(a)[4]
In computed tomography (CT scanning), a large number of X-ray images must be collected. Briefly outline the principles of CT scanning.
(b)[3]
A student builds a model of CT scanning. A 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 different 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 outcome 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.