As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. 

Positron Emission Tomography (PET) is a radiotracer-based molecular imaging technique that is used to observe metabolic processes in the living body. Current clinical PET scanners have an axial field of view (AFOV) ranging from ~15cm to ~30cm. This results in several limitations. Firstly, most of the emitted radiation is not detected, as most of the patient’s body is outside of the field of view this, combined with patient dose considerations results in long scan times and poor data quality.

System Design

The Mini EXPLORER II consists of a PET scanner and a standard 16-slice CT system (based on the CT 510, United Imaging Healthcare, Shanghai, China). The CTscanner provides data for attenuation correction as well as for anatomical correlation. The CT scanner has a maximum rotation speed of 0.5s/rotation. The CT detector has 24 physical detector rows with an axial extent of 19.2 mm, and a minimum slice thickness is 0.6 mm.

The x-ray tube has a focal spot of 0.5 mm x 1.0 mm, or 1.0 mm x 1.0 Mm, with voltage variable from 80 kV to 140 kV. The tube current is variable from 10 mA to 420 mA. The EXPLORER Consortium’s efforts to build small-scale prototype scanners are intended to serve several purposes: to explore issues and limitations arising from large acceptance angle imaging with detectors appropriate for human-scale scanners; to prototype applications in animals that can be translated to humans; and to prototype systems integration for the hardware and software components of the human-scale system.

The first area was addressed in part in work with the Mini EXPLORER I scanner, which also continues to offer opportunities in area 2. MiniEXPLORER II is primarily aimed at the third purpose in this list, and this goal has been successfully achieved. However, it also presents opportunities to address items 1 and 2, and further, to provide a platform for clinical veterinary applications, for investigations in comparative medicine with companion animals, and high performance human brain imaging.

Regarding addressing possible limitations about large acceptance angle imaging, the MiniEXPLORER II results are reassuring concerning matters relating to image uniformity and spatial resolution. demonstrates that no significant artifacts are apparent in a 20 cm diameter uniform cylinder with length adequate to encompass the entire axial field of view. shows excellent spatial resolution even with all lines of response accepted a result that is in agreement with what was seen with MiniEXPLORER I