Design and Fabrication of Multi-Pinhole Collimators for Brain Imaging on Clinical SPECT

1508 Objectives: Our goal was to design and fabricate multi-pinhole (MPH) collimators for human brain imaging using a clinical SPECT (single photon emission computed tomography) camera. One MPH collimator was designed specifically to image the striatum in order to improve detection of Parkinson’s Disease, and a second was designed for full brain imaging. Methods: MPH collimator designs were simulated and optimized for striatum and full brain imaging, which lead to two configurations with different magnification and field of view requirements. Based on these requirements, a fabrication strategy was developed based on modifying an existing collimator from a commercial SPECT system (BrightView SPECT/CT, Philips Healthcare) to facilitate interfacing of the new MPH collimators to the commercial detector head. The original single pinhole cone was removed and a larger opening created to accommodate the MPH collimators and asymmetrical four-sided pyramidal structures (frames) supporting them at the desired distances from the detector. The frames were created from machinable tungsten plates bolted together with an interlocking design to create gamma-ray leakage-free joints. An interlocking design was also used for the MPH plate. The shielding components were constructed with a 20mm thickness to reduce penetration of the low-abundance high-energy (>500 keV) gamma-rays of I-123. The physical design was constrained by a desire to not exceed the net weight of the original SPECT collimator, which was 131 kilograms. Lastly, the pinholes themselves, which have a mixture of symmetrical on-axis and asymmetrical off-axis geometries, were created with a metal rapid-prototype printer that operates by fusing fine tungsten powder according to a computer-aided drawing (CAD) design. Results: Using finite element analysis (FEA) it was determined that the proposed design has a sufficient strength and number of fasteners to hold all components in rigid alignment to each other throughout a 360-degree acquisition rotation. Additionally, we found that the stress on the shields will not cause failure or buckling at any contact points. The mass of the assembly was calculated to closely match the mass of the original single-pinhole collimator. The metal printed pinhole parts required minor printing alterations and minor post-curing alterations in order to fit precisely into the top plate assembly. Conclusions: We have found that it is possible to modify existing clinical SPECT system collimators to optimize them for striatum and whole brain imaging. Metal printing of the pinholes for these modified systems provides a convenient and cost-effective way to fabricate pinhole inserts with a variety of oblique axes and clearance cones. Acknowledgement: This work was partially supported by NIH/NIBIB grant 5R01EB022092-04