Monochromatic X-ray CT using fluorescent X-rays excited by synchrotron radiation

Monochromatic X-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white X-rays from an X-ray tube. Although various types of monochromatic X-ray CT systems using synchrotron radiation have been developed using a parallel X-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. The authors have developed a fan-beam monochromatic X-ray CT system for the large objects. The CT system consists of a fluorescent X-ray source, a rotating table, a CdTe array detector and a personal computer. The fluorescent X-ray source has several advantages such as wide beam size, wide energy range and rapid energy switching and no higher order harmonics. The 256-channel CdTe array detector was used in the photon counting mode. The size of the detector element was 1.98 mm(h)/spl times/1.98 mm(w)/spl times/0.5 mm(t) and the length of total sensitive area was 512 mm. The authors made phantom experiments using fluorescent X-rays ranging from 42 to 59 keV, CT images of relatively large phantoms such as head phantoms and test phantoms commonly used for conventional CT were obtained. Measured CT numbers were compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations. Monochromatic X-ray CT images of a head phantom containing gadolinium contrast medium were obtained at the energies just above and below the gadolinium K-edge. A gadolinium image was also obtained by K-edge subtraction.