Briefly explain the principles of CT scanning.
A simple section through a body consists of four voxels, as illustrated in figure I below.
I
An X-ray image of the section is obtained by viewing along each of the directions shown in figure I above. The detector readings for each direction of viewing are summed to give the pattern of readings shown in figure II below.
II
For any one direction, the total of the detector readings is 16.
For the pattern of readings of figure II, state the magnitude of the background reading.
On figure I, mark the pattern of pixels for the four-voxel section.
