Timing, Energy, and Spatial Characterization of Highly Sampled Monolithic PET Detectors with Different Thicknesses.

The HyPET project proposes a hybrid dedicated TOF-PET for prostate imaging, with pixelated detector blocks in the front layer and monolithic blocks in the back layer. In this work, four detector configurations have been experimentally evaluated for the rear detector layer. The detector configuration consists of LYSO monolithic blocks with the same size (25.

Performance Characteristics of a Dual-Sided Position-Sensitive Sparse-Sensor Detector for Gamma-ray Imaging.

Purpose: We characterize the performance of a dualsided position-sensitive sparse sensor (DS-PS3) array detector for positron emission tomography (PET). The DS-PS3 detector is designed as a high performance, cost effective PET detector for organ-specific imaging systems (e.g.

Development and testing of SPECT/CT lung phantoms made from expanding polyurethane foam.

Purpose: Currently, single-photon emission computed tomography (SPECT)/computed tomography (CT) lung phantoms are commonly constructed using polystyrene beads and interstitial radioactive water. However, this approach often results in a phantom with a density (typically -640 HU) that is considerably higher than that of healthy lung (-750 to -850 HU) or diseased lung (-900 to -950 HU). Furthermore, the polystyrene and water phantoms are often quite heterogeneous in both density and activity concentration, especially when reused.

Depth of Interaction Calibration and Capabilities in 2×2 Discrete Crystal Arrays and Digital Silicon Photomultipliers.

Digital silicon photomultiplers (dSiPMs) have potential in the advancement of PET detectors. Their advantages include decreased dark counts through selective microcell activation, fast timing, and flexibility configuring event triggering and collection. Further improvements in PET image resolution are possible when photon depth of interaction (DOI) is available, as this reduces parallax error caused by mispositioning events at the peripheral field of view.

Cherenkov luminescence measurements with digital silicon photomultipliers: a feasibility study.

Background: A feasibility study was done to assess the capability of digital silicon photomultipliers to measure the Cherenkov luminescence emitted by a β source. Cherenkov luminescence imaging (CLI) is possible with a charge coupled device (CCD) based technology, but a stand-alone technique for quantitative activity measurements based on Cherenkov luminescence has not yet been developed. Silicon photomultipliers (SiPMs) are photon counting devices with a fast impulse response and can potentially be used to quantify β-emitting radiotracer distributions by CLI.

Light-Sharing Interface for dMiCE Detectors Using Sub-Surface Laser Engraving.

We have previously reported on dMiCE, a method of resolving depth or interaction (DOI) in a pair of discrete crystals by encoding light sharing properties as a function of depth in the interface of a crystal-element pair. A challenge for this method is the cost and repeatability of interface treatment for each crystal pair. In this work, we report our preliminary results on using sub-surface laser engraving (SSLE) as a means of forming this depth-dependent interface in a dMiCE detector.

Effects of Detector Thickness on Geometric Sensitivity and Event Positioning Errors in the Rectangular PET/X Scanner.

We used simulations to investigate the relationship between sensitivity and spatial resolution as a function of crystal thickness in a rectangular PET scanner intended for quantitative assessment of breast cancers. The system had two 20 × 15-cm and two 10 × 15-cm flat detectors forming a box, with the larger detectors separated by 4 or 8 cm. Depth-of-interaction (DOI) resolution was modeled as a function of crystal thickness based on prior measurements.

Light-Sharing Interface for dMiCE Detectors using Sub-Surface Laser Engraving.

We have previously reported on dMiCE, a method of resolving depth or interaction (DOI) in a pair of discrete crystals by encoding light sharing properties as a function of depth in the interface of this crystal-element pair. A challenge for this method is the cost and repeatability of interface treatment for a crystal pair. In this work, we report our preliminary results on using sub-surface laser engraving (SSLE) as a means of forming this depth-dependent interface in a dMiCE detector.

SCOUT: a fast Monte-Carlo modeling tool of scintillation camera output.

We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout of a scintillation camera. In this work, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera.

Multiple-hit parameter estimation in monolithic detectors.

We examine a maximum-a-posteriori method for estimating the primary interaction position of gamma rays with multiple interaction sites (hits) in a monolithic detector. In assessing the performance of a multiple-hit estimator over that of a conventional one-hit estimator, we consider a few different detector and readout configurations of a 50-mm-wide square cerium-doped lutetium oxyorthosilicate block. For this study, we use simulated data from SCOUT, a Monte-Carlo tool for photon tracking and modeling scintillation- camera output.

A Prototype Detector for a Novel High-Resolution PET System: BazookaPET.

We have designed and are developing a novel proof-of-concept PET system called BazookaPET. In order to complete the PET configuration, at least two detector elements are required to detect positron-electron annihilation events. Each detector element of the BazookaPET has two independent data acquisition channels.

Use of Cramer-Rao Lower Bound for Performance Evaluation of Different Monolithic Crystal PET Detector Designs.

We have previously reported on continuous miniature crystal element (cMiCE) PET detectors that provide depth of interaction (DOI) positioning capability. A key component of the design is the use of a statistics-based positioning (SBP) method for 3D event positioning. The Cramer-Rao lower bound (CRLB) expresses limits on the estimate variances for a set of deterministic parameters.

List-mode MLEM Image Reconstruction from 3D ML Position Estimates.

Current thick detectors used in medical imaging allow recording many attributes, such as the 3D location of interaction within the scintillation crystal and the amount of energy deposited. An efficient way of dealing with these data is by storing them in list-mode (LM). To reconstruct the data, maximum-likelihood expectation-maximization (MLEM) is efficiently applied to the list-mode data, resulting in the list-mode maximum-likelihood expectation-maximization (LMMLEM) reconstruction algorithm.

Multiple-hit parameter estimation in monolithic detectors.

We examine a maximum-a-priori (MAP) method for estimating the primary interaction position of gamma rays with multiple-interaction sites (hits) in a monolithic detector. In assessing the performance of a multiple-hit estimator over that of a conventional one-hit estimator, we consider a few different detector and readout configurations of a 50-mm-wide square LSO block. For this study, we use simulated data from SCOUT, a Monte-Carlo tool for photon tracking and modeling scintillation-camera output.

Measurements of entrance-surface vs. conventional single-ended readout of a monolithic scintillator.

Availability of compact high-gain, low-noise Silicon Photomultipliers (SiPM) prompts us to examine readout sensors on the entrance surface (SES) as compared to the conventional single-ended readout with sensors on the opposing surface. We measured detector response statistics versus 3D position for these configurations using an 8×8 SiPM array on a 15-mm-thick by 32-mm-wide LYSO block. We calibrate an independently distributed multivariate-normal likelihood model and use it to generate maximum-likelihood estimates of 3D interaction position.

Parametric Design Study of a Long Axial Field-of-View PET Scanner using a Block-Detector Tomograph Simulation of a Cylindrical Phantom.

We are conducting a two-phase study, which aims to select design parameters of a long-axis positron emission tomography (PET) scanner that are a compromise between detection performance and cost. In this first phase, we examine the effects of axial length, detector thickness and collimator geometry on the noise equivalent count rate per axial length (λNEC) and noise equivalent count rate per slice (dNEC). We use these metrics as approximate, but quickly computed, indicators of a PET-scanner's performance at a detection task.

Measured Temperature Dependence of Scintillation Camera Signals Read Out by Geiger-Müller Mode Avalanche Photodiodes.

We are developing a prototype monolithic scintillation camera with optical sensors on the entrance surface (SES) for use with statistically-estimated depth-of-interaction in a continuous scintillator. We opt to use Geiger-Müller mode avalanche photodiodes (GM-APDs) for the SES camera since they possess many desirable properties; for the intended application (SES and PET/MR imaging), they offer a thin attenuation profile and an operational insensitivity to large magnetic fields. However, one issue that must be addressed in using GM-APDs in an RF environment (as in MR scanners) is the thermal dissipation that can occur in this semiconductor material.

Calibration Method for ML Estimation of 3D Interaction Position in a Thick Gamma-Ray Detector.

High-energy (> 100 keV) photon detectors are often made thick relative to their lateral resolution in order to improve their photon-detection efficiency. To avoid issues of parallax and increased signal variance that result from random interaction depth, we must determine the 3D interaction position in the imaging detector. With this goal in mind, we examine a method of calibrating response statistics of a thick-detector gamma camera to produce a maximum-likelihood estimate of 3D interaction position.

Maximum-Likelihood Methods for Processing Signals From Gamma-Ray Detectors.

In any gamma-ray detector, each event produces electrical signals on one or more circuit elements. From these signals, we may wish to determine the presence of an interaction; whether multiple interactions occurred; the spatial coordinates in two or three dimensions of at least the primary interaction; or the total energy deposited in that interaction. We may also want to compute listmode probabilities for tomographic reconstruction.

SCOUT: A Fast Monte-Carlo Modeling Tool of Scintillation Camera Output.

We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout. Presently, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera.

Method of Calibrating Response Statistics for ML Estimation of 3D Interaction Position in a Thick-Detector Gamma Camera.

High-energy photon detectors are often made thick in order to improve their photon-detection efficiency. To avoid issues of parallax and increased signal variance that result from random interaction depth, we must determine the 3D interaction position in the imaging detector. With this goal in mind, we examine a method of calibrating response statistics of a thick-detector gamma camera to produce a maximum- likelihood estimate of 3D interaction position.

SemiSPECT: a small-animal single-photon emission computed tomography (SPECT) imager based on eight cadmium zinc telluride (CZT) detector arrays.

The first full single-photon emission computed tomography (SPECT) imager to exploit eight compact high-intrinsic-resolution cadmium zinc telluride (CZT) detectors, called SemiSPECT, has been completed. Each detector consists of a CZT crystal and a customized application-specific integrated circuit (ASIC). The CZT crystal is a 2.

SemiSPECT: A Small-animal Imaging System Based on Eight CdZnTe Pixel Detectors.

We have constructed a SPECT system for small animals that utilizes eight CdZnTe pixel detectors. The eight detectors are arranged in a single octagonal ring, where each views the object to be imaged through a single pinhole. Additional projections are obtained via rotation of the animal.