Development of a next generation X-ray CT with energy spectra of incident photons

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In 2004 we have made a photon transporting code with Monte Carlo method for x-ray photon and evaluated the validity of our proposed photon counting method. The test was performed in terms of (1)improvement of the contrast resolution, (2)reduction of x-ray intensity, and (3)elimination of the beam hardening effect. The results of simulations showed that we could improve the low level contrast resolution about three times compared with the conventional CT method which used the energy fluence of x-rays. For the beam hardening effect we could eliminated the artifacts by weighing the measured energy spectra. And we applied this method to the energy spectra which could be obtained with the conventional modern X-ray system and good results. With this consideration we designed a new photon counting detector which was made of CdTe material and evaluated the performance of the detector with a micro focus x-ray tube.In 2005 we performed several experiment with the newly developed x-ray detector and the performance was compared with the results of Monte Carlo simulation data. For the tested materials we chosen water, Fe, Ca, alcohol and we measured transmitted x-rays with the photon counting method. In this experiment we set several thresholds for discriminating x-rays with their energy and the experiment value was compared with the ideal value. The experiment data showed that we could increase the low density contrast with energy weighted count data and also decrease the beam-hardening artifacts with energy weighted count data. Unfortunately the reconstructed CT images had some ring artifacts which were caused by the non-uniformity of sensitivity of the detector, but this problem could overcome with an appropriate interpolation method for the measured count data.