In vivo imaging
Molecular imaging such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) are major keystones in preclinical research for studying animal models of human diseases. Molecular imaging represents the link between discoveries at the molecular level and clinical implementation of novel diagnoses or treatment approach.
These tools provide a unique opportunity for studying disease and other physiological processes in 'real time', both quantitatively and at the molecular level. By using functional radioactive molecules, PET and SPECT have the ability to non-invasively observe specific cellular or molecular processes.
When combined with techniques such as blood sampling, kinetic modelling and Monte-Carlo simulation, a more comprehensive view of the processes being investigated can be obtained. Due to the non-invasive nature of PET and SPECT imaging this can be performed longitudinally to follow the processes over days, weeks, and months. This is a unique experimental paradigm, reducing variability within the population investigated and modelling individual subject’s response to the treatment.
- Functional imaging: PET/CT
- Functional imaging: SPECT/CT
- Functional imaging: PET/SPECT/CT
- Structural imaging: MicroCT
- Imaging Quantification.
Functional Imaging: PET/CT, SPECT/CT, PET/SPECT/CT
ANSTO operates three Siemens Inveon multimodality preclinical imaging systems designed for small animal (rat/mouse) applications: two dual-modality PET/CT systems and one tri-modality PET/SPECT/CT system. Each of these can be applied on their own or in combination with the other modalities, the most common being PET/CT or SPECT/CT.
PET has the advantage of high sensitivity and true dynamic imaging compared to SPECT imaging. The PET component has a field of view of 12.7cm (axial) by 8cm (trans-axial), with a 1.4mm spatial resolution. We also have the ability to image two mice simultaneously side-by-side (up to 35g each) with the vital signs of each animal being individually monitored.
SPECT has the advantage of a large array of radio-isotopes available for imaging while also having much higher spatial resolution but much lower sensitivity (due to requiring physical collimation), however the time intervals are not as flexible as PET thus performing dynamic imaging is more complex. The SPECT component is an opposing 2-head detector system with an energy range of 30-300keV and an array of pinhole collimator options: three for mouse imaging and three for rat imaging, with each set containing a single pinhole and two multi-pinhole collimators for each head. A Low-Energy All-Purpose (LEAP) parallel-hole collimator is also available for planar imaging using a single head with isotopes of energies less than 140keV. The available fields of view vary for each collimator and can extend up to 250mm axially, however the system is only capable of imaging a single animal at a time with the pinhole collimators due to small trans-axial fields of view. The spatial resolution for each collimator set ranges are: 0.8-1.5mm for the mouse pinhole set, 2.1-2.7mm for the rat pinhole set, and 2-8mm for the LEAP (from collimator face up to 10cm from collimator face respectively).
Structural Imaging: MicroCT
The microCT component of the Inveon system is primarily used for attenuation and scatter corrections of PET and SPECT data by performing a low-magnification CT scan in sequence with the PET(/CT) or SPECT(/CT) imaging with a known co-registration. This also has the advantage of providing structural information which can aid in generating more accurate regions of interest. The microCT is also capable of performing high-magnification scans up to a resolution of 40µm (high magnification has a maximum 20mm trans-axial field of view). All CT scans are reconstructed into a 3D volume which can be manipulated and viewed as virtual slices.
Experimental imaging studies on living organisms can offer only limited repeatability due to the intrinsic variability between individuals. In such cases, it may be preferable to perform high quality simulation-based studies as a precursor to an experimental study, in order to optimise the parameters of the study (such as dosage, parameters of the scanning protocol etc.) and to determine the expected range of signal quality. This reduces the uncertainties involved in experiments and minimises the time and resources required for the successful completion of the experimental study. ANSTO’s Radiobiology and Bioimaging capabilities include expertise in the simulation of dynamic PET studies, conducted on a Monte-Carlo simulation platform developed in-house by ANSTO scientists, with highly realistic and experimentally validated models of PET scanners including the Ecat Exact HR+ human scanner, the R4 and P4 preclinical scanners and for the Siemens Inveon preclinical scanners.
A key aspect of the PET capabilities within Radiobiology and Bioimaging is our expertise in advanced image reconstruction methods optimised for dynamic PET. These methods reduce the effect of a number of well known PET imaging artefacts (such as partial volume effect, spill over and positron range) and enable the extraction of largely noise-free 4D activity distributions in both simulation and experimental studies. These techniques have been proven effective in the in vivo quantification of the density and affinity of D2 dopamine receptors in rodent brains and has been applied successfully with other radiotracers and kinetic modelling techniques.
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Phone: +61 2 9717 3143