Figure - available from: Biomedical Physics & Engineering Express
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Activity recovery (%) at the iteration-of-interest for the 17 brain structures in the brain perfusion phantom for the simulated acquisition schemes with low-count and high-count scenarios. The true activity recovery value is 100%. Note the MUX-free ground truth scheme was simulated with 5 times higher phantom activity level than that of schemes #1—3 to compensate for its lower sensitivity. Shown are mean values over the noise realizations plus one standard deviation. Note that some of the standard deviation values are too small to be clearly visualized on the graphs.
Source publication
Application of multi-pinhole collimator in pinhole-based SPECT increases detection sensitivity. The presence of multiplexing in projection images due to the usage of multiple pinholes can further improve the sensitivity at the cost of adding data ambiguity. We are developing a next-generation adaptive brain-dedicated SPECT system -AdaptiSPECT-C. Th...
Citations
... We are constructing a multi-pinhole, stationary, adaptable SPECT system dedicated to clinical brain imaging and capable of dynamic imaging, which we named AdaptiSPECT-C (Zeraatkar et al 2020, Auer et al 2021, Zeraatkar et al 2021a, 2021b. Some research groups have described the usage of SPECT simulation employing mesh modeling of a few system components, such as the collimator, but the limited number of detector modules arranged in a simple configuration remains modeled via primitive objects and replicate tools for which projections can be generated automatically via the built-in tools currently available in GATE (Nguyen et al 2019). ...
... Each module of AdaptiSPECT-C can be irradiated by up to 5 pinholes, the status (i.e. closed or opened) and size of which can be adapted to the imaging task for highperformance imaging (Momsen et al 2018, Zeraatkar et al 2021b. For the purposes of this study, each of the 23 modules was associated to a single knife-edge pinhole, 4 mm in diameter, with an 80.5°opening angle (Auer et al 2021). ...
Objective:
Monte-Carlo simulation studies have been essential for advancing various developments in SPECT imaging, such as system design and accurate image reconstruction. Among the simulation software available, GATE is one of the most used simulation toolkits in nuclear medicine, which allows building systems and attenuation phantom geometries based on the combination of idealized volumes. However, these idealized volumes are inadequate for modeling free-form shape components of such geometries. Recent GATE versions alleviate these major limitations by allowing users to import triangulated surface meshes.
Approach:
In this study, we describe our mesh-based simulations of a next-generation multi-pinhole SPECT system dedicated to clinical brain imaging, called AdaptiSPECT-C. To simulate realistic imaging data, we incorporated in our simulation the XCAT phantom, which provides an advanced anatomical description of the human body. An additional challenge with the AdaptiSPECT-C geometry is that the default voxelized XCAT attenuation phantom was not usable in our simulation due to intersection of objects of dissimilar materials caused by overlap of the air containing regions of the XCAT beyond the surface of the phantom and the components of the imaging system.
Main results:
We validated our mesh-based modeling against the one constructed by idealized volumes for a simplified single vertex configuration of AdaptiSPECT-C through simulated projection data of 123I-activity distributions. We resolved the overlap conflict by creating and incorporating a mesh-based attenuation phantom following a volume hierarchy. We then evaluated our reconstructions with attenuation and scatter correction for projections obtained from simulation consisting of mesh-based modeling of the system and the attenuation phantom for brain imaging. Our approach demonstrated similar performance as the reference scheme simulated in air for uniform and clinical-like 123I-IMP brain perfusion source distributions.
Significance:
This work enables the simulation of complex SPECT acquisitions and reconstructions for emulating realistic imaging data close to those of actual patients.
Objective. Single-photon emission computed tomography (SPECT) with pinhole collimators can provide high-resolution imaging, but is often limited by low sensitivity. Acquiring projections simultaneously through multiple pinholes affords both high resolution and high sensitivity. However, the overlap of projections from different pinholes on detectors, known as multiplexing, has been shown to cause artefacts which degrade reconstructed images. Approach. Multiplexed projection sets were considered here using an analytic simulation model of AdaptiSPECT-C—a brain-dedicated multi-pinhole SPECT system. AdaptiSPECT-C has fully adaptable aperture shutters, so can acquire projections with a combination of multiplexed and non-multiplexed frames using temporal shuttering. Two strategies for reducing multiplex artefacts were considered: an algorithm to de-multiplex projections, and an alternating reconstruction strategy for projections acquired with a combination of multiplexed and non-multiplexed frames. Geometric and anthropomorphic digital phantoms were used to assess a number of metrics. Main results. Both de-multiplexing strategies showed a significant reduction in image artefacts and improved fidelity, image uniformity, contrast recovery and activity recovery (AR). In all cases, the two de-multiplexing strategies resulted in superior metrics to those from images acquired with only mux-free frames. The de-multiplexing algorithm provided reduced image noise and superior uniformity, whereas the alternating strategy improved contrast and AR. Significance. The use of these de-multiplexing algorithms means that multi-pinhole SPECT systems can acquire projections with more multiplexing without degradation of images.
