Evaluation of no-grid radiography using the digital scattered x-ray removal processing

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1 Evaluation of no-grid radiography using the digital scattered x-ray removal processing Poster No.: C-0416 Congress: ECR 2016 Type: Authors: Scientific Exhibit R. Suzuki 1, T. Goto 1, H. Ogawa 2, N. Amimoto 3 ; 1 Oguni/JP, 2 Sendai/JP, 3 Tokyo/JP Keywords: DOI: Computer applications, Digital radiography, Physics, Artifacts /ecr2016/C-0416 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 15

2 Aims and objectives In portable exposure using Grids, cut off often uneven image density and contrast reduction caused by grid misalignment to the incident x-ray become a problem. In recent years, Virtual Grid Processing has developed by Fujifilm to enable non-grid exposure in digital Radiography. In Virtual Grid Processing, image acquisition is expected to not be affected by the artifact of the cut-off. We have evaluated and compared the image quality of incorrect alignment exposure images and tilted alignment exposure images for using Grid images and Virtual Grid Processing images. Methods and materials Materials: Diagnostic x-ray high voltage unit KXO-50SS (Toshiba Medical Systems, Japan) Flat Panel Detector System CALNEO C 1417 Wireless SQ and CONSOLE ADVANCE Ver. 8.1 (Fujifilm Co., Japan) Anti-scatter grid Real Grid: MS X-RAY GRID (Mitaya MFG Co., Japan) Grid ratio, strip density, focus distance and interspace material were 8:1, 40 lines/cm, 120 cm, aluminum respectively. Virtual Grid: Virtual Grid was set to the same characteristic parameters with Real Grid. Page 2 of 15

3 Dosimeter RaySafe X2 (Unfors RaySafe, Sweden) Step Phantom Polymethyl methacrylate plates (Fig. 1) Analysing software Image J (National Institutes of Health, USA) Exposure technique: Two Step Phantoms (R, L) were located covering whole width of Flat Panel Detector. The step of Step Phantom is orthogonal to grid line. X-ray exposure was done by correct alignment (0 degree) and titled misalignment (3, 6, 9 degrees of flux angle of incorrect x-ray). (Fig. 2) Tube voltage was set to 80 kv, and mas was set to 0.3 mgy (Incident Air Kerma at the surface of Step Phantom: IAK) for Grid exposure, and 0.15 mgy (IAK) for Virtual Grid processing exposure. Qualitative evaluation: It was visually evaluated for the uneven density and grid lines of the image. Quantitative evaluation: 10 mm x 10 mm ROI was set in the image, and moved every 5 mm in horizontal direction in the image, and average value and standard deviation of pixel value were calculated. (Fig. 3) Density profile curve was made from average value of pixel value. Contrast to Noise Ratio (CNR) was calculated by average value and standard deviation, and profile curve was obtained. Formula for CNR is shown in Fig. 4. Page 3 of 15

4 Images for this section: Fig. 1: Diagram of PMMA Step Phantom Page 4 of 15

5 Fig. 2: Experimental setup for image acquisition Page 5 of 15

6 Fig. 3: ROI for CNR measurement on the Step Phantom Image Page 6 of 15

7 Fig. 4: Formula for Contrast to Noise Ratio (CNR) Page 7 of 15

8 Results Exposure with Grid Correct alignment even uneven density has been confirmed. (Fig. 5) Grid line could be clearly visible in the incident angle 9 degrees. (Fig. 5) It became a density profile of different shapes for each incident angle. (Fig. 6) When the angle increase the contrast is lowered. (Fig. 6) CNR in the incident angle 9 degrees was reduced up to 40 % of correct alignment. (Fig. 7) Exposure with Virtual Grid Processing The density of the region far from the X-ray focal point in accordance with incident angle increases was reduced. (Fig. 8, 9) Image contrast was certain to be independent of the incident angle. (Fig. 9) Page 8 of 15

9 CNR in correct alignment was the same as the exposure with Grid. (Fig. 10) CNR of the distant region from the X-ray focal spot, the incident angle is slightly reduced in accordance with increase. (Fig. 10) Images for this section: Page 9 of 15

10 Fig. 5: Step Phantom Image obtained with Grid technique. Fig. 6: Density profile curve of Step Phantom Image obtained with Grid technique. Page 10 of 15

11 Fig. 7: CNR profile curve of Step Phantom Image obtained with Grid technique. Page 11 of 15

12 Fig. 8: Step Phantom Image obtained with Virtual Grid Processing. Page 12 of 15

13 Fig. 9: Density profile curve of Step Phantom Image obtained with Virtual Grid Processing. Page 13 of 15

14 Fig. 10: CNR profile curve of Step Phantom Image obtained with Virtual Grid Processing. Page 14 of 15

15 Conclusion In exposure with Virtual Grid Processing, even with half of dose of exposure with grid, equivalent image quality was obtained. The CNR does not change greatly when incident angle of X-ray of FPD become larger, however, gentle gradient of image density can be seen, therefore, in portable exposure, misalignment has to be small as much as possible. Personal information References Michael D. Carlin, Robert M. Nishikawa, Heber MacMahon, and Kunio Doi. The effect of x-ray beam alignment on the performance of antiscatter grids. Med. Phys. 23 (8): (1996). Page 15 of 15