Bengt Mandersson

Arteriovenous fistula stenosis detection using wavelets and support vector machines

The objective of this exploratory study was to develop signal processing methods for assisting in the diagnosis of arteriovenous fistula stenosis on patients suffering from endstage renal disease and undergoing haemodialysis treatments. The proposed method is based on the classification of vessels sounds utilizing parameter extraction from wavelets transform coefficients. The coefficients energy of selected scales (frequency bands) were fed to a support vector machine based system for classification. Results suggested that this technique can be useful for diagnosis purposes to physicians during the auscultation procedure.

Weighted least-squares pulse-shaping filters with application to ultrasonic signals

The resolution of adjacent surfaces in medical ultrasonic imaging depends on the duration of a reflected echo. By shaping the excitation signal of the transducer, this duration can be decreased. The authors present a method for effective calculation of the excitation pulse by introducing a weighting function that defines the resolution. A class of filter is obtained that includes the least-mean-squares filter, the pure inverse filter, and the matched filter. The method is demonstrated in an application that increases the resolution of an ultrasonic transducer.<<ETX>>

Acoustical detection of venous stenosis in hemodialysis patients using principal component analysis

In this paper, a feature extraction method based on principal component analysis was developed for classification of the vascular accesss condition in hemodialysis patients. The assessment of the method was carried out by discriminating between before and after angioplasty sound recordings as well as before angioplasty and reference recordings. The results showed that when before and after angioplasty recordings were compared by patient, the classification agreed with the result of angioplasty procedure. When all the available before and after angioplasty recordings were compared, it was still possible to discriminate them at a good rate. On the other hand, when the reference recordings substituted the after angioplasty recordings, almost a perfect discrimination was achieved.

Application of the Empirical Mode Decomposition in the study of murmurs from Arteriovenous fistula stenosis

The Empirical Mode Decomposition (EMD) is a method to decompose non linear, non stationary time series into a sum of different modes, named Intrinsical Mode Functions each one having a characteristic frequency. In the present work we used the EMD to investigate the properties of the recorded sounds from the Arteriovenous fistula on hemodialysis patients. Phonoangiographic signals coming from two different vessel conditions, stenotic and non-stenotic, were analyzed by using EMD, the mean energy and mean instantaneous frequency per IMF proved to be good features for classification. Three types of classification schemes were tested on data from the first IMf features achieving good results.

A Generalized Angle Domain Clusters PDF and Its Application in Geometrically Based Channel Models

In this paper we present analytical expressions for the angle-of-arrival (AOA) power density function (PDF) and its application in geometrically based channel models for urban environments. In order to evaluate the theoretical clusters PDF in angle domain proposed, we make computer simulations and comparisons with experimental results for wideband channel models, published in the open literature. The comparison with experimental results shows good agreement. The generalized clusters PDF derived in this paper can be used to simulate a power-delay-angle profile and to quantify second order statistics, i.e., angle spread for a given elliptical shape of the cluster

Time Domain Cluster PDF and its Application in Geometry-based Statistical Channel Models

This paper presents an approach to derivate the time of arrival (TOA) power density function (PDF) and its application in geometry-based statistical channel models for urban environments. The cluster PDF derived can be used to simulate temporal dispersion of the multipath signal grouped in clusters in a variety of urban propagation conditions to quantify second order statistics, i.e., delay spread for a given elliptical shape of the cluster. We propose a clustering approach channel model, and employ it to derive the PDF of TOA of the multipath signal. In order to evaluate the theoretical clusters PDF in time domain proposed, we make computer simulations for the geometry-based channel model proposed and compared it with experimental results published in the open literature. The comparison with experimental results shows good agreement.

An approach of the geometrical-based single bounce elliptical channel model for mobile environments

The simulation approach is an important tool used for the design and implementation of mobile radio systems with an emphasis on the propagation modeling for wireless channel. We carried out simulations for three different street positions scenarios of the receiver, (mobile station), using the geometrical-based single bounce elliptical channel model, as might be appropriate for microcellular applications and mobile-to-mobile communication. From the simulation results we use the parameters time-of-arrival (TOA) and angle-of-arrival (AOA), (delay and angular domain, respectively), to estimate the higher order channel statistics, such as the delay spread (DS) and the angle spread (AS), respectively.

Analysis of the vascular sounds of the arteriovenous fistula's anastomosis

In this paper, the vascular sounds of the arteriovenous fistula at the anastomosis and five centimeters downstream the anastomosis were analyzed. The analysis of the sounds was based on features extracted from the power spectral density (PSD) and wavelet decomposition. The database consists of 15 recordings at the anastomosis and 15 reference recordings obtained from 15 patients. The results showed that the vascular sounds at the anastomosis can be characterized as an extra energy in the higher frequencies (200–1000 Hz) i.e. higher mean frequency of the PSD than the reference recordings. Moreover, the wavelet decomposition of the anastomosis recordings showed a similar energy pattern, in the finer scales, to that found in studies of arterial and venous stenosis.

On Ultrasound Transducers with Curved Surface for Improvement of Lateral Resolution

Abstruct-In order to produce high-quality images in medical ultrasonics, high lateral resolution is required over a large depth. The properties of the acoustic field maintained by a transducer with an arbitrary gently curved surface and an arbitrary surface velocity distribution is discussed. The acoustic field pressure is calculated by means of the impluse response method. It is shown, that the impulse response in every space point is given by an integral, the integrand of which contains the curvature and velocity distribution of the transducer. The integral is evaluated numerically, and images of the acoustic field pressure are presented. These images show how the curvature and velocity of the surface influence the lateral resolution. The behavior of the pressure in the far field is also studied.

Clusters PDF in angle and time domain for geometrically based channel model

Advanced radio system designs have been proposed that are intended to overcome or even take advantage of the radio channel caused by multipath effects in urban environments to achieve even higher performance. We present analytical expressions for the angle-of-arrival power density function (PDF) and general analysis for time of arrival (expressed in terms of distance) respectively, for the channel model based on geometry for urban environments. Then we make comparisons with experimental results published in the open literature, in order to evaluate the theoretical PDF proposed. The comparison with experimental results shows good agreement. The derived PDF can be used to simulate a power-delay-angle profile and to quantify angle spread and delay spread for a given elliptical shape of the cluster.