Microwave applicator

• US 6,208,903 B1
• Filed: 06/23/1998
• Issued: 03/27/2001
• Est. Priority Date: 06/07/1995
• Status: Expired due to Fees

• Current Assignee: Medical Contouring Corporation
• Original Assignee: Medical Contouring Corporation
• Inventors: LeVay, Peter, Richards, William F.
• Primary Examiner(s): COHEN, LEE S
• Application Number:
  US09/107,908
• Time in Patent Office: 1,008 Days
• Field of Search: 607/100-102, 607/154-156, 218/746-748
• US Class Current: 607/101
• CPC Class Codes: A61B 18/1815 using microwaves
• CPC Class Codes: A61B 2018/00464 Subcutaneous fat, e.g. liposuction, lipolysis
• CPC Class Codes: A61N 5/025 Warming the body, e.g. hyperthermia treatment
• CPC Class Codes: A61N 5/04 Radiators for near-field treatment

Abstract

An apparatus and method for non-invasive removal of target tissues is disclosed. The apparatus includes a microwave applicator antenna element array for introducing a plurality of cylindrical, quasi-transverse electromagnetic surface waves adjacent the target tissue. The applicator is used for reducing fatty tissue within a subcutaneous fatty layer by taking into account the differing dielectric constants of the adjacent skin and muscle layers. A cooling bolus, made of water equivalent ceramic material, actively maintains skin surface temperature below a level at which cell damage or discomfort would occur. A control system for the applicator comprises a software driven digital computer including a program for choosing antenna array excitations. The control system further includes a phase shifting circuit including a compensating network for reducing the variation in insertion loss with phase shift. A monopole-like microstrip antenna element having a plurality of shorting pins is also disclosed for adjusting the resonant frequency and input impedance of the antenna elements. In operation, the fatty cells can be reduced through necrosis or apoptosis through the application of short pulse, high temperature doses of heat using the principle of the exponential time-temperature isoeffect relationship for tissue. In another embodiment of the present invention, the fatty tissue may be infiltrated with substances by transcutaneous injection before, during or after treatment to enhance the effectiveness of the microwave applicator.

Claims

1. A microwave applicator for inducing hyperthermia in target tissue comprising:

a plurality of antenna elements arranged in an array for launching a plurality of electromagnetic waves having a polarization adapted for generating a plurality of electromagnetic surface waves; and

a control system, comprising a system for choosing antenna array excitations and a phase shifter, so that the control system adjusts amplitude and phase of the antenna array elements for converging the electromagnetic surface waves at the target tissue, thereby heating the target tissue.

2. The apparatus of claim 1 wherein the system for choosing antenna array excitations is implemented in software for a digital computer having an output coupled to the phase shifter.

3. The applicator of claim 1 wherein the system for choosing antenna array excitations further comprises:

means for holding input voltage to the antenna elements substantially constant; and

means for adjusting phase to obtain constructive interference at a projected focus.

4. The applicator of claim 1 wherein the system for choosing antenna array excitations further comprises:

means for selecting a focal point;

means for fixing power level at the focal point; and

means for reducing power level at points other than the focal point.

5. The apparatus of claim 1 wherein the phase shifter comprises a two-way power divider for channeling power in a single direction to multiple ports, and a compensating network for reducing the variation in insertion loss with phase shift.

6. The apparatus of claim 1 wherein the plurality of antenna elements include microstrip antennas comprising:

a ground plane;

a top patch insulated by a physical gap from the ground plane;

a center pin connected to the top patch for feeding the antenna element;

a plurality of short circuiting pins placed symmetrically about the center pin for adjusting the resonant frequency and input impedance of the antenna element.

7. The apparatus of claim 1 further comprising an antenna protection circuit coupled to an antenna element, the antenna protection circuit comprising:

a PIN diode;

a PIN diode biasing circuit coupled to the PIN diode; and

a detector, coupled to a PIN diode biasing circuit, for detecting power reabsorbed by the antenna element and comparing the detected power to a threshold, wherein the detector causes the PIN diode biasing circuit to bias the PIN diode as a function of the detected power such that the antenna element appears as a continuous and nonperturbing ground plane when the detected power exceeds the threshold.

8. The apparatus of claim 1 wherein the operating frequency of the applicator is in the range of frequencies of between about 0.9 GHz and about 9 GHz.

9. The apparatus of claim 8 wherein the operating frequency is approximately 2.45 GHz.

10. The apparatus of claim 1 further comprising a bolus structure coupled to the antenna elements, the bolus including:

means for actively cooling skin during operation of the antenna array;

means for filtering undesired spatial frequency components; and

means for coupling the antenna elements to a desired surface wave.

11. The apparatus of claim 1 further comprising a bolus structure coupled to the antenna elements, the bolus including:

a high dielectric layer made of a material having a dielectric constant substantially equivalent to water;

a low dielectric layer adjacent the high dielectric layer;

a plurality of grooves disposed substantially within the high dielectric layer for channeling fluid, wherein the high dielectric layer is bonded to the low dielectric layer to enclose the grooves.

12. The apparatus of claim 11 wherein the bolus structure further comprises a lossy wedge, connected to the low and high dielectric layers, for absorbing surface waves incident upon the edges of the antenna array.

13. The apparatus of claim 12 wherein the respective thicknesses and dielectric constants of the high and low dielectric layers are selected to substantially match leaky wave pole with the complex intrinsic wavenumber of fat layer.

14. The apparatus of claim 1 further comprising a bolus structure coupled to the antenna elements, the bolus including:

a high dielectric layer;

a low dielectric layer adjacent the high dielectric layer;

a frame bonded to the low dielectric layer;

a plurality of posts made of a material having a dielectric constant substantially equivalent to water; and

a layer of plastic sheeting stretched over the posts and attached to the frame.

15. The apparatus of claim 13 wherein the bolus structure further comprises a lossy wedge, connected to the low and high dielectric layers, for absorbing surface waves incident upon the edges of the antenna array.