Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-02-25
2001-05-08
Kamm, William E. (Department: 3762)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06230042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and arrangement for determining the location of an active (i.e. a measurement and/or treatment) catheter within an animal (including human) body and in particular to such a method and arrangement of the type employing triangulation techniques in order to make the determination.
2. Description of the Prior Art
Systems for locating a catheter within an animal body using triangulation are well known and such a system is described, for example, in U.S. Pat. No. 5,042,486. In this known system, an electromagnetic or acoustic signal is transmitted between an antenna at the tip of an active catheter and three reference antennas placed on the outside of the animal. The distances between each reference antenna and the catheter antenna are then combined, using triangulation methods, to provide a determination of the active catheter in three-dimensions.
For many medical applications it is desirable to be able to locate an active catheter in a patient, e.g. in angiographic examinations and in cardiac diagnostics and therapy, with as high a degree of accuracy as possible.
One system that is used to locate such an active catheter with an improved accuracy is disclosed in PCT Publication WO 98/00060, and has a fixed reference catheter and an active catheter, between which acoustic or electromagnetic signals are transmitted. The transmitted signals are used to measure the distance between transducers mounted on the reference catheter and at least one transducer mounted on the active catheter. The location of the catheter is determined by triangulation. In the system described in WO 98/00060 both the reference and the active catheter are positioned inside the patient, with the consequence that the position measurements may be made more accurately since they are not affected by the movement or breathing of the patient. WO 98/00060 also describes a system in which the number of transducers that are mounted on the reference catheter exceeds the minimum number of transducers required mathematically to make the location determination. In this way a number of independent determinations of the catheter location may be made by using a different combination of reference transducers for each determination. An averaged location may then be calculated having an increased accuracy over a single determination.
Similarly, WO 96/31753 describes a digital ultrasound catheter tracking system that can employ up to 32 transducers to create a redundancy in distance measurements so that the three-dimensional location of the catheter can be determined even if some distance measurements are ignored, for example because of poor signal propagation through the measurement volume.
Nevertheless, even when using a system in which a greater number of distances are measured than are mathematically required to locate the catheter, the determined location may still have a relatively large error associated with it.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and arrangement for determining the location of an active catheter wherein the above disadvantage associated with known systems is reduced.
The above object is achieved in accordance with the principles of the present invention in a method and arrangement for determining the location of a catheter within a living body, wherein a distance between the catheter and a number of reference cites within the living body is measured, wherein at least two independent calculations of the location of the catheter are made, using triangulation, from the measured distances, and wherein the location of the catheter is determined using these independent calculations, by generating a weighting for each independently calculated location dependent on an error value associated with the calculation for that location, and by combining the weighted independent calculations thereby reducing the relative contributions of the independently calculated locations as their respectively associated error values increase.
Thus in the present invention a number of individually calculated locations are combined to provide an average location value in which the contribution of each calculated location to the average value reduces, as its error increases. The potential for determining a location having a large standard deviation is thereby reduced.
The method includes, for a number of calculated locations greater than 1, the step of reducing to zero the contribution of calculated locations having error values which exceed a predetermined maximum value. In this way the most inaccurate calculated locations may be eliminated from further consideration.
Preferably the method includes calculating the measurement error associated with each calculated location and generating an average location in which the contribution of each calculated location reduces as its calculated error increases.
REFERENCES:
patent: 5042486 (1991-08-01), Pfeiler et al.
patent: 5676673 (1997-10-01), Ferre et al.
patent: 5724978 (1998-03-01), Tenhoff
patent: WO 96/31753 (1996-10-01), None
patent: WO 98/00060 (1998-08-01), None
Hill & Simpson
Kamm William E.
Siemens Elema AB
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