
authors.forename: Yilin
authors.initials: Y
authors.lastname: Liu
authors.affiliation: MR R&D Collaborations, Siemens Healthcare, Atlanta, GA, 30354, USA.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhong
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Czito
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Manisha
authors.initials: M
authors.lastname: Palta
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, NC, 27710, USA.|Center for Advanced Magnetic Resonance Development, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Mustafa R
authors.initials: MR
authors.lastname: Bashir
authors.affiliation: MR R&D Collaborations, Siemens Healthcare, Cary, NC, 27511, USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Dale
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, NC, 27710, USA.|Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, NC, 27710, USA.|Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 27710, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Cai
mesh_terms: D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D005240:Feasibility Studies; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation / Q000379:methods*; D008954:Models, Biological; D009038:Motion; D009068:Movement; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D019047:Phantoms, Imaging; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012119:Respiration
keywords: 4D-MRI; DWI; IGRT; motion management; retrospective phase sorting