Showing papers in "IEEE Transactions on Nuclear Science in 1982"
TL;DR: In this paper, an approximate analytical solution expressed as I(t) = Io [exp(-?t) - exp (-st)] (1) where Io is approximately the maximum current, 1/? is the collection time constant of the junction, and 1/s is the time constant for initially establishing the ion track.
Abstract: The collection of charge from ion tracks can produce logic upset and memory change in high density integrated circuits. It has been experimentally observed that drift conduction usually plays a dominant role when the ion track penetrates a junction. The first charge collection analysis concentrated on the diffusion conduction process. A recent analysis emphasizes drift conduction and describes the "funnel" which produces drift collection from the substrate. The funneling phenomenon has been modelled using two-dimensional computer simulations. It is extremely desirable to develop analytical solutions tp better understand the problem and to provide the basis for modelling the effect in circuit and system analysis computer codes such as SYSCAP. This paper develops an approximate analytic solution expressed as I(t) = Io [exp(-?t) - exp (-st)] (1) where Io is approximately the maximum current, 1/? is the collection time constant of the junction, and 1/s is the time constant for initially establishing the ion track. The junction time constant is shown to be K?o/q?ND, and it increases slowly with funnel length when a funnel is present. The analysis shows that the excess carriers move almost exclusively by ambipolar diffusion for very early times, and that the fields present in semiconductor devices, including p-n junction fields, collapse. Ambipolar diffusion proceeds until the excess carrier concentration is reduced to approximately the background doping density at which time the junction field is restored and the carriers move by drift.
617 citations
TL;DR: The authors indicate what could be the flow chart of the processing of dynamic sequences in scintigraphy and the kind of material that would be necessary to implement it.
Abstract: Nuclear Medicine is one of the first domains in which the analysis of image sequences was introduced. The development of this analysis was achieved parallel to the one of the computer systems linked to the scintillation cameras. The number of works that were performed in the research laboratories and have received an application in clinical routine is however limited. The authors indicate what could be the flow chart of the processing of dynamic sequences in scintigraphy and the kind of material that would be necessary to implement it. The possibilities of using the factor and compartmental analyses in clinical routine are particularly emphasized. The authors indicate why the factors and their associated images obtained by means of the factor analysis can have a physiological meaning.
218 citations
TL;DR: In this article, the product of the atomic number density (D) and the electron mean free path (EMFP) as a function of depth for gate oxides was derived using an analytical method based on oxide/substrate intensity ratios.
Abstract: Device quality gate oxides (~ 850 A) grown on Si (100) substrates are irradiated with 0 - 20 eV electrons during in situ XPS measurements. These structures have been thinned stepwise to 25 to 60 A using a relatively benign wet-chemical depth-profiling procedure. An analytical method based on oxide/substrate intensity ratios is used to deduce the product of the atomic number density (D) and the electron mean free path (?) as a function of depth for these structures. Samples showing a wide variety of hole trapping efficiencies were examined. Si+3 species are formed in the region of the Si/SiO2 interface and are observed during the course of their relaxation and annihilation. These formation results are correlated with the presence of strained Si-O-Si bonds at the interfaces. Radiation hard and soft structures show different strained bond distributions in the interfacial region. The direct observation of bond cleavage and bond strain gradients in these samples is used to extend silica devitrification models to explain the generation of fixed oxide charge and interface states. This bond strain gradient (BSG) model is shown to be consistent with a variety of experimental EPR and electrical observations of hole- and electron-trap generation by ionizing radiation.
184 citations
175 citations
TL;DR: In this paper, a simple phenomenological model of the charge funneling effect is developed based on an effective funnel length and is compared with the experimental results for diffused p+-n and n+-p junctions.
Abstract: Enhanced charge collection via funneling may increase the vulnerability of integrated circuits to single particle induced upsets or errors. In this paper, measurements of the enhanced charge collection for diffused p+-n and n+-p junctions are compared for substrates of comparable resistivities and doping densities. Charge collection measurements on MOS capacitors are also presented. A simple phenomenological model of the charge funneling effect is developed based on an effective funnel length and is compared with the experimental results.
174 citations
TL;DR: In this paper, the authors present a simple method of calculating cosmic ray upset rates and compare the results of this method to results of an exact calculation and apply both methods to the prediction of upset rates as device feature sizes are scaled to submicron dimensions.
Abstract: Progression of VLSI circuitry to smaller feature sizes raises questions about an increased severity of the cosmic ray upset problem. In this paper we present a simple method of calculating cosmic ray upset rates. We compare the results of this method to results of an exact calculation and apply both methods to the prediction of upset rates as device feature sizes are scaled to submicron dimensions. The exact calculations are presented for several environmental predictions. We then discuss upset critical charge as a function of feature size. We consider upset rates versus scale parameter as a function of device size and critical charge. We conclude that upset rates do not increase catastrophically as devices scale down, but that the problem will be serious for all technologies. We also conclude that devices with small feature sizes will be susceptible to upsets by proton induced reactions, so that they will have serious problems in the proton radiation belt.
141 citations
TL;DR: Digital subtraction angiography (DSA), utilizing computerized x-ray imaging equipment for image acquisition and subtraction, will provide substantial improvements in blood vessel imaging.
Abstract: Digital subtraction angiography (DSA), utilizing computerized x-ray imaging equipment for image acquisition and subtraction, will provide substantial improvements in blood vessel imaging. With the high contrast sensitivity of these systems, visualization of major blood vessels using intravenous injections of radiographic contrast media is possible on a routine basis. Current technology, using digitized video fluoroscopy and temporal subtraction, may in the future be upgraded using energy subtraction, or a combination of time and energy (hybrid subtraction). Applications of line-scanned radiography to DSA have been demonstrated but improvements in frame rate and resolution of the line-scanned technology is needed for future systems.
139 citations
TL;DR: In this article, the general problems of pulse shaping to optimize resolution with constraints imposed by noise, counting rate and rise time fluctuations are discussed, and a tutorial is designed to provide a balanced perspective on the processing of signals produced by semiconductor detectors.
Abstract: This is a tutorial paper designed to provide a balanced perspective on the processing of signals produced by semiconductor detectors. The general problems of pulse shaping to optimize resolution with constraints imposed by noise, counting rate and rise time fluctuations are discussed.
135 citations
TL;DR: In this article, the effects of scatter and attenuation on single photon emission computed tomography (SPECT) images can be analyzed with the aid of sophisticated Monte Carlo simulation, which enables control of components which govern the emission and transport of radiation through the source and attenuating medium.
Abstract: The effects of scatter and attenuation on single photon emission computed tomography (SPECT) images can be analyzed with the aid of sophisticated Monte Carlo simulation. Correction procedures can be evaluated by comparing corrected images with images absent of scatter and attenuation. The simulation enables control of components which govern the emission and transport of radiation through the source and attenuating medium. The basic calculation involves sampling the probability density functions (pdf) which govern the photon transport process. First, the origin of a photon is selected by sampling. Variance reduction is applied so that a detection is "forced" and weighted by the probability of an initial direction within the acceptance angle of the collimator multiplied by the probability that the photon is not attenuated. Second, the photon history is continued by sampling for a direction. The photon is forced to interact within the attenuating medium and an appropriate weight is calculated. Variance reduction is again applied with a weight determined by the product of the probability of interaction within the attenuating medium, the probability of scatter, the probability of scattering into the acceptance angle of the collimator, and the probability that the photon reaches the detector. Finally, a new direction and energy is selected. If the new energy is below the baseline energy, the history is terminated; otherwise, the second step is repeated. Presently, the collimator's geometric efficiency is considered without septal penetration.
134 citations
TL;DR: In this paper, a laser-induced pressure-pulse (LIPP) method was proposed to determine the charge distribution in the thickness direction of thin polyethylene (PVDF) polymer films.
Abstract: Relative charge-density distributions in the thickness direction of thin (>10?m) polymer films are determined directly and accurately with a new laser-induced pressure-pulse (LIPP) method: A pressure pulse is generated in the sample by applying a short (70ps) and energetic (1-11mJ) light pulse from a Nd:YAG laser to a specially coated surface of the sample. Stress effects within this surface layer and possibly the recoil caused by ablation of some target material generate the desired pressure pulse of less than 1ns duration which propagates through the sample. From the electrode currents, the charge distribution can be evaluated. The new method is described in detail and some results for 20 to 50?m thick films of Teflon FEP, Mylar PETP, and Kynar PVDF are given.
93 citations
TL;DR: The first positron computed tomography system with cesium fluoride scintillation detectors, PETT VI, has been developed and adoption of CsF detectors decrease the random coincidence rate by achieving a short coincidence timing resolution.
Abstract: The first positron computed tomography system with cesium fluoride scintillation detectors, PETT VI, has been developed The system provides 7 slice images with 4 detector rings (57 cm) Performances of the system are discussed and clarified based on experimental data Adoption of CsF detectors decrease the random coincidence rate by achieving a short coincidence timing resolution The timing resolution of a pair of detector heads is 15 nsec FWHM and 30 nsec FWTM After a preliminary timing alignment of 288 detectors, the coincidence window width (2?) of 11 nsec or wiider has yielded maximum coincidence sensitivity, and operation at 59 nsec has given 91% of maximum The full sensitivity for a cyclindrical uniform phantom (20 cm dia × 13 cm) is 354 kcps/microCi/cc/7 slices in a low resolution mode (intrinsic resolution at center is 117 mm FWHM) In a high resolution mode (71 mm), it is 31% of the full sensitivity Coincidence rates ratio, [random/(true + scattered)], in the low resolution mode, is 016 ? with 59 nsec window width inside the phantom images reconstructed without a random correction, where ? is activity density (microCi/cc) The ratio is 1/3 of that obtained when operating at 20 nsec Scattered coincidence fraction at the center of the phantom images, without the random correction process, is 9% of the [true + scattered]
TL;DR: In this article, a fast gating control acting directly on the photodetector has been developed, in view of timing studies with closely-spaced ultrashort light pulses.
Abstract: Single-photon detection by avalanche photodiodes with uniform breakdown over the junction area (single--photon avalanche diodes SPADs) is well known. The active quenching method, introduced by the authors, has been shown to avoid drawbacks of passive-quenching circuits and provide accurate operation of the devices. New active-quenching circuits are here presented. Dead times below 20 ns are obtained. A fast gating control acting directly on the photodetector has been developed, in view of timing studies with closely-spaced ultrashort light pulses.
TL;DR: The sensitivity of polysilicon gate CMOS static RAM designs to logic upset by impinging ions has been studied using computer simulations and experimental heavy ion bombardment as discussed by the authors, and the results of the simulations are confirmed by experimental upset cross-section data.
Abstract: Cosmic ray interactions with memory cells are known to cause temporary, random, bit errors in some designs. The sensitivity of polysilicon gate CMOS static RAM designs to logic upset by impinging ions has been studied using computer simulations and experimental heavy ion bombardment. Results of the simulations are confirmed by experimental upset cross-section data. Analytical models have been extended to determine and evaluate design modifications which reduce memory cell sensitivity to cosmic ions. A simple design modification, the addition of decoupling resistance in the feedback path, is shown to produce static RAMs immune to cosmic ray-induced bit errors.
TL;DR: A second generation positron camera system is construction at the Department of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology, Clinical Neurophysiology and Radiation Physics at the Karolinska Hospital and Institute, and the Instrument AB Scanditronix.
Abstract: The exciting possibilities of regional, noninvasive and quantitative metabolic studies of the brain with positron emission tomography, have initiated the construction of a second generation positron camera system at the Department of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology, Clinical Neurophysiology and Radiation Physics at the Karolinska Hospital and Institute, and the Instrument AB Scanditronix. The camera is a four ring system with 96 bismuth germanate (BGO) detectors per ring. The spatial resolution is 7.7 mm FWHM and the sensitivity per ?Ci per ml for a 20 cm diameter cylinder phantom is 25000 c/s for direct slices and 35000 c/s for cross slices.
TL;DR: The Semiconductor X-ray Test Source (SXRS) as discussed by the authors was developed for total-dose irradiation testing of semiconductor electronic devices at the wafer stage of fabrication.
Abstract: An x-ray source has been developed for total-dose irradiation testing of semiconductor electronic devices at the wafer stage of fabrication. This Semiconductor X-ray Test Source, as it is designated, was designed to provide an intense, uniform exposure to the device under test. The dose-rate range of 50 to 2×105 rad(Si) per minute allows test flexibility, high throughput, and facilitates standardization with fixed dose-rate sources. Bias to the die being irradiated is applied by the wafer prober; and a collimator mounted on the probe card permits the irradiation of discrete areas of the wafer or individual die. An electronic shutter system permits manual or automatic operation. A silicon detector provides a direct measurement of the dose-rate delivered to the device under test. Good correlation between doses administered by a cobalt-60 source and the test source has been demonstrated. Routine probe testing sequences can be accomplished automatically through a computer interface. Safety features include an enclosure that is both radiation-safe and light-tight; a vital shutter system; interlocks; and a warning light.
TL;DR: A technique involving resistive decoupling has been developed and applied to the memory cells of a 1024-bit CMOS static RAM to provide immunity to single event upset by cosmic rays.
Abstract: A technique involving resistive decoupling has been developed and applied to the memory cells of a 1024-bit CMOS static RAM to provide immunity to single event upset by cosmic rays. Doped polysilicon resistors were inserted in the inverter-pair cross-coupling lines of an existing memory-cell design with negligible effect on the device operating characteristics. Computer simulations, as well as laboratory tests with energetic krypton ions, imply the effectiveness of this approach to solving the single event upset problem in satellites. This technique is expected to be applicable to other devices of this type, including those with higher levels of integration.
TL;DR: In this paper, a model of charge build-up is established which takes into account the hole trapping in neutral oxide states, the subsequent electron trapping in now positively charged states and detrapping of captured electrons.
Abstract: Results of irradiation and high field tunnel injection experiments on MOS capacitors are discussed. The midgap voltage shift as a function of dose is caused by hole trapping only. In the case of tunnel injection, the generation of electron-hole pairs by impact ionization requires a much larger electron density and high fields. Thus a model of charge build-up is established which takes into account the hole trapping in neutral oxide states, the subsequent electron trapping in now positively charged states and detrapping of captured electrons. By means of this model, the prediction of the radiation hardness of MOS devices is feasible, provided that the impact ionization coefficient a is known accurately. If this is not the case, the combined techniques of ionizing irradiation and tunnel injection can be utilized to determine ? = ?o exp(-H?/F) as a function of the electrical field F. Electron capture and detrapping crosssections ?n and sn, resp., can be deduced by fitting the model to the experimental results. An F-3 dependency for ?n and an exp(-Hs/F) dependency for sn are found. Only a weak dependence on different processing parameters is observed. The proposed model is verified by a sequence of irradiation and injection steps. The generation of oxide charge is accompanied by an increase in interface state density Dit with a distribution, which peaks at about 0.15 eV above midgap, in both experiments. The results indicate that the generation of interface states is proportional to the amount of trapped holes.
TL;DR: In this paper, the basic parameters which determine the accuracy of timing measurements and their effect in a practical application, specifically timing with thin-surface barrier detectors, are discussed, focusing on properties of the detector, low-noise amplifiers, trigger circuits and time converters.
Abstract: This tutorial paper discusses the basic parameters which determine the accuracy of timing measurements and their effect in a practical application, specifically timing with thin-surface barrier detectors. The discussion focusses on properties of the detector, low-noise amplifiers, trigger circuits and time converters. New material presented in this paper includes bipolar transistor input stages with noise performance superior to currently available FETs, "noiseless" input terminations in sub-nanosecond preamplifiers and methods using transmission lines to couple the detector to remotely mounted preamplifiers. Trigger circuits are characterized in terms of effective rise time, equivalent input noise and residual jitter.
TL;DR: In this paper, a planar version of 200, 50 and 20?m pitch parallel microstrip detectors have been realized using a beam of 10 GeV/c pions, which can be used as live target in high energy physics experiments.
Abstract: Planar process has been applied to the fabrication of nuclear radiation detectors. Combining techniques of oxide passivation, photoengraving and ion implantation any desired detector shape can be made with small tolerances in geometrical and electrical properties. Extremely low reverse currents are obtained (less than 1 nA cm-2/100 ?m at room temperature) and therefore excellent energy resolutions : 10.6 keV for 5.486 MeV alphas, 1.55 keV for 122 keV gamma-rays with 25 mm2 area detectors, 300 ?m thick. The detectors are capable to be backed at 200° C under vacuum. Due to the fact that arrangements of many detectors on one wafer can be made, new possibilities open up, especially for particle localization in high energy physics. Planar versions of 200, 50 and 20 ?m pitch parallel microstrip detectors have been realized. Results obtained using a beam of 10 GeV/c pions are presented. Close mounting of several detectors allows the construction of telescopes used as live target in high energy physics experiments.
TL;DR: In this paper, a technique of utilizing all the inter-slice coincidence lines was proposed for multi-slice positron tomograph reconstruction, where each coincidence event is localized in three dimensions and then placed in one of the imaae slices for tomographic reconstruction.
Abstract: Conventional multi-slice positron tomographs have suffered from an inefficient use of the inter-slice coincidence information due to a lack of an appropriate reconstruction algorithm. In order to overcome this deficiency, most multi-slice tomographs use the nearest neighbor coincidence lines and approximate the position of the slice by summing the two sets of lines. This still leaves a fair number of coincidence lines which are discarded. TOFPET, with its ability to localize the positions of the annihilation, overcomes this limitation with a new technique of utilizing all the inter-slice coincidence lines. Each coincidence event is localized in three dimensions and then placed in one of the imaae slices for tomographic reconstruction. With a proper design of the positron camera, this can result in a sensitivity increase of 60% over cameras of similar design but utilizing only the nearest neighbor inter-slice coincidences. We show how this new technique is implemented in the TOFPET camera being constructed at our institution.
TL;DR: The benefits and problems encountered in using a hydrogen ambient are reviewed in this paper, where the authors show that the hydrogen is strongly bound, either to defects or as H2 with a dissociation energy > 3eV.
Abstract: High-purity germanium crystals used for making nuclear radiation detectors are usually grown in a hydrogen ambient from a melt contained in a high-purity silica crucible. The benefits and problems encountered in using a hydrogen ambient are reviewed. A hydrogen concentration of about 2×1015cm-3 has been determined by growing crystals in hydrogen spiked with tritium and counting the tritium s-decays in detectors made from these crystals. Annealing studies show that the hydrogen is strongly bound, either to defects or as H2 with a dissociation energy > 3eV. This is lowered to 1.8eV when copper is present. Etching defects in dislocation-free crystals grown in hydrogen have been found by etch stripping to have a density of about 1×107cm-3 and are estimated to contain 108H atoms each.
TL;DR: The scintillation detectors considered in present and future instrumentation for XCT and PCT diagnostic imaging are Bi4Ge3O12 (BGO), CdWO4, Low Afterglow CsI(Tl) and CsF as mentioned in this paper.
Abstract: The scintillation detectors considered in present and future instrumentation for XCT and PCT diagnostic imaging are Bi4Ge3O12 (BGO), CdWO4, Low Afterglow CsI(Tl) and CsF. These crystals with the exception of BGO have been known to scintillate as far back as NaI(Tl); their importance emphasized by their current use in CT application is relatively new. Recent improvements in purification, growth and performance characteristics present new and valuable data to the instrument designer. An evaluation and comparison of their properties vis a vis suitability for CT applications with particular emphasis on detector efficiency, light conversion, afterglow, timing, emission spectra, and general handling properties are examined and discussed. Future trends and possible replacement by other scintillators are commented on.
TL;DR: The sequence of radiofrequency and magnetic field gradients used to form an NMR image produces changes in the signals emitted by moving blood when compared to the signals from stationary blood that can be used to measure the open area of vessels.
Abstract: The sequence of radiofrequency and magnetic field gradients used to form an NMR image produces changes in the signals emitted by moving blood when compared to the signals from stationary blood. These changes can be used to measure the open area of vessels. In addition, specific relaxation time signatures of lesions may help in identifying the nature of the obstructions.
TL;DR: In this paper, the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency was investigated, and it was shown that when internal trapping in clear, polished bismuth germanate (Bi4Ge3O12 or BGO) crystals is reduced by suitable crystal shaping, a PMTwindow with a high refractive ratio, or non-absorbing vacuum bubbles, it is possible to transfer more than 60% of the scintillation light to the POMT.
Abstract: The high density and atomic number of bismuth germanate (Bi4Ge3O12 or BGO) make it a very useful detector for positron emission tomography. Modern tomograph designs use large numbers of small, closely-packed crystals for high spatial resolution and high sensitivity. However, the low light output, the high refractive index (n=2.15), and the need for accurate timing make it important to optimize the transfer of light to the photomultiplier tube (PMT). We describe the results of a Monte Carlo computer program developed to study the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency. The program simulates total internal, external, and Fresnel reflection as well as internal absorption and scattering by bubbles. We show that when internal trapping in clear, polished BGO crystals is reduced by (a) suitable crystal shaping, (b) a PMT window with a high refractive index, or (c) non-absorbing vacuum bubbles, it is possible to transfer more than 60% of the scintillation light to the PMT. This transfer is greatly reduced by internal absorption.
TL;DR: The natural radiation environment in space has been shown to produce soft upsets in satellite-borne microelectronics and the uncertainties that result from deficiencies in our basic knowledge of the environment are discussed in this paper.
Abstract: The natural radiation environment in space has been shown to produce soft upsets in satellite-borne microelectronics. This environment varies with time, with position in the earth's magnetosphere and with depth inside the spacecraft. The nature of these variations will be described and the uncertainties that result from deficiencies in our basic knowledge of the environment will be discussed. Only those radiation components that can cause soft upsets will be considered in this report.
TL;DR: Using electron spin resonance, this article observed three radiation-induced paramagnetic defect centers in the SiO2 structures at room temperature, one resonance appears to be unambiguously associated with trivalent silicon bonded to three other silicons at the Si/SiO2 interface.
Abstract: We have subjected thermally grown films of SiO2 on Si substrates to Co60 gamma irradiation. Using electron spin resonance we observe three radiation-induced paramagnetic defect centers in the structures at room temperature. One resonance appears to be unambiguously associated with trivalent silicon bonded to three other silicons at the Si/SiO2 interface. Two other resonances are very much like resonances observed earlier in irradiated high purity bulk SiO2; those bulk SiO2 resonances have been associated with trivalent silicons bonded to three oxygens and unpaired electrons in nonbonding oxygen 2p orbitals.
TL;DR: In this article, the effect of scaling on the single event upset rate in CMOS memory cells in the galactic cosmic ray environment typical of high altitude satellite orbits was investigated, and a detailed computer aided modeling study was performed to predict the effect.
Abstract: As device feature size is scaled down for Very Large Scale Integration (VLSI) and Very High Speed Integrated Circuit (VHSIC) applications, consideration must be given to potential increased vulnerabiliity to single particle induced upset (memory soft error or processor logic error) from the natural radiation environment. This paper describes a detailed computer aided modeling study to predict the effect of scaling on the single event upset rate in CMOS memory cells in the galactic cosmic ray environment typical of high altitude satellite orbits.
TL;DR: In this paper, a computer simulation model which calculates the energy deposited within a small sensitive volume embedded in a larger volume as a result of nuclear interactions anywhere in the larger volume is outlined.
Abstract: A computer simulation model which calculates the energy deposited within a small sensitive volume embedded in a larger volume as a result of nuclear interactions anywhere in the larger volume is outlined. The model is tested by comparison with the pulse-height spectra measured in silicon surface barrier detectors as a result of exposure to protons at different energies. The model is then used to provide physical insight into the role played by the nuclear recoil in localized energy deposition about a nuclear interaction.
TL;DR: In this paper, the results of laboratory tests to determine the radiation damage effects induced on MOS devices from Co-60, electron, and proton radiation are reported, which can be expected with the electron and particle bombardments experienced in space applications.
Abstract: The results of laboratory tests to determine the radiation damage effects induced on MOS devices from Co-60, electron, and proton radiation are reported. The tests are performed to establish the relationship between the Co-60 gamma rays and the level of damage to the MOS devices in regards to different damages which can be expected with the electron and particle bombardments experienced in space applications. CMOS devices were exposed to the Co-60 gamma rays, 1 MeV electrons, and 1 MeV protons while operating at 3, 10, and 15 V. The test data indicated that the Co-60 source was reliable for an initial evaluation of the electron damages up to 2 MeV charge. A correction factor was devised for transferring the Co-60 measurements to proton damages, independent of bias and transistor types, for any orbit or environment.
TL;DR: The noise performance of an emission tomography system having time-of-flight measurements is shown in several examples to be superior for a confidence-weighted data array compared to a most likely position data array as mentioned in this paper.
Abstract: The noise performance of an emission tomography system having time-of-flight measurements is shown in several examples to be superior for a confidence-weighted data array compared to a most likely position data array. The examples range from a point to a planar distribution of radioactivity, and include a crude model of the left ventricle of a heart containing radioactive palmitate.