Array Position Research Articles

Effects of disturbance of seawater excited by internal wave on GNSS-acoustic positioning

Traditional Global Navigation Satellite System-Acoustic (GNSS-A) positioning assumes the Layered Model in the sound speed structure, and any of horizontal perturbation of seawater degrades its accuracy. However, the use of the Gradient Model analytically demonstrated that the horizontal gradient of the sound speed structure and displacement can simultaneously be solved using multiple transponders for each of ping. We applied this technique to our observed data and found it unsuitable for real data. We confirmed that a horizontal perturbation with wavelength shorter than the horizontal extent of the transponder array significantly violates the linear approximation in the Gradient Model. Our vertical 2D numerical simulation of internal waves (IWs) forced by tidal oscillation showed that such small-scale IWs could effectively be generated by nonlinear cascade from large-scale IWs of the major tidal constituents. In addition, a small-scale IW in deep water typically has a period of 3–4 h, which degrades positioning accuracy significantly, whereas an IW of much shorter period in shallow water has less effect after removal of the fluctuation by time averaging within a typical observation period. Apparent array position obtained in the synthetic test based on the simulated IW-derived sound speed structure showed features quite similar to that observed in real surveys. To incorporate such deeper perturbation, we proposed a Disturbance Model using dual sea surface platforms, that can solve time-varying perturbation in the vicinity of each transponder.

P14.38 Clinical experience with tumor treating fields (TTFields) treatment for posterior fossa tumors

Abstract Introduction: TTFields brought a new concept in the treatment of brain tumors. It was tested and recommended for use in supra-tentorial lesions. There is a paucity of data available about TTFields safety and efficacy for infra-tentorial lesion. Method: Patients with posterior fossa tumors were treated with the Optune® system. Initial transducer array positioning and all technical characteristic were performed with technical support from Novocure. Results: Two patients with posterior fossa glial tumors were treated. The first is a 27 years old male with DIPG (without pathological confirmation of the tumor grade) who was treated with Stupp protocol. Treatment with TTFields commenced with TMZ adjuvant phase. The second patient is a 33 years old female with cerebello-pontine astrocytoma WHO grade III, IDH I mutated. This patient was treated with partial resection and Stupp protocol. TTFields treatment was started after completing 12 TMZ adjuvant cycles with measurable stable disease. Duration and compliance of TTFields treatment for first patient is 286 days and 86% and for second patient is 168 days and 93.6%. The skin toxicity is minimal and did not require treatment interruption. There is no other TTFields related toxicity. The MRI evaluation had showed improvement in the first patient and stable disease in the second. Conclusion: According to our knowledge, this is the first report of clinical experience with TTFields treatment for posterior fossa tumors. In our experience, the treatment is feasible and with equal toxicity to previously reported supra-tentorial lesions. Small patient population and short follow up do not allow efficacy evaluation.

An Array Position Refinement Algorithm for Pencil Beam Pattern Synthesis With High-Order Taylor Expansion

In this letter, the array position refinement for low peak sidelobe level (PSLL) generation utilizing uniform element excitation is investigated. The array beam pattern is expressed as a polynomial function with respect to (w.r.t.) the array position variation, i.e., $\Delta {\bf x}$ , via the high-order Taylor expansion. An iterative algorithm is proposed to solve the optimization problem w.r.t. $\Delta {\bf x}$ to achieve the low PSLL. The algorithm, first, converts the original nonconvex problem into a convex one; thus, the problem can be solved efficiently by readily available tools. The array position is, thereafter, updated iteratively by adjusting $\Delta {\bf x}$ with a convex technique. Numerical simulations with both linear and planar array antennas are carried out to validate the effectiveness of the proposed algorithm. Compared with the existing algorithms, the proposed algorithm can further suppress the PSLLs with 0.9 and 0.4/1.2 dB for linear and planar array antennas, respectively.

Tumor-Treating Field Arrays Do Not Reduce Target Volume Coverage for Glioblastoma Radiation Therapy

PurposeTo inform development of procedures for using tumor-treating field arrays (TTFields) during glioblastoma radiation therapy by determining whether the placement and repositioning of arrays affects target volume coverage and cranial skin dose. Methods and MaterialsRadiation plans from 10 consecutive patients treated for glioblastoma were copied to a cranial phantom and reoptimized for phantom anatomy. Dose distributions were then recalculated on 3 additional computed tomographic scans of the phantom with the TTFields electrode arrays placed over distinct locations on the phantom scalp to compare planning target volume (PTV) coverage and skin dose with and without TTFields in place in varying positions. Percent depth dose curves were also measured for radiation beams passing through the electrodes and compared with commonly used bolus material. ResultsThe presence of TTFields arrays decreased PTV V97% and D97% by as much as 1.7% and 2.7%, respectively, for a single array position, but this decrease was mitigated by array repositioning. On averaging the 3 array positions, there was no statistically significant difference in any dosimetric parameter of PTV coverage (V95-97%, D95-97%) across all cases compared with no array. Mean increases in skin D1cc and D20cc of 3.1% were calculated for the cohort. Surface dose for TTFields electrodes was less than that with a 5-mm superflab bolus. ConclusionsOur work demonstrates that placement of TTFields arrays does not significantly affect target volume coverage. We show that repositioning of TTFields arrays, as is required in clinical use, further minimizes any dosimetric changes and eliminates the need for replanning when arrays are moved. A slight, expected bolus effect is observed, but the calculated increases in skin dose are not clinically significant. These data support the development of clinical trials to assess the safety and efficacy of combining concurrent chemoradiotherapy with TTFields therapy for glioblastoma.

Assessment of directional accuracy of GNSS-Acoustic measurement using a slackly moored buoy

We assessed the positioning accuracy of GNSS-Acoustic (GNSS-A) measurement using a slackly moored buoy. A key feature of real-time buoy-based GNSS-A measurement is that positioning must be performed via single ranging from an arbitrary observation position and encompassing the drifting range of the buoy. In this study, slack-line mooring was employed to resist strong Kuroshio current of up to 5.5 knots in the Nankai Trough. During a year-long sea trial, the buoy drifted within a circle of ~ 4000 m radius, which is much larger than the dimension of a seafloor transponder array. In the sea trial, more than 500 successful regular and on-demand ranging measurements were obtained at various observation positions. The results show that the horizontal positioning accuracy (2σ) of the array for single ranging was 46 cm when the buoy was inside the array and 97 cm when it was outside the array. These accuracies are comparable to those achieved through single ranging in traditional ship-based surveys at the same site. In addition to the distance dependency, we observed directivity in the accuracy, depending on the geometry between an observation point and seafloor transponders. To interpret the accuracy degradation and directivity as a function of observation position, we calculated error ellipses using a dilution-of-precision (DOP) analysis procedure for GNSS-A positioning. The error ellipses clearly illustrate that the variance in array positions is large in the line-of-sight direction from an observation point to the array center. We translated the error ellipses to positioning accuracies using the standard deviation of travel time residuals when an array position is estimated using all pings. The positioning accuracy resulting from the translation corresponded to that obtained using array positions in a buoy observation. The DOP analysis results and their translation into positioning accuracies enabled a detailed assessment of the directional accuracy of GNSS-A positioning at an arbitrary observation position, which is important for real-time measurement of seafloor movement in the event of a huge earthquake.

A Cluster-Based Channel Model for Massive MIMO Communications in Indoor Hotspot Scenarios

Characterization and modeling of massive multiple-input multiple-output (MIMO) channel has been one of the research hotspots in the field of wireless communications. One important feature of the massive MIMO channel is the spatial non-stationarity. To statistically model the spatial non-stationary massive MIMO channels, a cluster-based channel model is proposed in this paper. The model incorporates both inter- and intra-cluster properties and the cluster evolution over the large-scale array. A hybrid data processing scheme is applied to extract the multipath components (MPCs) and clustering the MPCs over a large-scale antenna array. The global angular spread, cluster angular spread, and cluster delay spread are modeled with log-normal distributions. Observed cluster length and MPC length within clusters, which are introduced to describe the cluster existence over the array and MPCs existence within the cluster, respectively, are statistically modeled with the exponential distributions. Moreover, both the cluster and MPC arrival intervals, which are used, respectively, to describe the cluster occurrence position on the array and MPC occurrence position within the cluster, can be statistically modeled with the uniform distributions. Finally, the model implementation is validated by comparing with the different channel performance metrics between measurements and simulations.

A Deep Convolutional Neural Network Approach to Classify Normal and Abnormal Gastric Slow Wave Initiation From the High Resolution Electrogastrogram.

Gastric slow wave abnormalities have been associated with gastric motility disorders. Invasive studies in humans have described normal and abnormal propagation of the slow wave. This study aims to disambiguate the abnormally functioning wave from one of normalcy using multi-electrode abdominal waveforms of the electrogastrogram (EGG). Human stomach and abdominal models are extracted from computed tomography scans. Normal and abnormal slow waves are simulated along stomach surfaces. Current dipoles at the stomachs surface are propagated to virtual electrodes on the abdomen with a forward model. We establish a deep convolutional neural network (CNN) framework to classify normal and abnormal slow waves from the multi-electrode waveforms. We investigate the effects of non-idealized measurements on performance, including shifted electrode array positioning, smaller array sizes, high body mass index (BMI), and low signal-to-noise ratio (SNR). We compare the performance of our deep CNN to a linear discriminant classifier using wave propagation spatial features. A deep CNN framework demonstrated robust classification, with accuracy above 90% for all SNR above 0dB, horizontal shifts within 3cm, vertical shifts within 6cm, and abdominal tissue depth within 6cm. The linear discriminant classifier was much more vulnerable to SNR, electrode placement, and BMI. This is the first study to attempt and, moreover, succeed in using a deep CNN to disambiguate normal and abnormal gastric slow wave patterns from high-resolution EGG data. These findings suggest that multi-electrode cutaneous abdominal recordings have the potential to serve as widely deployable clinical screening tools for gastrointestinal foregut disorders.

Method to quantitatively assess electrode migration from medical images: Feasibility and application in patients with straight cochlear implant arrays

Objective: To propose a method for quantitative assessment of the migration of lateral-wall, straight electrode arrays after surgery based on postoperative Cone Beam Computed Tomography (CBCT) images and automated medical image analysis techniques.Methods: A preliminary study is conducted on 19 implanted ears. For each implantation, two CBCT images are objectively analyzed. Electrode arrays are consistently projected into the same coordinate system in order to estimate precisely the migration of each electrode. Spatial configuration changes are characterized with the overall curvature of the electrode array.Results: From the samples analyzed no significant electrode migration, extrusion or electrode curvature changes were found. Mean infinitesimal local migration reveals a tendency where apical electrodes tend to move away from the modiolus and basal electrodes away from the round window.Conclusion: CBCT images demonstrate adequate resolution with limited artifacts to assess the electrode array position in vivo. Automated medical image analysis techniques and consistent coordinate system allow to quantitatively estimate migration and extrusion effect for lateral-wall, straight electrode array.

A general approach to optimizing tumor treating fields therapy.

e14668 Background: Tumor Treating Fields (TTFields) are alternating electric fields used to non-invasively treat cancer. TTFields are delivered via transducer arrays placed on the skin close to the tumor. Post-hoc analysis [1] has shown that delivering higher field power to the tumor and increasing usage (percent of time patient is actively treated) improve patient survival. Thus, optimizing the position of arrays to maximize TTFields power at the tumor could improve survival. At the same time, minimizing the array area to maximize patient comfort and consequently maximizing usage is also likely to improve survival. However, optimizing TTFields delivery is non-trivial since the field distribution is influenced by array positioning and geometry, the anatomy of the patient and the heterogeneous electric properties of different tissues. Here we present a general approach to optimizing Tumor Treating Fields using numerical simulations. Methods: Delivery of TTFields to the brains, lungs and abdomens of realistic computational models was investigated. The effect of the transducer array size and position on the field distribution within the phantoms was analyzed, and an approach for optimizing TTFields delivery developed. Results: Field power is generally highest in the region between the arrays, with larger arrays generally delivering higher field power. Anatomical features such as bones, the spine or a resection cavity significantly influence the field within this region. A general approach to optimizing TTFields delivery is: Maximize field power by using the largest arrays possible. To maximize patient comfort, array size are chose so that significant portions of the skin in the region of disease are not covered by the arrays. Place virtual arrays on a realistic computational model of the patient such that the tumor is located between them and simulate TTFields delivery to the patient. Apply an iterative algorithm to shift the arrays around their initial positions until field power in the tumor bed is maximized. Conclusions: We have developed a general approach to optimizing delivery of TTFields to the tumor. Effective TTFields treatment planning is expected to improve patient outcome. [1] Ballo et. al., submitted to RED Journal 2018.

Highly Uniform Resistive Switching in HfO2 Films Embedded with Ordered Metal Nanoisland Arrays

AbstractMemristors enter a critical developmental stage where emerging large‐scale integration methods face major challenges with severe switching instabilities in the oxide layer. Here, the superior uniformity is achieved within HfO2 films by embedding highly ordered metal nanoisland (NI) arrays. Embedded films exhibit a significant reduction in both SET and RESET while displaying enhanced uniformity in operating voltages and resistance states. This behavior is attributed to the concentration of electric fields along Pt and Ti NIs and their interactions with the surrounding oxide film matrix environment, which induce separate and distinct filamentary formation mechanisms that affect the stability. A method is reported to further optimize the uniformity of the SET voltage by translating the NI array position down the film‐thickness dimension towards the bottom electrode. A comparison of the density and distribution of the oxygen vacancies responsible for the formation/dissolution of conducting filaments is made via combined electrostatic force microscopy and conductive atomic force microscopy (c‐AFM) studies. Finally, complete observation of the morphological evolution of conducting filaments produced by Pt and Ti is enabled by 3D c‐AFM nanotomography and cross‐sectional scanning transmission electron microscopy–energy dispersive spectroscopy to provide direct correlations between NI‐oxide interactions and overall switching performance.

Logical Effort Framework for CNFET-Based VLSI Circuits for Delay and Area Optimization

Carbon nanotube field-effect transistors (CNFETs) show great potential to build digital systems on advanced technology nodes with big benefits in terms of power, performance, and area (PPA). However, CNFET-specific additional features such as the number of tubes, pitch (spacing between tubes), tube position, and diameter in array of tubes play a significant role in accurate PPA evaluation. Furthermore, count and density variations in carbon nanotubes (CNTs) due to manufacturing limitations, like the presence of metallic tubes in the CNFET channel, degrade the anticipated PPA benefits. Moreover, modeling the CNFET parameters, CNT variations and etching techniques for CNTs create additional complexity during performance optimization. Hence, for realistic optimization of CNFET circuit’s performance, it is imperative to incorporate the impact of these parameters and variations. In this paper, we propose delay models [pitch-aware logical effort (PALE) and position-aware pitch factor (PAPF)] for fast and accurate performance evaluation by including the impact due to CNFET-specific parameters and CNT variations. These models are developed based on industry standard logical effort framework. Furthermore, we present an optimization tool using PALE and PAPF to minimize the delay and area of CNFET circuits. We deploy several circuit-level techniques prior to optimizing the tubes (CNTs) in the logic gates to achieve globally optimum solution. For better optimization of the circuits, we also include the impact of wire parasitic in estimating the delay of the individual gates. Our optimization tool results in the maximum and average delay improvement by 27% and 17%, respectively, and $2.5\times $ reduction in area for standard ISCAS and OpenSPARC benchmark circuits. Fast and fairly accurate delay computation in our optimization framework offers great runtime benefits as compared to state-of-the-art simulation and statistical-based methods.

An efficient error estimation method for antenna distortions in space based radar

The phased array antenna plays an important role in determining the performance achievable in a space based radar system. However, the array position errors caused by the antenna distortions in the complex cosmic vacuum environment will distort the antenna pattern, which significantly degrades the performance of the radar systems. Most of the conventional estimation methods are proposed based on the random position errors without the consideration of the distortion character for spaceborne arrays, resulting in a large estimation error. In this paper, to address this issue, an efficient array error estimation method is proposed to compensate the antenna distortion errors. In the proposed method, the initial sensor positions can be obtained based on the measured results from the units distributed over the array surface. Then the distortion model parameters can be estimated by solving an optimization problem. Based on this, the sensor positions can be corrected with high accuracy at the lth iteration. In this way, the proposed method can improve the accuracy and the robustness of the estimation simultaneously. Several simulated results are presented to validate the proposed method for the position error estimation in a space based radar system.

Impact of Routine Plain X-ray on Postoperative Management in Cochlear Implantation.

To determine the benefit of a routine plain radiography (X-ray) for confirming the optimal electrode position in cochlear implant surgery. In total, 245 patients (135 males and 111 females) who underwent cochlear implantation in a single tertiary referral center were included in this study. Postoperative plain X-ray findings and electrophysiological tests were retrospectively analyzed. The mean age was 11.4±14.6 years (range, 1-70 years). Overall, 196 (80%) patients were pediatric patients (age, <18 years) and 49 (20%) were adults (age, >18 years). The mean rotation of electrode arrays was 1.03±0.17 turns. The plain X-ray revealed that electrode misplacement was present in 5 patients (2%); incomplete insertion in 3 patients, and tip rollover and electrode migration in 1 patient each. A revision was performed for the last patient who had an extracochlear electrode position in the plain X-ray. Postoperative imaging is mostly used to confirm the electrode array position after cochlear implant surgery. In addition, intraoperative evaluations have low positive predictive value and sensitivity. Thus, this study revealed that postoperative radiological imaging should be considered even when all intraoperative electrophysiological measures and surgical reports are normal.

Propagation and coalescence of en-echelon cracks under a far-field tensile stress regime: An experimental study

Experiments were carried out to observe the variation in propagation and linkage of parallel en-echelon cracks with varying orientation of the crack array and different relative position of the cracks within the array in an extensional regime. Two-layered analogue model, with a basal layer of pitch overlain by a layer of kaolin paste was used in the experiments. En-echelon cracks were pre-cut within the kaolin layer maintaining specific geometrical parameters of the cracks (e.g., length, centre spacing, separation) in such a manner that there was a weak (though not negligible) local tip-induced stress favouring curvature of adjacent crack tips towards one another. The results obtained were matched with natural pattern of linkage of veins, rift basins and spreading ridges, as described in the relevant literature. The experimental results showed that the final pattern of linkage between the cracks was a result of initial deflection of crack tip from its plane due to combined effect of local and far-field stress. When the deflection of tip from the crack plane was between \(0{^{\circ }}\) to \(45{^{\circ }}\), a ‘tip to wall’ linkage took place between adjacent cracks isolating a rhombohedral area in the interaction zone. The resultant structure could be geometrically comparable to a micro-plate-like structure isolated due to linkage of ridge segments initially forming an overlapping spreading centre (OSC). When the deflection of tip from the crack plane was greater than \(45{^{\circ }}\), a ‘tip to tip’ linkage between adjacent cracks took place resulting in a structure similar to a transform fault between spreading ridges and or rift basins. When effect of the remote stress opposed the tip induced stress, no linkage took place between the adjacent cracks, and finally the tips propagated straight along a plane perpendicular to the remote extension direction.

A Method to Determine the Coincidence of MRI-Guided Linac Radiation and Magnetic Isocenters.

To assure accurate treatment delivery on any image-guided radiotherapy system, the relative positions and walkout of the imaging and radiation isocenters must be periodically verified and kept within specified tolerances. In this work, we first validated the multiaxis ion chamber array as a tool for finding the radiation isocenter position of a magnetic resonance–guided linear accelerator. The treatment couch with the array on it was shifted in 0.2-mm increments and the reported beam center position was plotted against that shift and fitted to a straight line, in both X and Y directions. From the goodness-of-fit and intercepts of the regression lines, the accuracy and precision were conservatively estimated at 0.2 and 0.1 mm, respectively. This holds true whether the array is irradiated from the front or from the back, which allows efficient collecting the data from the 4 cardinal gantry angles with just 2 array positions. The average isocenter position agreed to within at most 0.4 mm along any cardinal axis with the linac vendor’s film-based procedure, and the maximum walkout radii were 0.32 mm and 0.53 mm, respectively. The magnetic resonance imaging isocenter walkout as a function of gantry angle was studied with 2 different phantoms, one employing a single fiducial at the center and another extracting the rigid displacement values from the distortion map fit of 523 fiducials dispersed over a large volume. The results were close between the 2 phantoms and demonstrated variation in the magnetic resonance imaging isocenter location as high as 1.3 mm along a single axis in the transverse plane. Verification of the magnetic resonance imaging isocenter location versus the gantry angle should be a part of quality assurance for magnetic resonance-guided linear accelerators.

Hydraulic-assist driver for compact insertion devices

We have developed and tested a novel type of driver for insertion devices. In our approach, we compensate for the magnetic forces acting on the insertion device (ID) arrays by installing a number of compact hydraulic cylinders along the ID.These assisting cylinders are connected to a single hydraulic line and activated by the same pressure. A computer-controlled closed-loop feedback system maintains the target ID array position and an acceptable load on the mechanical driver. This is accomplished by simultaneously controlling both the hydraulic assist pressure and the mechanical driver position. The quantity and location of the compact hydraulic cylinders are optimized to keep the deformation of ID structural components in an acceptable range.The hydraulic cylinders compensate for over 90% of the strong forces generated by the magnetic field. This reduces the load applied to a conventional mechanical driver to less than 10% of the total load. The implementation of this type of driver can make insertion devices much more compact without compromising their performance.In the proof-of-concept experiments, our novel hydraulic-assist driver demonstrated a long-term stability and reproducibility of the ID gap within 2μm. Magnetic field stability and reproducibility was within 6e−5 of the normalized field strength or better.Here we will describe the concept, details of our test setup and the results of the proof-of-concept experiments. We will also discuss the advantages of the hydraulic-assist driver over conventional mechanical drivers, as well as possible applications and future developments.

Airframe noise measurements in a large hard-walled closed-section wind tunnel

The airframe noise of a 1:2 scaled aircraft model is investigated through a series of experiments in the hard walled closed test section of a large non-anechoic wind tunnel. A surface mounted phased microphone array is used to acquire the wall pressure fluctuations generated by the interaction of the wind tunnel flow and the propagating noise. Data from two measurement campaigns are analysed. The wind tunnel acoustic behaviour and the array performance are first assessed evaluating the results obtained from a reference sound source installed in the centre of the test section. The combination of different airflow speeds, array positions and sound sources are tested. The airframe noise is evaluated acquiring pressure fluctuations in different configurations. The main parameters varied during the tests are the flight configuration, the speed of the airflow, the incidence angle of the model and the position of the microphone array. Data are processed and then analysed in the frequency domain and using a conventional beamforming algorithm to retrieve the sound source maps over the regions of interest. Source maps are deconvolved with a CLEAN-SC routine and single source contributions determined through integration of auto-powers. The resulting spectra are finally scaled determining the exponents of the pertinent scaling laws.

Extrusion of straight cochlear implant electrodes May be diminished by proximal fixation

ObjectivesTo determine if proximal fixation of the cochlear implant helps reduce the rate of straight electrode array extrusion/migration. MethodsRecords of 278 children implanted with a straight electrode at a tertiary pediatric hospital from 1990 to 2017 were reviewed. Demographics, operative reports, electrode type, radiological studies and audiological assessments including impedance and stimulation parameters were collected. Significant abnormalities were defined by >75% change in impedance relative to 1 month post-implant values. The main outcome is the incidence of electrode extrusion based on significant changes in impedance and comparative radiological imaging looking for electrode extrusion. ResultsDuring this period, straight electrodes were chosen infrequently (298/1781 devices implanted (16.73%) in 278 children). They were used prior to the introduction of pre-curved electrodes (153/298) and subsequently for hearing preservation (33/298) and in anomalous cochleae (48/298). Most recently they were used in a comparative study of children receiving one perimodiolar and one straight array (64/298). All electrodes were proximally fixated with a suture around the incus buttress (Ned's knot).None of the 298 electrodes required repositioning. Comparative radiographs after long duration implant use were available in 72 of 298 devices (24.2%) revealing no changes in electrode position. Significant impedance changes (>75%), indicative of open circuits, were noted in 6/298 devices (2%); ≤2 electrodes at various array positions were affected in each child. In one case, repositioning of the receiver/stimulator may have damaged the electrodes as they exited the device body but no changes in electrode position were evident on the post-repositioning radiograph. ConclusionsExtrusion of straight electrodes is a recognized complication of cochlear implant surgery but was not observed in our cohort with proximal electrode fixation.

Electric compound action potentials (ECAPs) and impedances in an open and closed operative site during cochlear implantation

Introduction: In patients undergoing cochlear implantation, intraoperative measures of impedance and electrically evoked compound action potentials (ECAPs) are used to confirm device integrity and electrode array position. However, these electrophysiological parameters have been shown to decrease over time, with a small decrement observable as early as 24 h post implantation and becoming more apparent after 6 months. Whether the intraoperatively measured impedances and ECAPs recorded immediately after electrode insertion versus later in the operation or in an open versus closed operative site vary has not been documented. Such variation in measurement procedure may affect the ultimate operative outcome.Patients and methods: Between February and October 2016, 38 patients received a cochlear implant (Cochlear®), with half receiving a CI 522 device and the other half receiving a CI 512 device. These patients were distributed into three groups. In the first (group A; n = 21), the impedance and threshold neural response telemetry (tNRT) measures were taken before (M1) and after cutaneous suture (M2), whereas in the second group (group B; n = 11) they were taken twice in the open operative site, once at the time of electrode insertion (M1) and then again 10 min later (M2). The last group (group C; n = 6) was measured only once after a 10 min waiting time before closing the operative site.Results: tNRTs of both group A and B were significantly higher at M1 than measured at M2. The magnitude of change in tNRT did vary significantly by group (P = .027) with group A having a bigger decrease than group B. For impedances there was evidence for a significant difference in M2 between the three groups (P = .012), with group C having significantly higher values compared to group A and B.Conclusion: Intraoperative tNRT measures change significantly over time, including within the first 10 min of implantation. One underlying etiology of this phenomenon for tNRTs seems to be the condition of the surgical site whereas changes of impedances can be best explained by the ‘electrochemical cleaning’ theory associated with the first stimulation of the electrode. However, for both impedances and tNRTs there also is an important impact of time as well as of acute perioperative changes in electrical conductivity.

A Computational Study Investigating the Optimization of Tumor Treating Fields Delivery When Treating Ovarian Cancer

Tumor Treating Fields (TTFields) are alternating electric fields in the intermediate frequency (100-300 kHz) known to inhibit the growth of solid tumors. TTFields are delivered through transducer arrays non-invasively to the tumor region. In-vitro studies show that TTFields’ efficacy is intensity-dependent, with a threshold intensity of about 1 V/cm below which the effect of the fields on the cells decreases significantly. This suggests that when treating with TTFields, it is important to optimize array placement to maximize field intensity at the tumor bed. A phase II clinical trial (INNOVATE) has demonstrated the feasibility and safety of TTFields for the treatment of advanced ovarian cancer. A Phase III trial in ovarian cancer is under development. In order to develop strategies for optimizing array placement when treating ovarian cancer, we performed a simulation-based study investigating how altering array positions on the abdomens of female computational phantoms influences the field distribution within their bodies. Here we report on the results of this study. To simulate delivery of TTFields to the abdomen, we used realistic computerized model of three human females with Body Mass Indices (BMI) of 21, 26 and 30. Two pairs of transducer arrays were placed on the skin of the models: one pair of arrays was placed on the abdomen and while the second pair of arrays was placed on the lateral aspects of the computerized models. To deliver TTFields, electric currents of 4A peak-to-peak at frequency of 200 KHz were delivered to the arrays. The location of the arrays on the models skins was altered systematically, and the field distributions within standard abdominopelvic regions were analyzed. In all models, the electric field was confined to the region located between the transducer arrays. In all simulations, the field was heterogeneous with intensity exceeding 1 V/cm in significant portions of the volumes located between the transducer arrays. The results suggest that by carefully choosing the position of the transducer arrays, it is possible to effectively deliver TTFields to target regions throughout the abdomen of female subjects regardless of BMI. This work forms the basis for developing optimal strategies for delivering TTFields when treating ovarian cancer.