Development of new educational apparatus to visualize scattered X-rays

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1 Development of new educational apparatus to visualize scattered X-rays Poster No.: C-0073 Congress: ECR 2015 Type: Scientific Exhibit Authors: H. Hayashi, K. Takegami, H. Okino, K. Nakagawa, Y Kanazawa ; Tokushima/JP, Kyoto/JP Keywords: Radiation physics, Radioprotection / Radiation dose, Conventional radiography, Digital radiography, Experimental, Education, Safety, Physics, Education and training DOI: /ecr2015/C-0073 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 27

2 Aims and objectives At X-ray inspections, management of scattered X-ray is important for a reduction of unneeded exposure doses. For people such as medical staff, patients and assistants, inessential exposure doses caused by scattered X-rays should be reduced (Fig.1). It is easy to reduce exposure doses for well-educated radiologists and radiological technologists, because the mechanism of scattered X-ray generation is completely clarified by theory. For the education of beginning radiologists and radiological technologists, to visualize scattered X-rays is effective. In physics textbooks [1,2], the Klein-Nishina formula (eq. (1)) is introduced as presented in Fig.2. Here, ds/dw is a differential cross-section, r0 is a 2 classical electron radius, a is hn/mc, and # is an angle between an incident and scattered directions. We can see that the differential cross-section (provability) is determined as functions of incident X-ray energy hn and an angle q. In general, provability is plotted by a two-dimensional graph (see Fig.2, Fig.3) in which the provability is normalized by a scattering angle of 0 degree. This two-dimensional graph is common and easy to understand for engineering students, but it seems that for students taking medical course it is difficult. Recently, Kishida et al. proposed a primary idea to visualize the scattered X-ray in a diagnostic X-ray region [3]. The aim of the present study is to introduce that idea, and to disclose the detail experimental and analytic methodologies. Our apparatus is made with a shielded box including a clinically-used computed radiography (CR) system, which is commonly used in the world. We hope that our educational methodology (idea) will be used extensively. Images for this section: Page 2 of 27

3 Fig. 1: Background of our study. Understanding of scattered X-rays is important for reducing exposure doses. Page 3 of 27

4 Fig. 2: Klein-Nishina formula. In physics textbooks, the generation of scattered X-ray is explained by an equation, and a two-dimensional plot. Page 4 of 27

5 Fig. 3: Some examples of descriptions in textbook. For students who belong to a medical course, these descriptions were difficult to understand, because the graphs and schematic drawings are not familiar to them. Page 5 of 27

6 Methods and materials #Development and experiments# Figure 4 shows a newly developed experimental apparatus by our group. The main body of the apparatus is made with a lead-shield box. A size of the box is 300 mm width, 340 mm length and 270 mm high. The thickness of the wall is 14 mm, consisting of 10 mm acrylic, 2 mm lead and 2 mm aluminum plates. Most of the background X-rays are absorbed by the 2 mm thick lead plate. At the side walls, there are four guides to insert a phosphor plate as shown in Fig.4. The distance (Z) between the phosphor plate and a sample can be set at 15 mm, 40 mm, 100 mm and 210 mm. We design these sizes based on the condition using a inch plate. The sample for generating the scattered X-rays is set at the center of the underside. The incident X-ray is well-collimated by the three lead plates having through holes of 6 mm. An experimental setup is summarized in Fig.5. For obtaining the scattered X-ray image, a phosphor plate (RP-3S) commercialized by Konica Minolta Healthcare was used. To generate the X-ray, diagnostic X-ray equipment commercialized by Toshiba Medical Systems Corporation was used. A typical irradiation condition was Vp =100 kv and tube current-time product of mas. A distance between the X-ray source and the foreground of our apparatus was set to be 750 mm. #Analytic procedure# The chart of the analytic procedure is presented in Fig.6. In the experiment, we determined the intensity of each angle as described later. These data were measured with a condition of a newly defined polar coordinate (angle of #) that differs from the definition of # used in the Klein-Nishina formula. Therefore, we changed the coordinate and theoretically predicted values that were calculated based on the Klein-Nishina formula. Figure 7 shows a schematic drawing of the change of coordinate to convert a variable # to #. In order to match the experimental conditions, we newly defined a polar coordinate on the phosphor plate. A variable Z in the figure shows a distance between a sample and the phosphor plate. Here, an arbitrary point on the polar coordinate is described by two variables of r and #. Then, focusing attention on the triangle (OO'P) area, a relationship between # and # can be summarized by the equation (2). In this equation, a relation between cos# and cos# is obviously written, but the relation between # and # is not clear. Page 6 of 27

7 The Klein-Nishina formula (eq.(1)) is described by cos#, so that the above changing of cos# to cos# can be sufficiently applied to our analysis. From equation (2), the following two considerations are carried out so as to reduce differences between ideal (#) and real (#) coordinates; first, Z closing in on zero, and second, r closing in on infinity. Figure 8 shows an example to calculate theoretically predicted values based on the angle #. Spreadsheet software such as Microsoft Excel is used for the analysis. In Fig.8, the first and second columns show angle # and cos#, respectively. In the third column, cos# is presented. Using the eq. (2), cos# is easily calculated from cos#. Then, based on the eq. (1), the theoretically predicted values are calculated in the fourth column, and they are normalized by data of #=0 degree. In Fig.9, the analytic procedure of the experimentally obtained image is presented. The whole lengths of the image are 250 mm width by 300 mm length. We define the polar coordinate (r,#) in which a center of the coordinate is in agreement with that of the image. Using software ImageJ [4], we set the ROIs as shown in Fig.9 and digital values were obtained. In an example of the analytic procedure in Fig.9, ROIs having diameter of 4 mm are set for every 45 degrees on the r=40 mm circle. The measured digital values were converted to the relative X-ray intensities using the input-output characteristic of the CR system [5,6]. Then, these data series were normalized by the data of 0 degree, and compared with theoretical values calculated above. Images for this section: Page 7 of 27

8 Fig. 4: Photograph and schematic drawing of the developed apparatus. Page 8 of 27

9 Fig. 5: Experimental setup. We use a phosphor plate and diagnostic X-ray equipment. Page 9 of 27

10 Fig. 6: Chart of analysis. Page 10 of 27

11 Fig. 7: Change of coordinate. The cos(theta) is converted to the cos(phi) using equation (2). Page 11 of 27

12 Fig. 8: Example of the theoretical predictions using spreadsheet software. Page 12 of 27

13 Fig. 9: Methodologies to determine the analyzed region (ROI). Page 13 of 27

14 Results The obtained images are represented in Fig.10. For (b) Z=40 mm and (c) Z=110 mm, correct images were measured. On the other hand, images of (a) Z=15 mm and (d) Z=210 mm were slightly improper. An image of (a) had a background contamination caused by scattered X-rays which were generated by the interaction between the air and the incident X-ray beam. For the result of (a) presented later, the background contamination was subtracted. In contrast, image (d) had low intensity that provided cause of larger uncertainties. Therefore, we precisely analyzed the data of Fig.10 (b). Figure 11 shows a comparison between an experimental image (left) and a quantitatively analyzed result (right) for an image of the Z=40 mm experiment. In the plot, a theoretical calculation is carried out assuming that an incident X-ray has monoenergetic energy of 40 kev because of this consideration there is an effective energy of Vp=100 kv X-ray spectrum [7,8]. As shown in the Fig.11, the experimental values are in good agreement with the theoretical values. The analysis is extended to the results which are measured with different Z values (Z= 15, 40, 110, 210 mm). Figure 12 shows comparisons of scattered X-ray distributions for different Z values. Here, the analyzed values are plotted against as a function of angle # by a classical-type plot. The blue circle presents the experimental value, and its error bar is defined by a range between minimum and maximum X-ray intensities in the ROI. For every Z value, the experimental values are consistent with the theoretical ones. These analyzed results are based on the r= 40 mm (see Fig.11), and then an effect of the selected r value is verified as follows. Figure 13 shows analyzed results based on different r values for determination of the ROIs. The left upper figure shows a profile curve of the obtained image. In Fig.13, every experimental result shows consistencies with the theoretical results. From this fact, we concluded that our analyzing method can be applied to all images. The phosphor plate commercialized by Konica Minolta is placed in a housing (cassette) having a carbon protection plate. Therefore, a low energy photon is considered to be absorbed by the carbon plate. We evaluate the effect of low energy photon absorptions as follows. Figure 14 shows comparison between two experiments; one is based on a commonly-used condition (with cassette), and the other is based on a particular condition in which the carbon protection is removed and the experiment is carried out in a dark room. As represented by Fig.14, there is no difference between these results with and without a cassette. This fact means that the absorption of low energy photons are negligibly small. This phenomenon is also explained by a theoretical estimation of scattered X-ray energies. Figure 15 shows energies of scattered X-rays according to the incident X-ray energies. In the diagnostic X-ray region, the scattered X-ray energy is Page 14 of 27

15 similar with the incident X-ray energy, therefore we do not need to consider the energy differences according to the scattered angles. We present the necessity of the shielded box (developed apparatus). In Fig.16, result of the preliminary experiment (left) is compared with the present experiment (right) using the newly developed apparatus. In the left figure, an incident X-ray is collimated by a thin (2 mm) lead plate, and the irradiation field is limited in the collimator. Nevertheless, the background X-rays are obviously derived in as shown in the obtained image. The background X-rays are generated by a movable diaphragm which is part of the X-ray equipment [9]. This result shows that our experimental apparatus works well to reduce background X-rays, and for the experiment to measure Compton scattered X-rays, our apparatus is absolutely imperative. Finally, we explain the importance to choice of sample types. In our earlier study, an aluminum sample was used, however good experimental results were not obtained this was caused by Bragg scattering [10]. Figure 17 shows experimental results in which a collimated X-ray beam [11] is used to irradiate acrylic and aluminum samples. As shown in the obtained images, when an aluminum sample is used, the effect of Bragg scattering appears. The intensity of the Bragg scattering is much higher than that of Compton scattering. Therefore, we consider that the acrylic sample is suitable to use, because this sample does not have a crystal structure causing Bragg scattering. Images for this section: Page 15 of 27

16 Fig. 10: Obtained images of the experiments. Page 16 of 27

17 Fig. 11: Comparison of scattered X-ray distribution between experimental and simulated values. Page 17 of 27

18 Fig. 12: Analyzed results for different Z values. For every distance, the experimental values are in good agreement with the theoretical calculations. Page 18 of 27

19 Fig. 13: Analyzed results for different r values. For all r values, the experimental values are in good agreement with the theoretical calculations. Page 19 of 27

20 Fig. 14: Comparison of two different experiments. One experiment is using a phosphor plate with cassette, and the other experiment is using a phosphor plate without cassette. As shown by the graph, there are no differences between these two experiments. Page 20 of 27

21 Fig. 15: Theoretical estimation of the energy of a scattered X-ray as a function of incident X-ray energy. Page 21 of 27

22 Fig. 16: Demonstration of the necessity of the shielded box. The developed apparatus works for proper reductions of background X-rays that are generated by a movable diaphragm which is part of the X-ray equipment. Page 22 of 27

23 Fig. 17: Demonstration of Bragg scattering using an aluminum sample. If an aluminum sample is used, the effect of Bragg scattering exists much higher than the Compton scattering. Therefore, we used an acrylic sample which does not have a crystal structure caused by the Bragg scattering. Page 23 of 27

24 Conclusion The image measured with our apparatus makes it possible to visualize scattered X-rays. The image can be analyzed quantitatively, and the results are in good agreement with the theoretical formula. Using our apparatus, this relatively simple experiment can educate radiologists and radiological technologists effectively. We summarized an overview of the present study in Fig.18. Actually, we use the developed apparatus to educate senior students who belong to the school of health sciences at Tokushima University. The apparatus has great educational effect. [Acknowledgement] The authors are grateful to M. Kishida, T. Kuboyabu, T. Inoue, H. Hanamitsu, S. Nishihara for contributions at the early stage of our experiments. Also we thanks to N. Kimoto and I. Maehata for their helps to write EPOS. Images for this section: Page 24 of 27

25 Fig. 18: Summary of our study. Page 25 of 27

26 Personal information 1) Hiroaki Hayashi Kazuki Takegami 2) 3) Hiroki Okino 3) Kohei Nakagawa Yuki Kanazawa ) Institute of Health Biosciences, Tokushima University, Japan. Graduate School of Health Sciences, Tokushima University, Japan. School of Health Sciences, Tokushima University, Japan. References Glenn F. Knoll, Radiation Detection and Measurement (3rd ed.), John Wiley & Sons, Inc Anthony Brinton Wolbarst, Physics of radiology (2nd ed.), Medical Physics Publishing, K. Mina, H. Hayashi, T. Kuboyabu et al., Fabrication of a visualization equipment for scattered X-rays in the diagnosis domain and proposal of a practical training, Japanese Journal of Radiological Technology, 69(5), , Abramoff MD, Magelhaes PJ, Ram SJ. Image Processing with ImageJ, Biophotonics International 2004, 11(7), 36-42, N. Kimoto, H. Hayashi, I. Maehata, et al., Development of all-in-one multi-slit equipment for measurements of the input-output characteristic of a phosphor plate, Japanese Journal of Radiological Technology, 69(10), , I. Maehata, H. Hayashi, K. Takegami, et al., Fabrication of improved multi-slit equipment to obtain the input-output characteristics of computed radiography systems: correction of the heel effect, and application to high tube-voltage experiments, Japanese Journal of Radiological Technology, 70(9), , Page 26 of 27

27 7. H. Hayashi, A. Fukumoto, H. Hanamitsu, et al., Practical calculation method of diagnostic X-ray spectrum using EGS5 code, Medical Imaging and Information Science, 29(3), 62-67, R. Birch, M. Marshall, Comparison of bremsstrahlung X-ray spectra and comparison with spectra measured with a Ge (Li) detector, Phys. Med. Biol., 24(3), , H. Hayashi, S. Taniuchi, N. Kamiya, et al., Development of a pin-hole camera using a phosphor plate, and visualization of the scattered X-ray distribution and optical image, Japanese Journal of Radiological Technology, 68(3), , B.D. Cullity and S.R. Stock, Elements of X-ray diffraction, Prentice Hall, K. Takegami, H. Hayashi, Y. Konishi, et al., Development of multistage collimator for narrow beam production using filter guides of diagnostic X-ray equipment and improvement of apparatuses for practical training, Medical Imaging and Information Sciences, 30(4), Page 27 of 27

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