title: Local noise estimation in low-dose chest CT images.
abstract: OBJECTIVE
  Image noise in computed tomography (CT) images may have significant local variation due to tissue properties, dose, and location of the X-ray source. We developed and tested an automated tissue-based estimator method for estimating local noise in CT images.
  
  
  METHODS
  An automated TBE method for estimating the local noise in CT image in 3 steps was developed: (1) Partition the image into homogeneous and transition regions, (2) For each pixel in the homogeneous regions, compute the standard deviation in a 15 x 15 x 1 voxel local region using only pixels from the same homogeneous region, and (3) Interpolate the noise estimate from the homogeneous regions in the transition regions. Noise-aware fat segmentation was implemented. Experiments were conducted on the anthropomorphic phantom and in vivo low-dose chest CT scans to validate the TBE, characterize the magnitude of local noise variation, and determine the sensitivity of noise estimates to the size of the region in which noise is computed. The TBE was tested on all scans from the Early Lung Cancer Action Program public database. The TBE was evaluated quantitatively on the phantom data and qualitatively on the in vivo data.
  
  
  RESULTS
  The results show that noise can vary locally by over 200 Hounsfield units on low-dose in vivo chest CT scans and that the TBE can characterize these noise variations within 5 %. The new fat segmentation algorithm successfully improved segmentation on all 50 scans tested.
  
  
  CONCLUSIONS
  The TBE provides a means to estimate noise for image quality monitoring, optimization of denoising algorithms, and improvement of segmentation algorithms. The TBE was shown to accurately characterize the large local noise variations that occur due to changes in material, dose, and X-ray source location.
authors.affiliation: School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA, jjp263@cornell.edu.
authors.forename: J
authors.initials: J
authors.lastname: Padgett
authors.forename: A M
authors.initials: AM
authors.lastname: Biancardi
authors.forename: C I
authors.initials: CI
authors.lastname: Henschke
authors.forename: D
authors.initials: D
authors.lastname: Yankelevitz
authors.forename: A P
authors.initials: AP
authors.lastname: Reeves
mesh_terms: D000465:Algorithms; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D013902:Radiography, Thoracic / Q000379:methods*; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods*