Evaluation of the Noise, Artifact and CT Number Accuracy of the CT Images Following Combined Use of Bismuth Shield and Bolus during CT Exams: A Phantom Study

Background and Objective: The bismuth shield has shown to be effective at reducing radiation exposure during CT exams. However, some drawbacks such as introduction of image noise, streak and beam-hardening artifacts and change in CT number of the images have limited their widespread clinically use. The aim of this study was to quantitative assessment of the combined use of bismuth shield and bolus on image noise, artifact and CT number variation during CT exams. Materials and Methods: A 32-cm body phantom was scanned using 16-slice GE CT scanner. The commercially available bismuth shield was placed directly on the anterior surface of the phantom and the second scan was performed. The next scans were obtained after placing 1, 2 and 3-cm foam as bolus between the shield and the phantom. Seven circular region-of-interests (ROI) with areas of 1.5 cm2 were applied in different regions of the phantom. The standard deviation (SD) of the CT number of each ROI was considered as a quantitative analysis of image noise. Artifacts were assessed using image criteria adopted from the European guidelines. Statistical analysis was performed with SPSS 20 software. Findings: A substantial increase in the image noise, artifact and CT number occurred, when the scan was performed with the shield than without the shield. The increased noise at the anterior portion of the phantom was 19.51, 3.92, 3.05 and 1.49 follow 0, 1, 2, and 3-cm shield-to-phantom distance, respectively. Furthermore, the increased CT number was 90.78, 45.9, 24.67 and 15.11, respectively. Streak artifacts were noted when the shield directly positioned upon the phantom surface or 1-cm shield-to-phantom distance. Conclusion: Combination of the bismuth shield with 3-cm shield-to-phantom distance has significantly reduced image noise and streak artifacts. However, increasing the CT number of the images at the anterior regions remains as a viable concern.

کلیدواژه ها:

Bismuth shield ، bolus ، CT ، image noise ، phantom