title: Investigation of sagittal image acquisition for 4D-MRI with body area as respiratory surrogate.
abstract: OBJECTIVE
  The authors have recently developed a novel 4D-MRI technique for imaging organ respiratory motion employing cine acquisition in the axial plane and using body area (BA) as a respiratory surrogate. A potential disadvantage associated with axial image acquisition is the space-dependent phase shift in the superior-inferior (SI) direction, i.e., different axial slice positions reach the respiratory peak at different respiratory phases. Since respiratory motion occurs mostly in the SI and anterior-posterior (AP) directions, sagittal image acquisition, which embeds motion information in these two directions, is expected to be more robust and less affected by phase-shift than axial image acquisition. This study aims to develop and evaluate a 4D-MRI technique using sagittal image acquisition.
  
  
  METHODS
  The authors evaluated axial BA and sagittal BA using both 4D-CT images (11 cancer patients) and cine MR images (6 healthy volunteers and 1 cancer patient) by comparing their corresponding space-dependent phase-shift in the SI direction (δSPS (SI)) and in the lateral direction (δSPS (LAT)), respectively. To evaluate sagittal BA 4D-MRI method, a motion phantom study and a digital phantom study were performed. Additionally, six patients who had cancer(s) in the liver were prospectively enrolled in this study. For each patient, multislice sagittal MR images were acquired for 4D-MRI reconstruction. 4D retrospective sorting was performed based on respiratory phases. Single-slice cine MRI was also acquired in the axial, coronal, and sagittal planes across the tumor center from which tumor motion trajectories in the SI, AP, and medial-lateral (ML) directions were extracted and used as references from comparison. All MR images were acquired in a 1.5 T scanner using a steady-state precession sequence (frame rate ∼ 3 frames/s).
  
  
  RESULTS
  4D-CT scans showed that δSPS (SI) was significantly greater than δSPS (LAT) (p-value: 0.012); the median phase-shift was 16.9% and 7.7%, respectively. Body surface motion measurement from axial and sagittal MR cines also showed δSPS (SI) was significantly greater than δSPS (LAT). The median δSPS (SI) and δSPS (LAT) was 11.0% and 9.2% (p-value = 0.008), respectively. Tumor motion trajectories from 4D-MRI matched with those from single-slice cine MRI: the mean (±SD) absolute differences in tumor motion amplitude between the two were 1.5 ± 1.6 mm, 2.1 ± 1.9 mm, and 1.1 ± 1.0 mm in the SI, ML, and AP directions from this patient study.
  
  
  CONCLUSIONS
  Space-dependent phase shift is less problematic for sagittal acquisition than for axial acquisition. 4D-MRI using sagittal acquisition was successfully carried out in patients with hepatic tumors.
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, North Carolina, 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Yilin
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, North Carolina, 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, North Carolina, 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Czito
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Manisha
authors.initials: M
authors.lastname: Palta
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Mustafa R
authors.initials: MR
authors.lastname: Bashir
authors.affiliation: Radiation Oncology, Henry Ford Hospital, Detroit, Michigan.
authors.forename: Yujiao
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Medical Physics Graduate Program, Duke University, Durham, North Carolina, 27710 and Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, 27710.
authors.forename: Jing
authors.initials: J
authors.lastname: Cai
mesh_terms: D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008113:Liver Neoplasms / Q000473:pathology / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009038:Motion; D019047:Phantoms, Imaging; D011446:Prospective Studies; D012119:Respiration