Performance Of Image Intensifier Research Articles

Phosphor screen's FM for LLL image intensifier

The luminescent properties of the phosphor screen of LLL image intensifier has a very close correlation with the performance of the LLL image intensifier. As for the research status of luminescent properties of phosphor screen of the LLL image intensifier, the test, analysis and evaluation research for the various performance parameters of its light-emitting properties, such as luminous efficiency, resolution, are relatively independent, which is not conducive to the overall performance evaluation of a phosphor screen. In view of this, on the basis of the analysis of the correlation between LLL image intensifier performance and the phosphor screen performance, and according to the concept of figure of merit (FM) of LLL image intensifier, a new FM concept of the phosphor screen is proposed. By the relevant experiments, the FM expression of a phosphor screen under different technical and excitation conditions was obtained. The performance of the phosphor screen can be evaluated intuitively and comprehensively by means of FM of the phosphor screen. The performance evaluation contributes to the in-depth study on FM of the LLL image intensifier.

Effect of pro-proximity pulse voltage on the third-generation low light level image intensifiers halo effect

In order to explore the proper working voltage for the third-generation low light level image intensifier, the influence of pro-proximity pulse voltage on image intensifier halo effect is investigated. The pulse voltage is applied to photocathode of image intensifier. Respectively change the high and low level voltage and duty ratio, image intensifier halo images are collected by high-resolution charge-coupled device (CCD). The gray distributions for pixel points on halo image central line are given and comparatively analyzed. The results show that as high level voltage and duty ratio increase, the number of pixel points whose gray value is 255 increases and the border between signal and background becomes clear. When high level voltage is above 200 V and duty ratio is above 60%, the pro-proximity voltage has not great influence on image intensifier halo effect. When low level voltage is above 2 V, photoelectrons escaping from photocathode cannot reach microchannel plate under low level voltage stage. The present investigation is beneficial to the exploration of the optimal working voltage for image intensifier and energy range of photoelectrons escaping from photocathode, and provides an experimental support for the improvement of the third-generation low light level image intensifier performance.

Influence of built-in electric filed on the energy and emergence angle spreads of transmission-mode GaAs photocathode

In order to research the transport characteristic of photoelectrons in different-structure transmission-mode GaAs photocathodes, the energy and emergence angle spreads of photoelectrons reaching the band-bending region are calculated and the photoemission properties are analyzed. Based on the established atomic configuration models and ionized impurity scattering formulas of the uniform-doping and exponential-doping photocathodes, the trajectories of photoelectrons in different GaAs photocathodes have been calculated. The results show that, the emergence angle spread of the exponential-doping photocathode is more centralized than that of the uniform-doping one. The influence of the built-in electric field on the photoemission is obvious in the short-wave region. The built-in electric field not only increases the quantum efficient, but also improves the resolution of photocathode. This research can be propitious to investigate the photoemission mechanism, and to analyze the effect of the excited photoelectrons on the image intensifier performance.

Characterizing an Image Intensifier in a Full-Field Range Imaging System

We are developing a high precision full-field range imaging system. An integral component in this system is an image intensifier, which is modulated at frequencies up to 100 MHz. The range measurement precision is dictated by the image intensifier performance, in particular, the achievable modulation frequency, modulation depth, and waveform shape. By characterizing the image intensifier response, undesirable effects can be observed and quantified with regards to the consequence on the resulting range measurements, and the optimal operating conditions can be selected to minimize these disturbances. The characterization process utilizes a pulsed laser source to temporally probe the gain of the image intensifier. The laser is pulsed at a repetition rate slightly different to the image intensifier modulation frequency, producing a continuous phase shift between the two signals. A charge coupled device samples the image intensifier output, capturing the response over a complete modulation period. Deficiencies in our measured response are clearly identifiable and simple modifications to the configuration of our electrical driver circuit improve the modulation performance.

Performance of image intensifier-equipped X-ray systems for three-dimensional imaging

The performance of image intensifier (II)-equipped C-arm systems for three-dimensional (3D) imaging was investigated. The three-dimensional image quality was evaluated in terms of spatial resolution (modulation transfer function, MTF), contrast resolution, geometrical accuracy and homogeneity depending on the image intensifier format, focal spot size, number of projections and the angular span covered during the data acquisition. Experiments have been performed on a vascular C-arm system equipped with a 38-cm image intensifier. Several objects, including CT performance, MTF and pelvis phantoms, were scanned under various conditions. It was shown that for reasonable acquisition parameters, a contrast resolution below 100 HU could be obtained with standard acquisition strategies. Focusing on the spatial resolution, an almost isotropic three-dimensional resolution of up to 22 lp/cm at 10% modulation could be obtained when a 17-cm II was used. The homogeneity in the resulting images was limited by the remaining scatter and truncations. The resulting geometrical accuracy was in the order of the voxel size.

X-ray image intensifier performance and patient doses for combinationsof supplemental beam filters and vascular contrast agents

We present an investigation of the fluoroscopic imaging and dosimetricperformances of iodine- and gadolinium-based vascular contrast agents incombination with K-absorption edge filters of atomic numbers between 50 (tin)and 82 (lead). These combinations were studied using a theoretical model for arange of diagnostic x-ray spectra (55 to 100 kVp) and for water phantomsrepresentative of thin and thick anatomies. Performance was characterized byradiographic contrast, a derived image quality index, the patient integral andentrance skin doses, and the x-ray tube load. For a given thickness of anatomy,an optimum combination of spectrum kVp, contrast agent and supplemental filterwas defined by maximum imaging performance for a minimum or tolerable x-raytube load and patient dose. It was possible to both improve imagingperformance and reduce dose by the use of an appropriate combination ofspectrum kVp and filter. For gadolinium-based contrast, performance wasoptimized with tungsten filtration at 90 kVp for both thin and thickanatomies. It was not possible, however, to optimize the iodinated contrastperformance with a single combination of supplemental filter and spectrum kVp.The optimal performance for iodinated contrast was achieved with gadoliniumfiltration at 60 kVp for thin anatomy and with ytterbium filtration at 80 kVpfor thick anatomy. The best performance for thin anatomy was that of thecombination of iodinated contrast/gadolinium filter at 60 kVp and the bestperformance for thick anatomy was that of the combination of gadolinium-basedcontrast/tungsten filter at 90 kVp.

Evaluation Of Image Intensifiers

The performance of image intensifiers is rated according to their capability of detecting, recognizing, and identifying objects at low light levels. The most important characteristics limiting these capabilities are noise and imaging parameters. Noise parameters are normally expressed in signal-to-noise ratios, whereas imaging parameters are described by the modulation transfer function and veiling glare. This paper will describe the methods used at the Night Vision Laboratory to determine these parameters and report typical results.

Limitations in Optical Imaging Devices at Low Light Levels

An examination is made of the influence of objective lens parameters on the resolution capabilities of low light level imaging devices. From the resulting characteristics the dependence of the perception range of a given target on the incident light level is deduced. The restrictions imposed by larger lenses on the depth of field of acceptable focus are investigated, and comparisons made with the thresholds set by quantum-noise and optical resolution limitations. Degradations in the performance of image intensifiers due to different levels of image tube dark noise are also discussed.