Updated on 2025/10/16

写真a

 
NARITA Akihiro
 
Organization
Academic Assembly Institute of Medicine and Dentistry Health Sciences Assistant Professor
Faculty of Medicine School of Health Sciences Radiological Technology Assistant Professor
Title
Assistant Professor
External link

Degree

  • 博士（保健学） ( 2018.3   新潟大学 )

  • 修士（保健学） ( 2011.3   新潟大学 )

Research Areas

  • Others / Others

Research History

  • Niigata University   Faculty of Medicine School of Health Sciences Radiological Technology   Assistant Professor

    2015.4

 

Papers

  • [Simple Method to Measure Slice Sensitivity Profile in Non-helical CT Using Tilted Metal Wire].

    Akihiro Narita, Masaki Ohkubo, Yuki Ohsugi

    Nihon Hoshasen Gijutsu Gakkai zasshi   80 ( 9 )   923 - 927   2024.9

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    Language：Japanese   Publishing type：Research paper (scientific journal)  

    PURPOSE: The measurement of slice sensitivity profile (SSP) in non-helical CT is conventionally performed by repeated scans with moving a micro-coin phantom little by little in the longitudinal direction at a small interval, which is reliable but laborious and time-consuming. The purpose of this study was to propose a simple method for measuring the SSP in non-helical CT based on a previous method that measured the slice thickness using a tilted metal wire. METHODS: In the proposed method, a CT image was obtained by scanning a wire tilted at an angle θ=30° to the scan plane. By deconvolving the image with the point spread function (PSF) measured at the scanner, we obtained an image that was not affected by the PSF blurring. The CT value profile along the wire was acquired on the obtained image. The SSP was determined by multiplying the profile by tan θ. In addition, the SSP was measured by the conventional method using a micro-coin phantom and compared with the SSP obtained by the proposed method. RESULTS: The SSP measured by the proposed method agreed well with that measured by the conventional method. The full-width at half-maximum values of these SSPs were the same. CONCLUSION: The proposed method was demonstrated to easily and accurately measure the SSP in non-helical CT.

    DOI： 10.6009/jjrt.2024-1486

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  • [Method for Measuring Noise Power Spectrum Depending on X-ray Tube Angle in Spiral Orbit of Helical CT Scan].

    Yuki Ohsugi, Akihiro Narita, Masaki Ohkubo, Kenichi Sakai, Takahiro Fukaya, Yoshiyuki Noto

    Nihon Hoshasen Gijutsu Gakkai zasshi   2023.9

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    Language：Japanese   Publishing type：Research paper (scientific journal)  

    PURPOSE: The noise power spectrum (NPS) in computed tomography (CT) images potentially varies with the X-ray tube angle in a spiral orbit of the helical scan. The purpose of this study was to propose a method for measuring the NPS for each angle of the X-ray tube. METHODS: Images of the water phantom were acquired using a helical scan. As a conventional method, we measured the two-dimensional (2D) NPS from each image and averaged them; the obtained 2D-NPS was referred to as NPSconventional. In the proposed method, we made the X-ray tube angle θ (0°≤θ<360°) to correspond to the image according to each slice position of the images that located within the travel distance of the CT scan table per 360° rotation of the X-ray tube. We obtained the 2D-NPS from each image and assigned the θ (0°, 30°, 60°, 90°, 120°, 150°, 180°); the obtained 2D-NPS was referred to as NPSsθ. The NPSsθ was compared to the NPSconventional. Also, we investigated the dependency of the NPSsθ on the θ. RESULTS: The NPSconventional was found to be isotropic, and in contrast, the NPSsθ was anisotropic. The NPSsθ showed a continuously rotational change while increasing the θ. There was an excellent correlation (R2>0.999) between the rotation angle of NPSθ and the θ. CONCLUSION: The proposed method was demonstrated to be effective for evaluating anisotropic noise characteristics depending on the X-ray tube angle.

    DOI： 10.6009/jjrt.2023-1363

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  • Method for measuring noise-power spectrum independent of the effect of extracting the region of interest from a noise image

    Akihiro Narita, Yuki Ohsugi, Masaki Ohkubo, Takahiro Fukaya, Kenichi Sakai, Yoshiyuki Noto

    Radiological Physics and Technology   2023.7

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    Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

    DOI： 10.1007/s12194-023-00733-2

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    Other Link： https://link.springer.com/article/10.1007/s12194-023-00733-2/fulltext.html

  • [An Easy-to-use Method for CT Image Simulation with Parameter Optimization Using a Water Phantom]. Reviewed

    Akihiro Narita, Kazuki Okamoto, Kengo Toyonaga, Masaki Ohkubo

    Nihon Hoshasen Gijutsu Gakkai zasshi   78 ( 7 )   732 - 740   2022.7

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    Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

    PURPOSE: We developed an easy-to-use method to generate computed tomography (CT) images that simulate the images obtained when using an actual scanner. METHODS: The developed method generates images by simulating the data acquisition and image reconstruction processes of a scanner from a linear attenuation coefficient map of an object numerically generated. This approach is similar to general image simulation methods. However, we introduced adjustable parameters for the CT data acquisition process, for example, parameters related to X-ray attenuation in the anode of the X-ray tube and the bowtie filter. These parameters were optimized in advance by minimizing the difference between the simulated and measured images of a water phantom. To verify the validity of the developed method, a simulated image was generated for a torso phantom and then compared with the measured image of the phantom obtained using the scanner. RESULTS: The simulated and measured images of the torso phantom were in good agreement. The spatial resolution and noise characteristics of these two images were also comparable, further indicating the accuracy of the developed method. CONCLUSION: In the existing methods, various information/data related to an actual scanner, including difficult-to-acquire ones, were essential for image simulation. In the developed method, instead of determining the difficult-to-acquire information/data, we introduced adjustable parameters. Therefore, the developed method was easier to use than the existing methods.

    DOI： 10.6009/jjrt.2022-1222

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  • [A Study of Longitudinal NPS Measurement in CT Images Based on the Central Cross-section Theorem]. Reviewed

    Akihiro Narita, Masaki Ohkubo, Yuki Ohsugi, Kenichi Sakai, Takahiro Fukaya, Yoshiyuki Noto

    Nihon Hoshasen Gijutsu Gakkai zasshi   78 ( 7 )   719 - 725   2022.7

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    Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

    PURPOSE: Various approaches in noise power spectrum (NPS) analysis are currently used for measuring a patient's longitudinal (z-direction) NPS from three-dimensional (3D) CT volume data. The purpose of this study was to clarify the relationship between those NPSs and 3D-NPS based on the central slice theorem. METHODS: We defined the 3D-NPS(fx, fy, fz) that was calculated by 3D Fourier transform (FT) from 3D noise data (3D-Noise(x, y, z), x-y scan plane). Here, fx, fy and fz are spatial frequencies corresponding to the axes of x, y and z, respectively. Based on the central slice theorem, we described three relationships as follows. (1) The fz-directional NPS calculated from the 3D-Noise(x=0, y=0, z) is equal to the profile obtained by projecting 3D-NPS(fx, fy, fz) in fx- and fy-directions. (2) The fz-directional NPS calculated from the profile obtained by projecting 3D-Noise(x=0, y, z) in the y-direction is equal to the profile at fy=0 in the data obtained by projecting 3D-NPS(fx, fy, fz) in the fx-direction. (3) The fz-directional NPS calculated from the profile obtained by projecting 3D-Noise(x, y, z) in x and y-directions is equal to the profile of 3D-NPS(fx=0, fy=0, fz). To verify them, we compared the NPSs measured from actual 3D noise data that were obtained using a cylindrical water phantom. RESULTS: In each relationship (1)-(3), the fz-directional NPS matched the profile obtained from the 3D-NPS(fx, fy, fz). CONCLUSION: Based on the central slice theorem, we clarified the relationships between fz-directional NPSs and 3D-NPS. We should understand them and then consider which method should be used for fz-directional NPS measurement.

    DOI： 10.6009/jjrt.2022-1267

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  • [A Study of 3D-NPS Analysis in CT Images Based on the Central Cross-section Theorem]. Reviewed

    Akihiro Narita, Masaki Ohkubo, Takahiro Fukaya, Kenichi Sakai, Yoshiyuki Noto

    Nihon Hoshasen Gijutsu Gakkai zasshi   78 ( 4 )   342 - 347   2022.4

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    Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

    PURPOSE: The noise power spectrum (NPS) of a CT scanner is commonly measured from a single noise image. However, since CT images are three-dimensional (3D) volume data, they have 3D noise characteristics (3D-NPS). In this study, we clarify the relationship among NPSs measured by various approaches in NPS analysis based on the central slice theorem. Its validity is verified by the NPS measurements using actual 3D noise data. METHODS: We defined the NPSz-projection(fx, fy) that was calculated by the 2D Fourier transform (FT) from the 2D projection of 3D noise data in the patient longitudinal direction, the 3D-NPS(fx, fy, fz) that was calculated by the 3D-FT from the 3D noise data, and the 2D-NPS(fx, fy) that was calculated by the 2D-FT from a single noise image; fx, fy, and fz are spatial frequencies corresponding to the axes of x, y, and z in the reconstructed CT volume, respectively. Based on the central slice theorem, we described that the NPSz-projection(fx, fy=0) was equal to the 3D-NPS(fx, fy=0, fz=0), and the NPS(2D-NPS(fx, fy=0)) was different from the 3D-NPS(fx, fy=0, fz=0). To verify them, we compared the NPSs calculated from actual 3D noise data that were obtained using a cylindrical water phantom. RESULTS: The 3D-NPS(fx, fy=0, fz=0) matched the NPSz-projection(fx, fy=0) and was different from the 2D-NPS(fx, fy=0). CONCLUSION: Based on the central slice theorem, we clarified the relationship among NPSs measured by various approaches in NPS analysis; it is important to understand this and then select an appropriate noise data handling and NPS measurement method.

    DOI： 10.6009/jjrt.2022-1217

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  • Method for determining slice sensitivity profile of iterative reconstruction CT images using low-contrast sphere phantom Reviewed

    Akihiro Narita, Masaki Ohkubo, Takahiro Fukaya, Yoshiyuki Noto

    Radiological Physics and Technology   2021.9

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    Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

    A novel method for measuring the slice sensitivity profile (SSP) of computed tomography (CT) images reconstructed using an iterative reconstruction (IR) algorithm is proposed herein. A phantom that included a low-contrast spherical object was scanned and consecutive cross-sectional images were reconstructed. The mean CT values in a region including the sphere were measured for all images and plotted as a function of slice position along the longitudinal [Formula: see text] direction to yield a mean CT value profile [Formula: see text]. Next, we numerically generated an object function corresponding to the sphere and obtained the mean CT value profile [Formula: see text]. Subsequently, the SSP was modeled as a product of the Gaussian and cosine functions. We convolved [Formula: see text] with the modeled SSP to obtain [Formula: see text]. The difference between [Formula: see text] and [Formula: see text] was evaluated using the root mean square error (RMSE), which was minimized via optimization of the SSP model parameters. To validate the methodology, we first used filtered back projection (FBP) images to compare the SSPs determined using the proposed and standard coin methods. Subsequently, the proposed method was applied to measure the SSPs of four types of IR algorithms in two scanners. The SSPs of the FBP images determined using the proposed and coin methods showed good agreement. Additionally, in the SSP measurements using the proposed method, [Formula: see text] agreed well with [Formula: see text] for every IR algorithm. The RMSEs for all measurements were less than 0.7 HU, indicating the accuracy of the SSPs. Thus, the proposed method is effective for obtaining valid SSPs.

    DOI： 10.1007/s12194-021-00636-0

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    Other Link： https://link.springer.com/article/10.1007/s12194-021-00636-0/fulltext.html

  • 放射線治療計画用CT画像における金属アーチファクトの簡易生成法の研究 ファントムを用いた検討 Reviewed

    麦嶋 大輔, 成田 啓廣, 大久保 真樹

    日本放射線技術学会雑誌   77 ( 5 )   445 - 453   2021.5

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  • Technical Note: A simple method for measuring the slice sensitivity profile of iteratively reconstructed CT images using a non‐slanted edge plane Reviewed International journal

    Akihiro Narita, Masaki Ohkubo, Takahiro Fukaya, Yoshiyuki Noto

    Medical Physics   48 ( 3 )   1125 - 1130   2021.3

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    Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

    PURPOSE: A method for measuring the slice sensitivity profile (SSP) of computed tomography (CT) images reconstructed with iterative reconstruction (IR) algorithms was reported by the AAPM Task Group 233 (TG233). In this method, the phantom plane edge is slightly slanted with respect to the scan plane to obtain a composite oversampled edge-spread function (ESF). However, it is expected that a fine-sampled ESF can be obtained directly from images reconstructed with a small slice increment without slanting the edge plane. This study aimed to investigate the validity of using a non-slanted edge plane. METHODS: In the proposed non-slanted edge method, the phantom was positioned so that the plane edge was perpendicular to the longitudinal z-axis, and images were reconstructed with a 1-mm slice thickness and 0.1-mm increment. The mean CT value was obtained in each slice and plotted as a function of slice position along the z-axis, thereby generating the ESF. The SSP was calculated from the ESF by differentiation. In the TG 233-recommended slanted edge method, the SSP was obtained by following the procedure described in the TG233 report. To validate the methodology, we first used filtered back projection (FBP) images to compare SSPs obtained using the non-slanted edge method, slanted edge method, and a standard method using a high-contrast thin object (coin). Next, for two types of IR algorithms, we compared the SSPs obtained using the non-slanted and slanted edge methods. RESULTS: For the FBP images, the SSP measured using the non-slanted edge method agreed well with SSPs measured using the coin and slanted edge methods. For the IR images, the SSPs measured using the non-slanted and slanted edge methods showed good agreement. CONCLUSIONS: The non-slanted edge method was demonstrated to be valid. The simplicity and practicality of the method allows routine and accurate determination of the SSP.

    DOI： 10.1002/mp.14668

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    Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.14668

  • Detecting MLC modeling errors using radiomics‐based machine learning in patient‐specific QA with an EPID for intensity‐modulated radiation therapy Reviewed International journal

    Madoka Sakai, Hisashi Nakano, Daisuke Kawahara, Satoshi Tanabe, Takeshi Takizawa, Akihiro Narita, Takumi Yamada, Hironori Sakai, Masataka Ueda, Ryuta Sasamoto, Motoki Kaidu, Hidefumi Aoyama, Hiroyuki Ishikawa, Satoru Utsunomiya

    Medical Physics   48 ( 3 )   991 - 1002   2021.3

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    Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

    PURPOSE: We sought to develop machine learning models to detect multileaf collimator (MLC) modeling errors with the use of radiomic features of fluence maps measured in patient-specific quality assurance (QA) for intensity-modulated radiation therapy (IMRT) with an electric portal imaging device (EPID). METHODS: Fluence maps measured with EPID for 38 beams from 19 clinical IMRT plans were assessed. Plans with various degrees of error in MLC modeling parameters [i.e., MLC transmission factor (TF) and dosimetric leaf gap (DLG)] and plans with an MLC positional error for comparison were created. For a total of 152 error plans for each type of error, we calculated fluence difference maps for each beam by subtracting the calculated maps from the measured maps. A total of 837 radiomic features were extracted from each fluence difference map, and we determined the number of features used for the training dataset in the machine learning models by using random forest regression. Machine learning models using the five typical algorithms [decision tree, k-nearest neighbor (kNN), support vector machine (SVM), logistic regression, and random forest] for binary classification between the error-free plan and the plan with the corresponding error for each type of error were developed. We used part of the total dataset to perform fourfold cross-validation to tune the models, and we used the remaining test dataset to evaluate the performance of the developed models. A gamma analysis was also performed between the measured and calculated fluence maps with the criteria of 3%/2 and 2%/2 mm for all of the types of error. RESULTS: The radiomic features and its optimal number were similar for the models for the TF and the DLG error detection, which was different from the MLC positional error. The highest sensitivity was obtained as 0.913 for the TF error with SVM and logistic regression, 0.978 for the DLG error with kNN and SVM, and 1.000 for the MLC positional error with kNN, SVM, and random forest. The highest specificity was obtained as 1.000 for the TF error with a decision tree, SVM, and logistic regression, 1.000 for the DLG error with a decision tree, logistic regression, and random forest, and 0.909 for the MLC positional error with a decision tree and logistic regression. The gamma analysis showed the poorest performance in which sensitivities were 0.737 for the TF error and the DLG error and 0.882 for the MLC positional error for 3%/2 mm. The addition of another type of error to fluence maps significantly reduced the sensitivity for the TF and the DLG error, whereas no effect was observed for the MLC positional error detection. CONCLUSIONS: Compared to the conventional gamma analysis, the radiomics-based machine learning models showed higher sensitivity and specificity in detecting a single type of the MLC modeling error and the MLC positional error. Although the developed models need further improvement for detecting multiple types of error, radiomics-based IMRT QA was shown to be a promising approach for detecting the MLC modeling error.

    DOI： 10.1002/mp.14699

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    Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.14699

  • ファントム画像を用いた最適化を伴う簡易的CT画像シミュレータの考案

    岡本 和樹, 成田 啓廣, 大久保 真樹

    日本放射線技術学会総会学術大会予稿集   77回   184 - 184   2021.3

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    Language：Japanese   Publisher：(公社)日本放射線技術学会  

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  • [Central Slice Theorem-based Relationship between 1D-NPS Obtained by the Slit Method and 2D-NPS for CT Images]. Reviewed

    Akihiro Narita, Masaki Ohkubo, Takahiro Fukaya, Yoshiyuki Noto

    Nihon Hoshasen Gijutsu Gakkai zasshi   77 ( 8 )   828 - 832   2021

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    PURPOSE: The method using a numerical slit (slit method) is used commonly to obtain the one-dimensional (1D) noise power spectrum (NPS) in computed tomography. However, the relationship between the 1D-NPS obtained by the slit method and the original two-dimensional (2D) NPS derived by the 2D Fourier transformation has not been elucidated clearly. The purpose of this study was to clarify their relationship based on the well-known central slice theorem (projection slice theorem) and validate it using computer simulation analysis. METHODS: With the application of the central slice theorem, we described that the 1D-NPS obtained by the slit method was equal to the central slice (profile) in the 2D-NPS when we set the slit length to the maximum (i.e. the matrix size of the noise image). To verify this, we generated computer-simulated noise images with the known 2D-NPS (true 2D-NPS). From those images, we obtained the 1D-NPS that was obtained by the slit method and compared it with the central slice in the true 2D-NPS. RESULTS: When we set the slit length to the maximum, the 1D-NPS obtained by the slit method showed good agreement with the central slice in the true 2D-NPS. CONCLUSION: We clarified the relationship between the 1D-NPS obtained by the slit method and the 2D-NPS using a theoretical approach and the computer simulation. We had to maximize the slit length to achieve the accurate measurement of the 1D-NPS using the slit method.

    DOI： 10.6009/jjrt.2021_JSRT_77.8.828

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  • 低コントラストファントムを用いた逐次近似再構成CT画像におけるmodulation transfer functionの測定

    酒井 健一, 成田 啓廣, 大久保 真樹

    新潟大学保健学雑誌   17 ( 1 )   7 - 15   2020.3

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  • 逐次近似再構成CT画像における球体ファントムを用いたSlice Sensitivity Profileの測定

    深谷 貴広, 成田 啓廣, 大久保 真樹

    日本放射線技術学会総会学術大会予稿集   76回   149 - 149   2020.3

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    Language：Japanese   Publisher：(公社)日本放射線技術学会  

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  • A pitfall of using the circular‐edge technique with image averaging for spatial resolution measurement in iteratively reconstructed CT images Reviewed International journal

    Akihiro Narita, Masaki Ohkubo

    Journal of Applied Clinical Medical Physics   21 ( 2 )   144 - 151   2020.2

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    Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

    The circular-edge technique using a low-contrast cylindrical object is commonly used to measure the modulation transfer functions (MTFs) in computed tomography (CT) images reconstructed with iterative reconstruction (IR) algorithms. This method generally entails averaging multiple images of the cylinder to reduce the image noise. We suspected that the cylinder edge shape depicted in the IR images might exhibit slight deformation with respect to the true shape because of the intrinsic nonlinearity of IR algorithms. Image averaging can reduce the image noise, but does not effectively improve the deformation of the edge shape; thereby causing errors in the MTF measurements. We address this issue and propose a method to correct the MTF. We scanned a phantom including cylindrical objects with a CT scanner (Ingenuity Elite, Philips Healthcare). We obtained cylinder images with iterative model reconstruction (IMR) algorithms. The images suggested that the depicted edge shape deforms and fluctuates depending on slice positions. Because of this deformation, image averaging can potentially cause additional blurring. We define the deformation function D that describes the additional blurring, and obtain D by analyzing multiple images. The MTF measured by the circular-edge method (referred to as MTF') can be thought of as the multiplication of the true MTF by the Fourier transformation (FT) of D. We thus obtain the corrected MTF (MTFcorrected ) by dividing MTF' by the FT of D. We validate our correction method by comparing the calculated images based on the convolution theorem using MTF' and MTFcorrected with the actual images obtained with the scanner. The calculated image using MTFcorrected is more similar to the actual image compared with the image calculated using MTF', particularly in edge regions. We describe a pitfall in MTF measurement using the circular-edge technique with image averaging, and suggest a method to correct it.

    DOI： 10.1002/acm2.12821

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    Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/acm2.12821

  • [Applications of 3D-PSF of CT Image to QA for Thoracic CT-CAD: Part 4. Application of 3D-PSF 2. Virtual Nodule Application to QA for Thoracic CT-CAD].

    Shinichi Wada, Masaki Ohkubo, Akihiro Narita, Kohei Murao, Toru Matsumoto, Shusuke Sone

    Igaku butsuri : Nihon Igaku Butsuri Gakkai kikanshi = Japanese journal of medical physics : an official journal of Japan Society of Medical Physics   39 ( 4 )   77 - 85   2019.12

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    Language：Japanese   Publishing type：Research paper (scientific journal)  

    DOI： 10.11323/jjmp.39.4_77

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  • 解説 CT画像3D-PSFの胸部CT-CADのQAへの応用 (3) 3D-PSFの応用1. CT画像の空間分解能特性変換と標準化

    和田 真一, 大久 保真樹, 成田 啓廣, 村尾 晃平, 松本 徹

    医学物理   39 ( 3 )   61 - 67   2019.10

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  • 解説 CT画像3D-PSFの胸部CT-CADのQAへの応用 (2) CT画像3D-PSF応用とPSF測定精度検証

    和田 真一, 大久 保真樹, 成田 啓廣, 村尾 晃平, 松本 徹

    医学物理   39 ( 2 )   42 - 49   2019.8

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  • Generation of realistic virtual nodules based on three-dimensional spatial resolution in lung computed tomography: A pilot phantom study Reviewed

    Akihiro Narita, Masaki Ohkubo, Kohei Murao, Toru Matsumoto, Shinichi Wada

    MEDICAL PHYSICS   44 ( 10 )   5303 - 5313   2017.10

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    Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1002/mp.12503

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  • A method for evaluating the performance of computeraided detection of pulmonary nodules in lung cancer CT screening: detection limit for nodule size and density Reviewed

    Hajime Kobayashi, Masaki Ohkubo, Akihiro Narita, Janaka C. Marasinghe, Kohei Murao, Toru Matsumoto, Shusuke Sone, Shinichi Wada

    BRITISH JOURNAL OF RADIOLOGY   90 ( 1070 )   20160313   2017

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    Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1259/bjr.20160313

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  • Technical Note: Image filtering to make computer-aided detection robust to image reconstruction kernel choice in lung cancer CT screening Reviewed

    Masaki Ohkubo, Akihiro Narita, Shinichi Wada, Kohei Murao, Toru Matsumoto

    MEDICAL PHYSICS   43 ( 7 )   4098 - 4105   2016.7

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    Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1118/1.4953247

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  • Characterization of the model-based iterative reconstruction algorithm: Confirmation of coexistence of dose reduction and spatial resolution improvement Reviewed

    Kayugawa A, Noto Y, Taga T, Fukaya T, Tasaki K, Fujioka T, Ohkubo M

    European Congress of Radiology   C-0946   1 - 24   2015.3

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    Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：European Society of Radiology  

    DOI： 10.1594/ecr2015/C-0946

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  • Accurate determination of ct point-spread-function with high precision Reviewed

    Akihiro Kayugawa, Masaki Ohkubo, Shinichi Wada

    Journal of Applied Clinical Medical Physics   14 ( 4 )   216 - 226   2013

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    Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Ltd  

    DOI： 10.1120/jacmp.v14i4.3905

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  • [Electronic portal imaging device (EPID) portal image filtering for simplifying registration on radiation therapy]. Reviewed

    Yamada M, Ohkubo M, Kayugawa A, Yamada H, Matsuura M, Miura T, Kusumoto T

    Nihon Hoshasen Gijutsu Gakkai zasshi   68 ( 5 )   593 - 601   2012

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  • Image filtering as an alternative to the application of a different reconstruction kernel in CT imaging: Feasibility study in lung cancer screening Reviewed

    Masaki Ohkubo, Shinichi Wada, Akihiro Kayugawa, Toru Matsumoto, Kohei Murao

    MEDICAL PHYSICS   38 ( 7 )   3915 - 3923   2011.7

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    Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1118/1.3590363

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  • [Simulation study for artifacts on Gd-EOB-DTPA-enhanced liver dynamic MR imaging in arterial dominant phase]. Reviewed

    Fukaya T, Naito K, Saitoh H, Takimoto M, Kayugawa A, Ohkubo M

    Nihon Hoshasen Gijutsu Gakkai zasshi   66 ( 9 )   1197 - 1203   2010.9

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  • Spatial Resolution Conversion on the Z-axis using CT SSP Reviewed

    KAYUGAWA Akihiro, OHKUBO Masaki, WADA Shinichi, MATSUMOTO Toru, MURAO Kohei, YAMAMOTO Shinji

    Japanese Journal of Medical Physics   30 ( 1 )   3 - 9   2010.8

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    Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Medical Physics  

    We propose a new method of converting thin-slice CT images to thick-slice images without image raw data. Slice sensitivity profiles (SSPs) were measured in the thin- and thick-slice settings. The spatial frequency property in the slice direction of the thin-slice images was converted to that of thick-slice images, based on the spatial frequency response calculated using the each SSP. In this study, we used CT images of seven subjects obtained in lung cancer screening, with a 4-slice scanner. The images were reconstructed with slice thicknesses of 5 and 8 mm, and the SSPs were measured in the scanner for the two slice settings, respectively. We calculated 8 mm-thick images from the 5 mm-thick images by the proposed method, and compared them with the actual 8 mm-thick images; this difference was evaluated by the root mean square error (RMSE). The mean value of RMSEs for seven subjects was approximately 6.0 Hounsfield Unit (HU). In addition, we obtained 8 mm-thick images by a conventional technique of weighted average from the 5 mm-thick images; the mean value of RMSEs was approximately 10.0 HU. The proposed method was demonstrated to be effective for converting thin-slice images to thick-slice images accurately.

    DOI： 10.11323/jjmp.30.1_3

    CiNii Article

    CiNii Books

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    Other Link： https://jlc.jst.go.jp/DN/JLC/20019128137?from=CiNii

  • 3D CT Image Simulation-based Analysis of Threshold Setting for Pulmonary Nodule Volumetric Evaluation Reviewed

    Ohno Ken

    Jpn. J. Med. Phys   30 ( 2 )   39 - 48   2010

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    Language：Japanese   Publishing type：Research paper (scientific journal)  

    DOI： 10.11323/jjmp.30.2_39

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  • Determination of point spread function in computed tomography accompanied with verification Reviewed

    Masaki Ohkubo, Shinichi Wada, Satoshi Ida, Masayuki Kunii, Akihiro Kayugawa, Toru Matsumoto, Kanae Nishizawa, Kohei Murao

    MEDICAL PHYSICS   36 ( 6 )   2089 - 2097   2009.6

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    Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1118/1.3123762

    Web of Science

    PubMed

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MISC

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Awards

  • 学術奨励賞

    2022.11   公益社団法人 日本放射線技術学会 東北支部  

    成田啓廣

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Research Projects

  • バーチャル3D結節像を用いた肺がんCT検診における最適な撮影線量の決定法

    Grant number：23K14833

    2023.4 - 2026.3

    System name：科学研究費助成事業

    Research category：若手研究

    Awarding organization：日本学術振興会

    成田 啓廣

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    Grant amount：\1950000 （ Direct Cost: \1500000 、 Indirect Cost：\450000 ）

    本研究は，CT装置の空間分解能指標である点広がり関数（Point spread function: PSF）およびスライス感度分布（Slice sensitivity profile: SSP）に基づき，仮想肺内結節像“Virtual nodule”を生成する．そして，様々な線量で撮影した遺体のCT画像にVirtual noduleを挿入し，観察者実験によって結節検出能を調べる．
    2023年度は，一般撮影領域における画像の画質評価の方法としてよく用いられるcontrast detail（C-D）ダイアグラム法にVirtual noduleを適用し，Virtual noduleの観察者実験への適応の可能性について検討した．C-Dダイアグラム法とは，対象物の大きさやコントラストを系統的に多数変化させたファントムの画像を視覚評価するものであり，検出可能な対象物の大きさやコントラストを評価することができる．C-Dダイアグラム法では，様々な大きさやコントラストを有する被写体を撮影する必要がある．一般撮影領域では，そのような被写体を作成することが容易である．しかし，CTでは三次元的なデータを扱うことから，スキャン平面だけではなく体軸方向のボケの影響を評価するために，被写体として球体などを用いる必要があり，直径やコントラストを系統的に多数変化させた球体を含むファントムを作製することは困難である．そこで，様々な大きさ・コントラストの病変信号を作成し，CT画像に挿入することができるVirtual noduleを用いて，CT画像におけるC-Dダイアグラム法を新たに考案し，読影医による観察者実験を行った．これにより，Virtual noduleの観察者実験への適応が有用であることが示されるとともに，観察者実験によるCT画像の新たな画質評価方法を考案した．

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  • 児童虐待に対応するための小児死後CTの至適条件、死後変化、診断の標準化の検討

    Grant number：23K20177

    2020.4 - 2025.3

    System name：科学研究費助成事業

    Research category：基盤研究(B)

    Awarding organization：日本学術振興会

    高橋 直也, 的場 光太郎, 成田 啓廣, 高塚 尚和, 舟山 一寿, 石川 浩志, 堀井 陽祐

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    Grant amount：\9360000 （ Direct Cost: \7200000 、 Indirect Cost：\2160000 ）

    １）小児死後CTの至適条件の検討について。新生児の体格とX線吸収値を模した新生児ファントムを新潟大学医学部法医学教室の16列DualエネルギーMDCTで撮像して得られたCT画像の画質を検討した。複数の管電流を用いて得られた頭部CT画像に、計算ソフトウェアを用いて作成した仮想模擬病変を挿入し、病変の検出能を検討した。模擬病変の直径が7.5 mmの場合，240mAsが最適線量であった．直径5 mmの病変でコントラスト差が小さい場合500 mAsでも検出が困難であった．この結果は、第79回日本放射線技術学会総会学術大会で発表した。同様に5歳幼児の体格とX線吸収値を模した幼児ファントムを複数の管電流を用いて撮像した頭部CT画像に、仮想模擬病変を挿入して、病変の検出能を検討した。管電流が高い場合、模擬病変の検出率は向上したが、直径8 mm以下の模擬病変で4HUのコントラストの差の場合，設定可能な最大の線量である400 mAsでも検出できなかった．コントラストの差が小さい場合、高線量でも検出が難しいことが明らかとなった。この結果は、第21回オートプシー・イメージング学会学術総会にて発表した。
    ２）小児死後CTにおける死後変化について。新潟大学と北海道大学で解剖を行った小児症例において、病院で死亡直後に撮影されたCTと死後数日間の冷蔵保存後に撮影されたCTの、肺の含気量を比較検討した。成人例でも同様の検討を行い、成人と小児における死後変化の差異を明らかとした。小児、成人とも死後冷蔵保存していたにも関わらず死後の時間経過で肺の含気領域は減少し、特に乳幼児でその傾向が強かった。肺の含気体積の減少は、小児の方が成人よりも減少率が大きかった。この結果は、第21回オートプシー・イメージング学会学術総会にて発表した。

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  • 児童虐待に対応するための小児死後CTの至適条件、死後変化、診断の標準化の検討

    Grant number：20H01654

    2020.4 - 2025.3

    System name：科学研究費助成事業

    Research category：基盤研究(B)

    Awarding organization：日本学術振興会

    高橋 直也, 的場 光太郎, 成田 啓廣, 高塚 尚和, 舟山 一寿, 石川 浩志, 堀井 陽祐

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    Grant amount：\9360000 （ Direct Cost: \7200000 、 Indirect Cost：\2160000 ）

    １）小児死後CTの至適条件の検討について。新生児の体格とX線吸収値を模した新生児ファントムを新潟大学医学部法医学教室の16列DualエネルギーMDCTで撮像して得られたCT画像の画質を検討した。CTでは管電流をあげると良好な画像が得られる。被曝の影響を考慮する必要がない遺体の場合、臨床で用いられない高い管電流を使用することが可能であるが、必要以上の管電流を使用すると、機器の負担が増える。複数の管電流を用いて得られた頭部CT画像に、計算ソフトウェアを用いて作成した仮想模擬病変を挿入し、病変の検出能を検討した。経験豊富な2名の放射線科医が、仮想模擬病変が挿入されたCT画像を観察し、この病変が検出できるかどうかを判断し、微細病変の検出に必要な最低限の撮像条件を明らかにした。今後は、小児ファントムを用いて、同様の撮像実験、病変検出能の検討を行い、体格の異なる小児におけるCTの至適条件を検討する予定である。
    ２）小児死後CTの画像収集について。２－１）2021年度に新潟大学法医学教室で死後CT検査が行われた小児は４例であった。このうち２例で解剖が行われ、体内の状態と死因についての結果が得られた。解剖が行われた症例については死後CTの画像所見と解剖における実際の所見を比較検討が可能であった。今後は、症例を蓄積し、死後画像所見における死因究明、死後変化について、さらなる検討を行う。２－２）新潟大学放射線医学教室の協力のもと、関連病院において小児死後CT画像の症例の提供を依頼した。各病院の倫理審査委員会で審議を行っていただき、症例提供の手続きを行った。関連病院から、2020年4月から2025年3月までの症例を提供していただき、死後CT所見における死後変化や死因究明の検討を行う。

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  • 逐次近似再構成CT画像における高精度な空間分解能測定法の開発

    Grant number：20K08046

    2020.4 - 2024.3

    System name：科学研究費助成事業

    Research category：基盤研究(C)

    Awarding organization：日本学術振興会

    大久保 真樹, 成田 啓廣

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    Grant amount：\4290000 （ Direct Cost: \3300000 、 Indirect Cost：\990000 ）

    X線CTにおける逐次近似再構成（iterative reconstruction：IR）法による画像（IR画像）の、体軸方向におけるスライス感度分布（slice sensitivity profile：SSP）の測定法の開発を行った。この考案法では、低コントラストの球体を撮像した画像を用いて、各スライス画像のスキャン平面における積分により得られた体軸方向のCT値プロファイルを用いてSSPを算出する。この算出過程において、得られたSSPからCT値プロファイルを計算し実際のプロファイルデータとの比較を行うことから、SSPの測定精度の評価（検証）も伴う手法といえる。まず、従来のフィルタ補正逆投影（filtered back-projection：FBP）法による再構成画像を用いた検討をした。すると、標準的な方法（コイン法）で測定したSSPと考案法によるSSPは非常に近い形状となり、それらの半値幅は一致する結果となった。次に、2機種のCT装置における異なるIRアルゴリズムであるiterative model reconstruction：IMR（Phlips社）およびadvanced modeled iterative reconstruction：ADMIRE（Siemens社）を用いて、スライス厚1 mmおよび2 mmの画像に考案法を適用した。その結果、いずれの条件においても得られたSSPから算出したCT値プロファイルが実際のプロファイルデータによく一致することが確認され、SSPの測定精度の高いことが示唆された。

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  • Realistic three-dimensional virtual nodule based on spatial resolution in lung computed tomography

    Grant number：17K09059

    2017.4 - 2020.3

    System name：Grants-in-Aid for Scientific Research

    Research category：Grant-in-Aid for Scientific Research (C)

    Awarding organization：Japan Society for the Promotion of Science

    Ohkubo Masaki

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    Grant amount：\4160000 （ Direct Cost: \3200000 、 Indirect Cost：\960000 ）

    To evaluate the performance of computer-aided detection (CAD) of lung cancer CT screening, we proposed a new method for generating computer-simulated nodule images ‘virtual nodules’. The performance of a CAD system is affected by CT scanning and image reconstruction conditions. Therefore, CAD performance should be evaluated by image data obtained under the same CT conditions as those used at each site providing CT screening. The virtual nodules were generated based on the spatial resolution of a CT system used in an institution providing cancer screening and were fused into lung images obtained at that institution, allowing site-specific virtual nodules with a realistic appearance. In phantom experiments using laboratory-made physical nodules, the virtual nodules were confirmed to agree well with CT images obtained by scanning the phantom nodules. Virtual nodules can be an effective means of evaluating site-specific CAD performance.

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Teaching Experience

  • 実践臨床画像学

    2024
    Institution name：新潟大学

  • 診療画像機器学実験II

    2024
    Institution name：新潟大学

  • 放射線撮影技術学III

    2024
    Institution name：新潟大学

  • 診療画像機器学II

    2024
    Institution name：新潟大学

  • 診療画像機器学実験I

    2024
    Institution name：新潟大学

  • 保健学総合

    2024
    Institution name：新潟大学

  • 電磁気学特論

    2023
    Institution name：新潟大学

  • 診療画像機器学I

    2023
    Institution name：新潟大学

  • 医学物理学演習

    2021
    Institution name：新潟大学

  • 医用放射線技術の歴史

    2021
    Institution name：新潟大学

  • 医療英語ベーシック(放射)

    2020
    Institution name：新潟大学

  • 保健学特別研究(放射線技術科学)

    2020
    Institution name：新潟大学

  • 疾病の原因と成り立ち

    2020
    -
    2021
    Institution name：新潟大学

  • 放射線関係法規及び演習

    2018
    Institution name：新潟大学

  • 放射線衛生学

    2018
    Institution name：新潟大学

  • 医用放射線科学概論

    2018
    Institution name：新潟大学

  • 放射線管理学及び演習

    2018
    -
    2023
    Institution name：新潟大学

  • 放射線撮影技術学演習

    2018
    -
    2023
    Institution name：新潟大学

  • 医学物理学入門

    2018
    Institution name：新潟大学

  • 医用放射線機器科学演習

    2017
    Institution name：新潟大学

  • 放射線撮影技術学実習

    2017
    Institution name：新潟大学

  • 放射線写真学

    2017
    Institution name：新潟大学

  • 放射線科学セミナー

    2016
    Institution name：新潟大学

  • 核医学検査技術学Ⅲ

    2016
    Institution name：新潟大学

  • 医用放射線機器科学特論

    2016
    Institution name：新潟大学

  • 卒業研究

    2016
    Institution name：新潟大学

  • 医療英語(放射)

    2016
    Institution name：新潟大学

  • 放射線機器工学Ⅰ

    2016
    -
    2023
    Institution name：新潟大学

  • 放射線機器工学実験Ⅱ

    2016
    -
    2023
    Institution name：新潟大学

  • スタディスキルズ (放射)

    2016
    -
    2023
    Institution name：新潟大学

  • 放射線機器工学Ⅱ

    2015
    -
    2023
    Institution name：新潟大学

  • 放射線機器工学実験Ⅰ

    2015
    -
    2023
    Institution name：新潟大学

  • 医用機器工学及び演習

    2015
    -
    2016
    Institution name：新潟大学

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