Computer Algorithms and Detector Electronics for the Transmission X-Ray Tomography

Abstract

This paper is addressed to the problem associated with transmission tomography and its implications in solving large numbers of simultaneous equations and associated parameters, such as multimillion weighting factors. Mathematical approaches to this problem in several directions are briefly reviewed and a technique (linear superposition technique with compensation) developed for this purpose, along with results obtained with this method is presented. Another important aspect of the multiple scanning tomography is counting statistics which requires the count rate be in the order of 5 MHz or more for the pulse counting to have statistical accuracy of 0.5% or better. Several alternative detectors besides conventional Sodium Iodine (NaI(Tl)) detector, namely, plastic scintillator (with enhanced photoelectric absorbtion by, for instance, tin loading) and various semiconductor detectors, such as CdTe and possible HgI2 are under investigation. Plastic scintillators will naturally be a suitable candidate owing to their fast light decay characteristics. A tin loaded plastic scintillator (HE 140 type) is under investigation and some of the preliminary results are reported. With the semiconductor detectors, the preliminary charge collection time observations and calculations indicate that these new exotic detectors (CdTe and HgI2) can be applicable to the high rate operations primarily by virtue of their short charge collection times and moderately good energy resolutions.