Development of G-APD small animal PET prototype: Phantom and animal imaging studies

Objectives Previously we reported the first point source image acquired using a G-APD (Geiger-mode avalanche photo-diode) small animal PET prototype (SNM 2009). In this study, we have further advanced the prototype system including the extension of transaxial field-of-view (FOV), and performed various phantom and in-vivo animal imaging studies to show the feasibility of the system.

Methods The G-APD small animal PET consists of 8 blocks, each of which is composed of 2 x 6 G-APDs and 4 x 13 LGSO (1.5 x 1.5 x 7 mm³) crystals. Its ring diameter (crystal face-to-face distance) and axial FOV are 60 mm and 6.4 mm, respectively. Bias voltage for each G-APD is powered by digitally controlled voltage supply with temperature sensor. Various phantoms were scanned for physical performance evaluation including ²²Na point source, capillary tubes separated by various distances, and cylindrical micro phantom with hot and cold rod inserts. Rat brain PET scans were acquired using [¹⁸F]FDG and [¹¹C]raclopride. In addition, mice bearing tumor xenografts were scanned with [¹⁸F]FDG and [⁶⁸Ga]RGD. EM and MAP image reconstructions were performed after normalization correction. The reconstructed PET images were registered with animal CT images.

Results The G-APD PET images of all phantoms and animals were successfully obtained. The spatial resolution of a ²²Na point source was 1.0 mm at the center with EM reconstruction (16 iterations). Capillary tubes at 5 mm and narrower intervals were clearly visible. The hot and cold rods were also distinguishable in the micro phantom. PET images of rat brains and tumor xenografts in mice were equivalent to the PMT-based animal PET data.

Conclusions G-APD PET images were obtained with various phantoms and animals. These results demonstrate that it is possible to acquire reasonable quality animal PET images employing G-APDs