Norbert Jung

Fluoroscopic x-ray imaging with amorphous silicon thin-film arrays

The dream of an all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realization in 2D thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency as a function of dose and spatial frequency. We further present an analysis of the different noise sources and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type of x-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.

Technical and clinical results of an experimental flat dynamic (digital) x-ray image detector (FDXD) system with real-time corrections

A clinical imaging system based upon an amorphous-Silicon (a- Si) flat dynamic (digital) X-ray image detector (FDXD) has been developed. The objectives of this experimental set-up were to determine the physical image quality and to establish the clinical feasibility of a flat-panel x-ray detector for radiography and fluoroscopy (R&F) applications. The FDXD acquires dynamic X-ray images at high frame rates in both continuous and pulsed fluoroscopic modes, lower frame rate exposures and single shots. The system has been installed in a clinical research room at The General Infirmary, Leeds (UK) and is being evaluated in a variety of universal R&F contrast medium aided examinations, including barium swallows, meals and enema examinations. In addition, general radiographic examinations have been performed. Both the established benefits and possible drawbacks of this type of system, together with the potential solutions, are discussed in this paper. Approach, design and set-up of the system are presented, and the dose efficiency and image quality achieved in clinical operation are explained. The technical and medical phantom images have been evaluated and analyzed. The results of the clinical examinations in mixed applications are discussed. The results of the measurements and examinations performed to date on this experimental FDXD system confirm the potential of this new type of digital X-ray image detector.

Dynamic X-ray imaging system based on an amorphous silicon thin-film array

In this paper we address design concepts and performance characterization with our laboratory x-ray detector system. Key component is a 1k2 pixel TFT switched photodiode array with a pixel pitch of 200 micrometer. It is built of a-Si:H with a CsI:Tl scintillator layer. The detector system can be used for radiography and fluoroscopy applications with up to 30 images/s. It shows a S/N-ratio better than 23dB at a dose of 10nGy/frame and reaches a value for DQE of more than 60% at low spatial frequencies. We have developed a new evaporation process for CsI:Tl deposition directly on the array. It yields an x-ray sensitivity close to the theoretical limit and a spatial resolution on a sufficiently high level. An optimized plate design in combination with a dedicated charge sensitive readout amplifier chip lead to a very low level of electronic noise. In particular sources and properties of electronic noise and signal crosstalk have shown to be crucial for the clinical use of the new technology. The visual impression of the remaining noise in the images from our system is isotropic. This means especially that synchronous noise has been reduced to the edge of visibility.

Real-time image processing platform for the correction of x-ray-detector-related artifacts

Novel detector systems based on large area thin film electronics have the potential for an excellent image quality. However, the raw images derived from such detectors show various artifacts that have to be removed in real-time before the image is visualized to the user. Hence, superior flexibility in the applicable algorithms, sufficient system performance scalability, and a short processing delay are the key factors for the choice of a well suited processing platform due to the nature of the artifacts and due to the requirements of the medical applications. Further the very rapid progress in the available processing hardware has to be taken into account. A system comprising multiple nodes of a modern digital signal processor family can properly fulfill the key demands: high processing performance, strong data handling, full programmability and a processor family roadmap linked to state-of-the-art chip technology. Architecture principles, implementation aspects and first results derived from our new demonstrator system based on the modern SHARC DSP family are presented. The given first generation of the multiprocessor system corrects the basic artifacts at pixel rates of 50 Mpixel/s in 32-bit floating point arithmetic at a processing delay in the millisecond range.

Digital high-resolution high-performance CCD camera with 2048 x 2048 pixels for dynamic applications

A modular, multi-channel digital camera system has been designed.It provides a platform for the investigation of high-speed, high-resolution CCD sensors that are suited for dynamic medical x-ray imaging. The system supports frame rates from 30 frames per second (fps) for images with 1024 X 1024 pixels and 6-8 fps for images with 2048 X 2048 pixels. The complete system comprises camera head and correction circuits and yields a consecutive output stream of data. The camera electronics permits the testing of sensors with up to four parallel readout channels. It offers a variable bandwidth of up to 25 MHz per channel with a digitization resolution of 12 bits. The modulatory and programmability allow the adaptation of the camera system to a wide range of interesting applications. The camera electronics consists of a majority of sensor independent and a relatively small section of sensor dependent components. A detailed description of the camera, methods for performance analysis, measurement results, images, and a noise analysis are presented and discussed. As an example, linearity, MTF and noise of the camera system equipped with the FTF2020, a 2k X 2k CCD sensor from Phillips Professional Imaging have ben measured. The noise contains fixed pattern and random components. The developed camera architecture is capable of fulfilling the high requirements of dynamic, high-resolution medical imaging.

Dynamic X-Ray Imaging System based on an all-solid-state Detector

New digital detector systems based on all-solid-state large area elec-tronics offer a number of advantages for the user, like no image distortions, flat and light weight housing, no veiling glare, and large dynamic range. On the other hand, they require a dedicated image preprocessing to exploit their full image quality. In this paper we address design concepts, performance charac-terization and resulting image preprocessing aspects of our experimental de-tector system. The system comprises the detector frontend and a realtime image preprocessing unit with an interface to a commercial digital video system. It is intended for clinical evaluation of this new technology.