Katsuyuki Nishimura

Three-dimensional monochromatic x-ray computed tomography using synchrotron radiation

We describe a technique of three-dimensional computed to- mography (3-D CT) using monochromatic x rays generated by synchro- tron radiation, which performs a direct reconstruction of a 3-D volume image of an object from its cone-beam projections. For the development, we propose a practical scanning orbit of the x-ray source to obtain com- plete 3-D information on an object, and its corresponding 3-D image reconstruction algorithm. The validity and usefulness of the proposed scanning orbit and reconstruction algorithm were confirmed by computer simulation studies. Based on these investigations, we have developed a prototype 3-D monochromatic x-ray CT using synchrotron radiation, which provides exact 3-D reconstruction and material-selective imaging by using the K-edge energy subtraction technique.

Fluorescent X-ray Source for Diagnostic Imaging Studies

In diagnostic imaging studies, the energy response of x-ray image sensors, such as newly developed screen/film systems, scintillators, storage phosphors, and CCD sensors is one of the most important characteristics. A monochromatic x-ray source with a wide energy range is necessary to determine the output of the sensor systems as a function of x-ray energy.

Heavy ion CT system based on the measurement of residual range distribution: Improvement of the optical detector system

We report on experimental results from the heavy ion CT (IonCT) system based on the measurement of residual range distribution; this technique was first investigated by Zygmanski et al. (2000) for proton beams. Experiments were done on the spatial and density resolution phantom by using 4He and 12C beams accelerated up to 230 MeV/u and 400 MeV/u by the Heavy Ion Medical Accelerator in Chiba (HIMAC), installed in the National Institute of Radiological Sciences (NIRS) in Japan, with a high performance intensified charged coupled device (ICCD) camera. We show that rods with a diameter of 1 mm can be successfully reproduced using the 12C beam with this technique. We also show that the MCS blurring effect in the reconstructed image can be reduced for the heavier ion beam. The reduction in the background neutron noise from the phantom and/or collimator, by using the data obtained from the improvement of the optical detector system in 2007, is also shown.

Fan-beam monochromatic x-ray CT using fluorescent x rays excited by synchrotron radiation

Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. Although various types of monochromatic x-ray CT systems using synchrotron radiation have been developed using a parallel x-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. We have developed a fan-beam monochromatic x-ray CT using fluorescent x-rays generated by irradiating metal targets by synchrotron radiation. A CdTe linear array detector of 512 mm sensitive width was used in the photon counting mode. We made phantom experiments using fluorescent x-rays ranging from 32 to 75 keV. Monochromatic x-ray CT images of a cylindrical lucite phantom filled with several contrast media have been obtained. Measured CT numbers are compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations.

Proposal for medical application beamlines of the SPring-8

We, a user group for medical applications of the SPring-8, have proposed the introduction of white X-rays from insertion devices to BMIC (BioMedical Imaging Center) for clinical uses so that enough photon fluxes to a subject is guaranteed. The photon flux, depending on various monochromatizing methods, was compared at the surface of the subject 200 m from a light source.

Accuracy of Attenuation Coefficients in Monochromatic X-ray CT

We have developed a monochromatic x-ray CT system which consists of a fluorescent x-ray source generated by synchrotron radiation, a CdTe array detector a rotating table and a computer system. We performed phantom experiments at NE5 station (KEK, Japan) and compared the experimentally obtained CT values with the theoretically calculated values. The measured and theoretically calculated CT values (linear attenuation coefficients) were within 6% agreement over a wide range of iodine concentrations.

Beamlines for Medical Applications on the Spring-8

Three medical application beamlines of the SPring-8 are planned to be installed. The first beamline is a beamline from a bending magnet. The remaining two beamlines are from insertion devices. Medical application user group of SPring-8 recommends that those beamlines should be from a wiggler and undulator. Our proposal is as follows: the first goal of the beamline is to develop a coronary cineangiographic system. Single-energy X-ray exposure with energy above K-edge of iodine (contrast medium) is proposed to reduce exposure dose. X-ray with this energy produces cineangiogram with high contrast. To reduce, furthermore, exposure dose to the patient, 37 keV monochromatic X-ray has been proposed, even though its image contrast might slightly deteriorate. A multipole wiggler should be installed in the medical beamline, mainly because we use nonsymmetric monochromator to obtain wide exposure field. Another beamline should be from an undulator. The first application of this beamline is a divergent and monochromatic X-ray source which is necessary for taking diagnostic images of human subjects. The X-ray source will be generated by fluorescent X-ray. Another application of this beamline will be development of diagnostic imaging system using a expanded X-ray by multi-layer and super mirror. Diagnostic imaging systems to be developed using both beamlines will be: 1. Monochromatic coronary angiography, 2. Monochromatic X-ray CT, based on transmitted, Compton scatter, Thomson scatter, fluorescent, and energy subtraction, 3. Microangiography, 4. Tumor detection imaging, 5. Phase-contrast X-ray imaging whose sensitivity is much higher than that of the absorption-contrast imaging, and so on.

Scanning Slit Radiography System with Synchrotron Radiation

From the study of performance of scanning slit X-ray radiography, the following results were obtained. (1) It is confirmed that, by choosing proper width of electronic slit on 2-dimensional detector, effect of scattered radiation can be almost removed. (2) With the narrower incident beam and the narrower electronic slit width, the more the contrast increases. (3)Stripe like artifact appearing on the case of narrow slit width can be removed by interpolation processing. (4) From the PSF (point spread function) calculated by Monte Carlo simulation, scatter rejection performance parameters were calculated.