As our aging of society, increasing numbers of people are suffering from osteoarthritis and rheumatoid arthritis. The latter, in particular, is an acute disorder that forces sufferers to become wheelchair-bound when it grows severe.
In monitoring the progress of these conditions, and checking the effects of treatment, diagnostic imaging of cartilage plays an essential role. At present, the technique principally used for diagnostic imaging of cartilage is magnetic resonance imaging (MRI). However, MRI involves the use of large devices, so imaging costs are high, and the images take a long time to capture, making the process stressful for the patient.
For the reasons mentioned above, there is a growing need for speedy, low-cost cartilage imaging. Images of soft tissue such as cartilage are difficult to capture using conventional X-ray photography. This is why a whole new imaging technology is needed. Diagnostic imaging of soft tissues is also required in treating breast cancer and many other diseases, so the new technology also has promising applications in a wide range of fields.
Through research pursued jointly with the University of Tokyo and the University of Hyogo, Konica Minolta has developed an innovative X-ray imaging device. Based on the principle of Talbot-Lau interferometry, this device produces images by detecting tiny refractions -- about 1/10,000 of a degree -- in X-rays. Thanks to its high sensitivity to refraction, Konica Minolta's imaging device can obtain X-ray images of cartilage and other soft tissues which have never observed with X-rays.
It uses an ordinary X-ray source like those used in hospitals and other institutions. Using phase shifts in the X-rays (displacements of the phase of the X-ray as the electromagnetic waveform), an object is posed in the X-rays, fine greyscale contrast is generated by an X-ray detector. Besides the conventional absorption contrast X-ray image produced by a single exposure, the device can also deliver a differential phase contrast image and a visibility contrast image.
When this device is used to capture images of a cherry, endosperm which is inside the seed is clearly depicted in the differential phase contrast image, and the internal vascular bundle is clearly depicted in the visibility contrast image. Neither of these features can be made visible in a conventional X-ray image.
In the differential phase contrast image generated by the Konica Minolta device, the outline of the cartilage is delineated. This cannot be done using conventional X-ray image.
When a person develops rheumatism, the disease is first manifested in changes in the cartilage tissue. The innovative X-ray imaging device is expected to be useful in the early detection of rheumatism. In the future, our device is also applied to clinical applications in diagnostic imaging of pathological tissue embedded in soft tissue (such as breast cancer), as well as pathological changes in the bone periphery.
The structure of the device, and how it works
The principal feature of this device is that, by using three X-ray gratings (G0, G1 and G2 in the diagram), the refraction of the X-rays by the subject is made visible in the form of moire patterns.
Emitted downwards from an X-ray source deployed at the top, the X-rays pass through G0, then through the subject, through G1 and G2, finally arriving at the X-ray detector. By passing through G0, the X-rays are phase-aligned. When the phase-aligned X-rays pass through the subject above G1, the subject produces phase changes, which are then reflected in the moire patterns formed when the X-rays pass through G1 and G2. These moire patterns are then detected by the image detector, and the pattern data is subjected to arithmetical processing. As a result, three images are generated: an absorption contrast image, a differential phase contrast image, and a visibility contrast image.
The three images
The image to be measured is read into the computer. Arithmetical processing is then carried out, and the final images are output. Three images are output simultaneously: an absorption contrast image, a differential phase contrast image, and a visibility contrast image.
Absorption contrast image: This is equivalent to the image obtained from a conventional X-ray device.
Differential phase contrast image: When the phase of the X-rays is shifted greyscale shading is obtained at the peripheral area of this shift. The outlines of the structure can then be captured easily.
Visibility contrast image: In places where detailed structures ranging in size from several microns to several tens of microns are packed together, the X-rays scatter strongly according to the grating structure, and their distribution appears as fine contrast. Fibrous tissue and sites with numerous microcalcifications, for example, can be detected this way.