title: Numerical deconvolution to enhance sharpness and contrast of portal images for radiotherapy patient positioning verification.
abstract: OBJECTIVE
  The quality of megavoltage clinical portal images is impaired by physical and geometrical effects. This image blurring can be corrected by a fast numerical two-dimensional (2D) deconvolution algorithm implemented in the electronic portal image device. We present some clinical examples of deconvolved portal images and evaluate the clinical advantages achieved by the improved sharpness and contrast.
  
  
  METHODS
  The principle of numerical 2D image deconvolution and the enhancement of sharpness and contrast thereby achieved are shortly explained. The key concept is the convolution kernel K(x,y), the mathematical equivalent of the smearing or blurring of a picture, and the computer-based elimination of this influence.
  
  
  RESULTS
  Enhancements of sharpness and contrast were observed in all clinical portal images investigated. The images of fine bone structures were restored. The identification of organ boundaries and anatomical landmarks was improved, thereby permitting a more accurate comparison with the x-ray simulator radiographs. The visibility of prostate gold markers is also shown to be enhanced by deconvolution.
  
  
  CONCLUSIONS
  The blurring effects of clinical portal images were eliminated by a numerical deconvolution algorithm that leads to better image sharpness and contrast. The fast algorithm permits the image blurring correction to be performed in real time, so that patient positioning verification with increased accuracy can be achieved in clinical practice.
authors.affiliation: Clinic for Radiation Therapy, Pius Hospital, Oldenburg, Germany. hui.k.looe@uni-oldenburg.de
authors.forename: H K
authors.initials: HK
authors.lastname: Looe
authors.forename: Y
authors.initials: Y
authors.lastname: Uphoff
authors.forename: D
authors.initials: D
authors.lastname: Harder
authors.forename: B
authors.initials: B
authors.lastname: Poppe
authors.forename: K C
authors.initials: KC
authors.lastname: Willborn
mesh_terms: D000465:Algorithms; D006801:Humans; D056888:Patient Positioning; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*