Andrew LaBella’s new paper titled ”Prismatoid light guide array for enhanced gamma ray localization in PET: a Monte Carlo simulation study of scintillation photon transport” was published in Phys. Med. Biol.
High spatial resolution PET relies on having excellent depth-of-interaction (DOI) resolution and small detector elements. Depth-encoding in PET modules has traditionally been performed using dual-ended readout. In recent years, researchers have explored the feasibility of replacing the second readout array with a light guide at the entrance layer that introduces intercrystal light sharing in order to reduce cost and make depth-encoding modules more compact. However, single-ended readout depth-encoding modules have suboptimal and non-uniform crystal separation and DOI performance due to the random light sharing patterns of the uniform light guide, resulting in degraded performance along the edges and corners of the detector arrays. In this paper, we introduce and characterize a segmented light guide composed of an array of prism mirrors which introduce deterministic intercrystal light sharing in single-ended readout PET detectors. We determined the expected spatial performance of our modules with our light guide using optical ray tracing Monte Carlo simulations. We demonstrate that having controlled, deterministic light sharing improves both DOI and crystal identification performance, enabling uniform spatial performance throughout the detector array. Designed specifically for high resolution PET, our prismatoid light guide array can be used to build cost-effective total-body and organ-dedicated PET systems with single-ended readout depth-encoding modules.
Our new paper titled “Ultra-low Dark Currents in Avalanche Amorphous Selenium Photodetectors using Solution-processed Quantum Dot Blocking Layer” was published in ACS Photonics.
In this paper, we propose a true solid-state alternative to the vacuum photomultiplier tube using amorphous selenium as the bulk avalanche i-layer. To achieve reliable and repeatable impact ionization gain without irreversible breakdown, a non-insulating metal oxide n-type hole-blocking/electron-transporting layer is needed. For the first time, we have deposited a solution-processed quantum dot (QD) hole blocking layer over an a-Se photoconductor at room temperature, without any surface or bulk crystallization. We have measured the lowest dark current density ever reported (30 pA/cm² at the onset of avalanche) compared to any other solid-state avalanche sensor at room temperature. Our results provide new strategies for the development of advanced solid-state photomultipliers via efficient QD-based interface layers to fully exploit the deterministic avalanche properties of a-Se.
Andrew LaBella’s third journal paper is accepted in the J Nucl Med. titled ” High Resolution Depth-Encoding PET Detector Module with Prismatoid Light Guide Array.”
Our work presents a revolutionary approach for performing high resolution PET imaging which is both practical and cost-eﬀective while being compatible with existing silicon photomultiplier-based readout systems and electronics. We’ve developed a light guide composed of a segmented array of prismatoids, which can be used to develop high resolution depth-encoding single-ended readout detector modules, which we call Prism-PET. We’ve fabricated and characterized Prism-PET detector modules with our prismatoid light guide using readout electronics currently employed in clinical PET systems. Prism-PET achieves perfect crystal identification accuracy throughout the entire detector array in both 4-to-1 and 9-to-1 coupled modules, along with 2.5 mm depth-of-interaction (DOI) resolution, which is the best reported experimental result in single-ended readout DOI modules. Our experimental results show that Prism-PET closely mimics the behavior and performance of dual-ended readout depth-encoding modules while also potentially enabling high count rate acquisition and excellent coincidence time resolution. Prism-PET can be used to develop PET systems for a wide array of applications, including small animal PET, organ-dedicated human PET and total-body human PET.
Andrew LaBella’s second paper “Convolutional Neural Network for Crystal Identification and Gamma Ray Localization in PET” is accepted for publication in IEEE Trans Rad Plasma Med Sc.
In this paper, we use convolutional neural networks (CNNs) for 3D gamma ray localization in PET detector arrays with multicrystal scintillators. We trained and tested our CNN on Monte Carlo simulated PET data. Our results demonstrate that our CNN can correctly identify the crystal where gamma ray absorption takes place with over 99% accuracy throughout the entire detector array, including at the edges and corners where crystal identification is most problematic. In addition, our CNN achieves 2.75 mm FWHM DOI resolution, which is similar to the performance of conventional DOI localization in dual-ended readout detectors. Preliminary results suggest our CNN may be able to overcome the spatial limitations of PET detectors and achieve sub-scintillator resolution. Additional studies will be performed with our CNN on experimental data to validate its utility in practice. Our CNN can be used to perform 3D gamma ray localization in cost-effective PET detector modules with high accuracy.
Andrew LaBella is awarded the 2019 Valentin T. Jordanov Radiation Instrumentation Travel Grant. Andy is the first author on all three papers accepted from Goldan Lab at the IEEE NSS/MIC conference in Manchester, UK. The papers cover topics ranging from our revolutionary and patented Prism-PET technology for ultra-high spatial resolution and ultra-high sensitivity TOF-DOI-Compton PET, to 100 ps TOF PET, and finally utilizing convolutional neural networks (CNNs) for enhanced 3D gamma-ray localization. Andy was also For more information, please click here.
Andrew LaBella publishes his first paper on “Picosecond Time Resolution with Avalanche Amorphous Selenium.”This paper appeared as a supplementary cover in ACS Photonics, vol. 6, issue 6. Congratulations Andy!
Picosecond timing in an avalanche amorphous selenium semiconductor is achieved by implementing Nano-Frisch grids along the collecting electrode to form a multiwell structure. The induced photocurrent following optical impulse exposure is independent of carrier motion outside the wells resulting in unipolar time-differential charge sensing via extended-state hot hole transport. This is the first experimental report of avalanche gain and picosecond time-resolution using an amorphous semiconductor. Further analysis suggests we may be able to achieve sub-100 picosecond coincidence timing resolution in time-of-flight PET using our multiwell selenium semiconductor as the photodetector.
Atreyo Mukherjee publishes his first paper on “Hole transport in selenium semiconductors using density functional theory and bulk Monte Carlo.” Congratulations Atreyo!
In this paper, we have considered effective mass approximations in the case of phonon-limited hole transport in selenium semi-conductors combined with simulated deformation potentials and Monte Carlo (MC) solutions to the Boltzmann transport equation (BTE). This method allows us to obtain microscopic access to carrier trajectories and relaxation dynamics, driven by acoustic and optical phonons, and ultimately calculate the low-field differential drift mobility and observe high field runaway effects. We first utilized density functional theory (DFT) simulations to calculate the density of states and acoustic/optical deformation potentials for the crystalline phases.
In general, we showed how holes in selenium can undergo both elastic (momentum relaxation) and inelastic (energy and momentum relaxation) collisions and yet get “hot,” thus gaining energy at a higher rate from the electric field than they lose to the lattice vibrations in the form of phonon scattering.
Dr. Goldan has been promoted to tenure-track assistant professor at Stony Brook University in the department of Radiology.
We are recruiting two PhD candidates and one Post Doctoral fellow for our work on medical imaging detectors. If you are interested, please forward your CV to Amirhossein.Goldan@stonybrookmedicine.edu. To learn more about our research, please click here.