Micro PET Facilities
The microPET P4 small animal scanner (Siemens, Knoxville, TN) creates images with 6 microliter volumetric resolution. It is used routinely for in vivo PET brain imaging of rhesus macaques and rats. Stereotactic head holders are provided along with electronic vitals monitoring and isoflurane anesthesia equipment. In the scanner, scintilator crystals are arranged in 32 rings of 332 elements each, which provides 7.8 cm axial and 19 cm transaxial field of view with 2% sensitivity. Detector modules consisting of 8x8 arrays of 2.2 mm x 2.2 mm x 10 mm lutetium oxyorthosilicate (LSO) crystals are coupled to position sensitive photomultiplier tubes.
The LSO crystals have good light output and fast time response permitting 26% energy resolution and 3.2 ns timing resolution. Energy and timing windows are user selectable and typically set at 350 - 750 keV and 6 ns, respectively. Data are acquired in 3D list mode with the time and crystal pair position recorded for each coincidence event. Normalization and transmission scans are performed using a mechanism that carries a point source on a helical path. Lists are histogrammed into sinograms with post hoc dynamic framing. Sinograms are corrected for accidental coincidences and scaled to correct for radioactive decay and deadtime. Images are typically generated using filtered back projection (FBP) or ordered subset expectation maximization (OSEM) algorithms with 2D rebinning of the 3D sinograms. During reconstruction, histograms are normalized for detector sensitivity, and transmission-based attenuation and scatter corrections are applied.