Abstract
Combining Positron Emission Tomography (PET) with Magnetic Resonance Imaging (MRI) results in a promising hybrid molecular imaging modality as it unifies the high sensitivity of PET for molecular and cellular processes with the functional and anatomical information from MRI. Digital Silicon Photomultipliers (dSiPMs) are the digital evolution in scintillation light detector technology and promise high PET SNR. DSiPMs from Philips Digital Photon Counting (PDPC) were used to develop a preclinical PET/RF gantry with 1-mm scintillation crystal pitch as an insert for clinical MRI scanners. With three exchangeable RF coils, the hybrid field of view has a maximum size of 160 mm × 96.6 mm (transaxial × axial). 0.1 ppm volume-root-mean-square B 0-homogeneity is kept within a spherical diameter of 96 mm (automatic volume shimming). Depending on the coil, MRI SNR is decreased by 13% or 5% by the PET system. PET count rates, energy resolution of 12.6% FWHM, and spatial resolution of 0.73 mm (3) (isometric volume resolution at isocenter) are not affected by applied MRI sequences. PET time resolution of 565 ps (FWHM) degraded by 6 ps during an EPI sequence. Timing-optimized settings yielded 260 ps time resolution. PET and MR images of a hot-rod phantom show no visible differences when the other modality was in operation and both resolve 0.8-mm rods. Versatility of the insert is shown by successfully combining multi-nuclei MRI ((1)H/(19)F) with simultaneously measured PET ((18)F-FDG). A longitudinal study of a tumor-bearing mouse verifies the operability, stability, and in vivo capabilities of the system. Cardiac- and respiratory-gated PET/MRI motion-capturing (CINE) images of the mouse heart demonstrate the advantage of simultaneous acquisition for temporal and spatial image registration.
Highlights
I N modern medicine and research, molecular, functional and anatomical information from different imaging modalities are combined to improve diagnostic accuracy [1]
The aim of this paper is to introduce the completed Positron Emission Tomography (PET)/Magnetic Resonance Imaging (MRI) insert “Hyperion II ”, to detail the technical improvements, and to demonstrate their effectiveness in experiments
1) -Distortion: With the PET/RF insert the total field is decreased by 5.7 ppm (value calculated from f compared to the RF-coil-only case, which decreases the field by 0.2 ppm compared to the integrated body coil (Hyperion I: 6.3 ppm)
Summary
I N modern medicine and research, molecular, functional and anatomical information from different imaging modalities are combined to improve diagnostic accuracy [1]. With the introduction of Positron Emission Tomography/Computed Tomography (PET/CT) [2] first hybrid imaging modality was implemented in the clinical routine, which improved registration accuracy and workflow. The combination of PET with Magnetic Resonance Imaging (MRI) reveals comprehensive and complementary information [3] and promises to be a valuable tool in research [4]. Multiple clinical applications are already suggested [5], often restricted to simultaneous PET/MRI [6]. E.g., photomultiplier tubes (PMTs), important elements of standard PET detectors, need to keep a certain distance from the MRI bore and require magnetic shielding. Sequential PET/MR scanner can be realized, which are commercially available as clinical [8] and preclinical [9] systems
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