KEYWORDS: Modulation transfer functions, Digital mammography, X-rays, Sensors, Scintillators, Computing systems, Quantum efficiency, Photodiodes, Signal detection, Signal processing
The physical performance characteristics of a clinical full-field digital mammography (FFDM) system were analyzed for different target/filter conditions using theoretical modeling and experimental measurements. The signal and noise propagation through the various stages of the FFDM system was simulated as a cascaded process and used to compute the frequency dependent detective quantum efficiency (DQE) of the system. The presampling modulation transfer function (MTF) of the system and the noise power spectra (NPS) of the system were measured under the different spectral conditions as used in the theoretical model at an exposure close to 10-mR from which corresponding DQEs were computed. The experimental zero frequency DQE after filtering the x-ray beam through 45-mm acrylic was estimated at 0.51, 0.48, and 0.46 for Mo/Mo, Mo/Rh, and Rh/Rh respectively. A good agreement between the theoretical and experimental results was observed. The clinical digital mammography system appears to exhibit favorable physical characteristics and similar models could be used to design and optimize other imaging systems.
KEYWORDS: Image compression, Mammography, Digital mammography, Image filtering, Eye, Digital imaging, Medical imaging, Eye models, Performance modeling, Data storage
The objective of this study was to evaluate an image compression technique for digital mammography using a nonprewhitening matched filter with an eye filter (NPWE) and channelized Hotelling numerical observer models. A total of 1024 images were cropped from clinical digital mammograms and used as backgrounds. The images were acquired using a clinical full-field digital mammography (FFDM) system and masses of sizes 30, 40, and 60 pixels (100 μm pixel size) were simulated. In addition, microcalcifications were synthetically extracted from clinical digital mammograms and used in the study. Image compression was achieved using a compression software (JPEG 2000, Aware Inc., Bedford, MA) at compression ratios 1:1, 15:1 and 30:1. The channelized Hotelling observer model was investigated only for the mass type lesions by transforming the images to channel space and computing the Hotelling trace for each compression condition. The NPWE model was investigated for both lesions and micocalcifications at all compression conditions and the detection indices were computed by assuming Gaussian statistics and by the 'percent correct’ detection method. The results of the study indicated a reduction in detection with increased compression for microcalcifications at 30:1 compression while almost no variation in detection index was observed for the simulated masses.
KEYWORDS: Digital mammography, Imaging systems, Data modeling, Signal to noise ratio, Signal detection, Error analysis, Sensors, Modulation transfer functions, X-ray imaging
In this investigation we studied the imaging characteristics of a mammographic screen-film (MinR-2000, Eastman Kodak Co.) and an amorphous-silicon flat-panel digital mammography system (Senographe 2000D, GE Medical Systems) based on information perception by human observers. The focus of the study was to utilize an effective means to estimate the contrast-detail characteristics of x-ray imaging systems at various threshold levels to evaluate system performance with reduced observer subjectivity. We obtained three images of a contrast-detail phantom (CDMAM, Nuclear Associates) with screen-film and three images with digital mammography under identical exposure conditions. The digital images were printed using dry film printer (DryView 8600, Eastman Kodak Co.) after being windowed/leveled appropriately by two experienced radiologists. Seven observers reviewed the images and 'proportion correct' detection data were computed for each observer. A psychophysical signal detection model that hypothesizes a continuous decision variable internal to the observer with Gaussian probability density functions was used to fit the experimental observer data. Projection data from the detection curves at 50%, 62.5%, and 75% threshold levels were used to generate contrast-detail diagrams. Digital mammography, on average, exhibited lower (better) threshold contrast-detail characteristics compared to screen-film mammography.
KEYWORDS: Sensors, Signal to noise ratio, Modulation transfer functions, X-ray detectors, X-rays, Electric field sensors, Spatial resolution, Tellurium, Semiconductors, X-ray characterization
In this paper, the detected signal-to-noise was measured and related to the tube current (mA) setting. The line spread function amplitude (LSF) dependence on drift distance of a 3 mm thick detector, for 100 kVp, 100 mA, with an applied electric field of 50 V/mm, and 100 V/mm, were measured. In addition, the dependence of the modulation transfer function [MTF(f)] of the x-ray detector system on the applied bias voltage has been experimentally determined. The experimental setup, although is not offered for large field-of-view imaging applications, offers capabilities for feasibility studies, research and evaluation of the temporal response and noise characteristics of a Cd1-xZnxTe detector, for fast digital radiographic and CT applications. The experimental results indicate that Cd1-xZnxTe detectors exhibit both a high signal-to-noise ratio and linear response, as well as a good spatial resolution within the diagnostic energy range. Tor system improves both with increasing applied bias voltage and decreasing detector thickness. A study is in process aimed at improving the spatial resolution of the x-ray system by suitable optimization of the system geometry as well as the system temporal response.
Bindu Pillai, George Giakos, Amlan Dasgupta, Samir Chowdhury, Srinivasan Vedantham, P. Ghotra, J. Odogba, Victor Vega-Lozada, Ravi Guntupalli, Sankararaman Suryanarayanan, Robert Endorf, Anthony Passalaqua, William Davros
The detected signal and noise contributions were measured and related to the radiation exposure and tube current tube setting. Furthermore, the detector contrast has been experimentally determined. The experimental results indicate that Cd1-xZnxTe detectors have high detector contrast resolution. Therefore, they appear to be very attractive for x-ray digital imaging applications.
Amlan Dasgupta, George Giakos, Samir Chowdhury, Srinivasan Vedantham, Sankararaman Suryanarayanan, Ravi Guntupalli, Bindu Pillai, Permjit Ghotra, Donna Richardson, Robert Endorf, Anthony Passalaqua
The purpose of the study is to optimize the input and the output parameters of a dual energy CdZnTe semiconductor detector for chest radiography. The optimal detector parameters were obtained by maximizing the figure of merit, defined as the ratio between the square of the signal-to- noise ratio and the absorbed dose, for chest radiography.
The goal of this study is to optimize the gas composition medium and strip geometry of a small-field of view gas- microstrip detector for medical imaging applications, such as x-ray digital imaging, computed tomography, quantitative autoradiography, including other nuclear medicine applications. The gas multiplication factor as well as the electrical parameters of the microstrip substrate have been studied. The results of this study indicate that an adequate gas multiplication process can be achieved with a Xe filled gas detector operating up to 10 atm.
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