US20070149959A1 - Cryoprobe for low pressure systems - Google Patents

Abstract

A cryoprobe for use in cryosurgery and other applications comprising a rigid outer tube, an inner coolant inlet tube a short rigid penetrating segment extending distally from the distal end of the outer tube and a helical-shaped baffle having a heating element disposed about the outer surface of the inlet tube. The baffle is adapted to produce turbulent fluid flow improving heat transfer and is able to warm target tissue during rapid freezing and thawing cycles.

Description

FIELD OF THE INVENTIONS
• The inventions described below relate the field of cryoprobes and more specifically to cryoprobes used in surgical procedures.
BACKGROUND OF THE INVENTIONS
• Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue masses, causing the tissue to die after which it will be absorbed by the body, expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases.
• A variety of cryosurgical instruments, referred to as cryoprobes, cryosurgical ablation devices, and cryostats and cryocoolers, have been available for cryosurgery. The preferred device uses Joule-Thomson cooling in devices known as Joule-Thomson cryostats. These devices take advantage of the fact that most gases, when rapidly expanded, become extremely cold. In these devices, a high pressure gas such as gaseous argon or gaseous nitrogen is expanded through a nozzle inside a small cylindrical sheath made of steel, and the Joule-Thomson expansion cools the steel sheath to sub-freezing cryogenic temperature very rapidly.
• Present cryoprobes utilizing Joule-Thomson systems have inherent disadvantages such as inefficient heat transfer, the possible occurrence of vapor lock and excessive use of cryogen. As a result, these systems require use of large quantities of gasses under high pressure and high flow rates, in part, to prevent vapor lock. Use of high-pressure gasses increases the overall costs of cryoprobes. This is due to the higher costs of materials required for use with systems utilizing high-pressure gases, the high cost associated with keeping source gases themselves at higher pressures and the large quantities of cryogen required for use with these systems. What is needed is a cryoprobe system requiring low pressure with low fluid volume and flow rates that avoids vapor lock and reduces the quantities of cryogen required by using cryogen more efficiently.
SUMMARY
• The devices and methods described below provide for the cryo-ablation of a mass of targeted tissue. The devices include a probe with structures that permit the surgeon to secure and form an ice mass of a suspect mass or tumor. The probe is provided with a rigid tube and a sharp distal segment. To secure the tumor to the probe, the surgeon pierces the tumor with the distal segment. Inlet tubing extending within the rigid tube directs coolant to the distal tip to cool the tip. A helical-shaped baffle comprising a heating element is provided in the distal section of the cryoprobe to create turbulent fluid and improve heat transfer. Since the baffle comprises a heating element, it can be further used in rapid freezing and warming cycles directed at targeted tissue masses.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates a cryoprobe.
• FIG. 2 shows a partial sectional side view of the distal end portion of the cryoprobe.
• FIG. 3 shows a partial isometric sectional view of the distal end portion of the cryoprobe.
• FIG. 4 illustrates a cryoprobe with a baffle having a cross-shaped cross-section disposed about the inlet tube.
• FIG. 5 illustrates a cryoprobe with a baffle having a sprocket cross-section disposed about the inlet tube.
• FIG. 7 depicts a cryoprobe having an outer tube with a grooved inner diameter.
• FIG. 8 illustrates a cryoprobe with a baffle comprising a tubular-shaped insulator and a heating element wound about the distal section of the inlet tube.
DETAILED DESCRIPTION OF THE INVENTIONS
• FIG. 1 illustrates a cryoprobe1. The cryoprobe uses liquid nitrogen cooling to create a cooled region at thedistal end2. This cooled region adheres to a targeted lesion or tumor and creates an ice mass from the targeted tissue. The cryoprobe comprises a long, slender yet rigidouter tube3. A short rigidpenetrating segment4 extends distally from the distal end of the rigid tube, and asuitable handle5 is mounted on the proximal end of the tube. The handle is placed in fluid communication with aconsole6 and the console is place in electrical communication with apower source7 and fluid communication with acryogen source8. The console has a control system that is able to regulate use of power and the flow of cryogen to the cryoprobe.
• FIG. 2 shows a partial sectional side view of the distal end portion of the cryoprobe1 whileFIG. 3 shows a partial isometric sectional view of the distal end portion of the cryoprobe1. The cryoprobe1 comprises a rigidouter tube3 and an innercoolant inlet tube9. A short rigidpenetrating segment10 extends distally from the distal end of theouter tube3. Thecoolant inlet9 tube passes through theouter tube3, extending to the distal end of theouter tube3, terminating just proximal of the distal tip of the penetrating segment leaving achamber11 between the distal end of theinlet tube9 and the proximal end of thepenetrating element4. The inlet tube may terminate by merely a straight cut or have a small nozzle of smaller internal diameter than the immediately upstream portion of the inlet tube. Theouter tube3 is made from stainless steel. However, the outer tube may also be manufactured from aluminum, brass, ceramics or MRI compatible materials. Theinlet tube9 is made from a polyetheretherketon (PEEK) or other lower thermally conductive material having a pressure and temperature capability sufficient for the pressures and temperatures anticipated for the particular application. Use of lower thermally conductive materials for theinlet tube9 reduces the amount of cryogen required by the cryoprobe1.Suitable inlet tube9 material includes fluoropolymer tubing (FEP), Teflon®, polyimide and polyurethane.
• Theouter tube3 has an outer diameter of about 2.7 mm, an internal diameter of about 2.4 mm, and a length of about 40 mm. Theinlet tube9 has an outer diameter of about 0.76 mm and an inner diameter of about 0.64 mm. These dimensions may vary depending on the materials used and the application for the cryoprobe. Thepenetrating segment4 comprises a sharpdistal tip12. As can be seen from the cross section, the sharp distal tip is solid and adapted for piercing through a tumor. The length of the penetrating segment is chosen to be approximately the same size as the target tissue mass to be sampled. This penetrating segment is forced into a lesion or tumor. Anannular cavity13 or lumen is created by the outer surface of the inlet tube and the inner surface of the rigidouter tube3. The liquid exiting the orifice of theinlet tube9 counter-flows along the annular cavity and is exhausted from the probe to a suitable point far removed from the probe.
• A helical-shaped baffle14 comprising aheating element15 is disposed about the outer surface of a distal portion of the inlet tube and extends proximally about 18 mm from the distal end of the inlet tube. However, thebaffle14 may extend up to about 40 mm proximal to the distal end of theinlet tube9. The helical-shaped baffle is adapted to produce turbulent fluid flow in fluid flowing past the outer surface of the inlet tube. Thebaffle14 improves heat transfer by creating turbulent flow and forcing the cryogen outward to come in contact with the inner diameter surface of the outer wall in the distal section of the cryoprobe. Thebaffle14 can comprise a separate extrusion, a machined part or a preformed wire. Thebaffle14 may be formed by winding theinlet tube9 about the longitudinal axis or a second helical-shaped baffle may also be provided in the distal section of the probe.
• Theheating element15 and thebaffle14 may be unitary and made from the same material or theheating element15 may be separate from the baffle and made from a different material. When the heating element and baffle14 are unitary thebaffle14 is manufactured from a material capable of being heated when placed in electrical communication with a power source. InFIG. 2, thebaffle14 is manufactured from nichrome wire placed in electrical communication with a power source. Thus, thebaffle14 provides both turbulent fluid flow while also able to function as a heating element. InFIG. 3, thebaffle14 is a helical structure machined from brass and theheating element15 is a separate material disposed within the baffle. The temperature of the heating element is regulated by the console. Athermocouple16 is disposed on the distal section of the cryoprobe1 to measure temperatures at the probe tip. InFIG. 6, the baffle
• FIGS. 4-6 illustrate cross-sections of various cryoprobes1 having anouter tube3 withbaffles14 comprising a heating element having differing configurations and disposed about the outer surface of the inlet tube.FIG. 4 illustrates a cryoprobe with a baffle having a cross-shaped17 cross-section disposed about the inlet tube.FIG. 5 illustrates a cryoprobe with a baffle having asprocket cross-section18 disposed about the inlet tube. InFIG. 6, the baffle comprises a cross-section with opposing arcuatetrapezoidal sections19 disposed about the inlet tube. The baffles inFIGS. 4-6 improve heat transfer by creating turbulent flow while forcing the cryogen outward towards the inner diameter surface of the outer wall in the distal section of the cryoprobe where the non-target body tissue can further act as a heat sink.
• FIG. 7 depicts a cryoprobe1 having anouter tube3 with a groovedinner diameter20. The cryoprobe comprises an outer3 tube and an innercoolant inlet tube9. A short rigid penetratingsegment4 extends distally from the distal end of the outer tube. The coolant inlet tube passes through the outer tube, extending to the distal end of the outer tube, terminating just proximal of the distal tip of the penetratingsegment4 leaving a chamber between11 the distal end of theinlet tube9 and the proximal end of the penetratingelement4.
• The inner diameter of theouter tube3 is provided with helical-shapedgroove21 disposed about the inner surface of a distal portion of the outer tube. The grooves are adapted to produce turbulent fluid flow in fluid flowing past the inner surface of the outer tube. Aheating element15 such as nichrome wire in electrical communication with a power source is disposed in the distal section of the probe. Thebaffle14 extends approximately 20 mm along the distal section of theinlet tube9. A thermocouple is also disposed on the distal section of the cryoprobe to measure temperatures at the probe tip.
• A cryoprobe1 with abaffle14 comprising a tubular-shapedinsulator30 and aheating element15 wound about the distal section of theinlet tube9 is illustrated inFIG. 8. The tubular insulator is manufactured from silicone while the heating element is manufactured from nichrome wire. This baffle and heating element configuration creates a tornado flow pattern in the exhaust cryogen. As the exhaust fluid flows past the baffle and heater wire, the pressure and inertia of the fluid creates a vortex while the exhaust fluid it forced towards the inner surface of theouter tube3. Acollar31 having low electrical conductivity, but high thermal conductivity, may also be provided and disposed within the inner diameter of the outer tube to prevent electrical current from flowing from the heating element to theouter tube3. InFIG. 8, thecollar31 is manufactured from a high purity, aluminum-nitride machineable ceramic with high strength and high thermal conductivity such as Shapal-M®.
• When the cryoprobe1 is in use, theinlet tube9 is placed in fluid communication with a lightly pressurizedliquid nitrogen source8 by means of an inlet fitting. The pressures at thenitrogen source8 can range from approximately 0.5 bar to about 30 bar. The liquid nitrogen at its source preferably has a source pressure of about 1.5 bar. The liquid nitrogen is supplied to the assembly through a pressure fitting, flows through a fluid supply line, flows through the inlet tube and exits the distal end of theinlet tube9. The distal end of theinlet tube9 is exposed to a cavity at the distal end of theouter tube3 closed by the rigid penetratingsegment4. After expanding in the chamber, the fluid is at lower pressure and exhausts over the exhaust pathway which includes flow over outside of the inlet tube and the baffle. Typical pressure drops for the cryoprobe can be up to about 10% in the supply line, about 30% in the inlet tube and about 30% over thebaffle14. The liquid nitrogen cools the distal tip of the probe to temperatures as low as −196° C. when steady flow has been established. The liquid nitrogen cools the inner surface of the rigid penetratingsegment4, thereby cooling the outer surface of the segment. The outer surface of the penetratingsegment4 is placed against the targeted tissue to be cooled by the physician and the targeted tissue becomes an ice mass. Fluid flowing past the outer surface of the inlet tube is placed in contact with the helical-shaped baffle creating a turbulent helical flow path and forcing the cryogen towards the inner surface of theouter tube3. Turbulent fluid flow provides for improved heat transfer between the cryoprobe and targeted tissue. As the liquid nitrogen boils, the exhaust gas flows through the remainder of the exhaust gas pathway which includes the flexible tube and the vent which vents the exhaust gas to atmosphere. Depending on the flow rates of the nitrogen, boiling can occur once the nitrogen flows past thebaffle14. In order to minimize cryogen consumption, flow rates can be reduced to a level where the nitrogen is about 90% vapor by the time it flows past thebaffle14. A second heating element may be disposed in the handle and placed in thermal communication with the exhaust gas, so the exhaust gas can be vented near room temperature at the handle and not vented at the console.
• In many surgical applications, it is beneficial to have a means for warming the cryoprobe1 quickly. This is desired for therapeutic and practical reasons. Current theory suggests that two cycles of rapid freezing and thawing provides better cryoablation than a single freeze. Practically, it can take a long time for the ice mass to thaw so that the cryoprobe can be withdrawn from the body. Unless natural thawing is medically indicated, natural thawing is a waste of time. Therefore, a means for heating the targeted tissue is also provided within the cryoprobe1. Since thebaffle14 is constructed from nichrome heater wire, thebaffle14 may be quickly heated during cycles of rapid freezing and warming of the targeted tissue. Once the ice mass has been formed, the heating element can heat the distal end of the cryoprobe to temperatures ranging between about 20 to about 60. For optimal results, temperatures of about are used for fast removal of the cryoprobe1 with minimizing risk of damage to tissue adjacent to the targeted tissue.
• While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. Other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims.

Claims (6)

1. A device comprising:

a rigid outer tube;

a coolant inlet tube disposed within the outer tube;

a short rigid penetrating segment extending distally from a distal end of the outer tube;

and a helical-shaped baffle having a heating element disposed about a distal outer surface of the inlet tube, said baffle adapted to create turbulent fluid flow in fluid and force cryogen towards an inner surface of the outer rigid tube.

2. The device ofclaim 1 wherein the baffle and the heating element are unitary.

3. The device ofclaim 2 wherein the baffle comprises nichrome wire.

4. The device ofclaim 1 wherein the baffle comprises an extrusion, a machined part or a preformed wire.

5. A device comprising:

a rigid outer tube having an inner diameter;

a coolant inlet tube disposed within the outer tube;

a short rigid penetrating segment extending distally from a distal end of the outer tube;

a helical-shaped baffle disposed about the inner diameter surface of the rigid outer tube; and

a heating element disposed within the distal section of the outer tube.

6. A system for use in cryogenic surgery comprising:

a liquid nitrogen cryogen source; and

a cryoprobe in fluid communication with the cryogen source, said cryoprobe comprising a handle;

a rigid outer tube coupled to the handle;

a coolant inlet tube disposed within the outer tube in fluid communication with the liquid nitrogen source;

a short rigid penetrating segment extending distally from a distal end of the outer tube;

and a helical-shaped baffle adapted to create turbulent fluid flow in fluid having a heating element, said baffle disposed about a distal section of the inlet tube.

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