Faculty Profiles - SAITO Masatoshi

Technical note: Implementing MRI/CT‐based elemental concentration data to Monte Carlo simulation for yielding positron emitters in proton therapy Reviewed

Masatoshi Saito, Ryuga Matsumoto

Medical Physics 51 ( 4 ) 2861 - 2870 2023.12

Authorship：Lead author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：Wiley

Abstract

Background

The elemental concentration (especially oxygen and carbon) and mass density must be accurately assigned to perform Monte Carlo (MC) simulations for predicting proton‐induced nuclear reactions in the human body. We recently proposed an approach to quantify elemental concentrations and mass densities of human soft tissues from water content (WC) data obtained by quantitative magnetic resonance (MR) imaging (which we called “MRWC”).

Purpose

This study presents the first implementation of MRWC‐derived elemental concentrations and mass densities as complementary inputs into MC simulations on a virtual head phantom, and demonstrates the simulation of positron emitter production yields in proton therapy.

Methods

An MC code, PHITS, was used to simulate proton therapy with a monoenergetic 140 MeV beam for a digital head phantom provided by BrainWeb. Three different head images were synthesized as inputs: a conventional CT image, an ideal CT image as a reference, and a WC image coupled with the bone‐only CT image for a hybrid approach (MRWC/CT). Thereafter, the performance of the MRWC/CT method was evaluated by comparing its accuracy in predicting the production yields of positron emitters (11C and 15O) with the gold‐standard CT‐only method.

Results

The MRWC/CT method could predict 11C and 15O production yield maps that closely resembled the corresponding reference maps, while the CT‐only method failed. The structural similarity index measures between the reference and CT‐ or MRWC/CT‐derived maps were improved from 0.67 (CT‐only) to 0.87 (MRWC/CT) for 11C and 0.76 (CT‐only) to 0.93 (MRWC/CT) for 15O. Furthermore, applying post‐processing normalizations to account for elemental density variations in the production yields of positron emitters facilitated the determination of distal fall‐off positions in depth activity profiles.

Conclusion

At least in the head area, the MRWC/CT method demonstrated potential for more precise predictions of proton‐induced positron emitter distributions via MC simulations than that of the CT‐only method.

DOI： 10.1002/mp.16896

MRI‐based quantification of carbon and oxygen concentrations in human soft tissues for range verification in proton therapy Reviewed

Masatoshi Saito

Medical Physics 50 ( 9 ) 5671 - 5681 2023.3

Authorship：Lead author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：Wiley

ABSTRACT

Background

In‐situ range verification of particle therapy based on the detection of secondary emitted radiation requires highly accurate assignment of elemental concentrations (particularly carbon and oxygen) in the human body.

Purpose

A method for quantitatively predicting carbon and oxygen concentrations in human soft tissues is proposed. This method relies on an empirical one‐to‐one correspondence between the mass fraction and water content (WC), which is a measurable tissue quantity based on magnetic resonance (MR) imaging (referred to as “MRWC‐based method”).

Methods

A numerical analysis of the MRWC‐based method was performed for 47 standard human soft tissues tabulated in the literature as objects of interest with unknown mass fractions of the four main elements—C, O, H, and N. Thereafter, the method was evaluated in terms of the mass‐fraction quantification accuracy by comparing it with the gold‐standard CT‐based method developed by Schneider et al. The MRWC‐based method was also applied to the MR imaging data of a virtual head phantom obtained from a three‐dimensional MRI‐simulated brain database.

Results

The predicted mass fractions in a range of human soft tissues were in better agreement with the reference values than those predicted by the CT‐based method. The mean absolute errors of the predicted mass% values for the overall standard soft tissues could be reduced from 4.8 percentage points (pp) (CT‐based) to 0.5 pp (MRWC‐based) for carbon and from 5.2 pp (CT‐based) to 0.4 pp (MRWC‐based) for oxygen. The application to the simulated MRI data confirmed the capability of the sufficient recognition of the boundaries between the white matter and gray matter in the brain that could not be realized by the CT‐based method. Thus, the MRWC‐based method exhibits superior performance in the prediction of carbon and oxygen concentrations in soft tissues.

Conclusions

This study is limited to a proof‐of‐concept scope but demonstrates the feasibility of the MRWC‐based method for the generation of elemental images of human soft tissues from MRI‐derived water‐content images.

DOI： 10.1002/mp.16353

Quadratic relation for mass density calibration in human body using dual‐energy CT data Reviewed

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.16353

Masatoshi Saito

Medical Physics 48 ( 6 ) 3065 - 3073 2021.6

Proton dose calculation based on converting dual-energy CT data to stopping power ratio (DEEDZ-SPR): a beam-hardening assessment Reviewed International journal

Sodai Tanaka, Yoshiyuki Noto, Satoru Utsunomiya, Takaaki Yoshimura, Taeko Matsuura, Masatoshi Saito

Physics in Medicine & Biology 65 ( 23 ) 235046 - 235046 2020.12

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

To achieve an accurate stopping power ratio (SPR) prediction in particle therapy treatment planning, we previously proposed a simple conversion to the SPR from dual-energy (DE) computed tomography (CT) data via electron density and effective atomic number (Z eff) calibration (DEEDZ-SPR). This study was conducted to carry out an initial implementation of the DEEDZ-SPR conversion method with a clinical treatment planning system (TPS; VQA, Hitachi Ltd., Tokyo) for proton beam therapy. Consequently, this paper presents a proton therapy plan for an anthropomorphic phantom to evaluate the stability of the dose calculations obtained by the DEEDZ-SPR conversion against the variation of the calibration phantom size. Dual-energy x-ray CT images were acquired using a dual-source CT (DSCT) scanner. A single-energy CT (SECT) scan using the same DSCT scanner was also performed to compare the DEEDZ-SPR conversion with the SECT-based SPR (SECT-SPR) conversion. The scanner-specific parameters necessary for the SPR calibration were obtained from the CT images of tissue substitutes in a calibration phantom. Two calibration phantoms with different sizes (a 33 cm diameter phantom and an 18 cm diameter phantom) were used for the SPR calibrations to investigate the beam-hardening effect on dosimetric uncertainties. Each set of calibrated SPR data was applied to the proton therapy plan designed using the VQA TPS with a pencil beam algorithm for the anthropomorphic phantom. The treatment plans with the SECT-SPR conversion exhibited discrepancies between the dose distributions and the dose-volume histograms (DVHs) of the 33 cm and 18 cm phantom calibrations. In contrast, the corresponding dose distributions and the DVHs obtained using the DEEDZ-SPR conversion method coincided almost perfectly with each other. The DEEDZ-SPR conversion appears to be a promising method for providing proton dose plans that are stable against the size variations of the calibration phantom and the patient.

DOI： 10.1088/1361-6560/abae09

PubMed

Simulation of photon-counting detectors for conversion of dual-energy-subtracted computed tomography number to electron density Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1361-6560/abae09/pdf

Masatoshi Saito

Radiological Physics and Technology 12 ( 1 ) 105 - 117 2019.3

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

DOI： 10.1007/s12194-018-00497-0

Comment on: Methodological accuracy of image‐based electron density assessment using dual‐energy computed tomography [Med. Phys. 44(6), 2429–2437 (2017)] Reviewed

Other Link： http://link.springer.com/article/10.1007/s12194-018-00497-0/fulltext.html

Masatoshi Saito

Medical Physics 46 ( 2 ) 1075 - 1076 2019.2

Comment on: Dual-energy CT quantitative imaging: A comparison study between twin-beam and dual-source CT scanners [Med. Phys. 44(1), 171-179] Reviewed

Masatoshi Saito

Medical Physics 45 ( 8 ) 3996 - 3996 2018.8

Simplified derivation of stopping power ratio in the human body from dual-energy CT data Reviewed

Masatoshi Saito, Shota Sagara

MEDICAL PHYSICS 44 ( 8 ) 4179 - 4187 2017.8

A simple formulation for deriving effective atomic numbers via electron density calibration from dual-energy CT data in the human body Reviewed

Masatoshi Saito, Shota Sagara

MEDICAL PHYSICS 44 ( 6 ) 2293 - 2303 2017.6

Technical Note: Relation between dual-energy subtraction of CT images for electron density calibration and virtual monochromatic imaging Reviewed

Masatoshi Saito

MEDICAL PHYSICS 42 ( 7 ) 4088 - 4093 2015.7

Initial implementation of the conversion from the energy-subtracted CT number to electron density in tissue inhomogeneity corrections: An anthropomorphic phantom study of radiotherapy treatment planning Reviewed

Masayoshi Tsukihara, Yoshiyuki Noto, Ryuta Sasamoto, Takahide Hayakawa, Masatoshi Saito

MEDICAL PHYSICS 42 ( 3 ) 1378 - 1388 2015.3

Technical Note: Exploring the limit for the conversion of energy-subtracted CT number to electron density for high-atomic-number materials Reviewed

Masatoshi Saito, Masayoshi Tsukihara

MEDICAL PHYSICS 41 ( 7 ) 071701 2014.7

Conversion of the energy-subtracted CT number to electron density based on a single linear relationship: an experimental verification using a clinical dual-source CT scanner Reviewed

Masayoshi Tsukihara, Yoshiyuki Noto, Takahide Hayakawa, Masatoshi Saito

PHYSICS IN MEDICINE AND BIOLOGY 58 ( 9 ) N135 - N144 2013.5

Potential of dual-energy subtraction for converting CT numbers to electron density based on a single linear relationship Reviewed

Masatoshi Saito

MEDICAL PHYSICS 39 ( 4 ) 2021 - 2030 2012.4

Optimized low-kV spectrum of dual-energy CT equipped with high-kV tin filtration for electron density measurements Reviewed

Masatoshi Saito

Medical Physics 38 ( 6 ) 2850 - 2858 2011

Structural Study of Zr_<50>Cu_<50> Amorphous Alloy by Anomalous X-ray Scattering Coupled with Reverse Monte-Carlo Simulation

KAWAMATA T., YOKOYAMA Y., SAITO M., SUGIYAMA K., WASEDA Y.

Materials Transactions, JIM 51 ( 10 ) 1796 - 1801 2010.10

Language：English Publisher：The Japan Institute of Metals and Materials

Anomalous X-ray scattering (AXS) analysis was applied for the structural analysis of a rapidly quenched Zr50Cu50 amorphous alloy. The present AXS analysis provided the environmental structural information round Cu and Zr, and the subsequent reverse Monte Carlo (RMC) simulation allowed us to obtain three partial pair distribution functions together with a three-dimensional structural model. The Voronoi polyhedral analysis of the nearest-neighbor region confirms that the structural features are similar to those of the dense random packing of hard spheres (DRPHS) model. The chemical oscillatory structure composed of alternating Cu-rich and Zr-rich coordination shells was realized in the middle range, up to 0.8 nm. The shell structure is suggested to be one of the fundamental structural features of medium-range ordering in the Zr50Cu50 amorphous alloy.

DOI： 10.2320/matertrans.MAW201016

The Structural Analysis of Non-crystalline Materials by the Anomalous X-ray Scattering Coupled with Reverse Monte Carlo Simulation Reviewed

Other Link： https://jlc.jst.go.jp/DN/JALC/00356579564?from=CiNii

Technical note: Optimization for improved tube-loading efficiency in the dual-energy computed tomography coupled with balanced filter method Reviewed

Masatoshi Saito

Medical Physics 37 ( 8 ) 4182 - 4185 2010

Electron density distribution in liquid Ga estimated from the anomalous X-ray scattering measurements Reviewed

Masatoshi Saito, Kazumasa Sugiyama, Yoshio Waseda

High Temperature Materials and Processes 29 ( 5-6 ) 393 - 403 2010

Structural study of liquid LiNbO3 by the high-temperature energy dispersive X-ray diffraction coupled with reverse Monte Carlo simulation Reviewed

K. Sugiyama, M. Saito, Y. Waseda

Journal of Crystal Growth 311 ( 3 ) 966 - 969 2009.1

Spectral optimization for measuring electron density by the dual-energy computed tomography coupled with balanced filter method Reviewed

Masatoshi Saito

Medical Physics 36 ( 8 ) 3631 - 3642 2009

Dielectric screening properties in molten noble-metal halides Reviewed

Shigeki Matsunaga, Masatoshi Saito, Takahiro Koishi, Shigeru Tamaki

JOURNAL OF ALLOYS AND COMPOUNDS 452 ( 1 ) 182 - 187 2008.3

Dual-energy approach to contrast-enhanced mammography using the balanced filter method: Spectral optimization and preliminary phantom measurement Reviewed

Masatoshi Saito

MEDICAL PHYSICS 34 ( 11 ) 4236 - 4246 2007.11

Dielectric screening effects in molten AgI-AgBr system Reviewed

S. Matsunaga, M. Saito, T. Koishi, S. Tamaki

Molecular Simulation 33 ( 1-2 ) 153 - 158 2007.1

Dielectric screening properties in molten salts Reviewed

Takahiro Koishi, Masatoshi Saito, Shigeki Matsunaga, Shigeru Tamaki

PHYSICS AND CHEMISTRY OF LIQUIDS 45 ( 2 ) 181 - 196 2007

SUGIYAMA Kazumasa, SAITO Masatoshi

Nihon Kessho Gakkaishi 48 ( 1 ) 81 - 85 2006.2

Language：Japanese Publisher：The Crystallographic Society of Japan

The anomalous X-ray scattering (AXS) coupled with model calculation using reverse Monte Carlo (RMC) simulation, has recently received much attention for analyzing the middlerange ordering for non-crystalline materials. The usefulness of this new method was demonstrated with some selected examples of a Bi30Ga70high temperature liquid alloy and an amorphous ZrO2.

DOI： 10.5940/jcrsj.48.81

Effective Pair Potentials of Molten AgBr Estimated from Experimental Partial Structure Factors

Structural characterization for a complex system by obtaining middle-range ordering Reviewed

Yoshio Waseda, Shigeru Suzuki, Masatoshi Saito

Characterization of Corrosion Products on Steel Surfaces 7 77 - 104 2006

Quasimonochromatic x-ray computed tomography by the balanced filter method using a conventional x-ray source Reviewed

M Saito

MEDICAL PHYSICS 31 ( 12 ) 3436 - 3443 2004.12

Fe (O, OH)(6) network structure of rusts formed on weathering steel surfaces

M Kimura, T Suzuki, G Sigesato, M Saito, S Suzuki, H Kihira, K Tanabe, Y Waseda

JOURNAL OF THE JAPAN INSTITUTE OF METALS 66 ( 3 ) 166 - 175 2002.3

MITEV Pavlin Dakev, SAITO Masatoshi, WASEDA Yoshio

MATERIALS TRANSACTIONS 42 ( 5 ) 829 - 832 2001.5

Language：English Publisher：The Japan Institute of Metals and Materials

Three effective pair potentials of Ag–Br, Br–Br and Ag–Ag pairs in molten AgBr have been calculated from measured partial structural data by applying the modified hypernetted-chain equation coupled with a predictor-corrector method. The present results of pair potentials were also compared with model potentials originally proposed by Vashishta and Rahman. The resultant potentials suggest two characteristic features. One is the relatively shallow minimum in the interaction of Ag–Br pair in the first nearest neighbor region at 0.27 nm, in comparison with the model potential case. The other is both positive and negative deviation from the simple asymptotic form detected in the interaction of Br–Br pair in the range of 0.3&sim;1.1 nm. These results may be attributed to a particular structural feature of molten AgBr, suggesting not only the purely ionic character.

DOI： 10.2320/matertrans.42.829

Transport Properties of Superionic Conducting Glasses (AgX)_<0.4>(Ag_2O)_<0.3>(GeO_2)_<0.3> (X=I, Br, Cl)

KANG Shinchul, SAITO Masatoshi, JACOB K. Thomas, WASEDA Yoshio

Materials Transactions, JIM 41 ( 12 ) 1670 - 1674 2000.12

Language：English Publisher：The Japan Institute of Metals

In order to identify the dominant mechanism of ionic conduction, the electrical conductivity and ionic mobility of the glasses (AgX)0.4(Ag2O)0.3(GeO2)0.3 (X=I, Br, Cl) were measured separately in the temperature range from 293 to 393 K by coupling the AC technique with the TIC method. Electronic conductivity was also measured at 293 K by the Wagner polarization method. The total electrical conductivity of these glasses was found to be as high as 10−1 Ω−1 m−1, and the mobility about 10−6 m2 V−1 s−1. The variation of total electrical conductivity and mobility at constant temperature and composition with the type of halide occurred in the sequence, Cl<Br<I. For each composition, both conductivity and mobility increased with temperature. The mobile ion concentration was found to be about 1023 m−3 at 293 K, and it was insensitive to the type of halide as well as temperature. The results suggest that the change in ionic conductivity with the temperature and the type of halide present is mainly attributable to the change in ionic mobility rather than carrier concentration. Moreover, the electronic conductivity was found to be about 10−6 Ω−1 m−1 at 293 K. Thus, the electronic contribution to the total conductivity is negligibly small.

DOI： 10.2320/matertrans1989.41.1670

Partial structural functions of molten copper halides CuX (X = Br, I) estimated from the anomalous x-ray scattering measurements

Y. Waseda, S. Kang, K. Sugiyama, M. Kimura, M. Saito

Journal of Physics Condensed Matter 12 2000.12

Structural Study of Amorphous Ge 50Al 40Cr 10 Alloy

Louzguine Dmitri, Saito Masatoshi, Waseda Yoshio, Inoue Akihisa

J Phys Soc Jpn 68 ( 7 ) 2298 - 2303 1999.7

Language：English Publisher：The Physical Society of Japan (JPS)

The structure of an amorphous Ge50Al40Cr10 alloy was studied by conventional X-ray diffraction, anomalous X-ray scattering and transmission electron microscopy including high-resolution imaging. The anomalous X-ray scattering profiles were obtained at Ge and Cr K-absorption edges. Structural information in the form of interference function obtained by the experimental methods was checked for its correctness by using the reverse Monte Carlo simulation method. The structure of the alloy studied is discussed on the basis of transmission electron microscopy images, an ordinary radial distribution function, partial structure functions and partial pair distribution functions.

DOI： 10.1143/JPSJ.68.2298

Partial structural functions of molten AgBr estimated from the anomalous X-ray scattering data coupled with neutron diffraction

Other Link： https://jlc.jst.go.jp/DN/JALC/00062001304?from=CiNii

Masatoshi Saito, Shinchul Kang, Kazumasa Sugiyama, Yoshio Waseda

Journal of the Physical Society of Japan 68 ( 6 ) 1932 - 1938 1999.1

Structure and Magnetic Properties of La(Co1-xMnx)13 Crystlline and Amorphous Alloys

K. Asada, A. Fujita, S.G. Kim, K. Fukamichi, E. Matsubara, M. Saito, Y. Waseda

J. Magn. Soc. Jpn. 23 480 - 482 1999

Structural Study of Pd-Based Amorphous Alloys with Wide Supercooled Liquid Region by Anomalous X-ray Scattering

Park Changyong, Saito Masatoshi, Waseda Yoshio, Nishiyama Nobuyuki, Inoue Akihisa

Materials Transactions, JIM 40 ( 6 ) 491 - 497 1999

Language：English Publisher：The Japan Institute of Metals

The anomalous X-ray scattering (AXS) measurements have been made to determine the local ordering structures around Ni and Cu in Pd40Ni10Cu30P20 and Pd40Ni40P20 alloys in both the liquid and amorphous state using the synchrotron radiation at incident X-ray energies close to the K-absorption edges of Ni and Cu. A characteristic small hump was clearly found at r=0.37 nm in the environmental radial distribution function (RDF) around Cu in liquid and amorphous Pd40Ni10Cu30P20 alloy. Such peak was not detected in the environmental RDF around Ni, and the local atomic arrangement around Ni was found to be similar to the Pd40Ni40P20 case. These experimental facts can be described when considering the trigonal prismatic packing related to Ni and the tetragonal dodecahedral packing related to Cu. This is in a sense a necessary condition at best, although it might not be the sufficient condition. However, the effect of elemental substitution with Cu for Ni in the Pd–Ni–Cu–P alloy is thought to induce the particular atomic association related to Cu, which is an important factor for exhibiting its wide supercooled liquid region and high reduced glass transition temperature.

DOI： 10.2320/matertrans1989.40.491

Effective Pair Potentials of Liquid CuBr Estimated from the Anomalous X-Ray Scattering Data

Omote Kazuhiko, Saito Masatoshi, Waseda Yoshio

J Phys Soc Jpn 66 ( 10 ) 3097 - 3101 1997.10

Language：English Publisher：The Physical Society of Japan (JPS)

We have proposed a method for calculating the effective pair potentials of molten salt from measured structural data in which a long-range Coulombic interaction is important [K. Omote and Y. Waseda: J. Phys. Soc. Jpn. 66 (1997)]. By applying this method, the effective pair potentials of liquid CuBr have been successfully estimated from the experimental partial structure factors obtained by anomalous X-ray scattering. The resultant potentials show two characteristic features. One is remarkable shielding for the Cu–Cu Coulomb repulsion in its nearest neighbor region. This might be a possible origin for the absence of marked structure in the Cu–Cu correlation and the penetration of Cu ions into the first like-ion coordination shell. The other is the deviation from the Coulomb potential in the range of 0.4∼0.9 nm in the interactions of Cu–Cu and Cu–Br pairs, suggesting a certain correlation to a pre-peak found in the Cu–Cu structure factor at about 10 nm-1.

DOI： 10.1143/JPSJ.66.3097

Structure Analysis of Disordered Materials by the Anomalous X-ray Scattering(AXS) Method. Reviewed

Other Link： https://jlc.jst.go.jp/DN/JALC/00049510119?from=CiNii

SUGIYAMA Kazumasa, SAITO Masatoshi, WASEDA Yoshio, MATSUBARA Eiichiro

Nihon Kessho Gakkaishi 39 ( 1 ) 20 - 25 1997.2

Language：Japanese Publisher：The Crystallographic Society of Japan

The anomalous X-ray scattering method has recently received much attention for obtaining the fine structure of disordered materials, coupled with the synchrotron radiation source. This paper demonstrates the usefulness of the AXS method for determining the local environmental structure around a specific element as a function of distance, by providing fundamentals with some selected examples of high temperature CuBr liquid, 70GeO230Bi2O3 oxide glass and Zr-Y-Al-Ni metallic glasses.

DOI： 10.5940/jcrsj.39.20