Power-Efficient Multiplexing for High Resolution TOF PET Modules with Intercrystal Light Sharing

Background

Positron emission tomography (PET) is a powerful technique used in diagnosis, treatment selection, monitoring, and research in cancer and neuropsychiatric disorders. However, the technology has not been able to achieve its full potential due to its relatively poor spatial resolution. There have been several attempts at achieving high resolution PET, but as spatial resolution improves, the amount of data per PET scan greatly increases. The data size problem is further exacerbated by depth‑encoding, which is necessary to mitigate parallax error and fully reap the benefits of high resolution.

A similar effect is found by combining high resolution with time‑of‑flight (TOF) readout. As the data increases, the number of connections between the optical sensors and readout application‑specific integrated circuit (ASIC) increase, which increases the heat generated by the device. Utilizing a one‑to‑one coupling between readout pixels and channels is an inefficient method since not all of the pixels need to be read out per event. Single multiplexing, where signals read out by multiple optical sensors (pixels) per event are summed together, has been proposed to reduce the data size and complexity in order to make PET less computationally expensive. However, where the signals are multiplexed, solutions must still be able to determine primary optical sensor (pixel) interaction, primary scintillator module interaction, depth‑of‑interaction (DOI), and TOF.

In some multiplexing systems, the detector modules don’t have depth‑encoding capabilities, which is vital to achieve spatial resolution uniformity. Additionally, multiplexing schemes may also impact the timing resolution. However, when done properly, multiplexing can improve power efficiency, data efficiency and cost-effectiveness without sacrificing detector module performance.

Technology

Researchers at Stony Brook University (SBU) have developed a multiplexing scheme for deterministic light sharing PET modules like Prism‑PET, which can have a multiplexed readout that minimally impacts performance. Prism‑PET only requires the 4 highest readout signals per event to provide optimal DOI localization results. Since Prism‑PET localizes intercrystal light sharing to within the 4 nearest neighbor crystals through the use of a segmented prismatoid light guide array, multiplexing can be implemented without sacrificing spatial or energy resolutions.

In this embodiment, the pixel‑to‑channel coupling scheme is chosen such that channels only read out groups of pixels that aren’t expected to have intercrystal light sharing with each other. The proposed design can achieve up to 64‑to‑1 crystal‑to‑channel ratio by coupling crystals‑to‑pixels at 4‑to‑1 and pixels‑to‑channel at 16‑to‑1. The multiplexing scheme also reads out timestamps on the ASIC level rather than for each channel, further reducing power consumption without sacrificing coincidence time resolution. Thus, researchers have achieved a PET particle detection system with increased power efficiency, increased data efficiency, and improved cost of PET readout.

Advantages

• 16-to-1 crystal-to-channel coupling
• High energy resolution
• Good coincidence time resolution
• High depth of interaction (DOI) resolution readout
• Increased power-efficiency in PET readout
• Increased data-efficiency in PET readout
• Improved cost-effectiveness of PET readout

Application

• Positron emission tomography (PET)
• High resolution PET (including systems with depth of interaction readout) Time-of-flight PET
• Organ-specific PET
• Preclinical PET
• Any field that requires multiplexed readout
• Any field that uses scintillation detection systems (with and without light sharing)