Improving timing performance of double-ended readout in TOF-PET detectors.

Scintillation crystals of 20mm length or longer are needed for clinical time-of-flight positron emission tomography (TOF-PET) to ensure effective detection efficiency for gamma photons. However, the use of long crystals would deteriorate the key performance of TOF-PET detectors, time and spatial resolution, because of the variations in the travel times of the photons in crystals and the effects of parallax errors. In this work, we studied double-ended readout TOF-PET detectors based on coupling a long scintillation crystal to SiPMs at both ends for correcting the depth-dependent effects to improve the coincidence time resolution (CTR).

Optimized Scintillator YAG:Pr Nanoparticles for X-ray Inducible Photodynamic Therapy.

We describe a sol-gel synthetic method for the production of praseodymium-doped yttrium aluminum garnet (YAG) nanoparticles suitable for X-ray inducible photodynamic therapy (X-PDT). Our sol-gel based approach was optimized by varying temperature and time of calcination, resulting in nanoparticles that were smooth, spherical, and 50-200 nm in crystallite size. The powders were uniformly coated with a thin (10 nm) layer of silica to facilitate surface conjugation with functional moieties.

Monte Carlo simulations of time-of-flight PET with double-ended readout: calibration, coincidence resolving times and statistical lower bounds.

This paper demonstrates through Monte Carlo simulations that a practical positron emission tomograph with (1) deep scintillators for efficient detection, (2) double-ended readout for depth-of-interaction information, (3) fixed-level analog triggering, and (4) accurate calibration and timing data corrections can achieve a coincidence resolving time (CRT) that is not far above the statistical lower bound. One Monte Carlo algorithm simulates a calibration procedure that uses data from a positron point source. Annihilation events with an interaction near the entrance surface of one scintillator are selected, and data from the two photodetectors on the other scintillator provide depth-dependent timing corrections.

Bright and ultra-fast scintillation from a semiconductor?

Semiconductor scintillators are worth studying because they include both the highest luminosities and shortest decay times of all known scintillators. Moreover, many semiconductors have the heaviest stable elements (Tl, Hg, Pb, Bi) as a major constituent and a high ion pair yield that is proportional to the energy deposited. We review the scintillation properties of semiconductors activated by native defects, isoelectronic impurities, donors and acceptors with special emphasis on those that have exceptionally high luminosities (e.

Monte Carlo calculations of PET coincidence timing: single and double-ended readout.

We present Monte Carlo computational methods for estimating the coincidence resolving time (CRT) of scintillator detector pairs in positron emission tomography (PET) and present results for Lu2SiO5 : Ce (LSO), LaBr3 : Ce, and a hypothetical ultra-fast scintillator with a 1 ns decay time. The calculations were applied to both single-ended and double-ended photodetector readout with constant-fraction triggering. They explicitly include (1) the intrinsic scintillator properties (luminosity, rise time, decay time, and index of refraction), (2) the exponentially distributed depths of interaction, (3) the optical photon transport efficiency, delay, and time dispersion, (4) the photodetector properties (fill factor, quantum efficiency, transit time jitter, and single electron response), and (5) the determination of the constant fraction trigger level that minimizes the CRT.

MODELING TIME DISPERSION DUE TO OPTICAL PATH LENGTH DIFFERENCES IN SCINTILLATION DETECTORS.

We characterize the nature of the time dispersion in scintillation detectors caused by path length differences of the scintillation photons as they travel from their generation point to the photodetector. Using Monte Carlo simulation, we find that the initial portion of the distribution (which is the only portion that affects the timing resolution) can usually be modeled by an exponential decay. The peak amplitude and decay time depend both on the geometry of the crystal, the position within the crystal that the scintillation light originates from, and the surface finish.

Fundamental limits of scintillation detector timing precision.

In this paper we review the primary factors that affect the timing precision of a scintillation detector. Monte Carlo calculations were performed to explore the dependence of the timing precision on the number of photoelectrons, the scintillator decay and rise times, the depth of interaction uncertainty, the time dispersion of the optical photons (modeled as an exponential decay), the photodetector rise time and transit time jitter, the leading-edge trigger level, and electronic noise. The Monte Carlo code was used to estimate the practical limits on the timing precision for an energy deposition of 511 keV in 3 mm × 3 mm × 30 mm Lu2SiO5:Ce and LaBr3:Ce crystals.

Shallow impurity level calculations in semiconductors using ab initio methods.

An ab initio method is presented to calculate shallow impurity levels in bulk semiconductors. This method combines the GW calculation for the treatment of the central-cell potential with a potential patching method for large systems (with 64,000 atoms) to describe the impurity state wave functions. The calculated acceptor levels in Si, GaAs, and an isovalent bound state of GaP are in excellent agreement with experiments with a root-mean-square error of 8.

Ba(11)La(4)Br(34): a new barium lanthanum bromide.

The structure of the title compound, barium lanthanum bromide (11/4/34), can be derived from the fluorite structure. The asymmetric unit contains two Ba sites (one with site symmetry 4/m..

A retrospective on the LBNL PEM project.

We present a retrospective on the LBNL Positron Emission Mammography (PEM) project, looking back on our design and experiences. The LBNL PEM camera utilizes detector modules that are capable of measuring depth of interaction (DOI) and places them into 4 detector banks in a rectangular geometry. In order to build this camera, we had to develop the DOI detector module, LSO etching, Lumirror-epoxy reflector for the LSO array (to achieve optimal DOI), photodiode array, custom IC, rigid-flex readout board, packaging, DOI calibration and reconstruction algorithms for the rectangular camera geometry.

Lu2SiO5 by single-crystal X-ray and neutron diffraction.

The structure of dilutetium silicon pentaoxide, Lu2SiO5, has isolated ionic SiO4 tetrahedral units and non-Si-bonded O atoms in distorted OLu4 tetrahedra. The OLu4 tetrahedra form edge-sharing infinite chains and double O2Lu6 tetrahedra along the c axis. The edge-sharing chains are connected to the O2Lu6 double tetrahedra by isolated SiO4 units.

Advances in positron tomography for oncology.

Development of PET instrumentation over the past 42 years has moved from simple dual-detector coincidence scanners, to proposed systems having 60,000 detectors and simultaneous coverage of 15-cm regions of the body with spatial resolutions better than 4 mm. The principal determinants of positron emission tomography (PET) instrumentation advances are positron range, noncollinearity of the annihilation photons, scattering, random event rates, detector size, efficiency, speed and light output; capability to correct for depth of crystal interaction, attenuation compensation, axial coverage, and rapid data analysis and presentation. While general-purpose systems with 2-mm resolution are expected, special-purpose PET devices are being built for breast and brain tumor studies with resolutions from 1.

Clinical evaluation of a high-resolution (2.6-mm) positron emission tomography.

The intrinsic resolution of the Donner 600-crystal positron emission tomograph (PET 600) is 2.6 mm full width at half maximum (FWHM) in-plane and 6 mm FWHM axially. More than 100 patients with glioma, radiation necrosis, Alzheimer disease, or epilepsy have been studied with this system.

Instrumentation for positron emission tomography.

Positron emission tomography with a spatial resolution of 2 mm full width at half maximum for quantitation in regions of interest 4 mm in diameter will become possible with the development of detectors that achieve ultrahigh resolution. Improved resolution will be possible using solid-state photodetectors for crystal identification or photomultiplier tubes with many small electron multipliers . Temporal resolution of 2 seconds and gating of cyclic events can be accomplished if statistical requirements are met.

Regional cerebral metabolic alterations in dementia of the Alzheimer type: positron emission tomography with [18F]fluorodeoxyglucose.

Alzheimer disease is the most common cause of dementia in adults. Despite recent advances in our understanding of its anatomy and chemistry, we remain largely ignorant of its pathogenesis, physiology, diagnosis, and treatment. Dynamic positron emission tomography using [18F]fluorodeoxyglucose (FDG) was performed on the Donner 280-crystal ring in 10 subjects with dementia of the Alzheimer type and six healthy age-matched controls.

Brain tumor evaluation using Rb-82 and positron emission tomography.

Positron emission tomography of the brain with 75-sec rubidium-82 obtained from a portable generator (25-day Sr-82 leads to Rb-82) was used to evaluate the integrity of the blood-brain barrier (BBB) in patients with brain tumors. Rubidium is normally excluded from the central nervous system by the intact BBB, but when the BBB is disrupted by a tumor. Rb enters and pools in the extravascular spaces of the central nervous system.

Method for optimizing side shielding in positron-emission tomographs and for comparing detector materials.

This report presents analytical formulas for the image-forming and background event rates seen by circular positron-emission tomographs with parallel side shielding. These formulas include deadtime losses, detector efficiency, coincidence resolving time, amount of activity, patient port diameter, shielding gap, and shielding depth. A figure of merit, defined in terms of these quantitites, describes the signal-to-noise ratio in the reconstructed image of a 20-cm cylinder of water with uniformly dispersed activity.

Quantitative potentials of dynamic emission computed tomography.

Statistical uncertainties in emission computed tomography were simulated in 60 computer studies involving various numbers of events and distributions of activity. Previous studies have shown that for a uniform disc of activity of rms percentage of uncertainty per resolution cell is: 120 X (number of resolution cells)1/4 X (number of events per resolution cell)- 1/2. In this work we examined the more general situation where one or two regions of uniform activity are surrounded by a uniform background, and found that for an equal number of recorded events the uncertainties were reduced when the activity was concentrated in a portion of the field.

Three dimensional imaging of the myocardium with radionuclides.

Transverse sections of the distribution of 129Cs and 201Ti in the human myocardium were obtained using 36 and 72 views of the thorax with a large field of view Anger camera. The cardiac cycle was divided into 100-msec intervals to obtain motion images of an average cycle of the beating heart. At least 300,000 events must be detected for each cardiac phase of each section for quantitative work.

Emission computer assisted tomography with single-photon and positron annihilation photon emitters.

Computed transverse section emission tomography using 99mTc with the Anger camera is compared to positron annihilation coincident detection using a ring of crystals and 68Ga. The single-photon system has a line spread function (LSF) of 9 mm full width at half maximum (FWHM) at the collimator and gives a transverse section reconstruction LSF of 11 mm FWHM with 144 views. The positron ring has a LSF of 6 mm at the center with a transverse section reconstruction LSF of 7.

Analytical study of a high-resolution positron ring detector system for transaxial reconstruction tomography.

This paper presents an analytical study of a high-resolution positron ring detector system for transaxial reconstruction tomography. Our goal is a combination of good spatial resolution, high sensitivity, rejection of scattered photons, variable section thickness, and the minimization of the number of photomultipliers and coincidence circuits. A circular ring of 288 NaI(Tl) crystals 0.