Rationale and Objectives
In conventional projection radiography, cartilage and other soft tissues do not produce enough radiographic contrast to be distinguishable from each other. Diffraction-enhanced imaging (DEI) uses a monochromatic x-ray beam and a silicon crystal analyzer to produce images in which attenuation contrast is greatly enhanced and x-ray refraction at tissue boundaries can be detected. The aim of this study was to test the efficacy of conventional x-ray tube–based DEI for the detection of soft tissues in experimental samples.
Materials and Methods
Cadaveric human tali (normal and degenerated) and a knee and thumb were imaged with DEI using a conventional x-ray tube and DEI setup that included a double–silicon crystal monochromator and a silicon crystal analyzer positioned between the imaged object and the detector.
Results
Diffraction-enhanced images of the cadaveric tali allowed the visualization of cartilage and its specific level of degeneration for each specimen. There was a significant correlation between the grade of cartilage integrity as assessed on the tube diffraction-enhanced images and on their respective histologic sections ( r = 0.97, P = .01). Images of the intact knee showed the articular cartilage edge of the femoral condyle, even when superimposed by the tibia. In the thumb image, it was possible to visualize articular cartilage, tendons, and other soft tissues.
Conclusion
DEI based on a conventional x-ray tube allows the visualization of skeletal and soft tissues simultaneously. Although more in-depth testing and optimization of the DEI setup must be carried out, these data demonstrate a proof of principle for further development of the technology for future clinical imaging.
Phase contrast imaging techniques are based on the use of information arising from the modification of the amplitude and phase of x-rays as they traverse an object. This allows for the detection of subject contrast due to tissue properties such as refraction. This contrast does not depend on x-ray attenuation, as is the case with contrast in conventional radiography. Thus, tissue contrast that is difficult to detect through x-ray attenuation, particularly at high energies, at which radiation dose is comparatively reduced, may be detected with phase contrast techniques. This includes soft tissues that do not have the composition to provide the necessary attenuation of x-rays and require techniques that exploit x-ray refraction at tissue boundaries to be visualized. One such technique is based on a system in which an analyzer crystal is positioned between the object and the detector. This allows only those x-rays satisfying the Bragg condition to be diffracted to the detector. Changes in x-ray reflection angle are converted to changes in x-ray intensity, through an intensity versus reflection angle curve (measured in microradians), described as the “rocking curve.” By altering the angle of the analyzer, it is possible to record different refraction angles and thus extract both refraction and absorption characteristics ( ).
What renders this technology pertinent to the study of joint disease is that soft tissues, including articular cartilage, menisci, tendons, and ligaments, are detected with reasonable clarity and contrast. Furthermore, it has been used to detect pathologic changes within these tissues, even at early stages of disease. The drawback has been that DEI has, until now, been used exclusively with synchrotron sources of x-rays, rendering it impractical for routine clinical use. This led to the development of a system that could use DEI technology but with a compact x-ray source, such as a commercially available tungsten tube (tube DEI).
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Materials and methods
Specimens
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Imaging Setup
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Imaging
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Histology
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Image Grading and Statistical Analysis
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Results
Tali
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Knee and Thumb
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Discussion
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