Fundamental study on ultra-high-speed tomography system utilizing intense flash x-ray generators

Abstract

A high-speed x-ray tomography system is useful for observing high-speed phenomena. The experimental setup for tomography consists of a tungsten-target x-ray generator, a tungsten collimator, and a computed radiography system. An object was exposed by a 2-mm-thick fun beam from the x-ray generator, and scattering x-rays from the slice plane were detected using an imaging plate through a tungsten collimator with hole diameters of 0.8 mm. Because the exposed dose for tomography was almost equal to those obtained using two intense flash x-ray generators, ultra-high-speed tomography could be performed.

Full text

Fundamental study on ultra-high-speed tomography system
utilizing intense flash x-ray generators
Eiichi Satoa, Toshiyuki Enomotob, Toshiaki Kawaic, Mitsuru Izumisawad, Koetsu Satoe,
Akira Ogawaf, Shigehiro Satog, Kazuyoshi Takayamah
aDepartment of Physics, Iwate Medical University, 2-1-1 Nishitokuta, Yahaba 028-3694, Japan
bThe 3rd Department of Surgery, Toho University School of Medicine, 2-17-6 Ohashi, Meguro-ku,
Tokyo 153-8515, Japan;
cElectron Tube Division #2, Hamamatsu Photonics K. K., 314-5 Shimokanzo, Iwata 438-0193,
Japan;
dDepartment of Oral Radiology, School of Dentistry, Iwate Medical University, 1-3-27 Chuo,
Morioka 020-0021, Japan;
eToreck Inc., 5-6-20 Tsunashima Higashi, Yokohama 223-0052, Japan;
fDepartment of Neurosurgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru,
Morioka 020-8505, Japan;
gDepartment of Microbiology, School of Medicine, Iwate Medical University, 19-1 Uchimaru,
Morioka 020-8505, Japan;
hTohoku University Biomedical Engineering Research Organization, 2-1-1 Katahira, Sendai
980-8577, Japan
ABSTRACT
A high-speed x-ray tomography system is useful for observing high-speed phenomena. The experimental setup for
tomography consists of a tungsten-target x-ray generator, a tungsten collimator, and a computed radiography system.
An object was exposed by a 2-mm-thick fun beam from the x-ray generator, and scattering x-rays from the slice plane
were detected using an imaging plate through a tungsten collimator with hole diameters of 0.8 mm. Because the
exposed dose for tomography was almost equal to those obtained using two intense flash x-ray generators,
ultra-high-speed tomography could be performed.
Keywords: scattering x-ray tomography, high-speed tomography, polychromatic fan beam, intense flash x-ray
generator, flash x-rays
1. INTRODUCTION
Flash x-ray generators are useful for carrying out high-speed radiography1-7 and have been developed corresponding to
radiographic objectives. Because soft flash x-ray generators with photon energies below 150 keV are usable for
performing biomedical radiography, and the several different generators have been developed. In particular, a
linear-plasma flash x-ray generator8-11 is useful for producing clean low-photon-energy K-series characteristic x-rays
of nickel and copper, and a spherical-plasma flash x-ray generator12-14 is usable for producing high-photon-energy K
rays of molybdenum, cerium, tantalum, and tungsten.
Recently, we have developed several x-ray computed tomography (CT) systems as follows: a high-sensitive CT
system, a K-edge CT (KT) system,15 and a fluorescence CT (FT) system.16 In KT and FT systems, we have employed
a cadmium telluride detector for discriminating x-ray photon energy using a multi-channel analyzer. In addition, we
have performed a fundamental study on fluorescence tomography system17 for cancer diagnosis with a computed
radiography (CR) system and a tungsten collimator for a gamma camera.
To perform ultra-high-speed tomography with an intense flash x-ray generator, a conventional CT system for taking
projection curves cannot be used. Therefore, we have to design a novel tomography system for high-speed imaging,
and an experimental setup for the fluorescence tomography can be employed.
For this research, we performed preliminary experiment for high-speed scattering x-ray tomography system utilizing
28th International Congress on High-Speed Imaging and Photonics, edited by Harald Kleine, Martha Patricia Butrón Guillén,
Proc. of SPIE Vol. 7126, 71261H · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.823077
Proc. of SPIE Vol. 7126 71261H-1

Scattering '-rays -.
Object Tunjten x-ray isncrator
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an x-ray generator in conjunction with a computed radiography (CR) system.18
2. SCATTERING X-RAY TOMOGRAPHY SYSTEM
2.1 Scattering x-ray tomography system
A block diagram of a scattering x-ray tomography system is shown in Fig. 1. This system can be employed to perform
high-speed tomography, and the system consists of a steady state x-ray generator, a tungsten collimator for a gamma
camera, and a CR system (Konica Minolta, Regius 150) with imaging plates. In the tomography system, when an
object is exposed by a 2.0-mm-thick fan beam, scattering x-rays are produced from a slice plane and are detected by
an imaging plate through a tungsten collimator.
2.2 X-ray generator
Figure 2 shows a block diagram of a 100-μm-focus x-ray generator used in this experiment, and consists of a main
controller, an x-ray tube, negative and positive Cockcroft-Walton circuits, and an insulation transformer. Tube voltage,
current, and exposure time can be controlled by a main controller. High-voltage line employs the Cockcroft-Walton
circuits, and positive and negative high voltages are applied to the anode and cathode electrodes, respectively. The
filament heating current is supplied by an AC power supply with an insulation transformer which is used for isolation
from the high voltage from the Cockcroft-Walton circuit. In this experiment, the tube voltage ranged from 40 to 70 kV,
and the tube current was regulated as 0.50 mA.
3. RESULTS
3.1 X-ray intensity
The x-ray intensity was measured by a Victoreen 660 ionization chamber at 1.0 m from the x-ray source (Fig. 3). At a
constant tube current of 0.50 mA, the x-ray intensity increased when the tube voltage was increased. The x-ray
intensity substantially decreased according to insertion of a 3.0-mm-thick aluminum filter. At a tube voltage of 80 kV
and a current of 0.50 mA, the intensity with and without filtering were 20.8 and 416 μGy/s.
3.2 Scattering x-ray tomography
The scattering x-ray tomography was performed at a tube voltage of 80 kV without filtering, and the distance between
the x-ray source and the objects was 0.15 m. Figure 4 shows scattering tomography of a 16.5-mm-diameter glass vial
and a vial filled with polymethylmeth acrylate (PMMA) particles. Using this tomography, the glass wall and PMMA
particles were seen. Figure 5 shows tomograms of glass vials filled with water and iodine medium with a density of 30
mg/mL. As compared with the image of water, the density of the iodine medium was high. For the tomography of a
PMMA tube, PMMA wall was observed clearly (Fig. 6). Because the ploychromatic x-rays are absorbed by the objects,
the density gradations were observed.
Fig. 1. Experimental setup of a scattering x-ray
tomography system.
Fig. 2. Block diagram of an x-ray generator.
Proc. of SPIE Vol. 7126 71261H-2

40
30
no tiltCi using 3.0-mm-thick rnngstcn titer
460
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440
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410 20
75 80 85 90 95 100 105 110
Tube voltage (kV)
75 80 85 90 95 100 105 110
Tube voltage (kY)
Grass vial
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Class vial filled vith water
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3.3 Design of ultra-high-speed x-ray CT system
Because the x-ray intensities are almost equal to those obtained using intense flash x-ray generators, ultra-high-speed
tomography is realizable using these flash generators instead of the steady state generator (Fig. 7). Although a linear
plasma x-ray generator (Fig. 8) is used to produce low-photon-energy K-series characteristic x-rays, the generator can
produce intense L-series and bremsstrahlung x-rays using a rod-shaped tungsten target. Next, because a
spherical-plasma generator (Fig. 9) produces high-photon-energy bremsstrahlung x-rays with a maximum energy of
160 kV, this generator can be employed to perform comparatively hard x-ray tomography.
Fig. 3. X-ray intensity measured at 1.0 m from x-ray source according
to changes in the tube voltage.
Fig. 4. Tomography of a glass vial and a vial filled with
PMMA particles.
Fig. 5. Tomography of glass vials filled with water and
30-mg/mL-density contrast medium.
Proc. of SPIE Vol. 7126 71261H-3

P\IMA lulir
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Fig. 6. Tomography of PMMA tube.
Fig. 7. Experimental setup of a high-speed scattering x-ray
tomography system utilizing an intense flash x-ray generator.
Fig. 8. Block diagram of a linear plasma flash x-ray
generator.
Fig. 9. Block diagram of a spherical plasma flash x-ray
generator.
Fig. 10. Experimental setup of a high-speed scattering x-ray tomography system utilizing two flash x-ray generators.
Proc. of SPIE Vol. 7126 71261H-4

4. CONCLUSIONS
In the present research, we performed a fundamental study on high-speed tomography utilizing polychromatic
scattering x-rays from the slice plane. Because the x-ray intensity for the scattering tomography is almost equal to
those obtained using two intense flash x-ray generators developed by the authors.
In scattering x-ray tomography, the gradation of the image density was observed, and high-photon-energy x-rays are
useful for decreasing the gradation of the image density. In addition, a tomography system with two flash x-ray
generators is usable for decreasing the gradation (Fig. 10).
To perform the scattering tomography, although we used an imaging plate for detecting x-rays, a photon-counting
panel detector may be useful to increase the sensitivity. However, because most flash x-ray generators produce
electromagnetic noises, the noise shielding is necessary.
ACKNOWLEDGMENTS
This work was supported by Grants-in-Aid for Scientific Research and Advanced Medical Scientific Research from
MECSST, Health and Labor Sciences Research Grants, Grants from the Keiryo Research Foundation, The Promotion
and Mutual Aid Corporation for Private Schools of Japan, the Japan Science and Technology Agency (JST), and the
New Energy and Industrial Technology Development Organization (NEDO).
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