AbstractThe combination of Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) as a multi-modality imaging technique allows the simultaneous acquisition of information about metabolic processes with very sensitivity from PET, and high-resolution anatomical or functional MR images with an excellent soft-tissue contrast from MRI. However, the design of PET/MRI systems providing an unaffected PET and MRI performance during simultaneous operation is challenging. An integration and operation of PET with a large field of view for clinical whole-body imaging can be realised through the use of semiconductorbased photo-detectors which are MR-compatible and very small compared to conventional photo-detectors. PET systems based on these new photo-detector require a dramatically higher, typically two orders of magnitude, number of detector channels to be read out by the PET acquisition system. The latter are usually designed for particular systems and are not based on architectural approaches to be easily adaptable to different detector configurations. The first aim of this thesis was to conceive a PET data acquisition architecture with concepts offering a high level of flexibility in order to meet the requirements of current and future, preclinical and clinical PET and PET/MRI detector configurations using semiconductor photo-detectors. This architecture was implemented for two preclinical PET inserts, Hyperion I and Hyperion IID, designed for simultaneous PET/MRI. The second system uses the latest detector technology known as the digital SiPM (made by Philips). The PET data acquisition platform design for Hyperion IID as well as investigations in the data transmission stability under different PET and PET/MRI operating conditions are presented.
PET detectors operated in an MRI bore commonly use radio-frequency (RF) shielding to reduce PET-related RF interference and hence preserve the MR image quality. However, shields require conducting materials which give rise to eddy currents within the switching MRI fields. These eddy currents lead to local MRI field disturbances and thus MR image artefacts. The drawbacks could be avoided by operating a PET system without RF shielding, which would, however, require the PET system not to couple spurious RF signals into the MRI RF signal receive coil. The second objective of the thesis was therefore to exploit the novel capabilities of the new data acquisition system and modify the RF emissions from the PET electronics in such ways that the RF noise coupling into the MRI coil can be lowered. Three different RF interference reduction (IR) techniques are proposed which are based on rmware of field-programmable gate array (FPGA) devices, thereby offering RF IR modifications at any time compared to permanently mounted PET shields. The techniques were studied by performing simulations PET and MRI measurements. The thesis closes with PET/MRI in vivo and ex vivo measurement results to demonstrate the feasibility and stability of the data acquisition system and the imaging capabilities of Hyperion IID.
|Date of Award
|Paul Marsden (Supervisor)