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.