Atsushi Momose

Demonstration of X-Ray Talbot Interferometry

First Talbot interferometry in the hard X-ray region was demonstrated using a pair of transmission gratings made by forming gold stripes on glass plates. By aligning the gratings on the optical axis of X-rays with a separation that caused the Talbot effect by the first grating, moire fringes were produced inclining one grating slightly against the other around the optical axis. A phase object placed in front of the first grating was detected by moire-fringe bending. Using the technique of phase-shifting interferometry, the differential phase corresponding to the phase object could also be measured. This result suggests that X-ray Talbot interferometry is a novel and simple method for phase-sensitive X-ray radiography.

Recent Advances in X-ray Phase Imaging

Since the middle of the 1990s, X-ray phase imaging including phase tomography has been attracting increasing attention. The advantage of X-ray phase imaging is that an extremely high sensitivity is achieved for weak-absorbing materials, such as biological soft tissues, which generate a poor contrast by conventional methods. Medical and biological imaging is the main target of X-ray phase imaging, and several trials using synchrotron radiation sources and laboratory sources have been made. Measuring and controlling the X-ray phase are also significant for X-ray microscopy with a high spatial resolution, and innovative techniques are attracting intense interest. The progress of X-ray phase imaging is supported by the developments in X-ray sources such as third-generation synchrotron radiation sources, optical elements, and image detectors. This article describes the advantages of using X-ray phase information and reviews various techniques studied for X-ray phase imaging.

Phase tomography by X-ray talbot interferometry for biological imaging

The X-ray phase tomography of biological samples is reported, which is based on X-ray Talbot interferometry. Its imaging principle is described in detail, and imaging results obtained for a cancerous rabbit liver and a mouse tail with synchrotron radiation are presented. Because an amplitude grating is needed to construct an X-ray Talbot interferometer, a high-aspect-ratio grating pattern was fabricated by X-ray lithography and gold electroplating. X-ray Talbot interferometry has an advantage that it functions with polychromatic cone-beam X-rays. Finally, the compatibility with a compact X-ray source is discussed.

Demonstration of phase-contrast X-ray computed tomography using an X-ray interferometer

Abstract Phase-contrast X-ray computed tomography (PCX-CT) using an X-ray interferometer is introduced for observing a density distribution inside an organic material. PCX-CT images are compared with an absorption-contrast X-ray CT image and shown to be highly sensitive. To convert an interference pattern into an image of phase-shift distribution, which is put into a CT algorithm, the author applied subfringe analysis techniques, such as the Fourier-transform method and the fringe scanning method. In the case presented here, a plastic sphere is used as a test sample, and the resulting spatial resolution of the PCX-CT image is less than 40 μm. The signal-to-noise ratio (S/N) for the PCX-CT image is increased to ten times that for an absorption-contrast CT image. The S/N can be further increased by suppressing the movement of the interference pattern caused by air flow around the interferometer.

Phase-sensitive imaging and phase tomography using X-ray interferometers

X-ray interferometry for imaging applications is discussed with a review of X-ray interferometric imaging activities reported to date. Phase measurement and phase tomography based on X-ray interferometry are also presented. Finally the advantage of X-ray interferometric imaging in comparison with other phase-sensitive X-ray imaging methods is discussed.

Phase-contrast radiographs of nonstained rat cerebellar specimen.

Phase-contrast radiography using an x-ray interferometer is presented for observing organic matter. High sensitivity of phase-contrast radiography is demonstrated with a rat cerebellar specimen without staining it with a contrast medium. The layer structure of the cerebellum can be observed in the obtained image while there is no clear structure in the corresponding absorption-contrast image. Quantitative image analysis is made possible by converting an x-ray interference pattern to an x-ray phase shift distribution. The lipid distribution in the cerebellum is discussed by evaluating x-ray phase shifts before and after lipid removal.

On the origin of visibility contrast in x-ray Talbot interferometry

The reduction in visibility in x-ray grating interferometry based on the Talbot effect is formulated by the autocorrelation function of spatial fluctuations of a wavefront due to unresolved micron-size structures in samples. The experimental results for microspheres and melamine sponge were successfully explained by this formula with three parameters characterizing the wavefront fluctuations: variance, correlation length, and the Hurst exponent. The ultra-small-angle x-ray scattering of these samples was measured, and the scattering profiles were consistent with the formulation. Furthermore, we discuss the relation between the three parameters and the features of the micron-sized structures. The visibility-reduction contrast observed by x-ray grating interferometry can thus be understood in relation to the structural parameters of the microstructures.

Phase‐contrast x‐ray computed tomography for observing biological specimens and organic materials

A novel three‐dimensional x‐ray imaging method has been developed by combining a phase‐contrast x‐ray imaging technique with x‐ray computed tomography. This phase‐contrast x‐ray computed tomography (PCX‐CT) provides sectional images of organic specimens that would produce absorption‐contrast x‐ray CT images with little contrast. Comparing PCX‐CT images of rat cerebellum and cancerous rabbit liver specimens with corresponding absorption‐contrast CT images shows that PCX‐CT is much more sensitive to the internal structure of organic specimens.

High-speed X-ray phase imaging and X-ray phase tomography with Talbot interferometer and white synchrotron radiation

X-ray Talbot interferometry, which uses two transmission gratings, has the advantage that broad energy bandwidth x-rays can be used. We demonstrate the use of white synchrotron radiation for high-speed X-ray phase imaging and tomography in combination with an X-ray Talbot interferometer. The moiré fringe visibility over 20% was attained, enabling quantitative phase measurement. X-ray phase images with a frame rate of 500 f/s and an X-ray phase tomogram with a scan time of 0.5 s were obtained successfully. This result suggests a breakthrough for time-resolved three-dimensional observation of objects that weakly absorb X-rays, such as soft material and biological objects.

Phase-contrast imaging with synchrotron x-rays for detecting cancer lesions

RATIONALE AND OBJECTIVES We obtained image contrast in pathologic specimens without the use of contrast material by using phase-contrast imaging with synchrotron X-rays. METHODS An experiment was performed at the three-pole superconducting vertical wiggler beam line BL-14B at the Photon Factory in Tsukuba, Japan. The X-ray phase-contrast imaging system consisted of a double crystal monochromator, an asymmetrically cut crystal monochromator, a triple Laue-case X-ray interferometer, and film. The pathologic specimen was a sample from human liver that had metastatic carcinoma. RESULTS The X-ray phase-contrast images of the pathologic specimen clearly depicted the cancerous lesion without the use of contrast enhancement, and the image showed good correlation with the photograph of the specimen. The X-ray absorption image did not differentiate between the normal liver tissue and the tumor. CONCLUSION The results of this preliminary experiment reveal that for materials such as biologic specimens with a low atomic number, X-ray phase-contrast imaging better differentiates tissues than does the absorption contrast imaging commonly used in radiology.