X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-10-29
2001-04-03
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S082000
Reexamination Certificate
active
06212254
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the observation of a structural feature of an object utilizing penetrating radiation such as x-rays. More particularly, but not exclusively, the invention relates to x-ray phase-contrast recordal, e.g. imaging, of internal boundary features.
The present applicant's international patent publication WO95/05725 (PCT/AU94/00480) and provisional patent application PN5811/95 disclose various configurations and conditions suitable for differential phase-contrast imaging using hard x-rays. Other disclosures are to be found in Soviet patent 1402871 and in U.S. Pat. No. 5,319,694. It is desired that relatively simpler conditions and configurations more closely related, at least in some embodiments, to traditional methods of absorption-contrast radiography, may be utilised for differential phase-contrast imaging with hard x-rays.
In accordance with the present invention there is provided a method of obtaining an image of a boundary of an object, said boundary representing a refractive index variation, said method including:
irradiating said boundary with penetrating radiation having high lateral spatial coherence and a propagation component transverse to said refraction index variation; and
receiving at least a portion of said radiation on an image plane so as to form said image, said radiation having been refracted by said boundary such that said boundary is represented on said image by a corresponding intensity variation.
The present invention further provides an apparatus for obtaining an image of a boundary of an object, said boundary representing a refractive index variation, said apparatus including:
a source for irradiating said boundary with penetrating radiation having high lateral spatial coherence and a propagation component transverse to said refraction index variation; and
a detector for receiving at least a portion of said radiation so as to form said image, said radiation having been refracted by said boundary such that said boundary is represented on said image by a corresponding intensity variation.
The present invention also provides a method of deriving a phase-contrast record of an internal boundary having a sharp refractive index variation or defined by a thickness variation, comprising:
irradiating the boundary with penetrating radiation having a propagation direction such that there is a significant component of the propagation vector transverse to the direction of said refractive index variation or in the direction of said thickness variation, and further having a lateral spatial coherence sufficiently high for the variation in refractive index or thickness to cause a detectable change in the local direction of propagation of the radiation wavefront at the boundary; and
detecting and recording at least a portion of said radiation after it has traversed said boundary in a manner whereby an effect of said change in the local direction of propagation is observable and thereby recorded as a local diminution or rapid variation of intensity of the radiation which thereby substantially images the boundary.
The present invention further provides an apparatus for deriving a phase-contrast record of an internal boundary having a sharp refractive index variation or defined by a thickness variation, comprising:
means to irradiate the boundary with x-ray radiation having a propagation direction such that there is a significant component of the propagation vector transverse to the direction of said refractive index variation or in the direction of said thickness variation, and further having a lateral spatial coherence sufficiently high for the variation in refractive index or thickness to cause a detectable change in the local direction of propagation of the radiation wavefront at the boundary; and
means to detect and record at least a portion of said radiation after it has traversed said boundary in a manner whereby an effect of said change in the local direction of propagation is observable and thereby recorded as a local diminution or rapid variation of intensity of the radiation which thereby substantially images the boundary.
The present invention also provides a method of obtaining an image of a boundary of an object, said boundary representing a refractive index variation, said method including:
irradiating said boundary with penetrating radiation having high lateral spatial coherence and a propagation component transverse to said refraction index variation; and
receiving at least a portion of said radiation on an image plane so as to form said image, said radiation having been Fresnel diffracted by said boundary such that said boundary is represented on said image by a corresponding intensity variation.
The present invention further provides an apparatus for obtaining an image of a boundary of an object, said boundary representing a refractive index variation, said apparatus including:
a source for irradiating said boundary with penetrating radiation having high lateral spatial coherence and a propagation component transverse to said refraction index variation; and
a detector for receiving at least a portion of said radiation so as to form said image, said radiation having been Fresnel diffracted by said boundary such that said boundary is represented on said image by a corresponding intensity variation.
The present invention also provides a method of determining the phase of an image, including processing phase-contrast image data of said image.
The intensity effect of a change in the local direction of propagation is preferably observable in an image comprising the record. The record and therefore the image may be photographic or electronic. The term “image” may thus refer, for example, to an observable effect in a set of intensity data, for example a table or other stored record of intensity values: the term is not confined to a visual context. The recording medium may comprise a two-dimensional pixilated detector, e.g. an electronic detector such as a charge-coupled device (CCD) array.
The irradiating means preferably includes a source of x-rays of diameter 20 micron or less, where diameter refers to the full width of intensity distribution of the source at half maximum intensity. The apparatus may advantageously further include a suitable stage or holder for samples containing the internal boundary being imaged.
The penetrating radiation, e.g. x-ray radiation, may be polychromatic and is preferably in the hard x-ray range, i.e. in the range 1 keV to 1 MeV.
The separation of the boundary and the detecting means is preferably selected to enhance the resolution of the image. For example, it has been observed that a sharper image, i.e. one with better contrast, is achieved by increasing separation. For instance contrast is improved at least for a separation of about 1 m relative to a separation of 0.4 m. This may partly be because background noise is diminished with increasing separation but the intensity variation effect arising from the change in the local direction of propagation is substantially preserved.
The term “lateral spatial coherence” herein refers to the correlation of the complex amplitudes of waves between different points transverse to the direction of propagation of the waves. Lateral spatial coherence is said to occur when each point on a wavefront has a direction of propagation which does not change over time. In practice, high lateral spatial coherence may, for example, be achieved by using a source of small effective size or by observing the beam at a large distance from the source. For example, for 20 keV x-rays a source size of 20 &mgr;m diameter or less would typically be appropriate. The smaller the source size the better for the purposes of this invention, provided total flux from the source is sufficient. Lateral spatial coherence may need to be preserved by careful selection of the x-ray window of the source, e.g. such that it is of highly uniform thickness and homogeneity.
REFERENCES:
patent: 4953188 (1990-08-01), Siegel et al.
patent: 5173928 (1992-12-01), Momose et a
Dunn Drew A.
Fulwider Patton Lee & Utecht
Porta David P.
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