title: Simultaneous PET/MR imaging with a radio frequency-penetrable PET insert.
abstract: OBJECTIVE
  A brain sized radio frequency (RF)-penetrable PET insert has been designed for simultaneous operation with MRI systems. This system takes advantage of electro-optical coupling and battery power to electrically float the PET insert relative to the MRI ground, permitting RF signals to be transmitted through small gaps between the modules that form the PET ring. This design facilitates the use of the built-in body coil for RF transmission and thus could be inserted into any existing MR site wishing to achieve simultaneous PET/MR imaging. The PET detectors employ nonmagnetic silicon photomultipliers in conjunction with a compressed sensing signal multiplexing scheme, and optical fibers to transmit analog PET detector signals out of the MRI room for decoding, processing, and image reconstruction.
  
  
  METHODS
  The PET insert was first constructed and tested in a laboratory benchtop setting, where tomographic images of a custom resolution phantom were successfully acquired. The PET insert was then placed within a 3T body MRI system, and tomographic resolution/contrast phantom images were acquired both with only the B0field present, and under continuous pulsing from different MR imaging sequences.
  
  
  RESULTS
  The resulting PET images have comparable contrast-to-noise ratios (CNR) under all MR pulsing conditions: The maximum percent CNR relative difference for each rod type among all four PET images acquired in the MRI system has a mean of 14.0 ± 7.7%. MR images were successfully acquired through the RF-penetrable PET shielding using only the built-in MR body coil, suggesting that simultaneous imaging is possible without significant mutual interference.
  
  
  CONCLUSIONS
  These results show promise for this technology as an alternative to costly integrated PET/MR scanners; a PET insert that is compatible with any existing clinical MRI system could greatly increase the availability, accessibility, and dissemination of PET/MR.
authors.affiliation: Stanford University, Departments of Bioengineering, Stanford, CA, USA.|Stanford University, Departments of Radiology, Stanford, CA, USA.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Grant
authors.affiliation: Stanford University, Departments of Radiology, Stanford, CA, USA.|Stanford University, Departments of Mechanical Engineering, Stanford, CA, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Lee
authors.affiliation: Stanford University, Departments of Radiology, Stanford, CA, USA.|Stanford University, Departments of Applied Physics, Stanford, CA, USA.
authors.forename: Chen-Ming
authors.initials: CM
authors.lastname: Chang
authors.affiliation: Stanford University, Departments of Bioengineering, Stanford, CA, USA.|Stanford University, Departments of Radiology, Stanford, CA, USA.|Stanford University, Departments of Electrical Engineering, Stanford, CA, USA.|Stanford University, Departments of Physics, Stanford, CA, USA.
authors.forename: Craig S
authors.initials: CS
authors.lastname: Levin
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D011846:Radio Waves; D059629:Signal-To-Noise Ratio; D013997:Time Factors
keywords: PET detectors; PET/MRI; RF-penetrable; image reconstruction; multimodality; positron emission tomography