Naoto Yagi

Construction and Commissioning of A 248 m‐long Beamline with X‐ray Undulator Light Source

A medium‐length beamline with undulator source, BL20XU at SPring‐8, was constructed, and opened to public use. The distance from source point to the end of the beamline is 248 m. By utilizing the long beam transport path, the beamline has advantages for experiment that requires high spatial coherence in hard X‐ray regions.

Development of fast (sub‐minute) micro‐tomography

An x‐ray fast micro‐tomography system was developed at medical and imaging beamline BL20B2 in SPring‐8. We attempted a “continuous rotation method” whereby the sample keeps rotating in the beam during the measurement. The image acquisitions are synchronized with the trigger pulses branched from the stepper motor controller. An electron multiplier (EM)‐CCD camera (C9100‐02, 1000×1000 pixels, 30 fps, 8 μm/pixel, Hamamatsu Photonics) and beam‐monitor AA40P (Hamamatsu Photonics) were used as an image detector. The effective pixel size of the detector was 4.9 μm/pixel and the spatial resolution was about 15 μm. The total measurement time for 900 projections has been reduced to 36 s. The reconstruction time was also reduced using GPGPU and SSD system. Using these techniques, preliminary experiment for 4‐D (time resolved 3‐D) micro‐imaging has also been performed.

PSF measurement of imaging detectors with an x-ray microbeam

Point spread functions (PSF) of some kinds of x-ray imaging detectors are directly measured using x-ray microbeam. The experiment has been performed at bending magnet beamline BL20B2 and undulator beamline BL2oXU of Spring-9. The microbeam is focused using a Fresnel zone plate (FZP) with coherent illumination to 0.3micrometers (almost outermost zone width of the FZP). The imaging detectors are put at the focal plane and directly detect the microbeam. Two types of high spatial resolving detectors are tested. One is x-ray- electron conversion type with electro-magnetic lens, and spatial resolution is estimated to 0.7micrometers . The other is x-ray-visible light conversion type with optical lens and the spatial resolution is estimated to 1.0micrometers .

Observation and analysis of microcirculation using high-spatial-resolution image detectors and synchrotron radiation

A microangiography system using monochromatized synchrotron radiation has been investigated as a diagnostic tool for circulatory disorders and early stage malignant tumors. The monochromatized X-rays with energies just above the contrast agent K-absorption edge energy can produce the highest contrast image of the contrast agent in small blood vessels. At SPring-8, digital microradiography with 6 - 24 micrometer pixel sizes has been carried out using two types of detectors designed for X-ray indirect and direct detection. The indirect-sensing detectors are fluorescent-screen optical-lens coupling systems using a high-sensitivity pickup-tube camera and a CCD camera. An X-ray image on the fluorescent screen is focused on the photoconductive layer of the pickup tube and the photosensitive area of the CCD by a small F number lens. The direct-sensing detector consists of an X-ray direct- sensing pickup tube with a beryllium faceplate for X-ray incidence to the photoconductive layer. Absorbed X-rays in the photoconductive layer are directly converted to photoelectrons and then signal charges are readout by electron beam scanning. The direct-sensing detector was expected to have higher spatial resolution in comparison with the indict-sensing detectors. Performance of the X-ray image detectors was examined at the bending magnet beamline BL20B2 using monochromatized X-ray at SPring-8. Image signals from the camera are converted into digital format by an analog-to- digital converter and stored in a frame memory with image format of 1024 X 1024 pixels. In preliminary experiments, tumor vessel specimens using barium contrast agent were prepared for taking static images. The growth pattern of tumor-induced vessels was clearly visualized. Heart muscle specimens were prepared for imaging of 3-dimensional microtomography using the fluorescent-screen CCD camera system. The complex structure of small blood vessels with diameters of 30 - 40 micrometer was visualized as a 3- dimensional CT image.

X-ray refraction-contrast imaging using synchrotron radiation at SPring-8

An edge-enhanced imaging technique using the X-ray refraction effect for high contrast outline imaging have been investigated using a third generation of synchrotron radiation source. This technique can be applied to imaging of soft tissues that can not be imaged by conventional absorption- contrast imaging. We have attempted to apply this method to accurate diagnosis of the lung cancer with reduced absorbed dose. In preliminary experiments, we took images of a glass capillary tube and a nude mouse with a long object-to-detector distance using monochromatized X-ray and a high-spatial- resolution CCD-based image detector. Compared to conventional absorption-contrast images, the image contrast is enhanced at an interface between two materials by the X-ray refraction. In a chest image of the mouse, outline images of the alveoli, the bronchi and the trachea were visualized with higher contrast than that of the ribs. It may be effective for early detection of small lung cancer lesions.

Synchrotron radiation microtomography of lung specimens

We have applied a synchrotron radiation computed tomography (SRCT) system to the lung specimens and evaluated its resolving power compared with the histopathologic appearances, precisely. An SRCT system has been constructed in the bending magnet beamline at the SPring-8. The system consists of a double-crystal monochromator, a rotating sample stage, a fluorescent screen, and a charge-coupled device (CCD) array detector (1024 X 1024 pixels with 12 X 12 micrometers 2 pixel size). The energy of the x-ray beam was tuned to 9 - 12 keV. The lungs obtained at autopsy were inflated and fixed by Heitzmans method. A cylindrical specimen (diameter, approximately 8 mm; height, 15 - 25 mm) was rotated in the plane parallel to the beam. The detected signal was transferred to a workstation; then, SRCT images (matrix size, 800 X 800 pixels) were reconstructed by a filtered back- projection. Finally, 6 - 12 micrometer-thick microscopic sections were obtained and stained with hematoxylin and eosin for histopathologic examination. SRCT images well depicted the terminal bronchiole, respiratory bronchiole, alveolar duct, alveolar sac, and alveolar septum. Different pathologic processes (alveolar hemorrhage, alveolitis) demonstrated on SRCT images were well correlated with the histopathologic appearances.

Refraction-contrast imaging using undulator radiation at SPring-8

Using parallel X-ray beam from undulator light source of the SPring-8, X-ray imaging based on refraction-enhanced contrast has been tested. Projection images were measured at X-ray energies of 8 keV and 28.8 keV with X-ray image detector that is placed at 5 - 6.5 m downstream from specimen. Transmission image of a test sample shows good agreement with ray-trace simulation. The intensity profile can be explained by refraction of X-rays. Deflection of transmitted beam is also measured by using fine X-ray beam collimated by a slit. The deflection angle of X-rays through the sample is around a few micro-radian. The result also well agrees with simple calculation based on geometrical optics. This technique is applied to observation of soft tissues of biological specimen. The result for lung image of nude mouse is presented, and difference between contact image (absorption-contrast) and refraction contrast image is discussed.

Development of submicrometer resolution x-ray CT system at SPring-8

A high spatial resolution x-ray CT system was developed at SPrng-8. The experiments were performed at the in-vacuum type undulator beamline BL47XU. A Si (111) double crystal monochromator is cooled with liquid nitrogen. A high precision rotation stage was used for sample rotation stage. Transmitted images were measured with an image detector. As the results of performance tests, it is considered that the spatial resolution of at least 1 micrometers was achieved with this system. The three-dimensional textures of eutectic alloy and a fossil of diatom were observed with this system.

Three-dimensional visualization of morphology and ventilation procedure (air flow and diffusion) of a subdivision of the acinus using synchrotron radiation microtomography of the human lung specimens

We have previously reported a synchrotron radiation (SR) microtomography system constructed at the bending magnet beamline at the SPring-8. This system has been applied to the lungs obtained at autopsy and inflated and fixed by Heitzman’s method. Normal lung and lung specimens with two different types of pathologic processes (fibrosis and emphysema) were included. Serial SR microtomographic images were stacked to yield the isotropic volumetric data with high-resolution (12 μm3 in voxel size). Within the air spaces of a subdivision of the acinus, each voxel is segmented three-dimensionally using a region growing algorithm (“rolling ball algorithm”). For each voxel within the segmented air spaces, two types of voxel coding have been performed: single-seeded (SS) coding and boundary-seeded (BS) coding, in which the minimum distance from an initial point as the only seed point and all object boundary voxels as a seed set were calculated and assigned as the code values to each voxel, respectively. With these two codes, combinations of surface rendering and volume rendering techniques were applied to visualize three-dimensional morphology of a subdivision of the acinus. Furthermore, sequentially filling process of air into a subdivision of the acinus was simulated under several conditions to visualize the ventilation procedure (air flow and diffusion). A subdivision of the acinus was reconstructed three-dimensionally, demonstrating the normal architecture of the human lung. Significant differences in appearance of ventilation procedure were observed between normal and two pathologic processes due to the alteration of the lung architecture. Three-dimensional reconstruction of the microstructure of a subdivision of the acinus and visualization of the ventilation procedure (air flow and diffusion) with SR microtomography would offer a new approach to study the morphology, physiology, and pathophysiology of the human respiratory system.