Drug – bio-affecting and body treating compositions – In vivo diagnosis or in vivo testing – Magnetic imaging agent
Patent
1995-05-04
1997-06-17
Hollinden, Gary E.
Drug, bio-affecting and body treating compositions
In vivo diagnosis or in vivo testing
Magnetic imaging agent
424 937, 424450, 514974, 1286534, 436173, A61B 5055
Patent
active
056394446
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP93/00006 filed Jan. 4, 1993, WO93/12717, Jul. 8, 1993.
This invention relates to the use of contrast media in electrical impedance imaging.
Electrical impedance imaging (EII), also referred to as electrical impedance tomography and applied potential tomography, is a medical imaging technique that was brought to a practical level during the 1980's, in particular by the Sheffield group of B H Brown, D C Barber et al.
The technique involves generation of images indicative of spatial, and if desired temporal, variations in electrical impedance or resistivity; images which, when of human or animal subjects, can provide information about the structure and functioning of the imaged tissues. The technique is attractive as a medical diagnostic tool since it is non-invasive and does not involve exposing the patient to potentially harmful ionizing radiation, it does not require the administration of radioactive species and it does not require the generation of strong, highly uniform magnetic fields.
In the version of EII developed by Brown, Barber et al., an array of evenly spaced electrodes is attached to the body about the region of interest, a very low alternating current is applied successively between adjacent pairs of electrodes and the potential difference between all other pairs is determined. Image construction is effected using a back projection technique.
Alternative approaches to data collection do exist and are described in the literature.
Thus for example reference may be made to Seagar et al. IEE Proceedings 134.A.:201-210 (1987), Barber et al. J. Phys. E. 17:723-733 (1984), Harris et al. Clin. Phys. Physiol. Meas. 8A:155-165 (1987), Brown et al. Clin. Phys. Physiol. Meas. 6:109-121 (1985), GB-A-2160323 (University of Sheffield), GB-A-2119520, WO-A-89/09564, WO-A-91/19454, Price IEEE Transactions on Nuclear Science NS-26:2736-2739 (1979), Webster et al. Clin. Phys. Physiol. Meas. 9A:127-130 (1988) and Kim et al. J. Microwave Power 18:245-257 (1983) and the documents cited therein.
Spatial variations revealed in electrical impedance (EI) images may result from variations in impedance between healthy and non-healthy tissues, variations in impedance between different tissues and organs or variations in apparent impedance due to anisotropic effects resulting for example from muscle alignment. Thus for example the difference in impedance between body fat and muscle tissue is such that the two should be differentiable in static EI images. Dynamic imaging techniques may be used to follow gastric emptying, heart and lung function and the like.
Static imaging is problematic insofar as the current image reconstruction techniques require a homogeneous reference data set--this can be calculated if an electrode array of known dimensions and spacings is used or if a data set is collected for a homogeneous reference sample of the same dimensions as the subject being imaged (e.g. a saline filled cast of the subject under investigation).
For dynamic imaging the problem does not arise as a data set collected before (or after) the event to be imaged may be used as the reference data set. The in vivo imaging reported thus far has concentrated heavily on dynamic imaging with the imaged event generally being the operation of a natural function such as breathing, gastric emptying, blood flow or heart function. In the first and last cases the reference data set may be chosen as the data set at one limit of the natural cycle, e.g. at maximum expiration, in the second the data set for a slice through the stomach before or after administration of a meal (e.g. water, saline, soup, "Oxo" or mashed potato) and in the third the data set before natural or artificial modification of blood flow (e.g. on haemorrhage, or by increasing the total blood volume by injection of relatively large quantities of isotonic saline, or by venous occlusion). In the case of gastric emptying, it has been found (see Avill et al. Gastroenterology 92:1019-1026 (1987)) that results are improved if natural variations of gas
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Hollinden Gary E.
Nycomed Imaging AS
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