AdaptiSPECT-C: Mechanical Design and Front-End Electronics

Abstract

Gamma-ray detectors operating under the tracer principle have been widely used in medical imaging for decades. One such application is single-photon computed tomography (SPECT), which reconstructs 3-dimensional images of radiotracer concentration in vivo, revealing regions of biological function inside a body. For most of SPECT's history, the dominant technology used to sense gamma energy deposition events was that of photomultiplier tubes (PMTs). A majority of gamma cameras used in SPECT applications employ an array of PMTs to isolate the location of gamma-ray interaction inside the camera; the collection of PMT signals provides essential information to determine the origin of the gamma-ray emission and reconstruct an image. Recent advances in solid-state detectors have introduced a viable alternative to PMTs as a means to detect signals with single-photon sensitivity: the silicon photomultiplier (SiPM). SiPMs have numerous attractive properties that make them well suited to the tasks required for gamma cameras; namely, fine pixelation, low profile, and high gain. Augmenting an array of PMTs in a gamma camera with SiPMs can produce higher resolution images, enabling radiologists and drug researchers to conduct studies with higher accuracy and lower probability of error. Another major development of the 21st century was the advent of 3-dimensional additive manufacturing techniques using metal. A 3-D tungsten printer enables entirely new geometries to fabricate, including pinhole apertures used as SPECT image forming devices. Moreover, the custom printed pinholes are easily made into formats having adjustable diameters to fine-tune imaging properties in a SPECT session. This, coupled with the new SiPM arrays, forms the foundation of the new technology brought to bear in AdaptiSPECT-C, a stationary clinical whole-brain SPECT imager. AdaptiSPECT-C will be used in drug discovery research targeting neurodegenerative diseases such as Parkinson's and Alzheimer's. The novel incorporation of hybrid PMT / SiPM cameras and dynamically adaptable apertures will produce images at higher resolution and with higher fidelity pharmacokinetic information than rival systems, positioning it as a leading technology in drug development for neurodegenerative disease. This dissertation covers the development of AdaptiSPECT-C hardware, addressing the early performance simulations, the mechanical design of its cameras and gantry structure, and the electrical design of its front-end electronics, with results from prototype unit testing. Ultimately, by demonstrating functional prototype cameras, the work in this dissertation establishes a strong proof-of-concept for AdaptiSPECT-C as a system, and offers a roadmap for its imminent completion.