Tomoko Gyobu, Presenter: Nothing to Disclose

Osamu Honda MD, PhD, Abstract Co-Author: Nothing to Disclose

Masahiro Yanagawa MD, PhD, Abstract Co-Author: Nothing to Disclose

Hiromitsu Sumikawa MD, Abstract Co-Author: Nothing to Disclose

Mitsuhiro Koyama MD, Abstract Co-Author: Nothing to Disclose

Noriyuki Tomiyama MD, PhD, Abstract Co-Author: Nothing to Disclose

To evaluate whether virtual monochromatic image acquired by dual energy computed tomography (CT) can reduce metal artifact and can improve the detection of pulmonary nodules.

Chest phantom and 12 simulated nodules (size; 3, 5, 8 and 10mm, density; -800, -630 and +100HU) were used for this study. The pacemaker was set on the anterior chest wall of phantom, and one simulated nodule was put in the lung field underneath the pacemaker. Then, Dual energy CT (Discovery CT750HD, GE healthcare) was performed, and five patterns of the virtual monochromatic images (40, 50, 65, 100 and 140KeV) were reconstructed with 5mm and 0.625mm slice thickness on the workstation. The same dual energy CT and the same reconstruction were performed for the chest phantom without simulated nodule. 260 series of virtual monochromatic images were obtained in total, and two independent observers assessed the metal artifact (3-point scale from 1; non to 3; severe) and the detection of the nodule (5-point scale from 1; definitely absent to 5; definitely present). The statistical analysis was performed with Wilcoxon signed rank test and Bonferroni correction for multiple comparisons, with p value of <0.01 (0.05/5).

In both 5mm and 0.625mm slice thickness, metallic artifact increased at 40 or 50KeV and decreased at 100 or 140KeV in comparison with that at 65KeV (p<0.01) (In 5mm slice thickness, the mean score was 3.0 ±0.0, 2.9±0.3, 2.3±0.5, 1.6±0.5, and 1.3±0.5 at 40, 50, 65, 100, and 140KeV. In 0.625mm slice thickness, the mean score was 3.0±0.2, 2.8±0.4, 2.4±0.5, 1.7±0.5, and 1.7±0.5 at 40, 50, 65, 100, and 140KeV). In 0.625 mm slice thickness, the detection score of the nodule was not statistically different between 65KeV and 40, 50, 100 or 140KeV (the mean score was 4.4±1.0, 4.5±1.0, 4.6±1.0, 4.5±1.1, and 4.4±1.2 at 40, 50, 65, 100, and 140KeV). However, the detection score of the nodule at 40KeV was significantly worse than that at 65 KeV (p<0.01) in 5 mm slice thickness (the mean score was 4.1±1.1, 4.3±1.1, 4.4±1.2, 4.3±1.4, and 4.3±1.2 at 40, 50, 65, 100, and 140KeV).

High KeV image can reduce metal artifact, but detection score of the nodule dose not change. Low KeV image increase metal artifact, and thick slice worsens the nodule detection.

High KeV image is useful to reduce metal artifact. Low KeV image with thick slice is not suitable for nodule detection.

Gyobu, T, Honda, O, Yanagawa, M, Sumikawa, H, Koyama, M, Tomiyama, N, Utility of the Virtual Monochromatic Spectral Imaging for Reducing the Metallic Artifact and Detecting Pulmonary Nodule.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12026682.html