Electric heating – Inductive heating – Specific heating application
Reexamination Certificate
2002-02-22
2004-05-18
Van, Quang T. (Department: 3742)
Electric heating
Inductive heating
Specific heating application
C219S670000
Reexamination Certificate
active
06737618
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a magnetic coil arrangement of a magnetic field applicator for treating biological tissue, and more particularly a magnetic oil arrangement for heating magnetic or magnetizable substances or solids in biological tissue.
Cancer diseases can be treated in a generally known manner by means of hyperthermia processes, wherein cancer tissue is specifically heated to temperatures of approximately 41° C. to 46° C. for irreversible damage. In a known hyperthermia process (WO 97/43005) for tumor therapy, magnetizable microcapsules are used which reach the area of the tumor through the blood stream. During a treatment, these microcapsules are charged with a magnetic alternating field generated outside of a patient, with hysteresis effects generating heat for hyperthermia in the microcapsules. A linear magnetic alternating field is used with a frequency in the range of 10 kHz to 500 kHz. The microcapsules should contain a highly magnetizable material so that the force of the magnetic alternating field, the required instrumentation structure, the required cooling system as well as the electrical energy supply can be manageable. A practical instrumentation structure is however not indicated.
In a very much similar, known hyperthermia process (EP 0 913 167 A2), rotating magnetic fields with a frequency in the range greater than 10 kHz are used as fields. To produce the rotating magnetic alternating fields a magnetic field applicator is indicated only sketchily and schematically.
A generic magnetic coil arrangement is shown in the (post-published) DE 199 37 492 publication. The magnetic field applicator for heating magnetic or magnetizable substances in biological tissue comprises a coolable magnetic yoke with two pole shoes facing each other and being separated by a gap to define an exposure volume on the magnetic yoke. To produce a magnetic alternating field, two magnetic coils are assigned to one pole shoe each. The magnetic coils are designed as disk coils with helicoidally extending coil windings and annularly surrounding the pole shoe end of the assigned pole shoes with an intermediate, circulating magnetic coil/pole shoe gap. The magnetic yoke and the pole shoes consist of ferrite block segments which are mounted together.
For hyperthermia, in particular with magnetic liquids, alternating field forces of approximately 15 to 20 kA/m at approximately 50 to 100 kHz are required. With a volume exposed by a magnetic field of 8 to 30 I, effective power of approximatelyl 18 kW to 80 kW must be produced by a hyperthermia installation. This energy must be produced in form of high frequency and must then be transmitted in form of heat with cooling since only a few watts are produced in the magnetic fluid for the hyperthermia in a patient's body. For cooling of the ferrite block segments, the magnetic yoke and the pole shoes, measures are specified with cooling air flow in cooling gaps. In contrast, the type of cooling of the magnetic coils as well as their mounting system is left open. However, cooling of the magnetic coils is problematic since there is a particularly high power loss which is higher per volume unit than the power loss in the ferrite block segments and since only a relatively small specified space for installation in the magnetic coil area is available for cooling devices and mounting systems.
It is therefore the object of the present invention to develop an improved magnetic coil arrangement for a magnetic field applicator to heat magnetic and magnetizable substances or solids in biological tissue so that effective cooling of the magnetic coils will be possible in combination with a compact arrangement and mounting.
SUMMARY OF THE INVENTION
The above objective is accomplished according to the present invention by providing a magnetic coil in a coil box annularly surrounding the assigned pole shoe. The coil box comprises at least one cooling air admission port for connection to a cooling air pump and at least one cooling air discharge port. Magnetic yoke cooling and magnetic coil cooling can be advantageously isolated and optimally adjusted to the different cooling requirements in terms of cooling air volume, cooling air pressure, and cooling air throughput and cooling air flow. Moreover, the coil box can be used, in addition to its duty as part of the magnetic coil/cooling device, for mechanically mounting the magnetic coil. Thus, an advantageously compact design is provided which is well suited to the confined space conditions of a magnetic field applicator in the area of the gap of the exposure volume and a patient's body areas. In a preferred embodiment, the magnetic yoke and the pole shoes consist of assembled ferrite block segments. The magnetic yoke is combined of cut-stone-shaped ferrite block segments, the surfaces of which are freed from sintering layers and, if necessary, ground to be plane-parallel. The cut-stone-shaped ferrite block segments consist of ferrite plates lined up in a row, aligned in the magnetic yoke along the magnetic flow. The ferrite plates are separated from each other by an insulation/cooling gap transverse to the magnetic flow through which cooling air for magnetic yoke cooling is conveyed. In the direction of magnetic flow, adjacent ferrite plates are separated only by narrow contact gaps. To form the insulation/cooling gap, plastic separators are inserted between the ferrite plates. The cut-stone-shaped ferrite block segments are formed by bonding together the ferrite plates and the separators. The pole shoes are cylindrically or round, as seen from the top, and have a similar structure of wedge-shaped ferrite block segments which are assembled like pieces of a pie. Between these ferrite block segments, insulation/ cooling gaps are also provided by means of separators for pole shoe cooling.
The power losses caused in the ferrite block segments during operation of a magnetic field applicator are so high that they are dissipated by introduction of cooling air into suitably designed insulation/cooling gaps between the ferrite block segments. It has been shown, however, that a possible combination of the magnetic coil cooling and the magnetic yoke and pole shoe cooling is difficult to design, expensive and ineffective. One problem with the possible combination is the fact that the magnetic coil produces a higher power loss in comparison per volume unit. Thus, especially with the arrangement and isolation of the cooling systems according to the present invention provide considerable benefits regarding the arrangement, dimensioning and operation of the two cooling systems. Moreover, its simple assembly also reduces the expenditures for installation, handling and maintenance as well as operating costs.
According to one aspect of the invention, the pole shoe end surfaces are each covered by a pole shoe plate. A laterally surrounding pole shoe plate extends beyond the assigned pole shoe end surface and forms a coil box bottom wall on the side of the exposure volume. Separators are inserted between the pole shoe end surfaces and the pole shoe plate to create insulation/cooling gaps. These separators are relatively small compared with the contact surface of the wedge-shaped ferrite block segments so that a cooling air flow through the separators passes radially between pole shoe end surface and pole shoe plate will hardly be obstructed. The pole shoe plate, in the area of the pole shoe end surface, has an indentation which is less thick than an adjacent area of the coil box bottom wall. The pole shoe end surface extends some-what into this indentation with the surrounding edge of the pole shoe end surface being rounded off. A surrounding annular gap is created as a cooling air outlet between the pole shoe plate and the pole shoe end surface. In this annular gap, it is possible to bypass the radial cooling air flow to an axial outlet direction. The pole shoe plate may be made of insulating material, such as glass. However, a high-quality, fiberglass reinforced plastic is preferably used, and th
Flint Cort
McNair Law Firm PA
MFH Hyperthermiesysteme GmbH
Van Quang T.
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