Development of a small-animal high-purity germanium SPECT-CT system

Objectives The objective of this work was the development of a small-animal SPECT system with a single pinhole collimator using a high-purity germanium double-sided strip detector mounted onto a microCT gantry. Germanium detectors provide excellent energy resolution in addition to depth-of-interaction position estimation, which may allow for improved image quality over standard scintillator-based systems.

Methods The germanium detector is a double-sided strip detector of 16 x 16 orthogonal strips, with a 5-mm strip pitch and a 0.25 mm gap between strips. The detector has approximately 1.5-mm intrinsic spatial resolution, less than 1% energy resolution at 140 keV, and provides depth estimates in 1-mm bins. A single 1-mm pinhole with a 70° opening angle was used for image acquisition. The image reconstruction algorithm used was MLEM with an analytical, on-the-fly calculated system matrix. Image data were acquired for both a hot-rod and a NEMA NU 4 image quality phantom. MicroCT images were acquired and registered to the SPECT images.

Results Preliminary hot-rod images indicate the ability to clearly visualize 1.7-mm rods but not 1.35-mm rods. Image quality measures similar to those described for the small-animal PET NEMA NU4 2008 specifications will be presented.

Conclusions We have developed a small-animal SPECT-CT system based on a high-purity germanium gamma camera. Current efforts include image quality comparisons to a commercially available small-animal SPECT system and acquisition of dual-isotope animal images.

Research Support DE-SC0002437 R25CA136440 R01EB013677