PET performance and MRI compatibility evaluation of a digital, ToF-capable PET/MRI insert equipped with clinical scintillators

We evaluate the MR compatibility of the Hyperion-II(D) positron emission tomography (PET) insert, which allows simultaneous operation in a clinical magnetic resonance imaging (MRI) scanner. In contrast to previous investigations, this work aims at the evaluation of a clinical crystal configuration. An imaging-capable demonstrator with an axial field-of-view of 32 mm and a crystal-to-crystal spacing of 217.6 mm was equipped with LYSO scintillators with a pitch of 4 mm which were read out in a one-to-one coupling scheme by sensor tiles composed of digital silicon photomultipliers from Philips Digital Photon Counting (DPC 3200-22). The PET performance degradation (energy resolution and coincidence resolution time (CRT)) was evaluated during simultaneous operation of the MRI scanner. We used clinically motivated imaging sequences as well as synthetic gradient stress test sequences. Without activity of the MRI scanner, we measured for trigger scheme 1 (first photon trigger) an energy resolution of 11.4% and a CRT of 213 ps for a narrow energy (NE) window using five (22)Na point-like sources. When applying the synthetic gradient sequences, we found worst-case relative degradations of the energy resolution by 5.1% and of the CRT by 33.9%. After identifying the origin of the degradations and implementing a fix to the read-out hardware, the same evaluation revealed no degradation of the PET performance anymore even when the most demanding gradient stress tests were applied. The PET performance of the insert was initially evaluated using the point sources, a high-activity phantom and hot-rod phantoms in order to assess the spatial resolution. Trigger schemes 2-4 delivered an energy resolution of 11.4% as well and CRTs of 279 ps, 333 ps and 557 ps for the NE window, respectively. An isocenter sensitivity of 0.41% using the NE window and 0.71% with a wide energy window was measured. Using a hot-rod phantom, a spatial resolution in the order of 2 mm was demonstrated and the benefit of time-of-flight PET was shown with a larger rabbit-sized phantom. In conclusion, the Hyperion architecture is an interesting platform for clinically driven hybrid PET/MRI systems.

[1]  David J. Schlyer,et al.  Preliminary studies of a simultaneous PET/MRI scanner based on the RatCAP small animal tomograph , 2007 .

[2]  P. Vaska,et al.  Preliminary Studies of a Simultaneous PET/MRI Scanner Based on the RatCAP Small Animal Tomograph , 2006, 2006 IEEE Nuclear Science Symposium Conference Record.

[3]  T. Frach,et al.  The digital Silicon Photomultiplier — A novel sensor for the detection of scintillation light , 2009, 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC).

[4]  Carsten Degenhardt,et al.  The digital silicon photomultiplier — System architecture and performance evaluation , 2010, IEEE Nuclear Science Symposuim & Medical Imaging Conference.

[5]  G. Delso,et al.  Performance Measurements of the Siemens mMR Integrated Whole-Body PET/MR Scanner , 2011, The Journal of Nuclear Medicine.

[6]  T. Frach,et al.  The digital silicon photomultiplier — Principle of operation and intrinsic detector performance , 2009, 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC).

[7]  Nadim Joni Shah,et al.  Analysis and Correction of Count Rate Reduction During Simultaneous MR-PET Measurements With the BrainPET Scanner , 2012, IEEE Transactions on Medical Imaging.

[8]  P. Vaska,et al.  A Simultaneous PET/MRI scanner based on RatCAP in small animals , 2007, 2007 IEEE Nuclear Science Symposium Conference Record.

[9]  S. Vandenberghe,et al.  Effects of dark counts on Digital Silicon Photomultipliers performance , 2013, 2013 IEEE Nuclear Science Symposium and Medical Imaging Conference (2013 NSS/MIC).

[10]  Ciprian Catana,et al.  Performance test of an LSO-APD detector in a 7-T MRI scanner for simultaneous PET/MRI. , 2006, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[11]  Volkmar Schulz,et al.  An MR-compatible singles detection and processing unit for simultaneous preclinical PET/MR , 2012, 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC).

[12]  V. Schulz,et al.  Data Processing for a High Resolution Preclinical PET Detector Based on Philips DPC Digital SiPMs , 2015, IEEE Transactions on Nuclear Science.

[13]  P Gebhardt,et al.  MR-compatibility assessment of the first preclinical PET-MRI insert equipped with digital silicon photomultipliers , 2015, Physics in medicine and biology.

[14]  T. Beyer,et al.  Putting ‘clear’ into nuclear medicine: a decade of PET/CT development , 2006, European Journal of Nuclear Medicine and Molecular Imaging.

[15]  Volkmar Schulz,et al.  MR compatibility aspects of a silicon photomultiplier-based PET/RF insert with integrated digitisation , 2014, Physics in medicine and biology.

[16]  Giacomo Borghi,et al.  Probabilities of triggering and validation in a digital silicon photomultiplier , 2014 .

[17]  Til Aach,et al.  Simultaneous Reconstruction of Activity and Attenuation for PET/MR , 2011, IEEE Transactions on Medical Imaging.

[18]  V. Schulz,et al.  First evaluations of the neighbor logic of the digital SiPM tile , 2012, 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC).

[19]  Volkmar Schulz,et al.  A preclinical PET/MR insert for a human 3T MR scanner , 2009, 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC).

[20]  Volkmar Schulz,et al.  Development of an MRI compatible digital SiPM based PET detector stack for simultaneous preclinical PET/MRI , 2012, 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC).

[21]  Josep F. Oliver,et al.  Singles-prompts-randoms: Estimation of spurious data rates in PET , 2012, 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC).

[22]  V. Schulz,et al.  PET/MRI insert using digital SiPMs: Investigation of MR-compatibility , 2014, Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment.

[23]  Volkmar Schulz,et al.  Design concept of world's first preclinical PET/MR insert with fully digital silicon photomultiplier technology , 2012, 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC).

[24]  René M. Botnar,et al.  A Digital Preclinical PET/MRI Insert and Initial Results , 2015, IEEE Transactions on Medical Imaging.

[25]  René M. Botnar,et al.  A Self-Normalization Reconstruction Technique for PET Scans Using the Positron Emission Data , 2012, IEEE Transactions on Medical Imaging.

[26]  B. Zwaans,et al.  Arrays of digital Silicon Photomultipliers — Intrinsic performance and application to scintillator readout , 2010, IEEE Nuclear Science Symposuim & Medical Imaging Conference.

[27]  Yong Choi,et al.  MR insertable brain PET using tileable GAPD arrays , 2010, IEEE Nuclear Science Symposuim & Medical Imaging Conference.

[28]  Volkmar Schulz,et al.  ToF Performance Evaluation of PET Modules With Digital Silicon Photomultiplier Technology During MR Operation , 2015, IEEE Transactions on Nuclear Science.

[29]  H. Malcolm Hudson,et al.  Accelerated image reconstruction using ordered subsets of projection data , 1994, IEEE Trans. Medical Imaging.