Nikiforos G. Theofanous

Image recognition and neuronal networks: Intelligent systems for the improvement of imaging information

Summary Intelligent computerised systems can provide useful assistance to the physician in the rapid identification of tissue abnormalities and accurate diagnosis in real-time. This paper reviews basic issues in medical imaging and neural network-based systems for medical image interpretation. In the framework of intelligent systems, a simple scheme that has been implemented is presented as an example of the use of intelligent systems to discriminate between normal and cancerous regions in colonoscopic images. Preliminary results indicate that this scheme is capable of high accuracy detection of abnormalities within the image. It can also be successfully applied to different types of images, to detect abnormalities that belong to different cancer types.

Photorealistic integral photography using a ray-traced model of capturing optics

We present a new approach for computer-generated integral photography (IP) based on ray tracing, for the reconstruction of high quality photorealistic 3-D images of increased complexity. With the proposed methodology, all the optical elements of a single-stage IP capturing setup are physically modeled for the production of real and virtual orthoscopic IP images with depth control. This approach is straightforward for translating a computer-generated 3-D scene to an IP image, and constitutes a robust methodology for developing modules that can be easily integrated in existing ray tracers. An extension of this technique enables the generation of photorealistic 3-D videos [integral videography (IV)] and provides an invaluable tool for the development of 3-D video processing algorithms.

Accurate lattice extraction in integral images

Integral imaging is one of the most promising techniques for delivering three-dimensional content. Most processing tasks usually require prior knowledge of the size and positions of the elemental images that comprise an integral image. In this paper we propose an automated method for calibrating the acquisition setup, by applying a preprocessing stage to an acquired integral image. The skew angle is extracted and the size and positions of the elemental images are accurately determined. For these purposes a method is developed to automatically identify an elemental image lattice that best matches the acquired integral image.

Use of an adaptive 3D-DCT scheme for coding multiview stereo images

Our work presents a novel way for compressing image sets that form multiview stereo images used in three dimensional display devices. These image sets exhibit high inter-image correlation that remains unexploited when classic image compression techniques are applied. Our efforts are focused in the development of a compression algorithm based on the three dimensional discrete cosine transform (3D-DCT) which is an extension of the two dimensional case, used widely in image compression. An adaptive 3D-DCT scheme is implemented based on the exploitation of the increased spatial redundancy of certain parts of the image set. This is primarily achieved by locating image parts that belong to the distant background and hence remain unaltered throughout the image set. This technique achieves high compression ratios while maintaining the quality needed for correct stereoscopic viewing

The electronics of a control system for micromirrors in a laser-scanning device

The electronics and software developed for the control system of a micromirror-based laser-scanning endoscope are presented in conjunction with features of the micromirrors and their driving requirements. These micromirrors, which are crucial for the laser-scanning operation of the endoscope device, are embedded in the endoscope head and have been manufactured using silicon MEMS (Micro Electro-Mechanical Systems) technology. The micromirrors are electrostatically deflected and driven by appropriate high-voltage waveforms created in the control system. This computer-based system, using appropriate software, generates the control waveforms, which, after adequate amplification, drive the scanning micromirrors. The electronics developed are capable of generating control voltages with amplitudes up to 440 V pk-pk, within a bandwidth from DC to 20 kHz, and ensures an electrostatic driving of scanning micromirrors with a high positioning accuracy in the sub-pixel range.

A High-Performance Imaging and Control System for a Micromirror-Based Laser-Scanning Endoscope Device

A novel reduced-size endoscope system based on a laser-scanning technology has been developed by the authors. This system employs specific silicon micromirrors and ensures a high-resolution color imaging with improved characteristics. A critical part of the device is its data-acquisition, control, and processing (DACP) system for real-time handling of the collected digital images. The supporting software is an event-driven application for the MS-Windows operating system that incorporates important features such as improved portability through the open PC architecture, cost effectiveness, high performance, and efficient scalability by using a symmetric multiprocessing desktop computer. In this paper, a presentation of the DACP system is performed with a focus in the software developed, which exploits the multithreading technology, resulting in a high-performance endoscope device

A laser-scanning endoscope based on polysilicon micromachined mirrors with enhanced attributes

A miniaturized laser scanning endoscope is presented which makes use of three lasers to illuminate a sample with a red, a green and a blue wavelength simultaneously. Scattered light from the sample is descanned and chromatically separated into the three channels for detection and postprocessing to compose a color image. The scanning subsystem consists of two micro-electro-mechanical mirrors suitable for mass production. The endoscope head can be assembled fast and at low cost. A resolution of the order of 16 lines per mm is achieved for a working distance common in endoscopy. Considerations of the system design include the operation of the mico mirrors, the filtering of reflected light by using polarization effects and a strategy to cope with color metamery. An expert system based on a neural network was found able to analyze endoscopic images to identify suspicious lesions.

A multichannel photon counting system for gas analysis with Raman-scattering technique

A microcontroller-based photon counting system has been developed by Laser and Medicine-Technology gGmbH, Berlin, Germany, in cooperation with the University of Athens. This microcontroller-based system controls, acquires, processes and stores the data from a high-resolution multichannel gas analyzer based on linear vibrational Raman scattering. The system described provides accurate photon-counting measurements using suitable photomultiplier tubes (PMTs) as detectors of the Raman signals. The implemented system amplifies, discriminates and counts the PMT pulses with a pulse-pair resolution of 5 ns. The specific implementation offers a number of important features such as portability, low power consumption, low cost, increased reliability, high sensitivity, and upgradability, and supports autocalibration and drift-compensation. Moreover, the described photon-counting system can be easily adapted to a broad field of applications, some of which are in the fields of medical electronics (confocal microscopy) and bio-electronics, air pollution measurements with Raman spectrometers, mass spectrometers, laser sounding of the atmosphere, and electro-optical systems, where photomultiplier tubes are typically used in the pulse-counting mode of operation.

Physical modeling of a microlens array setup for use in computer generated IP

One of the most promising techniques for visualizing three-dimensional objects is Integral Photography (IP). Two of the most common methods used in Computer Generated IP involve the development of simplified ray tracing algorithms for elementary 3D objects or the realization of pinhole arrays. We present an alternative technique based on the POV-Ray software package for ray tracing to generate synthetic, high quality and photorealistic integral images, by accurately modeling all the optical elements of the capturing setup. Our work constitutes a straightforward approach for translating a computer generated 3D model to an IP image and a robust method to develop modules that can be easily integrated in existing ray-tracers. The proposed technique simulates the procedure of a single stage IP capture for producing orthoscopic IP images, real or virtual. Full control is provided over geometry selection, size and refractive index of the elementary microlenses. Specifically our efforts have been focused on the development of arrays with different geometries (square or hexagonal) that demonstrates the parameterization capabilities of the proposed IP setup. Moreover detailed benchmarking is provided over a variety of sizes and geometries of microlens arrays.

Multichannel Raman gas analyzer: the data acquisition and control system. Measurement improvement with blue laser light

In this paper, the data acquisition and control system of a multichannel Raman effect-based gas analysis device is presented, together with the improvements achieved in measurement of gas concentration sensitivities as a result of the operation of the system with a new blue laser-light source. The multichannel Raman gas sensor (MRGS) is based on the linear Raman scattering effect and uses photo multiplier tubes (PMTs) in the photon-counting mode of operation. An embedded microcontroller-based data acquisition and control (MDAC) system collects, digitizes, processes, and stores in real time the data from six photon-counting modules and the accompanying sensors, along with an overall system control through appropriate actuators. Recent advances in the development of solid-state laser sources have enabled the use of a new, state-of-the-art, blue laser for the excitation of the Raman effect. Using this blue laser source, improvements in the sensitivities in measurements of concentration for all tested gases (SO/sub 2/, CO/sub 2/, CO, NO/sub 2/, C/sub 6/H/sub 6/, and N/sub 2/) have been substantiated, compared with the green laser source previously used and reported in a related article.