By G. Fredzell (auth.), Prof. Dr. H. Just, Prof. Dr. P. H. Heintzen (eds.)
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4. Under ideal conditions, the filtered analog signal may contain frequency components lower than half the sampling frequency_ However, as discussed above, quantization of the amplitude samples is always an approximation process . As will be discussed below, it is usually technically feasible to make the error of this approximation so small that it can be neglected when compared with the unavoidable noise in the filtered continuous input signal. The last step shown in Fig. 4 is signal coding. This transforms the quantized signal into a binary representation compatible with the organization of common digital storage elements and arithmetic functions; N bits (binary digits) are needed to code the P different amplitude levels defined in Eqs.
This complex system combines a number of complete X-ray systems with a high speed digital processor system. Pfeiler (1981) has discussed some basic problems of this approach which may limit its applicability. Because of the reasons described above, only the techniques collectively named "digital fluorography" in Fig. 1 are left for routine angiocardiographic imaging. They are characterized by the following features: 1. Image acquisition using fluoroscopic system components (area beam radiation source, image intensifier, video camera).
1981; Waldman et al. 1981). These problems may in future be solved by digital implementations of image data acquisition and processing. The data rate and capacity may be decreased in the coding process and both these parameters, and in addition the radiation dose, might in certain applications be reduced by noise reducers or temporal low-pass filters. These topics are discussed in the following paragraphs. Presently, the typical imaging rate is 50/s or 60/s in video angiocardiography and the radiation pulse (aperture time) should not be wider than 2ms to avoid motion blurring and a widening of the X-ray spectrum (Heintzen 1971 b; HaendIe 1979).