TECHNICAL FIELD OF INVENTION
The present invention generally relates to improved medical device and methods for treating tissues, and more particularly, to such a medical device and methods for treating the brain, nerve, capillary, coronary artery, tumor, atherosclerosis, or liver in a patient by delivering controlled therapeutic energy through a sensing element for treating the target tissue and sensing the tissue temperature for controlling energy therapy.
BACKGROUND OF THE INVENTION
A capillary blood vessel is one of the tube-shaped blood vessels that carry blood away from the arterioles to the body's tissues and organs. When a capillary is impaired, radiofrequency (RF) ablation therapy or cryogenic ablation therapy can be applied to the capillary to treat the tissue. To ensure proper treatment, temperature at the lesion is sensed and the temperature reading is transmitted to an external monitor for temperature monitoring and for controlling energy delivery. A conventional ablation device, for example the device disclosed by Webster, Jr. in U.S. Pat. No. 5,893,885 comprises an electrode for RF energy delivery with a temperature sensor soldered under the electrode for measuring tissue temperature. The bulky size of the conventional ablation device might pose safety concerns to a patient when it is forced into a place of a capillary. A miniaturized energy-delivery device is needed to pass into the tiny capillary opening for tissue treatment. The “ablation energy” in this invention is generally referred to either thermal energy (hyperthermic) or cryogenic energy (hypothermic).
A liver cancer or tumor is difficult to treat because of its softness and hard to reach. Ablation therapy, either hyperthermic or hypothermic, has been applied to treat the liver tissue. However, the existing ablation device can only treat the surface of the liver because of the device's bulky construction comprising at least one electrode with a temperature sensor secured under around the electrode. A miniaturized energy-delivery device is needed to reach a liver and optionally into the liver for therapeutic treatment.
Similarly, a nerve is located within a restricted space which is difficult for a bulky ablation device to get access to. A miniaturized energy-delivery device is needed to reach a nerve for therapeutic treatment.
One method of treating cellular tissues in vivo has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to or withdraws heat from the tissues, and causes cell apoptosis. It can be performed on a minimally invasive fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective.
In the hyperthermic therapy, RF therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. RF energy through a temperature sensing element of the present invention, when coupled with a temperature control mechanism, can be supplied precisely to the device-to-tissue contact site to obtain the desired temperature for treating a tissue.
Another type of tissue ablation methods might include “cold therapy”. Larsen et al. in U.S. Pat. No. 5,529,067 discloses methods and apparatus for use in procedures related to the electrophysiology of the heart. Specifically, Larsen et al. discloses an apparatus having thermocouple elements of different electromotive potential conductively connected at a junction, whereby an electrical current is passed through the thermocouple elements to reduce the temperature of the junction in accordance with the Peltier effect and thereby cool the contacted tissue. A detailed description of the Peltier effect and an apparatus utilizing the Peltier effect is set forth in U.S. Pat. No. 4,860,744 entitled “Thermoelectrically Controlled Heat Medical Catheter” and in U.S. Pat. No. 5,529,067 entitled “Methods For Procedures Related to the Electrophysiology of the Heart”, the entire contents of both of which are incorporated by reference herein.
The above-mentioned prior art has the advantage of using the device as a treatment apparatus; however, they do not provide any means for sensing temperature and applying ablation energy using the same miniaturized non-electrode sensing element to reach the target tissue at a restricted place.
A thermocouple is a temperature sensing device consisting of a junction or joint of two dissimilar metals which has a millivolt output proportional to the difference in temperature between the “hot” junction and the lead wires (cold junction). Temperature measurements using a thermocouple are based on the discovery by Seebeck in 1821 that an electric current flows in a continuous circuit of two different metallic wires if the two junctions are at different temperatures. In electric circuits, the current is dependent on the electromotive force developed and the resistance of the circuit. For accurate temperature measurements, the measuring instrument is constructed so that a no-current electromotive force is measured to eliminate the effects of circuit resistance. The materials used for the wires typically include copper, nickel-chromium, iron, platinum, nickel-aluminum, and Constantan. A good reference for more information on thermocouples is Perry's Chemical Engineer's Handbook 6th Edition, published by McGraw-Hill Book Company, 1973.
A thermister is a temperature-sensing device manufactured of a mixture of metal oxides. A large change in resistance is exhibited proportional to a change in temperature. Electrical conductors experience a change in resistance with temperature which can be measured with a Wheat-stone-bridge circuit. The relationship for platinum reference is very exact and hence serves as a primary standard over a wide temperature range. A good reference for more information on thermister is Mark's Standard Handbook for Mechanical Engineers 8th Edition, published by McGraw-Hill Book Company, 1978.
Thermostatic bimetal thermometers can be defined as a composite material made up of strips of two or more metals fastened together. Types of elements used in bimetal thermometers are flat spiral, single helix, and multiple helixes. This composite, because of different expansion rates of its components, tends to change curvature when subjected to a change in temperature.
One major drawback of the conventional ablation devices, either hyperthermic or hypothermic, is its bulkiness. For example, a conventional RF ablation catheter generally comprises at least one electrode with its associated temperature sensing element secured under, behind, or around the electrode. The total space needed for an electrode and its additional temperature sensing element makes the device not suitable for certain tissue ablation applications due to the tissue's restricted location or space. Therefore, there is a clinical need for an improved ablation device system having the capabilities of measuring tissue temperature, delivering therapeutic energy (hyperthermic, hypothermic or a combination thereof), and/or controlling the energy delivered for optimal effectiveness in the tissue treatment.
SUMMARY OF THE INVENTION
In general, it is an object of the present invention to provide a method and an improved ablation device system for treating the nerve, brain, capillary, liver, artery, prostate, other tissue, or atherosclerosis. It is another object of the present invention to provide a method and a device system for monitoring the temperature of the target tissue, and to control the temperature by utilizing a temperature control mechanism and/or algorithm for energy delivery. It is still another object of this invention to provide a method and an ablation device system for treating the nerve, brain, capillary, liver, artery, prostate, other tissues, or atherosclerosis in a patient by applying RF current through a temperature sensing wire to a temperature sensing element, wherein the temperature sensing element has duel functions of temperature sensing and energy delivery. It is another object of this invention to provide a method and an ablation device system for treating the nerve, brain, capillary, liver, artery, prostate, other tissues, or atherosclerosis in a patient by applying Peltier Effect principles through two temperature sensing wires having dissimilar electromotive potentials to a temperature sensing element as a joint of the two wires, wherein the temperature sensing element has duel functions of temperature sensing and cryogenic ablation therapy.
The “ablation energy” is this invention refers generally to hyperthermic energy (such as radiofrequency energy), hypothermic energy (such as cryogenic energy per Peltier effects), and a combination thereof for tissue treatment.
Briefly, heat is generated by supplying a suitable energy source to a device, such as radiofrequency, ultrasound, microwave energy, alternating current energy, or laser energy. In conventional radiofrequency applications, an electrode with its underside-secured temperature sensor constitutes as the tissue contact region for treating tissues. In the present invention, energy can be applied to the non-electrode temperature sensing element and consequently to the tissues directly without passing through an electrode of a conventional device. A DIP (dispersive indifferent pad) type pad, that contacts the patient, is connected to the Indifferent Returning Connector on the RF generator. Therefore, the RF energy delivery becomes effective when a close circuit from a RF generator through a patient and returning to the RF generator is formed. The generator should be grounded to avoid electrical interference. Heat is controlled by the power of the RF energy delivered, the delivery mode, and by the delivery duration. The standard RF energy generator means and its applications through a conventional electrode structure, to a patient are well known for those who are skilled in the art.
In a preferred embodiment, a method for treating tissue of a patient comprises sensing temperature of the tissue using a sensing element of a medical device and applying ablation energy to the tissue through said sensing element of the medical device. The ablation energy may be hyperthermic energy, hypothermic energy or a combination thereof. In one particular embodiment, the hyperthermic energy is radiofrequency energy.
The ablation device system may further comprise temperature control mechanism for receiving temperature readings from the temperature sensing element, wherein the temperature measured from the temperature sensing element is relayed to the temperature control mechanism and is adapted to effect the RF current delivery to the temperature sensing element of the ablation device system. The RF current is preferably within the range of 50 to 2,000 kHz; though it may cover from below 50 kHz to beyond 2,000 kHz.
The temperature sensing element may consist of a thermocouples type temperature probe, a thermistor type temperature probe, a bimetal thermometers type temperature probe, and the like. In a further embodiment, the temperature sensing element may be enclosed within an elongated tubular shaft, wherein the elongated tubular shaft may further comprise a fluid passageway adapted for receiving fluid from a fluid source and venting fluid out of the elongated tubular shaft. In another embodiment, a distal portion of the elongated tubular shaft is conductive and is in contact with a portion of the temperature sensing element.
In another preferred embodiment, a method for treating tissue of a patient comprises sensing temperature of the tissue using a sensing element of a medical device and applying ablation energy to the tissue through said sensing element of the medical device, wherein the temperature sensing element comprises a joint of two wires, the two wires having dissimilar electromotive potentials conductively connected at the joint. In one embodiment, the hypothermic ablation energy is provided to the joint according to Peltier effects. Furthermore, a delivery mode of the ablation energy to the sensing element is a combination of hyperthermic energy and hypothermic energy in an alternate mode or a pulsed mode.
A medical device for sensing tissue temperature and treating tissue of the present invention comprises a sensing element, wherein the sensing element comprises a joint; two wires conductively connected at the joint; and a source of radiofrequency current being connected to one of the two wires adapted for delivering radiofrequency current to the joint for tissue treatment.
In another preferred embodiment, a medical device for sensing tissue temperature and treating tissue of the present invention comprises a sensing element, wherein the sensing element comprises a joint; two wires conductively connected at the joint, wherein said two wires have dissimilar electromotive potentials; and a heat sink of thermal current being connected to said two wires according to Peltier effects and being adapted for providing cryogenic ablation therapy to the joint for tissue treatment. Alternately, the medical device may further comprise a source of radiofrequency current being connected to one of the two wires adapted for delivering radiofrequency current to the joint for the tissue treatment.
The method and medical devices of the present invention has several significant advantages over other known systems or techniques to treat the tissues located close to a restricted location. In particular, the ablation device system comprising the temperature sensing element and the ablation energy delivery capability using the same temperature sensing element results in a more effective therapeutic effect to the difficult-to-access tissues. The target tissue of the present invention may comprise, but not limited to, a brain tissue, a nerve, an artery, a liver, a prostate, an eye, a vein, a capillary vessel, a vulnerable plaque, an atherosclerotic plaque, a tumor, a cancer, and the like.