Various apparatus for x and (gamma) -ray computed tomography (CT) have been constructed by us during the last 20 years, with the aim of producing simple and low-cost systems for nondestructive testing. The first one was constructed in 1980 and used an Am241 radioactive source emitting 59.6 keV (gamma) -rays and a single NaI(Tl)-x ray detector. Successively, the radioactive source was substituted during the years by x-ray tubes, and the single detector by multi- detection system such as arrays of detectors and image intensifiers. The last CT-scanner employs a 160 kV x-ray tube and a 6' X 6' image intensifier coupled through a lens to a cooled CCD-camera. At the same time, also (gamma) CT-scanners were constructed for large size and/or high-density samples. These are based on Ir192 or Cs137 radioactive sources coupled to a single NaI(Tl)(gamma) -ray detector. The characteristics and properties of the CT-scanners based on the use of x-ray tubes, emitting x-rays in the energy range 20 - 100 keV, and on (gamma) emitting radioisotopes (Ir192 and Cs137) have been studied and will be described in this paper. Various types of objects have been studied: test objects and common objects such as tree trunks, wood fragments, nuts, ceramic samples, insulators and, etc. Samples have been imaged, after using iodine compounds as tracers.