Design Study for MRC-SPECT-II: A new generation of MR-Compatible SPECT System bioinspired by superposition compound eyes for ultrahigh resolution SPECT Imaging

91 Objectives We will report the results from a design study towards the second generation MRI compatible SPECT system, the MRC-SPECT-II [1], based on the synthetic inverted compound eye (S-ICE) gamma camera concept bioinspired by superposition compound eyes often found in small invertebrates [2]. Methods As an ommatidium is the photoreceptor unit in the natural compound eye, the basic element in the MRC-SPECT-II system is the micro-pinhole-camera-element (MPCE) that consists of a narrow-open-angle pinhole which projects a small fraction of the object volume onto a small and non-overlapping active area of the high-resolution gamma ray detector. A S-ICE gamma camera is a 3D arrangement of several S-ICE camera modules, dense 2D arrays in which different types of independent MCPEs are distributed with different density. The uniqueness of this system design is the ability to combine attractive features: on one hand, the very large number of different MCPEs surrounding the object ensures a dramatically improved sensitivity, maintains an excellent imaging resolution and shows an unprecedented density of angular sampling in the field-of-view (FOV), providing a much more flexibility in imaging performance due to the combination of different types of MCPEs. On the other hand, the compact system design could be placed inside small-bore pre-clinical MRI scanners allowing to take MRI and SPECT imaging simultaneously. The MRC-SPECT II design has 3 module rings along axial direction, each composed by 8 S-ICE modules (Fig. 1.A). Each S-ICE module consists of 8×8 array of independent and closely packed MPCEs, making a total of 1536 MPCEs in the whole system. In each MCPE, a custom-designed CdTe hybrid pixel detector that offers an active area of 2.56 cm × 2.56 cm, divided into 256 × 256 square pixels of 100 μm ×100 μm pitch, is coupled to a S-ICE aperture that is made of platinum (90%)-iridium (10%) alloy. Results The MRC-SPECT-II system and preliminary analysis of imaging performance will be presented. We specifically have carried out an experimental study to compare the imaging performance of the MRC-SPECT-II system against the MRC-SPECT-I system (Fig. 1.B) [3] to demonstrate its benefits. The MRC-SPECT-II system prototype is composed of 2-head S-ICE camera modules (Fig. 1.C) mounted on a 4D XYZ-rotation stage for experimentally acquiring the projection data, mimicking the dataset from the full MRC-SPECT-II system. Fig. 1.D compares the simulated image quality of the MRC-SPECT-II system and the MRC-SPECT-I system for imaging beta-amyloid plaques in mouse brain Parkinson’s disease model, while Fig. 1.E shows a comparison between the sensitivity offered by the MRC-SPECT-I system, and the MRC-SPECT-II system. We have also carried out a combined Monte-Carlo/analytical study to optimize the S-ICE gamma camera design: the composition and the distribution of different types of MCPEs inside each S-ICE camera module have been determined optimizing trade-offs among spatial resolution, sensitivity and imaging FOV. Fig. 1.F shows a comparison between the sensitivity offered by the “original” ICE-camera design that uniformly consists of high-resolution-small-FOV (HRSF) MCPEs only, and the S-ICE camera design composed of both HRSF and medium-resolution-large-FOV (MRLF) MCPEs. These results will be further discussed in this presentation. Conclusions We have explored the use of the S-ICE gamma camera design for ultrahigh resolution SPECT imaging. It shows the potential of dramatically improving the balance of spatial-resolution, sensitivity and FOV, providing unprecedented flexibility for different imaging applications and, at the same time, ensuring a compact design. This system could be used as the basis of the MRC-SPECT-II system, the second generation MR-compatible SPECT system that could offer a dramatically improved image quality over our existing MRC-SPECT-I system developed in our lab.