title: Radiation dose reduction in CT of the brain: can advanced noise filtering compensate for loss of image quality?
abstract: BACKGROUND
  Computed tomography (CT) of the brain is performed with high local doses due to high demands on low contrast resolution. Advanced algorithms for noise reduction might be able to preserve critical image information when reducing radiation dose.
  
  
  OBJECTIVE
  To evaluate the effect of advanced noise filtering on image quality in brain CT acquired with reduced radiation dose.
  
  
  METHODS
  Thirty patients referred for non-enhanced CT of the brain were examined with two helical protocols: normal dose (ND, CTDI(vol) 57 mGy) and low dose (LD, CTDI(vol) 40 mGy) implying a 30% radiation dose reduction. Images from the LD examinations were also postprocessed with a noise reduction software with non-linear filters (SharpView CT), creating filtered low dose images (FLD) for each patient. The three image stacks for each patient were presented side by side in randomized order. Five radiologists, blinded for dose level and filtering, ranked these three axial image stacks (ND, LD, FLD) as best to poorest (1 to 3) regarding three image quality criteria. Measurements of mean Hounsfield units (HU) and standard deviation (SD) of the HU were calculated for large region of interest in the centrum semiovale as a measure for noise.
  
  
  RESULTS
  Ranking results in pooled data showed that the advanced noise filtering significantly improved the image quality in FLD as compared to LD images for all tested criteria. No significant differences in image quality were found between ND examinations and FLD. However, there was a notable inter-reader spread of the ranking. SD values were 15% higher for LD as compared to ND and FLD.
  
  
  CONCLUSIONS
  The advanced noise filtering clearly improves image quality of CT examinations of the brain. This effect can be used to significantly lower radiation dose.
authors.affiliation: Department of Radiology, Lund University, Sweden. roger.siemund@med.lu.se
authors.forename: Roger
authors.initials: R
authors.lastname: Siemund
authors.forename: A
authors.initials: A
authors.lastname: Löve
authors.forename: D
authors.initials: D
authors.lastname: van Westen
authors.forename: L
authors.initials: L
authors.lastname: Stenberg
authors.forename: C
authors.initials: C
authors.lastname: Petersen
authors.forename: I M
authors.initials: IM
authors.lastname: Björkman-Burtscher
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*