A transXend Detector - Principle and Applications

Abstract

A transXend detector was developed to use energy information of X-rays in computed tomography (CT). In this paper, the operation principle of the transXend detector is described first. The way of applying it to CT is following. Some possible fields to apply it are shown. MG[YQTFU<"eqorwvgf"vqoqitcrj{."gpgti{"kphqtocvkqp."wphqnfkpi."Z/tc{u."eqpvtcuv"cigpv" " " K0 " Kpvtqfwevkqp"In computed tomography (CT) measurements, contrast agent such as iodine is injected into blood vessel (contrast enhanced CT) to make a cancer tissue visible with the absorption of X-rays by iodine. The portion of blood vessel in the cancer tissue is higher than the one of normal tissue, and as a result, iodine concentration in the cancer tissue is higher than the one of normal tissue. The iodine-marked cancer tissue absorbs X-rays more than normal tissue and is observed easily.The contrast enhanced CT, however, has two major shortcomings: the side effect of contrast agent 1) , and a "beam hardening effect"2) . The beam hardening effect happens when a subject is thick, and an X-ray tube voltage is high: after passing a thick subject, the number of X-rays, which are sensitive to the absorption by iodine, becomes less. As a result, the X-ray absorption by iodine cannot be seen very clearly.For avoiding these two disadvantages, the author employed the energy information of X-rays in CT measurement. The energy resolved CT measurements with using a CdZnTe detector demonstrated advantages over the conventional current measurement method in nearly twofold better iodine contrast, and insensitivity to the beam hardening effect 3) . The measurement time, however, was very long: nearly 10 minutes for one z/T position of the first generation CT measurement.In the X-ray CT, transmission measurement should be done quickly, if the subject is a human being. With this condition, the X-rays have been measured as electric current, k0g., the energy information of X-rays is discarded.In the energy measurement of photons such as X-rays and gamma-rays, we have a limitation in counting rate in any type of radiation detectors. We have to wait for the charges, g0i., electrons and ions, electrons and holes, arrive at positive and negative electrodes, respectively.Most radiation detectors pursue the ability of measuring the energy of radiation as precise as possible. For high precision energy measurement of photons, photons should be collimated to limit the incident rate to the radiation detector. The energy measurement and high-flux photon measurement are not compatible.In applications, the precise energy information, however, is not always necessary. Besides, it is not possible to measure the energy of high flux photons by conventional radiation detectors. Nevertheless, in some cases, even rough energy distribution of photons could bring useful information.To make the energy resolved CT as a practical measurement method, the author developed a new detector, called a transXend detector. This transXend detector consists of several segment detectors, which are aligned ...