Quantitative measurements of the phase shift of X-rays passing through a matter allow us to perform X-ray phase tomography for visualization of soft materials. Combination of an X-ray microscope and a grating interferometer is a promising approach to realize quantitative phase measurements with a microscopic spatial resolution. A Lau interferometer consisting of a source grating and a phase grating is available for this purpose with an incoherent laboratory X-ray source. We installed a Lau interferometer into a laboratory-based X-ray microscope adopting a copper rotating anode source and Fresnel zone plates (ZEISS Xradia 800 Ultra). A “twin-phase image”, which consists of positive and negative phase images overlaid with a certain separation, is generated through a fringe-scanning measurement with this microscope. A step for generating a quantitative phase image from the twin phase image should be developed to perform phase tomography. However, conventional deconvolution operations are not suitable because of artifacts and noise remained in resultant phase images. To reduce the artifacts and noise, an iterative calculation algorithm has been developed. The evaluation of the algorithm shows that the artifacts and noise are suppressed and quantitative phase images are obtained. Finally, results of phase tomography obtained for soft materials are demonstrated.
X-ray phase tomography by Talbot interferometry functions with X-rays of a broad energy band, and a pink- beam extracted by a multilayer mirror from white synchrotron radiation is used for four-dimensional X-ray phase tomography, which was developed at BL28B2, SPring-8, Japan. Polymer samples under infrared laser irradiation were observed as model experiments of laser processing. In this paper, laser ablation for a carbon-fiber reinforced polymer (CFRP) sample is reported. Thanks to the fact that the fibrous structure generates visibility (or dark-field) contrast, four-dimensional tomogram from the visibility reduction is presented. A technical effort to improve the temporal resolution from 1 s to 160 ms is also described.
X-ray phase/dark-field tomography by using an X-ray grating interferometer and white synchrotron radiation has been demonstrated to observe dynamics in materials consisting of light elements, because it is available with X-rays of a broad energy bandwidth. In this work, we combined X-ray phase/dark-field tomography with a stroboscopic technique, which synchronizes image acquisitions with repetitive tension applied to a sample. Snapshot images with a 200 μs temporal resolution are measured to reconstruct phase/dark-field tomograms. A result of stroboscopic X-ray dark-field tomography is described, which was obtained for a rubber sample under a 24 Hz repetitive compression-stretch motion of a 10 mm amplitude.
Talbot interferometer using white synchrotron radiation has been demonstrated for time-resolved X-ray phase imaging and tomography as well as four-dimensional phase tomography to observe dynamics in samples. In this study, X-ray phase tomography has been used to follow the time evolution of phase separation in polymer blend through heating treatment. For this purpose, we performed in-situ X-ray phase imaging and tomography with X-ray Talbot-Lau interferometer using white synchrotron radiation. The X-ray Talbot-Lau interferometer consisted of a source grating (30 μm in period), a π/2 phase grating (4.5 μm in period), an amplitude grating (5.3 μm in period) and a high-speed camera. A polymer blend sample of polystyrene (PS) (Mw = 76,500) and polymethyl methacrylate (PMMA) (Mw = 33,200) was used for the CT observation. A compound of the PS and PMMA was made by a twin-screw kneading extruder and put into an Al tube whose inner diameter was 6 mm. The sample temperature was maintained at desired temperature sequence by controlling a lamp for heating, and CT scans were repeated to track the changes in sample structures at a temporal resolution of 5 seconds. PS-rich phase and PMMA-rich phase changing with time evolution were revealed.
This paper review the configurations of grating-based X-ray interferometry for X-ray phase imaging/tomography and describes recent activities for four-dimensional X-ray phase tomography and nanoscopic X-ray phase tomog-
raphy. A multilayer mirror to produce a 10% bandwidth pink beam at 25 keV has been installed at SPring-8 for four-dimensional X-ray phase tomography, and an application to polymer laser ablation is presented. A 100-fold full-field X-ray microscope employing a Fresnel zone plate has been used successfully in combination with a Talbot interferometer to perform nanoscopic phase tomography for a malleal processus brevis of a mouse nine days after birth. Another development using a laboratory-based full-field X-ray microscope in combination with a Lau interferometer is also described.
An X-ray phase tomographic microscope that can quantitatively measure the refractive index of a sample in three dimensions with a high spatial resolution was developed by installing a Lau interferometer consisting of an absorption grating and a π/2 phase grating into the optics of an X-ray microscope. The optics comprises a Cu rotating anode X-ray source, capillary condenser optics, and a Fresnel zone plate for the objective. The microscope has two optical modes: a large-field-of-view mode (field of view: 65 μm x 65 μm) and a high-resolution mode (spatial resolution: 50 nm). Optimizing the parameters of the interferometer yields a self-image of the phase grating with ~60% visibility. Through the normal fringe-scanning measurement, a twin phase image, which has an overlap of two phase image of opposite contrast with a shear distance much larger than system resolution, is generated. Although artifacts remain to some extent currently when a phase image is calculated from the twin phase image, this system can obtain high-spatial-resolution images resolving 50-nm structures. Phase tomography with this system has also been demonstrated using a phase object.
We have launched a project to promote grating-based X-ray phase imaging/tomography extensively. Here, two main activities are presented for enabling dynamic, or four-dimensional, X-ray phase tomography and nanoscopic X-ray phase tomography by grating interferometry. For the former, while some demonstrations in this direction were performed with white synchrotron radiation, improvement in image quality by spectrum tuning is described. A preliminary result by a total reflection mirror is presented, and as a next step, preparation of a 10% bandpass filter by a multilayer mirror is reported. For the latter, X-ray microscopes available both at synchrotron radiation facilities and laboratories equipped with a Fresnel zone plate are combined with grating interferometry. Here, a preliminary result with a combination of a Lau interferometer and a laboratory-based X-ray microscope is presented.
X-ray grating interferometry has a great potential for X-ray phase imaging over conventional X-ray absorption imaging
which does not provide significant contrast for weakly absorbing objects and soft biological tissues. X-ray Talbot and
Talbot-Lau interferometers which are composed of transmission gratings and measure the differential X-ray phase shifts
have gained popularity because they operate with polychromatic beams. In X-ray radiography, especially for nondestructive
testing in industrial applications, the feasibility of continuous sample scanning is not yet completely revealed.
A scanning setup is frequently advantageous when compared to a direct 2D static image acquisition in terms of field of
view, exposure time, illuminating radiation, etc. This paper demonstrates an efficient scanning setup for grating-based Xray
phase imaging using laboratory-based X-ray source. An apparatus consisting of an X-ray source that emits X-rays
vertically, optical gratings and a photon-counting detector was used with which continuously moving objects across the
field of view as that of conveyor belt system can be imaged. The imaging performance of phase scanner was tested by
scanning a long continuous moving sample at a speed of 5 mm/s and absorption, differential-phase and visibility images
were generated by processing non-uniform moire movie with our specially designed phase measurement algorithm. A
brief discussion on the feasibility of phase scanner with scanning setup approach including X-ray phase imaging
performance is reported. The successful results suggest a breakthrough for scanning objects those are moving
continuously on conveyor belt system non-destructively using the scheme of X-ray phase imaging.
Four-dimensional X-ray phase tomography has been implemented by a combination of X-ray Talbot interferometry and white synchrotron radiation. While the Fourier-transform method has been used for the measurement of a differential phase image at every projection direction, an improved scan mode based on the fringe-scanning method is demonstrated to improve spatial resolution. The disadvantage of the fringe-scanning method, which requires multiple moiré images, is overcome by proposing a scan mode synchronously combining one-way continuous movements of sample rotation and grating displacement. In addition, the operation of an X-ray Talbot-Lau interferometer with white synchrotron radiation is reported. While an X-ray Talbot interferometer requires a horizontal sample rotation axis because of the condition of spatial coherency, such a horizontal rotation axis is not preferable for tomographic scans especially for soft objects. An X-ray Talbot-Lau interferometer overcomes this problem, allowing a vertical sample rotation axis. Although we encountered a vibration problem with the X-ray Talbot-Lau interferometer probably because of incomplete stage stability, our attempts have basically been successful, and we expect that various samples can be scanned by four-dimensional X-ray phase tomography, revealing dynamical properties in weakly absorbing objects that cannot be accessed by conventional X-ray phase tomography mainly performed for static samples.
Laminography is a technique for 3D volume reconstruction, extending the classical tomography to the estimation
of local areas in lamellar objects. We demonstrate X-ray phase laminography by using an X-ray Talbot
interferometer consisting of two transmission gratings, which has been used only for X-ray phase tomography.
In this presentation, experiments using 17.7 keV synchrotron radiation through a double-crystal monochromator
are reported. The X-rays passed through the sample placed in front of the first phase grating. The rotation axis
of the sample was set almost parallel to the sample plane normal, and inclined from the X-ray beam. Behind the
second amplitude grating, moiré fringe patterns were measured by displacing one of the gratings in the direction
parallel to its diffraction vector. Differential phase information were extracted through the fringe-scanning
method. For the reconstruction of the three-dimensional volume from the differential phase information, the filtered
back projection method was used with a specific filtering function. Promising results of phase laminography
reconstruction are obtained for simulation data as well as weakly absorbing lamellar objects such as a polymer
meshes and other samples. This advancement extends experiments with X-ray Talbot volume reconstruction to
a larger variety of samples.
Taking advantage of the fact that an X-ray Talbot interferometer functions with X-rays of a broad energy bandwidth, high-speed X-ray phase tomography has been demonstrated by using white synchrotron light. Time resolution in addition to three-dimensional spatial resolution has been attained, and we report this achievement as the first four-dimensional (4D) X-ray phase tomography. Moire image movies of samples rotating at a speed of 1 or 2 rps generated by a Talbot interferometer were recorded at a frame rate of up to 1 kf/s, and differential phase image movies of the same frame rate were created by the Fourier-transform method. Consequently, a sub-second time resolution was achieved in the 4D phase tomography, while the spatial resolution was below 0.1 mm and 0.05 mm in axial and in-plane directions, respectively. An X-ray Talbot interferometer generates visibility images in addition to differential phase images, showing the distribution of microstructures, which cause ultra-small angle scattering but cannot be resolved individually with system spatial resolution. Tomographic image reconstruction from the visibility images was also demonstrated.
The purpose of this study was to design an X-ray Talbot-Lau interferometer for the imaging of bone cartilage using a
practical X-ray tube and to develop that imaging system for clinical use. Wave-optics simulation was performed to
design the interferometer with a practical X-ray tube, a source grating, two X-ray gratings, and an X-ray detector. An
imaging system was created based on the results of the simulation. The specifications were as follows: the focal spot size
was 0.3 mm of an X-ray tube with a tungsten anode (Toshiba, Tokyo, Japan). The tube voltage was set at 40 kVp with an
additive aluminum filter, and the mean energy was 31 keV. The pixel size of the X-ray detector, a Condor 486 (Fairchild
Imaging, California, USA), was 15 μm. The second grating was a Ronchi-type grating whose pitch was 5.3 μm. Imaging
performance of the system was examined with X-ray doses of 0.5, 3 and 9 mGy so that the bone cartilage of a chicken
wing was clearly depicted with X-ray doses of 3 and 9 mGy. This was consistent with the simulation's predictions. The
results suggest that X-ray Talbot-Lau interferometry would be a promising tool in detecting soft tissues in the human
body such as bone cartilage for the X-ray image diagnosis of rheumatoid arthritis. Further optimization of the system
will follow to reduce the X-ray dose for clinical use.
The sensitivity of X-ray phase tomography based on Talbot(-Lau) interferometry is discussed. A criterion is described to evaluate the superiority of the technique in comparison to the conventional absorption-contrast method. An experimental result of X-ray phase tomography with a Talbot interferometer is compared with the criterion. The advantage of X-ray phase tomography based on Talbot(-Lau) interferometry is more prominent when smaller structures are observed with smaller pixels.
An X-ray Talbot interferometer for X-ray phase imaging and tomography was constructed using an amplitude grating of a gold pattern 8 μm in pitch and 30 μm in height developed by X-ray lithography and gold electroplating. The effective area of the grating was 20 mm x 20 mm, and was fully illuminated by synchrotron radiation at beamline 20XU, SPring-8, Japan. Almost whole body of a fish 3 cm in length was observed by phase tomography. Resulting images obtained with 0.07 nm and 0.045 nm X-rays revealed organs with bones in the same view successfully. A preliminary result of the combination with an X-ray imaging microscope is also presented, which was attempted to attain a higher spatial resolution. Finally, prospects of the compatibility with a conventional X-ray generator are discussed for practical applications such as clinical diagnoses.
Micro-phase-contrast X-ray computed tomography with an X-ray interferometer (micro-phase-contrast CT) is in operation to obtain high spatial resolution images of less than 0.01 mm at the undulator beam-line 20XU of SPring-8, Japan, and we applied micro-phase-contrast CT to observe the organs of rats and hamsters. The excised kidney and spleen fixed by formalin were imaged. The fine inner-structures such as vessels, glomeruli of kidney and white and red pulps of spleen were visualized clearly about 0.01-mm spatial resolutions without using contrast agent or staining procedure. The results were very similar to those by optical microscopic images with 20-fold magnification. These results suggest that the micro-phase tomography might be a useful tool for various biomedical researches.
X-ray phase tomography with X-ray Talbot interferometry (XTI) is reported. XTI employs two transmission gratings and generates a contrast corresponding to the differential phase shift caused by a sample. Quantitative phase measurement and tomographic image reconstruction with XTI are demonstrated for biological samples. Finally, the possibility of medical applications of XTI is discussed, based on the advantage of XTI that divergent and polychromatic X-rays are available.
Image quality of phase-contrast x-ray computed tomogram was evaluated by comparing tomograms obtained by using triple Laue-case x-ray interferometers with a thin or a thick crystal wafer. It was confirmed that the spatial resolution was improved when the wafer is thinned. A simulation study by means of the Takagi-Taupin equation was also carried out for theoretical understanding. According to the wavefront modulation transfer function calculated for Laue-case diffraction, it is suggested that using an interferometer with al thin wafer tends to improve image quality. However, a new problem is pointed out that the accuracy in quantitative measurement of high-frequency phase modulation is not secured even when the wafer is thinned.
We are investigating possible medical applications of phase- contrast X-ray imaging using an X-ray interferometer. This paper introduces the strategy of the research project and the present status. The main subject is to broaden the observation area to enable in vivo observation. For this purpose, large X-ray interferometers were developed, and 2.5 cm X 1.5 cm interference patterns were generated using synchrotron X-rays. An improvement of the spatial resolution is also included in the project, and an X-ray interferometer designed for high-resolution phase-contrast X-ray imaging was fabricated and tested. In parallel with the instrumental developments, various soft tissues are observed by phase- contrast X-ray CT to find correspondence between the generated contrast and our histological knowledge. The observation done so far suggests that cancerous tissues are differentiated from normal tissues and that blood can produce phase contrast. Furthermore, this project includes exploring materials that modulate phase contrast for selective imaging.
Recent development in phase-contrast X-ray computed tomography using an X-ray interferometer is reported. To observe larger samples than is possible with our previous X-ray interferometer, a large monolithic X-ray interferometer and a separated-type X-ray interferometer were studied. At the present time, 2.5 cm X 1.5 cm interference patterns have been generated with the X-ray interferometers using synchrotron X-rays. The large monolithic X-ray interferometer has produced interference fringes with 80% visibility, and has been used to measure various tissues. To produce images with higher spatial resolution, we fabricated another X-ray interferometer whose wafer was partially thinned by chemical etching. A preliminary test suggested that the spatial resolution has been improved.
Human tissues obtained from cancerous kidneys fixed in formalin were observed with phase-contrast X-ray computed tomography (CT) using 17.7-keV synchrotron X-rays. By measuring the distributions of the X-ray phase shift caused by samples using an X-ray interferometer, sectional images that map the distribution of the refractive index were reconstructed. Because of the high sensitivity of phase- contrast X-ray CT, a cancerous lesion was differentiated from normal tissue and a variety of other structures were revealed without the need for staining.
We have shown so far that 3D structures in biological sot tissues such as cancer can be revealed by phase-contrast x- ray computed tomography using an x-ray interferometer. As a next step, we aim at applications of this technique to in vivo observation, including radiographic applications. For this purpose, the size of view field is desired to be more than a few centimeters. Therefore, a larger x-ray interferometer should be used with x-rays of higher energy. We have evaluated the optimal x-ray energy from an aspect of does as a function of sample size. Moreover, desired spatial resolution to an image sensor is discussed as functions of x-ray energy and sample size, basing on a requirement in the analysis of interference fringes.
We have been developing phase-contrast x-ray computed tomography (CT) to make possible the observation of biological soft tissues without contrast enhancement. Phase-contrast x-ray CT requires for its input data the x-ray phase-shift distributions or phase-mapping images caused by an object. These were measured with newly developed fringe-scanning x-ray interferometry. Phase-mapping images at different projection directions were obtained by rotating the object in an x-ray interferometer, and were processed with a standard CT algorithm. A phase-contrast x-ray CT image of a nonstained cancerous tissue was obtained using 17.7 keV synchrotron x rays with 12 micrometer voxel size, although the size of the observation area was at most 5 mm. The cancerous lesions were readily distinguishable from normal tissues. Moreover, fine structures corresponding to cancerous degeneration and fibrous tissues were clearly depicted. It is estimated that the present system is sensitive down to a density deviation of 4 mg/cm3.