Euromedim 2006 :1st European Conference on Molecular Imaging Technology

High spatial and energy resolution lanthanum bromide SPET scanner for molecular imaging

12 May 2006, 14:30

15m

Palais du Pharo, Marseille

oral S11 Perpectives Perspectives

Speaker

Prof. Roberto Pani (INFN Dept Experimental Medicine and Pathology - University of Rome "La Sapienza"-Italy)

Description

Last year many research groups have been attracted from the first samples of LaBr3:Ce crystals available from St.Gobain. Different applications are under investigation in particular in the field of medical imaging. PET, SPECT and Compton camera instrumentation seem to take advantage from the performances of this new scintillation crystal. In fact, it shows many advantages with respect to previous scintillators: excellent energy resolution, (3% and 6% at 662 keV and 140 keV photon energy respectively)very good radiation absorption properties, high photofraction (similar to NaI(Tl)) and high response speed (16 ns of scintillation decay time. Although St.Gobain is able to produce volumes as large as 3 inch diameter by 3 inch thick, some limitations are arising from high hygroscopicity and material fragility that introduce serious concerns in pixelated manufacturing. At present time, LaBr3:Ce crystals are available with continuous shape covering 5x5 cm2 and thickness up to one inch. In 2004, trusting on election properties for SPECT application of lanthanum trihalides scintillators cerium-doped, INFN promoted the development of a scintillation camera based on continuous crystal shape. During the same year, the preliminary results have been obtained with a small LaCl3:Ce one inch square. In 2005, with the availability of LaBr3:Ce crystal, we realized a small 5x5 cm2 camera by integral assembling a continuous crystal with an Hamamatsu Flat panel PMT H8500. Such tube offers a superior imaging performance with respect to previous generation ones. The tube with, 64 anode matrix, when coupled to a continuous crystal well simulate a miniature Anger Camera. Taking into account the new scintillation properties offered by LaBr we revisited the potentiality of position arithmetic algorithm analysed 30 years ago. For the statistics nature of spatial resolution when position is carried out from the scintillation light centroide, a strong improvement in energy resolution could involve the same improvement in spatial resolution. In fact, the non-proportionality response of NaI(Tl) scintillation light with photon energy could affect the position response, as demonstrated from spatial resolution experimental variation of only 25% in the energy range of 70-511 keV. To this aim we realized three small gamma cameras based on LaBr3:Ce coupled to the Flat panel PMT. This detector optical configuration permits the narrowest light distribution and the highest light collection to obtain the best spatial and energy resolution values respectively.The crystal have the same detection areas (5 x 5 cm2) and various thickness (4 mm , 5 mm and 10 mm respectively). Ultimately, the detector responses have been compared with analogous ones obtained from a NaI(Tl) continuous crystal in the same detection assembly and with 1.5 mm thickness. All detectors have been scanned by gamma emitting radioactive sources collimated with 1 mm aperture diameter, in the energy range between 70 and 360 keV. Preliminary measurements confirm the linear dependence of spatial resolution on energy resolution providing better than 2 mm FWHM values at 245 keV photon energy with 10 mm crystal thickness. Energy resolution values were also measured by standard PMT, confirming the results previously reported for continuous LaBr3:Ce crystals. Excellent spatial resolution (around 1 mm) was obtained from LaBr3:Ce crystals of 4 and 5 mm thickness, at 140 keV photon energy, corresponding to a detection efficiency ranging between 70% and 80%. In conclusion, the results confirm that LaBr3:Ce gamma camera can give a consistent contribution to the imaging improvement in molecular field both for animal studies and for clinical applications.