X-ray spectrum of CT system acquired by Compton spectroscopy using high resolution Schottky CdTe detector

摘要

Recently, x-ray computed tomography (CT) systems were developed dramatically; e.g. a multi-detector-row CT or a four-dimensional CT, but it has been expressed anxiety that a patient dose is increased. Analysis of x-ray spectrum is important for quality assurance and quality control of radiographic systems to estimate a quality of an imaging system and to decrease a patient dose. The aim of this study is to measure the x-ray spectra of CT system under clinical conditions using a high resolution Schottky CdTe detector. When measuring diagnostic x-ray spectra, the long distance from the x-ray source to the detector is requested for reducing a number of photons detected per unit time to prevent pile-up of the detector. However, that is very difficult to set up the long source-to-detector distance in a gantry of a CT unit. For resolving this problem, the Compton spectroscopy is very suitable. Using this method, a number of photons detected per unit time can be reduced by detecting the scattered x-ray photons. If the 90° scattered photons can be detected, the energy correction and reconstruction of spectra can be calculated easily by use of the Klein-Nishina formula. So we attempt to acquire the primary x-ray spectra in the gantry of the CT unit by using Compton spectroscopy under a clinical (tube-rotating) condition. Moreover, to estimate the variation of x-ray spectra owe to changing position in the gantry, we measured the x-ray spectra and exposure doses at various points in the gantry.