title: Rapid estimation of 4DCT motion-artifact severity based on 1D breathing-surrogate periodicity.
abstract: OBJECTIVE
  Motion artifacts are common in patient four-dimensional computed tomography (4DCT) images, leading to an ill-defined tumor volume with large variations for radiotherapy treatment and a poor foundation with low imaging fidelity for studying respiratory motion. The authors developed a method to estimate 4DCT image quality by establishing a correlation between the severity of motion artifacts in 4DCT images and the periodicity of the corresponding 1D respiratory waveform (1DRW) used for phase binning in 4DCT reconstruction.
  
  
  METHODS
  Discrete Fourier transformation (DFT) was applied to analyze 1DRW periodicity. The breathing periodicity index (BPI) was defined as the sum of the largest five Fourier coefficients, ranging from 0 to 1. Distortional motion artifacts (excluding blurring) of cine-scan 4DCT at the junctions of adjacent couch positions around the diaphragm were classified in three categories: incomplete, overlapping, and duplicate anatomies. To quantify these artifacts, discontinuity of the diaphragm at the junctions was measured in distance and averaged along six directions in three orthogonal views. Artifacts per junction (APJ) across the entire diaphragm were calculated in each breathing phase and phase-averaged APJ¯, defined as motion-artifact severity (MAS), was obtained for each patient. To make MAS independent of patient-specific motion amplitude, two new MAS quantities were defined: MAS(D) is normalized to the maximum diaphragmatic displacement and MAS(V) is normalized to the mean diaphragmatic velocity (the breathing period was obtained from DFT analysis of 1DRW). Twenty-six patients' free-breathing 4DCT images and corresponding 1DRW data were studied.
  
  
  RESULTS
  Higher APJ values were found around midventilation and full inhalation while the lowest APJ values were around full exhalation. The distribution of MAS is close to Poisson distribution with a mean of 2.2 mm. The BPI among the 26 patients was calculated with a value ranging from 0.25 to 0.93. The DFT calculation was within 3 s per 1DRW. Correlations were found between 1DRW periodicity and 4DCT artifact severity: -0.71 for MAS(D) and -0.73 for MAS(V). A BPI greater than 0.85 in a 1DRW suggests minimal motion artifacts in the corresponding 4DCT images.
  
  
  CONCLUSIONS
  The breathing periodicity index and motion-artifact severity index are introduced to assess the relationship between 1DRW and 4DCT. A correlation between 1DRW periodicity and 4DCT artifact severity has been established. The 1DRW periodicity provides a rapid means to estimate 4DCT image quality. The rapid 1DRW analysis and the correlative relationship can be applied prospectively to identify irregular breathers as candidates for breath coaching prior to 4DCT scan and retrospectively to select high-quality 4DCT images for clinical motion-management research.
authors.affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Guang
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Marshall
authors.initials: M
authors.lastname: Caraveo
authors.affiliation: Department of Computer Science, City College of New York, New York, New York 10031.
authors.forename: Jie
authors.initials: J
authors.lastname: Wei
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Andreas
authors.initials: A
authors.lastname: Rimner
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Abraham J
authors.initials: AJ
authors.lastname: Wu
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Karyn A
authors.initials: KA
authors.lastname: Goodman
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10065.
authors.forename: Ellen
authors.initials: E
authors.lastname: Yorke
mesh_terms: D000465:Algorithms; D016477:Artifacts; D062485:Breath Holding; D004583:Electrons; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D009010:Monte Carlo Method; D009068:Movement; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012119:Respiration; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water