Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
1998-06-23
2001-03-27
Cohen, Lee (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C607S154000, C607S156000
Reexamination Certificate
active
06208903
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a microwave applicator and the operation of that applicator to achieve hyperthermia and, more particularly, to the employment of a microwave antenna array for use in, for example, thermally induced lipoatrophy.
BACKGROUND
Hyperthermia involves the heating of living tissues for therapeutic purposes, such as for increasing blood flow to a particular part of the body. Hyperthermia has been used as a method of treating tumors by means of raising the temperature of the tumor locally, or in the region surrounding the tumor. Hyperthermia can also be effective in reducing adipose tissue through fatty cell necrosis or apoptosis.
Electromedical methods and apparatus for removing target tissue have been disclosed in conjunction with various therapeutic procedures, some of which are non-invasive. For example, U.S. Pat. No. 4,527,550 to Ruggera et al. discloses a radio-frequency diathermy apparatus, including means for localizing the heat focus for eliminating tumor cells. U.S. Pat. No. 4,397,313 to Vaguine discloses a microwave hyperthermia apparatus, including a means for focusing electromagnetic energy at a particular region of the body. U.S. Pat. No. 3,958,559 to Glenn et al. discloses an ultrasonic transducer for focusing ultrasonic waves for non-invasive treatment of internal structures, for example, tumors, within the body.
Although these systems are useful for non-invasive treatment of target tissues, none are specifically directed to the more general application of removing either tumor cells in deeper tissue layers or fat cells within a largely intact subcutaneous fat layer. In fact, each of these systems recognizes the inherent differences between fatty tissue and tumor tissue and teaches the need for avoiding damage to adipose and other normal tissues adjacent to the tumor. Vaguine and Glenn, for example, point to the differing heat tolerance of tumor cells in the context of preserving fatty and other cells adjacent the target tumor cells, not reducing them. Furthermore, the device disclosed by Vaguine uses an element field polarization more appropriate for treating deep tissues below the fat layer, rather than for treating the fat layer itself.
Accordingly, those skilled in the art would desire a generally applicable substantially non-invasive microwave applicator that could be used to induce hyperthermia in living tissue for therapeutic purposes such as either tumor removal or fatty cell necrosis.
SUMMARY
There is, therefore, provided in practice of the present invention a general purpose microwave applicator for reducing or eliminating target tissue. The applicator comprises an antenna element array, a control system and a bolus. The antenna elements generate an electromagnetic surface wave. The control system adjusts the amplitude and phase of the antenna array elements for preferentially heating target tissue. The bolus conditions the microwaves and cools the skin surface upon application of the microwaves.
In a presently preferred embodiment, the microwave applicator is used to remove adipose tissue through hyperthermia-induced fatty cell necrosis or apoptosis. In operation, the applicator generates a cylindrical, converging, quasi-transverse electromagnetic surface wave within the fat layer as a function of the differing dielectric and conductivity characteristics of the skin layer and muscle layers surrounding the fat layer. By launching a wave trapped between these layers from substantially all directions surrounding an intended focus, a converging cylindrical wave is produced which induces a column of high power density along a focal line within the fat extending from the skin-fat interface to the muscle-fat interface. The amplitude and phase for the individual antenna elements on the microwave applicator can be adjusted to move the focal line within a target fat region. Simultaneously with application, the bolus actively cools the skin surface to prevent skin burns and acute pain. As a given fat region is treated, the applicator is moved and applied over adjacent regions until the desired fat reduction is achieved.
The control system includes a computer-implemented software program for choosing antenna array excitations, and a novel phase shifting circuit. In one embodiment, the system incorporates a relatively simple and efficient method of focusing in which the amplitudes of all of the antenna input voltages are held constant and the phase is adjusted to obtain constructive interference at the projected focus. In another embodiment, the system enables adjustment of not only the focal position projected on to the bolus of the applicator but also the depth. This method involves selecting the three dimensional coordinate of the focal point, fixing the power level at that point, and reducing as much as possible the power level everywhere else.
The novel phase shifting circuit includes a two-way power divider and unidirectional amplifier for channeling power in a single direction to multiple ports, and a compensating network for reducing variation in amplitude with phase shift. An advantage of the novel phase shifter is that it replaces the typically more expensive and larger circulators used in conventional phase shifters. The novel phase shifter also has a gain generally larger than unity (instead of a positive insertion loss), and reduced output amplitude variation versus phase.
The antenna array is preferably formed of a plurality of monopole-like antenna elements. Each element includes 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, and a plurality of short circuiting pins placed symmetrically about the center pin. The shorting pins enable adjustment of the resonant frequency and input impedance of the antenna element, thereby providing additional control.
The antenna elements are preferably coupled to a novel antenna protection circuit. The antenna protection circuit includes a PIN diode, a PIN diode biasing circuit, 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. In operation, the detector causes the 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.
The bolus preferably includes a water equivalent ceramic body and liquid-carrying channels disposed within the body. The ceramic is preferably chosen so the leaky wave pole associated with the bolus and tissue model matches the complex wave number of fat. The bolus further includes a lossy wedge encompassing the outer periphery of the applicator for absorbing power incident on the edge of the array and reducing reflections that can result in undesired hotspots.
At least two novel methods according to the present invention are also disclosed to reduce fat. The first involves the well-controlled noninvasive induction of lethal thermal damage to fat cells over defined volumes and with relatively short-duration periods of heating using the principle of the exponential time-temperature isoeffect relationship for tissue. The second involves the well-controlled noninvasive induction of heat at levels to induce apoptosis within fat cells using either the principle of the exponential time-temperature isoeffect relationship for tissue, or using conventional hyperthermia. In operation, the control system selects the amplitude and phase of the antenna element excitation voltages for a given set of sequential foci, determines the power density at each focus, sets the heating pulse duration at each focus, and sequences the foci to obtain a substantially uniform thermal dose within the targeted fat while minimizing the maximum thermal dose in the non-target tissues.
In another embodiment of the present invention, the fatty tissue may be infiltrated with substances by transcutaneous injection before, during or after trea
LeVay Peter
Richards William F.
Christie Parker & Hale LLP
Cohen Lee
Medical Contouring Corporation
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