Image Quality Evaluation Study of an RF-Penetrable Brain PET Insert: A Phantom Assessment Toward Clinical Translation

This work presents imaging studies from a brain dedicated radio frequency (RF)-penetrable PET insert compatible with clinical whole-body MRI systems. The brain dedicated PET system is composed of 16 detector modules. Each module employs an array of 3.2 x 3.2 x 20 mm3 LYSO crystal elements which are 1-1 coupled to arrays of silicon photomultipliers (SiPM). Front-end electronics multiplex the output of 128 pixels to 16 vertical-cavity surface-emitting lasers (VCSEL). The VSCELs generate unique optical output patterns per pixel which are passed via fiber optics to an external DAQ. To achieve RF-penetrability of the body coil RF excitation signal and maintain MRI compatibility, the modules in the assembled system are electrically isolated from the MRI and spaced with 1 mm gaps for the RF fields to enter. The PET system has an internal diameter of 32 cm which is reduced to 28 cm due to the addition of a very thin phased array receive coil. Two phantoms were imaged using the brain dedicated PET system: a custom 3D printed resolution phantom, and the Hoffman brain phantom. The resolution phantom had hot rods with diameters of 5.2 mm, 4.2 mm, 3.2 mm, and 2.8 mm, and a single cold rod region with rods of 4.2 mm diameters. For a gold standard, images from a GE Signa system were acquired and compared to the results of the dedicated brain PET insert. In comparison, the dedicated brain PET system was able to visualize the smallest hot rod feature (2.8 mm) whereas the GE Signa system was not and showed much better resolution and contrast for all rods, including the 4.2 mm diameter cold rod pattern. However, the Hoffman brain phantom scan was of higher quality in the GE system most likely due to the application of accurate image corrections (e.g. random, scatter, attenuation, and deadtime correction). Future work will focus on the inclusion of image correction in the processing workflow of the dedicated brain PET system to realize the benefit from its higher intrinsic spatial resolution.