(a)[4]
In computed tomography (CT scanning), a large number of X-ray images must be recorded. Outline briefly the principles of CT scanning.
(b)[3]
A student constructs a model for CT scanning. One section is split into four voxels, with pixel numbers A, B, C and D, as shown in Fig. 9.1. The section is observed from four directions $V_1$, $V_2$, $V_3$ and $V_4$, as shown in Fig. 9.1. The detector readings for each direction are recorded and then added together. The result is shown in Fig. 9.2. The background count is 26. Determine the pixel numbers A, B, C and D as shown in Fig. 9.1.