Speaker
Description
Introduction:
The META-scan, an ultra-high-field Magnetic Resonance Imaging (MRI) scanner developed to visualize metabolic processes in vivo in the entire human body, can potentially be used to study acute metabolic effects and fast interactions between the brain and other organs, such as the liver, gut, heart, and kidneys. However, due to its low sensitivity, studies involving drug tracing require unacceptable pharmacological doses. In addition, simultaneous imaging of fast direct metabolic interactions between organs more than 40 cm apart is currently not possible due to the limited field-of-view. We propose to address these two limitations by developing a positron emission tomography (PET) insert for the META-scan, to extend its metabolic MRI capabilities with the possibility to perform simultaneous PET for drug tracing and/or metabolic imaging anywhere in the body. Since the insert is aimed at enabling dynamic imaging of the fast metabolic processes for which simultaneous imaging is essential, the sensitivity of a long axial FOV (LAFOV) PET system design is needed. However, incorporating a LAFOV design into the META-scan presents a major challenge, since the available physical space is severely limited due to the relatively small diameter of its 7T bore coil. The aims of this study were to explore the possibilities of employing inorganic crystal fiber arrays with dual-ended side-readout to create a LAFOV detector geometry for a PET insert that fits within the physical space constraints of the META-scan, to give an initial estimation of the expected sensitivity and dynamic performance of the various options, and to compare them to the expected sensitivity of an optimized more traditional design based on back-readout of the crystals.
Methods:
For both design strategies (back-readout and side-readout), we modelled a range of system designs using GATE with varying axial FOV lengths, numbers of crystal arrays, crystal thicknesses, and axial gap sizes, while accounting for the physical space required for the crystals and the data readout and power supply cables. As a rough estimate of the expected sensitivity of each design, we simulated a 4-minute acquisition of a human body-mimicking phantom containing 33.55 MBq F-18-FDG and expressed the number of true coincidences as a percentage of the number of true coincidences recorded from the phantom in a GATE model of the uEXPLORER system.
Results:
Even when modelling only crystals and cables, assuming zero thickness for crystal readout electronics and cooling system, the side-readout designs achieved better sensitivity than the most optimal back-readout designs for axial FOVs longer than 1.5 m. Our preliminary side-readout design with 192 cm long axial FOV recorded 35.4% of the number of true counts recorded by the uEXPLORER system, suggesting such a system could acquire a total-body PET image of diagnostic quality in a time span in the order of 2 minutes and a temporal resolution of ~0.3 s.
Conclusion:
Using dual-ended side-readout, we expect to be able to develop a total-body PET insert for the META-scan system, with sufficient axial FOV length and sensitivity to perform simultaneous drug tracing or metabolic PET imaging anywhere in the human body.
| Track | PSMR |
|---|---|
| Presentation type | Oral |