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Akihiko Takahashi Last modified date:2021.05.18

Associate Professor / Fundamental Radiological Sciences
Department of Health Sciences
Faculty of Medical Sciences


Undergraduate School


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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/akihiko-takahashi
 Reseacher Profiling Tool Kyushu University Pure
Phone
092-642-6725
Fax
092-642-6674
Academic Degree
Ph.D of Engineering
Field of Specialization
Quantum Electronics Radiological Tecnology of Nuclear Medicine
Research
Research Interests
  • Study on evaluation of nuclear medicine imaging using a Monte Carlo simulation
    keyword :   nuclear medicine  Monte-Carlo simulation PET
    2011.06.
Current and Past Project
  • "Leading project for EUV lithography source developement"
    Ministry of Education,Culture,Science and Technology,Japan
Academic Activities
Reports
1. Application of the Monte Carlo Simulation 6: Monte Carlo Simulation in Nuclear Medicine, [URL].
Papers
1. Akihiko Takahashi, Keita Funada, Kazuhiko Himuro, Shingo Baba and Masayuki Sasaki, Impact of Collimator on DaT-SPECT Imaging: Monte Carlo Simulation Study, RADIOLOGY AND MEDICAL DIAGNOSTIC IMAGING, 2, 4, 1-6, 2020.01, Aim: The purpose of this study was to assess the impact of the collimator in viewing the dopamine transporter, using 123I ioflupane single-photon emission computed tomography (DaT-SPECT) images utilizing a Monte Carlo simulation.
Methods: For the purpose of this study, the Monte Carlo simulation of electrons and photons (MCEP)-SPECT was used. A numerical phantom was created from a real basal ganglia phantom and installed within the code. The specific binding ratios (SBRs) were 5.03 and 2.01 for the background concentration of 7.44 kBq/mL or 7.04 and 3.03 for a background concentration of 5.56 kBq/mL. The simulated images were evaluated using a recovery coefficient (RC). Initially, we simulated the performance of 14 collimators without resolution correction to investigate the impact of the collimator dimension. The effects of two resolution correction methods (collimator broad correction (CBC) and three-dimensional frequency–distance relationship (3D-FDR)) on two reconstruction methods (Ordered-Subsets Expectation Maximization (OSEM) and Filtered back projection (FBP)) was assessed for collimators that demonstrated a better RC value.
Results: Five low-energy high-resolution (LEHR) collimators and one medium-energy general-purpose (MEGP) collimator demonstrated superior RC values. These collimators had a high aspect ratio (hole-length/hole-diameter). The maximum RC value without resolution correction was 64.9% when the image was reconstructed with OSEM. The RC value improved to 79.7% when the resolution correction of CBC was applied. When the resolution collection was applied, the RCs improved by approximately 1.2 times when compared against those without the resolution correction. In terms of the reconstruction method, the RC obtained using OSEM was statistically insignificant when compared to the RC using FBP. The difference in the RC value with collimators decreased according to resolution correction.
Conclusion: The LEHR collimator with a high aspect ratio, and the OSEM with spatial resolution correction were confirmed to be appropriate for DaT-SPECT imaging. In terms of the reconstruction method, CBC was more favourable than FDR..
2. Akihiko Takahashi, Shingo Baba, Masayuki Sasaki, Assessment of collimators in Radium-223 imaging with channelized Hotelling observer: a simulation study, Annals of Nuclear Medicine, 10.1007/s12149-018-1286-4, 32, 10, 649-657, 2018.12, Objective Radium-223 (223Ra) is used in unsealed radionuclide therapy for metastatic bone tumors. The aim of this study is to apply a computational model observer to 223Ra planar images, and to assess the performance of collimators in 223Ra imaging.
Methods The 223Ra planar images were created via an in-house Monte Carlo simulation code using HEXAGON and NAI modules. The phantom was a National Electrical Manufacturers Association body phantom with a hot sphere. The concentration of the background was 55 Bq/mL, and the sphere was approximately 1.5–20 times that of the background concentration. The acquisition time was 10 min. The photopeaks (and the energy window) were 84 (full width of energy window: 20%), 154 (15%), and 270 keV (10%). Each 40 images, with and without hot concentration, were applied to a three-channel difference-of-Gaussian channelized Hotelling observer (CHO), and the signal-to-noise ratio (SNR) of the hot region was calculated. The images were examined using five different collimators: two low-energy general-purpose (LEGP), two medium-energy general-purpose (MEGP), and one high-energy general-purpose (HEGP) collimators.
Results The SNR value was linearly proportional to the contrast of the hot region for all collimators and energy windows. The images of the 84-keV energy window with the MEGP collimator that have thicker septa and larger holes produced the highest SNR value. The SNR values of two LEGP collimators were approximately half of the MEGP collimators. The HEGP collimator was halfway between the MEGP and LEGP. Similar characteristics were observed for other energy windows (154, 270 keV). The SNR value of images captured via the 270-keV energy window was larger than 154-keV, although the sensitivity of the 270-keV energy window is lower than 154-keV. The results suggested a positive correlation between the SNR value and the fraction of unscattered photons.
Conclusions The SNR value of CHO reflected the performance of collimators and was available to assess and quantitatively evaluate the collimator performance in 223Ra imaging. The SNR value depends on the magnitudes of unscattered photon count and the fraction of unscattered photon count. Consequently, in this study, MEGP collimators performed better than LEGP and HEGP collimators for 223Ra imaging.
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3. Akihiko Takahashi, Kazuhiko Himuro, Shingo Baba, Yasuo Yamashita, Masayuki Sasaki1, Comparison of TOF-PET and Bremsstrahlung SPECT Images of Yttrium-90: A Monte Carlo Simulation Study, Asia Oceania Journal of Nuclear Medicine and Biology, 10.22038, 6, 1, 24-31, 2018.01, Objective(s): Yttrium-90 (90Y) is a beta particle nuclide used in targeted radionuclide therapy which is available to both single-photon emission computed tomography (SPECT) and time-of-flight (TOF) positron emission tomography (PET) imaging. The purpose of this study was to assess the image quality of PET and Bremsstrahlung SPECT by simulating PET and SPECT images of 90Y using Monte Carlo simulation codes under the same conditions and to compare them.
Methods: In-house Monte Carlo codes, MCEP-PET and MCEP-SPECT, were employed to simulate images. The phantom was a torso-shaped phantom containing six hotspheres of various sizes. The background concentrations of 90Y were set to 50, 100,
150, and 200 kBq/mL, and the concentrations of the hot spheres were 10, 20, and 40 times of those of the background concentrations. The acquisition time was set to 30 min, and the simulated sinogram data were reconstructed using the ordered subset expectation maximization method. The contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR) were employed to evaluate the image qualities.
Results: The CRC values of SPECT images were less than 40%, while those of PET images were more than 40% when the hot sphere was larger than 20 mm in diameter. The CNR values of PET images of hot spheres of diameter smaller than 20 mm were larger than those of SPECT images. The CNR values mostly exceeded 4, which is a criterion to evaluate the discernibility of hot areas. In the case of SPECT, hot spheres of diameter smaller than 20 mm were not discernable. On the contrary, the CNR values of PET images decreased to the level of SPECT, in the case of low concentration.
Conclusion: In almost all the cases examined in this investigation, the quantitative indexes of TOF-PET 90Y images were better than those of Bremsstrahlung SPECT images. However, the superiority of PET image became critical in the case of low activity concentrations..
4. Hiroaki Shiba, Akihiko Takahashi, Shingo Baba, Yasuo Yamashita, Kazuhiko Himuro, Masayuki Sasaki, Analysis of the influence of 111In on 90Y-bremsstrahlung SPECT
based on Monte Carlo simulation, Annals of Nuclear Medicine, 10.1007/s12149-016-1112-9, 30, 8, 2016.08, Objective 90Y-ibritumomab tiuxetan (Zevalin) which is used for the treatment of malignant lymphomas can be used for SPECT imaging based on bremsstrahlung from 90Y beta particles. However, gamma rays emitted by 111In, which is administered to evaluate the indication for the treatment, contaminate the 90Y bremsstrahlung images. Our objective is to investigate the influence of 111In on the 90Y SPECT images using Monte Carlo simulation.
Methods We used an in-house developed simulation code for the Monte Carlo simulation of electrons and photons
(MCEP). Two hot spheres with diameters of 40 mm were put in an elliptical phantom. Both spheres (‘‘sphere 1’’ and ‘‘sphere 2’’) were filled with 90Y and 111In mixed solutions.
The activities of 90Y in sphere 1 and sphere 2 were 241 and 394 kBq/mL, respectively, and the ones of 111In were 8.14 and 13.3 kBq/mL, respectively. The background activity of 90Y was 38.6 kBq/mL, whereas that of 111In was 1.30 kBq/mL; moreover, the acquisition time was 30 min. Two energy windows were used: one is 90–190 keV included the 111In photopeak; the other is 90–160 keV. To evaluate the quality of the SPECT images, the contrast recovery coefficient (CRC) and the constant noise ratio (CNR) of the SPECT images were derived.
Results For the energy window between 90 and 160 keV, the 111In count was 74 % of the total. In that case, the CRC values were 30.1 and 30.7 % for ‘‘sphere 1’’ and ‘‘sphere 2’’, respectively, whereas the CNR values were 6.8 and 12.1, respectively. For the energy window between 90 and 190 keV, the 111In count reached 85 % of the total count. The CRC and CNR values were 38.6 and 40.0 % and 10.6 and 19.4, respectively.
Conclusions Our simulation study revealed that the cross talk between 111In and 90Y in SPECT imaging is rather serious. Even for the energy window excluding the 111In photopeak, the count ratio of 90Y was less than 30 % of the total. However, the influence of 111In on 90Y-SPECT imaging cannot be ignored, and the count ratio because of 111In is important to estimate the density of 90Y..
5. Akihiko Takahashi, Miwa Kenta, Masayuki Sasaki, Shingo Baba, A Monte Carlo study on 223Ra imaging for unsealed radionuclide therapy, Medical Physics, 43, 6, 2965-2974, 2016.06.
6. Toshitaka Wakayama, Hiroki Oikawa, Atsushi Sasanuma, Goki Arai, Yusuke Fujii, Thanh-Hung Dinh, Takeshi Higashiguchi, Kazuyuki Sakaue, Masakazu Washio, Taisuke Miura, Akihiko Takahashi, Daisuke Nakamura, Tatsuo Okada, Motoki Yonemura, Yukitoshi Otani, Generation of radially polarized high energy mid-infrared optical vortex by use of a passive axially symmetric ZnSe waveplate, Applied Physics Letters, 107, 8, 081112-1-081112-5, 2015.05, [URL].
7. 高橋 昭彦, 氷室和彦, 山下泰生, 小宮勲, 馬場眞吾, 佐々木 雅之, Monte Carlo simulation of PET and SPECT imaging of 90Y, Medical Physics, 10.1118/1.4915545, 42, 4, 1926-1935, 2015.04, [URL], Purpose: Yittrium-90 (90Y) is traditionally thought of as a pure beta emitter, and is used in targeted radionuclide therapy, with imaging performed using bremsstrahlung single-photon emission computed tomography (SPECT). However, because 90Y also emits positrons through internal pair production with a very small branching ratio, positron emission tomography (PET) imaging is also available. Because of the insufficient image quality of 90Y bremsstrahlung SPECT, PET imaging has been suggested as an alternative. In this article, the authors present the Monte Carlo-based simulation–reconstruction framework for 90Y to comprehensively analyze the PET and SPECT imaging techniques and to quantitatively consider the disadvantages associated with them.
Methods: Our PET and SPECT simulation modules were developed using Monte Carlo simulation of Electrons and Photons (MCEP), developed by Dr. S. Uehara. PET code (MCEP-PET) generates a sinogram, and reconstructs the tomography image using a time-of-flight ordered subset expectation maximization (TOF-OSEM) algorithm with attenuation compensation. To evaluate MCEP-PET, simulated results of 18F PET imaging were compared with the experimental results. The results confirmed that MCEP-PET can simulate the experimental results very well. The SPECT code (MCEP-SPECT) models the collimator and NaI detector system, and generates the projection images and projection data. To save the computational time, we adopt the prerecorded 90Y bremsstrahlung photon data calculated by MCEP. The projection data is also reconstructed using the OSEM algorithm. We simulated PET and SPECT images of a water phantom containing six hot spheres filled with different concentrations of 90Y without background activity. The amount of activity was 163MBq, with an acquisition time of 40 min.
Results: The simulated 90Y-PET image accurately simulated the experimental results. PET image is visually superior to SPECT image because of the low background noise. The simulation reveals that the detected photon number in SPECT is comparable to that of PET, but the large fraction (approximately 75%) of scattered and penetration photons contaminates SPECT image. The lower limit of 90Y detection in SPECT image was approximately 200kBq/mL, while that in PET image was approximately 100kBq/mL.
Conclusions: By comparing the background noise level and the image concentration profile of both the techniques, PET image quality was determined to be superior to that of bremsstrahlung SPECT. The developed simulation codes will be very useful in the future investigations of PET and bremsstrahlung SPECT imaging of 90Y.
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8. Takeshi Higashiguchi, Bowen Li, Yuhei Suzuki, Masato Kawasaki, Hayato Ohashi, Shuichi Torii, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Weihua Jiang, Taisuke Miura, Akira Endo, Padraig Dunne, Gerry O’Sullivan, Tetsuya Makimura, Characteristics of extreme ultraviolet emission from mid-infrared laser-produced rare-earth Gd plasmas, OPTICS EXPRESS(Optical Society of America ) , 10.1364, 21, 26, 31837-31845, 2013.12, We characterize extreme ultraviolet (EUV) emission from
mid-infrared (mid-IR) laser-produced plasmas (LPPs) of the rare-earth
element Gd. The energy conversion efficiency (CE) and the spectral purity
in the mid-IR LPPs at λL = 10.6 μm were higher than for solid-state LPPs at λL = 1.06 μm, because the plasma produced is optically thin due to the lower critical density, resulting in a CE of 0.7%. The peak wavelength remained fixed at 6.76 nm for all laser intensities studied. Plasma parameters at a mid-IR laser intensity of 1.3×1011 W/cm2 was also evaluated by use of the hydrodynamic simulation code to produce the EUV emission at 6.76 nm..
9. Development of a micromachining system for irradiation with narrow band soft X-ray at high power density and micromachining of silicone rubber.
10. Kota Okazaki, Shuici Torii, Tetsuya Makimura, Hiroshi Niino, Kouichi Murakami, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Sub-wavelength micromachining of silica glass by irradiation of CO2 laser with Fresnel diffraction, Applied Physics A -Material Science & Processing, 10.1007, 104, 2, 593-599, 2011.08, We investigated a simple and productive micromachining method of silica glass by ablation using a TEA CO2 laser (10.6 μm) with a spatial resolution down to subwavelength scale. The silica glass was irradiated by the TEA CO2 laser light through a copper grid bmask with square apertures of 20×20 μm2 attached to the silica glass surface. After the irradiation, circular holes with a diameter of several μm were formed on the silica glass surface at the centers of the apertures due to the Fresnel diffraction effect. The minimum diameter of the holes was 3.4 μm. The characteristics of the micromachining are discussed based on the electric field distributions of the CO2 laser light under the mask using a three-dimensional full-wave electromagnetic field simulation..
11. T. Makimura, S. Torii, Kota Okazaki, D. Nakamura; A. Takahashi, H. Niino, K. Murakami, Responses of polymers to laser plasma EUV light beyond ablation threshold and micromachining, SPIE Proceedings, vol.8077, 80770F, 2011.04, We have investigated responses of PDMS, PMMA and acrylic block copolymers (BCP) to EUV light from laserproduced plasma beyond ablation thresholds and micromachining. We generated wide band EUV light around 100 eV by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band EUV light at 11 and 13 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO2 laser light. The generated EUV light was condensed onto samples, using an ellipsoidal mirror. The EUV light was incident through windows of contact masks on the samples. We found that through-holes with a diameter of 1 μm can be fabricated in PDMS sheets with thicknesses of 10 μm. PDMS sheets are ablated if they are irradiated with EUV light beyond a threshold power density, while PDMS surfaces were modified by irradiation with the narrow band EUV light at lower power densities. Effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals using the practical apparatus. Furthermore, BCP sheets were ablated to have micro-structures. Thus, we have developed a practical technique for microma chining of PMMA, PDMS and BCP sheets in a micrometer scale..
12. S. Torii, T. Makimura, K. Okazaki, D. Nakamura, A. Takahashi, T. Okada, H. Niino, Micromachining of polydimethylsiloxane induced by laser plasma EUV light, SPIE Proceedings 2011, vol.8077, 807714, 2011.04, Polydimethylsiloxane (PDMS) is one of the most important materials in the field of biotechnology.
Because of its biocompatibility, microfabricated PDMS sheets are applied to micro reactors and
chips for cell culture. Conventionally, the micro structures were fabricated by means of molds. This
method has high productivity of micro structures, however it is difficult to fabricate the structures at
high aspect ratios such as through-holes/vertical channels. For fabricating high-aspect structures,
ablation by short wavelength light is promising. In the previous works, we have investigated ablation
of inorganic transparent materials such as silica glass induced by irradiation with laser plasma EUV
lights. We achieved smooth and fine nanomachining. In this work, we applied our technique to
PDMS micromachining. We irradiated a Ta target with Nd:YAG laser light to generate lights in the
range of 10–300 eV. In order to condense EUV lights onto PDMS surfaces at high power density, we
used an ellipsoidal mirror. In front of PDMS sheets, we placed Zr filter that transmitted the EUV
lights of 50–200 eV. We found PDMS sheet is ablated at a rate up to 230 nm/shot. It should be
emphasized that through hole with a diameter of 1 mm is fabricated in PDMS sheet with a thickness
of 4 mm. Thus we demonstrated that the micro structures at high aspect ratios of PDMS sheets are
fabricated by laser plasma EUV lights..
13. Akihiko Takahashi, Shuichi Torii, Tetsuya Makimura, Kouichi Murakami, Kota Okazaki, Daisuke Nakamura,Tatsuo Okada, Hiroyuki Niino , Micromachining of silica glass using EUV radiation of laser-produced plasma, 電気学会論文誌C, 130, 10, 1779, 2010.10.
14. Shuichi Torii, Tetsuya Makimura, KoutaOkazaki1, Daisuke Nakamura1, Akihiko Takahashi, Tatsuo Okada, Hiroyuki Niino, Direct Etching of Polymethylmethacrylate (PMMA) Using Laser Plasma Soft X-Rays, Applied Physics Express, 3, 066502, 2010.06.
15. K.Okazaki, D.Nakamura, T.Akiyama, K.Toya, A.Takahashi, T.Okada, Dynamics of debris from laser-irradiated Sn droplet for EUV lithography light source, SPIE Photonics West 2009, 72010T, 2009.01.
16. D.Nakamura, T.Akiyama, K.Okazaki, A.Takahashi, T.Okada, Ablation Dynamics of Tin Micro-Droplet Irradiated by Double Pulse Laser used for Extreme Ultraviolet Lithography Source, Journal of Physics D: Applied Physics, Vol.41, 245210, Vol.41, p. 245210, 2008.12.
17. Emission Characteristics of Debris from Laser-Produced Plasma EUV Light Source using Tin Target.
18. D.Nakamura, T.Akiyama, A.Takahashi, T.Okada, Imaging Diagnostics of Debris from Laser-Produced Tin Plasma with Droplet Target for EUV Light Source, Journal of Laser Micro/Nanoengineering, Vol.3, No.3, pp. 196–200, 2008.10.
19. D.Nakamura, K.Tamaru, T.Akiyama, A.Takahashi, T.Okada , Investigation of Debris Dynamics from Laser-Produced Tin Plasma for EUV Lithography Light Source, Applied Physics A, Vol.92, No.4, pp. 767–772, 2008.09.
20. A.Takahashi, D.Nakamura, K.Tamaru, T.Akiyama, T.Okada, Emission Characteristics of Debris from CO2 and Nd:YAG Laser-Produced Tin Plasmas for Extreme Ultraviolet Lithography Light Source, Applied Physics B, Vol.92, No.1, pp. 73–77, 2008.07.
21. D. Nakamura, K. Tamaru, Y. Hashimoto, T. Okada, H. Tanaka, A. Takahashi, Mitigation of fast ions generated from laser-produced Sn plasma for extreme ultraviolet light source by H2 gas, Journal of Applied Physics , 102, 1213310, Vol.102, 123310, 2007.11.
22. Daisuke Nakamura, Hiroki Tanaka, Yuki Hashimoto, Koji Tamaru, Akihiko Takahashi and Tatsuo Okada, Laser-Imaging Diagnostics of Debris Behavior from Laser-Produced Tin Plasma for EUV Light Sources, Photonics West 2007, 6458A-07 (2007) , 2007.05.
23. H. Tanaka, A. Matsumoto, A. Takahashi, T. Okada, Development of visualization system of neutral particles generated from laser-produced plasma for EUV light source, Journal of Physics : Conerence Series, 2007.04.
24. D. Nakamura, T. Hiroki, Y. Hashimoto, K. Tamaru, A. Takahashia, T. Okada, Laser-Imaging Diagnostics of Debris Behavior from Laser-Produced Tin Plasma for EUV Light Sources, Proc. SPIE, 2007.01.
25. Characteristics of Extreme Ultraviolet Emission from CO2 Laser-Produced Plasma.
26. Hirroki Tanaka,Yuki Hasshimoto, Kouji Tamaru, Akihiko Takahashi, Tatsuo Okada, Behavior of debris from laser-produced plasma for extreme ultraviolet light source measure by laser imaging technique, Applied Physics Letters, Vol.89 181109, 2006.11.
27. Hiroki Tanaka, Atsushi Matsumoto, Koji Akinaga, Akihiko Takahashi, T. Okada, Comparative study on emission characteristics of extreme ultraviolet radiation from CO2 and Nd:YAG laser-produced tin plasmas, Applied Physics Letters, 10.1063/1.1989441, 87, 4, Vol.87, 041503-1, 2005.06.
28. Y. Hashimoto, H. Tanaka, K. Tamaru, A. Takahashi, T. Okada, Emission characteristics of fast neutral particles an ions from Laser-Produced Plasma for EUV light source with Sn target, Technical Digest of The 4th International Congress on Laser Advanced Materials Processing, 353ページ, 2006.05.
29. Characteristics of Extreme Ultraviolet Emission from CO2 Laser-Produced Plasma.
30. Hiroki Tanaka, Kouji Akinaga, Akihiko Takahashi, Tatsuo Okada, Development of EUV light source by CO2 laser-produced Xe plasma, Proceedings of SPIE, 10.1117/12.596348, 5662, 361-366, Vol. 5662 pp361-366, 2004.06.
31. Hiroki Tanaka, Kouji Akinaga, Akihiko Takahashi, Tatsuo Okada, Development of EUV light source by CO2 laser-produced plasma with nano-structured SnO2 targets, Proceedings of SPIE, 10.1117/12.596357, 5662, 313-318, vol. 5662 pp313-318, 2004.06.
32. Hiroki Tanaka, Kouji Akinaga, Akihiko Takahashi, Tatsuo Okada, Development of target for laser-produced plasma EUV light source using Sn nano-particle, Applied Physics A, 10.1007/s00339-004-2828-2, 79, 4-6, 1493-1495, Vol.79 pp.1493-1495, 2004.06.
33. Hiroki Tanaka, Kouji Akinaga, Akihiko Takahashi, Tatsuo Okada, Emission characteristics of extreme ultraviolet radiation from CO2 laser-produced xenon plasma, Japanese Journal of Applied Physics, 10.1143/JJAP.43.L585, 43, 4B, L585-L587, Vol.43, No.4B, 2004.04.
34. Hiroki Tanaka, Akihiko Takahashi, Tatsuo Okada, T.Ariga, Ryoichi Nohdomi, Kazuaki Hotta, Hakaru Mizoguchi, Spectral dynamics of narrow-band F2 laser for optical lithography, Applied Physics B, 10.1007/s00340-003-1155-1, 76, 7, 735-740, Vol.74 pp.735-740, 2003.01.
35. Hiroki Tanaka, Akihiko Takahashi, Tatuo Okada, Mitsuo Maeda, Kiichiro Uchino, Toshihiro Nishisaka, Akira Sumitani, Hakaru Mizoguchi, Production of laser-heated plasma in high-pressure Ar gas and emission characteristics of vacuum ultraviolet radiation from Ar2 excimers, Applied Physics B, 10.1007/s003400200807, 74, 4-5, 323-326, Vol.74 pp.323-326, 2002.04.
36. Akihiko Takahashi, Tatsuo Okada, Mitsuo Maeda, Kiichiro Uchino, Ar2 excimer emission from laser-heated plasma, The 4th Pacific Rim Conference on Laser and Electro-Optics Tecnical Digest, 218-219, Volume-I pp.I-218 - 219, 2001.05.
37. Akihiko Takahashi, Tatsuo Okada, Takashi Hiyama, Mitsuo Maeda, Kiichiro Uchino, Ryoichi Nohdomi, Hakaru Mizoguchi, Ar2 excimer emission from a laser-heated plasma in a high-pressure argon gas, Appled Physics Latters, Vol.77 No.25 pp.4115-4117, 2000.12.
38. Shinji Nagai, Kiwamu Takehisa, Tatsuo Enami, Toshihiro Nishisaka, Junichi Fujimoto, Osamu Wakabayashi, Hakaru Mizoguchi, Akihiko Takahashi, Development of a 2kHz F2 Laser for 157 nm Lithography, Japanese Journal of Applied Physics, 10.1143/JJAP.38.7013, 38, 12B, 7013-7016, Vol.38 No.12B pp.7013-7016, 1999.12.
39. Naoki Kataoka, Motoya Igarashi, Kiichiro Uchino, Katsunori Muraoka, Akihiko Takahashi, Tatsuo Okada, Mitsuo Maeda, Tsukasa Hori, Katsumoto Terashima, Akira Sumitani, Tatsuo Enami, Hakaru Mizoguchi, Performance Improvement of a Discharge-Pumped ArF Excimer Laser by Xenon Gas Addition, Japanese Journal of Applied Physics, 10.1143/JJAP.38.6735, 38, 12A, 6735-6738, Vol.38 No.12A pp.6735-6738, 1999.12.
Presentations
1. Monte Carlo study on possibility of Ra-223 SPECT imaging.
2. Yuya Sekikawa, Keita Funada, Kazuhiko Himuro, Akihiko Takahashi, Shingo Baba, Masayuki Sasaki, Molecular imaging of 177Lu for hepatic tumor using Monte Carlo simulation and investigation of acquisition condition, SNMMI 2019 annual meeting, 2019.06, 【Background】
177Lu is used for therapy PRRT of neuroendocrine tumors. Although 177Lu formulation is not approved domestically. There is a possibility of being used clinically in the future, and it is necessary to establish imaging method and treatment effect prediction method before clinical use.
【Purpose】
This study aimed to generate 177Lu SPECT images using a homemade Monte Carlo simulation code and examine the influence of images due to changes in acquisition time.
【Methods】
This study is used result of a previous study have shown the time-activity curve for a 177Lu dose of 7.4GBq and an average weight of 77 kg. The simulation is an in-house code called HEXAGON NAI based on Monte Calro simulation of electron and photon (MCEP). The phantom is modeled on NEMA IEC BODY phantom and code in the simulation. The collimator type is middle energy general purpose (MEGP) and code in simulation. The background was assumed to be liver, the spherical insert was assumed to be a tumor. The radioactivity concentration of the background and the spherical insert were 155 kBq/ml and 2.12 MBq/ml at 24 hours after administration. Similarly, the radioactivity concentrations calculated for 6 hours and 72 hours later using time activity curve and 177Lu SPECT images were generated for each time. Also, images when the acquisition time was changed to 12, 6, 3, 2, 1.5 and 1.2 minutes was generated and contrast recovery coefficient (CRC) and contrast noise ratio (CNR) were calculated for each images.
【Results】
In 6 hours later images, CRC maximum value is 75.2%, CNR maximum value is 71.2. In 24 hours later images, CRC maximum value is 113.2%, CNR maximum value is 102.6. In 72 hours later images, CRC maximum value is 72.9%, CNR maximum value is 116.3. In the case that sphere size is 13 mmΦ, time is 6 hours later and acquisition time is 1.5 minutes, CNR is 4.8 and it was invisible. In the case that sphere size is 10 mmΦ, time is 6 hours later and acquisition time is all condition, it was invisible. In the case that sphere size is 10 mmΦ, time is 24 hours later and acquisition time is 3.0 minutes, CNR is 3.6 and it was invisible. In the case that sphere size is 10 mmΦ, time is 72 hours later and acquisition time is 2.0 minutes, CNR is 2.3 and it was invisible. Namely, in the case that sphere size is 17~37mmΦ and acquisition time is all condition, it was visible. Also, in the case that sphere size is 13mmΦ, time is 6 hours later, it is necessary to spend more than 1.5 minutes. In the case that sphere size is 10mmΦ, time is 6 hours later, it was invisible. In the case that sphere size is 10mmΦ and time is 24 hours later, it was necessary to spend more than 3 minutes. In the case that sphere size is 10mmΦ and time is 24 hours later, it was necessary to spend more than 2 minutes.
【Conclusions】
177Lu SPECT images were able to generate for each time using Monte Calro simulation. Also, acquisition time to generate 177Lu SPECT images was able to be shorted..
3. Monte Carlo Simulation of Ra-223 SPECT Images Using Digital Phantom.
4. Impact of difference in activity concentration and size of lesion on the detectability with Channelized Hotelling Observer.
5. Impact of positron range on PET images: A simulation study.
6. Keita Funada, Akihiko Takahashi, Kazuhiko Himuro, Shingo Baba, Masayuki Sasaki, Investigation of Collimator Broad Correction for Dopamine Transporter SPECT Imaging using Monte Carlo Simulation, SNMMI 2018 Annual Meeting, 2018.06, 【Purpose】Dopamine transporter (DaT) single-photon emission computed tomography (SPECT) is used in the diagnosis of Parkinson’s syndrome and dementia with Lewy bodies. The accumulation of 123I-ioflupane in a striatum decreases in these diseases. The collimator removes scattered rays and improves image quality in SPECT. However, the spatial resolution of images is decreased by the collimator septa. The striatum is a small tissue and deeply located; hence, it can be easily affected by spatial resolution deterioration in the SPECT device. Thus, correcting the spatial resolution in imaging the accumulation of 123I-ioflupane is essential. The widely used spatial resolution correction methods are collimator broad correction (CBC) and three-dimensional frequency distance relationship (3D-FDR). CBC is used for the ordered subset expectation maximization (OSEM) method, and 3D-FDR is used for the filtered back projection (FBP) method. The purpose of this study is to quantitatively assess the influence of spatial resolution correction on DaT SPECT images using Monte Carlo simulation.
【Method】The simulation is an in-house code called Monte Carlo simulation of electron and phantom (MCEP). The CT image of the striatum phantom data was installed in the simulation code as a voxel data. The number of voxels was 512 × 512 × 76, and the dimension of voxel was 0.6 × 0.6 × 1 mm . The radioactivity concentration of the background is 5.56 kBq/mL or 7.44 kBq/mL. The ratio of the activity concentrations in the striata to that in the background was (right striatum, left striatum) = (6.03, 3.01) and (8.04, 4.03). The collimator of the gamma camera was an LEHR collimator. The image reconstruction software used was the Prominence ProcessorTM (version 3.1). The Butterworth filter (cutoff frequencies: 0.5 cycles/cm, order: 8) was applied to the projection data. Image reconstruction was carried out using the OSEM (iteration = 6, subset = 10) with or without the CBC and the FBP with or without the 3D-FDR. The projection images were reconstructed with attenuation correction (Chang method) and scatter correction of a triple energy window. The reconstructed images were evaluated using contrast recovery coefficient (CRC). The CRC value was calculated using the region-of-interest of the right and left striata and the background.
【Result】The CRC value of the images reconstructed using FBP with 3D-FDR was 73.3%, and the CRC of the images without 3D-FDR was 62.4 %. On the contrary, the CRC of the images constructed using OSEM was 73.3%, and the CRC of the images without the CBC was 63.7%.
【Conclusion】The CRC values were improved more than 10% using the spatial resolution correction. There was little difference between the OSEM and the FBP method.
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7. Assessment of Ra-223 gamma-ray imaging using Channelized Hoteling Observer.
8. Assessment of optimal collimator in Ra-223 SPECT imaging: A Monte Carlo study.
9. 舟田 圭汰、高橋 昭彦 、氷室 和彦、馬場 眞吾、佐々木 雅之, モンテカルロシミュレーションによるドパミントランスポータSPECT画像におけるコリメータ開口補正の影響の検討, 第74回日本放射線技術学会総会学術大会, 2018.04, 【目的】ドパミントランスポータ(DAT)イメージング剤のSPECT画像のモンテカルロシミュレーション(MCS)を行い、コリメータ開口補正がDAT画像の画質や定量評価へ与える影響を調査した。【方法】MCSコードはガンマカメラコードHEXAGON/NAIをSPECT用に改造したものである。線条体ファントムを512×512×76(縦・横・奥行)、ボクセルサイズ0.6mm×0.6mm×1mmのボクセルデータとしてコードに組み込んだ。I-123濃度はバックグラウンド(BG)である大脳皮質部分で5.56kBq/mLと7.44kBq/mLとし線条体とBGの比はそれぞれ(右,左)=(8.04,4.03),(6.03,3.01)とした。核医学用画像処理ソフトProminence Processor(PP)を用いて線条体ファントムを画像化した。再構成法はOSEM、再構成条件はIteration=6, Subset=10とし、吸収補正はChang法、散乱補正はTEW法とした。右線条体、左線条体、BGに関心領域をそれぞれ設定して、線条体平均放射能濃度の回収率を算出した。3種類のコリメータについて点線源拡がりの距離依存性をMCSで求めPPの開口補正係数として設定して、開口補正再構成画像を作成した。【結果】低エネルギー汎用(LEGP)コリメータに対する回収率は(補正なし,開口補正あり) =(47.7%,57.4%)、低エネルギー高分解能(LEHR)コリメータに対する回収率は(補正なし,開口補正あり) =(53.1%,63.5%)、高エネルギー汎用(HEGP)コリメータに対する回収率は(補正なし,開口補正あり) =(41.6%,52.8%)となった。【結論】コリメータ開口補正によって、回収率が10%程度向上することがわかった。.
10. Investigation of lesion detectability in 223Ra images using Channelized Hotelling Obserber method.
11. Monte Carlo simulation of Ra-223 SPECT imaging.
12. Simulation of PET/SPECT imaging using MCEP code -for radionuclide therapy-.
13. Ryota Ohima, Akihiko Takahashi, Kazuhiko Himuro, Shingo Baba, Masayuki Sasaki, Impact of Collimator on 223Ra Imaging: a Monte-Carlo Study, The SNMMI(Sosiaty of Nuclear Medicine and Molecular Imaging)2017 Annual Meeting , 2017.06, Purpose: Radium-223 (223Ra) is an alpha-emitting radionuclide used in unsealed radionuclide therapy for bone-metastatic prostate cancer. Alpha rays have a short range and high energy. Thus, it is important to comprehend their movement in a patient’s body. In this study, we investigated the impact of collimator on 223Ra abdominal imaging using Monte Carlo simulation.
Methods: The Monte Carlo codes are HEXAGON and NAI; these were developed by Tanaka and Uehara. The HEXAGON code simulates the behavior of the photon and electron in the phantom and collimator, and then, the NAI code simulates their behavior in the gamma camera, including the optical components and scintillator, producing projection images. We installed a numeric phantom that was created using computed tomography (CT) images of an abdominal phantom. 223Ra was distributed in the third lumbar vertebral region, and 22 X-rays and gamma rays were installed. The width of the energy window was determined to be 20% of 84 keV-photopeak (76–92 keV), in accordance with previous studies. We examined two low-energy, general-purpose (LEGP) collimators (Collimators I and II) and two medium-energy, general-purpose (MEGP) collimators (Collimators III and IV). The collimator dimensions, i.e., septal thickness and hole diameter, were 0.017 cm and 0.178 cm for Collimator I, 0.025 cm and 0.190 cm for Collimator II, 0.084 cm and 0.26 cm for Collimator III, and 0.11 cm and 0.337 cm for Collimator IV, respectively. The collimator height was 4.0 cm. The event number of decay was 108.
Results: As the septal thickness increased, the simulated projection images seemed clearer. Detection sensitivity (cps/MBq) is an important factor in imaging. We simulated energy spectra for each image from which sensitivities were derived. The total sensitivities of the gamma camera were 131 cps/MBq for Collimator I, 80.1 cps/MBq for Collimator II, 41.9 cps/MBq for Collimator III, and 69.5 cps/MBq for Collimator IV. The fractions of sensitivity due to unscattered photons, indicating the image quality, were 6.35 (I), 11.0 (II), 27.4 (III), and 29.4 % (IV). The sensitivities for LEGP were much larger than those for MEGP; however, the fractions of unscattered photons for MEGP were larger than those for LEGP. This is because thick septa effectively removed scattered photons and lead fluorescence.
Conclusions: In this investigation, the most favorable collimator for superior image quality was the Collimator IV, which had the thickest septum and the largest hole diameter. However, an excessively large hole diameter increases photon scatter and degrades spatial resolution. Therefore, other collimators need to be investigated for various 223Ra distributions.
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14. Monte Carlo Simulation on Collimator Dependencies at 223Ra Imaging for Alpha Ray Radionuclide Therapy.
15. Investigation of Optimum Collimator Conditions for Dopamine Transporter SPECT Imaging using Monte-Carlo Simulation.
16. Akihiko Takahashi, Kazuhiko Himuro, Shingo Baba, Masayuki Sasaki, A Monte Carlo simulation of 223Ra imaging for unsealed radionuclide therapy, 22th International Conference on Medical Physics (ICMP2016), 2016.12, Purpose: Radium-223(Ra-223), an alpha-emitting radionuclide, is used in unsealed radionuclide therapy for metastatic bone tumors. Our purpose is to investigate the feasibility and utility of Ra-223 imaging using an in-house Monte Carlo simulation code.
Methods: A three-dimensional numeric phantom was installed in the simulation code. Ra-223 accumulated in a part of the spine, and 22 gamma rays between 80 and 450 keV were selected as the emitted photons. We also simulated technetium-99m(Tc-99m) imaging under the same conditions and compared the results.
Results: The sensitivities of the three photopeaks were 147 counts per unit of source activity (cps/MBq; photopeak: 84 keV, full width of energy window: 20%), 166 cps/MBq (154 keV, 15%), and 158 cps/MBq (270 keV, 10%) for a low-energy general-purpose (LEGP) collimator, and those for the medium-energy general-purpose (MEGP) collimator were 33 cps/MBq, 13 cps/MBq, and 8.0 cps/MBq, respectively. In the case of Tc-99m, the sensitivity was 55 cps/MBq (141 keV, 20%) for LEGP and 52 cps/MBq for MEGP. The fractions of unscattered photons of the total photons reflecting the image quality were 0.09 (84 keV), 0.03 (154 keV), and 0.02 (270 keV) for the LEGP collimator and 0.41, 0.25, and 0.50 for the MEGP collimator, respectively.
Conclusions: Our simulation study revealed that the most promising scheme for Ra-223 imaging is an 84-keV window using an MEGP collimator. The sensitivity of the photopeaks above 100 keV is too low for Ra-223 imaging..
17. 高橋 昭彦, 三輪 建太, 佐々木 雅之, 馬場 眞吾, Monte Carlo Simulation of 223Ra imaging for unsealed radionuclide therapy, 第72回日本放射線技術学会総会学術大会, 2016.04.
18. Monte Carlo Simulation of DAT-SPECT Imaging
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19. Akihiro Shiba, Akihiko Takahashi, Kazuhiko Himuro, Yasuo Yamashita, Singo Baba, Masayuki Sasaki, Comparison images between PET and SPECT of 90Y: A Monte-Carlo simulation study, The 2015 Society of Nuclear Medicine and Molecular Imaging (SNMMI) Annual Meeting, 2015.06, [URL].
20. 芝 弘晃, 高橋 昭彦, 佐々木 雅之, モンテカルロシミュレーションによる90Y-PET/SPECTの検知限界に関する研究, 第71回日本放射線技術学会総会学術大会, 2015.04, 【Purpose】The SPECT image for the bremsstrahlung emitted from Yttrium-90 used in targeted radionuclide therapy for malignant lymphoma and the PET image for the internal pair production were generated using our own custom Monte-Carlo simulation codes to examine the detection limit. 【Method】 We used an NEMA IEC Body Phantom containing six hot spheres. Each sphere included the activity concentrations of 1–6 MBq/mL of Yttrium-90 and the background concentration included 1/10–1/40 for the hot spheres. Acquisition time was set to 30 min. In the case of SPECT, the number of the projections was set to 120°/360°. We used the “Prominence Processor®” software to reconstruct the SPECT projection images and to evaluate some reconstructed images. In the case of PET, we used our own custom software to reconstruct the PET images. 【Result】 The contrast recovery coefficient (CRC) and the contrast noise ratio (CNR) for hot spheres decreased with decreasing diameter of the hot sphere and with the decreasing hot sphere-background concentration ratio. In the case of 1–6 MBq/mL concentration in the hot spheres, the CNR for a 10-mm hot sphere was lower than 5.0 in all conditions for SPECT. Therefore, a 10 mm hot sphere could not be identified by SPECT. The CNR for a 13 mm or larger hot sphere was higher than 5.0 only for the case of the hot sphere-background ratio of 1/40. In PET, when the hot sphere-background ratio was as high as 1/20.
21. Investigation on detection llimits of 90Y-PET and SPECT- part I.
22. Investigation on detection llimits of 90Y-PET and SPECT- part I.
23. Monte Carlo Simulation of PET and SPECT of 90Y.
24. Application to nuclear medicine of the Monte Carlo simulation.
25. Monte Carlo simulation of 131I-SPECT.
26. Development of the Monte Carlo simulation cord of 90Y-SPECT.
27. Investigation on the Time-of-Flight effect of the PET image using the Monte Carlo simulation.
28. Nobuhiko Siguura, Shuichi Torii, Tetsuya Makimura, Yoshiyuki Ichinosawa, Kota Okaaki, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Hiroyuki Niiro, Kouichi Murakami, Micromachining of PMMA using Laser Plasma Soft X-Rays for Fabrication of 3D Molds in a Micrometer Scale, The 14th International Symposium on Laser Precision Microfabrication , 2013.07.
29. Nbuhiro Sugiura, Shuichi Torii, Tetsuya Makimura, Kota Okazaki, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Hiroyuki Niiro, Kouichi Murakami, Ablation Process of PMMA Induced by Irradiation with Laser Plasma EUV light, The 10th Conference on Laser and Electro-Optics Pacific Rim, 2013.07.
30. Shintaro Fukami, Shuichi Torii, Tetsuya Makimura, Kota Okazaki, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Hiroyuki Niiro, Kouichi Murakami, Micromachining of Polydimethylsiloxane usining Laser Plasma Soft X-rays, The 14th International Symposium on Laser Precision Microfabrication, 2013.07.
31. Tetsuya Makimura, Shuichi Torii, Daisuke Nakamura, Akihiko Takahashi, Tatsuo Okada, Hiroyuki Niiro, Kouichi Murakami, Responses of organic and inorganic materials to intense EUV radiation from laser-produced plasmas, SPIE Optics + Optelectronics 2013, 2013.04.
32. Micromachining of PMMA using Laser Plasma Soft-X rays for Fabrication of 3D Molds in a Micrometer Scale.
33. Development of the Monte-Carlo simulation cord of PET scanner.
34. Monte-Carlo simulation of the 90Y-PET imaging.
35. Micromachining using EUV radiation from laser produced plasma.
36. Micromachining of Poly(methyl methacrylate) Using Laser Plasma Soft X-Rays.
37. Monte Carlo Simulation of Retinal Vessel Image.
38. Characteristics of micromachining of Silicon Rubber Using Laser Plasma Soft X-rays.
39. Testuya Makimura, Shuichi Torii, Kota Okazaki, Daisuke Nakamura, Akihiko Takahashi, Hiroyuki Niiro, Tatsuo Okada, Kouichi Murakami, Responce of polymers to laser plasma EUV light beyond ablation threshold and micromachining , SPIE Optics + Optelectronics 2011, 2011.04.
40. Influence of Light Scattering on Retinal Vessel Oxymetry.
41. Monte Carlo Simulation of Retinal Vessel Oxymetry.
42. Micromachining of transparent materials using laser plasma x-rays.
43. Micromachining of Silicon Rubber Using Laser Plasma Soft X-rays.
44. Micromachining of transparent materials using Fresnel diffraction of infrared radiation.
45. Micromachining of SiO2 by TEA CO2 laser Fresnel diffraction light through the metal mask.
46. Micromachining of SiO2 by near-field ablation using 10.6μm TEA CO2 laser..
47. Micromachining of SiO2 by Fresnel diffraction of TEA CO2 laser light with the metal mas.
48. Micromachining of SiO2 by TEA CO2 laser near-field light.
49. Direct micromachining of transparent materials using EUV radiation from laser produced plasma.
50. Development of Laser-Produced Plasma Extreme Ultraviolet Light Source for Micromachining of Transparent Materials.
51. Study on Micromachining of Transparent Materials Using Laser Plasma Soft X-rays.
52. Micromachining of transparent materials using EUV radiation from CO2 laser produced plasma.
53. Micromachining of transparent materials using EUV radiation from CO2 laser produced plasma.
54. Development of Extra-ultraviolet Lithography Light Source.
55. Comparative study on emission characteristics of debris from CO2 and Nd: YAG laser-produced plasmas.
56. CO2 laser-produced Sn plasma for optical lithography.
57. The Triggering Effect on Discharge of Laser-Produced Plasma with Tin Target.
58. Measurement of ion energy generated in laser-produced plasma.
59. Visualization of Particle Behavior from Laser-Produced Plasma.
60. Development of Extreme Ultraviolet Light Source in Kyushu University.
61. Ar2 dimer production by laser-heated plasma pumping.
Membership in Academic Society
  • Japan Society of Medical Physics
  • The Japan Society of Applied Physics
  • The Institute of Electrical Engineering of Japan
Awards
  • 学外