title: Quantification of artifact reduction with real-time cine four-dimensional computed tomography acquisition methods.
abstract: OBJECTIVE
  To quantify the magnitude and frequency of artifacts in simulated four-dimensional computed tomography (4D CT) images using three real-time acquisition methods- direction-dependent displacement acquisition, simultaneous displacement and phase acquisition, and simultaneous displacement and velocity acquisition- and to compare these methods with commonly used retrospective phase sorting.
  
  
  METHODS
  Image acquisition for the four 4D CT methods was simulated with different displacement and velocity tolerances for spheres with radii of 0.5 cm, 1.5 cm, and 2.5 cm, using 58 patient-measured tumors and respiratory motion traces. The magnitude and frequency of artifacts, CT doses, and acquisition times were computed for each method.
  
  
  RESULTS
  The mean artifact magnitude was 50% smaller for the three real-time methods than for retrospective phase sorting. The dose was approximately 50% lower, but the acquisition time was 20% to 100% longer for the real-time methods than for retrospective phase sorting.
  
  
  CONCLUSIONS
  Real-time acquisition methods can reduce the frequency and magnitude of artifacts in 4D CT images, as well as the imaging dose, but they increase the image acquisition time. The results suggest that direction-dependent displacement acquisition is the preferred real-time 4D CT acquisition method, because on average, the lowest dose is delivered to the patient and the acquisition time is the shortest for the resulting number and magnitude of artifacts.
authors: Stanford University Cancer Center, Department of Radiation Oncology, Radiation Physics Division, 875 Blake Wilbur Drive, Stanford, California 94305-5847, USA. ulrich.langner@uky.edu
authors: Ulrich W
authors: UW
authors: Langner
authors: Paul J
authors: PJ
authors: Keall
mesh_terms: D000465:Algorithms; D016477:Artifacts; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D009068:Movement; D011829:Radiation Dosage; D012119:Respiration; D013997:Time Factors