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Development of a combined microPET-MR system
A J Lucas1, R C Hawkes, R E Ansorge
1Wolfson Brain Imaging Centre, University of Cambridge, Box 65, Addenbrookes Hospital, Cambridge CB2 2QQ, UK.
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 field-insensitive 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 (approximately 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.
Insights
Combining Positron Emission Tomography (PET) and Magnetic Resonance (MR) imaging offers advantages for cancer screening. This study modifies a PET scanner to work within an MR system, overcoming magnetic field interference for improved small animal imaging.
Area of Science:
- Medical Imaging
- Biomedical Engineering
- Nuclear Medicine
Background:
- Combining PET and MR imaging (PET-MR) offers superior soft tissue contrast and reduced radiation dose compared to PET-CT.
- Conventional PET detectors using photomultiplier tubes (PMTs) are sensitive to magnetic fields, posing a challenge for PET-MR integration.
- Alternative approaches include using magnetic field-insensitive detectors (APDs, SiPMs) or modifying existing systems.
Purpose of the Study:
- To develop and test a modified PET system compatible with a 1T MR scanner for small animal imaging.
- To evaluate methods for mitigating magnetic field effects on PMT-based PET detectors within an MR environment.
Main Methods:
- A microPET Focus 120 scanner was modified and integrated into a novel 1T superconducting magnet.
- Fiber optic bundles were used to shield PMTs from the main magnetic field, placing them in a ~30mT region.
- Key system features, including the use of long fiber optic bundles and the magnetic field's impact on PMTs, were tested.
Main Results:
- The design for a modified microPET-MR system for small animal imaging has been completed.
- Assembly and initial testing of the modified system are currently in progress.
- The study is evaluating the performance of PMTs shielded by fiber optics within the MR's magnetic field.
Conclusions:
- The integration of PET and MR imaging is feasible with system modifications to address magnetic field interference.
- This approach enables simultaneous PET-MR imaging, potentially improving diagnostic accuracy and reducing radiation exposure.
- The modified system is expected to advance small animal research and preclinical imaging applications.
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