Biomedical subjects

Philippe Lemmerling

Publications and source records attributed to Philippe Lemmerling.

4 recordsLinked to original sources

PubMed2007

An automated quantitation of short echo time MRS spectra in an open source software environment: AQSES.

This paper describes a new quantitation method called AQSES for short echo time magnetic resonance spectra. This method is embedded in a software package available online from www.esat.kuleuven.be/sista/members/biomed/new/ with a graphical user interface, under an open source license, which means that the source code is freely available and easy to adapt to specific needs of the user. The quantitation problem is mathematically formulated as a separable nonlinear least-squares fitting problem, which is numerically solved using a modified variable-projection procedure. A macromolecular baseline is incorporated into the fit via nonparametric modelling, efficiently implemented using penalized splines. Unwanted components such as residual water are removed with a maximum-phase FIR filter. Constraints on the phases, dampings and frequencies of the metabolites can be imposed. AQSES has been tested on simulated MR spectra with several types of disturbance and on short echo time in vivo proton MR spectra. Results show that AQSES is robust, easy to use and very flexible.

Humans↗

PubMed2003

Nonlinear analysis of heart rate variability in infants with apparent life-threatening events.

Some studies have shown that neonates having experienced an Apparent Life-Threatening Event (ALTE) have an increased risk of dying of the Sudden Infant Death Syndrome (SIDS). In this study the heart rate variability in neonates has been analyzed through a study of the long range correlations and scale invariance (self-similarity) in their cardiac rhythm. The goal is to see whether it is possible to distinguish normal infants from infants with ALTEs using the previously mentioned nonlinear measures of the heart rate variability. Twelve ALTE infants are included in this study. To determine the degree to which these neonates suffer from ALTEs two examinations are performed: a polysomnography and home monitoring. Using the nonlinear measures obtained from the nonlinear analysis of the heart rate variability, the group suffering most from ALTEs can clearly be separated from the other neonates.

Heart↗

PubMed2003

Quantitation of the concordance between cerebral intravascular oxygenation and mean arterial blood pressure for the detection of impaired autoregulation.

Since some important forms of brain injury in premature infants are caused in considerable part by disturbances in cerebral blood flow (CBF), it is important to be able to detect whether the cerebrovascular autoregulation, the mechanism by which CBF is maintained constant despite alterations in mean arterial blood pressure (MAP), is working properly. A recent study suggested that concordant changes in MAP and cerebral intravascular oxygenation (HbD), measured non-invasively by near-infrared spectroscopy (NIRS) as the difference between the concentration changes of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb), reflect impaired cerebrovascular autoregulation. Consequently, premature infants with impaired cerebrovascular autoregulation could be identified by simultaneous, continuous measurements of HbD and MAP. From several premature babies, MAP, HbD and arterial oxygen saturation (SaO2) were measured simultaneously at the University Hospital Leuven, Belgium. The concordance between MAP and HbD was quantitated using three different measures, among which a newly developed measure that looks for similarity of the dynamics between signals. Some preliminary results obtained from the measured data are given.

Blood Pressure↗

PubMed2002

A subspace time-domain algorithm for automated NMR spectral normalization.

Recently, two methods have been proposed for quantitatively comparing NMR spectra of control and treated samples, in order to examine the possible occurring variations in cell metabolism and/or structure in response to numerous physical, chemical, and biological agents. These methods are the maximum superposition normalization algorithm (MaSNAl) and the minimum rank normalization algorithm (MiRaNAl). In this paper a new subspace-based time-domain normalization algorithm, denoted by SuTdNAl (subspace time-domain normalization algorithm), is presented. By the determination of the intersection of the column spaces of two Hankel matrices, the common signal poles and further on the components having proportionally varying amplitudes are detected. The method has the advantage that it is computationally less intensive than the MaSNAl and the MiRaNAl. Furthermore, no approximate estimate of the normalization factor is required. The algorithm was tested by Monte Carlo simulations on a set of simulation signals. It was shown that the SuTdNAl has a statistical performance similar to that of the MiRaNAl, which itself is an improvement over the MaSNAl. Furthermore, two samples of known contents are compared with the MiRaNAl, the SuTdNAl, and an older method using a standard. Finally, the SuTdNAl is tested on a realistic simulation example derived from an in vitro measurement on cells.

Journal Article↗