Simultaneous PET/MR imaging with a radio frequency‐penetrable PET insert

Abstract

Purpose 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 non-magnetic 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 B0 field 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.

From simultaneous to synergistic MR‐PET brain imaging: A review of hybrid MR‐PET imaging methodologies

“…For example, RF interference to PET front-end electronics may cause an increase in PET random count rates, triple coincidence count rates and dead time problems (Delso & Ziegler, 2009 Bandwidth (Hz) <2x10 9 <1x10 9 NA potential utilisation of build-in body coil for MR imaging (Grant, Lee, Chang, & Levin, 2017). Integration of PET and the MR RF components requires special consideration to avoid crosstalk between the operating frequencies in both systems.…”

“…Integration of PET and the MR RF components requires special consideration to avoid crosstalk between the operating frequencies in both systems. For example, RF interference to PET front-end electronics may cause an increase in PET random count rates, triple coincidence count rates and dead time problems (Delso & Ziegler, 2009 Bandwidth (Hz) <2x10 9 <1x10 9 NA potential utilisation of build-in body coil for MR imaging (Grant, Lee, Chang, & Levin, 2017). In general, integration of the two components requires additional shielding which must be carefully considered, as the shielding itself may degrade the uniformity of the static B 0 magnetic field or interact with the gradients of the scanner (Truhn, Kiessling, & Schulz, 2011 (Sander et al, 2015).…”

Initial experience with a SiPM-based PET/CT scanner: influence of acquisition time on image quality

“…The differences between standard and SiPM PET detectors are significant. SiPMs having a small physical profile and a negligible electronic noise, offering high gain, and requiring low operating voltage offer several advantages over previously used technologies such as photomultiplier tubes (PMTs) and avalanche photodiodes (APDs) [ 13 , 14 ]. Among the potential advantages of SiPM-based PET/CT over standard PET/CT are decreased required dosage of PET radiopharmaceuticals, higher sensitivity, and temporal resolution.…”

Performance evaluation of RF coils integrated with an RF‐penetrable PET insert for simultaneous PET/MRI

“…Although EPI sequence is a common sequence for brain imaging, it was not performed in the study. As presented from earlier publications, 10,28,29 the intense gradient field slew rate of EPI sequence induced eddy current on the solid copper shielding cage of the RF-penetrable PET insert and suffered from the Nyquist ghosting artifact. To allow the PET ring operable with EPI, various designs and materials for the shielding cage with sufficiently high shielding effectiveness and low induced eddy current have been investigated.…”