USE OF IMPLANT WITH MAGNETIC PROPERTIES TO DETERMINE THE POSITION OF A PATIENT

Abstract: Use of an implant having magnetic properties for reproducible determination of the position of a patient in time in relation to external treatment equipment, and an apparatus for reproducibly determining the position of a patient in relation to external treatment equipment. The apparatus comprises at least one magnetic device (1) which is so designed that it can be attached to a body part, the position in relation to the intended treatment target is substantially constant, and at least one sensor means (4) which is capable of detecting magnetic fields and/or changes of magnetic fields for determining the position of the patient in the space based thereon.

Description: Use of implant with magnetic properties to determine the position of a patient. Technical Field The present invention relates to the determination of the position of special points or areas on or in live creatures. The term live creatures relates to both humans and animals and they will in the following specification and claims, for simplicity reasons, jointly be called "patients". Bakground of the Invention In medicine it is common to make diagnoses, perform other investigations and treat patients by means of external equipments such as x-ray apparatuses, radiation treatment apparatuses and other types of apparatuses. For simplicity reasons such external diagnosis, other investigation or treatment will in the following jointly be referred to as "treatment". In many cases it is necessary to be able to reproduce the position of the patient in relation to the external equipment as accurately as possible in all space dimensions from one treatment to another. This is in particular true when the treatment might cause damages on surrounding organs, tissue etc., like in, for example, the case with radiation treatment. Disclosure of Prior Art The presently most common method for determining the position of a patient in relation to the external treatment-equipment from one treatment to another, is to make markings on the skin of the patient, for example in the form of "crosses" or the like. This procedure is not very reliable since the skin moves in relation to the internal organs, tissues, etc. which are to be treated. There is, therefore, a great chance that the treatment, in particular if it is radiation treatment, damages healthy internal organs, tissues, etc. in the patient. There is therefore a great need of being able to accurately and in a reproducable manner be able to align a patient in relation to the external equipment from one treat¬ ment to another. It is also previously known to use magnetic implants for various purposes. One example is US-A-4, 978,323 which discloses systems and methods in which magnets are used for preventing opturation of such body channels, especially the air ducts, in which gas or liquid has to be able to flow. A combination of implan¬ ted and external permanent magnets, or only implanted magnets, are used in order to keep the body channel in question open. As an alternative to implanted magnets, for the same purpose, there are disclosed magnets which are swallowed by the patient as a "pill". An electronic system such as a Hall element can be used for e.g. checking that the magnets fulfil their function to keep the body channel in question open. Also disclosed is the use of magnets for keeping prostheses or endotracheal tubes in place. US-A-5, 125,888 discloses a method for transporting, by means of an electromagnetic field, a drug with attached magnetic object to a desired location in the body, especially the brain, for administration of the drug to that spot, and retraction of the magnetic object. SU-A-1,338,154 discloses a method of matching the radiation parameters in proton therapy, wherin detectors interrupt the treatment if permitted radiation parameters are exceeded. FI,B, 79458 discloses a method and a device for eliminating errors which are caused by the patient's movements in a treatment situation, wherein a mark is made on the skin in the very treatment area. The momentaneous position of this mark is followed by continuously determining the position coordinates of the mark, and treatment is started when the position coordinates of the mark correspond to pre-determined comparison coordinates. WO, Al, 93/00039 discloses a device for detecting and localizing, by means of an electomagnetic field, a metallic object which has been penetrated or implanted into a human or animal body. There are also a number of publications which make use of similar methods and devices for detecting objects in a human and animal body, e.g. SE 0314231, SE 0193509, US-A-4,987,309, US-A-4,502,147, JP 63-286170, US-A-4,618,980, US- A-4,445,501 and FI 81012. In summary it is true that the above indicated documents make use of magnets as implants in connection with medical treatment, but none of said documents neither indicate or intimate the use of magnetic implants for solving the above mentioned problems with reproducable determination of the position of a patient on different occasions. Short Description of the Drawing An example of the presently preferred embodiment of the invention is illustrated in the enclosed drawings, in which Figure 1 is a diagrammatic sectional view showing a patient having a magnetic implant and an external sensor, and Figure 2 is a schematic elevational view showing an example of external equipment for recordal and presentation of the position of the implant in the body. Description of the Invention and Preferred Embodiments In Figure 1 the reference numeral 1 shows a magnetic implant which e.g. may be an implanted permanent magnet. It is, however, within the scope of the invention possible to choose an arbitrary implant having the ability to produce, as such or in combination with any other material, produce detectable magnetic fields (including electromagnetic fields) and/or changes of magnetic fields, etc. In accordance with the invention the implant 1 is attached to a suitable body part 2 which, in contrast to the skin, has a comparatively constant position in the body. In the shown embodiment the body part is a bone in the body. Reference numeral 3 represents the skin of the patient. It is preferred to position the implant as close as possible to the respective area of treatment, but outside the same. It can also often be suitable to encapsulate the implant in a more tissue-friendly material. The implant is also preferably provided with devices and/or materials which are known per se and makes an accurate securing of the implant in bones possible, for example screws, plates, orthopedical supports and the like. In an alternative embodiment the implant can be an "explant", i.e. be located in a corresponding position outside the body, preferably in the vicinity of, and positionally connected to, underneath parts, e.g. a bone. The schematically shown device 4, which is located outside the patient, represents one or more sensors detecting magnetic fields and/or changes of magnetic fields, e.g. from the implant 1 and/or another device cooperating therewith. The number and the type of sensors, implants and detection method will be chosen with regard to i.a. the desired accuracy. Thus, the magnetic field can be generated in any manner which fulfil the indicated purpose, for example by means of permanent magnets, induction with in-operated spool and power source in or outside the body. It is also possible, by induction to build up a voltage in the implant which subsequently can provide a magnetic field through a spool. It is not necessary for the implant as such to generate a magnetic field, but it can be so designed that its magnetic properties will change the applied magnetic field (for example a steel plate), and this change will be detected by the sensor. Thus the implant as such does not have to provide a magnetic field but only provide a change of a magnetic field, applied from the outside. In this case the implant has magnetic properties which can be detected by the sensor. It is also possible to combine an outer magnetic field with a magnetic field which is generated by the implant in an optional manner. Since the implant does not have to be magnetic as such, but is capable of acting by induction, it will be possible to use e.g. magnetically insensitive spools of copper which do not interfere with investigations using magnetic resonanse tomography. Since the position of the sensor 4 is known, the position of the im- plant/explant 1 can be calculated in a simple manner. Since the position of the implant in the patient is known, as is also its relation to the target of the treatment such as a radiation target, it is also possible to determine the positions for the patient and the target of the treatment. The design of the sensors 4 can be varied as needed in the individual case, from a simple spool to more advanced elements which are sensitive to magnetic fields, e.g. Hall instruments, magnetic resistive sensors or the like which together build up a sensor. Such a sensor may contain one or more elements of the same or different type which are sensitive to magnetic fields. The elements may be grouped into different configurations (circular, in rows, etc.). The sensors may be movable or stationary. The elements of the sensors can also be immobile or movable in order to increase the area in which the magnetic field is detected. This is technique which is well known as such and which a person skilled in the art can apply on the present invention without any further description. Figure 2 shows a sensor 4 built-up from 25 analogous Hall sensors which are arranged in 5 rows of 5 sensors each. By reading the signals from the sensors into a computer 6, using an analogue-to-digital converter 5, each sensor can be read rapidly. Each sensor provides a voltage which is proportional to the magnetic field in which it is located. The magnets which are located closer to the center of the magnetic field provide the maximum deflection. By using this device the center of the magnetic field can be determined accurately in two directions and the accuracy increases when using more devices. The invention is not intended to be restricted to the embodiments which have been described and/or shown, but many modifications and variations are possible within the scope of the appended claims.

Claims: CLAIMS 1. Use of an implant having magnetic properties for in time reproducable determination of the position of a patient in relation to external treatment equipment. 2. Use according to claim 1, characterized in that the implant comprises a permanent magnet. 3. Use according to claim 1, characterized in that the implant comprises at least one material which, in co- oporation with at least one external material, producing a magnetic field by means of which the position of the patient in the space can be determined. 4. Use according to any one of claims 1 to 3, characterized in that the implant is attached to a body part whose position in relation to an intended treatment target is substantially constant. 5. Use according to any one of claims 1 to 4, characterized in that the body part is a bone in the body. 6. Use according to any one of claims 1 to 5, characterized in that the implant is an explant. 7. A device for in time reproducible determination of the position of a patient in relation to external treatment equipment, characterized in that it comprises a) at least one device (1) which has magnetic properties and is so designed that it can be attached to a body part, the position of which is substantially constant in relation to an intended treatment target, b) at least one sensor device (4) being capable of detecting a magnetic field and/or changes of a magnetic field and, based thereon, determine the position of the patient in the space.

Inventors: LENNERNAES BO, LENNERNAES, BO
Applicants: LENNERNAES BO, LENNERNAES, BO
Application year: 1995
Main classification: A61B5
IPC codes: A61B5, A61B6, A61B19, A61N5