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ABSTRACT: We present the complete image generation methodology developed for the RatCAP PET scanner, which can be extended to other PET systems for which a Monte Carlo-based system model is feasible. The miniature RatCAP presents a unique set of advantages as well as challenges for image processing, and a combination of conventional methods and novel ideas developed specifically for this tomograph have been implemented. The crux of our approach is a low-noise Monte Carlo-generated probability matrix with integrated corrections for all physical effects that impact PET image quality. The generation and optimization of this matrix are discussed in detail, along with the estimation of correction factors and their incorporation into the reconstruction framework. Phantom studies and Monte Carlo simulations are used to evaluate the reconstruction as well as individual corrections for random coincidences, photon scatter, attenuation, and detector efficiency variations in terms of bias and noise. Finally, a realistic rat brain phantom study reconstructed using this methodology is shown to recover >; 90% of the contrast for hot as well as cold regions. The goal has been to realize the potential of quantitative neuroreceptor imaging with the RatCAP.
IEEE Transactions on Nuclear Science 11/2011; · 1.45 Impact Factor
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B. Ravindranath,
S.S. Junnarkar,
M.L. Purschke,
S.H. Maramraju,
X. Hong,
D. Tomasi,
D. Bennett,
K. Cheng,
S.S. Southekal,
S.P. Stoll,
J.-F. Pratte,
P. Vaska,
C.L. Woody, D.J. Schlyer
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ABSTRACT: At Brookhaven National Laboratory, we are developing a simultaneous PET-MRI breast imaging system. A prototype II version of the PET system has been constructed. This device consists of 24 detector blocks where each block consists of a 4 Ã 8 array of 2.2 Ã 2.2 Ã 15 mm<sup>3</sup> LYSO crystal directly coupled to a 4 Ã 8 non-magnetic APD array. The scanner has an inner diameter of 100 mm and an axial extent of 18 mm. Resolution measurements were carried out for the prototype system to evaluate the depth of interaction effects. Average resolution less than 2 mm FWHM was maintained throughout the field of view. The prototype PET system was operated unshielded inside the RF coil of the Aurora 1.5 T dedicated breast MRI machine. Artifact free MRI images with good SNR were obtained.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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B. Ravindranath,
S. H. Maramraju,
S. S. Junnarkar,
S. S. Southekal,
S. P. Stoll,
J.-F. Pratte,
M. L. Purschke,
X. Hong,
D. Bennett,
K. Cheng,
D. Tomasi,
D. S. Smith,
S. Krishnamoorthy,
P. Vaska,
C. L. Woody, D. J. Schlyer
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ABSTRACT: We propose to develop a high resolution scanner for simultaneous PET and MRI breast imaging that is capable of providing highly sensitive and specific breast cancer examinations. The addition of high resolution positron emission tomography capability to an existing dedicated MRI system will give a device in which each of the modalities contributes its strengths to compensate for the weaknesses of the other. In this combined modality scanner, we have the anatomical information from the MRI to compensate for the somewhat poorer resolution in PET, and we have the predictive power of PET in identifying the type of lesion to overcome the high false positive rate of MRI. This device is based on the technical approach used in the RatCAP scanner with the innovation of detecting coincident events in separate rings of the RatCAP scanner. We are presenting the design and GATE simulations of the full breast imaging system and preliminary PET and MRI results from the prototype system.
Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE; 11/2008
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ABSTRACT: The RatCAP has been designed and constructed to image the awake rat brain. In order to maximize system performance, offline digital coincidence data processing algorithms including offset delay correction and prompt and delayed coincidence detection have been developed and validated. With offset delay correction using a singular value decomposition (SVD) technique, overall time resolution was improved from 32.6 to 17.6 ns FWHM. The experimental results confirm that the ratio of prompts to randoms was improved because a narrower timing window could be used. <sup>18</sup>F-fluoride rat bone scan data were reconstructed using our fully 3-D ML-EM algorithm with a highly accurate detector response model created from Monte Carlo simulation.
IEEE Transactions on Nuclear Science 03/2008; · 1.45 Impact Factor
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ABSTRACT: Tracer kinetic modeling techniques for quantitative Positron emission tomography (PET) require an accurately measured radiotracer concentration in arterial blood as a function of time as an input to the model (arterial input function). Since the input function (IF) is derived from blood samples from the wrist arteries, a scanner is begin devised to detect radioactivity in the wrist as a function of time and extract an IF. A prototype using two detector pairs has been evaluated. The spatial resolution, sensitivity and the masking of the arterial signal by the surrounding wrist tissue radioactivity are determined. The results show that the detector was able to discriminate the arterial and venous flows from each other using planar coincidence images. MicroPET images of the wrist show that the radioactivity from the tissue does not interfere with the arterial signal. Minimization of venous and tissue interference, optimal number and placement of the detectors are being evaluated. The two detector pair prototype was used in a routine PET study.
Bioengineering Conference, 2007. NEBC '07. IEEE 33rd Annual Northeast; 04/2007
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ABSTRACT: The RatCAP is a miniaturized, head-mounted PET scanner designed to image the brain of conscious rats. This eliminates the need for anesthesia which is known to severely depress brain function. The small field of view of the RatCAP allows a highly accurate Monte Carlo based system matrix for fully 3D maximum likelihood image reconstruction. A number of issues have been addressed in an attempt to realize the full potential of quantitative imaging with RatCAP, including corrections for detector efficiencies, random coincidences, photon scatter and attenuation. In particular, a new method to correct for scatter originating outside the field of view is presented, which takes advantage of the RatCAP iterative reconstruction framework. Preliminary results show significant qualitative and quantitative improvements in the bias and variance of the data.
Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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S.-J. Park,
S. Southekal,
M. Purschke,
S.S. Junnarkar,
J.-F. Pratte,
V. Radeka,
P. O'Connor,
S.P. Stoll,
R. Lecomte,
R. Fontaine,
C.L. Woody, D.J. Schlyer,
P. Vaska
[show abstract]
[hide abstract]
ABSTRACT: The RatCAP has been designed and constructed to image the awake rat brain. In order to maximize system performance, offline digital coincidence data processing algorithms including offset delay correction and prompt and delayed coincidence detection have been developed and validated. With offset delay correction using a singular value decomposition (SVD) technique, overall time resolution was improved from 32.6 ns to 17.6 ns FWHM. The experimental results confirm that the ratio of prompts (or trues) to randoms was improved because a smaller timing window could be used. <sup>18</sup>F-fluoride rat bone scan data was reconstructed with our fully 3-D MLEM with a highly accurate detector response model using Monte Carlo simulation.
Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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ABSTRACT: Kinetic modeling permits quantification of radiotracer dynamics in tissue by using the amount of radioactivity in blood as an input function to a kinetic model. This usually requires obtaining multiple blood samples during dynamic PET scans. As this procedure is considered a health risk for the patient and medical personnel, a wrist scanner has been devised that can be used to obtain an input function with minimum discomfort to the patient and without drawing arterial blood. A prototype using two detector pairs has been evaluated. The spatial resolution, sensitivity and the masking of the arterial signal by the surrounding wrist tissue radioactivity are determined. The results show that the detector was able to discriminate the arterial and venous flows from each other using planar coincidence images. MicroPET images of the wrist show that the radioactivity from the tissue does not interfere with the arterial signal. Minimization of venous and tissue interference, optimal number and placement of the detectors are being evaluated. The two detector pair prototype was used in a routine PET study.
Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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ABSTRACT: In order to assess the kinetics of radiotracer accumulation in tissue, the amount of radioactivity in the blood must be quantitatively measured as an input function to the kinetic model. Due to safety and comfort issues with invasive determination of the input function, a non-invasive method for arterial measurement of blood radioactivity is investigated using a wrist scanner. A prototype consisting of two detector pairs of LSO and APD detector arrays is used to obtain planar images of an anatomically correct wrist phantom. The spatial resolution and sensitivity of the prototype is determined. The results showed the detector was able to discriminate the arterial and venous flows from each other when using planar coincidence images.
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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ABSTRACT: Spatial resolution in positron emission tomography has steadily improved over the years, but remains substantially worse than in other imaging modalities, currently at ~2 mm for the most popular commercial tomographs. This is a serious limitation particularly for imaging mice, which have great potential in preclinical PET research because of their compatibility with genetic manipulation. A novel gamma-ray detector design which can achieve high resolution and sensitivity and also facilitates depth of interaction measurement has been developed. It consists of a slab of LSO and arrays of large-area avalanche photodiodes (APDs) on both sides which are used in a light sharing (Anger-type) scheme. A fully instrumented prototype detector has been constructed comprising a 10 mm thick LSO crystal and an array of 7 square APDs (each 11 mmtimes11 mm in area) optically coupled to each side. Preliminary measurements carried with a collimated source mounted on a computer controlled X-Y translational stage demonstrate a resolution of ~2.5 mm FWHM between the center of two APDs. Optimization of electronics noise factors is critical to improving detector performance
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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P. Vaska,
C.L. Woody, D.J. Schlyer,
V. Radeka,
P. O'Connor,
J.-F. Pratte,
S. Shokouhi,
S.P. Stoll,
S.S. Junnarkar,
M. Purschke, [......],
T. Aubele,
R. Kristiansen,
A. Villanueva,
S. Boose,
A. Kandasamy,
B. Yu,
A. Kriplani,
S. Krishnamoorthy,
R. Lecomte,
R. Fontaine
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ABSTRACT: The first fully functional prototype of the RatCAP (Rat conscious animal PET) scanner has been constructed and preliminary evaluations have been performed. RatCAP is a miniature, high performance PET scanner designed specifically to image the brain of a rat while directly attached to its head. The goal is to eliminate the need for anesthesia which can confound quantitative brain studies and prevent simultaneous correlations of neurochemistry and behavior. RatCAP is a fully 3D tomograph with a transaxial (axial) field-of-view of 38(18) mm, outside diameter 72 mm, and weight <200 g which is supported by a small tether. A total of 384 LSO crystals are divided among 12 independent detector blocks, each of which contains an avalanche photodiode (APD) photosensor array and a custom-designed ASIC for highly integrated front-end processing. A custom FPGA-based time-stamp module has been designed and implemented, achieving a preliminary system resolution of 13.9 ns FWHM. With a point source in the FOV center, spatial resolution is 2.1 mm FWHM, energy resolution averages 23% FWHM, and sensitivity is 0.7% at an average threshold of 150 keV. Novel offline data processing algorithms have been developed including methods for time and energy calibrations, corrections for physical effects, and a highly accurate iterative image reconstruction. Initial phantom and rat brain images have been obtained
Nuclear Science Symposium Conference Record, 2005 IEEE; 11/2005
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ABSTRACT: The capability to create high quality images from data acquired by the Rat Conscious Animal PET tomograph (RatCAP) has been evaluated using modified versions of the PET Monte Carlo code Simulation System for Emission Tomography (SimSET). The proposed tomograph consists of lutetium oxyorthosilicate (LSO) crystals arranged in 12 4 × 8 blocks. The effects of the RatCAPs small ring diameter (∼40 mm) and its block detector geometry on image quality for small animal studies have been investigated. Since the field of view will be almost as large as the ring diameter, radial elongation artifacts due to parallax error are expected to degrade the spatial resolution and thus the image quality at the edge of the field of view. In addition to Monte Carlo simulations, some preliminary results of experimentally acquired images in both two-dimensional (2-D) and 3-D modes are presented.
IEEE Transactions on Nuclear Science 11/2005; · 1.45 Impact Factor
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ABSTRACT: Small-animal PET has become a rapidly growing approach to problems in human health, from addiction to cancer to drug development. However, the best presently available PET technology (∼2 mm resolution) still has significant limitations in spatial resolution and sensitivity which are particularly problematic for applications attempting to take advantage of powerful transgenic mouse models. Most currently proposed approaches to improving resolution face a number of technical obstacles which force trade-offs in performance. A novel design which circumvents many of these compromises is a miniaturized and modernized "Anger" or "gamma" camera, with a principle similar to well-known detectors for SPECT, in which a continuous scintillator crystal is used and position is determined from light-sharing among groups of photodetectors. Critical improvements over the traditional Anger design include a more appropriate scintillator for PET (LSO), a thinner crystal for higher spatial resolution, and large-area avalanche photodiode (APD) technology as the photodetector which allows layering of the detector to improve sensitivity, among other benefits. The feasibility of the approach has been studied in terms of spatial and energy resolution, sensitivity, and cost, with promising results. A prototype is complete and preliminary measurements have been performed.
Nuclear Science Symposium Conference Record, 2004 IEEE; 11/2004
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ABSTRACT: We have made a comparison between experimentally determined light output from various size LSO crystals and the Monte Carlo simulations using the program Opticad. The results show good agreement between the predicted results and the experimental measurements. These results show that it is possible to accurately simulate the light output using these calculations. This allows testing of many parameters quickly and the determination of the critical parameters in maximizing the light output and photoelectron yield from these detector modules.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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ABSTRACT: Earlier works, including a recent one at BNL, demonstrated that PET is a promising technique to verify the dose distribution of proton therapy, which is increasingly used in radiation oncology because the dose conforms more tightly to the tumor than common x-ray radiation therapy. Proton therapy produces positron-emitting isotopes along the beam path, allowing the therapy dose distribution to be imaged by PET as a form of quality assurance of the treatment. This is especially important when treating inhomogeneous organs such as the lungs or the head-and-neck, where the calculation of the expected dose distribution for treatment planning is more difficult. In this paper, we present Monte Carlo simulations of the yield of positron emitters produced by proton beams up to 250 MeV, followed by statistically realistic Monte Carlo simulation of the images expected from a clinical PET scanner. The emphasis of this study is to accurately predict the positron emitter distribution and to determine the quality of the PET signal in the region near the Bragg peak which is critical to the success of PET imaging for verification of proton beam location and dosimetry. In this paper, we also demonstrate that the image results depend strongly on the available nuclear reaction cross section data. We determine quantitatively the differences in the calculated positron emitter yields resulting from four different sets of input nuclear reaction cross section data. They are compared to the simulated distributions of positron emitter productions and absorbed proton energies.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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ABSTRACT: The current method for measuring the input function of a PET tomograph is by withdrawing arterial blood from a patient's wrist In this study, the possibility of making a noninvasive measurement of the arterial blood is explored to determine the feasibility of using a planar set of detectors situated around the wrist. The arterial measurement was simulated using a peristaltic pump and an anatomically correct wrist phantom with attenuation. A step function was used to measure the activity flowing through arterial and venous tubing in the phantom. The detector was tested for spatial resolution and counting efficiency. The results showed the detector was able to discriminate the arterial and venous flows from noise when using planar coincidence images.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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P. Vaska,
C L Woody, D J Schlyer,
S. Shokouhi,
S P Stoll,
J.-F. Pratte,
P O'Connor,
S.S. Junnarkar,
S. Rescia,
B Yu,
M. Purschke,
A. Kandasamy,
A. Villanueva,
A. Kriplani,
V. Radeka,
N Volkow,
R. Lecomte,
R. Fontaine
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ABSTRACT: Anesthesia is currently required for PET studies of the animal brain in order to eliminate motion artifacts. However, anesthesia profoundly affects the neurological state of the animal, complicating the interpretation of PET results. Furthermore, it precludes the use of PET to study the brain during natural behavior. The RatCAP tomograph (rat conscious animal PET) is designed to eliminate the need for anesthesia in rat brain studies. It is a miniaturized full-ring PET scanner which is attached directly to the head, covering nearly the entire brain. RatCAP utilizes arrays of 2 mm × 2 mm LSO crystals coupled to matching avalanche photodiode arrays, which are in turn read out by full custom integrated circuits. Principal challenges have been addressed considering the physical constraints on size, weight, and heat generation in addition to the usual requirements of small-animal PET such as high spatial resolution in the presence of parallax error. A partial prototype has been constructed and preliminary measurements and optimization completed. Realistic Monte Carlo simulations have also been carried out to optimize system performance, which is predicted to be competitive with existing microPET systems.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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ABSTRACT: We are evaluating the image reconstruction capabilities of RatCAP by using different modified versions of SimSET (Simulation System for Emission Tomography). We have been able to model the proposed tomograph that will consist of lutetium oxyorthosilicate (LSO) crystals arranged in 12 4×8 blocks and have investigated how far the RatCAP's ring diameter (∼40 mm) and its block detector geometry will affect its image reconstruction for small animal studies. Since the field of view will be almost as large as the ring diameter, radial elongation artifacts due to parallax error are expected to degrade the spatial resolution and thus the image quality at the edge of the FOV. In addition to Monte Carlo simulation, we are presenting some preliminary results of experimentally acquired images in both 2D and 3D modes.
Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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S. Shokouhi,
S.P. Stoll,
A. Villanueva,
P. Vaska, D.J. Schlyer,
C.L. Woody,
Bo Yu,
P. O'Connor,
J.-F. Pratte,
V. Radeka,
N. Volkow,
J.S. Fowler
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ABSTRACT: A study has been carried out to investigate the possibility of using a pair of LSO + APD detector arrays to obtain a noninvasive measurement of the arterial input function for use in PET. The main focus of this study was to determine the spatial resolution and sensitivity required to obtain a high quality image that would permit a precise determination of the region of interest around the wrist artery. From these data a quantitative arterial input function that has minimal interference from the tissue and vein background can be obtained. The detector arrays were operated in coincidence counting mode to obtain planar images of various phantoms to demonstrate the feasibility of the concept.
IEEE Transactions on Nuclear Science 11/2003; · 1.45 Impact Factor
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ABSTRACT: One of the most promising high resolution positron emission tomography detector designs comprises an array of small, optically isolated scintillator crystals each coupled to an independent photosensor, such as an avalanche photodiode (APD). However, crosstalk between crystals (due to Compton scatter, photoelectron escape, or incomplete optical isolation) can significantly degrade performance and is expected to increase as crystals become narrower to improve spatial resolution. Various measures of crosstalk have been determined for different configurations of 4 × 8 blocks of 2 mm × 2 mm lutetium oxyorthosilicate (LSO) crystals coupled to matched Hamamatsu APD arrays. Results indicate that ignoring crosstalk signals could lead to a ∼ 30% loss in coincidence sensitivity for a tomograph using these detectors and a decrease in energy resolution of ∼ 2 percentage points. Spatial and time resolution would not be significantly affected with most practical front-end architectures.
IEEE Transactions on Nuclear Science 07/2003; · 1.45 Impact Factor
