title: High-quality t2-weighted 4-dimensional magnetic resonance imaging for radiation therapy applications.
abstract: OBJECTIVE
  The purpose of this study was to improve triggering efficiency of the prospective respiratory amplitude-triggered 4-dimensional magnetic resonance imaging (4DMRI) method and to develop a 4DMRI imaging protocol that could offer T2 weighting for better tumor visualization, good spatial coverage and spatial resolution, and respiratory motion sampling within a reasonable amount of time for radiation therapy applications.
  
  
  METHODS
  The respiratory state splitting (RSS) and multi-shot acquisition (MSA) methods were analytically compared and validated in a simulation study by using the respiratory signals from 10 healthy human subjects. The RSS method was more effective in improving triggering efficiency. It was implemented in prospective respiratory amplitude-triggered 4DMRI. 4DMRI image datasets were acquired from 5 healthy human subjects. Liver motion was estimated using the acquired 4DMRI image datasets.
  
  
  RESULTS
  The simulation study showed the RSS method was more effective for improving triggering efficiency than the MSA method. The average reductions in 4DMRI acquisition times were 36% and 10% for the RSS and MSA methods, respectively. The human subject study showed that T2-weighted 4DMRI with 10 respiratory states, 60 slices at a spatial resolution of 1.5 × 1.5 × 3.0 mm(3) could be acquired in 9 to 18 minutes, depending on the individual's breath pattern. Based on the acquired 4DMRI image datasets, the ranges of peak-to-peak liver displacements among 5 human subjects were 9.0 to 12.9 mm, 2.5 to 3.9 mm, and 0.5 to 2.3 mm in superior-inferior, anterior-posterior, and left-right directions, respectively.
  
  
  CONCLUSIONS
  We demonstrated that with the RSS method, it was feasible to acquire high-quality T2-weighted 4DMRI within a reasonable amount of time for radiation therapy applications.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri.
authors.forename: Dongsu
authors.initials: D
authors.lastname: Du
authors.affiliation: Philips Healthcare, Cleveland, Ohio.
authors.forename: Shelton D
authors.initials: SD
authors.lastname: Caruthers
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Carri
authors.initials: C
authors.lastname: Glide-Hurst
authors.affiliation: Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, California.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri.
authors.forename: H Harold
authors.initials: HH
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri.
authors.forename: Sasa
authors.initials: S
authors.lastname: Mutic
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri; Department of Radiation Oncology, Mayo Clinic in Arizona, Phoenix, Arizona. Electronic address: Hu.Yanle@mayo.edu.
authors.forename: Yanle
authors.initials: Y
authors.lastname: Hu
mesh_terms: D000328:Adult; D000465:Algorithms; D004526:Efficiency; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008099:Liver; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards; D008297:Male; D009068:Movement; D011878:Radiotherapy / Q000379:methods* / Q000592:standards; D012119:Respiration; D012984:Software; D013997:Time Factors
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