METHOD AND APPARATUS FOR TREATMENT OF SIGNALS OBTAINED FROM PHOTOMULTIPLIER TUBES

摘要

An apparatus for treatment of signals obtained from photomultiplier tubes, in particular for carrying out a PET, by at least one couple of scintillators associated to photomultiplier tubes (100, 200). For each head (100) of sensors, a relative phototube (3) generates current pulses that are weighed by two resistive chains (6), each of which generates two output currents, and respectively X'A, X'B for the first chain and Y'A, Y'B for the second chain. The phototube (3) generates also a synchronization signal (S'), or last dynode signal, that serves as signals synchronism indicator for a coincidence comparation with signals coming from the other phototube of a paired head (200). The current pulses are transformed into voltage pulses and processed by correcting circuits (40, 41, 42 and 43), obtaining respective transformed signals XA, XB, and YA, YB, whereas the last dynode signals S' are amplified at S by a amplifying block (44). The signals reach a board (47) that carries out a sampling of the signals, their conversion into numeric values, a coincidence comparation and transfers them to a PC (49) through an USB interface (48). The software present on the PC (49) computes then the received signals and carries out a reconstruction of the images, which are then final result of the PET. The correcting circuits (40, 41, 42 and 43) of the position signals of the phototube at the same obtain a position signal with a controlled peak value, in order to retrieve the position immediately after the detection of a coincidence, and a quick decay of the signals after the peak value, within a time such that the probability of pile-up between different signals is minimum.