LEGO CT scanner

Exhibitor: Chi Hou José Ho

Supervisor: Stephen Wilson

Research Group: Electromagnetics and Imaging

Industry Sector: Health / Medical Technology

Computerised Tomography (CT) imaging, also known as Computed Axial Tomography (CAT), is one of the most frequently used modern diagnostic imaging modalities. It based on the principle of conventional X-ray tomography. Instead of using films, images are processed stored and displayed by using computers. The first CT scanner, which utilised a “translate-rotate” principle, was built in 1972 by Dr. Hounsfield in the UK. Translate means the X-ray source and detector are rigidly coupled and form a pencil beam to sweep through the sampling object to obtain a projection. Rotate means a certain angle of rotation by the coupled source and detector after the translation. A set of projections is then obtained after a full 360° rotation and they are used for reconstructing a tomographic image.

In order to understand the modern advanced CT imaging technology, one should know the basic operation principle of it. But now it is difficult to find a 1st generation CT Scanner for demonstration. Moreover, X-ray has been proved to be harmful and many people are scared of it. Therefore it will be desirable to have a teaching model, which can demonstrate the operation of a 1st generation CT scanner harmlessly. This thesis project is working toward this goal – to build a teaching model of CT scanner using some harmless, easy access components.

LEGO blocks are used as the major structural component in this model. They are easily accessible and offer a great degree of freedom for designing, constructing and modifying the structure of the model. Since a steady and precise movement and controllability are needed for the translate-rotate process, stepper motors are chosen as the mechanical components. They are powered and controlled by a microcontroller. The microcontroller also serves as the signal-processing unit, which performs data acquisition from the photo detector and transmission to and from the computer via the RS-232 link. A type I laser source, which is essentially the light source for laser pointers, and a light-to-frequency converter are used to mimic the function of true X-ray source/detector without emitting any dangerous radiation. In order to make this teaching model more complete, a graphical user interface on PC is developed in Visual Basic. It performs as a soft switch and step-size controller. It also extracts the return data of projections from the microcontroller. Another program developed in Matlab will process the data and output the tomographic image of the given sample.

Since this model is built on components which can be modified easily, based on this design, it is feasible to build the other generations of CT scanners teaching models in future.

Thesis Document (PDF)