SSR-SPECT
The use of scintigraphic technologies dedicated to the study of small animals, is closely linked to the verification of the animal model, with regard to the development of new radio-drugs or peptides, which however require in-depth analysis in this regard. Innodesi, with the Department of Bioimaging of the CNR (IBIS-CNR), directed by Dr. Alessandro Soluri, has undertaken a collaboration with the University of Beijing, in order to design and produce some specimens of SPECT detectors to be inserted in an advanced device to four modes (PET-SPECT-CT-Fluorescence), pre-clinical imaging for small animals. The solution proposed by CNR researchers, has introduced innovative methods applicable to PET-SPECT techniques, based on the SSR (Super Spatial Resolution), which show a considerable improvement in terms of total spatial resolution of the devices, which can be estimated in a first approximation with an improvement between 35-70% of spatial resolution, compared to standard SPECT / PET technologies.
Camera Structure
The camera developed is composed of a square hole Tungsten collimator and a LYSO scintillator structure, the Hamamatsu H9500 Flat Panel PSPMT, a pure Lead shielding housing, a miniaturized charge readout electronics and a data acquisition system. The parallel square hole collimator is made of pure Tungsten with 200-mm-thick septa and consisting of a 36 mm block collimator mounted over the crystals. The size of each hole is 1.6×1.6 mm2. The scintillation structure is composed of 28×28 LYSO scintillation crystals (Hamamatsu Photonics-Japan) with a FOV of 45.4×45.4 mm2. The crystals have a size of 1.52×1.52×3.0 mm3 and are covered by 80 μm of reflective film on their five blind surfaces. The space left to reach the height of the collimator primary module is filled with 0.4 mm of Teflon tape.
Electronic Readout
Innodesi have developed the readout system based on a high performance resistive chain connected to a dedicated data acquisition system that is connected via USB to a PC. The H9500 PSPMT (49×49 mm2 active area) has a charge collection system featuring a smaller anodic pitch with respect to the H8500 one. This implies a better charge sampling with consequent improving of the system spatial resolution and position linearity. It requires a more complex readout electronic as it has 256 anodes (instead of the 64 of the H8500). We have developed an equivalent miniaturized network for the H9500 combined with a dedicated new compact 4-channel ADC board. The detection head uses a parallel holes collimator allowing fast acquisition and quantitative analysis on functional images. The readout system consists of three electronic boards, with the same form factor of the PSPMT, about 52 × 52 mm2 :
- Resistive chain
- ADC board acquisition ( 4 x Channel 12 bits @ 125 MSample/s )
- Power board
Electronic boards are stacked on each other to minimize the device overall size. The readout is connected to the PSPMT and includes four low-noise charge preamplifiers, while the ADC board is connected to the readout. The data acquisition system provides 4 independent channels with 80-125MSample/s and is connected via USB bus for transfer the data to a PC.
Measure & Results
IBIS-CNR have characterized the electronic signals, optimizing the system response on the LYSO scintillation for low energies, as the 99mTC emission. The system was calibrated to obtain a good pixel identification on the whole FOV. The raw image (see “Small Animal SPECT Imager with LYSO Scintillator Arrays and PSPMTs “– Biomedical Engineering International Conference –BMEiCON-2013), for LYSO crystals array with 2 mm × 2mm × 3 mm pixel size, shows good separation of the single pixels.