Impedance imaging in the newborn

Abstract

We have been investigating the use of electrical impedance methods for the study of cerebral haemodynamics in the newborn for many years. Of particular interest has been the early detection of intraventricular haemorrhage, which is a major cause of death or handicap in low birthweight infants. Several problems exist in obtaining representative impedance measurements from the newborn, most notably movement artefact, respiratory-based modulation and a blood-flow related pulsatile component. Movement artefact is by far the most significant problem; in order to perform long-term monitoring we have developed an effective algorithm for rejection of corrupted data. To remove the respiratory component, which can be 1-2% of the impedance measurement, we link to the output of a respiratory monitor (standard in intensive care units) as a means of synchronising measurements to a fixed point in the respiratory cycle. Similarly, to remove the blood-flow pulsatile component, measurements are gated from the R-wave of the recorded ECG. Our total system consists of a front-end measurement system that passes image data over a serial link to a host computer. Data storage, image reconstruction and display is performed on the host, which can be any of a wide range of personal computers. The front-end contains the impedance measurement circuit, electrode switching electronics and a microprocessor for control, and is of a sufficiently small size to fit into the incubator next to the baby. Incorporating a microprocessor into the front-end produces a very flexible system that has many benefits, including: asynchronous operation from host, 'intelligent' pre-processing of measurements, command driven operation from host, etc. Software development for the front-end is performed on the host with program down-load for interactive debugging. Details of the front-end electronics and software, system performance, preliminary clinical results and other application areas of the impedance imaging technique to the care of the newborn are presented.

Electrode configurations for detection of intraventricular haemorrhage in the premature neonate

“…These data were, however, significantly affected by artefacts. Murphy et al (1987) found that breathing movements and variations in cerebral blood flow caused the largest signal artefacts—up to 1% variation in their baseline signal at a frequency of approximately 0.5 Hz. The other significant artefact was synchronous with heart electrical activity, causing a variation of about 0.1% in signals.…”

Detection of intraventricular blood using EIT in a neonatal piglet model

“…EIT was briefly tested to the detection of neonatal intraventricular hemorrhage in the late 1980s [7], [8], with a result showing detection of ventricular bleeding in one neonatal patient. However, artifacts significantly affected these data.…”

Biological tissue characterization by magnetic induction spectroscopy (MIS): requirements and limitations

“…If the latter restriction could be obviated, monitoring of the PEP would represent a valuable tool for applications in the central nervous system, as suggested previously, e.g., for the early detection of brain edema by monitoring of the conductivity [2], [3]. Other intracranial applications so far suggested refer to the monitoring of ventricular hemorrhage [4], [5], stroke, the evolution of spreading depressions, and epilepsy [6].…”