Volume 15 (2009): Issue 3 (January 2009)

The aim of the present work was creating a virtual phantom of a human head for BNCT, as a part of the BNCT programme project. This model is an amplification of the simple model described in earlier publications. It takes into account the major head organs as well as the scalp and skull. The chemical composition of all tissues was modelled according to the recommendations of the ICRP. The organs were parameterized using mathematical formulas based on the human head magnetic resonance images. The model was used for calculating the thermal neutron flux and the injuring (fast neutron, nitrogen and gamma) dose components for the head irradiated using the therapeutic neutron beam, whose parameters were obtained as the result of the modelling of the filter/moderator system for the BNCT therapeutic beam from the MARIA reactor.

A uniform dose to the target site is required with a knowledge of delivered dose, central axis depth dose and beam flatness for successful electron treatment at an extended source to surface distance (SSD). In an extended SSD treatment under dosage of the lateral tissue may occur due to reduced beam flatness. To study the changes in beam characteristics, the depth dose curves, beam flatness and isodose distributions were measured at different SSDs from 100 to 120 cm for clinically used field sizes from (4×4) to (25×25) cm² and beam energies ranging from 6 MeV to 20 MeV. Our results suggest that the change in depth dose is minimal except in the buildup region for most energy. In general surface dose is decreased as the SSD increased moderately. It was observed that the loss in beam flatness is significant for smaller fields, higher isodose lines, and lower energies. The penumbra enlarged and the uniformity index reduced with increasing SSD.

Early diagnosis of congenital defect of hearing poses new challenges for a multidisciplinary team of pedoaudiologists, ENT (ear-nose-throat) specialists and speech therapists. This study assessed the perception of phonemes in children with a cochlear implant and the possibilities of applying acoustical solutions in the audiologic evaluation. The participants were 17 implanted children, aged 5-9 years, who received a cochlear implant when they were from 18 months to 3 years old. Detection thresholds and discrimination score were assessed. This study also aimed at verifying the possibilities of applying the digital audioprocessing algorithm in clinical practice. The test based on the phonemes aa, uu, ii, ss, sh (Ling 5 sound test) was used. The test was modified in the frequency domain - the main aim of this modification was to improve the precision of the reconstruction of the audible threshold. The results indicated significant correlations between pure tone audiometry results and thresholds of phoneme detection [dB SPL]. The identification score in this group was 95-100% for sound pressure level 65 dB SPL.

The purpose of the study was to determine an optimal hearing aid fitting procedure for a patient with well diagnosed high-frequency ‘dead regions’ in both cochleas. The patient reported non-symmetrical hearing problems of sensorineural origin. For binaural amplification two similar independent hearing aids were used as well as a pair of dependent devices with an ear-to-ear function. Two fitting methods were used: DSLi/o and NAL-NL1, and four different strategies of fitting were tested: the initial fitting based on the DSLi/o or NAL-NL1 method with necessary loudness corrections, the second fitting taking into account all the available functions of hearing instruments, the third fitting (based on the second one) but with significantly reduced amplification well above one octave of frequency inside dead region, and the final fitting with significantly reduced gain slightly below one octave inside dead regions. The results of hearing aids fitting were assessed using an APHAB procedure.

Different preservation methods are currently used in bone banks, even though their effects on allograft quality are not fully understood. Freezing is one of the most popular methods of preservation in tissue banking. Yet, there is not a lot of data on dynamic mechanical properties of frozen bone. Material used in this study was femoral bones from adult bovine that were machine cut and frozen to the temperature 140°C. Both elastic modulus and loss modulus were measured at 1, 3, 5, 10, and 20 Hz in the temperature range of 30-200°C. Differences between frozen and control samples were observed. The frequency increase always led to the increase in elastic modulus values and decrease in loss modulus values. Freezing reduced the elastic modulus values of about 25% and the loss modulus values of about 45% when measured at 20°C.

Mobile phones are being widely used throughout the world. Although there is no clear evidence of harmful effects of radiofrequency (RF) radiation at the levels used by these devices, there is widespread public concern that there may be potential for harm. Of all anatomical structures, the ear is closest to the mobile phone, which may lead to relatively high energy deposition in the ear compared to other parts of the body. Till the year 2000 only a few studies had addressed potential adverse effects of EMFs on the hearing system. The potential adverse effects of mobile phone exposure on the hearing system should be investigated, because mobile phones are usually held close to the ear. Until now, most studies have assessed the influence of RF radiation on the central or peripheral auditory system. However, clear conclusions cannot be drawn from these studies regarding the presence or absence of effects because of the limitations in the audiological and/or dosimetric approaches and limited sample sizes. results. Although the presence of possible effects on hearing threshold levels cannot be dismissed entirely, the evidence available is not sufficiently strong to conclude that there are adverse effects. A replication study with a shift in hearing threshold levels at high frequencies as the a priori hypothesis is desirable to resolve this issue.