Development of a Combined microPET®-MR System

Abstract

As evidenced by the success of PET-CT, there are many benefits from combining imaging modalities into a single scanner. The combination of PET and MR offers potential advantages over PET-CT, including improved soft tissue contrast, access to the multiplicity of contrast mechanisms available to MR, simultaneous imaging and fast MR sequences for motion correction. In addition, PET-MR is more suitable than PET-CT for cancer screening due to the elimination of the radiation dose from CT.A key issue associated with combining PET and MR is the fact that the performance of the photomultiplier tubes (PMTs) used in conventional PET detectors is degraded in the magnetic field required for MR. Two approaches have been adopted to circumvent that issue: retention of conventional, magnetic field-sensitive PMT-based PET detectors by modification of other features of the MR or PET system, or the use of new, magnetic fieldinsensitive devices in the PET detectors including avalanche photo-diodes (APDs) and silicon photomultipliers (SiPMs).Taking the former approach, we are assembling a modified microPET ® Focus 120 within a gap in a novel, 1T superconducting magnet. The PMTs are located in a low magnetic field (~30mT) through a combination of magnet design and the use of fiber optic 'bundles'.Two main features of the modified PET system have been tested, namely the effect of using long fiber optic bundles in the PET detector, and the impact of magnetic field upon the performance of the position sensitive PMTs.The design of a modified microPET ® -MR system for small animal imaging is completed, and assembly and testing is underway.

Multi-modality nuclear medicine imaging: artefacts, pitfalls and recommendations

“…[38] were encouraging. Recently, the design of a micro-PET/MRI system has been completed, and assembly and testing is underway [39] .…”

Simultaneous PET–MRI in oncology: a solution looking for a problem?

“…The first publications reporting combined PET-MRI systems appeared in the mid to late 1990’s, as groups from the University of California at Davis and King’s College London [19-21], the University of Tubingen [22,23], and the University of Cambridge [24] all explored various approaches to integrating PET and MRI scanners. Shortly thereafter, exciting data in small-animal tumor studies began to emerge displaying the ability to simultaneously acquire quantitative PET and MRI data [14,25,26].…”

Principles of Simultaneous PET/MR Imaging

“…Alternatively, minimally modified PET detectors have been integrated in specialized MRI scanners (e.g. split-magnet (13) or field-cycled (14, 15)).…”