Authors: MolletPieter 1, DeprezKarel 1,Vandeghinste Bert 1, Neyt Sara1, Marcinkowski Radoslaw2,Vandenberghe Stefaan2, Van Holen Roel2 Affiliations
MOLECUBES NV, Ghent Belgium.
IBiTech – MEDISIP – INFINITY, Ghent University, Belgium.
To further improve preclinical PET, new systems should improve spatial resolution and sensitivity. Ideally this is obtained without increasing the total cost of the system. Based on monolithicscintillators with highly sampled readout and Depth-Of-Interaction capability,MOLECUBES developed a compact preclinical PET system, called the β-CUBE. Here,we report on the design, the specifications, performance evaluation and in-vivoimaging results.
The system consists of a ring of 9 detector modules with an inner diameter of 76 mm and a long axial FOV of 13.3 cm,enabling total body mouse and rat imaging. Each module contains five 25.4 x25.4 x 8 mm thick monolithic LYSO scintillators coupled to an analogue SiPM(Hamamatsu MPPC). Peltier coolers control the SiPM temperature at a stable 23degree Celsius. Dedicated read-out electronics read the signal of each pixel ofthe MPPC. All detector units are connected to 5 coincidence boards. Theacquisition and reconstruction servers are integrated inside the 54 cm x 54 cmx 54 cm system. The acquisition server performs on-the-fly GPU-based statistical event positioning of acquired pixel signals. The reconstruction server runs a GPU-based Tube of Response-based OSEM reconstruction and makesthe final images available to the user in DICOM format. The attenuation map forthe PET image reconstruction is obtained from the previously introduced X-cube,providing sub-minute microCT-imaging at low dose (less then 6 mGy for thefastest whole body mouse scan). Both systems are controlled wirelessly using atablet or a computer with a single integrated software. Sequential PET/CT isacquired with a single animal bed shared by both systems while co-registrationis performed automatically.
The resolution in image space is furtherimproved by using continuous Depth Of Interaction functions. Allreconstructions were done with 50 iterations of our OSEM reconstruction. ThePET detector intrinsic resolution was measured with a 0.4 mm collimated beamsource. Spatial resolution is evaluated using point sources and a hot-rodphantom and image uniformity and recovery with a NEMA image quality phantom.
The intrinsic detector resolution is 0.76 mmfull width at half maximum (FWHM). The reconstructed tangential and axial imagespatial resolution is 0.874 mm FWHM and 0.780 mm FWHM respectively at thecenter of the field of view (CFOV). Radial spatial resolution was nearlyconstant as a function of the radial offset, varying from 0.9 mm FWHM at aradial distance of 10 mm from the center to 1.15 mm FWHM at a distance of 25mm. Using a hot-rod phantom, the 0.8 mm rods are clearly visible while some ofthe 0.7 mm rods can be discriminated. Uniformity was 16.6% and the hot rodrecovery coefficients ranged from 0.28 to 0.96. The absolute peak sensitivity inthe CFOV is 10.2 %. In-vivo scans of a mouse and a rat using both NaF-F18 andF18-FDG shows that the resolution and sensitivity of our system is exquisiteover the entire FOV and has large potential for quantitative and dynamicimaging.
The design of the β-CUBE resulted in a trulyhigh-end PET imaging system for rodents. The compact and portable system can beinstalled in any certified environment on a standard lab table and allows forstationary total body mouse imaging with sub-millimeter resolution incombination with high sensitivity.
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