title: A novel fast helical 4D-CT acquisition technique to generate low-noise sorting artifact-free images at user-selected breathing phases.
abstract: OBJECTIVE
  To develop a novel 4-dimensional computed tomography (4D-CT) technique that exploits standard fast helical acquisition, a simultaneous breathing surrogate measurement, deformable image registration, and a breathing motion model to remove sorting artifacts.
  
  
  METHODS
  Ten patients were imaged under free-breathing conditions 25 successive times in alternating directions with a 64-slice CT scanner using a low-dose fast helical protocol. An abdominal bellows was used as a breathing surrogate. Deformable registration was used to register the first image (defined as the reference image) to the subsequent 24 segmented images. Voxel-specific motion model parameters were determined using a breathing motion model. The tissue locations predicted by the motion model in the 25 images were compared against the deformably registered tissue locations, allowing a model prediction error to be evaluated. A low-noise image was created by averaging the 25 images deformed to the first image geometry, reducing statistical image noise by a factor of 5. The motion model was used to deform the low-noise reference image to any user-selected breathing phase. A voxel-specific correction was applied to correct the Hounsfield units for lung parenchyma density as a function of lung air filling.
  
  
  RESULTS
  Images produced using the model at user-selected breathing phases did not suffer from sorting artifacts common to conventional 4D-CT protocols. The mean prediction error across all patients between the breathing motion model predictions and the measured lung tissue positions was determined to be 1.19 ± 0.37 mm.
  
  
  CONCLUSIONS
  The proposed technique can be used as a clinical 4D-CT technique. It is robust in the presence of irregular breathing and allows the entire imaging dose to contribute to the resulting image quality, providing sorting artifact-free images at a patient dose similar to or less than current 4D-CT techniques.
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California. Electronic address: dhthomas@mednet.ucla.edu.
authors.forename: David
authors.initials: D
authors.lastname: Thomas
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: James
authors.initials: J
authors.lastname: Lamb
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Benjamin
authors.initials: B
authors.lastname: White
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: Shyam
authors.initials: S
authors.lastname: Jani
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: Sergio
authors.initials: S
authors.lastname: Gaudio
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: Dan
authors.initials: D
authors.lastname: Ruan
authors.affiliation: Department of Radiological Sciences, University of California, Los Angeles, California.
authors.forename: Michael
authors.initials: M
authors.lastname: McNitt-Gray
authors.affiliation: Department of Radiation Oncology, University of California, Los Angeles, California.
authors.forename: Daniel
authors.initials: D
authors.lastname: Low
mesh_terms: D016477:Artifacts; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging*; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012119:Respiration; D036542:Tomography, Spiral Computed / Q000379:methods*