A review of errors in multi-frequency EIT instrumentation.

Multi-frequency electrical impedance tomography (MFEIT) was proposed over 10 years ago as a potential spectroscopic impedance imaging method. At least seven systems have been developed for imaging the lung, heart, breast and brain, yet none has yet achieved clinical acceptance. While the absolute impedance varies considerably between different tissues, the changes in the spectrum due to physiological changes are expected to be quite small, especially when measured through a volume. This places substantial requirements on the MFEIT instrumentation to maintain a flat system frequency response over a broad frequency range (dc-MHz). In this work, the EIT measurement problem is described from a multi-frequency perspective. Solutions to the common problems are considered from recent MFEIT systems, and the debate over four-terminal or two-terminal (multiple source) architecture is revisited. An analysis of the sources of MFEIT errors identifies the major sources of error as stray capacitance and common-mode voltages which lead to a load dependence in the frequency response of MFEIT systems. A system that employs active electrodes appears to be the most able to cope with these errors (Li et al 1996). A distributed system with digitization at the electrode is suggested as a next step in MFEIT system development.

Assessment and calibration of a low-frequency system for electrical impedance tomography (EIT), optimized for use in imaging brain function in ambulant human subjects.

An EIT system has been produced that has been optimized for imaging impedance changes with scalp electrodes during brain activity in ambulant subjects. It can record from 225 Hz to 65 kHz, has a small headbox on a lead 10 m long, and has software programmable electrode selection. In calibration experiments in a small cylindrical tank filled with potassium chloride solution and samples of cucumber, noise was less than 1% with averaging, and acceptable images were produced at frequencies down to 1800 Hz. This suggests that EIT can be performed at low frequencies, which are likely to give larger signals during brain activity. Future work will include trials in humans and improvement of the current source and isolation.

Ultrasound and abdominal hydatid disease.

Twenty-two hydatid cysts have been accurately located in the abdomens of seven patients by ultrasound B-scanning. Lapartomy has confirmed the presence of 19 of these cysts. Grey-scale techniques do not appear to add appreciably to the ease of diagnosis in this condition. Ultrasound can give the clinician a good idea of the extent of the disease process and has the advantage of being completely non-invasive.

Accuracy of imaging of the brains of newborn infants by linear-array real-time ultrasound.

Comparisons were made in 69 newborn infants of the appearance of the brain as visualised by linear-array real-time ultrasound, computerised tomography and at autopsy, in order to evaluate the accuracy of ultrasound for the detection of lesions in the brain. Ultrasound was found to give a good estimate of the presence and extent of haemorrhage into the germinal layer and ventricles, and also to be very useful for assessing the appearance of the ventricular system. Ultrasound diagnosed extradural haemorrhages but was unhelpful for identifying subarachnoid haemorrhages or lesions in the posterior fossa.

Design and performance of the UCLH mark 1b 64 channel electrical impedance tomography (EIT) system, optimized for imaging brain function.

The UCLH Mark 1b is a portable EIT system that can address up to 64 electrodes, which has been designed for imaging brain function with scalp electrodes. It employs a single impedance-measuring circuit and multiplexer so that electrode combinations may be addressed flexibly using software. It operates in the relatively low frequency band between 225 Hz and 77 kHz, as lower frequencies produce larger changes during brain activity, and has a videocassette-sized headbox on a lead 10 m long, connected to a base box the size of a video recorder, and notebook PC, so that recordings may be made in ambulant subjects. Its performance was assessed using a resistor-capacitor network, and two saline-filled tanks-a cylindrical Perspex one and a latex one which contained a human skull. System signal-to-noise ratio was better than 50 dB and the maximum reciprocity error less than 10% for most frequencies. The CMMR was better than 80 dB at 38 kHz and a sponge, 20 mm across, which caused a local 12% impedance increase, was correctly localized in images. This suggests that the system has adequate performance to image impedance changes of 5-50% known to occur in the brain during normal activity, epilepsy or stroke; clinical trials to image these conditions are in progress.

A system for logging incontinence events using a simple disposable sensor.

Many elderly people entering residential or nursing care are already incontinent to some degree, relying on incontinence pads to deal with the consequences. A proportion of these people have been shown to exhibit a regular pattern in their incontinence, which opens up the possibility of mitigating the problem by instituting an individual toileting regime for the person. This can reduce their reliance on incontinence pads, both improving their quality of life, and reducing the cost of care. This paper covers the development and evaluation of a sensor for detecting incontinence events, suitable for use in this setting, and describes the design of an associated electronic logger. The devices form part of an assessment system intended to identify a pattern in incontinence where it exists, and to help with the design of the toilet regime for an individual. The requirement is that the system must reliably record incontinence events, and present the information describing them in a manner appropriate to the users of the devices, who are likely to be non-technical and non-specialist.

Instrumentation of a mobilization couch for dynamic load measurement.

Spinal mobilization or manipulation techniques are frequently used by physiotherapists in the treatment of musculoskeletal disorders. Many of these techniques involve the application of a varying force to the affected joint. Despite the routine use of these techniques, there are no objective measures to quantify their use. This paper describes the principles of the instrumentation of a mobilization couch to enable measurement of the forces applied during mobilization of the lumbar spine. The couch was linked to a personal computer with a 286 processor and data card for data collection. The system was found to be reliable and sensitive over the range of forces applied during mobilization. It has potential for use in many situations where measurements of forces applied to the patient are required.

Ultrasound and amoebic liver abscess.

Eight of 12 patients referred to an ultrasound clinic were eventually found to have a liver abscess. All 8 abscesses were confirmed positively by ultrasonic examination. Using ultrasound, an amoebic abscess can be accurately located within the liver and the optimal site for needling suggested to the clinician. Ultrasound is an accurate, non-invasive, diagnostic aid in this condition.

MMPI-2 profiles of women differing in sexual abuse history and sexual orientation.

Four groups of women (N = 115) self-identified as having histories of childhood sexual abuse or no such histories and self-identified as either heterosexual or lesbian were compared using a questionnaire and the MMPI-2. Subjects ranged in age from 21-60 years with 60% between ages 30-50 years. Results of a Three-Way MANOVA for abuse history and sexual orientation repeated across MMPI-2 clinical scales showed a between-subjects effect for abuse, and within-subjects effects for orientation and abuse. T scores of women with abuse histories were significantly higher than those of women without abuse histories on Hs, D, Pd, Pa, Pt, Sc, and Ma scales of the MMPI-2. Profiles indicated an 8-4 codetype and a Scarlett O'Hara V configuration for the group with abuse history. Heterosexual women obtained significantly higher t scores than did lesbians on the Depression scale. Results show that the MMPI-2 can be used to help detect lesbian as well as heterosexual adults who were sexually molested as children.

Ultrasound and jaundice.

We have examined 26 consecutive jaundiced patients referred to the ultrasound clinic. A differentiation between extrahepatic and other causes of jaundice was possible in 23 of the 24 patients satisfactorily examined. The use of ultrasonic techniques in the jaundiced patient offers a high degree of accuracy to the clinician, and little or no discomfort to the patient.

Pneumothorax and cerebral haemorrhage in preterm infants.

Real-time ultrasound was used to examine the brains of all 95 infants born at less than 33 weeks of gestation who were admitted to the neonatal unit of University College Hospital in 1979. Evidence was obtained which strongly suggested that pneumothorax causes and aggravates haemorrhage into the germinal layer and ventricles of preterm infants.

Ultrasound detection of brain damage in preterm infants.

A linear-array real-time ultrasound scanner with a 5 MHz probe was used to examine the brains of 31 infants born at less than 33 weeks of gestation. The equipment was mounted on a small trolley and the infants could easily be scanned in their incubators. 7 of the 31 infants were shown to have cerebral lesions, including haemorrhages into the germinal layer and ventricles, hydrocephalus, and infarction of the periventricular region and cerebral cortex. The type and extent of the lesions were conformed by computerised tomography and at necropsy. Ultrasound scanning is a safe, simple, non-invasive technique that provides valuable information for the diagnosis, investigation, and treatment of lesions in the brains of newborn infants.