title: Radiation dose reduction with application of non-linear adaptive filters for abdominal CT.
abstract: OBJECTIVE
  To evaluate the effect of non-linear adaptive filters (NLAF) on abdominal computed tomography (CT) images acquired at different radiation dose levels.
  
  
  METHODS
  Nineteen patients (mean age 61.6 ± 7.9 years, M:F = 8:11) gave informed consent for an Institutional Review Board approved prospective study involving acquisition of 4 additional image series (200, 150, 100, 50 mAs and 120 kVp) on a 64 slice multidetector row CT scanner over an identical 10 cm length in the abdomen. The CT images acquired at 150, 100 and 50 mAs were processed with the NLAF. Two radiologists reviewed unprocessed and processed images for image quality in a blinded randomized manner. CT dose index volume, dose length product, patient weight, transverse diameters, objective noise and CT numbers were recorded. Data were analyzed using Analysis of Variance and Wilcoxon signed rank test.
  
  
  RESULTS
  Of the 31 lesions detected in abdominal CT images, 28 lesions were less than 1 cm in size. Subjective image noise was graded as unacceptable in unprocessed images at 50 and 100 mAs, and in NLAF processed images at 50 mAs only. In NLAF processed images, objective image noise was decreased by 21% (14.4 ± 4/18.2 ± 4.9) at 150 mAs, 28.3% (15.7 ± 5.6/21.9 ± 4) at 100 mAs and by 39.4% (18.8 ± 9/30.4 ± 9.2) at 50 mAs compared to unprocessed images acquired at respective radiation dose levels. At 100 mAs the visibility of smaller structures improved from suboptimal in unprocessed images to excellent in NLAF processed images, whereas diagnostic confidence was respectively improved from probably confident to fully confident.
  
  
  CONCLUSIONS
  NLAF lowers image noise, improves the visibility of small structures and maintains lesion conspicuity at down to 100 mAs for abdominal CT.
authors.affiliation: Sarabjeet Singh, Mannudeep K Kalra, Michael A Blake, Massachusetts General Hospital, Department of Radiology, Harvard Medical School, Boston, MA 02114, United States.
authors.forename: Sarabjeet
authors.initials: S
authors.lastname: Singh
authors.forename: Mannudeep K
authors.initials: MK
authors.lastname: Kalra
authors.forename: Mi Kim
authors.initials: MK
authors.lastname: Sung
authors.forename: Anni
authors.initials: A
authors.lastname: Back
authors.forename: Michael A
authors.initials: MA
authors.lastname: Blake