Diffraction enhanced x-ray imaging of articular cartilage

Details Diffraction enhanced x-ray imaging of articular cartilage Diffraction enhanced x-ray imaging of articular cartilage

2001-04-17

2003-06-10

Church, Craig E. (Department: 2882)

X-ray or gamma ray systems or devices

Specific application

Diffraction, reflection, or scattering analysis

C378S084000

Reexamination Certificate

active

06577708

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a contrast mechanism referred to as extinction contrast which can be used for a variety of x-ray imaging applications. The method and system of this invention relates to an x-ray imaging modality that uses an analyzer crystal after the object. The imaging contrast of this invention is based on attenuation and refraction.
2. Description of Related Art
One type of diffraction enhanced imaging (DEI) is described in Chapman et al., U.S. Pat. No. 5,987,095.
Articular cartilage covers the ends of bones in synovial joints and provides elasticity, distribution of load, resistance to compressive forces, smooth articulation and cushioning of the subchondral bone during joint movements. Tissue is composed of collagen, primarily type II collagen, entrapping compressed proteoglycan aggregates.
The degeneration of articular cartilage is a component of pathological processes that result in the destruction of the tissue and leads to the deformation of the entire joint. This serious condition, known as osteoarthritis, includes a number of related, overlapping osteoarthritic disorders that are among the leading causes of immobilization within our society and affects probably 85% of elderly people. Use-related joint pain is one of the first signs of disease; however, pain is not always an early warning sign. By the time pain becomes a symptom, successful conservative treatments that could lead to regeneration of the tissue are too late. Presently, several operative methods, including total joint replacement, exist for some but not all the joints. Conventional procedures for repairing of transplanting articular cartilage do not restore a normal articular surface.
Techniques have been applied to access the health or disease of articular cartilage based on x-ray, ultrasound or nuclear magnetic resonance. Among these techniques, conventional radiography has the highest resolution and is the first and most frequently used imaging method to detect joint abnormalities. Conventional radiographs allow the evaluation of articular cartilage only indirectly through the measurement of the height of the joint space, the distance between the corresponding bone surfaces within a joint. Consequently, conventional radiography is sensitive only in cases of advanced disease. Focal cartilage defects or structural abnormalities in early stages of the degenerative process are generally not visible in radiographs.
Conventional x-ray radiography relies on x-ray absorption differences between regions of the object to provide image contrast. Cartilage tissue has little x-ray absorption contrast because the x-ray absorption is similar to soft tissue and synovial fluid. Therefore cartilage cannot be easily seen in conventional radiograph. Diffraction Enhanced Imaging (DEI) is a x-ray radiographic technique that derives contrast from x-ray refraction and scatter rejection (extinction) in addition to the absorption of conventional radiography. These two new contrast sources can in some cases allow visualization of features that are not possible using conventional methods. Certain of DEI are described in U.S. Pat. No. 5,987,095, the entire disclosure of which is incorporated into the specification by reference. The method of this invention uses highly collimated x-rays prepared by x-ray diffraction from perfect single-crystal silicon. These collimated x-rays are of single x-ray energy, practically monochromatic, and are used as the beam to image an object. A schematic of the DEI setup used at the synchrotron is shown in FIG.
1
. In this case, the collimated x-rays are prepared by the two crystal sets identified as the Si (3,3,3) monochromator. Once this beam passes through the object, another crystal of the same orientation and using the same reflection is introduced. This crystal is called the analyzer. If this crystal is rotated about an axis perpendicular to the plane shown in
FIG. 1
, the crystal will rotate through the Bragg condition for diffraction and the diffracted intensity will trace out a profile that is called the rocking curve. The profile will be roughly triangular and will have peak intensity close to that of the beam intensity striking the analyzer crystal. The width of the profile is typically a few microradians wide (3.6 microradians within a full width of half maximum (FWHM) at 18 keV using the Si (3,3,3) reflection). The character of the images obtained change depending on the setting of the analyzer crystal. To extract refraction information, the analyzer is typically set to the half intensity points on the low and high angle sides of the rocking curve. For optimal scatter rejection sensitivity, the analyzer is typically set to the peak of the rocking curve. To image the rejected scatter, the analyzer is set in the wings of the rocking curve.
The DEI method and system of this invention have been applied to image human articular cartilage from the distal part (talas) of the ankle (talocrural) joint that are eight macroscopically normal or display damages typical of early degenerative stages. A human ankle joint indicating the position of the talus within a foot skeleton is shown in FIG.
2
.
The tali were obtained within 24 hours of death through the Regional Organ Bank of Illinois with institutional approval. None of the 12 donors used in this study has a known history of osteoarthritic disease. All tali were fixed in 4% paraformaldehyde. For the normal ankles (n=4), the ages were 34 to 54 years, and for the damaged ankles (n=8) that ages were 51 to 66 years. All experiments were performed at the X15A beamline at the National Synchrotron Light Source, Brookhaven National Laboratory, Upton, N.Y. The tali were x-rayed in a posterior to anterior direction.
Examples of a normal and several damaged tali with corresponding DEI according to this invention are shown in
FIGS. 3
,
4
and
5
. The cartilage tissue is clearly detected and distinguished from bone. These images were acquired at an 18 keV x-ray photon energy. The structure of cartilage on the normal talus looks homogeneous, with an average height of 1.5 mm and moderate density ( FIG.
4
and
FIG. 6
at 18 keV and
FIG. 10
at 30 keV). This pattern changes in damaged cartilage, the tissue is no longer homogeneous but shows patterns that suggest structural alterations (
FIGS. 7
,
8
,
9
at 18 keV and
FIGS. 11
,
12
,
13
at 30 keV) and that correspond with the sites of macroscopic damage (compare with photographs in
FIGS. 15
,
16
,
17
).
At higher magnification of certain areas, distinct structural alterations are visible. Of special interest are the thin white lines on a dark background (arrows shown in FIGS.
11
-
17
). It is possible that the white lines represent certain structural changes which give rise to specific refraction patterns, extinction effects and/or absorption contrasts detected by the DEI imaging system according to this invention, which would most likely develop at the edges of cartilage fibrillations, fissures or defects. However, condensed collagen fibrils may also cause such effects. The contrast may further be enhanced because the normally entrapped large proteoglycans are lost due to the damage of the collagen network and therefore the absorption of the x-ray beam is different in this area.
An example of how the character of a subject image changes depending on the setting of the analyzer crystal can be seen in FIG.
18
. This is a rocking curve with the corresponding images of the talar dome at various analyzer crystal angles and at the 30 keV energy level. Note the change in appearance of the contrast heterogeneities observed in the images throughout the rocking curve. In the subsequent data sets, images were obtained from at or near the top of the rocking curve (unless specified otherwise) and at either 18 keV or 30 keV, as specified.
As used in the claims and throughout this specification the phrase “at or near the peak of the rocking curve angle” is intended to relate to at 18 keV using the silicon (3, 3, 3) reflection w

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