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S Van Huffel

Publications and source records attributed to S Van Huffel.

10 recordsLinked to original sources
PubMed2000

Frequency-selective quantification of biomedical magnetic resonance spectroscopy data.

In this paper the possibility of obtaining accurate estimates of parameters of selected peaks in the presence of unknown or uninteresting spectral features in biomedical magnetic resonance spectroscopy (MRS) signals is investigated. This problem is denoted by frequency-selective parameter estimation. A new time-domain technique based on maximum-phase finite impulse response (FIR) filters is presented. The proposed method is compared to a number of existing approaches: the application of a weighting function in the time domain, frequency domain fitting using a polynomial baseline, and the time-domain HSVD filter method. The ease of use and low computational complexity of the FIR filter method make it an attractive approach for frequency-selective parameter estimation. The methods are validated using simulations of relevant (13)C and (31)P MRS examples.

Adenosine Triphosphate↗
PubMed2000

Detection and multichannel SVD-based filtering of trigeminal somatosensory evoked potentials.

Very weak and noisy trigeminal somatosensory evoked potentials (TSEPs) are considered, which are successfully evoked by electrical stimulation of the trigeminal nerve of 15 patients with endosseous oral implants. As TSEP analysis provides an objective means of assessing neuronal function, it is considered to be a promising tool for investigating tactile sensation through anchoring implants in bone. For this purpose, a study of TSEP signals acquired from patients with endosseous oral implants has been carried out. Since TSEPs are severely contaminated by background ongoing electrical activities of the brain, a methodology is developed for statistically detecting the transient signal (TSEP) in the biological noise (EEG). For nine out of 15 patients, transient signals are detected in the background EEG activity. The TSEPs of these nine patients are subjected to further analysis. A multichannel singular value decomposition (SVD)-based filtering method is applied which successfully separates out the most energetic TSEPs from the background EEG, thereby increasing significantly the SNR of the recorded signals and improving extraction of the characteristic components of the TSEPs. It is shown that the most prominent feature of the TSEP signals for patients with endosseous oral implants is a wave with peak latency between 9 and 15 ms, generally followed by a wave between 25 and 28 ms or 34 and 38 ms for the specific cortical response areas.

Dental Implantation, Endosseous↗
PubMed2000

Identification and characterization of a novel cell cycle-regulated internal ribosome entry site.

PITSLRE protein kinases are related to the large family of cyclin-dependent kinases. They have been proposed to act as tumor suppressor genes and have been shown to play a role in cell cycle progression. We report that two PITSLRE protein kinase isoforms, namely p11O(PITSLRE) and p58(PITSLRE), are translated from a single transcript by initiation at alternative in-frame AUG codons. p110(PITSLRE) is produced by classical cap-dependent translation, whereas p58(PITSLRE) results from internal initiation of translation controlled by an internal ribosome entry site (IRES) with unique properties. The IRES element is localized to the mRNA coding region, and its activity is cell cycle regulated, which permits translation of p58(PITSLRE) in G2/M.

Animals↗
PubMed1999

Non-specific effects of methyl ketone peptide inhibitors of caspases.

Caspases are a family of cysteine proteases which play a crucial role in apoptosis and inflammation. The involvement of caspases in these processes can be demonstrated by their irreversible inhibition with fluoromethyl ketone and chloromethyl ketone derivatives of peptides resembling the cleavage site of known caspase substrates. These inhibitors irreversibly alkylate the cysteine residue in the active site of caspases. In this study we show that a biotinylated fluoromethyl ketone peptide inhibitor of caspases (z-VAD.fmk) also efficiently affinity-labeled cathepsin B and cathepsin H. In addition, the caspase inhibitors z-VAD.fmk, z-DEVD.fmk and Ac-YVAD.cmk also efficiently inhibited cathepsin B activity in vitro and in tissue culture cells at concentrations that are generally used to demonstrate the involvement of caspases.

Affinity Labels↗
PubMed1999

Accurate quantification of (1)H spectra: from finite impulse response filter design for solvent suppression to parameter estimation.

A scheme for accurate quantification of (1)H spectra is presented. The method uses maximum-phase finite impulse response (FIR) filters for solvent suppression and an iterative nonlinear least-squares (NLLS) algorithm for parameter estimation. The estimation algorithm takes the filter influence on the metabolites of interest into account and can thereby correctly incorporate a large variety of prior knowledge into the estimation phase. The FIR filter is designed in such a way that no distortion of the important initial samples is introduced. The FIR filter method is compared numerically with the HSVD method for water signal removal in a number of examples. The results show that the FIR method, using an automatic filter design scheme, slightly outperforms the HSVD method in most cases. The good performance and ease of use of the FIR filter method combined with its low computational complexity motivate the use of the proposed method.

Algorithms↗
PubMed1999

Time-domain quantification of series of biomedical magnetic resonance spectroscopy signals.

Quantification of individual magnetic resonance spectroscopy (MRS) signals is possible in the time domain using interactive nonlinear least-squares fitting methods which provide maximum likelihood parameter estimates under certain assumptions or using fully automatic, but statistically suboptimal, black-box methods. In kinetic experiments time series of consecutive MRS spectra are measured in which information concerning the time evolution of some of the signal parameters is often present. The purpose of this paper is to show how AMARES, a representative example of the interactive methods, can be extended to the simultaneous processing of all spectra in the time series using the common information present in the spectra. We show that this approach yields statistically better results than processing the individual signals separately.

Adenosine Triphosphate↗
PubMed1998

Frequency-selective MRS data quantification with frequency prior knowledge.

Various signal processing techniques have been proposed to improve spectral estimation of closely spaced sinusoids in the presence of noise. This paper exploits frequency prior knowledge information to extract single peaks in magnetic resonance spectra, corresponding to metabolites of interest, by means of a highly selective finite impulse response filter. Thereafter the estimation of the parameters of the peaks is carried out using a singular-value-decomposition-based method known as HTLS. The new technique improves the performance of fully automated magnetic resonance spectroscopy data quantification when frequency prior knowledge is available.

Adenosine Triphosphate↗
PubMed1996

Evaluation of signal processing methods for the quantification of a multi-exponential signal: the glycogen 13C-1 NMR signal.

The 13C-1 NMR peak in proton-decoupled spectra of liver glycogen solution was quantitatively analyzed by three types of model-function fitting algorithms: iterative line-fitting in the frequency domain (MDCON); iterative least-squares fitting (VARPRO) in the time domain; and noniterative singular value decomposition-based analysis (HTLS), also in the time domain. Quantification results were compared with manual integration values. Performance of the algorithms was tested at different signal-to-noise ratios (S/N) of the glycogen C-1 peak. This was achieved by varying the number of scans summed prior to analysis. Since T2 relaxation in glycogen has been shown to be multiexponential [Overloop, K. et al. Magn. Reson. Med. 36, 45-51 (1996], the exact quantification of the C-1 glycogen signal requires a model function comprising a sum of Lorentzian components, each with a different broadening at the glycogen frequency. This paper focuses on the performances of the above methods to fit such a multicomponent resonance line. In the frequency domain, line fitting with two Lorentz lines gives good results at sufficiently high S/N. In the time domain, VARPRO performs better than HTLS because fixed values can be imposed to the linewidth of the components at the common C-1 frequency, thereby reducing convergence problems at low S/N.

Algorithms↗
PubMedDate not supplied

In situ 13C NMR quantification of hepatic glycogen.

We report on the 13C NMR visibility of the C-1 glycosidic carbon of alpha-particulate glycogen in perfused rat liver. We used rats fed ad libitum, animals refed after a 48 h fast with a sucrose supplement with or without glucocorticoid treatment, and gsd/gsd rats with a hepatic glycogen storage disease due to phosphorylase kinase deficiency. Thus we studied a wide range of glycogen levels (25-140 mg/g liver). All livers were perfused with 15 mM glucose, to maintain constant glycogen levels. Failure to activate glycogen phosphorylase ensures stable glycogen levels in gsd/gsd livers. Natural abundance 13C NMR signals were calibrated against a phantom containing a fixed amount of glycogen. Accumulated free induction decays were analysed after Fourier transformation by numerical integration, or by direct analysis of the signal in the time domain using a non-iterative method based on singular value decomposition. NMR quantification of the glycogen correlated well with the chemical determination over the whole concentration range. However, the precision (reproducibility) of glycogen determinations (be it by chemical methods or by NMR spectroscopy) may pose problems. Authors should be encouraged to report systematically on the precision of their methods.

Animals↗