Jung Jae Park MD, Presenter: Nothing to Disclose

Myung Jin Chung MD, Abstract Co-Author: Advisory Board, Samsung Advanced Institute of Technology Research Consultant, Samsung Mobile Display Company

Kun Jin Park RT, Abstract Co-Author: Nothing to Disclose

Ho Yun Lee MD, Abstract Co-Author: Nothing to Disclose

Chin A Yi MD, PhD, Abstract Co-Author: Nothing to Disclose

Kyung Soo Lee MD, PhD, Abstract Co-Author: Nothing to Disclose

ASIR allows one to reduce tube current as compared with FBP algorithms. However, unfamiliar images, when CT data were reconstructed by using ASIR, may cause difficulty in size measurement and diagnostic decision about some lesions especially in lung examinations. The purpose of this study was to compare directly the radiologist’s performance in the evaluation of ground glass opacity nodules (GGNs) on ASIR- and FBP-driven CT images within a same patient.

Forty patients who had a total of 42 pulmonary GGNs at chest CT were enrolled. CT scans were obtained with 120kVp under automatic exposure control on 64-row MDCT. Mean DLP was 148 ± 24 mGy·cm. ASIR- and FBP-driven axial CT images were reconstructed with 36 ~ 38 cm FOV, 2.5 mm thickness, and high spatial frequency algorithm. Applied ASIR ratio was 40%. Two thoracic radiologists with more than 10 years experience of chest CT interpretation reviewed both subsets of ASIR- and FBP-driven images independently. Nodule size was measured manually. The confidence level for the nodule being malignant was recorded with 9-point scale (Confidence score, CS; 1 definitely benign, 9 definitely malignant). Data assessed by each radiologist were compared.

Inter-method correlation was excellent between FBP- and ASIR-driven (R = .96, P < .01 for nodule size; R = .82, P < .01 for CS) images. On ASIR-driven images, nodule size was significantly larger than on FBP-driven images (paired T-test; 8.7 ± 5.0 mm and 9.6 ± 5.3 mm in observer 1, 7.6 ± 5.5 mm and 8.4 ± 6.2 mm in observer 2, respectively). CSs were significantly different between FBP- and ASIR-driven images (observer 1, 3.8 ± 2.1 vs. 4.6 ± 2.3; observer 2, 3.6 ± 2.1 vs. 4.6 ± 2.2, respectively). Regarding nodule size and CS for nodule characterization, inter-observer agreement was higher on ASIR-driven images than on FBP-driven images (R for nodule size were .94 vs. .96, Pearson’s correl.; R for CSs were .37 vs. .42, Spearman’s correl.).

When GGNs are interpreted on ASIR-driven CT images, they appear to be larger and tend to manifest more malignant morphology than on FBP-driven images. Radiologists should consider this difference when they interpret ASIR-driven chest CT images.

ASIR-driven chest CT images appear to be somewhat different from those reconstructed with conventional FBP. When radiologists interpret ASIR-driven images, they should be aware of this difference.

Park, J, Chung, M, Park, K, Lee, H, Yi, C, Lee, K, Adaptive Statistical Iterative Reconstruction (ASIR) Driven Chest CT: Influence on the Evaluation of Ground Glass Opacity Nodules Compared with Filtered Back Projection (FBP) Driven Images.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9001626.html