N.T. Vu

University of California, Los Angeles, Los Angeles, CA, United States

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Publications (21)27.99 Total impact

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    ABSTRACT: PETbox4 is a new, fully tomographic bench top PET scanner dedicated to high sensitivity and high resolution imaging of mice. This manuscript characterizes the performance of the prototype system using the National Electrical Manufacturers Association NU 4-2008 standards, including studies of sensitivity, spatial resolution, energy resolution, scatter fraction, count-rate performance and image quality. The PETbox4 performance is also compared with the performance of PETbox, a previous generation limited angle tomography system. PETbox4 consists of four opposing flat-panel type detectors arranged in a box-like geometry. Each panel is made by a 24 × 50 pixelated array of 1.82 × 1.82 × 7 mm bismuth germanate scintillation crystals with a crystal pitch of 1.90 mm. Each of these scintillation arrays is coupled to two Hamamatsu H8500 photomultiplier tubes via a glass light guide. Volumetric images for a 45 × 45 × 95 mm field of view (FOV) are reconstructed with a maximum likelihood expectation maximization algorithm incorporating a system model based on a parameterized detector response. With an energy window of 150-650 keV, the peak absolute sensitivity is approximately 18% at the center of FOV. The measured crystal energy resolution ranges from 13.5% to 48.3% full width at half maximum (FWHM), with a mean of 18.0%. The intrinsic detector spatial resolution is 1.5 mm FWHM in both transverse and axial directions. The reconstructed image spatial resolution for different locations in the FOV ranges from 1.32 to 1.93 mm, with an average of 1.46 mm. The peak noise equivalent count rate for the mouse-sized phantom is 35 kcps for a total activity of 1.5 MBq (40 µCi) and the scatter fraction is 28%. The standard deviation in the uniform region of the image quality phantom is 5.7%. The recovery coefficients range from 0.10 to 0.93. In comparison to the first generation two panel PETbox system, PETbox4 achieves substantial improvements on sensitivity and spatial resolution. The overall performance demonstrates that the PETbox4 scanner is suitable for producing high quality images for molecular imaging based biomedical research.
    Physics in Medicine and Biology 05/2013; 58(11):3791-3814. · 2.70 Impact Factor
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    ABSTRACT: A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm(2) position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as (18)F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for (18)F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm(-2) at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of (18)F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm(-2) for 1 min acquisitions and a 62 × 62 µm(2) pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm(2). We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ∼180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ∼200 µm of additional LDPE film. Lastly, we demonstrate the practical utilization of Betabox, with an imaging test of its linearity, when coupled to a polydimethylsiloxane microfluidic chip designed for cell based assays.
    Physics in Medicine and Biology 05/2013; 58(11):3739-3753. · 2.70 Impact Factor
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    ABSTRACT: This paper introduces a mouse atlas registration system (MARS), composed of a stationary top-view x-ray projector and a side-view optical camera, coupled to a mouse atlas registration algorithm. This system uses the x-ray and optical images to guide a fully automatic co-registration of a mouse atlas with each subject, in order to provide anatomical reference for small animal molecular imaging systems such as positron emission tomography (PET). To facilitate the registration, a statistical atlas that accounts for inter-subject anatomical variations was constructed based on 83 organ-labeled mouse micro-computed tomography (CT) images. The statistical shape model and conditional Gaussian model techniques were used to register the atlas with the x-ray image and optical photo. The accuracy of the atlas registration was evaluated by comparing the registered atlas with the organ-labeled micro-CT images of the test subjects. The results showed excellent registration accuracy of the whole-body region, and good accuracy for the brain, liver, heart, lungs and kidneys. In its implementation, the MARS was integrated with a preclinical PET scanner to deliver combined PET/MARS imaging, and to facilitate atlas-assisted analysis of the preclinical PET images.
    Physics in Medicine and Biology 09/2012; 57(19):6063-77. · 2.70 Impact Factor
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    ABSTRACT: PETBox4 is a preclinical system dedicated to imaging mice. This system is composed by four detector panels, each made by a 24 × 50 array of 1.825 × 1.825 × 7 mm BGO crystals. The face to face crystal separation of the detectors is 5 cm, generating a 4.5 × 4.5 × 9.4 cm field of view (FOV). The result is a tomograph with a large detection solid angle, which in combination with a wide open energy window achieves high peak detection efficiency (~17%). Despite the small size of the typical imaged subjects, these design features also increase the fraction of accepted crystal and object scattered events, which reduce the overall image signal to noise ratio. In this work, we investigated the system acquisition configuration settings necessary to optimize the NEC (Noise equivalent Counts) and image quality. A Monte Carlo simulation software package was used (GATE) to investigate the different types of events detected as a function of energy window settings and multiple event acceptance policy. This was done for a realistic distribution of activity and attenuation coefficients in the PETBox4 FOV, based on emission data from an in-vivo preclinical PET image from an average sized mouse (30g). Based on the simulations, the NEC rate was optimized for a dual energy window that accepts both low (50-175 keY) and high (410-650 keY) energy events. This indicates that low energy events that are composed mostly from single crystal scatter contribute useful image information, while events in the middle of the energy spectrum (175keV-410keV), tend to include large fractions of crystal backscatter as well as object scatter and do not contribute significantly in data signal to noise ratio. As a result of the same simulations, a new policy for the acceptance of multiple events was introduced, implementing a "KiIlAIl" multiple policy, further improving the NEe. Overall, these two optimization parameters improved the NEC rate by 56%, providing a signifi- ant advantage in image signal to noise ratio.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: PETbox is a low cost bench top preclinical PET scanner dedicated to pharmacokinetic and pharmacodynamic mouse studies. A prototype system was developed at our institute, and this manuscript characterizes the performance of the prototype system. The PETbox detector consists of a 20 × 44 bismuth germanate crystal array with a thickness of 5 mm and cross-section size of 2.05 × 2.05 mm. Two such detectors are placed facing each other at a spacing of 5 cm, forming a dual-head geometry optimized for imaging mice. The detectors are kept stationary during the scan, making PETbox a limited angle tomography system. 3D images are reconstructed using a maximum likelihood and expectation maximization (ML-EM) method. The performance of the prototype system was characterized based on a modified set of the NEMA NU 4-2008 standards. In-plane image spatial resolution was measured to be an average of 1.53 mm full width at half maximum for coronal images and 2.65 mm for the anterior-posterior direction. The volumetric reconstructed resolution was below 8 mm(3) at most locations in the field of view (FOV). The sensitivity, scatter fraction, and noise equivalent count rate (NECR) were measured for different energy windows. With an energy window of 150 - 650 keV and a timing window of 20 ns optimized for mouse imaging, the peak absolute sensitivity was 3.99% at the center of FOV and a peak NECR of 20 kcps was achieved for a total activity of 3.2 MBq (86.8 μCi). Phantom and in vivo imaging studies were performed and demonstrated the utility of the system at low activity levels. The quantitation capabilities of the system were also characterized showing that despite the limited angle tomography, reasonably good quantification accuracy was achieved over a large dynamic range of activity levels. The presented results demonstrate the potential of this new tomograph for small animal imaging.
    Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 10/2011; 13(5):949-61. · 2.47 Impact Factor
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    ABSTRACT: An integrated β-camera and microfluidic chip was developed that is capable of quantitative imaging of glycolysis radioassays using (18)F-FDG in small cell populations down to a single cell. This paper demonstrates that the integrated system enables digital control and quantitative measurements of glycolysis in B-Raf(V600E)-mutated melanoma cell lines in response to specific B-Raf inhibition. The β-camera uses a position-sensitive avalanche photodiode to detect charged particle-emitting probes within a microfluidic chip. The integrated β-camera and microfluidic chip system was calibrated, and the linearity was measured using 4 different melanoma cell lines (M257, M202, M233, and M229). Microfluidic radioassays were performed with cell populations ranging from hundreds of cells down to a single cell. The M229 cell line has a homozygous B-Raf(V600E) mutation and is highly sensitive to a B-Raf inhibitor, PLX4032. A microfluidic radioassay was performed over the course of 3 days to assess the cytotoxicity of PLX4032 on cellular (18)F-FDG uptake. The β-camera is capable of imaging radioactive uptake of (18)F-FDG in microfluidic chips. (18)F-FDG uptake for a single cell was measured using a radioactivity concentration of 37 MBq/mL during the radiotracer incubation period. For in vitro cytotoxicity monitoring, the β-camera showed that exposure to 1 μM PLX4032 for 3 days decreased the (18)F-FDG uptake per cell in highly sensitive M229 cells, compared with vehicle controls. The integrated β-camera and microfluidic chip can provide digital control of live cell cultures and allow in vitro quantitative radioassays for multiple samples simultaneously.
    Journal of Nuclear Medicine 05/2011; 52(5):815-21. · 5.77 Impact Factor
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    ABSTRACT: PETBox4, currently under development at the Crump Institute is a new tomograph dedicated to preclinical imaging of mice. This system presents a significant improvement on sensitivity and spatial resolution compared to the first generation PETBox. We report here on its design and initial performance characteristics.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2011 IEEE; 01/2011
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    ABSTRACT: BetaBox, a direct detection beta camera utilizing a 13.5×13.5mm2 active area position sensitive avalanche photodiode (PSAPD) (Radiation Monitoring Devices) is currently being developed to image distributions of charged particles in microfluidic chips. The previously reported signal processing chain incorporated charge sensitive amplifiers (Cremat Inc., CR-110) in the frontend readout design. Charge sensitive amplifiers, particularly the CR-110 product, are commonly used as preamplifiers when reading out PSAPDs. However, the 140µs pulse decay of this device suggests a possible count rate limitation in the performance of the beta camera. To address this limitation, the frontend readout was redesigned to replace the charge sensitive amplifiers with op-amps configured as transimpedance amplifiers. We hypothesize that, since the equivalent circuit of the PSAPD appears more like a charge division network loaded by a large semiconductor junction capacitance (∼150 pF) than an APD, this signal source can be optimally processed using the transimpedance amplifier approach. Results show that the designed signal processing chain using a transimpedance amplifier with 100ns RC time constant displays not only comparable image quality to the previous signal chain using the CR-110 but also reduced image distortion at high count rates.
    01/2011;
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    ABSTRACT: Oncogenic kinase activity and the resulting aberrant growth and survival signaling are a common driving force of cancer. Accordingly, many successful molecularly targeted anticancer therapeutics are directed at inhibiting kinase activity. To assess kinase activity in minute patient samples, we have developed an immunocapture-based in vitro kinase assay on an integrated polydimethylsiloxane microfluidics platform that can reproducibly measure kinase activity from as few as 3,000 cells. For this platform, we adopted the standard radiometric (32)P-ATP-labeled phosphate transfer assay. Implementation on a microfluidic device required us to develop methods for repeated trapping and mixing of solid-phase affinity microbeads. We also developed a solid-state beta-particle camera imbedded directly below the microfluidic device for real-time quantitative detection of the signal from this and other microfluidic radiobioassays. We show that the resulting integrated device can measure ABL kinase activity from BCR-ABL-positive leukemia patient samples. The low sample input requirement of the device creates new potential for direct kinase activity experimentation and diagnostics on patient blood, bone marrow, and needle biopsy samples.
    Cancer Research 11/2010; 70(21):8299-308. · 9.28 Impact Factor
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    ABSTRACT: PETbox is a low-cost benchtop PET scanner dedicated to high throughput preclinical imaging that is currently under development at our institute. This paper presents the design and characterization of the detectors that are used in the PETbox system. In this work, bismuth germanate scintillator was used for the detector, taking advantage of its high stopping power, high photoelectric event fraction, lack of intrinsic background radiation and low cost. The detector block was segmented into a pixelated array consisting of 20 × 44 elements, with a crystal pitch of 2.2 mm and a crystal cross section of 2 mm × 2 mm. The effective area of the array was 44 mm × 96.8 mm. The array was coupled to two Hamamatsu H8500 position sensitive photomultiplier tubes, forming a flat-panel type detector head with a sensitive area large enough to cover the whole body of a typical laboratory mouse. Two such detector heads were constructed and their performance was characterized. For one detector head, the energy resolution ranged from 16.1% to 38.5% full width at half maximum (FWHM), with a mean of 20.1%; for the other detector head, the energy resolution ranged from 15.5% to 42.7% FWHM, with a mean of 19.6 %. The intrinsic spatial resolution was measured to range from 1.55 mm to 2.39 mm FWHM along the detector short axis and from 1.48 mm to 2.33 mm FWHM along the detector long axis, with an average of 1.78 mm. Coincidence timing resolution for the detector pair was measured to be 4.1 ns FWHM. These measurement results show that the detectors are suitable for our specific application.
    IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
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    ABSTRACT: PETbox is designed to be a low cost and easy to use bench top small animal PET scanner dedicated for high throughput quantitative pharmacokinetic and pharmacodynamic studies. To achieve this goal, the scanner is integrated with a complete animal management system that provides life support including reproducible positioning, temperature control, anesthesia, real-time monitoring of animal respiration and a pathogen barrier. This approach minimizes the overall cost and complexity of preclinical PET imaging and should enable non-imaging scientists to embrace the technology. The system uses two opposing detector heads, each one consisting of a pixilated BGO array coupled to two H8500 multi-channel photomultiplier tubes. The BGO crystals were segmented into 20 ? 44 arrays with a pixel pitch of 2.2 mm and a total active area of 44 mm ? 96.8 mm. Position and timing signals from the photomultiplier tube readout circuitry were connected to a field programmable gate array (FPGA) board with eight ADC channels, each running at 100 MHz. Signal processing algorithms were developed for the FPGA to process received PET events and raw list-mode data were generated by the FPGA board and transferred to a host PC for storage. Basic system performance parameters were measured. The system has an average intrinsic spatial resolution of 1.72 mm FWHM along detector long axis and 1.84 mm FWHM along detector short axis. The coincidence timing resolution was measured to be 4.1 ns FWHM. The average energy resolution of the crystals was 19.8% and the absolute sensitivity of the system was measured to be 3.8% at the center of the gantry. Initial imaging studies were also performed with live mice. A mouse tumor xenograft was imaged 1 hour after a 32uCi [<sup>18</sup>F]FDG injection for 20 minutes. 3D images were generated using a ML-EM method. Results demonstrate the capability and potential of the PETbox system for dedicated high throughput mouse studies such as biodistribution and organ uptake q- - uantification.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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    ABSTRACT: Information on the transport and phosphorylation rate constants (k1,k2,k3,k4,Ki) of a tracer reflects the biological state of cells. A microfluidic cell culture chip coupled with PSAPD camera (MF-PSAPD) has been developed to give continuous measurements of radioactivity in individual wells. However, constant infusion (CI) of PET tracers through the chambers would give high background activity due to the relatively large volume space of the infusing medium in the wells of cultured cells that compromise the ability of the setup to estimate the k values. New strategies of controlling the infusion and tracer level are needed to provide reliable estimates of the parameters. A switching strategy (SS) was conceived that consists of multiple medium-infusion cycles, each of which has a tracer incubation (TI) period followed by a background-removed (BR) period (tracer-free medium). In this paper, equally switching strategy (ESS) with 12 cycles of constant TI and BR periods (5 min each) was evaluated by computer simulation and by experiments on MF-PSAPD using the tracer fluorodeoxy-glucose (FDG) and the four parameter FDG model. The SS was further optimized by using a simulated annealing algorithm and D-optimal criterion to obtain optimal switching strategy (OSS). Simulations showed that the 12-cycle ESS did not perform as well (i.e., with larger estimated variability of the model parameters) as a 5-cycle OSS that also has multiple practical advantages. Patterns of OSS were found to be insensitive to the variation of cell number and k values, and all tended to have longer TI at the beginning but longer BR at later times. Estimated k values with SS have large reduction in %CV compared to those of CI, with the largest reduction for Ki--from 762% down to 26% under the same count rate conditions. The new optimized strategy of tracer incubation/measurement is able to provide reliable estimates of FDG k's in MF-PSAPD.
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2009;
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    ABSTRACT: A new system is being developed to allow imaging of charged particles in microfluidic chip using position sensitive avalanche photodiodes (PSAPD). The new imaging system was created by placing the PSAPD detector with close proximity to the PDMS microchip. The new system therefore is capable of quantifying tiny amounts of these radiolabeled probes over time. The PSAPD can be used for the direct detection of positrons and other charged particles. In our studies, the performance of the system has been carried out. A gradient of solution containing radioactive positron emitting fluorodeoxyglucose (FDG) was imaged from a microchip. Results have shown that sensitivities as low as 56 plusmn 0.1 pCi in a 4 mm<sup>2</sup> region of interest (ROI) (14 pCi/mm<sup>2</sup>) and line pair spatial resolution of 0.5 mm can be achieved. Moreover, the application to cell biology was successfully performed in which currently radioactive signal from less than one hundred cells can be detected and resolved clearly in the system.
    Micro Electro Mechanical Systems, 2008. MEMS 2008. IEEE 21st International Conference on; 02/2008
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    ABSTRACT: Novel molecular imaging applications increasingly involve studies where very low amount of activity is present. This operation point can be challenging in terms of image quality especially when the intrinsic detector activity from scintillators such as LSO is considered. LSO crystals contain <sup>176</sup>Lu which emits beta<sup>-</sup> particles followed by gamma photons, resulting in the detection of true and random events. This background activity has been shown to contribute a significant percentage of the total detected true events, when a very weak activity distribution is imaged. This can affect the weakest signal that can be detected by an LSO PET scanner which determines its "detection limit" and is evaluated by the parameter of minimum detectable activity or MDA. A series of acquisitions was performed in order to study the effect of the energy window to the intrinsic true and randoms rate. The experiments were also simulated with GATE, and the results were validated by comparing them with the experiment. Four square regions each with a unique signal to background activity concentration ratio were used. The background activity level was held constant between the different regions, while the activity of the point sources varied in 4 selected levels. The signal to background ratio was calculated separately for each region. The energy spectrum of the intrinsic background activity and its contribution to the total energy spectrum both for singles and coincidences was estimated through the GATE simulation. We histogrammed both the measured and simulated data on various time frames, which we reconstructed using the filtered backprojection algorithm. Every image was quantified based on the Currie equation in order to associate an MDA value for each of the 4 point sources as a function of the frame length. In the case of the microPET Focus 220 a total amount of 4nCi/mm<sup>3</sup> can be reliably detected for frame lengths longer than 5 min and at regions where the- signal to background activity concentration ratio is higher than 4. In the case of higher contrast regions detection can be achieved even for frame lengths down to 1 min.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 12/2007
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    ABSTRACT: A new device has been developed that allows imaging of charged particle emitting probes in a microfluidic circuit using a position sensitive avalanche photodiode (PSAPD). Microfluidic chips are an emerging technology that have been used in applications such as the synthesis of new molecular probes and incubation of live cell cultures in microfluidic chambers. This new device works by direct contact of the PSAPD detector with the substrate layer of a microfluidic chip and provides 2- dimensional images of the distribution of beta emitting probes over time. The spatial resolution of the PSAPD detector for beta particle imaging was evaluated with <sup>18</sup>F line sources. The FWHM was measured to be 0.4 mm at the center of the field of view. The sensitivity of the device for <sup>18</sup>F beta particle detection was evaluated as a function of substrate thickness between the source and detector surface. One of the applications of this new detector system is for the imaging of live cell cultures in a microfluidic environment. Preliminary images have also been acquired showing the uptake of [<sup>18</sup>F]fluorodeoxyglucose ([<sup>18</sup>F]FDG) probes in live cells incubated in a microfluidic chamber. Images of [<sup>18</sup>F]FDG uptake were acquired with less than 200 incubated cells over a period of 3 days. An increase in cellular [<sup>18</sup>F]FDG uptake was also observed by increasing the time period between cell feeding and [<sup>18</sup>F]FDG incubation in the cell chamber.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2007
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    ABSTRACT: Microfluidic chips are an emerging technology that facilitates the study of molecular processes in nano-liter levels in a finely controlled manner. A prototype imaging system capable of detecting and quantifying very small amounts of beta particles in a microfluidic chip, utilizing a scintillator, an optical lens, and a charge coupled device (CCD), was developed and proof of concept was previously demonstrated [1]. In this study, we optimized the system design parameters, such as CCD binning and types of scintillators, and evaluated the system performance for spatial resolution and minimum detectable activity. Pixel binning of the CCD during readout process improved the signal-to-noise ratio with no spatial resolution degradation in beta particle imaging of <sup>18</sup>F, up to a binning of 3times3 in our study, which was equivalent to 44 mum times 44 mum pixels in an object plane with a magnification of 0.5. The full width at half maximum (FWHM) of line sources with a finite width of 115 mum were measured to be 493 mum with a plastic scintillator and 289 mum with a CsI(Tl) scintillator. The minimum detectable activities were measured to be 360 pCi/mm<sup>2</sup> with a plastic scintillator and 40 pCi/mm<sup>2</sup> with a CsI(Tl) scintillator for a 5-min acquisition.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2007
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    ABSTRACT: Spatial resolution and noise are strongly related properties and therefore meaningful evaluations of imaging systems and reconstruction algorithms should always include estimates of both. We have evaluated the performance of a statistical maximum a posteriori probability (MAP) reconstruction algorithm in terms of contrast recovery and signal to noise ratio (SNR) in comparison to filtered-backprojection (FBP) on a microPET Focus220 scanner. Printed <sup>18</sup>F point sources sitting on uniform backgrounds were used as contrast recovery phantoms to evaluate the MAP and FBP performance. With this inkjet printed source method, the contrast recovery phantom was created with well controlled contrast levels and no finite boundaries were introduced between signal and background. The activities and contrast levels we used in our experiment were close to tumor uptakes and tumor to background contrasts in realistic mouse scans. Contrast evaluation demonstrated that at any given noise level, MAP reconstruction performance was better than FBP. To evaluate the effects of scatter in the two image reconstruction algorithms, analytical scatter correction was applied on a small animal mouse phantom containing water and air filled cavities and then reconstructed with both FBP and MAP algorithm. Residual activity in non-radioactive regions after scatter correction was proved to be similar for MAP and FBP reconstructions.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2007
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    ABSTRACT: A new device is being developed that will allow imaging of the distribution of charged particles in microfluidic circuits, using a scintillator, a lens and a charge coupled device (CCD). Microfluidic chips are an emerging technology that will facilitate the study of molecular processes in pico-liter levels in a finely controlled manner. The ability to quantify low amounts of radioactivity in a microfluidic chip will provide researchers with a platform to investigate molecular processes in a controlled in-vitro environment. The new detector system consists of a plastic scintillator, a C-mount compact lens, and a Sony ICX285AL interline-transfer CCD cooled with a Peltier device. A microfluidic chip filled with fluoro-deoxy-glucose (FDG) solution was coupled to a plastic scintillator and the set up was placed inside a light-tight box for imaging. Preliminary studies were performed to test the feasibility of using the scintillator-based CCD detector system for this application. The CCD performance parameters were characterized by the photon transfer curve. The camera gain constant and read-out noise were measured to be 0.746 e-/ADU (analog-to-digital unit) and 8 e-, respectively. The dark current was also investigated with different temperatures and binning factors. The spatial resolution was measured and line pairs of FDG in a microfluidic chip were discernable down to a 0.5 mm separation. The system was able to quantify the activity level reliably down to 5 nCi/mm<sup>2</sup>.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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    ABSTRACT: A new device is being developed that will allow imaging of the distribution of charged particles in microfluidic circuits, using position sensitive avalanche photodiodes (PSAPD). Microfluidic chips are an emerging technology that will facilitate the synthesis and study of new molecular imaging probes. These poly-dimethylsiloxane (PDMS) chips are low in cost to custom design and produce, and their development/prototyping cycles are relatively short. They can contain a variety of microcircuitry and microwells for manipulating nanoliter volumes of solutions. The new imaging device will be created by direct contact of a PSAPD detector with the fluidic layer of a PDMS chip and will provide 2-dimensional images of the distribution of beta emitting radiolabeled probes on the chip. Furthermore, the new device will also be capable of quantifying small amounts of these radiolabeled probes over time. The PSAPD will be used for the direct detection of positrons and other charged particles. Preliminary studies were performed in our laboratory to test the feasibility of detecting small amounts of radioactive positron emitting fluorodeoxyglucose (FDG) in a prototype device. Results have shown that sensitivities as low as 56 plusmn 0.1 pCi in a 4 mm<sup>2</sup> ROI (14 pCi/mm<sup>2</sup>) and line pair spatial resolution of 0.5 mm can be achieved.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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    ABSTRACT: The Optical Positron Emission Tomography (OPET) system will provide the capabilities of bioluminescence and PET modalities in one combined imaging system. Bioluminescence light emitted in vivo has a spectrum ranging from 550 700 nm. The optical photon signals detected are approximately two orders lower in amplitude and one order shorter in duration compared to scintillation light pulses from a 511 keV gamma-event. In this study the performance characteristics of the OPET detectors for bioluminescence imaging were evaluated. The detection uniformity was measured for wavelengths between 400 700 nm and normalization maps were used to correct the acquired images. The spatial resolution along the transaxial and axial directions was 2.30 and 2.38 mm FWHM, respectively. The average dark counts for the detector was 76±30 cps at an ambient temperature of 20°.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; 569:563-566. · 1.14 Impact Factor