title: Robust primary modulation-based scatter estimation for cone-beam CT.
abstract: OBJECTIVE
  Scattered radiation is one of the major problems facing image quality in flat detector cone-beam computed tomography (CBCT). Previously, a new scatter estimation and correction method using primary beam modulation has been proposed. The original image processing technique used a frequency-domain-based analysis, which proved to be sensitive to the accuracy of the modulator pattern both spatially and in amplitude as well as to the frequency of the modulation pattern. In addition, it cannot account for penumbra effects that occur, for example, due to the finite focal spot size and the scatter estimate can be degraded by high-frequency components of the primary image.
  
  
  METHODS
  In this paper, the authors present a new way to estimate the scatter using primary modulation. It is less sensitive to modulator nonidealities and most importantly can handle arbitrary modulator shapes and changes in modulator attenuation. The main idea is that the scatter estimation can be expressed as an optimization problem, which yields a separation of the scatter and the primary image. The method is evaluated using simulated and experimental CBCT data. The scattering properties of the modulator itself are analyzed using a Monte Carlo simulation.
  
  
  RESULTS
  All reconstructions show strong improvements of image quality. To quantify the results, all images are compared to reference images (ideal simulations and collimated scans).
  
  
  CONCLUSIONS
  The proposed modulator-based scatter reduction algorithm may open the field of flat detector-based imaging to become a quantitative modality. This may have significant impact on C-arm imaging and on image-guided radiation therapy.
authors.affiliation: Ziehm Imaging, Nürnberg 90451, Germany.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Ritschl
authors.affiliation: Radiological Science Laboratory, Stanford University, 1201 Welch Road Palo Alto, Stanford, California 94304.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Fahrig
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Knaup
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
authors.forename: Joscha
authors.initials: J
authors.lastname: Maier
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Kachelrieß
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D012542:Scattering, Radiation