Faculty Profiles - KOYAMA Shuji

Papers - KOYAMA Shuji

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Importance of Considering the Response Function of Photon Counting Detectors with the Goal of Precise Material Identification Reviewed

Asakawa Takumi, Hayashi Hiroaki, Kimoto Natsumi, Asahara Takashi, Maeda Tatsuya, Koyama Shuji, Yamamoto Shuichiro, Okada Masahiro

2019 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (NSS/MIC) 2019

未来へ繫ぐCTの線量評価技術 Invited

小山修司

インナービジョン Vol. 33 ( 10 ) page： 10-14 2018.10

Accuracy validation of incident photon fluence on detective quantum efficiency in mammography. Reviewed

Haba T, Koyama S, Otani N

Australasian physical & engineering sciences in medicine page： https://doi.org/10.1007/s13246-018-0679-y 2018.8

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

X-ray image evaluation is commonly performed by determining the detective quantum efficiency (DQE). DQE is calculated with a presampled modulation transfer function (MTF), incident photon fluence, and digital noise power spectrum (NPS). Accurate evaluation of MTF, incident photon fluence, and NPS is important for precise DQE determination. In this study, we focused on the accuracy of the incident photon fluence in mammography. The incident photon fluence is calculated using the squared signal-to-noise ratio (SNRin2) value as specified in the International Electrotechnical Commission (IEC) 62220-1-2 report. However, the reported SNRin2 values were determined using a computer program, and the reported values may differ from those calculated from an X-ray spectrum that is measured with actual mammography equipment. Therefore, we evaluated the error range of reported SNRin2 values in mammography to assess the accuracy of the incident photon fluence. First, X-ray spectra from various mammography systems were measured with a CdTe spectrometer. Six mammographic X-ray units were used in this study. Second, the SNRin2 values were calculated from the measured X-ray spectra. The calculated values were compared to the reported values. The results show that the percentage differences between the calculated and reported SNRin2 values were within -4.1% of each other. The results obtained in this study indicate that the SNRin2 values provided in the IEC report are a robust and convenient tool for calculating the incident photon fluence for DQE evaluation in mammography.

DOI： 10.1007/s13246-018-0679-y

PubMed

Using Scattered X-Rays to Improve the Estimation Accuracy of Attenuation Coefficients: A Fundamental Analysis Reviewed

Toda Naohiro, Nakagami Tetsuya, Yamazaki Yoichi, Yoshioka Hiroki, Koyama Shuji

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E101A ( 7 ) page： 1101 - 1114 2018.7

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

In X-ray computed tomography, scattered X-rays are generally removed by using a post-patient collimator located in front of the detector. In this paper, we show that the scattered X-rays have the potential to improve the estimation accuracy of the attenuation coefficient in computed tomography. In order to clarify the problem, we simplified the geometry of the computed tomography into a thin cylinder composed of a homogeneous material so that only one attenuation coefficient needs to be estimated. We then conducted a Monte Carlo numerical experiment on improving the estimation accuracy of attenuation coefficient by measuring the scattered X-rays with several dedicated toroidal detectors around the cylinder in addition to the primary X-rays. We further present a theoretical analysis to explain the experimental results. We employed a model that uses a T-junction (i.e., T-junction model) to divide the photon transport into primary and scattered components. This division is processed with respect to the attenuation coefficient. Using several T-junction models connected in series, we modeled the case of several scatter detectors. The estimation accuracy was evaluated according to the variance of the efficient estimator, i.e., the Cramer-Rao lower bound. We confirmed that the variance decreases as the number of scatter detectors increases, which implies that using scattered X-rays can reduce the irradiation dose for patients. Copyright © 2018 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transfun.E101.A.1101

Web of Science

Effects of Gradient Coil Noise and Gradient Coil Replacement on the Reproducibility of Resting State Networks Reviewed

Bagarinao Epifanio, Tsuzuki Erina, Yoshida Yukina, Ozawa Yohei, Kuzuya Maki, Otani Takashi, Koyama Shuji, Isoda Haruo, Watanabe Hirohisa, Maesawa Satoshi, Naganawa Shinji, Sobue Gen

FRONTIERS IN HUMAN NEUROSCIENCE Vol. 12 page： 148 2018.4

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

The stability of the MRI scanner throughout a given study is critical in minimizing hardware-induced variability in the acquired imaging data set. However, MRI scanners do malfunction at times, which could generate image artifacts and would require the replacement of a major component such as its gradient coil. In this article, we examined the effect of low intensity, randomly occurring hardware-related noise due to a faulty gradient coil on brain morphometric measures derived from T1-weighted images and resting state networks (RSNs) constructed from resting state functional MRI. We also introduced a method to detect and minimize the effect of the noise associated with a faulty gradient coil. Finally, we assessed the reproducibility of these morphometric measures and RSNs before and after gradient coil replacement. Our results showed that gradient coil noise, even at relatively low intensities, could introduce a large number of voxels exhibiting spurious significant connectivity changes in several RSNs. However, censoring the affected volumes during the analysis could minimize, if not completely eliminate, these spurious connectivity changes and could lead to reproducible RSNs even after gradient coil replacement.

DOI： 10.3389/fnhum.2018.00148

Web of Science

PubMed

Orthodontic tooth separation activates the hypothalamic area in the human brain Reviewed

Ariji Yoshiko, Kondo Hisataka, Miyazawa Ken, Tabuchi Masako, Koyama Syuji, Kise Yoshitaka, Togari Akifumi, Gotoh Shigemi, Ariji Eiichiro

INTERNATIONAL JOURNAL OF ORAL SCIENCE Vol. 10 page： https://doi.org/10.1038/s41368-017-0001-y 2018.3

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

OBJECTIVES: An animal experiment clarified that insertion of an orthodontic apparatus activated the trigeminal neurons of the medulla oblongata. Orthodontic tooth movement is known to be associated with the sympathetic nervous system and controlled by the nucleus of the hypothalamus. However, the transmission of both has not been demonstrated in humans. The purpose of this study were to examine the activated cerebral areas using brain functional magnetic resonance imaging (MRI), when orthodontic tooth separators were inserted, and to confirm the possibility of the transmission route from the medulla oblongata to the hypothalamus.
METHODS: Two types of alternative orthodontic tooth separators (brass contact gauge and floss) were inserted into the right upper premolars of 10 healthy volunteers. Brain functional T2*-weighted images and anatomical T1-weighted images were taken. RESULTS: The blood oxygenation level dependent (BOLD) signals following insertion of a brass contact gauge and floss significantly increased in the somatosensory association cortex and hypothalamic area.
CONCLUSION: Our findings suggest the possibility of a transmission route from the medulla oblongata to the hypothalamus.

DOI： 10.1038/s41368-017-0001-y

Web of Science

Stability and linearity of luminescence imaging of water during irradiation of proton-beams and X-ray photons lower energy than the Cerenkov light threshold Reviewed

Yamamoto Seiichi, Koyama Shuji, Yabe Takuya, Komori Masataka, Tada Junki, Ito Shiori, Toshito Toshiyuki, Hirata Yuho, Watanabe Kenichi

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Vol. 883 page： 48-56 2018.3

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

Luminescence of water during irradiations of proton-beams or X-ray photons lower energy than the Cerenkov-light threshold is promising for range estimation or the distribution measurements of beams. However it is not yet obvious whether the intensities and distributions are stable with the water conditions such as temperature or addition of solvable materials. It remains also unclear whether the luminescence of water linearly increases with the irradiated proton or X-ray energies. Consequently we measured the luminescence of water during irradiations of proton-beam or X-ray photons lower energy than the Cerenkov-light threshold with different water conditions and energies to evaluate the stability and linearity of luminescence of water. We placed a water phantom set with a proton therapy or X-ray system, luminescence images of water with different conditions and energies were measured with a high-sensitivity cooled charge coupled device (CCD) camera during proton or X-ray irradiations to the water phantom. In the stability measurements, imaging was made for different temperatures of water and addition of inorganic and organic materials to water. In the linearity measurements for the proton, we irradiated with four different energies below Cerenkov light threshold. In the linearity measurements for the X-ray, we irradiated X-ray with different supplied voltages. We evaluated the depth profiles for the luminescence images and evaluated the light intensities and distributions. The results showed that the luminescence of water was quite stable with the water conditions. There were no significant changes of intensities and distributions with the different temperatures. Results from the linearity experiments showed that the luminescence of water linearly increased with their energies. We confirmed that luminescence of water is stable with conditions of water. We also confirmed that the luminescence of water linearly increased with their energies.

DOI： 10.1016/j.nima.2017.11.073

Web of Science

A proposed new image display method with high contrast-to-noise ratio using energy resolved photon-counting mammography with a CdTe series detector

Suzuki R., Nakajima A., Sasaki M., Kodera Y., Iida Y., Ito F., Koshiba Y., Yamakawa T., Yamamoto S., Okada M., Hashimoto D., Koyama S.

MEDICAL IMAGING 2018: PHYSICS OF MEDICAL IMAGING Vol. 10573 2018

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

In this study, we propose a new image display method to obtain high contrast-to-noise ratio (CNR) using energy resolved photon-counting mammography (ERPCM) with a cadmium telluride (CdTe) series detector manufactured by JOB CORPOLATION. The CdTe series detector can detect high-energy photons with high sensitivity, enabling users to image with high-energy X-rays. Using this detector, it is possible to reduce the dose given to a patient while increasing the CNR. First, the spectrum was divided into three bins and their corresponding linear attenuation coefficients were calculated from input and output photon numbers. Further, absorption vector length (AVL) and average absorption length (AAL) were calculated from the linear attenuation coefficients and from thicknesses of objects after beam-hardening correction. We further compared the CNR between ERPCM and general mammography images under the constant average glandular dose (AGD). We imaged an acrylic plate (1 mm thick) on RMI-156 phantom, determined regions of interest (ROIs) on an acrylic plate and background, and calculated the CNR. Our ERPCM generated two types of images: an AVL image and an AAL image. AMULET Innovality manufactured by FUJIFILM generated an integrated image. MicroDose SI manufactured by Philips generated a count image and removed electrical noise by the photon-counting technique. The four images, in order of decreasing CNR, were the AAL image, AVL image, MicroDose image, and AMULET image. The proposed method using ERPCM generated an image with higher CNR than images using general mammography under the constant AGD.

DOI： 10.1117/12.2292871

Web of Science

Development of energy-resolved photon-counting mammography with a cadmium telluride series detector to reduce radiation exposure and increase contrast-to-noise ratio using the high-energy X-rays

Suzuki Reina, Koyama Shuji, Kodera Yoshie, Nakajima Ai, Sasaki Mariko, Kimura Hiroto, Hayashi Hiroaki, Yamakawa Tsutomu, Yamamoto Shuichiro, Hashimoto Daisuke, Okada Masahiro

14TH INTERNATIONAL WORKSHOP ON BREAST IMAGING (IWBI 2018) Vol. 10718 2018

Identification of breast tissue using the X-ray image measured with an energy-resolved cadmium telluride series detector based on photon-counting technique

Sasaki Mariko, Koyama Shuji, Kodera Yoshie, Suzuki Reina, Nakajima Ai, Nishide Hiroko, Mizutani Mitsuhiro, Watanabe Megumi, Yoshida Naoko, Hayashi Hiroaki, Yamakawa Tsutomu, Yamamoto Shuichiro, Hashimoto Daisuke, Okada Masahiro

14TH INTERNATIONAL WORKSHOP ON BREAST IMAGING (IWBI 2018) Vol. 10718 2018

New weighting factor of weighted CTDI equation for PMMA phantom diameter from 8 to 40 cm: A Monte Carlo study Reviewed

Haba Tomonobu, Koyama Shuji, Kinomura Yutaka, Ida Yoshihiro, Kobayashi Masanao

MEDICAL PHYSICS Vol. 44 ( 12 ) page： 6603 - 6609 2017.12

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

PURPOSE:The weighted computed tomography dose index (CTDIw ) uses measured CTDI values at the center and periphery of a cylindrical phantom. The CTDIw value is calculated using conventional, Bakalyar's, and Choi's weighting factors. However, these weighting factors were produced from only 16- and 32-cm-diameter cylindrical phantoms. This study aims to devise new weighting factors to provide more accurate average dose in the central cross-sectional plane of cylindrical phantoms over a wide range of object diameters, by using Monte Carlo simulations.
METHODS:Simulations were performed by modeling a Toshiba Aquilion ONE CT scanner, in order to compute the cross-sectional dose profiles of polymethyl methacrylate (PMMA) cylindrical phantoms of each diameter (8-40 cm at 4-cm steps), for various tube voltages and longitudinal beam widths. Two phantom models were simulated, corresponding to the CTDI100 method and the method recommended by American Association of Physicists in Medicine (AAPM) task group 111. The dose-computation PMMA cylinders of 1 mm diameter were located between the phantom surfaces and the centers at intervals of 1 mm, from which cross-sectional dose profiles were calculated. By using linear least-squares fits to the obtained cross-sectional dose profiles data, we determined new weighting factors to estimate more accurate average doses in the PMMA cylindrical phantoms by using the CTDIw equation: CTDIw = Wcenter x CTDIcenter + Wperiphery * CTDIperiphery. In order to demonstrate the validity of the devised new weighting factors, the percentage difference between average dose and CTDIw value was evaluated for the weighting factors (conventional, Bakalyar's, Choi's, and devised new weighting factors) in each calculated cross-sectional dose profile.
RESULTS:With the use of linear least-squares techniques, new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8 where Wcenter and Wperiphery are weighting factors for CTDIcenter and CTDIperiphery ) were determined. The maximum percentage differences between average dose and CTDIw value were 16, -12, -8, and -6% for the conventional, Bakalyar's, Choi's, and devised new weighting factors, respectively.
CONCLUSIONS:We devised new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8) to provide more accurate average dose estimation in PMMA cylindrical phantoms over a wide range of diameter. The CTDIw equation with devised new weighting factors could estimate average dose in PMMA cylindrical phantoms with a maximum difference of -6%. The results of this study can estimate the average dose in PMMA cylindrical phantoms more accurately than the conventional weighting factors (Wcenter = 1/3 and Wperiphery = 2/3).

DOI： 10.1002/mp.12601

Web of Science

PubMed

Luminescence imaging of biological subjects during X-ray irradiations lower energy than Cerenkov-light threshold Reviewed

Yamamoto Seiichi, Koyama Shuji, Yamauchi-Kawaura Chiyo, Komori Masataka

OPTICAL REVIEW Vol. 24 ( 3 ) page： 428-435 2017.6

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

It is commonly thought that UV or visible-light luminescence imaging of biological subjects during X-ray irradiation at the energy below 120 keV is impossible because the secondary electrons produced in this energy range do not emit Cerenkov light. Contrary to this consensus, we found UV or visible-light luminescence imaging of the subjects were possible with X-ray irradiations of this energy range. We placed one of the biological subjects in a black box; visible-light luminescence images were measured with a high-sensitivity, cooled charge coupled device (CCD) camera during X-ray irradiation at energy below 120 keV. We also conducted the imaging of air without subjects during irradiation of the same X-ray. The biological subjects emitted visible-light luminescence, and the imaging was possible with the irradiation of the X-ray below 120 keV. The luminescence images were observed in only the X-ray irradiated areas. Also air luminescence images could be obtained and the intensity of the luminescence measured from the images was proportionally increased with the exposure dose. UV or visible-light luminescence imaging of biological subjects was possible during X-ray irradiations lower energy than the Cerenkov-light threshold. The phenomenon was different from general X-ray fluorescence because wavelength of the luminescence is UV or visible-light. The luminescence imaging method is promising for estimating the irradiated area with X-ray, which could be used for interventional radiology (IVR). Also air luminescence imaging would be applied to the exposure dose distribution measurements for X-ray of diagnostic X-ray systems.

DOI： 10.1007/s10043-017-0325-z

Web of Science

Detection of microcalcifications and tumor tissue in mammography using a CdTe-series photon-counting detector

Nakajima Ai, Ihori Akiko, Nishide Hiroko, Koyama Shuji, Yamakawa Tsutomu, Yamamoto Shuichiro, Okada Masahiro, Kodera Yoshie

MEDICAL IMAGING 2017: PHYSICS OF MEDICAL IMAGING Vol. 10132 2017

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

In this study, we proposed a method for detecting microcalcifications and tumor tissue using a cadmium telluride (CdTe) series linear detector. The CdTe series detector was used as an energy resolved photon-counting (hereafter referred to as the photon-counting) mammography detector. The CdTe series linear detector and two types of phantom were designed using a MATLAB simulation. Each phantom consisted of mammary gland and adipose tissue. One phantom contained microcalcifications and the other contained tumor tissue. We varied the size of these structures and the mammary gland composition. We divided the spectrum of an x-ray, which is transmitted to each phantom, into three energy bins and calculated the corresponding linear attenuation coefficients from the numbers of input and output photons. Subsequently, the absorption vector length that expresses the amount of absorption was calculated. When the material composition was different between objects, for example mammary gland and microcalcifications, the absorption vector length was also different. We compared each absorption vector length and tried to detect the microcalcifications and tumor tissue. However, as the size of microcalcifications and tumor tissue decreased and/or the mammary gland content rate increased, there was difficulty in distinguishing them. The microcalcifications and tumor tissue despite the reduction in size or increase in mammary gland content rate can be distinguished by increasing the x-ray dosage. Therefore, it is necessary to find a condition under which a low exposure dose is optimally balanced with high detection sensitivity. It is a new method to indicate the image using photon counting technology.

DOI： 10.1117/12.2253576

Web of Science

Ｘ線ＣＴの診断参考レベル（DRL）:CTDIvolとDLP Invited

小山修司

Rad Fan Vol. 14 ( 15 ) page： 35-38 2016.11

ＣＴにおける医療被ばくの指標 Invited

小山修司

日獨医報 Vol. 61 ( 1 ) page： 13-25 2016.9

Authorship：Lead author Language：Japanese

X線CTにおける医療被ばく線量の最適化を図るための診断参考レベルとして使用されている，CTDI_vol（volume CT Dose Index）とDLP（Dose Length Product）について解説した．また，米国医学物理学会（AAPM）の提案する新しい指標である，SSDE（Size Specific Dose Estimation）についても解説した．

DOI： 13-25

Influence of 320-detector-row volume scanning and AAPM report 111 CT dosimetry metrics on size-specific dose estimate: a Monte Carlo study Reviewed

HABA Tomonobu, KOYAMA Shuji, KINOMURA Yutaka, IDA Yoshihiro, KOBAYASHI Masanao

Australasian Physical & Engineering Sciences in Medicine Vol. 39 ( 3 ) page： 697-703 2016.7

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

The American Association of Physicists in Medicine (AAPM) task group 204 has recommended the use of size-dependent conversion factors to calculate size-specific dose estimate (SSDE) values from volume computed tomography dose index (CTDI_vol) values. However, these conversion factors do not consider the effects of 320-detector-row volume computed tomography (CT) examinations or the new CT dosimetry metrics proposed by AAPM task group 111. This study aims to investigate the influence of these examinations and metrics on the conversion factors reported by AAPM task group 204, using Monte Carlo simulations. Simulations were performed modelling a Toshiba Aquilion ONE CT scanner, in order to compute dose values in water for cylindrical phantoms with 8-40-cm diameters at 2-cm intervals for each scanning parameter (tube voltage, bow-tie filter, longitudinal beam width). Then, the conversion factors were obtained by applying exponential regression analysis between the dose values for a given phantom diameter and the phantom diameter combined with various scanning parameters. The conversion factors for each scanning method (helical, axial, or volume scanning) and CT dosimetry method (i.e., the CTDI₁₀₀ method or the AAPM task group 111 method) were in agreement with those reported by AAPM task group 204, within a percentage error of 14.2 % for phantom diameters 11.2 cm and over. The results obtained in this study indicate that the conversion factors previously presented by AAPM task group 204 can be used to provide appropriate SSDE values for 320-detector-row volume CT examinations and the CT dosimetry metrics proposed by the AAPM task group 111.

DOI： 10.1007/s13246-016-0465-7

Luminescence imaging of water during alpha particle irradiation Reviewed

Seiichi Yamamoto, Masataka Komori, Shuji Koyama, Toshiyuki Toshito

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Vol. 819 page： 6 - 13 2016.5

Luminescence imaging of water during carbon-ion irradiation for range estimation Reviewed

Seiichi Yamamoto, Masataka Komori, Takashi Akagi, Tomohiro Yamashita, Shuji Koyama, Yuki Morishita, Eri Sekihara, Toshiyuki Toshito

Medical Physics Vol. 43 ( 5 ) page： 2455 - 2463 2016.4

人体ファントムを用いた前置癒着胎盤に対する総腸骨動脈バルーン閉塞術時の胎児被曝線量の推定 Reviewed

西條貴哉，瀬口繁信，石川芳信，小山修司，祖父江亮嗣，加藤紀子

IVR会誌 Vol. 30 ( 2 ) page： 148-153 2015.6

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

胎盤は受梢卵が子宮内膜に着床することにより形成され始め,子宮底部近くに付着することが一般的であるが,その胎盤が通常よりも低位に形成され,内子宮口の全部または一部を覆っている状態を前置胎盤といい,その頻度は全分娩の0.26~0.57%といわれている')。また,その中でも胎盤と子宮との癒着が強く胎盤が剥がれない前置癒着胎盤は,前置胎盤での癒着胎盤発生率が0.04%であり,常位の癒着胎盤の発生率である 0.0045%に比べ10倍高く2),剥離する際の大量出血により出血性ショックや播種性血管内凝固症候群(DIC) を併発し母体死亡につながるリスクの高い重大な産科合併症である。そのため,前置癒着胎盤が強く疑われる患者の帝王切開術の直前には,総腸骨動脈バルーン閉塞術(commoniliacarteryballoonocclusion，以下, CIABO)が併用される。これは,局所麻酔下でバルーンカテーテルを両側の鼠径部から対側の総腸骨動脈に留置し,帝王切開の術中.胎児を取り出した後にバルーンを拡張させ.胎盤の剥離手技に伴う出血量の軽減を目的とした処置である.しかし,この手技はX線透視を使用したinterventionalradiology(以下,IVR)であり,X線照射範囲内に胎児が位置するため,母体はもとより子宮内の胎児に対してX線が照射される。胎児では成人に比べて放射線感受性が高いため,放射線被曝による影響が懸念される。しかしながら,CIABO における胎児の被曝線鼠について記述された論文はない．そこで,本研究は小型のフォトダイオード線量計を人体ファントムの各臓器位置に埋め込んだ臓器吸収線避計測システムを使用して,当院での臨床データをもとに人体ファントム内の胎児の位置における吸収纏量(以下,胎児線量)を実測し,評価するとともに.胎児線量低減方法の検討を目的とする．

DOI： 148-153

脳動脈瘤の患者がX線診断・治療・経過観察によって受ける放射線被ばく線量

瀬口繁信，西條貴哉，石川芳信，小島隆生，小山修司

脳神経外科 Vol. 43 ( 5 ) page： 411-418 2015.5

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Papers - KOYAMA Shuji