Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Akihiko Takahashi Last modified date:2021.05.18

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

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.
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.
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. Mistuhiro Higashihata, Tadashi Nakamura, Akihiko Takahashi, Yoshiki Nakata, Tatsuo Okada, Broadband light source based on stimulated Raman scatterring in silica optical fiber for optical coherence tomography, Japanese Journal of Applied Physics, 10.1143/JJAP.43.4195, 43, 7A, 4195-4197, Vol.43, No.7A, pp.4195-4197, 2004.07.
34. 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.
35. 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.
36. 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.
37. 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.
38. 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.
39. 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.
40. 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.
41. Akihiko Takahashi, Tatsuo Okada, Numerical Analysis of Ar2* Excimer Production in Laser-Produced Plasmas, Japanese Journal of Applied Physics, 10.1143/JJAP.37.L390, 37, 4A, L390-L393, Vol.37, No.4A, pp. L390-L393, 1998.04.
42. Akihiko Takahashi, Kiyoto Nishijima, Kinetic Model of Gas Heating of Laser-Produced Plasmas by CO2 Laser in Atmosepheric Air, Japanese Journal of Applied Physics, 10.1143/JJAP.37.313, 37, 1, 313-319, Vol.37 No.1, pp313-319, 1998.01.