Hayashi, Hiroaki

Kanazawa, Yuki

Kimoto, Natsumi

Maehata, Itsumi

Okino, Hiroki

Takegami, Kazuki

Yamakawa, Tsutomu

Yamamoto, Shuichiro

Tokushima University Institutional Repository

Page 1 of 33Fabrication and analysis of phantoms providing the equal-image-density for basic experiment of next-generation-typeX-ray diagnosisPoster No.: C-0012Congress: ECR 2016Type: Scientific ExhibitAuthors: N. Kimoto1, H. Hayashi1, H. Okino1, K. Takegami1, I. Maehata1,Y. Kanazawa1, T. Yamakawa2, S. Yamamoto3; 1Tokushima/JP,2Osaka/JP, 3Kanagawa/JPKeywords: Image verification, Technical aspects, Dosimetry, Diagnosticprocedure, Experimental, Conventional radiography,Radioprotection / Radiation dose, Radiation physicsDOI: 10.1594/ecr2016/C-0012Any information contained in this pdf file is automatically generated from digital materialsubmitted to EPOS by third parties in the form of scientific presentations. Referencesto any names, marks, products, or services of third parties or hypertext links to third-party sites or information are provided solely as a convenience to you and do not inany way constitute or imply ECR's endorsement, sponsorship or recommendation of thethird party, information, product or service. ECR is not responsible for the content ofthese pages and does not make any representations regarding the content or accuracyof material in this file.As per copyright regulations, any unauthorised use of the material or parts thereof aswell as commercial reproduction or multiple distribution by any traditional or electronicallybased reproduction/publication method ist strictly prohibited.You agree to defend, indemnify, and hold ECR harmless from and against any and allclaims, damages, costs, and expenses, including attorneys' fees, arising from or relatedto your use of these pages.Please note: Links to movies, ppt slideshows and any other multimedia files are notavailable in the pdf version of presentations.Page 2 of 33www.myESR.orgPage 3 of 33Aims and objectivesX-ray equipment is widely used for diagnosis in the medical field. It requires shortexamination time, and this characteristic leads to many examinations with only a smallburden to patients. Using traditional radiography systems, signal (contrast) of the imageis determined by the products of the energy and quantity of X-rays. Therefore, when theproducts of linear attenuation coefficient and thickness are similar among the materialsthe same digital value is obtained. The situation is schematically explained in Fig. 1,and in reality the contamination rate from scattered X-rays plays an important role.Identification of the materials is valuable for X-ray diagnosis, therefore it becomesproblem that the same digital values are obtained when different materials are measuredwith the traditional system. Recently a photon counting system is attracting attentionin the medical field [1-4], because the system has energy resolving capability. TheX-ray spectrum shown in Fig. 1 shows the schematic drawing of the typical photoncounting system which can measure three energy regions. Using them, it is expected thatinformation about the attenuation coefficients can be derived, namely the materials willbe identified by analyzing the spectrum. At present, the system has been progressing,but currently a fundamental study is needed. In the diagnostic X-ray examination, thedigital value is affected by, kind of materials, the contamination rate from the scatteredX-ray and the heel effect. When we fabricate the "equal-image-density materials" whichgive the same digital values, evaluation of the sensitivity analysis for the contaminationrate from scattered X-ray [5] and heel effect [6] is needed.Figure 2 shows the aim of this study; to fabricate equal-image-density materialsnecessary for basic experiment of a photon counting system and to analyze the materialsin term of the influence on the contamination rate from scattered X-ray and heel effect onthe obtained image. These data are valuable in the study of a photon counting system.The chart of our study is presented in Fig. 3. There are two different process; one isfabrication of equal-image-density materials, and the other is experimental procedurefor measuring the contamination rate from the scattered X-ray and the heel effect. Eachprocess of our study is represented in the chart.Images for this section:Page 4 of 33Fig. 1: Introduction of our study. Using a traditional system, on occasion when differentmaterials are measured, the same digital value can be obtained.© - Tokushima/JPPage 5 of 33Fig. 2: The aim of the present study: to fabricate equal-image-density materials, and toanalyze them in terms of contamination rate from scattered X-ray and heel effect on theobtained image.© - Tokushima/JPPage 6 of 33Fig. 3: Chart of our study. The process of fabricating equal-image-density materialsand the details of the materials are presented in figures 4-5, 8-10. Furthermore weinvestigate the influence of contamination rate from scattered X-ray and heel effect usingour fabricated materials, as shown in figures 6-7, 11-15.© - Tokushima/JPPage 7 of 33Methods and materialsFigure 4 shows the procedure for fabricating the equal-image-density materials. First,we prepared soft tissues-equivalent material (SZ-207, Kyoto Kagaku Ltd., Kyoto, Japan)having thicknesses of 20 mm, 40 mm, 80 mm and 160 mm. They are used as a standard;namely, the thickness of other materials will be determined so as to obtain the samedigital value with those of the standard materials. Second, we prepared aluminum, acrylicand bone-equivalent material (BE-H, Kyoto Kagaku Ltd., Kyoto, Japan) having certainthicknesses. Then, the thickness of these materials were modified in accordance to thefollowing procedure; first, we took the X-ray image, second, we measured digital valuesof it, and third, we plotted the digital value as a function of phantom thickness. Theseprocesses were iterated until the digital value became the same as that of the standard.As described above, aluminum, acrylic and bone-equivalent material, giving the samedigital value with soft tissues-equivalent material, were fabricated.Figure 5 shows process of fabricating the equal-image-density materials using machinetools. We prepared rods having cross-sectional surfaces of 40 mm square. The materials(rods) were cut piece by piece using a circular saw and then finely ground down usinga boring machine.Figure 6 shows the schematic drawing for measuring of the contamination rate fromscattered X-rays. We applied the collimator method proposed by Hayashi et al. [5]. Theexperimental setup consists of diagnostic X-ray equipment (Toshiba Medical SystemsCorporation, MRAD-A 50S/70), CR (computed radiography) system (phosphor plate:RP-4S, Konica Minolta Health Care Co., Ltd., Tokyo, Japan), and collimators havingdiameters 5-30 mm. The collimators were composed of a lead plate being 2 mm inthickness supported by aluminum. Distance between phosphor plate and collimator, X-ray equipment are 20 cm and 100 cm, respectively. Tube voltages are 40kV and 100 kVand tube current-time products are 10 mAs in 40kV, and 0.5 mAs in 100 kV.Figure 7 shows a schematic drawing of measurement of the heel effect [6]. The heeleffect appeared in differences of X-ray spectra of which X-rays emitted for orientationof the long axis of the X-ray tube; the maximum difference was presented between thedirections of anode and cathode. When we used an 8 inch phosphor plate under typicalclinical conditions (source to image receptor distance of 100 cm), the solid angle became5 degrees. Hence, we examined the influence of X-ray image caused by the heel effectusing the following three settings; as shown in Fig. 7, "Normal position" uses X-rayson the center, "Cathode side" uses X-rays differed from central axis by 5 degrees, and"Anode side" uses X-rays in the opposite direction of "Cathode side".Page 8 of 33Images for this section:Fig. 4: Procedure for fabricating the equal-image-density materials. We preparedcommercially available materials of soft tissue, bone, acrylic and aluminum. Thethickness which gives the same digital value in X-ray image was determined by theprocedure described in the figure.© - Tokushima/JPPage 9 of 33Fig. 5: The procedure used to fabricate materials by means of machine tools. At first,samples were cut roughly using a circular saw, and then ground down finely using aboring machine.© - Tokushima/JPPage 10 of 33Fig. 6: Schematic drawing of experiment to measure contamination rate from scatteredX-ray. The irradiation condition is indicated in the figure.© - Tokushima/JPPage 11 of 33Fig. 7: Schematic drawings of experiments to evaluate heel effect on the obtained image.By tilting X-ray equipment at an angle of 5 degrees, corresponding X-ray images wereobtained in cathode and anode sides.© - Tokushima/JPPage 12 of 33ResultsFigure 8 shows a typical example of fabricated materials. The graph representsrelationship between thickness of materials and digital value measured with CR system.There are linear relationships between thickness and digital value as indicated by thesolid line. In this case, the standard material having thickness of 80 mm represents adigital value of 1660, and we found that bone being 35.3 mm thick gives the same digitalvalue. Results for all fabricated samples were summarized in Fig. 9. Left and right figuresshow results of 40 kV and 100 kV X-rays, respectively. Trends for soft tissue and acrylicare most of the same, and those of aluminum and bone are similar.Figure 10 shows a summary of fabricated materials. Left figure shows photograph; thematerials on the left side are soft tissue adopted as standard, the materials made ofacrylic, bone and aluminum in the middle show equal-image-density materials at 40kV X-ray, and the right is at 100 kV X-ray. The right table shows detailed informationof thickness. The materials in the same row belong to a group of equal-image-densitymaterial. The upper half rows indicate equal-image-density material for 40 kV X-ray andthe lower are for 100 kV.The calculation methodology for intensity from digital value using a CR system is shownin Figure 11. The obtained X-ray image was analyzed by ImageJ software [7] and themeasured digital value was converted into intensity using the input-output characteristicof the CR system [8,9]. In the analysis of contamination rates from scattered X-ray andthe heel effect, the calculated intensity described above was also used.In order to explain the analysis procedure, we exemplify the analysis of contaminationrate from scattered X-ray of soft tissue. The contamination rate from scattered X-raywas measured by collimator method as represented in the right figure of Fig. 12; first,experimental values (intensities) concerning different diameters were measured, second,they were normalized by the data without collimator (whole of the upper surface of thephantom was irradiated) and plotted as a function of collimator size, third, extrapolatedvalue (fraction of direct X-ray) concerning collimator size of 0 mm was derived, finally,the contamination rate from scattered X-ray was determined by subtracting "the fractionof direct X-ray" from 1. The left figure of Fig. 12 summarizes the contamination rate fromscattered X-ray for thicknesses of 20 mm, 40 mm, 80 mm and 160 mm.In a similar way, the collimator method was applied to all fabricated materials. The resultswere summarized in Fig. 13. The upper and lower columns show condition of 40 kV X-rays and 100 kV X-rays, respectively. As the thicknesses of materials increased, the morePage 13 of 33contamination rate from scattered X-ray increased. The numerical values were 8-60 %for 40 kV X-rays and 10-53 % for 100 kV X-rays.We exemplify the analysis methodology of heel effect using Fig. 14. On the left, schematicdrawings of the experimental setup and corresponding X-ray image are presented. Inthe normal position, all of the phosphor plate was irradiated. On the other hand, only apart of the phosphor plate was irradiated in the cathode and anode positions. Measuredintensities for the three different positions were normalized by that corresponding to thenormal position. In the right figure of Fig. 14, the dependences of the intensities areplotted as a function of phantom thickness; blue and red symbols indicate the resultsof the cathode and anode sides, respectively. In the present case for 40 kV X-rays,the maximum differences from the normal position are found to be 5% and 13% for thecathode and anode sides, respectively.In a similar way, the analyses were applied to the all materials and they were summarizedin Fig. 15. The figures in the upper and lower columns show conditions of 40 kV X-raysand 100 kV X-rays, respectively. The heel effect affected on the intensity difference was1-15 % for 40 kV X-rays and 0.1-9 % for 100 kV X-rays.Images for this section:Page 14 of 33Fig. 8: Typical example to determine the thickness of fabricated materials. The properthickness of fabricated materials which gives the same digital value with that of thestandard material was determined.© - Tokushima/JPPage 15 of 33Fig. 9: Relationship between material thickness and digital value for all fabricatedmaterials. Trends for soft tissue and acrylic are most of the same, and those of aluminumand bone are similar.© - Tokushima/JPPage 16 of 33Fig. 10: Summary of fabricated equal-image-density materials. The left figure shows aphotograph of the materials. The right table indicates the determined thickness of thematerials.© - Tokushima/JPPage 17 of 33Fig. 11: Calculation methodology of intensity from digital value using CR system. Input-output characteristics of CR system were applied to convert intensity from the digitalvalue.© - Tokushima/JPPage 18 of 33Fig. 12: Analysis methodology of contamination rate from scattered X-ray. Contaminationrate from scattered X-ray is measured by collimator method.© - Tokushima/JPPage 19 of 33Fig. 13: Results of measured contamination rate from scattered X-ray.© - Tokushima/JPPage 20 of 33Fig. 14: Analysis methodology of heel effect on obtained image. The derived intensity isnormalized by that of normal position.© - Tokushima/JPPage 21 of 33Fig. 15: Results of measured heel effect on obtained image.© - Tokushima/JPPage 22 of 33ConclusionFigure 16 summarized our study. In order to perform fundamental experiments for aphoton counting technique, we fabricated equal-image-density materials for 40 kV and100 kV X-rays using soft tissue, acrylic, aluminum and bone. The developed group ofmaterials gave the same digital values when phosphor plate (CR system) was used asthe X-ray detector. In the CR system, the digital value is determined by the amount ofincident and scattered X-rays. Scattered X-rays vary as a function of phantom thickness,and incident X-rays are affected by the heel effect. Therefore, we examined their influencewhen using our fabricated materials. The experiments were carried out by means ofclinically used diagnostic X-ray equipment. The contamination rate from scattered X-raywas determined by the collimator method. The heel effect on the obtained image wasmeasured by an experiment in which the X-ray equipment was tilted at a 5 degree angle.As a result, we found that the contamination rate from scattered X-ray were 8-60 % for40 kV X-rays and 10-53 % for 100 kV X-rays. For the heel effect the intensity differenceswere 1-15 % for 40 kV X-rays and 0.1-9 % for 100 kV X-rays. In Figs. 17-24, the thicknessof fabricated materials and corresponding results of the experiments are presented.They are considered to be valuable for fundamental studies for next-generation detectionsystems such as a photon counting system.Images for this section:Page 23 of 33Fig. 16: Conclusion of our study.© - Tokushima/JPPage 24 of 33Fig. 17: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 25 of 33Fig. 18: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 26 of 33Fig. 19: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 27 of 33Fig. 20: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 28 of 33Fig. 21: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 29 of 33Fig. 22: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 30 of 33Fig. 23: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 31 of 33Fig. 24: Appendix of our study. Photographs and corresponding data of contaminationrate from scattered X-ray and heel effect are presented.© - Tokushima/JPPage 32 of 33Personal informationName: Natsumi KimotoAffiliation: School of Health Sciences, Tokushima University, JapanEmail: c201204012@tokushima-u.ac.jpReferences[1] K. Taguchi, JS. Iwanczyk. Vision 20/20: Single photon counting x-ray detectors inmedical imaging. Medical Physics 40, 100901, 2013.[2] Seppi E., Zentai G., Partain L. et al., New method for breast tumor tracking, IEEEInternational Conference on Imaging Systems and Techniques, 442-445, 2012.[3] Hasegawa B.H., Stebler B., Rutt B.K. et al., A prototype high-purity germaniumdetector system with fast photon-counting circuitry for medical imaging, Medical Physics,18(5), 900-909, 1991.[4] Schlomka J.P., Roessl E., Dorscheid R. et al., Experimental feasibility of multi-energy photon-counting K-edge imaging in pre-clinical computed tomography, Physicsin Medicine and Biology, 53, 4031-4047, 2008.[5] H. Hayashi, K. Takegami, Y. Konishi, et al., Indirect Method of Measuring theScatter X-ray Fraction Using Collimators in the Diagnostic Domain, Japanese Journal ofRadiological Technology, 70, 213-222, 2014.[6] Fritz SL, Livingston WH. A comparison of computed and measured heel effect forvarious target angles. Medical Physics, 9, 216-219, 1982.[7] Abramoff MD, Magelhaes PJ, Ram SJ. Image Processing with ImageJ. BiophotonicsInternational, 11, 36-42, 2004.[8] I. Maehata, H. Hayashi, K. Takegami, et al., Fabrication of Improved Multi-slit Equipment to Obtain the Input-output Characteristics of Computed RadiographyPage 33 of 33Systems: Correction of the Heel Effect and Application to High Tube-voltageExperiments, Japanese Journal of Radiological Technology, 70, 867-876, 2014.[9] N. Kimoto, H. Hayashi, I. Maehata, et al., Development of All-in-one Multi-slitEquipment for Measurements of the Input-output Characteristic of a Phosphor Plate,Japanese Journal of Radiological Technology, 69, 1165-1171, 2013.

Fabrication and analysis of phantoms providing the equal-image-density for basic experiment of next-generation-type X-ray diagnosis

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Fabrication and analysis of phantoms providing the equal-image-density for basic experiment of next-generation-type X-ray diagnosis

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