Dual isotope imaging with LaBr3:Ce crystal and H8500 PSPMT

The introduction of Lanthanum Bromide crystal, characterized by a fast and high light emission, offers the possibility to improve both imaging spatial resolution and energy resolution in SPECT in the 80-300 kev energy range, without compromising detection efficiency. The expected performances may be limited if the crystal is used with a multi-anode PMT with Position Sensitive response due to the wide differences in the segmented anode pad gains, ranging from 2:1 to 10:1,. These characteristics may strongly deteriorate the overall energy resolution and, consequently, impair the detector imaging capability. For this reason, a 256 independent channel electronic read out was developed, based on an FPGA control, to individually read the charge on each anode. The electronics features a very low electronic noise (< 1%) and a wide dynamic range. The readout electronics was used to build a gamma camera based on a single 100mm x 100mm continuous LaBr3:Ce crystal coupled to a 2x2 array SBA photocatode (38% QE) Hamamatsu H8500. An offline calibration procedure is also shown in order to compensate the anode gain variation and to exploit the LaBr3:Ce capabilities, obtaining on the whole detection area an 8.0-8.5% energy resolution at 140 kev. The high energy resolution performances of this gamma camera permitted to discriminate emissions from two different isotope (Tc-99m and Co-57) with very close photon energy (140 and 122 kev respectively). This capability can be used to provide the gamma image with references coming from Co-57 point sources (marker) fixed at known positions. These results confirm the LaBr3:Ce crystals as one of the most interesting for all single photon emission applications.