MR-compatibility assessment of the first preclinical PET-MRI insert equipped with digital silicon photomultipliers

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...

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Bibliographic Details
Published in:	Physics in medicine & biology Vol. 60; no. 6; p. 2231
Main Authors:	Wehner, J, Weissler, B, Dueppenbecker, P M, Gebhardt, P, Goldschmidt, B, Schug, D, Kiessling, F, Schulz, V
Format:	Journal Article
Language:	English
Published:	England 21-03-2015
Subjects:	Amplifiers, Electronic Magnetic Resonance Imaging - instrumentation Magnetic Resonance Imaging - methods Multimodal Imaging - instrumentation Multimodal Imaging - methods Photons Positron-Emission Tomography - instrumentation Positron-Emission Tomography - methods Signal-To-Noise Ratio Silicon
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Summary:	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.
ISSN:	1361-6560
DOI:	10.1088/0031-9155/60/6/2231