Researchers Submit Patent Application, "Grating-Based Differential Phase Contrast Imaging System with Adjustable Capture Technique for Medical Radiographic Imaging", for Approval
No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: "Conventional medical x-ray imaging devices are based on the attenuation through photoelectric absorption of the x-rays penetrating the object to be imaged. However, for soft tissues including vessels, cartilages, lungs, and breast tissues with little absorption, this provides poor contrast compared with bone images. This problem of low contrast in soft tissues can be addressed with phase contrast imaging (PCI) techniques.
"The principle of PCI is based on the wave nature of x-rays, where refraction and diffraction properties need to be considered. As an electromagnetic wave, the x-ray is usually characterized by its frequency, amplitude, and phase. When an electromagnetic wave penetrates a medium, its amplitude is attenuated and its phase is shifted. In x-ray technology, the refractive index n of a material can be expressed by a complex number
"The imaginary part .beta. contributes to the attenuation of the amplitude and the real part .delta. is responsible for the phase shift. It has been shown that .delta. is about 10.sup.3 to 10.sup.4 times larger than .beta.. But in conventional medical imaging, only the information of .beta. is recorded while the information of .delta. is completely lost. In recent years, several PCI techniques have been explored to make use of the phase shift to form the image, which is expected to provide more information about the object. These include (i) the interferometer technique, (ii) the diffraction-enhanced imaging (DEI) technique, and (iii) the free-space propagation technique.
"However, there are various practical problems associated with all three techniques such as efficiency and limited field of view. In the case of perfect crystal interferometers and crystal diffractometers, high temporal coherence (i.e., a high degree of monochromaticity) is required; as a result, only a synchrotron or a well-defined wavelength of the whole spectrum from a radiation source is used. A synchrotron radiation source is costly and incompatible with a typical clinical environment. Both techniques are also limited by the accepted beam divergence of only a very small angle (a few mrad) due to the use of crystal optics. The free-space propagation technique is limited in efficiency since it requires high spatial coherence, which can only be obtained from an x-ray source with a very small focal spot. The three PCI techniques differ greatly in the way the image is recorded, the instrumental setup, and the requirements on the radiation source (especially its spatial and temporal coherence). Although some of the techniques yield excellent results for specific applications, none is very widely used and none has so far found application in medical diagnostics.
"In all x-ray imaging systems, scattered radiation from the object has been shown to degrade the image quality in terms of subject contrast and contrast-to-noise ratio significantly. Currently, anti-scatter grid is the most widely used device for scatter rejection with most radiography and mammography systems. In mammography, with anti-scatter grid the amount of scattered radiation measured by the scatter-to-primary ratio can be reduced to between 0.1 and 0.3 from about 0.25 to 1.2. However, intrinsic to the anti-scatter grid method is the attenuation of a significant fraction of the primary x-rays."
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors' summary information for this patent application: "An aspect of this application is to advance the art of medical radiographic imaging.
"Another aspect of this application to address in whole or in part, at least the foregoing and other deficiencies in the related art.
"It is another aspect of this application to provide in whole or in part, at least the advantages described herein.
"Another aspect of the application is to provide methods and/or apparatus embodiments for digital radiographic medical imaging. Another aspect of the application is to provide methods and/or apparatus embodiments for multi-energy medical imaging. Another aspect of the application is to provide methods and/or apparatus embodiments for detuned multi-energy slot-scanning phase contrast imaging for large field of view (FOV) (e.g., greater than 100 mm square) radiographic medical imaging.
"In accordance with one embodiment, the invention can provide a digital radiographic (DR) phase-contrast imaging (PCI) system that can include an x-ray source for radiographic imaging, a beam shaping assembly comprising a source grating G0, an x-ray grating interferometer including a phase grating G1 and an analyzer grating G2, and an area x-ray detector; where the beam shaping assembly and x-ray grating interferometer are adjustable for different mean energies of the x-ray source.
"In accordance with one embodiment, the invention can provide a method that can include providing an x-ray generator for radiographic imaging, providing a beam shaping assembly including a beam limiting apparatus and a source grating G0, providing an x-ray grating interferometer including a phase grating G1 and an analyzer grating G2, offsetting a pitch of the analyzer grating G2 relative to a pitch of an interference pattern produced by the phase grating G1 at a prescribed distance from the phase grating G1, and adjusting the beam shaping assembly and the x-ray grating interferometer responsive to different mean energies of a beam passing the beam shaping assembly.
"These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
"The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.
"FIG. 1 is a diagram that shows a side view of an exemplary embodiment of a scanning-slot phase contrast digital mammography imaging system according to the application.
"FIG. 2 is a diagram that shows a functional block diagram of an embodiment of a slot-scanning grating-based phase contrast digital mammography imaging system as shown in FIG. 1.
"FIG. 3 is a diagram that shows an exemplary embodiment of a slot-scanning grating-based phase contrast digital mammography imaging system according to the application.
"FIG. 4 is a diagram that shows another exemplary embodiment of a slot-scanning grating-based phase contrast digital mammography imaging system according to the application.
"FIG. 5 is a diagram that shows an embodiment of a long and narrow grating (e.g., formed by abutting two or more small gratings together) according to the application.
"FIG. 6A is a diagram that shows a schematic of an exemplary three-grating phase contrast imaging system, and FIG. 6B is a diagram that shows a schematic of another exemplary three-grating phase contrast imaging system.
"FIG. 7 is a diagram that shows intensity variation for one detector pixel (i, j) when one of the gratings (e.g., G2) is scanned along x.sub.g and the corresponding Fourier series coefficients.
"FIG. 8 is a flow chart that shows a method embodiment for operating a slot-scanning grating-based phase contrast digital mammography imaging system according to the application.
"FIG. 9 is a flow chart that shows another method embodiment for operating a slot-scanning grating-based phase contrast digital mammography imaging system according to the application.
"FIGS. 10A-10C are diagrams that show schematic side, front and perspective views of another slot scanning grating based phase PCI system embodiment according to the application.
"FIG. 11 is a diagram that illustrates schematics for exemplary embodiments of tuned phase-contrast digital imaging systems and exemplary embodiments of detuned phase-contrast digital imaging systems.
"FIG. 12 is a diagram that illustrates examples of the open field images measured in the detector plane for tuned and detuned configurations of phase contrast imaging system embodiments.
"FIG. 13A is a diagram that shows several MTFs plotted for different alpha slopes, and FIG. 13B is a diagram that shows the percentage of the contrast drop as a function of MTF slope .alpha., spatial frequency f0 at 50% MTF drop, and the degree of the system detuning .DELTA.f.
"FIG. 14 is a diagram that illustrates exemplary motion of interferometer with respect to objects or vise versa for a phase contrast imaging system embodiment.
"FIG. 15 is a diagram that illustrates exemplary of object scan schematics that project individual slices of the object onto one-period modulated fringe pattern measured in the detector plane according to embodiments of the application.
"FIG. 16 is a diagram that shows schematics of image formation mechanism that retrieves the intensity curves of individual slices of the scanned object, such as triangles, circles, and squares according to embodiments of the application.
"FIGS. 17(a)-17(b) are diagrams that show linear attenuation and phase shift per unit of length for various exemplary materials, respectively.
"FIG. 18 is a diagram that shows absorption (left axis) and phase (right axis) contrasts between two exemplary materials.
"FIG. 19 is a diagram that shows signal to noise ratio between glandular and adipose tissues for different thicknesses of compressed breast.
"FIGS. 20(a)-20(b) are diagrams that show embodiments of three G1 gratings with same pitch p1 and different height arranged on a low absorbing holder according to the application.
"FIG. 21 is a diagram that shows schematics of the array of phase gratings G1 disposed in front of analyzer grating G2 and detector D according to the application.
"FIG. 22 is a functional block diagram that shows an embodiment of an adjustable DR PCI system that is capable of imaging different mean energies of an x-ray source.
"FIG. 23 is a flow chart that shows a method embodiment for operating a slot-scanning grating-based phase contrast digital mammography imaging system according to the application."
For additional information on this patent application, see: Baturin, Pavlo; Shafer,
Keywords for this news article include: Patents, Electronics, Electromagnet, Digital Imaging, Breast Cancer Screening.
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