Bruce Campbell Amm

Peripheral nerve stimulation characteristics of an asymmetric head-only gradient coil compatible with a high-channel-count receiver array

To characterize peripheral nerve stimulation (PNS) of an asymmetric head‐only gradient coil that is compatible with a commercial high–channel‐count receive‐only array.

Dielectric properties of polydicyclopentadiene and polydicyclopentadiene-silica nanocomposite

Conventional thermoset materials, such as epoxy, polyester, silicone and polyurethane, have relatively high dielectric losses and high dielectric constants, which are not desirable for a high frequency and high voltage application. Polydicyclopentadiene (PDCPD) is a polyolefinic thermoset material that has outstanding dielectric characteristics: low dielectric constant, low dielectric loss and high breakdown strength that are similar to polypropylene but higher thermal stability similar to epoxy. In addition, it also has great mechanical strength and fracture toughness. Due to its extremely low viscosity, PDCPD is easy to process and has flexibility for various reaction injection moldings. Dielectric performance, such as corona resistance, is further enhanced by PDCPD-nanosilica composites. In this paper, dielectric properties of PDCPD will be presented and discussed.

Efficient Simultaneous Reconstruction of Time-Varying Images and Electrode Contact Impedances in Electrical Impedance Tomography

Objective: In electrical impedance tomography (EIT), we apply patterns of currents on a set of electrodes at the external boundary of an object, measure the resulting potentials at the electrodes, and, given the aggregate dataset, reconstruct the complex conductivity and permittivity within the object. It is possible to maximize sensitivity to internal conductivity changes by simultaneously applying currents and measuring potentials on all electrodes but this approach also maximizes sensitivity to changes in impedance at the interface. Methods: We have, therefore, developed algorithms to assess contact impedance changes at the interface as well as to efficiently and simultaneously reconstruct internal conductivity/permittivity changes within the body. We use simple linear algebraic manipulations, the generalized singular value decomposition, and a dual-mesh finite-element-based framework to reconstruct images in real time. We are also able to efficiently compute the linearized reconstruction for a wide range of regularization parameters and to compute both the generalized cross-validation parameter as well as the L-curve, objective approaches to determining the optimal regularization parameter, in a similarly efficient manner. Results: Results are shown using data from a normal subject and from a clinical intensive care unit patient, both acquired with the GE GENESIS prototype EIT system, demonstrating significantly reduced boundary artifacts due to electrode drift and motion artifact.

Real-time 3D electrical impedance imaging for ventilation monitoring of the lung: Pilot study.

We report an Electrical Impedance Tomography device capable of detecting gravity-induced regional ventilation changes in real-time without averaging or using a contrast medium. Changes in lung ventilation are demonstrated in right and left lateral decubitus position and compared to those seen in an upright and supine normal subject.

Simulation Environment to Predict the Effect of Eddy Currents on Image Quality in MRI

Gradient coils generate a magnetic field with a linear spatial variation that superimposes over the main magnetic field of a magnetic resonance imaging (MRI) system; such superimposition of the magnetic fields enables the encoding of the spatial position in MRI. A rapid change in the gradient field induces eddy currents in the conducting structures of an MRI system, resulting in the production of image artifacts. An objective of the gradient coil design phase is to predict both the coils performance with respect to eddy currents and the image quality (IQ) before the coil is manufactured. In this paper, an integrated simulation environment is presented that combines the gradient coil design with an image formation simulation to predict the IQ. Here, an unshielded, uni-planar gradient set was simulated. Further, a study was conducted to determine the effect of frequency on the eddy currents induced in the conducting structures of the main magnet coil while exciting the uni-planar gradient set. The knowledge acquired from this study was applied to the IQ simulation, and a time-dependent simulation of a gradient echo pulse sequence was performed. The IQ of the uni-planar gradient set was predicted, and the input and reference images as well the images distorted by the eddy currents are shown.

Comparison of impedance measurements near the skin of newborns and adults.

Electrical impedance tomography (EIT) is a non-invasive imaging technology that has been extensively studied for monitoring lung function of neonatal and adult subjects, especially in neonatal intensive care unit (NICU) and intensive care unit (ICU) environments. The sources of the total impedance in these applications include internal organs, near-boundary tissues, electrode-skin impedance, electrodes and conducting wires. This total impedance must be considered for system design and setting voltage gain since it will contribute to the measured voltage. To adapt a single instrument for use on infants and adults, we studied the difference between the impedance near the skin in both classes of patients. We used a simultaneous multi-source EIT (SMS-EIT) system to make impedance measurements. Characteristic resistance was calculated for two different current patterns: one that is more sensitive to boundary region impedance and another that is more sensitive to interior changes. We present ratios of these resistances to assess the relative contribution of near-skin effects to the overall impedance. Twenty adult ICU subjects (10 male, 10 female, age: 49.05  ±  16.32 years (mean  ±  standard deviation)) and 45 neonates (23 male, 22 female, gestational age: 37.67  ±  2.11 weeks, postnatal age, 2.56  ±  2.67 d) were studied at Columbia University Medical Center. Impedance measurements at 10 kHz were collected for approximately one hour from each subject. The characteristic resistance ratio for each subject was computed and analyzed. The result shows the impedance at or near the skin of newborns is significantly higher than in adult subjects.

Real-time 3D electrical impedance imaging for ventilation and perfusion of the lung in lateral decubitus position

We report a prototype Electrical Impedance Imaging System. It is able to detect the gravity-induced changes in the distributions of perfusion and ventilation in the lung between supine and lateral decubitus positions. Impedance data were collected on healthy volunteer subjects and 3D reconstructed images were produced in real-time, 20 frames per second on site, without using averaging or a contrast agent. Imaging data also can be reconstructed offline for further analysis.