Performance evaluation of the 32-module quadHIDAC small-animal PET scanner

The 32-module quadHIDAC is a commercial, high-resolution animal PET scanner, based on gas multiwire proportional chambers.

Several scanner parameters that characterize the performance of the system were evaluated in this study, such as spatial resolution, absolute sensitivity, scatter, and count rate performance. The spatial resolution has been determined with filtered back-projected images of a point source. A line source, a mouse phantom, and a rat phantom have been used to characterize the count rate performance. The scatter fraction and photon absorption have been measured with a mouse scatter phantom. The absolute sensitivity has been determined using a line source with aluminum shields of different thickness.

Spatial resolution (full width at half maximum) offers values of 1.08, 1.08, and 1.04 mm in the radial, tangential, and axial directions, respectively. The maximum count rate is 370 kcps for a line source of 19 MBq activity. Registration of scattered coincidences is caused primarily by photons scattering in the large coincidence detectors. For a mouse-sized object, only 5% of the measured coincidences scatter inside the animal, whereas 32% of the coincidences scatter inside the detectors. Photon attenuation within a mouse phantom was 22%. After scatter corrections, the absolute sensitivity of the system is 15.2 cps/kBq for a point source and 13.7 cps/kBq for a 7.8-cm-long line source. The peak noise equivalent count rates are 67 kcps@209 kBq/mL for the mouse phantom and 52 kcps@96 kBq/mL for the rat phantom. Finally, a comparison has been made with the microPET R4, a commercial scintillation crystal-based PET camera.

The results confirm that the quadHIDAC PET scanner, with its large cylindric field of view (165-mm diameter, 280-mm axial length), is particularly suitable for imaging small animals such as mice or rats.