Catálogo de publicaciones - libros

Two diodes have been calibrated as in vivo dosimeters for entrance and exit dose measurements in radiotherapy with 15 MV photon beams. Their response dependencies on dose, dose rate, focus skin distance, field size, gantry angle and patient thickness have been investigated. 1243 routine measurements have been performed in 302 rectal and prostate cancer patients irradiated with four field box technique. Measurement statistics is presented.

A newly developed lumped parameter model of the left ventricle contraction and a computational fluid dynamics (CFD) representation of the fluid structure interaction (FSI) of a single leaflet mechanical heart valve are coupled to investigate the cavitation potential of a single leaflet prosthetic heart valve. The left ventricle model gives a “more-realistic” representation of the cardiac muscle contraction, from the level of the contractile proteins, up to the hemodynamics of the whole ventricle. A commercial finite volume CFD code (ANSYS-CFX) is coupled to the lumped parameter ventricle model through the inlet and outlet boundary conditions. Cavitation potential is evaluated from the negative pressure gradients occurring on the surface of the occluder and vortex formations adjacent to its atrial aspect.

In this study, quantitative evaluation of a proposed digital density equalization technique in mammography was carried out. The evaluation was performed on a set of 90 mammograms, based on wavelet-generated measurable parameters of image quality, such as contrast, noise and contrastto- noise ratio (CNR). These parameters were estimated for dense mammary gland and breast periphery, for both initial and corresponding corrected mammograms. The equalization character of the technique was also examined. A statistically significant (p<0.05) or highly significant increase (p<0.0005) was observed in breast periphery and mammary gland contrast, noise and CNR values. The proposed technique was found to result in density equalization, since the decrease in equalization index is statistically highly significant (p<0.0005).

The interaction between charged membrane surfaces, separated by a solution containing charged nanoparticles was studied experimentally and theoretically. The nonlocal theory for the nanoparticles was developed where finite size of nanoparticles and spatial distribution of charge within a particle were taken into account. It was shown that for large enough membrane surface charge densities and large enough dimensions of nanoparticles, the force between equally charged membranes may be attractive due to spatially distributed charges within the nanoparticles.

An optical biopsy system for early breast cancer diagnostics is reported. Its specific features and calibration and data preprocessing method are described.

A method of thermal suppression of abnormal brain activity observed in epileptic patients during preictal stage was considered for seizure blockage. The development of an implantable brain microcooler as a part of a closed-loop epileptic seizure prevention system is reported. An array of 7 needle-like probes of the diameter ~1 mm and length ~2 cm provides cooling of 1 cubic inch of brain tissue from ~37°C to ~16°C in ~30 sec. Convective method of heat exchange with tube in a tube design was adopted. Two coaxial steel tubes formed channels for the direct and reverse flows of precooled water. Theoretical studies and numerical modeling based on Pennes' equation were performed to investigate the process of brain tissue cooling. Experimental tests demonstrated good agreement with calculations. A closed cycle cooling system with a peristaltic pump and thermoelectric cooling device is being prepared for animal tests. As an additional option a single-probe microcooler of the probe length ~5 cm was developed, fabricated, and tested for cooling of deep brain areas such as hippocampus.

The electroretinogram is the record of the electrical response of the retina to a light stimulus. The two main components are the a-wave and the b-wave, the former is related to the early photoreceptoral activity. Aim of this paper is to acquire useful information about the time-frequency features of the human a-wave, by means of the wavelet analysis. This represents a proper approach in dealing with nonstationary signals. We have used the Mexican Hat as mother wavelet. The analysis, carried out for four representative values of the luminance, comprehends the frequency dependence of the variance and the skeleton. The results indicate a predominance of low frequency components, their time distribution depends on the luminance whereas that of the high frequency components is little affected by the luminance.

The aim of this study was to assess the possibility of using electrically elicited stapedius muscle reflex (ESR) for estimation of most comfortable loudness level (MCL), one of the most important electrical stimulation parameter in cochlear implant system fitting. The material of this study consisted of 48 adult patients, sampled from the group of MedEl Combi 40+ and MedEl Pulsar users, implanted in the Institute of Physiology and Pathology of Hearing. Their cochlear implant system was fitted according to the results of psychophysical tests: loudness scaling and electrical amplitude growth function. ESR measurement was performed, and ESR thresholds and MCL values were compared. Good correlation after 12 months of using cochlear implant system was observed. Results indicate that ESR can be included in cochlear implant system fitting procedure as objective measurement for prediction of optimal MCL values.

Our experiences show that patients wish to replace the lost part of their body with a prosthesis – epithesis that is a mirror image of the relevant healthy part of the body. Four years ago we linked up with other institutions, companies and the University of Ljubljana in order to search for new more advanced technological possibilities to bring the form of epitheses closer to the form of a healthy hand or part of a face. A healthy and impaired part of the body were scanned. A digital virtual model was made by using a computer programme. 3D printing technology, DMLS (Direct Metal Laser Sintering) and SLS (Select Laser Sintering) technology were used to build up the first model or mould for manufacturing a silicone epithesis. Through our development project we have found the way for the high-resolution digitising of body parts and technology to produce a prototype model and mould allowing the fine recognition of skin details. By using CAD-CAM high resolution technology, the highest-quality prosthetic design can be achieved even when the prosthetist lacks artistic skills.

We developed this program for the purpose of a rehabilitation method that requires a patient to move an object around with his hand. Using a black and white firewire camera the program determines the position and orientation of a black rectangle on a white plane. The user must enter the length and width of the rectangle before the start. With this information the position is determined even if a part of the rectangle is obscured by a user’s hand. The program works in real-time (15 to 20 frames per second).