Phase Contrast Imaging System Research Articles

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.

On the optimization of experimental parameters for x-ray in-line phase-contrast imaging

General principles and results for the optimization of the performance of x-ray in-line phase-contrast imaging systems for spatially incoherent sources are investigated. In particular, formulas expressing the dependence of image contrast, spatial resolution, and signal-to-noise ratio on instrumental parameters including source size, detector resolution, geometrical factors, x-ray energy as well as sample properties are derived for different models of sample features. The results for some special cases of interest are presented. Optimization procedures are proposed that are expected to be useful in the design of imaging systems seeking to exploit x-ray in-line phase contrast.

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.

Observation and modelling of ion cyclotron range of frequencies waves in the mode conversion region of Alcator C-Mod

The fast magnetosonic wave, mode converted ion cyclotron wave (MC ICW) and mode converted ion Bernstein wave (MC IBW) have all been observed and unambiguously identified in the mode conversion region of Alcator C-Mod. The influences of the species mix, mode conversion location and Bpol/Btot have been studied in D(3He) plasmas at B0 ∼ 5.4 T (fRF = 50 MHz) and B0 ∼ 8 T (fRF = 78 MHz). The RF waves were measured by a phase contrast imaging (PCI) system. The experimental observation is compared with the result from a synthetic PCI diagnostic based upon the full wave code TORIC. Good agreement between the observation and modelling has been obtained on the spatial structure of the RF waves. When the mode conversion layer was off axis, both MC ICW and MC IBW were observed. In 5.4 T near-axis mode conversion discharges, the double hump spatial structure of the MC waves was observed experimentally and reproduced by the synthetic PCI. Such a structure is an indication of the up–down asymmetry of the MC ICW. In 8 T near-axis mode conversion discharges, we had the first definitive observation of IBW dominated MC in Alcator C-Mod.

Optimization of X-ray phase-contrast imaging based on in-line holography

This paper introduces a newly conceived formalism for clinical in-line phase-contrast X-ray imaging. The new formalism applies not only to ideal “thin” objects analyzed in previous studies, but also applies to the real-world tissues used in actual clinical practice. Moreover we have identified the four clinically important factors that affect phase-contrast characteristics. These factors are: (1) body part attenuation, (2) the spatial coherence of incident X-rays from an X-ray tube, (3) the polychromatic nature of the X-ray source and (4) radiation dose to patients for clinical applications. Techniques of phase image-reconstruction based on the new X-ray in-line holography theory are discussed. Numerical simulations are described which were used to validate the theory. The design parameters of an optimal clinical phase-contrast mammographic imaging system which were determined based on the new theory, and validated in the simulations, are presented. The theory, image reconstruction algorithms, and numerical simulation techniques presented in this paper can be applied widely to clinical diagnostic X-ray imaging applications.

Experimental validation of the Wigner distributions theory of phase‐contrast imaging

Recently, a new theory of phase-contrast imaging has been proposed by Wu and Liu [Med. Phys. 31, 2378-2384 (2004)]. This theory, based upon Wigner distributions, provides a much stronger foundation for the evaluation of phase-contrast imaging systems than did the prior theories based upon Fresnel-Kirchhoff diffraction theory. In this paper, we compare results of measurements made in our laboratory of phase contrast for different geometries and tube voltages to the predictions of the Wu and Liu model. In our previous publications, we have used an empirical measurement (the edge enhancement index) to parametrize the degree of phase-contrast effects in an image. While the Wu and Liu model itself does not predict image contrast, it does measure the degree of phase contrast that the system can image for a given spatial frequency. We have found that our previously published experimental results relating phase-contrast effects to geometry and x-ray tube voltage are consistent with the predictions of the Wu and Liu model.

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.

Collagen But Not Fibrinogen Surfaces Induce Bleb Formation, Exposure of Phosphatidylserine, and Procoagulant Activity of Adherent Platelets: Evidence for Regulation by Protein Tyrosine Kinase-Dependent Ca2+ Responses

With a combined phase-contrast and fluorescence video imaging system, changes in morphology and cytosolic [Ca2+]i were investigated of fura-2–loaded platelets during adhesion to fibrinogen or collagen matrices. The Ca2+ signals were, on the level of single platelets, compared to the secretion and procoagulant responses, using fluorescent-labeled AK-6 antibody against P-selectin and labeled annexin V for detection of surface-exposed phosphatidylserine (PS), respectively. Platelets in contact with fibrinogen developed filapods and spread over the matrix, in most of the cells without detectable Ca2+ signal. Thrombin induced repetitive spiking in [Ca2+]i , followed by the expression of P-selectin but not of PS on the platelet surface. Platelet interaction with collagen resulted in spreading and transformation of the cells into blebbing, “balloon”-like structures (diameter about 5 μm). The latter morphological changes were accompanied by high and prolonged increases in [Ca2+]i , by the exposure of both P-selectin and PS, and by the ability of the platelets to convert prothrombin into thrombin. Thrombin addition accelerated the onset of the Ca2+ signals and the appearance of surface-exposed PS. Collagen-induced PS exposure was slightly reduced by treatment of the platelets with aspirin, and strongly inhibited by suppression of the Ca2+ responses with prostaglandin E1 or the Ca2+ chelator, dimethyl-BAPTA. Inhibition of protein tyrosine phosphorylation with genistein, U73343, or wortmannin resulted in spiking Ca2+ responses in many of the platelets and in almost complete reduction of bleb formation and PS exposure. In contrast, genistein did not suppress bleb formation and PS exposure of platelets stimulated with the Ca2+ ionophore A23187. We conclude that a collagen but not fibrinogen matrix acts as a potent activator of the procoagulant response through activation of tyrosine kinases and subsequent generation of sustained intracellular Ca2+ signals.

Collagen But Not Fibrinogen Surfaces Induce Bleb Formation, Exposure of Phosphatidylserine, and Procoagulant Activity of Adherent Platelets: Evidence for Regulation by Protein Tyrosine Kinase-Dependent Ca2+ Responses

AbstractWith a combined phase-contrast and fluorescence video imaging system, changes in morphology and cytosolic [Ca2+]i were investigated of fura-2–loaded platelets during adhesion to fibrinogen or collagen matrices. The Ca2+ signals were, on the level of single platelets, compared to the secretion and procoagulant responses, using fluorescent-labeled AK-6 antibody against P-selectin and labeled annexin V for detection of surface-exposed phosphatidylserine (PS), respectively. Platelets in contact with fibrinogen developed filapods and spread over the matrix, in most of the cells without detectable Ca2+ signal. Thrombin induced repetitive spiking in [Ca2+]i , followed by the expression of P-selectin but not of PS on the platelet surface. Platelet interaction with collagen resulted in spreading and transformation of the cells into blebbing, “balloon”-like structures (diameter about 5 μm). The latter morphological changes were accompanied by high and prolonged increases in [Ca2+]i , by the exposure of both P-selectin and PS, and by the ability of the platelets to convert prothrombin into thrombin. Thrombin addition accelerated the onset of the Ca2+ signals and the appearance of surface-exposed PS. Collagen-induced PS exposure was slightly reduced by treatment of the platelets with aspirin, and strongly inhibited by suppression of the Ca2+ responses with prostaglandin E1 or the Ca2+ chelator, dimethyl-BAPTA. Inhibition of protein tyrosine phosphorylation with genistein, U73343, or wortmannin resulted in spiking Ca2+ responses in many of the platelets and in almost complete reduction of bleb formation and PS exposure. In contrast, genistein did not suppress bleb formation and PS exposure of platelets stimulated with the Ca2+ ionophore A23187. We conclude that a collagen but not fibrinogen matrix acts as a potent activator of the procoagulant response through activation of tyrosine kinases and subsequent generation of sustained intracellular Ca2+ signals.

A phase contrast imaging system for KT-5C tokamak

A CO 2 laser phase contrast imaging system has been developed for tokamak KT-5C. The system properties have been explored using a step phase modulator. It has been found that by setting the focus of an undiffracted beam outside the groove of the phase plate, a single-point detection system can still be used to measure fluctuations with resolution of wavenumber.

First results from the phase contrast imaging system on TEXT-U

A phase contrast imaging (PCI) diagnostic with a vertical beam covering the central third of the plasma was successfully operated to study density fluctuations in the TEXT-U tokamak. The diagnostic had a wave number range of 0.5–12 cm−1, a bandwidth of 500 kHz and a sensitivity of about 1010 cm−3. We present the optical design of the system and discuss three calibration techniques. We compare density fluctuation spectra obtained with spectra from Langmuir probes at the edge and the heavy ion beam probe diagnostic in the core of the plasma. This provides evidence that the PCI diagnostic is sensitive to both edge and core turbulence.

Visualization of a Phase Object by Two-Wave Coupling in a Photorefractive Bismuth Silicon Oxide Crystal

We propose a method to visualize a phase object using a locally-controllable image amplification scheme we developed earlier which is based on two-wave coupling in a bismuth silicon oxide (Bi12SiO20, or BSO) crystal. In this method the BSO crystal is used as a phase plate in the configuration of Zernike’s phase contrast imaging system. The principle of the phase-visualization with two-wave coupling is presented. An experimental result to verify the proposed method is shown.

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.

Phase contrast imaging system for TEXT-U

A diagnostic to study plasma density fluctuations, phase contrast imaging has been developed for the Texas Experimental Tokamak-Upgrade. The diagnostic has a sensitivity of about 10−4 ne0 and is capable of detecting a wide range of wave numbers (0.5–12 cm−1) with a bandwidth of 500 kHz. The design of the diagnostic, some results of acoustic calibration tests, and preliminary results of simulation of expected spectra are presented.

Conservation of Acoustic Phase in Ultrasonic Imaging by Bragg Diffraction

Acoustic-phase conservation in ultrasonic imaging by Bragg diffraction is experimentally verified by optical heterodyning. The results suggest the possibility of a phase-contrast Bragg imaging system with simultaneous display of phase and amplitude information.