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Biomedical subjects

H Duifhuis

Publications and source records attributed to H Duifhuis.

12 recordsLinked to original sources
PubMed2007

Design and implementation of gradient vector flow snake to detect a reference object in pelvic x-rays for preoperative total hip arthroplasty planning application.

The main interest of this research project is to promote automation in performing preoperative planning for hip joint replacement surgery using a special medical image viewing software, ViewPro. Preoperative planning is performed to carefully prepare the surgery and to accurately select the hip implants. The first step of preoperative planning is to calibrate the x-ray image to adjust the magnification factor. A femoral head implant is used as magnification factor reference. Automation is introduced by developing an algorithm to automatically detect this reference object in the image. The algorithm used for performing the automatic detection of the reference object is gradient vector flow (GVF) snake. A study has been performed to compare the newly developed semiautomatic algorithm to the old manual calibration algorithm. The results show a close relation between the two algorithms (less than 1% of average relative difference). It is concluded that the developed semiautomated algorithm can be used as an alternative for performing the manual calibration.

Algorithms↗
PubMed2006

Distortion product otoacoustic emissions: a time domain analysis.

Distortion product otoacoustic emissions (DPOAEs) provide relatively easily accessible external information about internal properties of the inner ear. A primary result is that the detection of normal DPOAE components is a strong indicator of normal functioning of the cochlear mechanics. The details of amplitude and phase behavior of the DPOAEs, and the development over time (DPOAE delay) are not fully understood and subject of some debate. In this paper, I would like to emphasize the view that precise time domain experiments and time domain model analysis provide a superb tool, the power of which is generally underestimated. Results are presented from a model analysis in which the primary-tone phase variation technique introduced by Whitehead et al. was employed successfully.

Acoustic Stimulation↗
PubMed1996

Spatial periodicity in the cochlea: the result of interaction of spontaneous emissions?

In this study the results of simulations with a nonlinear macromechanical model of the human cochlea are presented. In this model it is possible to investigate the interactions between large numbers of spontaneous emissions. The focus of this study is on the effect of a local maximum in emission strength on its direct surroundings. The suppression that such an emitter causes depends on the distance between suppressor and suppressee in a strongly nonmonotonic manner. This nonmonotonicity leads to natural minimal distances between emission frequencies, without additional assumptions about the mechanics of the cochlea. The origin of this nonmonotonicity in the suppression lies in reflection of the generated energy at the stapes. The fact that these minimum distances correspond to distances observed between measured SOAE frequencies in adults, but not in newborns, suggests that the nonmonotonicity may play a role in the development of the cochlea in the early years of childhood.

Acoustic Stimulation↗
PubMed1987

Numerical methods for solving one-dimensional cochlear models in the time domain.

In this article, a robust numerical solution method for one-dimensional (1-D) cochlear models in the time domain is presented. The method has been designed particularly for models with a cochlear partition having nonlinear and active mechanical properties. The model equations are discretized with respect to the spatial variable by means of the principle of Galerkin to yield a system of ordinary differential equations in the time variable. To solve this system, several numerical integration methods concerning stability and computational performance are compared. The selected algorithm is based on a variable step size fourth-order Runge-Kutta scheme; it is shown to be both more stable and much more efficient than previously published numerical solution techniques.

Cochlea↗
PubMed1982

Measurement of pitch in speech: an implementation of Goldstein's theory of pitch perception.

Recent developments in hearing theory have resulted in the rather general acceptance of the idea that the perception of pitch of complex sounds is the result of the psychological pattern recognition process. The pitch is supposedly mediated by the fundamental of the harmonic spectrum which fits the spectrum of the complex sound optimally. The problem of finding the pitch is then equivalent to finding the best harmonic match. Goldstein [J. Acoust. Soc. Am. 54, 1496-1516 (1973)] has described an objective procedure for finding the best fit for stimuli containing relatively few spectral components. He uses maximum likelihood criterion. Application of this procedure to various data on the pitch of complex sounds yielded good results. This motivated our efforts to apply the pattern recognition theory of pitch to the problem of measuring pitch in speech. Although we were able to follow the main line of Goldstein's procedure, some essential changes had to be made. The most important is that in our implementation not all spectral components of the complex sound have to be classified as belonging to the harmonic pattern. We introduced a harmonics sieve to determine whether components are rejected or accepted at a candidate pitch. A simple criterion, based on the components accepted and rejected, led to the decision on which candidate pitch was to be finally selected. The performance and reliability of this psychoacoustically based pitch meter were tested in a LPC-vocoder system.

Humans↗
PubMed1982

Masking and partial masking in listeners with a high-frequency hearing loss.

3 listeners with sensorineural hearing loss ranging from moderate to moderate-severe starting at frequencies higher than 1 kHz participated in two masking experiments and a partial masking experiment. In the first masking experiment, fM = 1 KHz and LM = 50 dB SPL, higher than normal masked thresholds were obtained for listeners whose hearing was impaired in the frequency region of clear hearing loss as well as in the region of near-normal absolute thresholds. The second masking experiment showed that for hearing-impaired listeners the elevation of the masked thresholds, in decibels, in this frequency region of "near-normal' absolute thresholds was equal to the elevation of the absolute thresholds, in decibels. The third experiment, a partial masking experiment with fM = 975-1025 Hz and LM = 75 dB SPL, showed similar partial-masking functions for hearing-impaired and normal listeners, but the functions for the hearing-impaired listeners were at much higher levels of the partially masked probe tone. Thus the higher masked thresholds of the hearing-impaired can result in a dramatic reduction of the dynamic range of hearing under masking in the frequency region of the hearing loss and also in the region with only a small hearing loss (less than 30 dB). It is suggested that this may explain the speech perception difficulties which these listeners experience, especially in the presence of ambient noise.

Adult↗
PubMed1980

Mechanics and nonlinearity of hair cell stimulation.

Many nonlinear auditory phenomena are described with a BPNL model, which consists of a nonlinear element preceded and followed by a linear filter. We aim at identifying these elements with cochlear processes. The directional sensitivity of the hair cell is assumed to provide a basis for the second filter. The nonlinearity is hypothesized at the level of mechanical impedance of the hair cell. On the basis of an approximate solution for the cochlear traveling wave, we determine radial and longitudinal components of the driving force on the hair cell. It is shown that appropriate two-tone suppression and sharpening can be obtained only if radial tuning is sharper than longitudinal tuning. This imposes severe constraints on the model. It requires specific assumptions about physical properties of, for example, the tectorial membrane. For instance, if this has significant stiffness in a direction at a small angle with the radial direction, and if stretch in this direction is nonuniform, then sharpening and two-tone suppression are explainable in terms of cochlear mechanics.

Biomechanical Phenomena↗
PubMed1980

Level effects in psychophysical two-tone suppression.

Measurements of psychophysical two-tone suppression in a number of subjects are described. Levels of the stimulus components (suppressee, L1, and suppressor, L2) were the primary experimental variables. In all experiments the pulsation threshold was used with the probe frequency fr fixed at the suppressee frequency f1. In an initial experiment f1 was fixed at 1 kHz. The suppressor frequency f2 ranged from 0.2 to 1.4 kHz. At appropriate levels all subjects showed significant suppression. Suppression was found to decrease to zero as f2 approached f1. The amount of suppression depended on both L1 and L2 in a way not accounted for by any of the current theories of two-tone suppression. At higher overall levels suppression became increasingly prominent. The amount of two-tone suppression in a given stimulus condition depended strongly on the subject. The maximum amount of suppression measured was about 35 dB. In a second experiment it was verified that suppression follows the same pattern at other frequencies f1 (0.5, 2, and 4 kHz). Data for equal f2/f1 ratios were quite similar. The two-tone suppression effect decreased in a noisy environment. Within a 20-dB range of signal-to-noise ratios the effect of noise changed from negligible to the virtually complete elimination of two-tone suppression.

Acoustic Stimulation↗