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Biomedical subjects

P Record

Publications and source records attributed to P Record.

10 recordsLinked to original sources
PubMed1996

Feasibility of neonatal lung imaging using electrical impedance tomography.

The feasibility of detecting the lungs in preterm babies using electrical impedance tomography (EIT) was investigated. A single frequency instrument using 16 electrodes to apply current and detect peripheral voltages was constructed. The instrument applied AC current of 1.5 mA peak-peak at a carrier frequency of 20 kHz. Images were reconstructed using a sensitivity-regions backprojection method. A 9-day-old preterm baby was tested and data were collected at a speed of 10 frames/s. A dynamic image showing the lungs at full inspiration referenced to expiration is illustrated in this paper. Impedance measurements taken across the chest during the first 2 s did not show a clear pattern thus demonstrating irregular breathing. Region of interest analysis were carried out on the reconstructed images and tracked with time. Fourier transforms were then performed on these signals and a fundamental frequency at 1 Hz, corresponding to normal breathing rate of 60 breaths/min, was detected. Harmonics of the signal caused distortion especially on the left lung where the effects of cardiac events were more dominant.

Electric Impedance↗
PubMed1996

Data recovery from reduced electrode connection in electrical impedance tomography.

In electrical impedance tomography, a single channel failure causes distortion to the overall image. Mathematical modelling and curve-fitting techniques were used to recover corrupted data. A single channel was disconnected in two experiments on a saline-filled dish with one and two objects, respectively. Voltage gradient data were then synthesized from the overall shape of the curve and reconstructed. The technique demonstrated a considerable improvement in the image quality. We conclude that the technique can be adapted in applications where channel failure can occur regularly such as neonatal monitoring.

Biomedical Engineering↗
PubMed1995

Conducting boundary strategy: a new technique for medical EIT.

A medical application of a new measurement strategy developed for process tomography is presented. By exchanging the current streamlines with the equipotential lines impedance tomography can be performed using unipolar measurements. The equipotential lines are now parallel to the conducting boundary and voltage measurement is made between this boundary and an insulated electrode. A set of 32 electrodes was placed around the chest with every alternate electrode connected to form the 'conducting boundary'. A total of 120 independent measurements were available. Reciprocity error without common mode feedback was 0.5% with a dynamic range of only 1:1.12. The images were comparable to that reconstructed using adjacent drive strategy.

Electric Impedance↗
PubMed1992

Electrical impedance tomography. A sensitivity region reconstruction algorithm using adjacent drive current injection strategy.

The 'sensitivity region' method of back projection is converted from polar drive to adjacent drive current injection strategy and individual sensitivity coefficients incorporated. For each projection sensitivity coefficients for each pixel were established and pixels were grouped together into the 'sensitivity regions'. These contain all pixels that have their largest sensitivity coefficients associated with a particular measurement pair. Back projection of measurement data was performed using these coefficients as the basis of the reconstruction and less sensitive measurement pairs were ignored. Formulae for the back projection are discussed and images from computer simulated data and raw data supplied by Sheffield as part of this concerted action are presented. Comparison with polar current injection strategy is discussed.

Algorithms↗
PubMed1989

Neurosurgical stimulation, impedance monitoring and data acquisition system.

We describe the design of a programmable neurosurgical stimulator with impedance monitoring facilities. The computer is used both to control a stimulator and for the storage of various parameters employed in the process. The stimulator is designed to minimize tissue damage by injecting net zero charge; its output is a current, independent of load resistance. By measuring electrode voltage, the load impedance can be calculated. Software is provided in order to log patient data, and trajectory details with reference to coordinates calculated from other imaging systems such as CAT scanners.

Computer Systems↗
PubMedDate not supplied

An electronically controlled micro-welder.

An electronically controlled micro-welding apparatus has been designed and built for the manufacture of clinical electrodes. Using the principle of electrical resistance welding, the device is simple and inexpensive to construct, using readily available components. It is easy to operate and has proved to be a quick and reliable method of producing electrodes to the exact specifications of neurosurgeons.

Electrodes↗