Advanced X-ray imaging at beamline 07 of the SAGA Light Source.

The SAGA Light Source provides X-ray imaging resources based on high-intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi-monochromatic SR obtained by the newly installed water-cooled metal filter and monochromatic SR selected by a Ge double-crystal monochromator (DCM) with high-resolution lens-coupled X-ray imagers, fast and low-dose micro-computed tomography (CT), fast phase-contrast CT using grating-based X-ray interferometry, and 2D micro-X-ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large-area fiber-coupled X-ray imagers, high-sensitivity phase-contrast CT using crystal-based X-ray interferometry can be performed. Low-temperature CT can be performed using the newly installed cryogenic system, and time-resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time-resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented.

Feasibility study of interferometric phase-contrast X-ray imaging using the hard-X-ray free-electron laser of the SPring-8 Angstrom Compact Free-Electron Laser.

Aiming for the fine observation of fast physical phenomena such as phonon propagation and laser ablation, phase-contrast X-ray imaging combined with a crystal X-ray interferometer and the X-ray free-electron laser (XFEL) of the SPring-8 Angstrom Compact Free-Electron Laser has been developed. An interference pattern with 70% visibility was obtained by single-shot exposure with a 15 keV monochromated XFEL. In addition, a phase map of an acrylic wedge was successfully obtained using the fringe scanning method.

Feasibility study of phase-contrast X-ray laminography using X-ray interferometry.

For fine observation of laminar samples, phase-contrast X-ray laminography using X-ray interferometry was developed. An imaging system fitted with a two-crystal X-ray interferometer was used to perform the observations, and the sectional images were calculated by a three-dimensional iterative reconstruction method. Obtained images of an old flat slab of limestone from the Carnic Alps depicted fusulinids in the Carboniferous period with 3 mg cm-3 density resolution, and those of carbon paper used for a fuel-cell battery displayed the inner fibrous structures clearly.

Novel Zeff imaging method for deep internal areas using back-scattered X-rays.

Elemental kinds, composition ratios, effective atomic number (Zeff), and spatial distributions are the most basic information on materials and determine the physical and chemical properties of materials. X-ray fluorescence analysis have conventionally been used for elemental mapping, however maps on deep internal areas cannot be obtained because the escape depth of fluorescence X-rays is limited to a few mm from the surface of samples. Herein, we present a novel Zeff imaging method that uses back-scattered X-rays. The intensity ratio of elastic and inelastic back-scattered X-rays depends on the atomic number (Z) of a single-element sample (Zeff for a plural-element sample), and so Zeff maps in deep areas can be obtained by spectrum analysis of the scattered high-energy incident X-rays. We demonstrated the feasibility of observing a phantom covered by an aluminum plate by using synchrotron radiation X-ray. A fine Zeff map that can be used to identify materials was obtained from only front-side observation. The novel method opens up a new way for Zeff mapping of deep areas of thick samples from front-side observation.

[Evaluation of low contrast resolution in cone beam CT using FPD].

We examined the low contrast resolution of cone beam CT (CBCT) equipped with an indirect-type flat panel detector and compared it with a commercial CT unit (Robusto) . In CBCT, the X-ray tube voltage of 110 kV was used, and in the Robusto, the usual 120 kV was used for examinations. The computed tomography dose index (CTDI) of the two systems was measured, and images scanned at about the same exposure to radiation were compared. The modulation transfer factors of the two systems were measured, and the convolution kernel that was the nearest to the characteristic of CBCT was chosen among kernels of the Robusto. A water phantom with a diameter of 200 mm was scanned, Wiener spectra were calculated, and signal-to-noise ratios were compared. The low contrast resolution phantom was scanned, and detectability and contrast-to-noise ratio (CNR) were measured. In addition, we placed diluted contrast medium into a phantom, scanned the phantom, and measured the detectability and CNR. When the X-ray irradiation condition of CBCT was 75 mAs at 110 kV, the equal dose of radioactivity in the Robusto was 50 mAs at 120 kV. In the low contrast resolution phantom, detectability was 8.7%mm in CBCT, and 9.4%mm in the Robusto. In the low contrast resolution evaluation phantom, CNR was 1.39 in CBCT, and 2.69 in the Robusto. With diluted contrast medium, CNR was 1.28 in CBCT, and 0.60 in the Robusto. CBCT was inferior to the Robusto in a low contrast resolution phantom, but CBCT was superior to the Robusto using diluted contrast medium. We found that CBCT was useful in examinations using contrast media.

Comparison of flat-panel detector and image-intensifier detector for cone-beam CT.

We evaluated a flat-panel detector (FPD) (scintillator screen and a-Si photo-sensor array) for use in a cone-beam computed tomography (CT) detector and compared it with an image-intensifier detector (IID). The FPD cone-beam CT system has a higher spatial resolution than the IID system. At equal pixel sizes, the standard deviation of noise intensity of the FPD system is equal to that of the IID system. However, the circuit noise of the FPD must be reduced, especially at low doses. Our evaluations show that the FPD system has a strong potential for use as a cone-beam CT detector because of high-spatial resolution.

Cone-beam CT with flat-panel-detector digital angiography system: early experience in abdominal interventional procedures.

We developed a cone-beam computed tomography (CBCT) system equipped with a large flat-panel detector. Data obtained by 200 degree rotation imaging are reconstructed by means of CBCT to generate three-dimensional images. We report the use of CBCT angiography using CBCT in 10 patients with 8 liver malignancies and 2 hypersplenisms during abdominal interventional procedures. CBCT was very useful for interventional radiologists to confirm a perfusion area of the artery catheter wedged on CT by injection of contrast media through the catheter tip, although the image quality was slightly degraded, scoring as 2.60 on average by streak artifacts. CBCT is space-saving because it does not require a CT system with a gantry, and it is also time-saving because it does not require the transfer of patients.