3D Spatial resolution proprieties of Molecubes β-Cube: characterization with different isotopes

The preclinical β-Cube PET scanner features a design with monolithic crystal detectors and DOI estimation. Images are reconstructed with a 3D list mode algorithm that should preserve the full spatial resolution of the system. This design is supposed to provide isotropic spatial resolution in the whole field of view. To test this claim we measured the effective reconstructed spatial resolution using a micro Derenzo phantom (Diameter 40 mm), using 3 isotopes with different positron ranges:
¹⁸
F,
¹¹
C,
⁶⁸
Ga. The phantom was first acquired to measure the transverse resolution positioned in center of the field of view. Then it was shifted radially to the most extreme position allowed and scanned twice: once with the smallest rod in the outermost position, then rotated by 180°. For the
¹⁸
F acquisition the phantom was also acquired with its axis orthogonal to that of the scanner, to measure the axial resolution. Resolution was quantified using the modulation transfer function. The maximum spatial resolution was observed with
¹⁸
F, while with
⁶⁸
Ga only the 4.7 mm rods were clearly distinguishable. Modulation transfer function analysis confirms that the spatial resolution is identical along all 3 axes. The resolution loss with the radial distance from the center is minimal.