Photon Imaging System Research Articles

Trials of transmission imaging using clinically used Ir-192 source for high-dose-rate brachytherapy

In high-dose-rate (HDR) brachytherapy, verification of an Ir-192 source's position during treatment is required. One of the methods for this used a high-energy pinhole gamma camera to image the position of the source, but the absolute position of the source cannot be measured. To confirm the absolute position, it will be useful to acquire the transmission image of a subject in addition to the gamma photon image at the same time without using an additional X-ray system. To measure the transmission images, we tried to use the high-energy gamma photons emitted from the Ir-192 source used for the therapy. We developed a high-energy gamma photon imaging system composed of 1-mm-thick Pr doped Gd2O2S (GOS), a surface mirror, and a cooled charge-coupled device (CCD) camera. The developed imaging system achieved transmission imaging of high-energy gamma photons by transporting the Ir-192 source in front of the imaging system. The spatial resolution of the imaging system was better than 2.4 mm FWHM with and without a 10-cm-thick acrylic block set between the imaging system and the source. Moderate spatial resolution and contrast images of phantoms were obtained with the system. For the dynamic imaging mode, continuous images of the phantoms were measured with 1-sec intervals. There was no observable difference in the transmission images by the movement of the Ir-192 source. Transmission imaging of subjects using an Ir-192 source for HDR brachytherapy could be achieved using our developed imaging system. The system offers a new method to measure the real-time transmission images of the subject during HDR brachytherapy.

Design and fabrication of single photon detector with ultra-large area superconducting nanowire array

<sec>Superconducting nanowire single-photon detector (SNSPD) is one of the most mainstream single-photon detectors at present, which possesses excellent comprehensive performance, including low time jitter, high efficiency, low dark count, and wide spectrum. However, the traditional single-pixel SNSPD suffers a lack of spatial resolution and a small photosensitive surface, which becomes a bottleneck associated with optical coupling efficiency. In addition, a single-pixel detector has no ability to resolving the photon number, whose working speed cannot be further improved due to the existence of dead time. While array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, the relevant researches have been conducted and great progress has been achieved. However, the large-area SNSPD array is facing some intractable problems, including complex process, low yield, and difficult fabrication, owing to the photosensitive surface consisting of a large number of superconducting nanowires. Photons imaging is verified with this device. At present, in the existing studies mainly used is the three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus.</sec><sec>In this work, we design an ultra-large area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ (hydrogen silsesquioxane polymer) forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a full-superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation, and other related work.</sec><sec>This work provides an idea for designing and fabricating ultra-large array SNSPD, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity can be realized.</sec>

Design and fabrication of large-area superconducting nanowire single photon detector arrays

Superconducting nanowire single-photon detectors (SNSPDs) are currently one of the most mainstream single-photon detectors with excellent comprehensive performance, including low time jitter, high efficiency, low dark count and wide spectrum. However, the traditional single-pixel SNSPD suffers from a lack of spatial resolution and a small photosensitive surface, which creates bottlenecks associated with optical coupling efficiency. In addition, a single-pixel detector does not have the photon number resolution ability, whose working speed cannot be further improved due to the existence of dead time. In this case, array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, experimental groups at home and abroad have started relevant research and have made great progress. However, the large-area SNSPD array faces intractable problems, including complex processes, low yield and difficult fabrication, owing to the photosensitive surface consisting of large amounts of superconducting nanowires. At present, the existing studies mainly use three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus.<br>In this paper, we design a large-area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a fully superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation and other related work.<br>This work provides an idea for the design and fabrication of ultra-large array SNSPDs, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity will be realized.

Photon counting correction method to improve the quality of reconstructed images in single photon compressive imaging systems.

Compressive sensing has been widely used in single photon imaging systems because of its advantages of high efficiency and low cost. However, when the received photon flux is large, some photons cannot be recorded by single photon detectors due to the dead time effect, which introduces nonlinear errors between the measurement results and actual values and further damages the imaging quality. In this paper, a photon counting correction method specific to paralyzable detectors is proposed to improve the quality of reconstructed images in single photon compressive imaging systems. To verify this method, a single photon compressive imaging system is built, which uses a digital micromirror device (DMD) to modulate the light and a PMT as the single photon detector. The Monte Carlo simulation is also implemented to double validate the performance of the proposed method and the results from the experiment. Peak signal-to-noise ratio (PSNR) is used as the imaging quality evaluation standard. The experimental and simulation results indicate that our method can overcome negative effect of the dead time and accurately recover the intensity and waveform shape of echo signal, which can significantly improve the quality of reconstructed images and has a better performance than traditional methods in the single photon compressive imaging system.

Interactions between Amyloid-Β Proteins and Human Brain Pericytes: Implications for the Pathobiology of Alzheimer's Disease.

Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is the most common cause of dementia, especially among aging populations. Despite advances in AD research, the underlying cause and the discovery of disease-modifying treatments have remained elusive. Two key features of AD pathology are the aberrant deposition of amyloid beta (amyloid-β or Aβ) proteins in the brain parenchyma and Aβ toxicity in brain pericytes of the neurovascular unit/blood–brain barrier (NVU/BBB). This toxicity induces oxidative stress in pericytes and leads to capillary constriction. The interaction between pericytes and Aβ proteins results in the release of endothelin-1 in the pericytes. Endothelin-1 interacts with ETA receptors to cause pericyte contraction. This pericyte-mediated constriction of brain capillaries can cause chronic hypoperfusion of the brain microvasculature, subsequently leading to the neurodegeneration and cognitive decline observed in AD patients. The interaction between Aβ proteins and brain pericytes is largely unknown and requires further investigation. This review provides an updated overview of the interaction between Aβ proteins with pericytes, one the most significant and often forgotten cellular components of the BBB and the inner blood–retinal barrier (IBRB). The IBRB has been shown to be a window into the central nervous system (CNS) that could allow the early diagnosis of AD pathology in the brain and the BBB using modern photonic imaging systems such as optical coherence tomography (OCT) and two-photon microscopy. In this review, I explore the regulation of Aβ proteins in the brain parenchyma, their role in AD pathobiology, and their association with pericyte function. This review discusses Aβ proteins and pericytes in the ocular compartment of AD patients as well as strategies to rescue or protect pericytes from the effects of Aβ proteins, or to replace them with healthy cells.

Substrate-modulated directional far field scattering behavior of individual plasmonic nanorods

Steering the energy of the incident light into the specific directions by using plasmonic nanostructures plays a key role for future micro-nano photonic integration and optical imaging systems, but the influence of the dielectric substrate on the full-space far-field scattering image of metal nanostructures remains unintuitive. In this paper, the influence of dielectric substrate on the far-field scattering behavior of surface plasmon resonance mode is systematically investigated. By using a simple model, we found that the dielectric substrate could suppress the backscattering energy of plasmon mode. The greater the refractive index of the substrate, the stronger the inhibition effect. In addition, the forward scattering energy of plasmon mode will be concentrated as the refractive index of the substrate increased. We also realized a directional forward scattering of plasmon mode energy by combining the dielectric substrate and dielectric/metal structures. Our research provides a new strategy for the directional control of the incident light energy in a dielectric substrate.

Fast Method for Liquid Crystal Cell Spatial Variations Estimation Based on Modeling the Spectral Transmission.

Liquid crystal phase retarders are utilized by photonic devices and imaging systems for various applications, such as tunable filtering, light modulation, polarimetric imaging, remote sensing and quality inspection. Due to technical difficulties in the manufacturing process, these phase retarders may suffer from spatial non-uniformities, which degrade the performance of the systems. These non-uniformities can be characterized by measuring the spectral transmission at each voltage and each point on the liquid crystal cell, which is time consuming. In this work, we present a new fast and simple method for measuring and computationally estimating the spatial variations of a liquid crystal phase retarder with planar alignment. The method is based on measuring the spectral transmission of the phase retarder at several spatial locations and estimating it at others. The experimental results show that the method provides an accurate spatial description of the phase retarder and can be employed for calibrating relevant systems.

Ocular amyloid imaging at the crossroad of Alzheimer's disease and age-related macular degeneration: implications for diagnosis and therapy.

Alzheimer's disease (AD) and age-related macular degeneration (AMD) are important disorders of aging, but significant challenges remain in diagnosis and therapy. Amyloid-beta (Aβ), found in the brain and a defining feature of AD, has also been observed in the retina in both AD and AMD. While current diagnostic modalities for detecting Aβ in the brain are costly or invasive, Aβ in the retina can be noninvasively and conveniently imaged using modern photonic imaging systems such as optical coherence tomography (OCT). Moreover, since many of these retinal changes occur before degenerative changes can be detected in the brain, ocular amyloid biomarkers could be utilized to detect AD as well as AMD in their earliest stages when therapy may be most effective in halting disease progression. Novel technologies to quantify retinal biomarkers have the potential to facilitate early diagnosis and noninvasive monitoring of disease progression with important therapeutic implications.

X-ray imaging of high velocity moving objects by scanning summation using a single photon processing system

X-ray imaging has been used extensively in the manufacturing industry. In the paper and paperboard industry X-ray imaging has been used for measuring parameters such as coat weight, using mean values of X-ray absorption inline in the manufacturing machines. Recently, an interest has surfaced to image paperboard coating with pixel resolved images showing material distribution in the coating on the paperboard, and to do this inline in the paper machine. Naturally, imaging with pixel resolution in an application where the paperboard web travels with velocities in the order of 10 m/s sets harsh demands on the X-ray source and the detector system to be used. This paper presents a scanning imaging method for single photon imaging systems that lower the demands on the source flux by hundreds of times, enabling a system to be developed for high velocity industrial measurement applications. The paper presents the imaging method, a discussion of system limitations, simulations and real measurements in a laboratory environment with a moving test object of low velocity, all to verify the potential and limits of the proposed method.

Single Photon Avalanche Diode Imaging Systems for Biomedical Applications

Ever since the discovery of the photon by Einstein and Planck, scientists have continually strived to achieve single photon imaging; considered the holy grail of photosensing, since it represents the ultimate detection and precision limit of electromagnetic radiation. With the invention of the photomultiplier tube (PMT) in the 1930s, single-photon detection became feasible. Since then, PMTs have been developed to meet a wide range of application needs. For the most demanding time-resolved measurements, micro-channel plate (MCP) PMTs have been used. However, PMT devices are inherently limited due to their large size, high-cost, fragility, high operating voltages, and magnetic field susceptibility. On the other hand, Geiger-mode APDs realized in CMOS technology do not suffer from these limitations, and in recent years, their performance has significantly improved so they are now comparable to PMTs. As such, single photon imagers based on CMOS single-photon avalanche detectors (SPAD) have been realized for applications where speed, cost, miniaturization and power consumption are critical [1].The main components of a high-speed single photon imaging system is the SPAD, which converts a single photon to an electrical pulse, the SPAD front-end circuit, which shapes the pulse and controls the SPAD, and the time-to-digital converter (TDC), which converts the time interval between the detected photon and a reference pulse, or the time between two detected photons, into a digital code. Deep sub-micron (DSM) CMOS technology lends itself very well to the realization of such a system; all the components can be integrated together with very high reliability at a very low cost, digital processing can be readily applied to the detected photons, and dense arrays can be realized for multi-dimensional processing. Over the last decade, CMOS single-photon imaging systems have been applied in the fields of biomedical research, astronomy, nuclear physics, ranging and communications [2], [3], [4].This work describes the design of the main components of a high-speed single photon imaging system for biomedical applications, implemented in a standard, commercial CMOS 0.13 μm technology from IBM. A passively-quenched SPAD pixel was characterized in terms of its noise, temporal resolution, efficiency, and temperature performance. By fabricating the SPAD in a DSM technology, we were able to take advantage of the inherent speed, lower parasitic capacitance, and increased integration density afforded by the CMOS process. Indeed, a dead-time down to 20 ns was achievable with the SPAD front-end circuit, since the total capacitance of the 9.6 x 8.5 μm2 SPAD remained below 100 fF. Also, a new dual-interpolating tapped-delay-line TDC prototype chip was designed and evaluated for a future integration with an SPAD in a multichannel fluorescent lifetime imaging / positron emission tomography (FLIM/PET) system. The design goals were to achieve simultaneously a high-resolution, high throughput, good linearity, wide measurement range, small size and low power. The 8-bit TDC chip measures time intervals with a 156 ns least-significant bit (LSB) between a common STOP pulse from a laser and a START pulse generated by an SPAD, as in a typical time-correlated single-photon counting (TCSPC) acquisition chain shown in figure 1. In this presentation, details of the key design issues and the results from extensive testing will be provided and discussed.

Towards adapting a normal patient database for SPECT brain perfusion imaging

Single-photon emission computerized tomography (SPECT) is a tool which can be used to image perfusion in the brain. Clinicians can use such images to help diagnose dementias such as Alzheimer's disease. Due to the intrinsic stochasticity in the photon imaging system, some form of statistical comparison of an individual image with a ‘normal’ patient database gives a clinician additional confidence in interpreting the image. Due to the variations between SPECT camera systems, ideally a normal patient database is required for each individual system. However, cost or ethical considerations often prohibit the collection of such a database for each new camera system. Some method of adapting existing normal patient databases to new camera systems would be beneficial. This paper introduces a method which may be regarded as a ‘first-pass’ attempt based on 2-norm regularization and a codebook of discrete spatially stationary convolutional kernels. Some preliminary illustrative results are presented, together with discussion on limitations and possible improvements.

Decoding algorithms of single photon counting imager based on two-dimensional Vernier anodes

The decoding algorithms of two-dimensional Vernier anodes are deduced theoretically. The precision of decoding and uniqueness of encoding are proved. The influencing factors of detection sensitivity and spatial resolution are discussed. The single photon imaging system is constructed, and the two-dimensional Vernier collector is fabricated. The image of the ultra-weak emission source is reconstructed. The spatial resolution of the system is about 100 μm.

197 THE TRPV4 CATION CHANNEL MEDIATES STRETCH-EVOKED CA2+ INFLUX AND ATP RELEASE IN PRIMARY UROTHELIAL CELL CULTURES USING ORIGINAL CULTURE CELL STRETCH SYSTEM

You have accessJournal of UrologyBladder and Urethra: Anatomy, Physiology and Pharmacology I1 Apr 2010197 THE TRPV4 CATION CHANNEL MEDIATES STRETCH-EVOKED CA2+ INFLUX AND ATP RELEASE IN PRIMARY UROTHELIAL CELL CULTURES USING ORIGINAL CULTURE CELL STRETCH SYSTEM Mochizuki Tsutomu, Hiroshi Nakagomi, Tatsuya Miyamoto, Isao Araki, Mitsuharu Yoshiyama, and Masayuki Takeda Mochizuki TsutomuMochizuki Tsutomu More articles by this author , Hiroshi NakagomiHiroshi Nakagomi More articles by this author , Tatsuya MiyamotoTatsuya Miyamoto More articles by this author , Isao ArakiIsao Araki More articles by this author , Mitsuharu YoshiyamaMitsuharu Yoshiyama More articles by this author , and Masayuki TakedaMasayuki Takeda More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.253AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The transient receptor potential vanilloid 4 (TRPV4), a possible mechanoreceptor, has been reported to be expressed in the urothelium and urinary bladder smooth muscle cells, and activation of TRPV4 by specific ligands leads to augmentation of bladder contraction amplitude in cystometry and induction or bladder over activity in vivo (J Clin Invest, 2007, J Pharmacol Exp Ther, 2007). However, whether urothelial TRPV4 is required for sensing mechanical stretch, or to what extent urothelial TRPV4 contributes to stretch-evoked ATP release, has not been precisely determined. In the present study, we examined the functional contribution of TRPV4 to stretch-dependent urothelial cell responses and to stretch-evoked adenosine triphosphate (ATP) release in vitro using an original uni-axial cell stretch system. METHODS Eight to12 weeks male WT (C57BL/6Cr) mice and TRPV4KO mice backcrossed on a C57BL/6Cr background were used. (1) RT-PCR method using mouse urothelial primary culture cells. (2) Immunofluorescent method using mouse whole bladder specimen and urothelial primary culture cells. (3) Ca2+-imaging system for the responses to application of 4alpha-phorbol 12, 13 didecanoate (4A-PDD), a TRPV4-selective agonist, and mechanical stretch stimulation in the urothelial primary culture cells. (4) Photon imaging system for direct measurement of ATP released from the urothelial primary cultures. RESULTS TRPV4 mRNA and protein were highly expressed in WT mouse urothelial cells, typically in the basal and intermediate layers, much lesser extent in other cell types of the bladder, but not in the TRPV4KO mice. Urothelial primary culture cells from WT mice, but not TRPV4KO mice, revealed a response to 4A-PDD. Stretch stimulation by our original cell-stretch system evoked intracellular Ca2+ increase in WT urothelial cells, but not in TRPV4KO cells. Potent ATP release occurred following stretch stimulation or 4A-PDD administration in WT urothelial cells, which was dramatically suppressed in TRPV4KO cells. CONCLUSIONS In the present study, we provided the evidence that TRPV4 channel is the candidate molecule involved in mechanosensory transduction in urinary bladder. Chuo, Japan© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e78 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Mochizuki Tsutomu More articles by this author Hiroshi Nakagomi More articles by this author Tatsuya Miyamoto More articles by this author Isao Araki More articles by this author Mitsuharu Yoshiyama More articles by this author Masayuki Takeda More articles by this author Expand All Advertisement Advertisement PDF DownloadLoading ...

Gain characteristic of ultraviolet single photon imaging system

Single-photon-counting imaging technology has been widely used in ultraweak bioluminescence, space environment detection and nuclear radiation detection. The structure and working principle of an ultraviolet single photon imaging system based on the microchannel plates and the wedge and strip anode are introduced. The gain characteristic of dark count of two and three microchannel plates is investigated under different voltages respectively. The experimental and fitted results show that the dark count pulse height distribution of microchannel plate has exponential distribution, and the dark count rate rises as the voltage increases. It is shown that the gain becomes more homogeneous as the voltage increases by measuring the pulse height distribution under different voltages. Then the effects of microchannel plate voltage and distance on system resolution with two microchannel plates are tested. It is revealed that the system resolution rises as the voltage of microchannel plate increases, and can be improved also by increasing the distance of microchannel plate properly.

A Single Photon Imaging System Based on Wedge and Strip Anodes

A new prototype of single photon imaging system based on wedge and strip anodes is developed. The prototype can directly measure the intensity and position information for an ultra-weak radiant source which takes on the character of single photons. The image of the ultra-weak radiant source can be reconstructed with a wedge and strip anodes detector and an electronic readout subsystem by photon counting and photon position sensitive detecting in a period of time. With proper evaluation, the prototype reveals a spatial resolution superior to 150 μm, a 66-kHz maximal counting rate and a dark-count below 0.67 count/cm2s.

紫外单光子计数图像畸变校正

Single photon counting imaging technology has been widely used in space environment detection, astronomy observation, nuclear physics, and ultraweak bioluminescence. However, the distortion of the single photon counting image will badly affect the measurement results. Therefore, the correction of distortion for single photon counting image is very significant. Ultraviolet single photon imaging system with wedge and strip anode is introduced and the influence factor leading to image distortion is analyzed. To correct original distorted image, three different image correction methods, namely, the physical correction, the global correction, and the local correction, are applied. In addition, two parameters, i.e., the position index and the linearity index, are defined to evaluate the performance of the three methods. The results suggest that the correction methods can improve the quality of the initial image without losing gray information of each counting light spot. And the local correction can provide the best visual inspections and performance evaluation among the three methods.

Study of ultraviolet single photon imaging system

An ultraviolet single photon imaging system was built and its structure,working principle and spatial resolution are reported. Ultraviolet single photon can be obtained by ultraviolet lighr emitted by a mercury lamp and is attenuated by filters. Single photon irradiates on the microchannel plate directly, producing the multiplied electrons. The multiplied electrons are collected by wedge and strip anode. The charge signal coming from the anode is transformed to voltage signal by a charge_sensitive preamplifier. Then the voltage signal is filtered and shaped by a main amplifier. The output wave signal is collected by high speed data collection card continuously and processed with software. Finally, a ten-minute counting image of ultraviolet single photon is acquired and its revised image is obtained by image processing. The spatial resolution of this system can reach 150 micrometers as tested with the self-designed resolution board. The system can be used widely for very faint luminescence detecting/imaging, biological luminescence and space environment weak light detection.

Chemiluminescence microscopy as a tool in biomedical research.

Chemiluminescence has become a standard tool in biomedical research. Chemiluminescent probes are used for immunoassays, nucleic acid identification, reporter gene assays, measuring enzyme activity, and the detection of ions and small molecules such as Ca2+, ATP, NO, O2- and H2O2. Along with the development of new chemiluminescent probes, significant progress has been made in techniques to measure chemiluminescence. Ultra-sensitive photometers or luminometers have become widely available and can be obtained with automatic injectors and microplate readers. In addition, imaging photon detectors have been developed that allow the imaging of chemiluminescence from gels, blots, and microplates. Imaging photon detectors have also been attached to microscopes and allow imaging of chemiluminescent probes and reporter genes in cells and tissues. Specific methods of photon collection, storage, and analysis have been developed for microscopic imaging of chemiluminescence. Two of these methods are discussed in detail. The first is a method of data storage that allows days of continuous imaging without creating oversized files. The second is a method for calibrating photon imaging microscopes using a low-light standard. Such calibration will be helpful for comparing the performance of various photon imaging systems and for comparing data obtained in different laboratories.

Wavelet-domain filtering for photon imaging systems

Many imaging systems rely on photon detection as the basis of image formation. One of the major sources of error in these systems is Poisson noise due to the quantum nature of the photon detection process. Unlike additive Gaussian white noise, the variance of Poisson noise is proportional to the underlying signal intensity, and consequently separating signal from noise is a very difficult task. In this paper, we perform a novel gedankenexperiment to devise a new wavelet-domain filtering procedure for noise removal in photon imaging systems. The filter adapts to both the signal and the noise, and balances the trade-off between noise removal and excessive smoothing of image details. Designed using the statistical method of cross-validation, the filter is simultaneously optimal in a small-sample predictive sum of squares sense and asymptotically optimal in the mean-square-error sense. The filtering procedure has a simple interpretation as a joint edge detection/estimation process. Moreover, we derive an efficient algorithm for performing the filtering that has the same order of complexity as the fast wavelet transform itself. The performance of the new filter is assessed with simulated data experiments and tested with actual nuclear medicine imagery.

A YSO/LSO phoswich array detector for single and coincidence photon imaging

The performance of a phoswich array detector module for possible use in a combined single and coincidence photon imaging system has been evaluated. The detector consist of a linear array of discrete 4/spl times/4/spl times/15 mm/sup 3/ YSO elements coupled to a combined detector array/light guide of LSO, 10 mm thick. Since the scintillation light decay time is different in YSO and LSO (70 and 40 ns, respectively), events originating from the two detector materials can be separated by pulse shape discrimination. The front layer of YSO could then be used for detection of low energy, single photon events and the LSO layer for coincidence detection of annihilation radiation. The light collection of the PMTs coupled to the detector was found to be adequate to accurately identify each detector element in the array using the same positioning logic used in conventional EGO block detectors. The average energy resolution of the YSO elements at 140 keV for the block detector was found to be 14.5% FWHM, ranging from 13.8 to 15.4%. Spatial resolution of the detector block in single photon mode, using a high resolution collimator (geometric resolution 6.5 mm at 10 cm) was measured by scanning a /sup 99m/Tc line source. The resolution at 5 and 10 cm from the collimator face was found to be 5.9 and 8.5 mm FWHM, respectively.