GB2264642A - Broad loop based hyperthermic applicator - Google Patents

Abstract

An RF field with high magnetic H and low electric E components is applied to a patient Pa by a loop BLA comprising one or more cylindrical sheet metal elements a which may be in the form of series of separate arcs. Elements may be spaced by gaps g which may be varied together with current magnitude and phase. The field may be controlled using pieces of magnetic material. Impedance matching is also disclosed. <IMAGE>

Description

Broad Loop Based Flyperthermic Applicators I Rohammad Javad Birjandi of 88 Stockethill Court, Aberdeen, A82 SUQ, Scotland, Great Britain, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to: provision of radical inprovements in the design of the broad loop nyperthermic applicators; provision of a novel, uultitasking, family of broad loop based hyperthernic applicators; and provision of means as well as methods for influencing or steering the electromagnetic fields of said applicators as reasonably (and/or possibly) desired.

Assessment of the dosimetry of the non-ionising radiation or electromagnetic waves, radiated or emitted by the earlier, and by the most recent prototype broad loop regional hyperthermic applicators, has exhibited two major drawbacks associated with their original design: 1. variation in the magnetic field distribution along the central axis; 2. deposition of minimum electromagnetic power along the central axis.

It is an object of the invention: 1. to introduce neans as well as methods for improving the basic design of the broad loop hyperthermic applicators; while retaining their favorable radical characteristics; 2. to provide means as well as methods for influencing or steering the electromagnetic waves or radiation emitted or radiated by the said broad loop based hyperthermic applicators as reasonably (and/or possibly) desired; 3. to achieve steerable deep treatment as well as steerable, localized or regional, superficial treatment; 4. to introduce and to provide means as well as methods for achieving a family of balanced, efficient, non-contact, non-invasive, inductive, broad loop based hyperthermic applicators.

Embodiments of the present invention will now be described, by way of examples, with reference to the accompanying drawings and diagrams, in which: Figure 1 is schematic visualization of the basic principles of a single turn broad loop hyperthermic applicator.

Figure 2 shows perspective view of a broad loop based hyperthernic applicator means, comprising a number of coaxial, identical (preferable, or as desired), current sheet elenents a; with said elements a comprising pitch (g+l) -preferably variable, or as desired, not necessarily uniform or constant throughout the applicator length, lengths 1 (as desired, and not necessarily identical to those of the neighboring elements al, variable gaps g -not necessarily uniform or constant throughout the applicator length-, providing: individual or a plurality of tuned circuits, and a number of degrees of freedom, part of the invention claimed herein.

Figure 3 is longitudinal section of: 1. said applicator claimed hereinbefore in figure 21 2. yet another broad loop based hyperthermic applicator, claimed hereinafter in figure 4.

Figure 4 is a vertical cross sectional view of the hereinbefore claimed said applicator's constituent single elements a, modified to provide a plurality of complementing-elements a', with the said complementing-elements a' capable of operating under any one of the following conditions: 1. 11-12 -0' phase difference between the currents in the complementing-elements a'; 2. I1=-I2 -180' phase difference between the currents in the complementing-elements a'; 3. I1 and I2 in phase quadrature -90 phase difference between the currents in the complementing-elements a'; providing a number of degrees of freedom, part of the invention claimed herein.

Figure 5 is vertical cross sectional view of an exemplary modification of the hereinbefore claimed complementing-elements a' (cf figure 4 claimed hereinbefore), introducing a number of complementing-elements a", capable of operating under a variety of conditions (discussed hereinafter), providing a number of degrees of freedom.

Figure 6 shows perspective view of non-invasive ferrimagnetic materials fm of appropriate desired geometry and dimensions, placed within and or nearby the hereinbefore said applicators, and used: 1. for influencing the electromagnetic fields of said applicators, or, 2. for provision of partial steering of the said fields of the said applicators, as desired; constituting part of the invention claimed herein.

Figure 7 shows both a perspective view of and a vertical cross sectional view of a non-invasive, power controlled ferrimagnetic block (or material) fb, a plurality of whicn encompass the hereinbefore said applicators, providing: I. effects to influence the electromagnetic fields of said applicators as reasonably desired; 2. partial steering -as desired- of the electro magnetic fields ct said applicators; 3. a number of degrees of freedom; constituting part of the invention claimed herein.

faith reference to figure 1, a broad loop hyperthermic applicator BLA is a non-contact, non-invasive, single turn of a cylindrical broad strip inductor, fabricated from rolled metal sheet of high conductivity, and designed to resonate at the required Industrial Scientific and Nedical -or as desired- frequency Iradiofrequency -RF, commonly:: 13.56 and 27.12 He2). The capacitance required for resonance of the said BLA is formed, partly, by the proximity of the edges of the said applicator, which overlap in a non-contacting (i.e. no direct contact) manner -either as shown here in figure 1 or such that the said applicator continues to exhibit an approximately circular cross section-, firmly sandwiching a pre-selected dielectric material (preferably with low losses) of chosen thickness d'.

The principle aim in the case of said BLA, is to achieve maximum power transfer into a load leg. a patient pa, accommodated within the said BLA).

This nay only be obtained when the impendance of the power source becomes equal to that of the said BLA.

Empirical and nunerical attempts have verified that the difference between the impedance of the said BLA (whether loaded -low inpedance- or unloaded -high impedance) and that of its nominated power source may not be smoothed away purely by modifying the BLA parameters. Therefore, additional matching units are required to minimize both the reflected power and the evoked standing wave ratio.

with reference to the preceding sentences, an impedance matching unit, comprising respectively (fron the low inpedance end to the high impendance end): - an unbalanced to balanced ferrimagnetic material based transformer, with a desired (preferably 1:2) turns ratio; - a balanced four-terminal n network (preferab ly with identical, ganged, series arm capacitances; or, with a desired phase shift, - a balanced, manually or automatically controlled capacitor (preferably shunted -i.e low pass filter); has been invented, which, being part of the invention claimed herein, provides optimum matching (i.e. with a standing wave ratio close to unity) between the said applicator and its nominated power source, as well as a high power transfer efficiency. This said, herein-clained impedance matching unit, or a plurality of its constituents in any desired combinations, with or without the existence of one or a plurality of appropriate power conbiners prior to or at any stage during or after (or any desired combinations there of) the matching network, provide also the desired matching for the hereinafter claimed broad loop based applicators.

With reference to figure 1, upon introduction of RF power to the said BLA, tine-varying circulating currents I are produced in the loop structure, which in turn create electromagnetic fields. The alternating. magnetic field component H of the fields (NB. the dimensions of the said BLA are smaller than the hereinbefore mentioned commonly used wavelengths, thus, we are essentially in the near-field region where the said H is high and the electric field component is low) is produced parallel to the axis of the said BLA, along the axis of the load (eg. a patient pa). The said H in turn induces electric field lines E with which are associated eddy currents.

These run circumferentially on cylindrical surfaces parallel to the tissue interlayer boundaries, and generate heat at depth (reducing the necessity to use bolus).

Owing to the body being essentially non-magnetic (i.e. little perturbation of the said H-field), and to the reasons discussed hereinbefore (see NB above), the state of tuning (or resonance) of the said BLA is not greatly affected by minor movements associated with the patient pa. However, the said tuning is subject to alterations, mainly, due to variations in the electrical characteristics of the potential load upon heating. This with the view to maintain resonance and to minimize personnel exposure, necessitates the adoption of automatic tuning. The said non-invasive, nonperturbing automation approach provides the objective of an independent patent application.

with reference to figure 1, due to the closed loop nature of the induced electric field surfaces E, the power deposition along the central axis of the said BLA is theoretically a null, thus giving rise to the hereinbefore said two major drawbacks, associated with the original design of the said BLA. As part of the invention claimed herein, means as well as methods, for improving the basic design of the said BLA, are introduced and provided hereinafter.

with reference to figures 2 to 3, a novel broad loop based applicator, part of the invention claimed herein, comprising a plurality of coaxial (along line 1-1), parallel (along line 2-2) or tilted (with respect to line 2-2) current sheet elements a of desirable dimensions, wherein said elements a comprise reasonably desired (not necessarily uniform or constant throughout the said applicator length): pitch (g+l), gapsg, lengths 1, diameter d, overlap dimensions; provides: 1. individual or a plurality of tuned circuits, wherein: - tuning -the degree of which may be varied desirably- is achieved partially (or wholly if possible) by the proximity of the edges of the said elements a, in accordance with the methods described hereinbefore, - the desired power is introduced to or induced in the said elements a either separately or in combinations or in a plurality, with the appropriate impendance matching unit falling in the scopes described hereinbefore, - the said tuned circuits can be inter coupled or decoupled, - the phase difference between the said elements a can be varied as desired; 2. improved variation in the magnetic field distribution along the central axis of the said applicator;; 3. a number of degrees of freedom, which help to influence or partially steer the electro magnetic fields of the said applicator.

The said applicator claimed herein, is mounted on reasonably desired non-metallic support structure, with the said support structure providing a number of degrees of freedom.

With reference to figure 3 to 4, a yet further novel broad loop based applicator has been invented, forming a constituent part of the invention claimed herein. The said applicator comprises a plurality of coaxial (along line 1-1), parallel (along line 2-t) or tilted (with respect to line 2-2), current sheet based complementing- elements a' -paired face to face-l wherein these said paired complementing-elements a' have: a variable pitch (g+l, as desired), variable gaps 9 (as desired), lengths 1 (as desired), dianèter d (as desired), and dimensions as desired, wherein these said parameters are not necessarily uniform or constant throughout the length of the said applicator.

The herein claimed paired complementing-elements a' are capable of operating under the hereinbefore claimed conditions: 1. I1=I2 (this setup behaves as a standard BLA), 2. I1=-I2 (this setup gives rise to a central region Co where the power deposition is a maximum, and two neighboring regions Cl h C2 where there is minimum power deposition.

3. Il and 12 are in phase quadrature (in this setup, every point in the patient or phantom experiences an induced current, i.e. there are no nulls of power deposition).

These preceding operating conditions can be applied in any combinations, along the length of the herein claimed applicator, to each pair of complementing-element a'. Also, the current input to any desired paired complementing-elements at can be switched on or switched off or varied as desired.

The ends of each hereinbefore claimed complementing element a' is folded back non-linearly. However, without departing from the scope of the invention, the said ends may be folded back linearly, eq. as shown by the dotted lines in figure 4.

The herein claimed individual or paired complementing elements a' are tuned in accordance with the hereinbefore claimed methods.

The matching of the herein claimed individual or paired or a plurality of complementing-elements a', are achieved in accordance with the hereinbefore claimed methods.

The herein claimed complementing elements a' can be intercoupled or decoupled or their state of tuning may be varied as desired.

The hereinabove claimed applicator (of figure 4) provides a number of degrees of freedom which help to improve the variation of the electromagnetic fields along the central axis of the said applicator, and to influence or to steer partially the electromagnetic fields of the said applicator, part of the invention claimed herein.

The said applicator claimed herein, is mounted on a desired non-netallic support structure, with the said support structure providing a number of degrees of freedom.

With reference to figure 5, an exemplary modification of the hereinbefore claimed complementing-elements a' (of figure 4 claimed hereinbefore) can be introduced -without departing from the scope of the invention- comprising co#plementing-elements. a#. The said complementing-elements a" nay he made: 1. in accordance with the claims made herein before for the constituent elements or complementing-elements of the hereinbefore claimed applicators; 2. to operate under a variety of conditions, i.e.:: - with Il=Il'=I2=I2' -0 phase difference between the complementing-elements a", acting like the applicator claimed hereinbefore in figure 2, - with Il=Il' and I2=I2' -acting like the applicator claimed hereinbefore in figure 4, - with any remaining combinations of the currents Il,Il',I2,I2'; 3. to operate under the hereabove mentioned conditions, with the said conditions being applied, in any possible combinations, to the plurality of the said complementing-elements a"; I 4. to provide intercoupling or decoupling, as desired; 5. to provide a number of degrees of freedom, eq.:: - with the complementing-elements 3t capable of moving -independently or in harmony or in combinations- along the X-, the Y-, or the Z- axes; or tilting; - with the gaps g and dimensions of the complementing-elements a" selected as desired: thus helping to improve the variation of the electromagnetic fields along the central axis of the said applicator, and to influence or to steer partially the electromagnetic fields of the said applicator.

The ends of each said complementing-element a" may, as yet another exemplary modification, be folded back linearly, eg. as shown by the dotted lines in figure 5.

with reference to figure 6, cylindrical ferrimagnetic materials fm (of desired geometry and permeability) nay be magnetized by an (time-varying) external magnetic field He which, depending on the amplitude of the original RF current (generated by the BLA), give rise to a magnetic field Ho at the centre of said material fm. Also, owing to the finite size of the said materials fm, free poles are induced at their ends which in turn give rise to a magnetic field Hd that opposes the direction of the magnetization.

Consequently, the said ferrimagnetic materials fm, when placed nearby a region containing alternating electromagnetic fields (eg. inside the hereinbefore claimed applicators), can, depending on their permeability influence these fields.

With reference to figure 6, a series of arrangements of ferrimagnetic materials fm, introduced into and/or nearby the hereinbefore claimed applicators, modify -desirably- the electromagnetic fields of said applicators, forming part of the invention claimed herein.

With reference to figure 7, a number of (or individual) ferrimagnetic blocks fb -of desired dimensions and characteristics- encompass the hereinbefore claimed applicators, providing: .1. effects to influence -desirably- the electromagnetic fields of said applicators; 2. partial steering -as desired- of the electro magnetic fields of said applicators; 3. a number of degrees of freedom; constituting part of the invention claimed herein.

The power to these ferrimagnetic blocks fb can be switched on or switched off or varied, as desired; and the effects of said blocks fb can be applied in a number of combinations; forming part of the invention claimed herein.

The said blocks fb claimed herein, are mounted on a desirable non-metallic support structure, with the said support structure providing a number of degrees of freedom.

Modifications may be incorporated without departing from the scope of the invention. for example, the applicator (of figure 4) claimed herein may be modified in accordance with that introduced in figure 5.

Claims (23)

WHAT I CLAIM IS:

1. A Broad Loop Applicator, hereinafter referred to as a BLA, surrounding the load (for example a patient) or part of the load, to apply high frequency magnetic fields to the said load or part of load in a controlled manner. The BLA consists of sheet metal surrounding, but not in contact with, the load, and the high frequency electric current is caused to flow circumferentially round the metal in order to produce a high frequency magnetic field within the load.

2. A BLA as claimed in claim 1, wherein the sheet metal is divided into a plurality of loops separated axially.

3. A BLA as claimed in claim 1, wherein the sheet metal is divided into a plurality of co-axial loops (illustrated in Figure 2) separated axially.

4. A BLA as claimed in claim 3, wherein the said co-axial loops are not in electrical contact with each other.

5. A multiple-loop BLA as claimed in any one of claims 2 to 4, wherein the high frequency currents are caused to flow circiinferentlally in each loop, with means to control the magnitude of the high frequency current in each loop separately. By this means the high frequency magnetic field distribution inside the set of loops can be adjusted to approach a desired optimum.

6. A multiple-loop BLA as claimed in claim 5, wherein the high frequency currents in each loop, or in a plurality of loops, are applied at different phase angles, in addition to different magnitudes. By this means, more control of the high frequency magnetic field inside the set of loops can be achieved,

7. A BLA as claimed in claim 1, wherein the sheet metal is divided into a plurality of arcs separated circumferentially.

8. A BLA as claimed in claim 1, wherein the sheet metal is divided into a plurality of arcs (as illustrated in Figures 4 and 5) separated circumferentially and not in electrical contact with each other.

9. A BLA comprising a plurality of 'multiple-arc BLAs as claimed in any one of claims 7 to 8', separated axially.

10. A BLA comprising a plurality of co-axial 'nultiple-arc BLAB as claimed in any one of claims 7 to 8', separated axially.

11. A BLA as claimed in any one of claims 9 to 10, wherein the said multiple-arc BLAs are not in electrical contact with each other.

12. A BLA as claimed in any one of claims 7 to 11, wherein the high frequency currents are caused to flow circumferentially in each arc, with means to control the magnitude of the high frequency current in each arc separately.

In order to maintain continuity of high frequency current flow, partial return arcs of metal are required as shown in Figures 4 and 5, and would normally be positioned at a greater radius than the main arcs.

13. A BLA as claimed in claim 12, wherein the high frequency currents in each arc, or in a plurality of arcs, or in any plurality of arcs constituting the said BLA, are applied at different phase angles, in addition to different magnitudes. This allows substantial additional control of the high frequency magnetic field distribution inside the said set of arcs, and, in particular, can be used to avoid "cold spots" in hyperthermic treatment of patient.

14. A BLA as claimed in claim 13, wherein a plurality of arcs are intercoupled or decoupled.

15. A BLA system as claimed in any of claims 1 to 14, wherein pieces of ferromagnetic or ferrimagnetic material introduced into and/or nearby the metal structure, but outside the load or the patient, are used to control the high frequency magnetic field distribution in their vicinity (illustrated in Figure 6).

16. Pieces of ferromagnetic or ferrimagnetic material as claimed in claim 15, wherein the high frequency magnetic properties can be varied.

17. Pieces of ferromagnetic or ferrinagnetic material as claimed in claim 15, wherein the high frequency magnetic properties can be varied electrically by means of partial magnetic saturation produced by direct current applied to appropriate windings of wire conductor on the said pieces of material (illustrated in Figure 7).

18. Tuning to the working frequency of each of the loops as claimed in claims 2 to 6, and each of the arcs as claimed in claims 7 to 14, wholly or partly by a capacitor formed by parallel plates of the same metal sheet which form the loop or arc, separated by a layer of suitable solid dielectric (illustrated by CP in Figure 1, and by the overlap area with separation d' in Figure 2).

19. Means of electrically matching any tuned element as per claim 18 to a standard impedance high frequency power source.

20. Means of impendance matching as claimed in claim 19, wherein use is made of: - ferrite material based transformer(s) (balanced or unbalanced; with a desired turns ratio), - four terminal network(s) (for example, an network with identical, ganged, series arm capacitances, and with a desired phase shift), - variable capacitor(s) that is (are) controlled manually and/or automatically and/or remotely, in the given order, or in any other orders and/or combinations.

21. A BLA substantially as hereinbefore described with reference to Figures 2 to 3.

22. A BLA substantially as hereinbefore described with reference to Figures 3 to 4.

23. A BLA substantially as hereinbefore described with reference to Figures 3 to 4 and modified by Figure 5 and/or Figure 6 and/or Figure 7.