X-ray Phase Contrast Imaging System Research Articles

In vivophysiological saline-infused hepatic vessel imaging using a two-crystal-interferometer-based phase-contrast X-ray technique

Using a two-crystal-interferometer-based phase-contrast X-ray imaging system, the portal vein, capillary vessel area and hepatic vein of live rats were revealed sequentially by injecting physiological saline via the portal vein. Vessels greater than 0.06 mm in diameter were clearly shown with low levels of X-rays (552 µGy). This suggests that in vivo vessel imaging of small animals can be performed as conventional angiography without the side effects of the presently used iodine contrast agents.

Design of a novel phase contrast X-ray imaging system for mammography

X-ray phase contrast imaging is a very promising technique which may lead to significant advancements in medical imaging. One of the impediments to the clinical implementation of the technique is the general requirement to have an X-ray source of high coherence. The radiation physics group at UCL is currently developing an X-ray phase contrast imaging technique which works with laboratory X-ray sources. The design of this system requires rigorous simulation of the imaging system and the interaction of X-rays with healthy and unhealthy breast tissue. We present in this paper the results of such simulations showing the expected gain in contrast arising from the proposed system and the system's initial design.

Source size and temporal coherence requirements of coded aperture type x-ray phase contrast imaging systems

There is currently much interest in developing X-ray Phase Contrast Imaging (XPCI) systems which employ laboratory sources in order to deploy the technique in real world applications. The challenge faced by nearly all XPCI techniques is that of efficiently utilising the x-ray flux emitted by an x-ray tube which is polychromatic and possesses only partial spatial coherence. Techniques have, however, been developed which overcome these limitations. Such a technique, known as coded aperture XPCI, has been under development in our laboratories in recent years for application principally in medical imaging and security screening. In this paper we derive limitations imposed upon source polychromaticity and spatial extent by the coded aperture system. We also show that although other grating XPCI techniques employ a different physical principle, they satisfy design constraints similar to those of the coded aperture XPCI.

Design of a novel phase contrast x-ray imaging system for mammography

It is hoped that x-ray phase contrast imaging (XPCi) will provide a generational improvement in the effectiveness of mammography. XPCi is sensitive to the refraction which x-rays undergo as a result of the variation in x-ray propagation speeds within an object. XPCi is, however, seldom used in clinical applications owing mainly to a lack of suitable systems. The radiation physics group at UCL has previously designed and built an XPCi system sensitive to phase gradients in one dimension for application in security inspection. We present here the design methodology and final design of a prototype XPCi system sensitive to phase gradients in two directions for use in mammography. The technique makes efficient use of the flux available from a laboratory x-ray source, thus making it suitable for clinical use.

Limitations imposed by specimen phase gradients on the design of grating based x-ray phase contrast imaging systems

X-ray phase contrast imaging is a very promising technique that may lead to significant advancements in a variety of fields, perhaps most notably, medical imaging. The radiation physics group at University College London is currently developing an x-ray phase contrast imaging technique that works with laboratory x-ray sources. This system essentially measures the degree to which photons are refracted by regions of an imaged object. The amount of refraction that may be expected to be encountered in practice impacts strongly upon the design of the imaging system. In this paper, we derive an approximate expression between the properties of archetypal imaged objects encountered in practice and the resulting distribution of refracted photons. This is used to derive constraints governing the design of the system.

The relationship between wave and geometrical optics models of coded aperture type x-ray phase contrast imaging systems.

X-ray phase contrast imaging is a very promising technique which may lead to significant advancements in medical imaging. One of the impediments to the clinical implementation of the technique is the general requirement to have an x-ray source of high coherence. The radiation physics group at UCL is currently developing an x-ray phase contrast imaging technique which works with laboratory x-ray sources. Validation of the system requires extensive modelling of relatively large samples of tissue. To aid this, we have undertaken a study of when geometrical optics may be employed to model the system in order to avoid the need to perform a computationally expensive wave optics calculation. In this paper, we derive the relationship between the geometrical and wave optics model for our system imaging an infinite cylinder. From this model we are able to draw conclusions regarding the general applicability of the geometrical optics approximation.

Imaging and density mapping of tetrahydrofuran clathrate hydrates by phase-contrast x-ray computed tomography

In situ observations of tetrahydrofuran (THF) hydrates in THF solution using a phase-contrast x-ray imaging system at 273K are reported. Density analysis measurements using phase-contrast x-ray imaging suggest that the inhomogeneous growth of THF hydrate crystals occurs due to differences in the cage occupancy of guest molecules, caused by the diffusion of solute. Phase-contrast x-ray imaging developed in this study can also be applied to the time-resolved imaging and density analysis of the growth and dissociation processes for a variety of hydrates besides THF hydrates.

Phase-space formulation for phase-contrast x-ray imaging

Phase-space formulation based on the Wigner distribution has been presented for analyzing phase-contrast image formation. Based on the statistical nature and affine canonical covariance of Wigner distributions in the phase space, we show that the partial coherence effects of incident x-ray wave field on image intensity are simply accounted for by a multiplication factor, which is the reduced complex degree of coherence of the incident x-ray wave field. We show especially that with the undulator sources one cannot obtain the phase-contrast intensity by summing over the contributions from all electron positions, since the van Cittert-Zernike theorem fails in general for undulators. We derive a comprehensive formula that quantifies the effects of partial spatial coherence, polychromatic spectrum, body attenuation, imaging-detector resolution, and radiation dose on phase-contrast visibility in clinical imaging. The results of our computer modeling and simulations show how the formula can provide design guidelines and optimal parameters for clinical x-ray phase-contrast imaging systems.

Quantitative and qualitative studies on high-contrast X-ray radiography with an asymmetrical crystal set-up at Elettra

An analyzer-based X-ray phase contrast imaging (ABI) system with an asymmetrical crystal set-up was mounted at Elettra's SYRMEP beamline. It was the first time that this set-up was implemented at Elettra. Advantages and disadvantages of such a set-up were exploited with quantitative and qualitative studies. For quantitative studies a simple hollow tube and strands were used as samples. Qualitative studies were developed using this technique with ox brain tissue, which has never been previously examined in this manner. Minute details were found in the ABIs and in the diffraction enhanced images. This could indicate the possibility of using these techniques with computerized tomography in the future as an auxiliary method in diagnosing brain illnesses such as Alzheimer and Creutzfeldt-Jacob disease. Propagation-based X-ray phase contrast imaging was also qualitatively exploited and compared with ABI using a Loxosceles gaucho spider as a sample.

A phase-contrast X-ray imaging system—with a 60×30 mm field of view—based on a skew-symmetric two-crystal X-ray interferometer

A phase-contrast X-ray imaging system—with a 60×30 mm field of view—for biomedical observations was developed. To extend the observation field of view, the system is fitted with a skew-symmetric two-crystal X-ray interferometer. To attain the required sub-nanoradian mechanical stability between the crystal blocks for precise operation, the interferometer was mounted on two extremely rigid positioning tables (one with a sleeve bearings) and was controlled by a feedback positioning system using phase-lock interferometry. The imaging system produced a 60×30 mm interference pattern with 60% visibility using 17.7 keV monochromatic synchrotron X-rays at the Photon Factory. It was then used to perform radiographic observation (i.e., phase mapping) of rat liver vessels. These results indicate that this imaging system can be used to perform observations of large and in vivo biological samples.

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

We obtained image contrast in pathologic specimens without the use of contrast material by using phase-contrast imaging with synchrotron X-rays. 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. 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. 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.