Large area x-ray detectors based on phosphors coupled to flat panel amorphous silicon diode technology offer significant
advances for cargo radiologic imaging. Flat panel area detectors provide large object coverage offering high throughput
inspections to meet the high flow rate of container commerce. These detectors provide excellent spatial resolution when
needed, and enhanced SNR through low noise electronics. If the resolution is reduced through pixel binning, further
advances in SNR are achievable. Extended exposure imaging and frame averaging enables improved x-ray penetration
of ultra-thick objects, or "select-your-own" contrast sensitivity at a rate many times faster than LDAs. The areal
coverage of flat panel technology provides inherent volumetric imaging with the appropriate scanning methods. Flat
panel area detectors have flexible designs in terms of electronic control, scintillator selection, pixel pitch, and frame
rates. Their cost is becoming more competitive as production ramps up for the healthcare, nondestructive testing (NDT),
and homeland protection industries. Typically used medical and industrial polycrystalline phosphor materials such as
Gd2O2S:Tb (GOS) can be applied to megavolt applications if the phosphor layer is sufficiently thick to enhance x-ray
absorption, and if a metal radiator is used to augment the quantum detection efficiency and reduce x-ray scatter.
Phosphor layers ranging from 0.2-mm to 1-mm can be "sandwiched" between amorphous silicon flat panel diode arrays
and metal radiators. Metal plates consisting of W, Pb or Cu, with thicknesses ranging from 0.25-mm to well over 1-mm
can be used by covering the entire area of the phosphor plate. In some combinations of high density metal and phosphor
layers, the metal plate provides an intensification of 25% in signal due to electron emission from the plate and
subsequent excitation within the phosphor material. This further improves the SNR of the system.
In recent years, the scan speed of computed tomography (CT) has increased significantly. Not long ago, the state-of-the- art CT was only capable of completing a single scan in 1.0 s per gantry rotation. Nowadays, 0.5 s per revolution is nearly an industry standard. Faster scan speeds demand faster sampling of the projections to combat aliasing artifacts, and higher x-ray tube output to ensure sufficient x-ray photon flux delivered to the scan. These demands often exceed the technological capability of these components. In this paper we performed a detailed analysis on the characteristics of the view aliasing artifact. Based on our analysis and clinical observations, we propose an adaptive view synthesis (AVS) scheme that effectively reduces the demands on the data acquisition system. Detailed performance comparison between the full view sampling and the adaptive view synthesis are performed through computer simulations and phantom experiments. Our analysis indicates that AVS is adequate for routine clinical applications.
Several x-ray parameters must be optimized to deliver exceptional fluoroscopic and radiographic x-ray Image Quality (IQ) for the large variety of clinical procedures and patient sizes performed on a cardiac/vascular x-ray system. The optimal choice varies as a function of the objective of the medical exam, the patient size, local regulatory requirements, and the operational range of the system. As a result, many distinct combinations are required to successfully operate the x-ray system and meet the clinical imaging requirements. Presented here, is a new, configurable and automatic method to perform x-ray technique and IQ optimization using an x-ray spectral model based simulation of the x-ray generation and detection system. This method incorporates many aspects/requirements of the clinical environment, and a complete description of the specific x-ray system. First, the algorithm requires specific inputs: clinically relevant performance objectives, system hardware configuration, and system operational range. Second, the optimization is performed for a Primary Optimization Strategy versus patient thickness, e.g. maximum contrast. Finally, in the case where there are multiple operating points, which meet the Primary Optimization Strategy, a Secondary Optimization Strategy, e.g. to minimize patient dose, is utilized to determine the final set of optimal x-ray techniques.
Laser-generated, hard x-rays are produced in a > 1018 W/cm2 focus of an ultrashort-pulse laser system. The application of ultrashort-duration, laser-generated x-rays to diagnostic medical imaging is discussed. Time-gated detection allows removal of scattered radiation, improved image quality and possible reduction of patient exposure. Methods for improvement of x-ray yield, design of appropriate drive lasers, and applications to mammography and angiography are also discussed.
A first of its kind, multiterawatt, ultrashort pulse laser system is described. The system is capable of producing 125 mJ, 35 fs, 800 nm pulsed with near diffraction limited beam quality at a 10 Hz repetition rate. Methods for control of phase and amplitude distortion during sub- 100 fs amplification are presented.
We report the generation and measurement of 804 nm pulses with durations as short as 20 fs and with peak powers as high as 500 kW from a regeneratively initiated, self-mode-locked Ti:sapphire laser. Pulse duration is shown to decrease, and spectral content to increase, as intracavity power is increased. Control of intracavity focusing and a high-modulation-depth, acousto-optic modulator allow the intracavity power to be maximized. Cavity cubic phase error is minimized by correct design and placement of a GDD compensating prism pair. Methods for accurate determination of the pulse duration without assumption of pulse shape are discussed. Interferometric autocorrelation is accomplished with an interferometer which intrinsically balances dispersion and loss in each arm. Techniques for eliminating pulse distortions during amplification are also presented.