Johan E. Carlson

Human cerebral malaria: association with erythrocyte rosetting and lack of anti-rosetting antibodies

Plasmodium falciparum isolates from 24 Gambian children with cerebral malaria and 57 children with mild forms of the disease were assessed for their ability to form erythrocyte rosettes. All isolates from the children with cerebral malaria were able to form rosettes, whereas those from children with mild forms of the disease did not form rosettes, or had a significantly lower rosetting rate. Plasma of children with cerebral malaria lacked anti-rosetting activity, whereas plasma of children with mild disease could often disrupt rosettes in vitro. A monoclonal antibody to P falciparum histidine rich protein (PfHRP1/KP/KAHRP) disrupted rosettes of many of the isolates in vitro indicating that the rosetting ligand is relatively conserved compared with ligands associated with endothelial cytoadherence. The findings strongly support the hypothesis that erythrocyte rosetting contributes to the pathogenesis of cerebral malaria and suggest that anti-rosetting antibodies protect against cerebral disease.

An ultrasonic pulse-echo technique for monitoring the setting of CaSO4-based bone cement

We present a new ultrasonic technique for monitoring the entire setting process of injectable bone cement. The problem with existing standards is their subjectivity. Because of this the results are not comparable between different research groups. A strong advantage with the proposed technique is that it is non-invasive and non-destructive, since no manipulation of the cement sample is needed once the measurement has started. Furthermore, the results are reproducible with small variations. The testing was performed on calcium sulfate cement using an ultrasonic pulse-echo approach. The results show that the acoustic properties of the cement are strongly correlated with the setting time, the density, and the adiabatic bulk modulus. The measured initial and final setting times agree well with the Gillmore needles standard. An important difference compared to the standards, is that the technique presented here allows the user to follow the entire setting process on-line.

Frequency and temperature dependence of acoustic properties of polymers used in pulse-echo systems

In ultrasonic pulse-echo systems, polymers like PMMA (polymethylmethacrylate) and PEEK (polyetheretherketone) are often used as buffer-rods, placed between the ultrasound transducer and the unknown material (liquid, gas, or solid material). Provided the acoustic properties of the buffer-rods are known, it is possible to calculate these also for the unknown material, based on reflections between the buffer-rod and the unknown medium. However, temperature changes also affect these properties. In this paper we present a method for measuring acoustic attenuation, speed of sound and density, for buffer-rod materials. We also give experimental values for PMMA and PEEK, for temperatures between 5/spl deg/C and 37/spl deg/C, and for 5 MHz and 10 MHz ultrasound frequency.

Monitoring the setting of calcium-based bone cements using pulse-echo ultrasound.

We present a new technique, based on pulse-echo ultrasound, for monitoring the entire setting process of injectable bone cement. This research has been motivated by the lack of satisfying standards. The main problem with existing standards is the subjectivity, which leads to poor reproducibility. Because of this the results are not comparable between different research groups. A strong advantage with the proposed technique is that if low-intensity ultrasound is used, it provides a non-destructive analysis method. Once the cement paste has been applied to the measurement cell, no manipulation is needed throughout the entire setting process. The problem of the ultrasound affecting the setting of certain cement materials has been investigated, and solutions are discussed. The propagation of ultrasound is temperature-dependent, and therefore a technique for automatic compensation for temperature variations is discussed briefly. The testing was performed on α-calcium sulfate hemihydrate (CSH) and mixtures of CSH and α-tricalcium phosphate (α-TCP). The results show that the acoustic properties of the cement are strongly correlated with the setting time, the density, and the adiabatic bulk modulus. The measured initial and final setting times agree well with the Gillmore needles standard. An important difference compared to the standards, is that the technique presented here allows the user to follow the entire setting process on-line.

Complete post-separation of overlapping ultrasonic signals by combining hard and soft modeling

In some ultrasonic measurement situations, an adequate signal separation is difficult to achieve. A typical situation is material characterization of thin media using pulse-echo or through-transmission techniques, when the time-of-flight in the media is shorter than the emitted signals time support. Separated signals are necessary to obtain accurate estimates of material properties and transit times. In this paper a new method is proposed that enables complete post-separation of measured coinciding signals. The method is based on a combination of hard physical and soft empirical models, which allows for a description of both known and unknown properties making a complete separation possible. The validity and limitations of the model and the separation results are thoroughly addressed. The proposed technique is verified using real measurements on thin dispersive samples and validated using residual analysis. The experimental results show a complete separation with uncorrelated and normally distributed residuals. The method enables characterization and/or flow analysis in difficult overlapping situations.

Model-Based Estimation of Thin Multi-Layered Media Using Ultrasonic Measurements

In ultrasonic measurement situations, when dealing with media of multi-layered structures consisting of 1 or more thin layers, analysis of the measured ultrasonic waveform can be difficult because of overlapping and reverberant echoes. Information from the individual layers is then difficult to extract because the individual echoes cannot be detected. In this study, we use a parametric layer model to analyze the multi-layered material in a system identification approach. The parameters of the model are connected to physical properties of the investigated material, e.g., the reflection coefficients, the time-of-flight, and the attenuation. The main advantage using this model is that the complexity of the model is connected to the number of layers rather than the number of observable echoes in the received ultrasonic waveform. A system of linear equations is presented, giving the opportunity to find the model for both pulse-echo and through-transmission measurements. A thorough effort is made on the parameter estimation and optimization algorithm. The model is validated with practical measurements on a 3-layered structure using both pulse-echo and through-transmission techniques. The 3-layered material consists of a thin embedded middle layer with the time-of-flight in that layer shorter than the emitted signals time support, giving rise to overlapping echoes. Finally the relation between the model parameters and physical properties of the material is established.

A simple scattering model for measuring particle mass fractions in multiphase flows

In this paper we present a simple theoretical model of how pulsed ultrasound is attenuated by the particles in a solid/liquid flow. The theoretical model is then used to predict the attenuation of sound, given the mass fraction, the density, and the size distribution of the solid particles. The model is verified experimentally for suspensions of 0-10% (by mass) Dolomite ((Ca,Mg)CO3) particles and water. The experimental results show that the attenuation of sound due to particles varies linearly with mass fraction, and that the proposed theoretical model can be used to predict this attenuation. In all experiments the transmitter and receiver array were clamped onto the pipe wall, thus providing a completely non-invasive and non-intrusive measurement technique.

Model-based phase velocity and attenuation estimation in wideband ultrasonic measurement systems

A parametric method to estimate frequency-dependent phase velocity and attenuation is presented in this paper. The parametric method is compared with standard nonparametric Fourier analysis techniques using numerical simulations as well as real pulse-echo experiments. Approximate standard deviations are derived for both methods and validated with numerical simulations. Compared to standard Fourier analysis, the parametric model gives considerably lower variance when estimating attenuation and phase velocity. In contrast to nonparametric techniques, the proposed estimator avoids the phase unwrapping problem because analytical expressions for the continuous phase velocity and attenuation can be derived

Vortex imaging using two-dimensional ultrasonic speckle correlation

In previous work, it has been shown that ultrasonic speckle velocimetry can be used to measure local particle velocities in flows. So far the technique has been applied to monitor stationary processes. In this paper, we show how ultrasonic speckle velocimetry can be used to dynamically map the two-dimensional velocity profiles of vortices caused by an obstacle within a flow. Thanks to the great versatility of our multi-channel system, it is possible to capture as much as 5000 images per second, thus enabling us to monitor very fast moving processes. To date, two transducer arrays are used to estimate the 2D motion vector of local particles. We also discuss possible modifications and improvements of the system that could lead to the use of a single array of transducers to dynamically map the vectorial velocity fields of flows.

Prediction of molar fractions in two-component gas mixtures using pulse-echo ultrasound and PLS regression

The composition, and thus the energy content and monetary value of natural gas and biogas, vary considerably depending on the source. Present energy measurement techniques are riot suitable for online use. We show with experiments on mixtures of ethane (C/sub 2/H/sub 6/) and oxygen (O/sub 2/) how partial least squares regression (PLSR) can be used to predict the molar fraction of ethane in the mixtures, given spectral data from ultrasonic pulse-echo measurements. The PLSR technique is compared with the standard principal component regression (PCR), and we show that PLSR yields better predictive performance.