Rudolf Kemner

Real-time Diagnostic Imaging with a Novel X-ray Detector with Multiple Screen CCD Sensors

In reference 1 we have presented the principle of an X-ray detector based upon a screen coupled to an array of multiple CCD sensors. In reference 2 we focus on the characterization of the image quality: resolution (MTF) and noise behavior in the overlap area. Simple (and cheap) low F# lenses likely show distortion which means that not all imaged pixels have the same magnification. This may affect resolution. Lenses with (some) barrel distortion have the benefit of less vignetting. The correction of distortion in combination with a rotation adjustment requires interpolation. Interpolation affects the noise properties so care must be taken in order to avoid that the noise characterization of the reconstructed image mosaic i.e. the noise texture becomes spatially non uniform. We present an analysis of the influence of lens distortion and interpolation in cases of small rotation correction on the image mosaic. The image processing appears not to diminish the image quality provided the processing parameters are set correctly. The calibration of the imaging mosaic geometry is crucial. We therefore present a robust extraction algorithm. In this paper our main interest is on MTF and quantum noise properties. The lab prototype hardware is designed such (cubic spline interpolation) that also the lens distortion can be compensated. For this purpose ASICs are designed by the company AEMICS. This enables relative cheap optical components with low F# and a short building length. We have obtained and will present radiographic exposures of static phantoms.

Physical image quality evaluation of a CCD-based x-ray image intensifier digital fluorography system for cardiac applications

An evaluation of the physical imaging performance of a prototype CCD-based TV camera (XTV16) cardiac Digital Fluorography system is presented. A tube-based TV camera (XTV11) operates in parallel, via a 50% mirror, allowing a direct comparison between the two different TV image recording technologies. The MTF, Noise Power Density (NPD) spectrum and the DQE of the system have been determined. The NPD analysis has been completed in both horizontal and vertical directions and, for completeness, a two dimensional noise analysis of the system has also been carried out. An audit of the main sources of noise in the systems is presented. The effectiveness of image corrections in minimizing systematic noise due to the CCD camera is demonstrated. The DQE spectra of both systems at zero frequency are X-ray quantum noise limited and they are both operating dose efficiently. The DQE spectrum in the horizontal direction of the XTV16 at high spatial frequencies is shown to be superior to that of the XTV11 which may translate to improved rendition of small features in clinical images. The CCD camera system described here s now used in the Cardio-Vascular systems of a major European company.

Image quality characteristics of a novel x-ray detector with multiple screen: CCD sensors for real-time diagnostic imaging

We have presented the principle of an x-ray detector based upon a screen coupled to an array of multiple CCD sensors. We now focus on the characterization of the image quality: resolution (MTF) and noise behavior in the overlap area. Simple low F lenses likely show distortion which means that not all imaged pixels have the same magnification. This may affect resolution. In the overlap area the image is reconstructed by interpolation between two sensors. Interpolation affects the noise properties so care must be taken in order to avoid that the noise characterization of the reconstructed image mosaic becomes spatially non uniform.We present an analysis of the influence of lens distortion and interpolation in the overlap area on the image mosaic. The image processing appears not to diminish the image quality provided the processing parameters are set correctly. We therefore present a robust extraction algorithm. In order to evaluate in real-time the image quality of the proposed detector system, we are building a 2 by 2 lens-CCD sensor system as a lab prototype. The main interest is on MTF and quantum noise properties. The hardware is designed such that also the lens distortion can be compensated. This enables relative cheap optical components with low F and a short building length. We have obtained and will present radiographic exposures of static phantoms.

Novel x-ray detector with multiple-screen-CCD sensors for real-time diagnostic imaging

In this contribution we propose an alternative x-ray detector based upon multiple screen-CCD sensor combinations. The impinging x-ray quanta are detected by a scintillator screen (e.g. CsI) and converted to light photons (typ. 1200 photons per absorbed x-ray quantum). We propose a number of lens-CCD sensors for standard video performance to detect the light photons coming out of an x-ray intensifying screen. Due to the smaller demagnification the coupling efficiency is better even with moderate quality (F number) lenses. We thus obtain a matrix of subimages, the system is constructed such that the subimages partially overlap. With digital image processing we construct from the subimages a single high quality image. Special hardware (incl. ASICS) has been developed for imaging at video rates, enabling (almost) fluoroscopy with this new detector. We show a viable digital x-ray imaging detector concept by means of our 2 by 2 CCD camera prototype and real-time processing engine. The image quality, MTF and noise properties are satisfactory and well in the diagnostic application range.

Improving display quality by a digital convergence correction system for multibeam CRTs

In the field of medical imaging there is a need for high-resolution high-brilliance monochromatic CRT displays. However, at higher brightness levels the resolution of these displays decreases, due to the increasing spot size. In order to improve the performance of the CRT display a relatively simple method, called the multi-beam concept, is introduced. Using this technique a higher brightness can be realized without an increase of the spot size and therefore a better display quality can be achieved. However, for successful exploitation of the multi-beam concept it is necessary to minimize the convergence error of the CRT display. For this purpose two circuits have been realized, where the convergence error is reduced by an analogue and a digital method respectively. The analogue implementation means an improvement for the applicability of the multi-beam concept, however, in order to achieve major image quality improvement the use of the digital system is necessary.

Improving display quality by means of real-time image processing for multibeam CRTs

In this paper we address the correction of the convergence error of a monochrome multi-beam Cathode Ray Tube (CRT) by means of digital video-signal processing. Correction of the convergence (horizontal misalignment) of the three electron beams with respect to each other in the CRT, will improve the resolution and brightness of the CRT. We apply the theory of fractional delay filtering to design a digital Finite Impulse Response (FIR) filter that is capable of interpolating the digital video signal. Emphasis is on small four-tap filters, to reduce the necessary amount of processing power. The variable filter has been implemented on a TMS320C80 signal processor to assess the performance of standard DSP hardware on this type of filtering. The analysis of four-tap fractional delay filters has led to useful designs in our application. The implementation on the TMS320C80 processor shows that the variable filter can be implemented with about 10 (parallel) instructions, yielding a maximum throughput of 16 M pixels/s on the TMS320C80 DSP at 40 MHz. We demonstrate (results of) a real-time DSP (TMS320C80) implementation of a variable delay video processing for horizontal convergence correction. The image quality, MTF and brightness are quite satisfactory and well in the diagnostic application area.