X-ray or gamma ray systems or devices – Specific application – Telescope or microscope
Reexamination Certificate
2000-12-27
2003-07-15
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Telescope or microscope
C378S119000, C378S143000
Reexamination Certificate
active
06594335
ABSTRACT:
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FIELD OF THE INVENTION
This invention relates to systems and methods for creating a beam of penetrating radiation, that is to be deflected within an object, to image the internal structure of the object, in particular, of biological soft-tissues and other materials that are not significantly absorbing to x-rays.
BACKGROUND OF THE INVENTION
X-rays are widely used to study the internal structure of various objects. X-ray imaging is a subject of great international interest because of its capacity for high penetrability into animal soft-tissues, which is related to the short wavelength of x-rays.
Conventional radiographic imaging methods, are based upon the difference between photoelectric absorption of x-rays between soft-tissue and bones or contrast media. Unfortunately, at high energies utilized to image deep body tumors, the image contrast of soft-tissues due to absorption decreases markedly. This is because low-Z elements, such as carbon-based biological soft-tissue with an average atomic number of Z equal to 7.64, do not appreciably absorb high energy medical x-rays (which are between 15 KeV and 100KeV). Soft-tissue are mostly transparent to these hard x-ray photons. The calcium in bones has a much higher Z-value of 20, iodine in contrast media has a Z-value of 53.
Soft-tissue imaging is perhaps the most vexing problem in clinical radiography, while magnetic resonance imaging of soft-tissues has inadequate resolution for this purpose in many cases. Some “partial-exceptions” to soft-tissue x-ray imaging limitations exist, but they are profoundly limited in there clinical utility. For example, in x-ray computed tomography, one may delineate some soft-tissue contrast, from the summation of many views of very small differences in x-ray absorption, provided that the detail is not too small. Mammography is another partial-exception to soft-tissue x-ray imaging limitations. With mammography, photoelectric absorption of molybdenum k-alpha x-rays by glandular soft-tissues of the breast is sometimes able to transfer low amounts of contrast from larger tumors, provided that the breast tissue is not very thick. Mammography can detect submillimeter “microcalcifications” that may indicate cancer, however, several common benign conditions may also produce microcalcifications. And mammography still does not delineate tumor architecture, such as margins, invasiveness, small metastasis, or a microscopically-detailed vascular signature, with capillaries ranging in size from 8-to-20 microns in diameter.
Statistically, mammography currently has a very high rate of false positives and false negatives. In a population of undiagnosed women advised by their doctors to have regular diagnostic screening, only five women out of 1000 will actually have breast cancer. But for that same population, the rate of positive mammograms will be 10%--the ratio of false positives to true negatives is nearly 20:1. And for about 10-20% of women who have palpable abnormalities, the mammograms won't show anything. There is thus a driving need to improve breast cancer detection technology. (Fitzgerald)
Compared to x-ray absorption imaging, phase-contrast imaging is better suited for delineating soft-tissue structures that do not appreciably absorb x-rays, but that may contain many non-absorptive structural details with diameters between one micron and one millimeter. Phase-contrast imaging is any technique that renders variations in the refractive index of a non-absorbing object visible. A phase-shift of x-ray photons is characterized by slight deviations from their incident path as they traverse through an object, such as animal soft-tissues, which occurs after the photons interact briefly and elastically with the atoms in their path. A phase-shift is a type of deflection of the incident beam within a material that is typically in the range of one-to-ten microradians. The phase-shift, when adequately large, shifts the intensity of the deflected ray to a different place on a detector, such as an adjacent pixel (in the x- or y-direction).
Coherent light, a requirement for phase-contrast imaging may be represented as a bundle of rays that are each parallel to the optical axis. A coherent beam of light may be produced by lasers at visible, UV or IR frequencies, but presently, only by using synchrotron undulators can a coherent beam of “light” be produced with hard x-rays. The x-ray phase-shifts experienced by an incident beam can be observed as a microradian deflection only when employing a coherent beam of incident light, with no transverse beam divergence, to illuminate the object under investigation.
Coherent light may also be represented as a train of unperturbed planar wavefronts, that are aligned parallel to the detector plane and that propagate along the optical axis. After a homogenous, planar incident wavefront interacts with the constituent low atomic number atoms of the specimen, a wrinkle (i.e., a warping) is produced in the formerly perfect planar wavefront, because of refractory effects. In other words, spatial three-dimensional distortions may be impressed upon the planar incident wavefront by specific density-dependent and chemical-dependent biological soft-tissue interfaces within the illuminated object. Thus, the incident plane-waves are converted in the object into a three-dimensionally distorted and indented wavefront, which possesses a phase-shifted profile, capable
Dunn Drew A.
Yun Jurie
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