Performance Evaluation of Small Animal PET Scanners With Different System Designs (original) (raw)
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2003 IEEE Nuclear Science Symposium. Conference Record (IEEE Cat. No.03CH37515), 2003
We present a preliminary study on the design of a small animal positron emission tomograph with octagonal geometry. The main goal is to evaluate the impact of critical design parameters on the quality of the reconstructed images. Monte Carlo simulations take into account the depth of interaction in individual crystals. The activity sources are simulated as parametric distributions within the field of view and images are reconstructed with iterative algorithms based on the estimation of maximum likelihood and Bayesian regularization. The probability system matrix used by these algorithms is also calculated based on statistical models and Monte Carlo simulation. 2D and 3D techniques have been employed.
Impact of System Design Parameters on Image Figures of Merit for a Mouse PET Scanner
IEEE Transactions on Nuclear Science, 2004
In this study, an analytical simulation model was developed to investigate how system design parameters affect image figures of merit and task performance for small animal positron emission tomography (PET) scanners designed to image mice. For a very high resolution imaging system, important physical effects that may impact image quality are positron range, annihilation photon acollinearity, detector point-spread function (PSF) and coincident photon count levels (i.e., statistical noise). Modeling of these effects was included in an analytical simulation that generated multiple realizations of sinograms with varying levels of each effect. To evaluate image quality with respect to quantitation and detection task performance, four different figures of merit were measured: 1) root mean square error (RMSE); 2) a region of interest SNR (SNR ROI ); 3) nonprewhitening matched filter SNR (SNR NPW ); and 4) recovery coefficient. The results indicate that for very high resolution imaging systems, the increase in positron range of C-11 compared to F-18 radiolabeling causes a significant reduction of quantitation (SNR ROI ) and detection (SNR NPW ) accuracy for small regions. In addition, changing the shape of the detector PSF, which depends on crystal thickness, causes significant variations in quantitation and detection performance. However, while increasing noise levels significantly increase RMSE and decrease detectability (SNR NPW ), the quantitation task performance (SNR ROI ), is less sensitive to noise levels. These results imply that resolution is more important than sensitivity for quantitation task performance, while sensitivity is a more significant issue for detection. The analytical simulation model can be used for estimating task performance of small animal PET systems more rapidly than existing full Monte Carlo methods, although Monte Carlo methods are needed to estimate system parameters.
IEEE Transactions on Nuclear Science, 2000
Minimizing dead space is one way to increase the detection efficiency of small-animal PET scanners. By using monolithic scintillator crystals (e.g., 20 mm 10 mm 10 mm LSO), loss of efficiency due to inter-crystal reflective material is minimized. Readout of such crystals can be performed by means of one or more avalanche photo-diode (APD) arrays optically coupled to the crystal. The entry point of a gamma photon on the crystal surface can be estimated from the measured distribution of the scintillation light over the APD array(s). By estimating the entry point, correction for the depth-of-interaction (DOI) is automatically provided. We are studying the feasibility of such detector modules. To this end, a 64-channel test setup has been developed. Experiments to determine the effect on the spatial resolution of crystal surface finish and detector geometry have been carried out. The first results of these experiments are presented and compared to simulation results. The crystal surface finish has only a small influence on the spatial resolution. The spatial resolution of 20 mm 10 mm 10 mm detectors is significantly better when read out on the front side than when read out on the back side. With a 20 mm 10 mm 20 mm crystal coupled to two APD arrays, a very small resolution degradation of only 0 2 mm is observed for an incidence angle of 30 compared to normal incidence.
Characterization of the Ferrara animal PET scanner
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2002
A dedicated small animal PET scanner, YAPPET, was designed and built at Ferrara University. Each detector consists of a 20Â20 matrix of 2Â2Â30 mm 3 YAP:Ce finger-like crystals glued together and directly coupled to a Hamamatsu position sensitive photomultiplier. The scanner is made from four detectors positioned on a rotating gantry at a distance of 7:5 cm from the center and the field of view (FOV) is 4 cm both in the transaxial direction and in the axial direction. The system operates in 3D acquisition mode. The performance parameters of YAPPET scanner such as spatial, energy and time resolution, as well as its sensitivity and counting rate have been determined. The average spatial resolution over the whole FOV is 1:8 mm at FWHM and 4:2 mm at FWTM. The sensitivity at the center is 640 cps=mCi: r (G. Di Domenico).
Design of a very high-resolution small animal PET scanner using a silicon scatter detector insert
Physics in Medicine and Biology, 2007
A small animal positron emission tomography (PET) instrument using a high-resolution solid-state detector insert in a conventional PET system was investigated for its potential to achieve sub-millimeter spatial resolution for mouse imaging. Monte Carlo simulations were used to estimate the effect of detector configurations (thickness, length and radius) on sensitivity. From this initial study, a PET system having an inner cylindrical silicon detector (4 cm ID, 4 cm length and 1.6 cm thickness composed of 16 layers of 300 µm × 300 µm × 1 mm pads), for scattering, surrounded by an outer cylindrical BGO scintillation detector (17.6 cm ID, 16 cm length and 2 cm thickness segmented into 3 mm × 3 mm × 20 mm crystals), for capture was evaluated in detail. In order to evaluate spatial resolution, sensitivity and image quality of the PET system, 2D images of multiple point and cylinder sources were reconstructed with the simulation data including blurring from positron range and annihilation photon acollinearity using filtered backprojection (FBP). Simulation results for 18 F demonstrate 340 µm FWHM at the center of the field of view with 1.0% sensitivity from the coincidence of single scattering events in both silicon detectors and 1.0 mm FWHM with 9.0% sensitivity from the coincidence of single scattering in the silicon and full energy absorption of the second photon in the BGO detector.
Image quality evaluation of a small animal PET scanner
Brazilian Journal of Radiation Sciences, 2020
Performance testing of small animal PET scanners is very important to ensure the high performance required for this particular type of PET scanner. In this sense, National Electrical Manufactures Association (NEMA) published its NU 4/2008 standards, a consistent and standardized methodology for measuring scanner performance parameters for small animal PET imaging. Imaging capabilities of the scanner LabPET SOLO 4 were tested during two years according NEMA NU 4/2008 methodology. Results indicates that the equipment, despite a decade of use, presents performance appropriated and similar to performance of equipments reported in Literature.
6 Performance Characteristics of PET Scanners
A major goal of the PET studies is to obtain a good quality and detailed image of an object by the PET scanner, and so it depends on how well the scanner performs in image formation. Several parameters associated with the scanner are critical to good quality image formation, which include spatial resolution, sensitivity, noise, scattered radiations, and contrast. These parameters are interdependent, and if one parameter is improved, one or more of the others are compromised. A description of these parameters is given below. Spatial Resolution The spatial resolution of a PET scanner is a measure of the ability of the device to faithfully reproduce the image of an object, thus clearly depicting the variations in the distribution of radioactivity in the object. It is empirically defined as the minimum distance between two points in an image that can be detected by a scanner. A number of factors discussed below contribute to the spatial resolution of a PET scanner. Detector size: One factor that greatly affects the spatial resolution is the intrinsic resolution of the scintillation detectors used in the PET scanner. For multidetector PET scanners, the intrinsic resolution (R i) is related to the detector size d. R i is normally given by d/2 on the scanner axis at midposition between the two detectors and by d at the face of either detector. Thus it is best at the center of the FOV and deteriorates toward the edge of the FOV. For a 6-mm detector, the R i value is ∼3 mm at the center of the FOV and ∼6 mm toward the edge of the FOV. For continuous single detectors, however , the intrinsic resolution depends on the number of photons detected, not on the size of the detector, and is determined by the full width at half maximum of the photopeak. Positron range: A positron with energy travels a distance in tissue, losing most of its energy by interaction with atomic electrons and then is annihilated after capturing an electron (Fig. 6.1). Thus, the site of β + emission differs from the site of annihilation as shown in Fig. 6.1. The distance (range) traveled
Physics in Medicine and Biology, 2010
Improvements to current small animal PET scanners can be made by improving the sensitivity and the spatial resolution of the scanner. In the past, efforts have been made to minimize the crystal dimensions in the axial and transaxial directions to improve the spatial resolution and to increase the crystal length to improve the sensitivity of the scanner. We have designed tapered PET detectors with the purpose of reducing the gaps between detector modules and optimizing the sensitivity of a future generation small animal PET scanner. In this work, we investigate spatial resolution and sensitivity of a scanner based on tapered detector elements using Monte Carlo simulations. For tapered detector elements more scintillation material is used per detector resulting in a higher sensitivity of the scanner. However, since the detector elements are not uniform in size, degradation in spatial resolution is also expected. To investigate characteristics of tapered PET detectors the spatial resolution and sensitivity of a one-ring scanner were simulated for a system based on traditional cuboid detectors and a scanner based on tapered detectors. Additionally, the effect of depth of interaction (DOI) resolution on the spatial resolution for the traditional and tapered detectors was evaluated.
Initial Evaluation of the Indiana Small Animal PET Scanner
IEEE Nuclear Science Symposium Conference Record, 2005, 2005
The Indiana small animal PET scanner is a new generation PET scanner with design goals of 1 microliter volumetric spatial resolution, a point source sensitivity of greater than 5 percent, and an imaging field-of-view suitable for whole body mouse imaging. The scanner design uses 12 planar detector banks each consisting of a 48 × 108 array of 20 mm long LSO crystals with an array pitch of 0.87 mm coupled to two Hamamatsu H8500 large area, 64-anode photomultiplier tubes. The detector modules are mounted on a rotatable gantry and are offset from the center of rotation to give an increased sampling density. Eight detector banks are currently installed in the scanner, and this report presents an initial performance evaluation of the scanner for this configuration. Using a 30 gauge needle (ID=0.15 mm, OD=0.30 mm) positioned near the center of the scanner, the transaxial resolution has been measured to be 1.1 mm FWHM and the axial resolution has been measured to be 1.5 mm FWHM. The sensitivity has been measured to be 4.0% of all decays. The scatter fraction is 0.26 and the peak noise equivalent countrate is 80 kcps at an activity of 0.22 mCi. Sample images demonstrate good imaging capabilities.
Development of continuous detectors for a high resolution animal PET system
IEEE Transactions on Nuclear Science, 1995
We propose a design for a high resolution, gamma-camera style detector that is suitable for use in a positron emission tomograph dedicated to small animal research. Through Monte Carlo simulation we modeled the performance of a detector composed of one 76.2×76.2×8 mm thick LSO crystal coupled to a 3" square position sensitive photomultiplier tube (PS-PMT). We investigated the effect of optical coupling compounds, surface treatment and depth of interaction on the quantity (efficiency) and distribution (spread) of scintillation photons reaching the photocathode. We also investigated linearization of the position response. We propose a PET system consisting of fourteen of these detectors in 2 rings, yielding a 16 cm diameter by 15 cm long tomograph. It would operate in 3-D mode subtending a 68% solid angle to the center. The expected spatial resolution is 52 mm, with a system efficiency of ~10% at the center (200 keV lower threshold) and a singles count rate capability of approximately 106 cps per detector