Radu Mutihac

Mining in chemometrics

Some of the increasingly spread data mining methods in chemometrics like exploratory data analysis, artificial neural networks, pattern recognition, and digital image processing with their highs and lows along with some of their representative applications are discussed. The development of more complex analytical instruments and the need to cope with larger experimental data sets have demanded for new approaches in data analysis, which have led to advanced methods in experimental design and data processing. Hypothesis-driven methods typified by inferential statistics have been gradually complemented or even replaced by data-driven model-free methods that seek for structure in data without reference to the experimental protocol or prior hypotheses. The emphasis is put on the ability of data mining methods to solve multivariate-multiresponse problems on the basis of experimental data and minimal statistical assumptions only, in contrast to classical methods, which require predefined priors to be tested against some null-hypothesis.

Enhancement of Temporal Resolution and BOLD Sensitivity in Real-Time fMRI using Multi-Slab Echo-Volumar Imaging

In this study, a new approach to high-speed fMRI using multi-slab echo-volumar imaging (EVI) is developed that minimizes geometrical image distortion and spatial blurring, and enables nonaliased sampling of physiological signal fluctuation to increase BOLD sensitivity compared to conventional echo-planar imaging (EPI). Real-time fMRI using whole brain 4-slab EVI with 286 ms temporal resolution (4mm isotropic voxel size) and partial brain 2-slab EVI with 136 ms temporal resolution (4×4×6 mm(3) voxel size) was performed on a clinical 3 Tesla MRI scanner equipped with 12-channel head coil. Four-slab EVI of visual and motor tasks significantly increased mean (visual: 96%, motor: 66%) and maximum t-score (visual: 263%, motor: 124%) and mean (visual: 59%, motor: 131%) and maximum (visual: 29%, motor: 67%) BOLD signal amplitude compared with EPI. Time domain moving average filtering (2s width) to suppress physiological noise from cardiac and respiratory fluctuations further improved mean (visual: 196%, motor: 140%) and maximum (visual: 384%, motor: 200%) t-scores and increased extents of activation (visual: 73%, motor: 70%) compared to EPI. Similar sensitivity enhancement, which is attributed to high sampling rate at only moderately reduced temporal signal-to-noise ratio (mean: -52%) and longer sampling of the BOLD effect in the echo-time domain compared to EPI, was measured in auditory cortex. Two-slab EVI further improved temporal resolution for measuring task-related activation and enabled mapping of five major resting state networks (RSNs) in individual subjects in 5 min scans. The bilateral sensorimotor, the default mode and the occipital RSNs were detectable in time frames as short as 75 s. In conclusion, the high sampling rate of real-time multi-slab EVI significantly improves sensitivity for studying the temporal dynamics of hemodynamic responses and for characterizing functional networks at high field strength in short measurement times.

High-speed real-time resting-state FMRI using multi-slab echo-volumar imaging.

We recently demonstrated that ultra-high-speed real-time fMRI using multi-slab echo-volumar imaging (MEVI) significantly increases sensitivity for mapping task-related activation and resting-state networks (RSNs) compared to echo-planar imaging (Posse et al., 2012). In the present study we characterize the sensitivity of MEVI for mapping RSN connectivity dynamics, comparing independent component analysis (ICA) and a novel seed-based connectivity analysis (SBCA) that combines sliding-window correlation analysis with meta-statistics. This SBCA approach is shown to minimize the effects of confounds, such as movement, and CSF and white matter signal changes, and enables real-time monitoring of RSN dynamics at time scales of tens of seconds. We demonstrate highly sensitive mapping of eloquent cortex in the vicinity of brain tumors and arterio-venous malformations, and detection of abnormal resting-state connectivity in epilepsy. In patients with motor impairment, resting-state fMRI provided focal localization of sensorimotor cortex compared with more diffuse activation in task-based fMRI. The fast acquisition speed of MEVI enabled segregation of cardiac-related signal pulsation using ICA, which revealed distinct regional differences in pulsation amplitude and waveform, elevated signal pulsation in patients with arterio-venous malformations and a trend toward reduced pulsatility in gray matter of patients compared with healthy controls. Mapping cardiac pulsation in cortical gray matter may carry important functional information that distinguishes healthy from diseased tissue vasculature. This novel fMRI methodology is particularly promising for mapping eloquent cortex in patients with neurological disease, having variable degree of cooperation in task-based fMRI. In conclusion, ultra-high-real-time speed fMRI enhances the sensitivity of mapping the dynamics of resting-state connectivity and cerebro-vascular pulsatility for clinical and neuroscience research applications.

Entropic approach to information coding in DNA molecules

The amount of information carried by the binding site patterns in the deoxyribonucleic acid (DNA) molecules is subject of interpretation in the light of the maximum entropy methods, within the framework of classical information theory, in view of characterizing the sequence conservation at nucleic acid binding sites.

PHYSICOCHEMICAL PARAMETERS OF THE TRANSPORT OF AMINES AND AMINO ACIDS THROUGH LIQUID MEMBRANES BY MACROCYCLIC LIGANDS

Both interphasic water/organic solvent transfer and transport through liquid membranes may be influenced to a certain extent by several physicochemical factors like the structure of the ligand, the nature of the cation, the type of the anion (acting as a counterion), the interfaces thermodynamic equilibria, and the nature of the membrane solvent. The effects of these factors upon both the transfer and the transport through liquid membranes of complexes of some amino acids (L-tryptophane, L-methionine, L-phenylalanine, L-leucine, L-isoleucine, and L-valine) and amines (methylamine, dimethylamine, and n-propylamine) in cationic forms with various macrocyclic ligands (18-crown-6, benzo-18-crown-6, and dibenzo-18-crown-6) have been investigated.

The transport of amino acids by 18-crown-6 through liquid membranes

The possibility of separating in cationic form some α-amino acids (L-Methionine, L-Leucine, L-Isoleucine, L-Valine, L-Phenylalanine, L-α-Alanine and L-Cysteine) from mixtures in the presence of picrate anion has been investigated by means of active transport assisted by a pH gradient through liquid membranes. 18-Crown-6 in 1,2-dichloroethane has been used as a selective carrier. The effect of stirring rates at different volumes of the membrane, suggests a diffusional rate-limiting process of the amino acid transport.

PCA and ICA neural implementations for source separation - a comparative study

A comparative study of neural implementations running principal component analysis (PCA) and independent component analysis (ICA) was carried out. Both artificially generated data and real biomedical time series were employed in order to critically evaluate and assess the performance of various algorithms under study. The assumption of independence, even if weak, was proved reach in relevant interferences on brain activity. The ICA algorithms were proved more realistic in terms of neurophysiological relevance as compared to PCA.

LIQUID MEMBRANE TRANSPORT OF SUPRAMOLECULAR COMPLEXES OF SOME AMINES AND AMINO ACIDS WITH MACROCYCLIC LIGANDS

The transport of some amines in protonated form was studied (viz. methylamine, dimethylamine, diethylamine andn-propylamine) and α-amino acids (l-leucine,l-methionine,l-isoleucine,l-phenylalanine,l-valine,l-α-alanine andl-cysteine). The following macrocyclic ligands were used as carriers throughout the experiments: 15-crown-5 (15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), diazacrown ether [2.2] (1,7,10,16-tetraoxa-4,13-diazacyclooctadecane) and cryptand [2.2.2] (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo [8.8.8] hexacosane). The active transport, assisted by pH gradient, of amino acids and amines in protonated form as ion pairs in the presence of picrate anion was performed. The experiments suggested the influence of the ligand size, the donor atom type, and the substituents on the transport phenomena.

Neural network implementations of independent component analysis

The performance of six neuromorphic adaptive structurally different algorithms was analyzed in blind separation of independent artificially generated signals using the stationary linear independent component analysis (ICA) model. The estimated independent components were assessed and compared aiming to rank the neural ICA implementations. All algorithms were run with different contrast functions, which were optimally selected on the basis of maximizing the sum of individual negentropies of the network outputs. Both subGaussian and superGaussian one-dimensional time series were employed throughout the numerical simulations.

MAXIMUM ENTROPY IMPROVEMENT OF X-RAY DIGITAL MAMMOGRAMS

Our approach to X-ray digital image enhancement was based on entropy maximization, which allows distributions to be estimated in cases when incomplete or corrupt information is only available. In data analysis, maximum entropy (ME) techniques are generally used to reconstruct positive distributions, such as images and spectra, from blurred or noisy data. Within this framework, positive distributions ought to be assigned probabilities which are based on the entropy of these distributions. If we consider a complete collection of images corresponding to all possible intensity distributions, then measurements act as a filter over the collection by restricting our attention to the images that satisfy the data with noise. Among these, a natural choice may be the one that could have arisen in the maximum number of ways, depending on our counting rule.