Computed Tomography is basically a process of collection of transmission data through an object and subsequent mathematical reconstruction of an image corresponding to the cross section of the object. In NDT, CT technique is used to obtain mapping of the linear attenuation coefficients inside an object. The design envisages high speed computers as an essential part of instrumentation for fast data processing and to display CT images.

The entire CITIS system consists of a gamma ray beam generator, a collimated detector assembly, a precisely computer controlled mechanical manipulator, data acquisition sub-system and a processor coupled with a display monitor. The beam generator is equipped with a locking arrangement. The reconstruction algorithm is usually based on Fourier transform method or Filtered Back Projection (FBP) method. FBP normally operates in the spatial frequency domain, whereas a simplified version called Convolution Back Projection (CBP) method operates in the spatial domain and is easy to implement. In the current CT programme, CBP method is employed for reconstruction whereas a separate programme is used for processing the image.

The detection capability of the CT system to present a density or linear coefficient map across a slice through the specimen enables to visualise many types of structures, flaws, voids and inclusions, porosity and relative density distribution.

CT systems find extensive applications in NDT of solid propellant rocket motors, nuclear fuel assemblies, composite materials and ceramics. Industrial CT systems demand capability to handle objects of wide range of density and size to operate in varying environmental conditions. The major limitations of Computed Tomography Systems are the relatively high cost of equipment and limited throughput.

The authors have developed a Computed Industrial Tomographic Imaging System with Cesium-137 gamma radiation source for nondestructive examination of engineering and industrial specimens on a laboratory scale. An automated prototype CT unit with 260 GBq of Cesium-137 source and NaI(Tl) scintillation detection system in parallel beam geometry is complete and is in operation. This presentation highlights the design and development of a prototype system and its software for image reconstruction, simulation and display. The paper also describes results obtained with several tests specimens including sample reactor uranium fuel assembly and possibility of using neutrons as well as high energy X-rays in computed tomography.

Currently, development is on for a totally automated industrial CT system incorporating a wide energy-range, microprocessor controlled X-ray source and a scintillation detector array system. The entire software is being developed on the MS-WINDOWS platform for greater ease of operation and interpretation of the CT images.