title: Correction of Bowtie-Filter Normalization and Crescent Artifacts for a Clinical CBCT System.
abstract: To present our experiences in understanding and minimizing bowtie-filter crescent artifacts and bowtie-filter normalization artifacts in a clinical cone beam computed tomography system.
  
  
  
  Bowtie-filter position and profile variations during gantry rotation were studied. Two previously proposed strategies (A and B) were applied to the clinical cone beam computed tomography system to correct bowtie-filter crescent artifacts. Physical calibration and analytical approaches were used to minimize the norm phantom misalignment and to correct for bowtie-filter normalization artifacts. A combined procedure to reduce bowtie-filter crescent artifacts and bowtie-filter normalization artifacts was proposed and tested on a norm phantom, CatPhan, and a patient and evaluated using standard deviation of Hounsfield unit along a sampling line.
  
  
  
  The bowtie-filter exhibited not only a translational shift but also an amplitude variation in its projection profile during gantry rotation. Strategy B was better than strategy A slightly in minimizing bowtie-filter crescent artifacts, possibly because it corrected the amplitude variation, suggesting that the amplitude variation plays a role in bowtie-filter crescent artifacts. The physical calibration largely reduced the misalignment-induced bowtie-filter normalization artifacts, and the analytical approach further reduced bowtie-filter normalization artifacts. The combined procedure minimized both bowtie-filter crescent artifacts and bowtie-filter normalization artifacts, with Hounsfield unit standard deviation being 63.2, 45.0, 35.0, and 18.8 Hounsfield unit for the best correction approaches of none, bowtie-filter crescent artifacts, bowtie-filter normalization artifacts, and bowtie-filter normalization artifacts + bowtie-filter crescent artifacts, respectively. The combined procedure also demonstrated reduction of bowtie-filter crescent artifacts and bowtie-filter normalization artifacts in a CatPhan and a patient.
  
  
  
  We have developed a step-by-step procedure that can be directly used in clinical cone beam computed tomography systems to minimize both bowtie-filter crescent artifacts and bowtie-filter normalization artifacts.
authors.affiliation: 1 Department of Radiation Oncology, Georgia Regents University, Augusta, GA, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.affiliation: 1 Department of Radiation Oncology, Georgia Regents University, Augusta, GA, USA.
authors.forename: Vic
authors.initials: V
authors.lastname: Kong
authors.affiliation: 1 Department of Radiation Oncology, Georgia Regents University, Augusta, GA, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Huang
authors.affiliation: 1 Department of Radiation Oncology, Georgia Regents University, Augusta, GA, USA.|2 Department of Radology, Georgia Regents University, Augusta, GA, USA.
authors.forename: Jian-Yue
authors.initials: JY
authors.lastname: Jin
mesh_terms: D000465:Algorithms; D016477:Artifacts; D054893:Cone-Beam Computed Tomography / Q000379:methods* / Q000592:standards*; D006801:Humans; D008962:Models, Theoretical; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000592:standards; D061089:Radiotherapy, Image-Guided / Q000379:methods* / Q000592:standards*
keywords: bowtie-filter crescent artifacts; bowtie-filter normalization artifacts; cone-beam CT image; geometric calibration; geometric nonideality; image artifacts; normalization calibration
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