Brief Article
Copyright ©2012 Baishideng Publishing Group Co., Limited. All rights reserved.
World J Radiol. Jan 28, 2012; 4(1): 21-28
Published online Jan 28, 2012. doi: 10.4329/wjr.v4.i1.21
Radiation dose reduction with application of non-linear adaptive filters for abdominal CT
Sarabjeet Singh, Mannudeep K Kalra, Mi Kim Sung, Anni Back, Michael A Blake
Sarabjeet Singh, Mannudeep K Kalra, Michael A Blake, Massachusetts General Hospital, Department of Radiology, Harvard Medical School, Boston, MA 02114, United States
Mi Kim Sung, Myongji Hospital, Kwandong University, 522 Naegok-dong, Gangneung-si, Gangwon-do 220-801, South Korea
Anni Back, ContextVision AB, Linköping 58002, Sweden
Author contributions: Singh S helped in patient recruitment, organizing study, literature search, manuscript writing; Kalra MK helped in overall study design and manuscript writing; Sung MK helped in manuscript revision; Back A helped in image processing; Blake MA helped in image quality evaluation and manuscript editing.
Correspondence to: Dr. Sarabjeet Singh, Massachusetts General Hospital, Department of Radiology, Harvard Medical School, 55 Fruit St, Boston, MA 02114, United States.
Telephone: +1-617-6430264 Fax: +1-617-6430111
Received: February 10, 2011
Revised: July 8, 2011
Accepted: July 15, 2011
Published online: January 28, 2012

AIM: 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.

CONCLUSION: NLAF lowers image noise, improves the visibility of small structures and maintains lesion conspicuity at down to 100 mAs for abdominal CT.

Keywords: Noise reduction filters, Computed tomography radiation dose reduction, Abdominal computed tomography image quality, Non-linear adaptive filters