Marker for determining its position in a cavity inside the...

Drug – bio-affecting and body treating compositions – In vivo diagnosis or in vivo testing – Magnetic imaging agent

Utility Patent

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C424S009322, C424S009300, C128S899000

Utility Patent

active

06168780

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a marker, the position of which in a cavity inside a living organism is to be determined, in particular for determining local passage speeds of the marker while passing through a gastro-intestinal tract, preferably, a small bowel area. The marker is particularly adapted for use in a method and apparatus according to WO 97/09640.
There are medical examinations known which require repeated detection of local passage speeds of a marker while passing through the gastro-intestinal tract. This is the case, for example, with chronic inflammatory intestinal diseases such as Morbus Chron, functional gastro-intestinal diseases, and in physiological examinations of the gastro-intestinal tract. Conventional diagnosis techniques, such as X-ray examination under use of contrast meals, may not be utilized in the cases mentioned due to the radiation exposure. The same comes true for scintigraphic methods.
Known techniques which avoid radiation exposure are nuclear spin tomography [M. Reiser, W. Semmler (editor) “Magnetoresonanztomograhpie”, Springer press, Berlin/Heidelberg, 1992], the sonography [M. Amend, C. Jakobeit, L. Greiner, Verdauungskrankheiten 13 (1995), No. 1, pg. 21], use of metal detectors [K. Ewe, Therapiewoche 41 (1991), pg. 77], inductive detection of soft magnetic tracers [Y. Benmair, B. Fischel, E. H. Frei, T. Gilat, The American Journal of Gastroenterology 68 (1977), pg. 170], and local position detection of permanent magnetic markers [L. Trahms, R. Stehr, J. Wedemeyer, W. Weitschies, Biomedizinische Technik 35 (1990), pg. 158].
Nuclear spin tomography, or magneto-resonance, is an expensive method which is not suitable for examinations which have to be repeated very often, and too slow for the detection of local passage speeds, which require time intervals in an order of size of 10 s for the successive position detection of markers [K. Fitzgerald, IEEE Spectrum 27 (1990), pg. 52].
Sonographic examinations have not been employed for the detection of local passage speeds up to now, but only for measuring general transit times of larger sections of the gastro-intestinal tract [M. Amend, C. Jakobeit, L. Greiner, Verdauungskrankheiten 13 (1995), No. 1, pg. 21], since air volumes in the abdominal cavity cannot be penetrated by ultrasound and would result in an erroneous position detection of the marker. Such deficiencies could be reduced by completely filling the bowel with a liquid, however, a filled bowel is not suited for a diagnosis due to the changed peristalsis.
It is feasible to determine the position of metal particles by metal detectors. However, the lateral accuracy of the position detection decreases with the increasing distance from the body surface and is worse than 1 cm at a distance of <10 cm [K. Ewe, Therapiewoche 41 (1991), pg. 77]. Said paper does not report of the accuracy of these depth-measurements. Since the accuracy of depth-measurements is generally worse than the lateral accuracy, this method is insufficient for local passage speed measurements.
The accuracy of position detection obtained with an inductive measurement of a soft-magnetic tracer satisfies examinations of the gastric contents decrease per unit time of a soft-magnetic meal having an initial volume of more than 100 cm
3
[Y. Benmair, B. Fischel, E. H. Frei, T. Gilat, The American Journal of Gastroenterology 68 (1977), pg. 170]. However, on the one hand, a measurement of the local passage-speed in the bowels is not feasible, since the large test meal volume uncontrollably distributes while passing the bowels. On the other hand, the test volume cannot be reduced substantially since, otherwise, the secondary magnetic field produced by the tracer, even when highly compensated, will become so small that it cannot be separated from the residual signal of a primary magnetic field applied during measurement.
Furthermore, it is known to magnetize permanent magnetic markers before being administered to a patient [W. Weitschies, J. Wedemeyer, R. Stehr, L. Trahms, IEEE Trans. Biomed. Eng. 41 (1994), pg. 192], [DE 39 40 260]. However, the detection of the position of the markers via their secondary magnetic field is considerably affected by interference fields (for example, by the magnetic field of the earth) so that the measurements have to be carried out in an extremely magnetically screened special chamber. Even then this method is not suited for detection of the local passage speed i the entire gastro-intestinal tract. Hence, position detection is only feasible i the stomach or in the large bowel, due to the transversal and rotational movements of the marker, and even in these ranges, where the retention time of the marker is comparatively high, the accuracy is insufficient.
In WO 97/09640 an arrangement for and method of determining the position of a magnetizable marker has been proposed, whereby the marker is adapted to comprise a semi-hard magnetic material of a coercive force within a range of from 10
4
up to 10
5
A/m, and is spherosymmetrically embodied. Furthermore, according to the specification mentioned, the marker is made of an isotropic magnetic material of a relative residual magnetism of preferably >0.8, wherein the marker is substantially made of &ggr;-Fe
2
O
3
and/or Fe
3
O
4
. A disadvantage of the marker embodiment proposed consists in that the primary magnetic field for the magnetic reversal of the marker is very considerable.
It is an object of the present invention to provide a marker which is designed to be captured by a magnetic coil arrangement, whereby the magnetizing of the marker is reversible by virtue of comparatively low field strengths at a change of a pulse-shaped current flow in the magnetic coil arrangement.
SUMMARY OF THE INVENTION
According to the invention a magnetizable marker is manufactured of two parts, a first part being a substantially spherical part which is adapted to receive a magnetizable material or body. The first part being received by a second part in such a manner that it floats permitting all around rotation in the second part. While passing through the gastro-intestinal tract, a position of the external second part is determined by forces which are executed by feed pulp, intestinal wall, and by the peristalsis. In contrast thereto, the orientation of the internal and substantially spherical first part is determined by the field, for example, the magnetic field of the earth, exerted on the magnet. The orientation can be adjusted at will by an externally applied field which is stronger than the magnetic field of the earth, or by an accidentally present laboratory magnetic field. To this end, already a magnetic field strength of about 80 A/m is sufficient, which very easily can be produced by current-carrying coils or permanent magnets outside of a patient's body.
In order to eliminate the external interfering fields in the case of use of the marker in an apparatus, for example, according to WO 97/09640, a magnetic moment of the first part is rotated into a desired orientation, for example, at right angles to a plane of the patient's back by applying an external field H
ext
for a short time. Then the applied field is turned off for a short time and directly following, as fast as possible, the marker field is measured by sensors. After this measurement, the field H
ext
is applied in the opposite direction for a short time and the above procedure is repeated. By difference formation of both measured marker fields, the entire interfering effects are eliminated which did not change remarkably between both measurements. The times which are required for the orientation in the externally applied magnetic field and for a reverse rotation in the direction of the field of the earth or of the laboratory depend on, inter alia, a residual magnetic moment of a first part and on the viscosity of a liquid in which the first part is embedded. A simple electronic circuit, which does not re

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