Equivalent threshold sound pressure levels (ETSPLs) for Oscilla H210A circumaural audiometric headphones.

OBJECTIVE: To determine ETSPLs for the Oscilla H210A circumaural audiometric headphones. DESIGN: ETSPL measurements were performed for 11 audiometric frequencies with the ISO 8253-1 (2010) bracketing procedure. STUDY SAMPLE: The study was based on 25 otologically normal test subjects. RESULTS: ETSPLs are provided for an ear simulator according to IEC 60318-1 (2009) along with a detailed measurement uncertainty budget. CONCLUSIONS: ETSPLs for the Oscilla H210A headphones may be used to update ISO 389-8 (2004), the reference ETSPL standard for circumaural audiometric headphones.

Influence of response-time limits on automated hearing threshold determination.

OBJECTIVE: In automated hearing threshold determination procedures, prespecified response- time limits can be applied to evaluate whether a stimulus was truly heard by checking whether the test subject reacts to the onset and the offset of the stimuli within given time intervals. The influence of different response-time limits on the threshold of normal-hearing test subjects was investigated. DESIGN: Two-stage hearing threshold level measurements applying the ISO 8253-1 (2010) bracketing procedure were performed. Pre-tests at 125 Hz and 1000 Hz were carried out with maximum accepted response times of 600 ms, 1000 ms, and 1200 ms. Subsequently, thresholds were measured at the seven octaves between 125 Hz and 8000 Hz with maximum accepted response times of 600 ms and 1000 ms. STUDY SAMPLE: 15 test subjects in pre-tests, 25 test subjects in the main study. RESULTS: Threshold levels determined with a maximum accepted response time of 1000 ms are 2.6 dB lower than those obtained with a maximum accepted response time of 600 ms (95% CI -1.6 dB to 6.9 dB). The threshold shift was similar at all frequencies. CONCLUSIONS: Based on this study, response-time limits after both stimulus onset and offset of at least 1000 ms are recommended.

Air-conducted ultrasound below the hearing threshold elicits functional changes in the cognitive control network.

Air-conducted ultrasound (> 17.8 kHz; US) is produced by an increasing number of technical devices in our daily environment. While several studies indicate that exposure to US in public spaces can lead to subjective symptoms such as 'annoyance' or 'difficulties in concentration', the effects of US on brain activity are poorly understood. In the present study, individual hearing thresholds (HT) for sounds in the US frequency spectrum were assessed in 21 normal-hearing participants. The effects of US were then investigated by means of functional magnetic resonance imaging (fMRI). 15 of these participants underwent three resting-state acquisitions, two with a 21.5 kHz tone presented monaurally at 5 dB above (ATC) and 10 dB below (BTC) the HT and one without auditory stimulation (NTC), as well as three runs of an n-back working memory task involving similar stimulus conditions (n-ATC, n-BTC, n-NTC). Comparing data gathered during n-NTC vs. fixation, we found that task performance was associated with the recruitment of regions within the cognitive control network, including prefrontal and parietal areas as well as the cerebellum. Direct contrasts of the two stimulus conditions (n-ATC & n-BTC) vs. n-NTC showed no significant differences in brain activity, irrespective of whether a whole-brain or a region of interest approach with primary auditory cortex as the seed was used. Likewise, no differences were found when the resting-state runs were compared. However, contrast analysis (n-BTC vs. n-ATC) revealed a strong activation in bilateral inferior frontal gyrus (IFG, triangular part) only when US was presented below the HT (p < 0.001, cluster > 30). In addition, IFG activation was also associated with faster reaction times during n-BTC (p = 0.033) as well as with verbal reports obtained after resting-state, i.e., the more unpleasant sound was perceived during BTC vs. ATC, the higher activation in bilateral IFG was and vice versa (p = 0.003). While this study provides no evidence for activation of primary auditory cortex in response to audible US (even though participants heard the sounds), it indicates that US can lead to changes in the cognitive control network and affect cognitive performance only when presented below the HT. Activation of bilateral IFG could reflect an increase in cognitive demand when focusing on task performance in the presence of slightly unpleasant and/or distracting US that may not be fully controllable by attentional mechanisms.

Intercomparison of nanodosimetric distributions in nitrogen simulated with Geant4 and PTra track structure codes.

To facilitate the use of Geant4-DNA for radiation transport simulations in micro- and nanodosimeters, which are physically operated with tissue-equivalent gases such as nitrogen (and propane), this work aims to extend the cross section data available in Geant4-DNA to include those of nitrogen for electron energies ranging from 1 MeV down to the ionisation threshold. To achieve this, interaction cross section data for nitrogen that have been used with the in-house PTB PTra track structure code have been implemented in the current state-of-the-art Geant4-DNA simulation toolkit. An intercomparison has been performed between the two codes to validate this implementation. To quantify the agreement between the cross section models for nitrogen adopted in PTra and those implemented in Geant4-DNA, the simulation results of both codes were analysed using three physical parameters describing the ionisation cluster size distribution (ICSD): mean ionisation cluster size, variance of the cluster size and the probability to obtain a single ionisation within the target. Statistical analysis of the results indicates that the interaction cross section models for nitrogen used in PTra (elastic scattering, impact ionisations and electronic excitations) have been successfully implemented in Geant4-DNA. In addition, simulated ICSDs were compared to those measured with the Jet Counter nanodosimeter for energies between 100 and 2000 eV. For greater energies, the ICRP data for LET and particle range were used as a reference. The modified Geant4-DNA code and data successfully passed all these benchmarks fulfilling the requirement for their public release in the next version of the Geant4 toolkit.

Dependence of binaural gain for infrasound on interaural phase difference.

Increasing complaints about infrasound have generated interest in understanding its perception, including binaural effects. This study investigated the level difference between monaural and binaural presentation required for detection and equal loudness (binaural gain) for pure tones with frequencies of 8, 32, and 400 Hz and an 8 Hz sinusoidally amplitude-modulated tone with diotic 400 Hz carrier. Monaural stimuli were compared to binaural stimuli with interaural phase differences (IPDs) of 0°, 90°, and 180° in two experiments: absolute threshold measurements and loudness matching at 40 phons. The latter was repeated with transposed tones (400 Hz carrier multiplied by a half-wave-rectified 8 Hz sinusoid). When expressed as differences in sound pressure level, similar binaural gain was found across all stimulus types under the diotic condition. Confirming previous studies, the gain was larger at supra-threshold levels (40 phons) than at threshold. However, when the loudness-matching results were expressed as binaural gain with respect to the loudness level, they became 17.5, 11.2, and 5.8 phons for the 8, 32, and 400 Hz stimuli, respectively. Results for the 8 Hz pure tone and the transposed stimulus were IPD dependent.

Free-field correction values for RadioEar DD65v2 circumaural audiometric headphones.

OBJECTIVE: Free-field correction values were measured for RadioEar DD65v2 audiometric headphones. DESIGN: Free-field correction values, that is, the difference GF-GC between the free-field sensitivity level GF and the ear simulator sensitivity level GC, were determined by loudness level comparisons between the headphone and a plane progressive wave in a free sound field. STUDY SAMPLE: The study was based on 17 otologically normal test subjects. RESULTS: Frequency-dependent free-field correction values are provided. The free-field correction of the speech level was determined to be 3.2 dB. CONCLUSIONS: Free-field correction values were determined for RadioEar DD65v2 audiometric headphones with an expanded measurement uncertainty.

Equivalent threshold sound pressure levels (ETSPLs) for RadioEar DD65v2 circumaural audiometric headphones.

Objective: Equivalent threshold sound pressure levels (ETSPLs) were determined for RadioEar DD65v2 audiometric headphones.Design: The pure-tone hearing threshold levels were measured for 11 audiometric frequencies between 0.125 and 8 kHz, according to the conditions specified in ISO 389-9. ETSPLs are provided for an ear simulator according to IEC 60318-1, complemented by a comprehensive uncertainty budget.Study sample: The study was based on 25 otologically normal test subjects.Results: ETSPL values are provided with expanded measurement uncertainty. The data are compared for left/right ears as well as male/female test subjects.Conclusions: The results of both studies may be used to update ISO 389-8, the RETSPL standard for circumaural audiometric headphones.

Equivalent hearing threshold levels for the RadioEar IP30 insert earphone and short-term stimuli: comparison of peak-equivalent and RMS-based measures.

Objective: To determine equivalent threshold sound pressure levels (ETSPL) for the RadioEar IP30 insert earphone for standardised short-term stimuli: IEC 60645-3 reference clicks and tonebursts in the frequency range from 250 Hz to 6 kHz, using the standardised peak-equivalent ETSPL procedure (peETSPL) and a new proposal based on the unweighted equivalent continuous sound pressure level LZeq. of the periodically repeated short-term stimuli (LZeqETSPL).Design: Determination of peETSPL and LZeqETSPL hearing threshold levels with otologically normal test subjects under the conditions given in ISO 389-9 using the standardised occluded-ear simulator according to IEC 60318-4.Study sample: The study was based on tests with 25 subjects.Results: The peETSPLs for the RadioEar IP30 insert earphone were compared with the respective reference threshold levels of the insert earphone ER-3A as standardised in the ISO 389 standards series. The LZeqETSPL approach was tested by estimating the LZeqETSPLs from the peRETSPLs and comparing the estimate with the direct results.Conclusions: Equivalent hearing threshold levels for standardised short-term stimuli for the RadioEar IP30 insert earphone were determined according to ISO 389-9 and given as both peETPSL and LZeqETSPL. The RMS-based LZeqETSPL approach turned out to be well applicable for the RadioEar IP30 insert earphone.

CONSIDERATIONS ON THE TARGET SIZE IN A WALL-LESS NANODOSIMETER.

In nanodosimetry, the ionization component of charged particle track structure is characterized by measuring the frequency distribution of ionizations in target volumes that simulate nanometric sites in liquid water. For the Ion Counter nanodosimeter at PTB, the sensitive volume is defined by the electrical field and the extraction aperture. In this paper, a procedure is presented to define a cylindrical effective measurement target based on the second moments of the detection efficiency map. An analytical model of the efficiency map is developed to investigate the dependence of the simulated site size on the nanodosimeter's operating parameters. Within the limits of the simplifying assumptions, the model gives a reasonable approximation of the efficiency map.

Double differential cross sections for proton induced electron emission from molecular analogues of DNA constituents for energies in the Bragg peak region.

For track structure simulations in the Bragg peak region, measured electron emission cross sections of DNA constituents are required as input for developing parameterized model functions representing the scattering probabilities. In the present work, double differential cross sections were measured for the electron emission from vapor-phase pyrimidine, tetrahydrofuran, and trimethyl phosphate that are structural analogues to the base, the sugar, and the phosphate residue of the DNA, respectively. The range of proton energies was from 75 keV to 135 keV, the angles ranged from 15° to 135°, and the electron energies were measured from 10 eV to 200 eV. Single differential and total electron emission cross sections are derived by integration over angle and electron energy and compared to the semi-empirical Hansen-Kocbach-Stolterfoht (HKS) model and a quantum mechanical calculation employing the first Born approximation with corrected boundary conditions (CB1). The CB1 provides the best prediction of double and single differential cross section, while total cross sections can be fitted with semi-empirical models. The cross sections of the three samples are proportional to their total number of valence electrons.

Ionization cross section data of nitrogen, methane, and propane for light ions and electrons and their suitability for use in track structure simulations.

Track structure Monte Carlo simulations are frequently applied in micro- and nanodosimetry to calculate the radiation transport in detail. The use of a well-validated set of cross section data in such simulation codes ensures accurate calculations of transport parameters, such as ionization yields. These cross section data are, however, scarce and often discrepant when measured by different groups. This work surveys literature data on ionization and charge-transfer cross sections of nitrogen, methane, and propane for electrons, protons, and helium particles, focusing on the energy range between 100 keV and 20 MeV. Based on the evaluated data, different models for the parametrization of the cross section data are implemented in the code ptra, developed for simulating proton and alpha particle transport in an ion-counting nanodosimeter. The suitability of the cross section data is investigated by comparing the calculated mean ionization cluster size and energy loss with experimental results in either nitrogen or propane. For protons, generally good agreement between measured and simulated data is found when the Rudd model is used in ptra. For alpha particles, however, a considerable influence of different parametrizations of cross sections for ionization and charge transfer is observed. The ptra code using the charge-transfer data is, nevertheless, successfully benchmarked by the experimental data for the calculation of nanodosimetric quantities, but remaining discrepancies still have to be further investigated (up to 13% lower energy loss and 19% lower mean ionization cluster size than in the experiment). A continuation of this work should investigate data for the energy loss per interaction as well as differential cross section data of nitrogen and propane. Interpolation models for ionization and charge-transfer data are proposed. The Barkas model, frequently used for a determination of the effective charge in the ionization cross section, significantly underestimates both the energy loss (by up to 19%) and the mean ionization cluster size (up to 65%) for alpha particles. It is, therefore, not recommended for particle-track simulations.

Effect of a static magnetic field on nanodosimetric quantities in a DNA volume.

PURPOSE: With the advent of magnetic resonance imaging (MRI)-guided radiation therapy it is becoming increasingly important to consider the potential influence of a magnetic field on ionising radiation. This paper aims to study the effect of a magnetic field on the track structure of radiation to determine if the biological effectiveness may be altered. METHODS: Using the Geant4-DNA (GEometry ANd Tracking 4) Monte Carlo simulation toolkit, nanodosimetric track structure parameters were calculated for electrons, protons and alpha particles moving in transverse magnetic fields up to 10 Tesla. Applying the model proposed by Garty et al., the track structure parameters were used to derive the probability of producing a double-strand break (DSB). RESULTS: For simulated primary particles of electrons (200 eV-10 keV), protons (300 keV-30 MeV) and alpha particles (1-9 MeV) the application of a magnetic field was shown to have no significant effect (within statistical uncertainty limits) on the parameters characterizing radiation track structure or the probability of producing a DSB. CONCLUSIONS: The null result found here implies that if the presence of a magnetic field were to induce a change in the biological effectiveness of radiation, the effect would likely not be due to a change in the track structure of the radiation.

Simulation of ionisation clusters formed in nanometric volumes of the deoxyribose-substitute tetrahydrofuran.

PURPOSE: To investigate the implications of using interaction cross sections of liquid water for the target volume when studying radiation action at the DNA level by particle track structure simulations. MATERIALS AND METHODS: Absolute interaction cross sections for low energy electrons between 20 eV and 1 keV were measured for tetrahydrofuran (THF), which is a substitute for deoxyribose. From these data a complete interaction cross section data set was derived and integrated in our PTB Track structure Monte Carlo code 'PTra'. Simulations of electron track structure in THF and water were performed and ionisation cluster size distributions in nanometric target volumes were determined. From these a nanodosimetric estimate for the probability to produce a double strand break was derived. RESULTS: The probability distribution of ionisation cluster sizes was found to be shifted towards smaller values for a THF-filled target as compared to a water-filled one. For all electron energies investigated, the nanodosimetric estimates for double-strand break probability in the THF-filled target have lower values than for a target of liquid water. CONCLUSION: The preliminary results indicate that simulations based on cross sections of water would overestimate the initial direct radiation damage to the DNA.