Development of Radiography Using Proton-Induced X-Rays to Reduce the Dosages of Contrast-Medium and Radiation

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Characteristic-line radiation from heavy metal targets bombarded by MeV proton beams has been tested as an X-ray source for angiography based on iodinated contrast media. To utilize the strong absorption by iodine (Z=53) at its K-absorption edge (33.2 keV), we used K-alpha line of La (lanthanum, Z=57) at 33.4 keV. As a reference, also K-alpha emission of Sn (tin, Z =50) at 25.2 keV was employed. Metallic plates of La and Sn were irradiated by 7-MeV protons to produce these X-rays. Dual-energy K-edge subtraction method was tested using Lucite phantoms which contain aqueous solutions of potassium iodide. Also Calcium compound was stuffed in these phantoms to simulate bones. The transmission images of the phantoms were recorded on imaging plates. We found that the contrast of images of iodide solutions taken with La X-rays was higher than that with Sn X-rays. Also the energy subtraction procedure was successfully applied to reduce the graphical noise due to the bones and inhomogeneity of the soft tissue. However, for actual clinical use, the X-ray intensity must be increased by several orders of magnitude.To increase spatial resolution of images, we constructed a compact proton micro-beam system using a tapered glass capillary tube with a tip diameter on the order of 10 microns. The transport efficiency of 2-3-MeV protons through the capillary was examined as a function of the capillary tilt angle and the tip diameter. We obtained transport efficiencies of approximately three times larger than would be expected from the geometrical shape of the capillary. A metallic thin foil was irradiated with the micro beam and quasi-monochromatic X-rays were produced. We demonstrated magnification radiography of a small object to show that a spatial resolution on the order of 10 microns was achievable in our system.