Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5255_Библиотеки_им_академика_М_И_Перельмана

present in the system. When the number of DAS channels is less then the number of physical detector elements, the output of the elements is summed prior to sampling by the DAS channels. For example, as shown in figure 2a, on a four DAS channel scanner (mistakenly called a four detector scanner) employing a detector with 16 equal detector elements, sampling the inner four elements results in the acquisition of 4 × 1.25 millimeter slices per rotation. Summing the elements in groups of two, three or four prior to sampling, results in 4 × 2.5 millimeter slices (Figure 2b), 4 × 3.75 millimeter slices (Figure 2c) or 4 × 5 millimeter slices (Figure 2d) respectfully. The number of detectors or the number of slices obtained per rotation is dramatically increased from 4 slices to 16 slices per rotation to 64 slices and beyond per gantry rotation. Figure 3a, shows the detector elementary design in a 4-slice MDCT scanner. The detector array design is often categorized as uniform, non-uniform and hybrid. In hybrid design, we have thin detectors in the center and thick detectors adjacent to them. 4-slice MCT scanners were replaced by scanners capable of obtaining 16-slices per gantry rotation. As shown in figure 3b, the detector elements in a 16 section MDCT scanner all have thin sections in the center and thick detectors in the adjacent each enabling 16-simultaneous slices per gantry rotation. Figure 3c, shows the detector array design of 64-slices MDCT scanners capable of yielding 64 thin slices per gantry rotation.