Computed tomography (CT)

which uses penetrating radiation from many directions to reconstruct cross-sectional or 3D images of object

has widely applied in medical diagnosis and treatment

industrial NDT and NDE. So it is significant for college students to understand the fundamental of CT. In this article we describe the CD-50BG CT instrument developed for experimental teaching at colleges. With 50 mm field-of-view and the transla- tion-rotation scanning mode

the system makes use of a single plastic scintillator + photomultiplier detector and a 137Cs radioactive source with 0.74 GBq activity

which is housed in a tungsten alloy shield. At the same time

an im- age processing software has been developed to process the acquired data

so that cross-sectional and 3D images can be reconstructed. High quality images with 1 lp·mm-1 spatial resolution and 1% contrast sensitivity are obtained. So far in China

more than ten institutions including Tsinghua University and Peking University have already applied the system to elementary teaching.