A comparison of two EIT systems suitable for imaging impedance changes in epilepsy

Fabrizi, L,McEwan, A,Oh, T,Woo, E J,Holder, D S IOP Pub 2009 PHYSIOLOGICAL MEASUREMENT Vol.30 No.6

<P>Electrical impedance tomography (EIT) has the potential to produce functional images of the conductivity changes associated with epilepsy to help localization of epileptic foci. Scalp voltage changes associated with internal conductivity changes due to focal seizures have been shown at the limit of detectability for present EIT systems. The performances of two EIT systems, which may be employed in clinical recordings during presurgical assessment of intractable epilepsy, were compared. Those were the 32-channel serial UCH Mk2.5 and the 16-channel semi-parallel KHU Mk1. Images of three conductivity perturbations, simulating epileptic foci, in a head-shaped saline tank without and with a real human skull were recorded using 31-channel and 16-channel protocols with the UCH Mk2.5, while only 16-channel protocols with the KHU Mk1. The UCH Mk2.5 employing the 31-channel protocol had better overall performance with a localization error of 12.7% of the tank diameter, which would be sufficient for lateralization of the epileptic activity. More blurred images, but with similar localization, were obtained using 16 electrodes.</P>

An electrode addressing protocol for imaging brain function with electrical impedance tomography using a 16-channel semi-parallel system

Fabrizi, L,McEwan, A,Oh, T,Woo, E J,Holder, D S IOP Pub 2009 PHYSIOLOGICAL MEASUREMENT Vol.30 No.6

<P>Electrical impedance tomography of brain function poses special problems because applied current is diverted by the resistive skull. In the past, image resolution was maximized with the use of an electrode addressing protocol with widely spaced drive electrode pairs and use of a multiplexer so that many electrode pairs could be flexibly addressed. The purpose of this study was to develop and test an electrode protocol for a 16-channel semi-parallel system which uses parallel recording channels with fixed wiring, the Kyung Hee University (KHU) Mk1. Ten protocols were tested, all addressing pairs of electrodes for recording or current drive, based on recording with a spiral, spiral with suboccipital electrodes (spiral s-o) and zig-zag configurations, and combinations of current injection from electrode pairs at 180°, 120° and 60°. These were compared by assessing the image reconstruction quality of five simulated perturbations in a homogenous model of the human head and of four epileptic foci in an anatomically realistic model in the presence of realistic noise, in terms of localization error, resolution, image distortion and sensitivity in the region of interest. The spiral s-o with current injection at 180°+ 120°+ 60° gave the best image quality and permitted reconstruction with a localization error of less than 10% of the head diameter. This encourages the view that it might be possible to obtain satisfactory images of focal abnormalities in the human brain with 16 scalp electrodes and improved instrumentation avoiding multiplexers on recording circuits.</P>

Analysis of resting noise characteristics of three EIT systems in order to compare suitability for time difference imaging with scalp electrodes during epileptic seizures

Fabrizi, L,McEwan, A,Woo, E,Holder, D S IOP Pub 2007 PHYSIOLOGICAL MEASUREMENT Vol.28 No.7

<P>Electrical impedance tomography measurements in clinical applications are limited by an undesired noise component. We have investigated the noise in three systems suitable for imaging epileptic seizures, the UCH Mark1b, UCH Mark2.5 and KHU Mark1 16 channel, at applied frequencies in three steps from 1 to 100 kHz, by varying load impedance, single terminal or multiplexed measurements, and in test objects of increasing complexity from a resistor to a saline filled tank and human volunteer. The noise was white, and increased from about 0.03% rms on the resistor to 0.08% on the human; it increased with load but was independent of use of the multiplexer. The KHU Mark1 delivered the best performance with noise spectra of about 0.02%, which could be further reduced by averaging to a level where reliable imaging of changes of about 0.1% estimated during epileptic seizures appears plausible.</P>

Assessment of the Microstructure Evolution of an Austempered Ductile Iron During Austempering Process Through Strain Hardening Analysis

Riccardo Donnini,Alberto Fabrizi,Franco Bonollo,Franco Zanardi,Giuliano Angella 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5

The aim of this investigation was to determine a procedure based on tensile testing to assess the critical range ofaustempering times for having the best ausferrite produced through austempering. The austempered ductile iron(ADI) 1050 was quenched at different times during austempering and the quenched samples were tested in tension. The dislocation-density-related constitutive equation proposed by Estrin for materials having high density ofgeometrical obstacles to dislocation motion, was used to model the flow curves of the tensile tested samples. Onthe basis of strain hardening theory, the equation parameters were related to the microstructure of the quenchedsamples and were used to assess the ADI microstructure evolution during austempering. The microstructure evolutionwas also analysed through conventional optical microscopy, electron back-scattered diffraction techniqueand transmission electron microscopy. The microstructure observations resulted to be consistent with the assessmentbased on tensile testing, so the dislocation-density-related constitutive equation was found to be a powerfultool to characterise the evolution of the solid state transformations of austempering.

Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

Funaioli, Tiziana,Leoni, Piero,Marchetti, Lorella,Albinati, Alberto,Rizzato, Silvia,Fabrizi de Biani, Fabrizia,Ienco, Andrea,Manca, Gabriele,Mealli, Carlo American Chemical Society 2013 Inorganic Chemistry Vol.52 No.8

<P>This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>X<SUB>3</SUB> (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e<SUP>–</SUP>. The new species were obtained by an apparent bielectronic oxidation of the 44e<SUP>–</SUP> monohalides Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>(CO)<SUB>2</SUB>X with the corresponding dihalogen X<SUB>2</SUB>. Their X-ray structures are close to the <I>D</I><SUB>3<I>h</I></SUB> symmetry, similarly to the 44e<SUP>–</SUP> analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>I<SUB>3</SUB>, the redox potentials indicated that I<SUB>2</SUB> can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e<SUP>–</SUP> intermediate [Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>(CO)<SUB>2</SUB>I]<SUP>+</SUP> was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>I<SUB>3</SUB>, the transient 44e<SUP>–</SUP> species [Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>(CO)<SUB>3</SUB>]<SUP>+</SUP> is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e<SUP>–</SUP> intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e<SUP>–</SUP> associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e<SUP>–</SUP> phosphido-bridged Pt<SUB>3</SUB> clusters can be attributed to the simultaneous presence of three terminal halides.</P><P>This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>X<SUB>3</SUB> (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e<SUP>−</SUP>. The new species were obtained by an apparent bielectronic oxidation of the 44e<SUP>−</SUP> monohalides Pt<SUB>3</SUB>(μ-PBu<SUP><I>t</I></SUP><SUB>2</SUB>)<SUB>3</SUB>(CO)<SUB>2</SUB>X with the corresponding dihalogen X<SUB>2</SUB>. According to MO arguments, the unique stability of the 42e<SUP>−</SUP> phosphido-bridged Pt<SUB>3</SUB> clusters can be attributed to the simultaneous presence of three terminal halides.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2013/inocaj.2013.52.issue-8/ic400251y/production/images/medium/ic-2013-00251y_0014.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic400251y'>ACS Electronic Supporting Info</A></P>