Digital slit-scan

Fig. 13.7. Example of a tumor that is difficult to see on the original digital mammogram (right) and in slit-scan DBT.

The scanning of a track of a developed plate by a slit-scanner yields the space dependent measuring curve of the reflectance (Fig. 6). From this curve data must be taken for calibration or for calculating the analytical result. This may be the peak-height or the integrated area under the curve. We also may produce the derivative of this curve to obtain data, or in the case of a digital system we may obtain data for approximation of the peak. 

Single channel pmt detection of the same spectrum with the same HR 320 spectrometer exhibits at least on order of magnitude lower signal to noise ratio. For the pmt measurements, entrance and exit slits of 1.0 mm were employed and the HR 320 wavelength was scanned digitally. The total accumulation time was the same for the PDA and pmt determinations. 

The current situation offers two different approaches to the quantification of TLC. In the classic mode, data collections are done with densitometers that are equipped with sensitive photomultipliers. Information from a plate comes in the form of a unique signal, integrated in the analog mode, from a relatively big scanning slit, which moves at a speed of a few mm per second (in more modem equipment, it can even increase to a few cm per second). The signal from the illuminated or nonilluminated side is collected, digitized, and processed using a personal computer. 

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