title: MR-compatibility assessment of the first preclinical PET-MRI insert equipped with digital silicon photomultipliers.
abstract: PET (positron emission tomography) with its high sensitivity in combination with MRI (magnetic resonance imaging) providing anatomic information with good soft-tissue contrast is considered to be a promising hybrid imaging modality. However, the integration of a PET detector into an MRI system is a challenging task since the MRI system is a sensitive device for external disturbances and provides a harsh environment for electronic devices. Consequently, the PET detector has to be transparent for the MRI system and insensitive to electromagnetic disturbances. Due to the variety of MRI protocols imposing a wide range of requirements regarding the MR-compatibility, an extensive study is mandatory to reliably assess worst-case interference phenomena between the PET detector and the MRI scanner. We have built the first preclinical PET insert, designed for a clinical 3 T MRI, using digital silicon photomultipliers (digital SiPM, type DPC 3200-22, Philips Digital Photon Counting). Since no thorough interference investigation with this new digital sensor has been reported so far, we present in this work such a comprehensive MR-compatibility study. Acceptable distortion of the B0 field homogeneity (volume RMS = 0.08 ppm, peak-to-peak value = 0.71 ppm) has been found for the PET detector installed. The signal-to-noise ratio degradation stays between 2-15% for activities up to 21 MBq. Ghosting artifacts were only found for demanding EPI (echo planar imaging) sequences with read-out gradients in Z direction caused by additional eddy currents originated from the PET detector. On the PET side, interference mainly between the gradient system and the PET detector occurred: extreme gradient tests were executed using synthetic sequences with triangular pulse shape and maximum slew rate. Under this condition, a relative degradation of the energy (⩽10%) and timing (⩽15%) resolution was noticed. However, barely measurable performance deterioration occurred when morphological MRI protocols are conducted certifying that the overall PET performance parameters remain unharmed.
authors: Department for Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging Systems, RWTH Aachen University, Pauwelsstrasse 19, 52074 Aachen, Germany.
authors: J
authors: J
authors: Wehner
authors: B
authors: B
authors: Weissler
authors: P M
authors: PM
authors: Dueppenbecker
authors: P
authors: P
authors: Gebhardt
authors: B
authors: B
authors: Goldschmidt
authors: D
authors: D
authors: Schug
authors: F
authors: F
authors: Kiessling
authors: V
authors: V
authors: Schulz
mesh_terms: D000669:Amplifiers, Electronic; D016477:Artifacts; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods*; D017785:Photons; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D059629:Signal-To-Noise Ratio; D012825:Silicon
chemical_list: D012825:Silicon