Sarabjeet Singh MBBS, Presenter: Nothing to Disclose

Mannudeep Karanvir Singh Kalra MD, Abstract Co-Author: Research grant, General Electric Company

Sjirk Jan Westra MD, Abstract Co-Author: Nothing to Disclose

Michael Moore MBBCh, Abstract Co-Author: Nothing to Disclose

Although post processing non-linear filters have been used in adults for improving image quality of low dose CT images, to the best of our knowledge, use of 2D non linear adaptive filters (2D-NLAF) has not been reported for reducing radiation dose in children. The purpose of our study was to assess if 2D-NLAF can be used for improving image quality with low radiation dose follow up chest and abdominal CT in children.

26 children (age range 3-16 years, M:F 12:14) underwent follow up chest (n= 11) and abdominal (n=15) CT after initial CT examinations. Follow up CT examinations were performed at 25-30% lower dose compared to the initial CT study with use of automatic exposure control, Auto mA using higher noise index (7-13), lower minimum (50-90) and maximum (100-160) mA. The low dose follow up chest and abdominal CT images were post processed with 2D-NLAF. The initial routine, follow up low dose and post-processed low dose CT images were de-identified and interpreted in a blinded manner to assess the effect of 2D-NLAF post-processed low dose images on image noise, visibility of small structures, lesion conspicuity and diagnostic confidence using a five point scale (1= unacceptable, 5= excellent). CT numbers and objective image noise were measured in all image series. Maximum transverse diameter of the body region scanned was measured on initial and follow up CT.

There was no difference in subject size between the initial (20.4 cm) and follow up low dose CT (21.3 cm) (p=0.99). There was no difference between low dose unprocessed and following 2D-NLAF application for HU value in liver or descending thoracic aorta, visibility of small structures, lesion conspicuity and confidence in diagnosis (p>0.5). However, following 2D-NLAF application, there was significant improvement versus unfiltered low dose images for both qualitative noise (3.0 versus 3.7, p<0.05) as well as objective noise (12.6 versus 16.3, p<0.0001) but no difference in HU values was noted between 2D-NLAF and initial standard dose CT images.

2D-NLAF can help reduce radiation dose for pediatric chest and abdominal CT, by increasing the acceptability of low dose follow up CT imaging.

2D-NLAF Post processing of low dose CT images increases the acceptability of low dose images without compromising the diagnostic information.

Singh, S, Kalra, M, Westra, S, Moore, M, Can Adaptive Filters Help Reduce Radiation Dose for Follow-up Chest and Abdominal CT in Children?.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6016172.html