研究者詳細 - 大久保　真樹

Magnetic Resonance Imaging of Neurotransmitter-Related Molecules 査読

Hironaka Igarashi, Satoshi Ueki, Ken Ohno, Masaki Ohkubo, Yuji Suzuki

JOURNAL OF NIPPON MEDICAL SCHOOL 84 ( 4 ) 160 - 164 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MEDICAL ASSOC NIPPON MEDICAL SCH

Molecular imaging implies the method capable of pictorially displaying distribution of target molecules and their relative concentration in space. In clinical medicine, where non-invasiveness is mandatory, diagnostic molecular imaging has been considered virtually identical to positron emission tomography (PET). However, there is another powerful, apparently underutilized molecular imaging, namely, proton magnetic resonance spectroscopic imaging (H-1-MRSI). The technique can detect target molecules endogenous in brain in virtue of their own specific resonance frequencies (chemical shift) and can create quantitative images of each molecule. H-1-MRSI is conventionally utilized for imaging relatively easily detectable molecules such as N-acetyl-aspartate or lactate. More recently, however, the method is extended into imaging of more challenging molecules such as glutamate or gamma-aminobutyric acid (GABA). In this small review, we summarize basic concept of H-1-MRSI and introduce an advanced technique, i.e. chemical exchange saturation transfer magnetic resonance imaging (CEST MRI), which made realistic glutamate imaging in vivo possible.

DOI： 10.1272/jnms.84.160

Measurement of thin slice thickness in MRI using an improved wedge method 査読

Kanazawa T, Ohkubo M, Kondo T

European Congress of Radiology C-1063 1 - 14 2017年3月

パーソナルコンピュータ上で動作するDICOMデータのCT画像からの体積測定プログラムの開発と評価(PC用のDICOM体積測定プログラムの開発と評価)(The development and assessment of program for volume measurement for CT images of: DICOM data running on a personal computer: (Development and assessment of volume measurement program for DICOM on PC)) 査読

Takahashi Naoya, Kobayashi Arashi, Nishihama Saori, Minamizawa Natsuki, Suzuki Noriko, Higuchi Takeshi, Ohkubo Masaki, Narita Akihiro, Sasamoto Ryuta

新潟大学保健学雑誌 14 ( 1 ) 27 - 33 2017年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：新潟大学医学部保健学科

著者等は数値計算言語(MATLAB)を使ってPC上で動作するDICOM画像から体積を算出するプログラムを開発し、その有用性と正確度を検討した。CTの水平断像上に関心領域(ROI)を設置し、設定した閾値で必要な領域を抽出して三次元表示し、体積測定を行うこととした。本プログラムを用いて、64列CTで実施した死後CT検査5例について、肝、脾、腎を抽出した。ImageJにて目的とする臓器にROIを設定して面積を算出し、厚さを乗じて体積を測定した。臓器ごとに、ImageJにて求めた体積に最も近い値が得られるように閾値を決定した。著者等が開発したプログラムとImageJで測定した平均体積は、肝がそれぞれ1690.3±505.1cm3と107.9±60.7cm3、脾が107.9±60.7cm3と105.5±62.4cm3、腎が141.1±26.4cm3と143.9±32.1cm3であり、有意差は認められなかった。体積測定に要した平均時間は開発したプログラムの方が有意に短かった。著者等が開発したPC上で動作するDICOM画像の体積測定プログラムを用いると、簡便かつ正確に臓器の体積を測定することが可能であった。

その他リンク： http://dspace.lib.niigata-u.ac.jp/dspace/bitstream/10191/47194/1/14%281%29_27-33.pdf

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

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

BRITISH JOURNAL OF RADIOLOGY 90 ( 1070 ) 1 - 10 2017年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：BRITISH INST RADIOLOGY

Objective: We propose the application of virtual nodules to evaluate the performance of computer-aided detection (CAD) of lung nodules in cancer screening using lowdose CT.
Methods: The virtual nodules were generated based on the spatial resolution measured for a CT system used in an institution providing cancer screening and were fused into clinical lung images obtained at that institution, allowing site specificity. First, we validated virtual nodules as an alternative to artificial nodules inserted into a phantom. In addition, we compared the results of CAD analysis between the real nodules (n=6) and the corresponding virtual nodules. Subsequently, virtual nodules of various sizes and contrasts between nodule density and background density (Delta CT) were inserted into clinical images (n=10) and submitted for CAD analysis.
Results: In the validation study, 46 of 48 virtual nodules had the same CAD results as artificial nodules (kappa coefficient = 0.913). Real nodules and the corresponding virtual nodules showed the same CAD results. The detection limits of the tested CAD system were determined in terms of size and density of peripheral lung nodules; we demonstrated that a nodule with a 5- mm diameter was detected when the nodule had a Delta CT> 220 HU.
Conclusion: Virtual nodules are effective in evaluating CAD performance using site-specific scan/reconstruction conditions.
Advances in knowledge: Virtual nodules can be an effectivemeans of evaluating site-specific CAD performance. The methodology for guiding the detection limit for nodule size/density might be a useful evaluation strategy.

DOI： 10.1259/bjr.20160313

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

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

MEDICAL PHYSICS 43 ( 7 ) 4098 - 4105 2016年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS

Purpose: In lung cancer computed tomography (CT) screening, the performance of a computer-aided detection (CAD) system depends on the selection of the image reconstruction kernel. To reduce this dependence on reconstruction kernels, the authors propose a novel application of an image filtering method previously proposed by their group.
Methods: The proposed filtering process uses the ratio of modulation transfer functions (MTFs) of two reconstruction kernels as a filtering function in the spatial-frequency domain. This method is referred to as MTFratio filtering. Test image data were obtained from CT screening scans of 67 subjects who each had one nodule. Images were reconstructed using two kernels: f(STD) (for standard lung imaging) and f(SHARP) (for sharp edge-enhancement lung imaging). The MTFratio filtering was implemented using the MTFs measured for those kernels and was applied to the reconstructed f(SHARP) images to obtain images that were similar to the f(STD) images. A mean filter and a median filter were applied (separately) for comparison. All reconstructed and filtered images were processed using their prototype CAD system.
Results: The MTFratio filtered images showed excellent agreement with the f(STD) images. The standard deviation for the difference between these images was very small, similar to 6.0 Hounsfield units (HU). However, the mean and median filtered images showed larger differences of similar to 48.1 and similar to 57.9 HU from the f(STD) images, respectively. The free-response receiver operating characteristic (FROC) curve for the f(SHARP) images indicated poorer performance compared with the FROC curve for the f(STD) images. The FROC curve for the MTFratio filtered images was equivalent to the curve for the f(STD) images. However, this similarity was not achieved by using the mean filter or median filter.
Conclusions: The accuracy of MTFratio image filtering was verified and the method was demonstrated to be effective for reducing the kernel dependence of CAD performance. (C) 2016 American Association of Physicists in Medicine.

DOI： 10.1118/1.4953247

[Measurement of the Dose Rate Using Dosimeters in Interventional Radiology and Its Difficulty]. 査読

Hidenori Yoshida, Chiharu Takahashi, Nobuhiro Narita, Yasuhiko Mizusawa, Masaru Sekiya, Masaki Ohkubo

Nihon Hoshasen Gijutsu Gakkai zasshi 72 ( 1 ) 63 - 72 2016年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）

In equipment used for interventional radiology (IVR), automatic exposure control (AEC) is incorporated to obtain the X-ray output suitable for the treatment of targeted lesions. For the AEC, users select a region as the signal sensing region (measuring field, MF) in the flat panel detector; MFs with various sizes and shapes were pre-defined and prepared in the system. The aim of this study was to examine the change of measured dose rate with the selection of MFs, the type of dosimeters (the ionization chamber dosimeter and the semiconductor dosimeter), and the dosimeter placement relative to the direction of X-ray tube (from cathode to anode). The IVR equipment was Allura Xper FD20/10 (Philips Medical Systems), and six kinds of built-in MFs were used. It was found that dose rate measured by the ionization chamber dosimeter showed a variation of -2 mGy/min with the MFs and the ionization chamber dosimeter placement. The dose rate measured by the semiconductor dosimeter showed more variation than the ionization chamber dosimeter. The change of dose rate with the dosimeter placement would be caused by the MF overlapping the dosimeter which would affect the AEC (the X-ray output). Also, the change of dose rate with the dosimeter placement was considered to be related to the heel effect of the X-ray beam. When performing dose rate measurements, we should notice that the selection of MFs, the type of dosimeters, and the dosimeter placement would affect the measured values.

DOI： 10.6009/jjrt.2016_JSRT_72.1.63

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

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

European Congress of Radiology C-0946 1 - 24 2015年3月

Quality assurance of lung cancer CT screening CAD system by applying PSF-based reference virtual nodule set 査読

Marasinghe JC, Ohkubo M, Kobayashi H, Yoshida A, Murao K, Matsumoto T, Sone S, Wada S

European Congress of Radiology C-1125 1 - 11 2015年3月

Diffuse Brain Abnormalities in Myotonic Dystrophy Type 1 Detected by 3.0 T Proton Magnetic Resonance Spectroscopy 査読

Yuhei Takado, Kenshi Terajima, Masaki Ohkubo, Kouichirou Okamoto, Takayoshi Shimohata, Masatoyo Nishizawa, Hironaka Igarashi, Tsutomu Nakada

EUROPEAN NEUROLOGY 73 ( 3-4 ) 247 - 256 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：KARGER

Patients with myotonic dystrophy type 1 (DM1) (n = 14) were compared with healthy controls (n = 13) using 3.0 T proton magnetic resonance spectroscopy (H-1-MRS) to investigate brain pathophysiology. H-1-MRS imaging revealed reduced N-acetylaspartate to creatine ratio (NAA/Cr) in multiple brain regions (average 24%), suggesting diffuse brain abnormalities among patients with DM1. Single-voxel H-1-MRS among patients with DM1 showed (1) reduced NAA in both the frontal cortex (23%) and frontal white matter (31%) and unaltered myo-inositol, suggesting neuronal abnormalities without significant gliosis; and (2) elevated glutamine in the frontal cortex (36%) and reduced glutamate in the frontal white matter (20%) among patients with DM1, suggesting abnormalities in the glutamatergic system in the brain of patients with DM1. We consider that these results reflect brain abnormalities that cannot be detected by neuropathological assessment in patients with DM1. (C) 2015 S. Karger AG, Basel

DOI： 10.1159/000371575

Validation of using PSF-based virtual nodules to assess the basic performances of lung cancer CT screening CAD system 査読

Marasinghe JC, Ohkubo M, Wada S, Kobayashi H, Yoshida A, Murao K, Matsumoto T, Sone S

Computer Assisted Radiology and Surgery 2014, 28th International and Exhibition 9 ( 1 (S236) ) 2014年6月

Feasible method to assess the performance of a lung cancer CT screening CAD system in clinical practice: dependence on nodule size and density 査読

Marasinghe JC, Ohkubo M, Kobayashi H, Murao K, Matsumoto T, Sone S, Wada S

International Journal of Medical Physics, Clinical Engineering and Radiation Oncology 3 ( 2 ) 107 - 116 2014年5月

[15O]H2O OSEM法PET画像でのsubset とiterationの組み合わせによる画素値の検討： FBP法を基準として査読

山野井理恵, 岡本浩一郎, 河村和紀, 大久保真樹, 鈴木雄治, 中村亨弥

日本核医学会機関紙 51 ( 4 ) 373 - 382 2014年

Evaluation of lung CT CAD performance by using PSF-based virtual nodules: a validation of the methodology 査読

Marasinghe JC, Ohkubo M, Kobayashi H, Murao K, Matsumoto T, Sone S, Wada S

MEDICAL PHYSICS INTERNATIONAL Journal 1 ( 2 ) 350 - 350 2013年9月

Observer-independent nodule-detectability index for low-dose lung cancer screening CT: A pilot study 査読

Masaki Ohkubo, Shinichi Wada, Satoshi Kanai, Kazuhiro Ishikawa, Janaka C. Marasinghe, Toru Matsumoto

Radiological Physics and Technology 6 ( 2 ) 492 - 499 2013年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

For the wide dissemination of lung cancer screening by low-dose computed tomography (CT), it is important to determine the optimal conditions for scan and image reconstruction based on objective standards of evaluation. Our aim in this study was to propose a quantitative index of nodule detectability without an observer test. It was essential to determine the apparent size and density of nodules visible on CT images for developing the nodule-detectability index based on a statistical observer-independent method. Therefore, we introduced a computer simulation technique for CT images based on the spatial resolution of the system to evaluate the size and density accurately. By use of scan/reconstruction parameter settings as employed for low-dose CT screening, a detectability index was obtained for target nodules (ideal spheres) of various sizes and with varying contrast (ΔCT) between nodule density and background density. The index was compared with the qualitative results of observer tests of nodule detectability. As the target nodule diameter or ΔCT was increased, the index value increased, implying improved nodule visibility. According to the index, the detection limits for nodules with ΔCTs of 70, 100, or 150 Hounsfield units were approximately 6, 5, and 4 mm in diameter, respectively. Index values were well correlated with nodule detectability as assessed by four observers. The proposed index was effective for quantifying nodule detectability, and its validity was confirmed by an observer test. This index has potential use in the determination of optimal scan/reconstruction parameters for lung cancer screening by low-dose CT without observer test. © 2013 Japanese Society of Radiological Technology and Japan Society of Medical Physics.

DOI： 10.1007/s12194-013-0225-2

Scopus

Accurate determination of ct point-spread-function with high precision 査読

Akihiro Kayugawa, Masaki Ohkubo, Shinichi Wada

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

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：John Wiley and Sons Ltd

The measurement of modulation transfer functions (MTFs) in computed tomography (CT) is often performed by scanning a point source phantom such as a thin wire or a microbead. In these methods the region of interest (ROI) is generally placed on the scanned image to crop the point source response. The aim of the present study was to examine the effect of ROI size on MTF measurement, and to optimize the ROI size. Using a 4 multidetector-row CT, MTFs were measured by the wire and bead methods for three types of reconstruction kernels designated as 'smooth', 'standard', and 'edge-enhancement' kernels. The size of a square ROI was changed from 30 to 50 pixels (approximately 2.9 to 4.9 mm). The accuracies of the MTFs were evaluated using the verification method. The MTFs measured by the wire and bead methods were dependent on ROI size, particularly in MTF measurement for the 'edge-enhancement' kernel. MTF accuracy evaluated by the verification method changed with ROI size, and we were able to determine the optimum ROI size for each method (wire/bead) and for each kernel. Using these optimal ROI sizes, the MTF obtained by the wire method was in strong agreement with the MTF obtained by the bead method in each kernel. Our data demonstrate that the difficulties in obtaining accurate MTFs for some kernels such as edge-enhancement can be overcome by incorporating the verification method into the wire and bead methods, allowing optimization of the ROI size to accurately determine the MTF.

DOI： 10.1120/jacmp.v14i4.3905

Scopus

Application of PSF-based virtual nodules to assess the performance of lung cancer CT screening CAD system 査読

Marasinghe JC, Ohkubo M, Kobayashi H, Murao K, Matsumoto T, Niizuma S, Sone S, Wada S

Proceedings of Asia-Oceania Congress of Medical Physics 12 ( 1 ) 249 - 252 2012年12月

Application of CT-PSF-based computer-simulated lung nodules for evaluating the accuracy of computer-aided volumetry 査読

Ayumu Funaki, Masaki Ohkubo, Shinichi Wada, Kohei Murao, Toru Matsumoto, Shinji Niizuma

Radiological Physics and Technology 5 ( 2 ) 166 - 171 2012年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

With the wide dissemination of computed tomography (CT) screening for lung cancer, measuring the nodule volume accurately with computer-aided volumetry software is increasingly important. Many studies for determining the accuracy of volumetry software have been performed using a phantom with artificial nodules. These phantom studies are limited, however, in their ability to reproduce the nodules both accurately and in the variety of sizes and densities required. Therefore, we propose a new approach of using computer-simulated nodules based on the point spread function measured in a CT system. The validity of the proposed method was confirmed by the excellent agreement obtained between computer-simulated nodules and phantom nodules regarding the volume measurements. A practical clinical evaluation of the accuracy of volumetry software was achieved by adding simulated nodules onto clinical lung images, including noise and artifacts. The tested volumetry software was revealed to be accurate within an error of 20 % for nodules[5 mm and with the difference between nodule density and background (lung) (CT value) being 400-600 HU. Such a detailed analysis can provide clinically useful information on the use of volumetry software in CT screening for lung cancer. We concluded that the proposed method is effective for evaluating the performance of computer-aided volumetry software. © Japanese Society of Radiological Technology and Japan Society of Medical Physics 2012.

DOI： 10.1007/s12194-012-0150-9

Scopus

放射線治療における位置照合の容易化を目的としたEPID ポータル画像の周波数処理に関する検討査読

山田昌法, 大久保真樹, 粥川啓廣, 山田宏美, 松浦将孝, 三浦貴, 楠本敏久

日本放射線技術学会雑誌 68 ( 5 ) 593 - 601 2012年5月

脳動脈瘤クリップにおける磁化率アーチファクトの角度依存性の検討

金沢勉, 内藤健一, 斉藤宏明, 粥川啓廣, 岩崎友也, 大久保真樹, 木村元政

日本放射線技術学会東北部会雑誌 21 ( 21 ) 86 - 89 2012年1月

記述言語：日本語掲載種別：研究論文（研究会，シンポジウム資料等）出版者・発行元：(公社)日本放射線技術学会-東北支部

磁化率アーチファクトによる画像歪みの影響が、静磁場(Bo)方向と脳動脈瘤クリップの長軸方向とのなす角度に依存するか検討した。磁化率アーチファクトの影響を低減させるには、バンド幅が非常に重要であることが再認識された。Boと脳動脈瘤クリップの長軸方向とのなす角度が大きくなると、磁化率アーチファクト領域は大きくなり、0度〜90度でSE系が2.3倍、GE系が1.5倍となり、Boと垂直で最大となった。また、SE系に比べGE系の撮像法は磁化率アーチファクト領域が2.5〜3倍ほど大きくなった。Bo方向に対する脳動脈瘤クリップの長軸方向の角度が、磁化率アーチファクト領域に対し依存性があることが示唆された。