No abstract

The electrical resistivity of mammalian tissues varies widely (1-5) and is correlated with physiological function (6-8). Electrical impedance tomography (EIT) can be used to probe such variations in vivo, and offers a non-invasive means of imaging the internal conductivity distribution of the human body (9-11). But the computational complexity of EIT has severe practical limitations, and previous work has been restricted to considering image reconstruction as an essentially two-dimensional problem (10,12). This simplification can limit significantly the imaging capabilities of EIT, as the electric currents used to determine the conductivity variations will not in general be confined to a two-dimensional plane (13). A few studies have attempted three-dimensional EIT image reconstruction (14,15), but have not yet succeeded in generating images of a quality suitable for clinical applications. Here we report the development of a three-dimensional EIT system with greatly improved imaging capabilities, which combines our 64-electrode data-collection apparatus (16) with customized matrix inversion techniques. Our results demonstrate the practical potential of EIT for clinical applications, such as lung or brain imaging and diagnostic screening (8).

reduced fluorescence yield (an approximately one-third reduction relative to ethanol) are observed for the premicellar 4,0-THex J-aggregates relative to the monomer.

Applied potential tomography (APT) or electrical impedance imaging has received considerable attention during the past few years and some in vivo images have been produced. This paper reviews the current situation in terms of what in vivo results have been and are likely to be obtained in the near future. Both static and dynamic imaging are possible and these two areas are dealt with separately. Features of the existing in vivo imaging system are good tissue contrast, high-speed data collection, good sensitivity to resistivity changes, low spatial resolution, low cost and no known hazard. It is concluded that the most promising way forward to clinical application in the short term is to use dynamic as opposed to static imaging. An example of lung imaging is shown and the application to measuring regional ventilation and pulmonary oedema is discussed. Use of APT for the detection of intraventricular bleeding in neonates is discussed as is the proven ability to study gastric physiology by imaging resistivity distribution changes following the ingestion of conducting or insulating fluids. Other areas of possible application which are considered are blood flow measurement, cell counting, measurement of lean-fat ratios and the detection of soft tissue lesions.

The reduction of the enormous quantity of data in a radionuclide dynamic study to a few diagnostic parameters presents a problem. Conventional methods of data reduction using regions-of-interest or functional images have several defects which potentially limit their usefulness. Using a principal components analysis of the elemental curves representing the change of activity with time in each pixel, followed by a further factor analysis, it is possible to extract the fundamental functional changes of activity which underly the observed variation of activity. An example of this analysis on a dynamic brain scan suggests that the three fundamental phases of activity represent activity in the arterial system, the venous system and diffusion of tracer into the tissues.

We have investigated the effect of loperamide (4 mg tds) on the continence to a standard volume of rectally infused saline and anorectal manometry in 26 patients complaining of chronic diarrhea complicated by fecal incontinence and severe urgency. Each patient was treated for one week with loperamide (4 mg tds) and for one week with an identical placebo in a double-blind cross-over trial. Our results showed that as well as its established effects of improving stool consistency and reducing stool weight, frequency and episodes of incontinence and severe urgency, loperamide also significantly improved continence to a standard volume of rectally infused saline. This action was associated with an increase in the maximum basal sphincter pressure, an increase in the rectal volume required to abolish recovery of the rectoanal inhibitory reflex, and a reduction in rectal compliance. These results suggest that loperamide may have a specific action on the anal sphincter, which may aid continence in patients who complain of diarrhea and fecal incontinence.

No abstract

No abstract