Tissue Electrical Conductivity Research Articles

Role of saline concentration during saline-infused radiofrequency ablation: Observation of secondary Joule heating along the saline-tissue interface

Infusion of saline prior to radiofrequency ablation (RFA) is known to enlarge the thermal coagulation zone. The abundance of ions in saline elevate the electrical conductivity of the saline-saturated region. This promotes greater electric current flow inside the tissue, which increases the amount of RF energy deposition and subsequently enlarges the coagulation zone. In theory, infusion of higher concentration of saline should lead to larger coagulation zone due to the greater number of ions. Nevertheless, existing studies on the effects of concentration on saline-infused RFA have been conflicting, with the exact role of saline concentration yet to be fully elucidated. In this paper, computational models of saline-infused RFA were developed to investigate the role of saline concentration on the outcome of saline-infused RFA. The elevation in tissue electrical conductivity was modelled using the microscopic mixture model, while RFA was modelled using the coupled dual porosity-Joule heating model. Results obtained indicated that the presence of a concentration threshold to which no further elevation in tissue electrical conductivity and enlargement in thermal coagulation can occur. This threshold was determined to be at 15% NaCl. Analysis of the Joule heating distribution revealed the presence of a secondary Joule heating site located along the interface between wet and dry tissue. This secondary Joule heating was responsible for the enlargement in coagulation volume and its rapid growth phase during ablation.

A numerical study on the effect of conductivity change in cell kill distribution in irreversible electroporation

Abstract Introduction: irreversible electroporation (IRE) is a tissue ablation technique and physical process used to kill the undesirable cells. In the IRE process by mathematical modelling we can calculate the cell kill probability and distribution inside the tissue. The purpose of the study is to determine the influence of electric conductivity change in the IRE process into the cell kill probability and distribution. Methods: cell death probability and electric conductivity were calculated with COMSOL Multiphysics software package. 8 pulses with a frequency of 1 Hz, pulse width of 100 µs and electric field intensity from 1000 to 3000 V/Cm with steps of 500 V/Cm used as electric pulses. Results: significantly, the electrical conductivity of tissue will increase during the time of pulse delivery. According to our results, electrical conductivity increased with an electric field intensity of pulses. By considering the effect of conductivity change on cell kill probability, the cell kill probability and distribution will change. Conclusion: we believe that considering the impact of electric conductivity change on the cell kill probability will improve the accuracy of treatment outcome in the clinic for treatment with IRE.

Electrical conductivity of graft tissues of pome crops is an indicator of accretion quality

The article presents experimental data on the electrical conductivity of tissues of grafted apple and pear crops to identify patterns of electrical conductivity in qualitative accretion of grafting components at early stages. For the fastest implementation of the varieties and clonal rootstocks obtained by breeding, it is important to select stable scion-stock combinations. The main task remains to detect incompatibility of the components of grafts at an early age, since its manifestation in adult plants causes significant damage to production. The studies were carried out in different years on winter and summer grafts. Patterns of the electrical conductivity dynamics are established: with qualitative fusion of grafting components, a monotonous increase in electrical conductivity is observed when the values of electrical conductivity change between the 1st and 14th day within 80 μS. In case of poor quality growth of grafting components, values of electric conductivity of tissues practically do not change (±5-10 μS). In rotting tissue (in visually unchanged tissues) values of electrical conductivity of all components of grafting in the period from the 8th to the 18th day after grafting are sharply increased by 100 mS, which is connected with water ion exchange disorder in tissues. When reproduction by budding in its initial period, in compatible combinations, the drop in tissue conductivity values at the grafting site was no more than 20 μS compared to the indications on the rootstock above the grafting site. On the 16th day of measurements, the readings of the electrical conductivity tissues at the grafting site and on the reverse side were practically unchanged (± 5 μS) — this indicate a gradual repair of the grafting tissues.

In-vivo pilot study at 3 Tesla: Feasibility of Electric Properties Tomography in a rat model of stroke

BackgroundElectrical Properties Tomography (EPT) is a new sequence which delivers information on tissue electrical conductivity. It has been mostly used for tumor imaging. Ischemic stroke is another promising application. The aim of this study was to demonstrate the feasibility of EPT in a rodent model of stroke. MethodsWistar rats with and without temporary middle cerebral occlusion (MCAo) were examined in a 3T scanner. EPT was performed using a Steady-State Free-Precession (SSFP) sequence. From the transceive phase ɸ of these SSFP scans, conductivity σ was estimated by the equation σ = Δɸ/(2μ0ω) with Δ the Laplacian operator, μ0 the magnetic permeability, and ω the Larmor frequency. Subsequently, a median filter was applied. ResultsHealthy cortical grey matter, white matter and cerebrospinal fluid showed significantly different conductivity (0.83 ± 0.14 S/m, 0.63 ± 0.06 S/m, 2.33 ± 0.49 S/m, p < 0.05). Infarcted tissue exhibited increased conductivity (1.937 ± 1.347 vs. 0.782 ± 0.429 S/m, p < 0.05). ConclusionEPT is feasible in a rodent model of stroke. Infarcted tissue after MCAo exhibited increased conductivity. Further in-vivo experiments with examination of the influence of reperfusion status and temporal evolution of the infarcted areas should be conducted.

Two-compartment mathematical modeling in RF tumor ablation: New insight when irreversible changes in electrical conductivity are considered.

The objective was to explore variations of temperature distribution and coagulation zone size computed by a two-compartment radiofrequency ablation (RFA) model when including simultaneously reversible changes in the tissue electrical conductivity (σ) due to temperature and irreversible changes due to thermal coagulation. Two-compartment (tumor and healthy tissue) models were built and simulated. Reversible change of σ was modeled by a piecewise function characterized by increments of +1.5%/℃ up to 100 ℃, and a 100 times smaller value from 100 ℃ onwards. Irreversible changes of σ were modeled using an Arrhenius model. We assumed that both tumor and healthy tissue had a different initial σ value (as suggested by the experimental data in the literature) and tended towards a common value as thermal damage progressed (necrotized tissue). We modeled a constant impedance protocol based on 90 V pulses voltage and three tumor diameters (2, 3 and 4 cm). Computer simulations showed that the differences between both models were only 0.1 and 0.2 cm for axial and transverse diameters, respectively, and this small difference was reflected in the similar temperature distributions computed by both models. In view of the available experimental data on changes of electrical conductivity in tumors and healthy tissue during heating, our results suggest that irreversible changes in electrical conductivity do not have a significant impact on coagulation zone size in two-compartment RFA models.

A New Bio-Impedance Forceps Sensor for Measuring Electrical Conductivity of the Biological Tissues

Tissue electrical conductivity measurements are very important for diagnostic purposes. In this paper, an electrical bio-impedance sensor with a biopsy forceps shape was introduced for measuring electrical conductivity of the tissue inside the body. For this purpose, based on the Laplace’s equation and the forced boundary conditions in the mouth of the forceps, the relation between electrical conductivity of the tissue and measured electrical potential was analytically obtained. The obtained analytical formula was verified by modeling the electrical bio-impedance forceps and biological tissue in COMSOL software. A prototype of the designed bio-impedance forceps was fabricated and experimentally validated. The validation process was performed by measuring electrical conductivity of the Phosphate -Buffered Saline (PBS) solution with different concentrations. Finally, by measuring electrical impedance spectrum of pulmonary tissues in three different samples at a frequency band of 50 kHz to 5 MHz, it was found that this sensor could be potentially beneficial to discriminate tumoral tissues from healthy ones in biopsy process.

Conductivity change with needle electrode during high frequency irreversible electroporation: a finite element study

Abstract Irreversible electroporation (IRE) is a process in which the cell membrane is damaged and leads to cell death. IRE has been used as a minimally invasive ablation tool. This process is affected by some factors. The most important factor is the electric field distribution inside the tissue. The electric field distribution depends on the electric pulse parameters and tissue properties, such as the electrical conductivity of tissue. The present study focuses on evaluating the tissue conductivity change due to high-frequency and low-voltage (HFLV) as well as low-frequency and high-voltage (LFHV) pulses during irreversible electroporation. We were used finite element analysis software, COMSOL Multiphysics 5.0, to calculate the conductivity change of the liver tissue. The HFLV pulses in this study involved 4000 bipolar and monopolar pulses with a frequency of 5 kHz, pulse width of 100 µs, and electric field intensity from 100 to 300 V/cm. On the other hand, the LFHV pulses, which we were used, included 8 bipolar and monopolar pulses with a frequency of 1 Hz, the pulse width of 2 ms and electric field intensity of 2500 V/cm. The results demonstrate that the conductivity change for LFHV pulses due to the greater electric field intensity was higher than for HFLV pulses. The most significant conclusion is the HFLV pulses can change tissue conductivity only in the vicinity of the tip of electrodes. While LFHV pulses change the electrical conductivity significantly in the tissue of between electrodes.

A Novel Method to Increase Tumor Ablation Zones With RFA by Injecting the Cationic Polymer Solution to Tissues: In Vivo and Computational Studies.

This study aims to examine, for the first time, the introduction of cationic polymer solutions to improve radiofrequency ablation (RFA) in terms of a potentially enlarged ablation zone. By using in vivo and computational RFA studies, two cationic polymers, Chitooligosaccharides (COS) and carboxymethyl chitosan (CMC), diluted in deionized water, were injected into tissues separately surrounding the RF bipolar electrode prior to power application. A total of 9 rabbits were used to 1) measure the increase in electrical conductivity of tissues injected with the cationic polymer solutions, and 2) explore the enhancement of the ablation performance in RFA trials. A computer model of RFA comprising a model of the solution diffusion with an RF thermal ablation model was also built, validated by the in vivo experiment, to quantitatively study the effect of cationic polymer solutions on ablation performances. Compared to the control group, the electrical conductivity of rabbit liver tissues was increased by 42.20% (0.282 ± 0.006 vs. 0.401 ± 0.048S/m, P = 0.001) and 43.97% (0.282 ± 0.006 vs. 0.406 ± 0.042S/m, P = 0.001) by injecting the COS and CMC solution at the concentration of 100 mg/mL into the tissues, denoted COSDW100 and CMCDW100, respectively. Consequently, the in vivo experiments show that the ablation zone was enlarged by 95% (47.6 ± 6.3 vs. 92.6 ± 11.5 mm2, P < 0.001) and 87% (47.6± 6.3 vs. 88.8 ± 9.6 mm2, P < 0.001) by COSDW100 and CMCDW100, respectively. The computer simulation shows that the ablation zone was enlarged by 71% (51.9 vs. 88.7 mm2) and 63% (51.9 vs. 84.7 mm2) by COSDW100 and CMCDW100, respectively. The injection of the cationic solution can greatly improve the performance of RFA treatment in terms of enlarging the ablation zone, which is due to the increase in the electrical conductivity of liver tissues surrounding the RF electrode. This study contributes to the improvement of RFA in the treatment of large tumors.

Vigor tests in seeds creole of Phaseolus lunatus L.

Seeds with a good physiological quality are essential to high productivity. However, for some seeds, Phaseolus lunatus L., the viability and vigor analyze show deficiency in quality. This work aimed to evaluate the physiological quality of Phaseolus lunatus L. seeds using several vigor tests. The study was realized at the Laboratory of Seed Analysis of the Agricultural Sciences Center of the Federal University of Paraíba, in Areia – PB, Brazil. We used seeds from five cultivars of P. lunatus (Branca, Orelha de Vó, Cearense, Rosinha, and Roxinha). To determine the physiological quality, we measured the water content, the viability and vigor test (germination, emergence, electrical conductivity, tetrazolium, first germination count and emergence, seedling length and dry mass). We used a completely randomized design for seeds evaluation, and the field test was performed in randomized blocks. The water content of P. lunatus did not differ among the cultivars, indicating a uniformity in the percentage of moisture. Also, the percentage and speed of emergency and the dry mass of seedlings did not differ among the varieties. The tetrazolium and electrical conductivity tests indicated that Rosinha cultivar had the worst viability concerning the other cultivars, showing a low percentage of living tissue and lower electrical conductivity. The seeds of Roxinha cultivar had the better physiological quality, and the Cearense cultivar had the worst quality evaluation. We recommend the tetrazolium test but not the electrical conductivity test to evaluate the vigor of P. lunatus.

Mitigation of Drought Stress Effects on Pepper Seedlings by Exogenous Methylamine Application

The study was conducted to determine effects of a new synthesis of methylamine on the plant growth, physiological and biochemical characteristics in pepper. There were four irrigation levels [full irrigation (100%) (I0), 80% (I1), 60% (I2) and 40% (I3)] and two methylamine (MA) treatments (0, 2.5 mM). At the end of the study, it was observed that there were significant differences between applications and levels. Effects of MA treatments on plant growth (plant height, stem diameter, fresh, dry weight etc.), plant physiological and biochemical parameters [tissue electrical conductivity (TEC), tissue relative water content (TRWC), hydrogen peroxide (H2O2), malondialdehyde (MDA), proline, antioxidant enzyme activity], and plant nutrient element content of pepper seedlings under different irrigation levels were significantly important. The results of the study showed that the drought stress conditions negatively affected the plant growth, increased the content of TEC, H2O2 and MDA, and decreased the TRWC and plant mineral content in pepper. However, MA application improved plant growth and decreased TEC, H2O2 and MDA content compared to control in pepper under drought conditions. MA treated plants at I3 had higher shoot fresh weight and shoot dry weight than non-treated plants by 12 and 20%, respectively. In conclusion, MA application could mitigate the deleterious effects of the drought stress on the pepper seedlings.

Mitigation of Drought Stress Effects on Pepper Seedlings by Exogenous Methylamine Application

The study was conducted to determine effects of a new synthesis of methylamine on the plant growth, physiological and biochemical characteristics in pepper. There were four irrigation levels [full irrigation (100%) (I0), 80% (I1), 60% (I2) and 40% (I3)] and two methylamine (MA) treatments (0, 2.5 mM). At the end of the study, it was observed that there were significant differences between applications and levels. Effects of MA treatments on plant growth (plant height, stem diameter, fresh, dry weight etc.), plant physiological and biochemical parameters [tissue electrical conductivity (TEC), tissue relative water content (TRWC), hydrogen peroxide (H2O2), malondialdehyde (MDA), proline, antioxidant enzyme activity], and plant nutrient element content of pepper seedlings under different irrigation levels were significantly important. The results of the study showed that the drought stress conditions negatively affected the plant growth, increased the content of TEC, H2O2 and MDA, and decreased the TRWC and plant mineral content in pepper. However, MA application improved plant growth and decreased TEC, H2O2 and MDA content compared to control in pepper under drought conditions. MA treated plants at I3 had higher shoot fresh weight and shoot dry weight than non-treated plants by 12 and 20%, respectively. In conclusion, MA application could mitigate the deleterious effects of the drought stress on the pepper seedlings.

Putrescine, Spermine and Spermidine Mitigated the Salt Stress Damage on Pepper (Capsicum annum L.) Seedling

In order to evaluate the effects of polyamines on plant growth, physiological and biochemical characteristics of pepper seedlings grown under salt stress (0, 50 and 100 mM NaCl), putrescine (Put), spermine (Spr) and spermidine (Spd) were foliarly applied to the seedlings under controlled greenhouse conditions. The effects of polyamines on plant height, number of leaves, stem diameter, chlorophyll reading value (CRV), stoma conductance (SC), tissue electrical conductivity (TEC), leaf relative water content (LRWC), enzyme activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) of pepper seedlings were significant under salt stress. As salt concentration increased, plant height, stem diameter, number of leaves, CRV, plant and root fresh and dry weight, and LRWC lowered but an increase in TEC occurred. However, polyamine treatments improved the parameters investigated under salt stress. In the study, it has been determined that the negative effects of salt stress can be mitigated with exogenously polyamine applications to the pepper seedlings.

Variation in Reported Human Head Tissue Electrical Conductivity Values

Electromagnetic source characterisation requires accurate volume conductor models representing head geometry and the electrical conductivity field. Head tissue conductivity is often assumed from previous literature, however, despite extensive research, measurements are inconsistent. A meta-analysis of reported human head electrical conductivity values was therefore conducted to determine significant variation and subsequent influential factors. Of 3121 identified publications spanning three databases, 56 papers were included in data extraction. Conductivity values were categorised according to tissue type, and recorded alongside methodology, measurement condition, current frequency, tissue temperature, participant pathology and age. We found variation in electrical conductivity of the whole-skull, the spongiform layer of the skull, isotropic, perpendicularly- and parallelly-oriented white matter (WM) and the brain-to-skull-conductivity ratio (BSCR) could be significantly attributed to a combination of differences in methodology and demographics. This large variation should be acknowledged, and care should be taken when creating volume conductor models, ideally constructing them on an individual basis, rather than assuming them from the literature. When personalised models are unavailable, it is suggested weighted average means from the current meta-analysis are used. Assigning conductivity as: 0.41 S/m for the scalp, 0.02 S/m for the whole skull, or when better modelled as a three-layer skull 0.048 S/m for the spongiform layer, 0.007 S/m for the inner compact and 0.005 S/m for the outer compact, as well as 1.71 S/m for the CSF, 0.47 S/m for the grey matter, 0.22 S/m for WM and 50.4 for the BSCR.

Effects of Lead Stress on Growth and Some Physiological Characteristics of Bean

This study was conducted to determine the effects of different lead (0, 1000, 1500 and 2000 mg/kg) levels on physiological and morphological responses of bean plants in 2019 in Atatürk University, Faculty of Agriculture, Department of Horticulture under laboratory and greenhouse conditions. Bean (Phaseolus vulgaris L.) Gina cultivar was used as plant material in the experiment. According to study findings, it was determined that differences between treatments were statistically important. The bean plants grown under heavy metal stress conditions were affected regarding to plant growth parameters (fresh and dry weight ect.), some plant physiological parameters such as tissue electrical conductivity (TEC), tissue rational water content (TRWC). Lead stress conditions negatively affected plant growth. Plants grown under heavy metal stress had more TEC and less TRWC values compared to the control plants. Heavy metal stress caused the decreased chlorophyll a, chlorophyll b and caretenoid content in bean plants. In conclusion, bean plants responded to lead stress by reducing growth, TRWC and pigment concentration, increasing TEC.

Biophysical Modeling for Brain Tissue Conductivity Estimation Using SEEG Electrodes.

We aimed at providing an accurate estimation of human brain tissue electrical conductivity in clinico, using local, low-intensity pulsed stimulation. Using the quasi-static approximation of Maxwell equations, we derived an analytical model of the electric field generated by intracerebral stereotactic-EEG (SEEG) electrodes. We coupled this electric field model with a model of the electrode-electrolyte interface to provide an explicit, analytical expression of brain tissue conductivity based on the recorded brain tissue response to pulse stimulation. We validated our biophysical model using saline solutions calibrated in electrical conductivity, rat brain tissue, and electrophysiological data recorded in clinico from two epileptic patients during SEEG. This new model-based method offers a fast and reliable estimation of brain tissue electrical conductivity by accounting for contributions from the electrode-electrolyte interface. This method outperforms standard bioimpedance measurements since it provides absolute (as opposed to relative) changes in brain tissue conductivity. Application for diagnosis is envisioned since conductivity values strongly differ when estimated in the healthy versus hyperexcitable brain tissue.

OA019] Human in-vivo Magnetic Resonance Current Density Imaging (MRCDI) and MR Electrical Impedance Tomography (MREIT)

Purpose Information on the electrical tissue conductivity might be useful for the diagnosis and characterization of pathologies such as tumors [1] . MRCDI and MREIT are two emerging non-invasive techniques for imaging of weak currents and ohmic conductivities. In this study, we demonstrated human in vivo brain MRCDI to pave the way for its clinical use [2] , [3] . Methods In short, weak alternating currents up to 1–2 mA are injected into human head in synchrony with tailored phase-sensitive MRI. The currents create a magnetic field Δ B z , c , which shifts the precession frequency of the magnetization and modulates the acquired MR images. The acquired images are used to measure Δ B z , c and reconstruct the current flow and conductivity distributions. We employed a steady-state free precession free-induction-decay (SSFP-FID) sequence in five subjects, and injected currents of 1 mA by an MR-conditional current source via electrodes attached to the scalp (two current profiles: Right-left (RL), electrodes placed near the temporoparietal junctions; anterior-posterior (AP), one attached to the forehead and one above the inion). Additionally, an ultra-short-echo-time sequence was performed to track the feeding cables for correcting the stray magnetic fields induced by cable currents. Corrected Δ B z , c measurements were used to calculate current flow distributions and compared with Finite-Element simulations of the current flow based on individualized head models [4] . Results The current-induced magnetic field Δ B z , c with ≤ 1 nT was reliably measured and the reconstructed current flows showed good agreement with the simulations (average coefficient of determination R2= 71%). The injected current flow differed substantially among individuals according to the electrode placements and anatomical differences. The calculated currents are stronger in CSF-filled highly conductive regions, e.g. the longitudinal fissure. Conclusions The strong correlation between the simulations and measurements validates the accuracy of the method and demonstrates the potential of the method for determining accurate brain tissue conductivities. These initial current flow recordings pave the way for human brain MREIT that might complement standard MR methods for tumor characterization.

Electrochemotherapy Effectiveness Loss due to Electric Field Indentation between Needle Electrodes: A Numerical Study.

Electrochemotherapy is an anticancer treatment based on applying electric field pulses that reduce cell membrane selectivity, allowing chemotherapy drugs to enter the cells. In parallel to electrochemotherapy clinical tests, in silico experiments have helped scientists and clinicians to understand the electric field distribution through anatomically complex regions of the body. In particular, these in silico experiments allow clinicians to predict problems that may arise in treatment effectiveness. The current work presents a metastatic case of a mast cell tumor in a dog. In this specific treatment planning study, we show that using needle electrodes has a possible pitfall. The macroscopic consequence of the electroporation was assessed through a mathematical model of tissue electrical conductivity. Considering the electrical and geometrical characteristics of the case under study, we modeled an ellipsoidal tumor. Initial simulations were based on the European Standard Operating Procedures for electrochemotherapy suggestions, and then different electrodes' arrangements were evaluated. To avoid blind spots, multiple applications are usually required for large tumors, demanding electrode repositioning. An effective treatment electroporates all the tumor cells. Partially and slightly overlapping the areas increases the session's duration but also likely increases the treatment's effectiveness. It is worth noting that for a single application, the needles should not be placed close to the tumor's borders because effectiveness is highly likely to be lost.

Real-time estimation of lesion depth and control of radiofrequency ablation within ex vivo animal tissues using a neural network

Background: Radiofrequency ablation (RFA), a method of inducing thermal ablation (cell death), is often used to destroy tumours or potentially cancerous tissue. Current techniques for RFA estimation (electrical impedance tomography, Nakagami ultrasound, etc.) require long compute times (≥ 2 s) and measurement devices other than the RFA device. This study aims to determine if a neural network (NN) can estimate ablation lesion depth for control of bipolar RFA using complex electrical impedance – since tissue electrical conductivity varies as a function of tissue temperature – in real time using only the RFA therapy device’s electrodes.Methods: Three-dimensional, cubic models comprised of beef liver, pork loin or pork belly represented target tissue. Temperature and complex electrical impedance from 72 data generation ablations in pork loin and belly were used for training the NN (403 s on Xeon processor). NN inputs were inquiry depth, starting complex impedance and current complex impedance. Training-validation-test splits were 70%-0%-30% and 80%-10%-10% (overfit test). Once the NN-estimated lesion depth for a margin reached the target lesion depth, RFA was stopped for that margin of tissue.Results: The NN trained to 93% accuracy and an NN-integrated control ablated tissue to within 1.0 mm of the target lesion depth on average. Full 15-mm depth maps were calculated in 0.2 s on a single-core ARMv7 processor.Conclusions: The results show that a NN could make lesion depth estimations in real-time using less in situ devices than current techniques. With the NN-based technique, physicians could deliver quicker and more precise ablation therapy.

P079 Electroconvulsive therapy induced hippocampal electric field strength and structural plasticity

Introduction Recent neuroimaging investigations of electroconvulsive therapy (ECT) in patients with severe treatment-resistant depression suggest that ECT-induced neuroplasticity of the hippocampus is related to improved clinical response. The relationship between stimulus dose, particularly the pulse current amplitude, with structural plasticity of the hippocampus induced by ECT remains unknown. Objectives To assess the relationship between ECT induced electric field strength and volumetric changes in the hippocampus. Patients & methods The study was approved by the Human Research Protections Office at the University of New Mexico. Fifteen depressed patients (age 55–78) were referred for ECT. Ultrabrief pulse right unilateral ECT was performed using a Thymatron System IV (n = 10, pulse amplitude = 900 mA, pulse width = 0.25 ms; Somatics LLC, Lake Bluff, IL) or a MECTA Spectrum 5000Q (pulse amplitude = 700 mA (n = 2) and 500 mA (n = 3), pulse width = 0.3 ms; MECTA Corp., Tualatin, OR) both delivering stimulation at six-times seizure threshold. The patients underwent neuroimaging within 2 days of starting ECT, and >5 days after the ECT treatment course. High resolution T1-weighted structural MRI were collected on a 3T Siemens Trio scanner. Baseline MRIs were segmented into white matter, gray matter, cerebrospinal fluid, skull, scalp using SPM 12. The volumes defining the head tissues and the attached electrodes were meshed into finite elements using the Simpleware ScanIP and ScanCAD modules. Tissue electrical conductivity and permittivity values were derived from the literature. The electric field was computed using COMSOL Multiphysics. Hippocampus segmentation and volume changes were computed using FreeSurfer. Results In a generalized linear model, ECT pulse amplitude is correlated with the induced electric field strength in the right hippocampus (p Fig. 1 shows the scatterplot of volume change with mean electric field strength and unadjusted regression lines for the left and right hippocampus. Conclusion ECT elicited structural plasticity is a function of stimulus strength. Computational electric field models can be helpful in guiding stimulus dosing in ECT. Download : Download high-res image (143KB) Download : Download full-size image

Optimization of Peripheral Vascular Sizing with Conductance Guidewire: Theory and Experiment.

Although the clinical range of interventions for coronary arteries is about 2 to 5 mm, the range of diameters of peripheral vasculature is significantly larger (about 10 mm for human iliac artery). When the vessel diameter is increased, the spacing between excitation electrodes on a conductance sizing device must also increase to accommodate the greater range of vessel diameters. The increase in the excitation electrodes distance, however, causes higher parallel conductance or current losses outside of artery lumen. We have previously shown that the conductance catheter/guidewire excitation electrode distances affects the measurement accuracy for the peripheral artery lumen sizing. Here, we propose a simple solution that varies the detection electrode distances to compensate for parallel conductance losses. Computational models were constructed to simulate the conductance guidewire with various electrodes spacing combinations over a range of peripheral artery lumen diameters and surrounding tissue electrical conductivities. The results demonstrate that the measurement accuracy may be significantly improved by increased detection spacing. Specifically, an optimally configured detection/excitation spacing (i.e., 5-5-5 or an equidistant electrode interval with a detection-to-excitation spacing ratio of 0.3) was shown to accurately predict the lumen diameter (i.e., -10% < error < 10%) over a broad range of peripheral artery dimensions (4 mm < diameter < 10 mm). The computational results were substantiated with both ex-vivo and in-vivo measurements of peripheral arteries. The present results support the accuracy of the conductance technique for measurement of peripheral reference vessel diameter.