This PDF file contains the front matter associated with SPIE Proceedings Volume 8853 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

X-ray photons are detected using an Lu₂(SiO₄)O [LSO] single-crystal scintillator with a decay time of 40 ns and a multipixel photon counter (MPPC). The photocurrent from the MPPC is amplified by a high-speed current-voltage amplifier with an 80 MHz-gain-band operational amplifier, and the 200-ns-width event pulses are sent to a multichannel analyzer to measure X-ray spectra. The MPPC is driven in the pre-Geiger mode at a bias voltage of 70.7 V and a temperature of 23°C. Photon-counting computed tomography (PC-CT) is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by linear scanning. The exposure time for obtaining a tomogram was 10 min with scan steps of 0.5 mm and rotation steps of 1.0°. At a tube voltage of 100 kV, the maximum count rate was 350 kcps/pixel. We carried out PC-CT using gadolinium media and confirmed the energydispersive effect with changes in the lower level voltage of event pulses using a comparator.

We report on our efforts toward the development of silicon (Si) strip detectors for energy-resolved clinical breast imaging. Typically, x-ray integrating detectors based on scintillating cesium iodide CsI(Tl) or amorphous selenium (a- Se) are used in most commercial systems. Recently, mammography instrumentation has been introduced based on photon counting silicon Si strip detectors. Mammography requires high flux from the x-ray generator, therefore, in order to achieve energy resolved single photon counting, a high output count rate (OCR) for the detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel, provided that the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions. We present our methods and results from the optimization of prototype detectors based on Si strip structures. We describe the detector optimization and the development of ASIC readout electronics that provide the required spatial resolution, low noise, high count rate capabilities and minimal power consumption.

X-ray photon counting was performed using a silicon X-ray diode (Si-XD) at a tube current of 2.0 mA and tube voltages ranging from 50 to 70 kV. The Si-XD is a high-sensitivity Si photodiode selected for detecting X-ray photons, and Xray photons are directly detected using the Si-XD without a scintillator. Photocurrent from the diode is amplified using charge-sensitive and shaping amplifiers. To investigate the X-ray-electric conversion, we performed the event-pulseheight (EPH) analysis using a multichannel analyzer. Photon-counting computed tomography (PC-CT) is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The exposure time for obtaining a tomogram was 10 min at a scan step of 0.5 mm and a rotation step of 1.0°. In PC-CT at a tube voltage of 70 kV, the image contrast of iodine media fell with increasing lower-level voltage of the event pulse using a comparator.

X-ray photon counting was performed using a readymade silicon-PIN photodiode (Si-PIN-PD) at tube voltages ranging from 42 to 60 kV, and X-ray photons are directly detected using the 100 MHz Si-PIN-PD without a scintillator. Photocurrent from the diode is amplified using charge-sensitive and shaping amplifiers. Using a multichannel analyzer, X-ray spectra at a tube voltage of 60 kV could easily be measured. The photon-counting computed tomography (PCCT) is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. In the PC-CT, we confirmed the energy-dispersive effect with changes in lower-level voltage of the event pulse using a comparator.

An adaptive pinhole aperture that fits a GE MaxiCam Single-Photon-Emission Computed Tomography (SPECT) system has been designed, built, and is undergoing testing. The purpose of an adaptive aperture is to allow the imaging system to make adjustments to the aperture while imaging data are being acquired. Our adaptive pinhole aperture can alter several imaging parameters, including field of view, resolution, sensitivity, and magnification. The dynamic nature of such an aperture allows for imaging of specific regions of interest based on initial measurements of the patient. Ideally, this mode of data collection will improve the understanding of a patient’s condition, and will facilitate better diagnosis and treatment. The aperture was constructed using aluminum and a low melting point, high-stopping-power metal alloy called Cerrobend. The aperture utilizes a rotating disk for the selection of a pinhole configuration; as the aluminum disk rotates, different pinholes move into view of the camera face and allow the passage of gamma rays through that particular pinhole. By controlling the angular position of the disk, the optical characteristics of the aperture can be modified, allowing the system to acquire data from controlled regions of interest. First testing was performed with a small radioactive source to prove the functionality of the aperture.

This work outlines the development of a multi-pinhole SPECT system designed to produce a synthetic-collimator image of a small field of view. The focused multi-pinhole collimator was constructed using rapid-prototyping and casting techniques. The collimator projects the field of view through forty-six pinholes when the detector is adjacent to the collimator. The detector is then moved further from the collimator to increase the magnification of the system. The amount of pinhole-projection overlap increases with the system magnification. There is no rotation in the system; a single tomographic angle is used in each system configuration. The maximum-likelihood expectation-maximization (MLEM) algorithm is implemented on graphics processing units to reconstruct the object in the field of view. Iterative reconstruction algorithms, such as MLEM, require an accurate model of the system response. For each system magnification, a sparsely-sampled system response is measured by translating a point source through a grid encompassing the field of view. The pinhole projections are individually identified and associated with their respective apertures. A 2D elliptical Gaussian model is applied to the pinhole projections on the detector. These coefficients are associated with the object-space location of the point source, and a finely-sampled system matrix is interpolated. Simulations with a hot-rod phantom demonstrate the efficacy of combining low-resolution non-multiplexed data with high-resolution multiplexed data to produce high-resolution reconstructions.

AdaptiSPECT is a pre-clinical adaptive SPECT imaging system under final development at the Center for Gamma-ray Imaging. The system incorporates multiple adaptive features: an adaptive aperture, 16 detectors mounted on translational stages, and the ability to switch between a non-multiplexed and a multiplexed imaging configuration. In this paper, we review the design of AdaptiSPECT and its adaptive features. We then describe the on-going integration of the imaging system.

To achieve high spatial resolution required in nuclear imaging, scintillation light spread has to be controlled. This has been traditionally achieved by introducing structures in the bulk of scintillation materials; typically by mechanical pixelation of scintillators and fill the resultant inter-pixel gaps by reflecting materials. Mechanical pixelation however, is accompanied by various cost and complexity issues especially for hard, brittle and hygroscopic materials. For example LSO and LYSO, hard and brittle scintillators of interest to medical imaging community, are known to crack under thermal and mechanical stress; the material yield drops quickly with large arrays with high aspect ratio pixels and therefore the pixelation process cost increases. We are utilizing a novel technique named Laser Induced Optical Barriers (LIOB) for pixelation of scintillators that overcomes the issues associated with mechanical pixelation. In this technique, we can introduce optical barriers within the bulk of scintillator crystals to form pixelated arrays with small pixel size and large thickness. We applied LIOB to LYSO using a high-frequency solid-state laser. Arrays with different crystal thickness (5 to 20 mm thick), and pixel size (0.8×0.8 to 1.5×1.5 mm²) were fabricated and tested. The width of the optical barriers were controlled by fine-tuning key parameters such as lens focal spot size and laser energy density. Here we report on LIOB process, its optimization, and the optical crosstalk measurements using X-rays. There are many applications that can potentially benefit from LIOB including but not limited to clinical/pre-clinical PET and SPECT systems, and photon counting CT detectors.

A Monte Carlo simulation of micro-channel plate (MCP) with particular interest in its effect on energy resolution performance is presented. Important physical processes occurring in MCP channels are described and modeled, including secondary electron (SE) yield, SE emission, and primary electron reflection. The effects causing channel saturation are also introduced. A two dimensional Monte Carlo simulation is implemented under the assumption of unsaturated channel. Simulation results about basic MCP performances and especially gain and energy resolution performances are presented and analyzed. It’s found that energy resolution as an intrinsic property of MCP cannot be improved simply by adjusting system parameters; however it can be improved by increasing input signal or number of photoelectrons (PEs) in the context of image intensifier. An initial experiment with BazookaSPECT detector and CsI(Tl) scintillator is performed to validate and correlate with the simulation results and good agreement is achieved.

The plasma display panel (PDP) is popular in the large area flat panel display market due to its relatively simple cell structure, low cost materials, and uncomplicated manufacturing process. The cell structure of PDP, which consists of electrodes and gas mixture, could be utilized in the manufacture of radiation detectors. In this study, we developed a plasma display panel based x-ray detector (PXD) based on Monte-Carlo simulation. This prototype detector panel has row and column strips, and it can thus be utilized as an imaging detector. To achieve the 2D x-ray image from the developed panel, a PXD dedicated driving and data acquisition circuit has been developed. Now we integrate the individual modules into a system. We hope to further study signal processing to achieve the first x-ray image of PXD.

Conventional radiography uses a single point x-ray source with a fan or cone beam to visualize various areas of the human body. An imager records the transmitted photons—historically film and now increasingly digital radiography (DR) flat panel detectors—followed by optional image post-processing. Some post-processing techniques of particular interest are tomosynthesis, and dual energy subtraction. Tomosynthesis adds the ability to recreate quasi-3D images from a series of 2D projections. These exposures are typically taken along an arc or other path; and, tomosynthesis reconstruction is used to form a three-dimensional representation of the area of interest. Dual-energy radiography adds the ability to enhance or “eliminate” structures based on their different attenuation of well-separated end-point energies in two exposures. These advanced capabilities come at a high cost in terms of complexity, imaging time, capital equipment, space, and potentially reduced image quality due to motion blur if acquired sequentially. Recently, the prospect of creating x-ray sources, which are composed of arrays of micro-emitters, has been put forward. These arrays offer a flat-panel geometry and may afford advantages in fabrication methodology, size and cost. They also facilitate the use of the dual energy technology. Here we examine the possibility of using such an array of x-ray sources combined with high frame-rate (~kHz) DR detectors to produce advanced medical images without the need for moving gantries or other complex motion systems. Combining the advantages of dual energy imaging with the ability to determine the relative depth location of anatomical structures or pathological findings from imaging procedures should prove to be a powerful diagnostic tool. We also present use cases that would benefit from the capabilities of this modality.

Glaucoma was diagnosed or tracked by the intraocular pressure (IOP) generally because it is one of the physiology parameters that are associated with glaucoma. But measurement of IOP is not easy and consistence under different measure conditions. An infrared videopupillography is apparatus to monitor the pupil size in an attempt to bypass the direct IOP measurement. This paper propose an infrared videopupillography to monitoring the pupil size of different light stimulus in dark room. The portable infrared videopupillography contains a camera, a beam splitter, the visible-light LEDs for stimulating the eyes, and the infrared LEDs for lighting the eyes. It is lighter and smaller than the present product. It can modulate for different locations of different eyes, and can be mounted on any eyeglass frame. An analysis program of pupil size can evaluate the pupil diameter by image correlation. In our experiments, the eye diameter curves were not smooth and jagged. It caused by the light spots, lone eyelashes, and blink. In the future, we will improve the analysis program of pupil size and seek the approach to solve the LED light spots. And we hope this infrared videopupillography proposed in this paper can be a measuring platform to explore the relations between the different diseases and pupil response.

Modern imaging modalities, such as Computed Tomography (CT), Digital Breast Tomosynthesis (DBT) or Magnetic Resonance Tomography (MRT) are able to acquire volumetric images with an isotropic resolution in micrometer (um) or millimeter (mm) range. When used in interactive telemedicine applications, these raw images need a huge storage unit, thereby necessitating the use of high bandwidth data communication link. To reduce the cost of transmission and enable archiving, especially for medical applications, image compression is performed. Recent advances in compression algorithms have resulted in a vast array of data compression techniques, but because of the characteristics of these images, there are challenges to overcome to transmit these images efficiently. In addition, the recent studies raise the low dose mammography risk on high risk patient. Our preliminary studies indicate that by bringing the compression before the analog-to-digital conversion (ADC) stage is more efficient than other compression techniques after the ADC. The linearity characteristic of the compressed sensing and ability to perform the digital signal processing (DSP) during data conversion open up a new area of research regarding the roles of sparsity in medical image registration, medical image analysis (for example, automatic image processing algorithm to efficiently extract the relevant information for the clinician), further Xray dose reduction for mammography, and contrast enhancement.

Having the ability to take an accurate 3D image of a tumor greatly helps doctors diagnose it and then create a treatment plan for a patient. One way to accomplish molecular imaging is to inject a radioactive tracer into a patient and then measure the gamma rays emitted from regions with high-uptake of the tracer, viz., the cancerous tissues. In large, expensive PET- or SPECT-imaging systems, the 3D imaging easily is accomplished by rotating the gamma-ray detectors and then employing software to reconstruct the 3D images from the multiple 2D projections at different angles of view. However, this method is impractical in a very compact imaging system due to anatomical considerations, e.g., the transrectal gamma camera under development at Brookhaven National Laboratory (BNL) for detection of intra-prostatic tumors. The camera uses pixilated cadmium zinc telluride (CdZnTe or CZT) detectors with matched parallel-hole collimator. Our research investigated the possibility of using a collimator with slanted holes to create 3D pictures of a radioactive source. The underlying concept is to take 2D projection images at different angles of view by adjusting the slant angle of the collimator, then using the 2D projection images to reconstruct the 3D image. To do this, we first simulated the response of a pixilated CZT detector to radiation sources placed in the field of view of the camera. Then, we formulated an algorithm to use the simulation results as prior knowledge and estimate the distribution of a shaped source from its 2D projection images. From the results of the simulation, we measured the spatial resolution of the camera as ~7-mm at a depth of 13.85-mm when using a detector with 2.46-mm pixel pitch and a collimator with 60° slant angle.