IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium最新文献

Sparse k-means clustering (Sparse_kM) can exclude uninformative variables and yield reliable parsimonious clustering results, especially for p≫n. In this work, Sparse_kM and data resampling were combined to identify variables of greatest interest and define confidence levels for the clustering. The method was evaluated by statistical simulation and applied to PiB PET amyloid imaging data to identify normal control (NC) subjects with (+) or without (-) evidence of amyloid, i.e., PiB(+/-).

Simulations: A dataset of n=60 observations (3 groups of 20) and p=500 variables was generated for each simulation run; only 50 variables were truly different across groups. The dataset was resampled 20 times, Sparse_kM was applied to each sample and average variable weights were calculated. Probabilities of cluster membership, also called confidence levels, were computed (n=60). Simulations were performed 250 times. The 50 truly different variables were identified by variable weights that were 13-32 times greater than those for the 450 uninformative variables.

Human data: For the PiB PET dataset, images (ECAT HR+, 10-15 mCi, 90 min) were acquired for 64 cognitively normal subjects (74.1±5.4 yrs). Parametric PiB distribution volume ratio images were generated (Logan method, cerebellum reference) and normalized to the MNI template (SPM8) to produce a dataset of n=64 subjects and p=343,099 voxels/image. The dataset was resampled 10 times and Sparse_kM was applied. An average voxel weight image was computed that indicated cortical areas of greatest interest that included precuneus and frontal cortex; these are key areas linked to early amyloid deposition. Seven of 64 subjects were identified as PiB(+) and 47 as PiB(-) with confidence ≥ 90%, where another subject was PiB(+) at lower confidence (80%) and the other 9 subjects were PiB(-) at confidence in the range of 50-70%. In conclusion, Sparse_kM with resampling can help to establish confidence levels for clustering when p≫n and may be a promising method for revealing informative voxels/spatial patterns that distinguish levels of amyloid load, including that at the transitional amyloid +/- boundary.

We developed and evaluated an x-ray photon-counting imaging system using an energy-resolving cadmium zinc telluride (CZT) detector coupled with application specific integrated circuit (ASIC) readouts. This x-ray imaging system can be used to identify different materials inside the object. The CZT detector has a large active area (5×5 array of 25 CZT modules, each with 16×16 pixels, cover a total area of 200 mm × 200 mm), high stopping efficiency for x-ray photons (~ 100 % at 60 keV and 5 mm thickness). We explored the performance of this system by applying different energy windows around the absorption edges of target materials, silver and indium, in order to distinguish one material from another. The photon-counting CZT-based x-ray imaging system was able to distinguish between the materials, demonstrating its capability as a radiation-spectroscopic decomposition system.

A method of attenuation correction in Single Photon Emission Computed Tomography (SPECT), based on emission data only is presented. The algorithm uses the well known Helgason-Ludwig consistency conditions. However, it does not attempt to find the attenuation map, but rather the correction factors for the projection data, which makes the problem simpler and does not need to assume any particular template of the attenuation map. Although the method alone gives only approximate correction, it can be combined with other approaches to provide an effective improvement for scanning systems without the transmission scan functionality.

During image guided interventional procedures, superior resolution and image quality is critically important. Operating the MAF in the new High Definition (HD) fluoroscopy mode provides high resolution and increased contrast-to-noise ratio. The MAF has a CCD camera and a 300 micron cesium iodide x-ray convertor phosphor coupled to a light image intensifier (LII) through a fiber-optic taper. The MAF captures 1024 × 1024 pixels with an effective pixel size of 35 microns, and is capable of real-time imaging at 30 fps. The HD mode uses the advantages of higher exposure along with a small focal spot effectively improving the contrast-to-noise ratio (CNR) and the spatial resolution. The Control Acquisition Processing and Image Display System (CAPIDS) software for the MAF controls the LII gain. The interventionalist can select either fluoroscopic or angiographic modes using the two standard foot pedals. When improved image quality is needed and the angiography footpedal is used for HD mode, the x-ray machine will operate at a preset higher exposure rate using a small focal spot, while the CAPIDS will automatically adjust the LII gain to achieve proper image brightness. HD mode fluoroscopy and roadmapping are thus achieved conveniently during the interventional procedure. For CNR and resolution evaluation we used a bar phantom with images taken in HD mode with both the MAF and a Flat Panel Detector (FPD). It was seen that the FPD could not resolve more than 2.8 lp/mm whereas the MAF could resolve more than 5 lp/mm. The CNR of the MAF was better than that of the FPD by 60% at lower frequencies and by 600% at the Nyquist frequency of the FPD. The HD mode has become the preferred mode during animal model interventions because it enables detailed features of endovascular devices such as stent struts to be visualized clearly for the first time. Clinical testing of the MAF in HD mode is imminent.

The low electronic noise, high resolution, and good temporal performance of electron-multiplying CCDs (EMCCDs) are ideally suited for applications traditionally served by x-ray image intensifiers. In order to improve an expandable clinical detector's field-of-view and have full control of the system performance, we have successfully built a solid-state x-ray detector. The photon transfer technique was used to quantify the EMCCD quantum performance in terms of sensitivity (or camera gain constant, K), read noise (RN), full-well capacity (FW), and dynamic range (DR). Measured results show the system maintains a K of 11.3 ± 0.9 e(-)/DN at unit gain, with a read noise of 71.5±6.0 e(-)rms at gain 1, which decreases proportionally with higher gains. The full well capacity was measured to be 31.3±2.7 ke(-), providing a dynamic range of 52.8±0.7 dB using the chip manufacturer specified clocking scheme. Similar performance was measured with other commercial camera systems. The manufacturer data sheet indicates a dynamic range of 66 dB is plausible with improved read noise and full well capacity. Different clocking schemes are under investigation to assess their impact on improving performance towards idealized values. EMCCD driver clock voltage levels were adjusted individually to check the influence on quantum performance. The clocks work to transfer charge from the image area to readout amplifier through the storage area, horizontal and multiplication registers. Results indicate that the clock that contributes to lateral overflow drain bias is essential to the system performance in terms of dynamic range and full well capacity. The serial register clocks used for transporting charge stored in the pixels of the memory lines to the output amplifier had the largest effect on RN, while others had less of an impact. Initial adjustment of these clocks resulted in a variability of 16% in the performance of dynamic range, 38% in read noise and 56% in full well capacity. Quantifying the quantum performance provides valuable insight into overall performance and enables optimal adjustment of the clocking scheme. Further improvements are expected.

Our laboratory has previously reported on the basic design concepts of an updated FireWire based data acquisition system for depth-of-interaction detector systems designed at the University of Washington. The new version of our data acquisition system leverages the capabilities of modern field programmable gate arrays (FPGA) and puts almost all functions into the FPGA, including the FireWire elements, the embedded processor, and pulse timing and integration. The design is centered around an acquisition node board (ANB) that includes 64 serial ADC channels, one high speed parallel ADC, FireWire 1394b support, the FPGA, a serial command bus and signal lines to support a rough coincidence window implementation to reject singles events from being sent on the FireWire bus. Adapter boards convert detector signals into differential paired signals to connect to the ANB. In this paper we discuss many of the design details, including steps taken to minimize the number of layers in the printed circuit board and to avoid skewing of parallel signals and unwanted bandwidth limitations.

Performance of indirect digital x-ray imagers is typically limited by the front-end components. Present x-ray-to-light converting phosphors significantly reduce detector resolution due to stochastic blurring and k-fluorescent x-ray reabsorption. Thinner phosphors improve resolution at the cost of lowering quantum detection efficiency (QDE) and increasing Swank noise. Magnifying fiber optic tapers (FOTs) are commonly used to increase the field-of-view of small sensor imagers, such as CMOS, CCD, or electron-multiplying CCD (EMCCD) based detectors, which results in a reduction in detector sensitivity and further reduces the MTF. We investigate performance trade-offs for different front-end configurations coupled to an EMCCD sensor with 8 μm pixels. Six different columnar structured CsI(Tl) scintillators with thicknesses of 100, 200, 350, 500, and 1000 μm type high-light (HL) and a 350 μm type high-resolution (HR) (Hamamatsu) and four different FOTs with magnification ratios (M) of 1, 2.5, 3.3, and 4 were studied using the RQA5 x-ray spectrum. The relative signal of the different scintillators largely followed the relative QDE, indicating their light output per absorbed x-ray was similar, with the type HR CsI emitting 57% of the type HL. The efficiency of the FOTs was inversely proportional to M(2) with the M = 1 FOT transmitting 87% of the incident light. At 5 (10) cycles/mm, the CsI MTF was 0.38 (0.22), 0.33 (0.17), 0.37 (0.19), 0.23 (0.09), 0.19 (0.08), and 0.09 (0.03) for the 100, 200, 350HR, 350, 500, and 1000 μm CsI, respectively and the FOT MTF was 0.89 (0.84), 0.80 (0.72), 0.70 (0.60), and 0.69 (0.37) for M = 1, 2.5, 3.3, and 4, respectively. The 1000, 500, and 350HR μm CsI had the highest DQE for low, medium, and high spatial frequency ranges of 0 to 1.6, 1.6 to 4.5, and 4.5 to 10 cycles/mm, respectively. Larger FOT M resulted in a reduction in DQE. Quantifying performance of different front-end configurations will enable optimal selection of components for task-specific designs.

The Solid-State X-ray Image Intensifier (SSXII) is a novel dynamic x-ray imager, based on an array of electron-multiplying CCDs (EMCCDs), that can significantly improve performance compared to conventional x-ray image intensifiers (XIIs) and flat panel detectors (FPDs). To expand the field-of-view (FOV) of the SSXII detectors while maintaining high resolution, a scalable component level modular design is presented. Each module can be fit together with minimum dead-space and optically coupled to one contiguous x-ray converter plate. The electronics of each of the modules consists of a detachable head-board, on which is mounted the EMCCD, and a driver board. The size of the head-boards is minimized to ensure that the modules fit together properly. The driver boards connect with the head-boards via flat cables and are designed to be plugged into the main mother-board that contains an FPGA chip that generates the driving clock signals for the EMCCDs and analog-to-digital converter (ADC). At the front-end, a high speed ADC on each of the driver boards samples and digitizes the EMCCD analog output signal and an extensible modular digital multiplexer back-end is used to acquire and combine image data from multiple modules. The combined digital data is then transmitted to a PC via a standard Camera Link interface. Eventually, this modular design will be extended to a 3×3 or larger array to accomplish full clinical FOVs and enable the SSXII to replace conventional lower-resolution XIIs or FPDs.

Explicit fusion of perfusion data from Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) with coronary artery anatomy from Computed Tomographic Coronary Angiography (CTCA) has been shown to improve the diagnostic yield for coronary artery disease (CAD) compared to either modality alone. However, most clinically available methods were developed for multimodal scanners or require interactive alignment prior to display and analysis. A new approach was developed to register and display the two distributions obtained either from a single multimodal imager or from separate scanners, and a preliminary validation was undertaken using interactive alignment by experts.

Use of an extensible array of Electron Multiplying CCDs (EMCCDs) in medical x-ray imager applications was demonstrated for the first time. The large variable electronic-gain (up to 2000) and small pixel size of EMCCDs provide effective suppression of readout noise compared to signal, as well as high resolution, enabling the development of an x-ray detector with far superior performance compared to conventional x-ray image intensifiers and flat panel detectors. We are developing arrays of EMCCDs to overcome their limited field of view (FOV). In this work we report on an array of two EMCCD sensors running simultaneously at a high frame rate and optically focused on a mammogram film showing calcified ducts. The work was conducted on an optical table with a pulsed LED bar used to provide a uniform diffuse light onto the film to simulate x-ray projection images. The system can be selected to run at up to 17.5 frames per second or even higher frame rate with binning. Integration time for the sensors can be adjusted from 1 ms to 1000 ms. Twelve-bit correlated double sampling AD converters were used to digitize the images, which were acquired by a National Instruments dual-channel Camera Link PC board in real time. A user-friendly interface was programmed using LabVIEW to save and display 2K × 1K pixel matrix digital images. The demonstration tiles a 2 × 1 array to acquire increased-FOV stationary images taken at different gains and fluoroscopic-like videos recorded by scanning the mammogram simultaneously with both sensors. The results show high resolution and high dynamic range images stitched together with minimal adjustments needed. The EMCCD array design allows for expansion to an M×N array for arbitrarily larger FOV, yet with high resolution and large dynamic range maintained.