PET imaging and biodistribution

PET imaging was performed on a Focus 120 microPET (Concorde Microsystems, Knoxville, TN), with animals under 2% isoflurane anesthesia delivered via nose cone in 2 l/min medical air. A total of five mice were imaged for the study. The same animals were sacrificed after imaging for biodistribution analysis. After acquisition (10 min with >20 million counts/scan) list mode emission data were sorted into 2-dimensional sinograms via Fourier rebinning; data were normalized to correct for non-uniform detector response, deadtime count losses, and positron branching ratio, but no attenuation, scatter, or partial-volume averaging corrections were applied. Sinogrammed data were reconstructed into a 128×128×95 matrix (0.87×0.87×0.77 mm voxel size) by filtered back-projection. Image counts per voxel per second were converted to activity concentrations (%ID/cc) using a system-specific calibration factor derived from imaging a mouse-sized water-equivalent phantom containing fluorine-18. Reconstructed data were processed and VOIs drawn using Inveon Research Workplace software (Siemens). After image acquisition, mice were sacrificed, their organs dissected into previously weighed culture tubes, the tubes weighed, activity counted on a gamma-counter (Wizard² 3” 2480, Perkin-Elmer, Waltham, MA) with internal fluorine-18 standards, and the data converted to %ID/g.