AU2004200764A1 - Method and apparatus for controlling the freezing temperature and sculpturing the shape of the iceball formation in cryosurgery - Google Patents

Description

Australia Patents Act 1990 Complete specification Standard Patent Method and Apparatus for Controlling the Freezing Temperature and Sculpturing the Shape of the Ice Ball Formation in Cryosurgery Tortal et al. (March 05, 200 3 The following statement is a full description of this invention, including the best method of informing it known to me: Method and Apparatus for Controlling the Freezing Temperature and Sculpturing the Shape of the Ice Ball Formation in Cryosurgery FIELD OF THE RESEARCH io The cryogenic equipment in this invention is programmable to enable the surgeon's own technique of cryoablation. The system operation involved in this/her invention usually relies on a number of 'IF-THEN' statements. This permits the surgeon to implement his/her own strategy based on the surgeon's expert knowledge to solve problems in cryosurgery by allowing ones reasonable intuition.

An operator panel in this equipment provides an independent interface between the operator and the controller using a dedicated function called a man-machine interface (MMI) that will display messages, data and alarms. It can input values to the controller variables making it user-friendly and has a versatile tool for implementation of ones treatment plan and technique. An application page defines operator dialogue screens providing a user-friendly man-machine interface to monitor and modify the values of cryogenic automated program developed. The cryogenic equipment mentioned can also be networked giving capability to be controlled and diagnosed over the Internet. Since it is incorporated to a PC server acting as a primary domain controller, access to the system can only be granted by administrative permission.

A pressurized cryogenic system provides a constant flow of LN2 to maintain the preset temperature. The automated method of control is dependent on two important factors, temperature and pressure. The LN2 from the pressurized vessel is made to flow through the cryogenic probe, freezing the tip of the probe by Joule-Thompson effect. The cryogenic probe is made of medical grade stainless steel of diameter 3mm-Smm designed to maintain laminar flow of LN2. Type T- thermocouple is placed at the inner tip of the probe.

BACKGROUND OF THE INVENTION Several cryoprobes are placed invasively into the patient in contact with the tissue to be frozen during cryosurgery. Several thermocouples are positioned around the vicinity of the probes. Some within the substance of the tumour volume and others in the tissue and organs protected. These thermocouples are assigned to control (set to 0, set to 1) the cryogenic valves connected to the probes thus, stopping or allowing the flow of LN2 into the probe eventually ceasing or continuing the freezing process. The assignment of thermocouples to control the probe, giving and changing temperature set points are done via the user interface MMI by accessing application pages developed. This method gives a precise control of temperature and shaping of the ice ball ensuring the entire tumour volume has been covered with ice. Temperature of about -20 to 40C necessary to cause tissue necrosis, should be attained.

The prevalent practice in cryosurgery for the treatment of a tumour' as discussed by Onik and Fred Lee is by utilizing multiple probes (normally 5 or 6 cryoprobes) imbedded into the substance of the tissue to be frozen. The size of the ice ball formation is monitored by the ultrasound. The extent of freezing and size of the ice ball is dependent on the capability of the surgeon and the sonographer acquired through experience (Onik GM, Cohen

JK,

Reyes GD, et al. in "Percutaneous radical cryosurgical ablation of the prostate under transrectal ultrasound guidance". Cancer 1993; 72: 1291-1299) and (Lee F, Balmhn DK, Me Hugh TA, et al. "Ultrasound guided percutaneous cryoablation of prostate cancer".

Radiology 1994; 192:769-776.). However, determining the ice ball formation by ultrasound guidance alone could pose serious injury of freezing nearby tissues and vasculatures. The ultrasound beams tends to create a shadow on the US monitor slightly larger than the partially coalesced ice ball; this gives a wrong signal to the sonographer to stop the freezing process thus, there were reported cases of recurrence of the disease. The introduction of thermocouples to monitor the temperature of the nearby tissue helps the surgeon decide when to stop the freezing process to prevent damage to the surrounding tissue.

As liquid nitrogen travels through the tip of the probe, which is in contact with the tissue to be frozen, it conducts heat and readily turns into gas. Moreover, a slim diameter probe will bring more resistance to the viscous flow of the liquid. This condition causes gas blockage as LN2 can increase up to several times its volume when it evaporates. Also, LN2 in its gaseous state has a lower heat transfer coefficient than in its liquid state. This resulted in poor freezing temperature at the tip of the probe. For this reason, other probes were designed to use liquids like Argon, Carbon Dioxide and Helium for starting and or cessation of cooling process.

Baust et al Patent 5,254,116) tried to solve the above complication by incorporating holes between the inner supply tube and the outer exhaust. This will cool off the returning nitrogen.

Arnold S. J. Lee Patent No. 3,298,371) and Robert Mitchiner Patent No.

4,275,734) describe cryoprobes that have flow regulators to increase the rate of gas flow coming out through the exhaust chamber, and a pressure regulator to control the incoming flow rate of the refrigerant fluid. Robert Mitchiner further provided a probe that has a switchable valve for freezing and defrosting supply of fluids for faster extraction of the probe from the frozen tissue.

Other developments in cryosurgical devices involve cryosurgical probes and ultrasound guidance in the placement of the probe at the precise location of the tissue as described by Downey et al.(US Patent 64,230,009). Control of the freezing (on and off) is normally done manually as decided by the surgeon which in turn relies on the ice ball depiction by the ultrasound. There is not much emphasis given on how to control the shape of the ice balls once the probes are placed and as a result, a need of second thaw-freeze is necessary which involves sliding the probes further from its previous location before delivering the second freeze to cover the entire tumour (Fred Lee, Duke K. Bahn, Timothy A. Mchugh, Gary M, Onik and Fred T. Lee Jr., "How I do it?, US guided percutaneous cryoablation of the prostate", http://www.prostateDointers.org/ee/big/lee 3 .htm The object of this invention to optimise the lethal freezing temperature to the entire targeted tumour volume and sculpture the shape of the ice ball so as to evade the damage brought about by freezing healthy tissues and vasculatures.

It is also the object of this invention to eliminate the gas blockage and poor freezing temperature associated with liquid nitrogen cryoprobes of slim design.

It is also the object of this invention to provide an efficient cooling and thawing process.

It is also the object of this invention to provide cryogenic automated control with network capability so as to provide easy control, diagnostic and maintenance for biomedical engineers.

It is also the object of this invention to provide a programmable control to surgeons for his/her implementation of cryosurgical technique.

SUMMARY OF THE INVENTION The invention pertains to the integration of all the physical operating context to create an automated process in controlling the freezing temperature and shape of the partially coalesced ice ball formation by using several probes controlled by thermocouples in cryosurgery.

The above objectives are achieved by means of devices and method as described below: 1) Hardware Configuration- Composed of a) Man-Machine Interface (MMI) which is an independent interface between the operator and the controller, b) Programmable Controller which defines the 1/O (input and output) logic of the process and executes either cyclically or periodically the process loop, c) cryosurgical probe of 2.0 to mm in diameter which is directly in contact with the tissue to be frozen, d) computer server for network connection and creating a run-timne screen (real-time data acquisition and measurement) e) thermocouples which monitors temperatures and control the cryogenic probes as define on the set point application page on the interface panel f) Other physical operating context taken into consideration including wiring, piping, connection points and other devices connected to any link to provide efficient cooling and thawing process based on the principle of Joule-Thompson effect.

2) Controller Configuration- A designed process program to implement the automated temperature control.

3) MMI Configuration- A designed graphical application pages for user interface.

4) Variable Pressure Cryogenic Source, which can deliver liquid nitrogen at a steady to periodic flow rate, automatically maintaining a preset freezing temperature.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1. The ice ball depiction as a result of ice sculpture formed by using four thermocouples to control two probes.

Figure 2. The flow control of LN2 in the cryogenic system, hardware, piping. and devices and electronic control.

The cryogenic system flow diagram shows a cryosource that has a dual purpose of delivering and collecting the liquid nitrogen and vice-versa in a closed loop process system. It also manifests how to achieve effectively the Joule-Thompson effect by expansion through a vacuum, ensuring an effective freezing temperature and the best method to sculpture the shape of the ice ball.

Figure 3. Temperature measurements of different distances from the probe tip centre and ice ball diameter formed at 30 min. freezing time and at LN2 pressure of2 atm.

2 Figure 4. Size of ice ball created by using 3.0mm diameter Probe at 1.5 atm. LN2 pressure.

Table 1. 30 min. freezing time using 30mm. diameter probe with four thermocouples Ti, T2, T3, T4 placed 5mm, 10mm, 15mm, 20mm respectively from the probe tip centre.

Table 2. Ice ball diameter and temperature of 3.0 mm. diameter probe at 1.5 atm.

LN2 Pressure.

DETAILED DISCUSSION OF THE INVENTION In this invention the program can utilize several thermocouples to monitor the freezing temperature at real time. It also controls the probe's (on/off) status, depending on the thermocouples set point and probe assignment. One or more thermocouples placed at different tumour site or tissue to be protected will monitor and control a single probe or more, depending on its assignment as defined by the operator using MMI (see Figure 1,2).

In Figure 1, two cryoprobes of 3mm in diameter were inserted into the substance of an irregular shape tumour (X=50mm, Y= 30mm and z20mm). Four thermocouples were then placed randomly at certain distances from the probes. Temperature set points were assigned to each thermocouples: T1 -1 0 C, T2= -47 0 C, T3= -28 0 C, T4= -18 0 C. The probe temperatures were also set to: Pl= -75 0 C and P2 -185 0 C at a freezing rate of 7°C/min..

The four thermocouples were further configured by using the PLC program, to control the two cryoprobes automatically. The purpose of this set-up is to show how to manipulate the shape and size of the ice ball formation during cryoablation by changing temperature setpoints on the thermocouples as well as the temperature setting on the probe whilst in situ.

From Figure 1, the temperature of probe 1 was lowered further to -180 0 C, T1l -10 0 C and T3 -40 0 C to cover the entire tumour with ice. From this experiment set-up, it could be asserted further the success of cryosurgery by simulation of the freezing using a created phantom tissue with the same shape and dimension as the actual tumour before the actual surgery. To ensure -40 0 C, which is essential to cause tissue necrosis, several cryoprobes should be placed around the volume of the tumour with an increased freezing rate. We varied the freezing rate in this experiment by increasing the flow rate of the LN2. The number of probes to be utilized depends on the volume and size of the tumour.

The assignment of the thermocouples and temperature set-points, selection of probes and io temperature setting, temperature monitoring and data gathering are executed by accessing the application pages developed. An application page defines operator dialogue screens providing a user-friendly man-machine interface to monitor and modify the values of freezing automation designed.

CRYOGENIC

SYSTEM

Because of non-linear behaviour of a viscous flow and highly volatile LN2 when made to travel through a very slim diameter cryoprobes, the algorithm considered in sculpturing the shape of the ice ball leads to the integration of hardware and devices, creating an automated cryogenic process control system aimed to contain the LN2flow in a closed loop process; from the cryogenic source through to the cryoprobe tip and back to the collecting Dewar. From our earlier experiments, volatile natunre of LN2 (evaporates at 196C) and its viscous flow characteristic, renders it incapable to produce freeze if made to flow through a smaller diameter probe 4.0 mm. diameter.

LN2 evaporates more easily as it conducts heat from the walls of the probe and acquires heat due to friction.

The cryogenic system designed in this invention eliminates the problems associated with cryoprobe such as: gas blockage, insufficient delivery of freezing temperature, excessive losses of LN2 to the atmosphere and dangerously high pressurize system.

Two pressurized vessels (Dewar A will serve as the storage supply, collecting vessel and vice-versa. Dewar A will be three quarters filled with liquid nitrogen at the initial operating procedure. Dewar B will be filled with nitrogen gas at If Dewar A is the one filled with LN2 at the initial operation as in Figure flow restriction valves 33,7 and 35 shall be closed while 4,8,19 and 30 valves shall be kept open.

Once the run command from the controller is initiated the compressor pump 6 will start pumping from the high pressure fitting 1 of Dewar B to the moisture filter 3, through the fully open restriction valve 4, to the low-pressure side of the compressor (Note that gas cannot pass through line 34 because of the check valve and the close valve The nitrogen gas will continue to flow from the high-pressure side of the compressor through the open valve 8 9 and eventually to the high pressure fitting 11 of Dewar B. At this point pressure at Dewar B will start to build-up and consequently pushing the liquid nitrogen down making it to rise up to high pressure fitting 12 of Dewar B. LN2 will continue to travel to line 13 and continue to increase its velocity as the pressure in Dewar A increases. Liquid nitrogen will accumulate into the pressure manifold 14 for distribution to the cryogenic probes connected in 15. Each of these probes are connected after the cryogenic valves. Solenoid controlled cryogenic valve 16 will open/closed periodically and automatically as commanded by the controller when the set-point temperature setting on thermocouple 40 (normally negative 190 to 195 0 C) has been reached. Thermocouple sits on the outlet of the pressure manifold 14 inline with cryogenic valve 16.

This on and off action of valve 16 is the most important in the process. It implements the Joule-Thompson effect necessary to cool down the heated liquid nitrogen when thermocouple 40 sensed the increase in temperature of the liquid during the process of pressurizing and blocking (valve actions) and the viscous flow through the orifices generating heat by friction When the liquid nitrogen temperature increases and turned into gaseous form when it reach the pressure manifold 14, thermocouple 40 will feed back the reading to the controller; since the temperature is higher than the set-point of -195 0 C, it will command cryogenic valve 16 to open passing the fluid to check valve 18 through the open valve 19 and the end destination, Dewar B. At this stage, Dewar B is at a lesser pressure and approaching vacuum. This will have an abrupt cooling effect on the LN2, which is initially from a high pressure to a sudden neg. atmospheric Pressure. Based from my experience during the experiment, there can never be any freezing occurrence using a very slim probe without this abrupt expansion of liquid nitrogen to the atmosphere or better, expansion to a vacuum vessel as demonstrated in this invention.

The cryoprobe cooling is delivered on the action of the solenoid controlled-cryogenic valve in which it is connected. Thermocouple 42 located at the interior tip of the probe determines the temperature set-point of the probe. It is the actual freezing temperature administered to the tissue.

Cryogenic valve 21 automatically turns on and off to maintain the temperature setting on the probe tip. Other group of thermocouples 41 (8 to16 pieces) are placed around the tumour site and the tissue to be protected, with a certain proximity to the probe end tip.

This will give the surgeon a leeway to enter values to the controller variables, which has the result of actually sculpturing the shape of the ice ball formation while operating in situ.

When Dewar B is full of LN2 and Dewar A is empty, the process is reversed. This time valve 4,8,19, and 30 are close whilst valves 33,7 and 35 are open.

This system is more economical in LN2 consumption, safer by using moderate operating pressure and prevents much evaporation of the liquid nitrogen into the operating room during cryosurgical operation, which could pose the risk of asphyxiation. Moreover, the ability to maintain and control the lethal freezing temperature at the end tip of the probe is assured.

THAWING

For thawing, the valve 16 is closed and cryogenic valve of the probe to be thawed is opened continuously. This will heat up the LN2 (start of freezing cessation). Fast thawing can further be achieved by opening valve 41 and closing valves 8 and 30. In this way, warm- pressurized nitrogen gas will circulate to speed-up the thawing process.

BEST MODE FOR CARRYING OUT THE INVENTION For sculpturing the ice ball formation during cryosurgery several thermocouples (type T) are placed within the substance of the tumour volume and around the tissues to be protected.

Several cryoprobes (3.0 mm diam.) are also imbedded within the substance of the tumour to 25mm. distances between them. This will give a mean effective frezing radius of ice ball. From our experimental table on Figure 3 (ice ball depiction on a 3.0mm diam.

Probe), it shows that effective freezing of -20 to -40 0 C necessary to cause tissue necrosis is achieved within 5mm to 10 mm distance from the probe tip centre. Thermocouples are then assigned temperature set points by assigning values to the variables on the manmachine-interface application page. Thermocouples are further assigned the probe(s) to control within its proximal location. The thermocouple is giving feedback to the controller cyclically every 4ms depending on the configuration. When it reaches the set-point temperature the controller will shut-off the valve that corresponds to the probe where that particular thermocouple has been assigned. Now, with several thermocouples with different set-points controls several probes, it has the overall effect of shaping the partially coalesced ice ball. With the ability to change the set-points on the thermocouple and to set the temperature on the probe, it's like sculpturing the ice ball formation giving a lethal freeze to the targeted tissue and preventing damage to the protected tissue. It should also be noted from Table 1 2 that by increasing the pressure on the nitrogen, freezing rate will also change considerably. Note that in figure 3 the freezing time for the probe to reach -1951C took 30 min. at 2 atm pressure of LN2 compare in Figure 4 at 1.5 atm where the freezing time took 40 min.just to reach -180'C Cryogenic Vessel (Dewar A&B).

Dewar A&B are made of double wall stainless steel separated with cryogenic foam, or aerogel beads, or fibre glass or perlite. It has 35 litres and pressure burst capacity of up to 700 kpa. It has an air tight lid cover made of joined fibre and hard rubber with two high pressure diam. fitting for nitrogen gas and liquid nitrogen. The LN2 tubing will extend up to 80mm. from the bottom of the tank. The nitrogen gas tubing protrudes down 100mm.

distance from the lid cover.

Piping and Pneumatic Devices Piping is diam. stainless steel wrapped with flexible rubber insulation. All pneumatic control devices such as: flow control valve, pressure switch, check valve etc. are designed for low temperature operation. Solenoid controlled cryogenic valve is a two-way valve for liquid nitrogen application, normally closed operation, 1/8" NPT port size, 3.2mm. orifice, 0-9 bar operating pressure, 24Vdc. The number of solenoid controlled cryogenic valve equals the number of the probes to be used. The pressure manifold is made of brass with linear holes for connection of valves, fittings and other pneumatic devices. Relief valves 37 38 are set to maintain the operating pressure of the system (normally 40 psi).

Pressure switches 2 10 have the pressure setting within the Dewar (30-40 psi) and will give signal to the controller to start/ stop the compressor pump.

Controller The control associated with this invention is a closed loop (feedback) control with consideration to preset disturbances (thermocouples inputs at various locations). The controller calculates corrective actions based on gathered input and give commands to output devices.

The controller comprises: An application processor with 1024 discreet 1/O, 80 Analog 1O, 48 Kwords memory on board, 128 Kwords extension memory and speed of0.3 ms/Kboolean.

A 100/240 VAC, 55W power supply.

Analog input modules capable of handling 16 inputs of ranges 0 to 10V, 0 to 5V, 4 to 20 mA depending on the choice made during configuration. Function to digitised signal: 12- bit Analog/Digital conversion, convert input measurements to user format e.g. recalibration coefficient, filtering, scaling.

Analog thermo input module is a multi- range input module with 4 channels isolated from each other. The following ranges are available for its inputs: thermocouples B,E,J,K,N,R,S,T,U, or -13 to +63mV electrical range, 2 or -wire PT100, PT1000 or ohmic range 0-400 ohms.

SAnalog output module with 8 outputs with common point. Depending on the choice made during configuration, the modules offer the following range for each of its inputs: 0 to 20mA and 4 to 20mA without external supply. Its function is to convert digital signals to Analog signal.

Athlon 2000 XP or Intel Pentium 4- 2.4 Gig PC with windows 2000 advance server system.

17" TFT computer monitor screen.

Magellis XBT-F Graphic Terminal Screen for user interface with back-lit colour 10.4" TFT screen, with keypad or touch screen.

Claims (17)

1. A method for automatic control of freezing and the sculpturing of the ice ball formation.

2. A method as in claim 1 wherein several thermocouples were deployed within the substance of the tumour volume and around the tissue to be protected for the purpose of real-time temperature monitoring and signalling the controller to cease the freezing in the affected area when the temperature passed the thermocouple set-point.

3. A method as in claim 1 wherein the thermocouple inside the cryoprobe is given a set point to determine the operating temperature of the probe.

4. A method as in claim 2 3 wherein the surgeon assign changes set points to the thermocouples and the cryoprobes while doing cryosurgery to sculpture the shape of the ice ball formation during cryosurgery in situ.

A method as in claim 1 wherein the rich expertise of the surgeon is incorporated to the system by allowing him/her to provide and alter values into the variables of the program, i.e. set-points, selection of probes and thermocouples to use, assignment of thermocouples to probes, timer setting, alarm setting, thawing or freezing operation.

6. A cryosurgical system comprisingof: a variable pressure liquid nitrogen source; a pressure manifold where the Joule-Thompson effect takes place and the distribution of the LN2 into several connected probes; 0 a programmable controller to implement an automated freezing process system; 9 cryosurgical probes which are placed invasively into the patient and where LN2 circulates; patient thermocouples which are placed into the tumour substance and the tissues being protected; a man-machine interface used for cryosurgical procedure that will serve as the surgeon control panel and for his/her programming hence a user friendly and independent interface between the operator and the controller;

7. A system as in claim 6 wherein producing a cryogenic temperature (cryogenic refers to less than -150'C) on a slim diameter probe using pressurized liquid nitrogen is by expansion of LN2 to a lower pressure Dewar or vacuum.

8. A system as in claim 6 wherein the pressure of LN2 can be varied by adjustment of relief valve.

9. A system as in claim 6 wherein LN2 on the supply Dewar is pressurized by pumping in nitrogen gas from another Dewar initially filled with 30 psi of nitrogen gas.

I A system as in claim 9 wherein the Dewar initially filled with nitrogen gas is made vacuum by transferring the nitrogen gas to the supply Dewar filled with nitrogen and vice-versa.

11. A system as in claim 10 wherein gas blockage in the cryoprobe tip associated with evaporation of highly volatile LN2 is diminished by connecting the returning nitrogen to a vacuum, acting as a collecting vessel.

12. A system as in claim 12 wherein the LN2 is circulated within a closed loop process thereby preventing it to spill into the atmosphere and preventing incidences that could cause asphyxiation.

13. A system as in claim 9 can raise and maintain its own pressure due to some percentage of evaporation of the liquid nitrogen as it acquires energy by heat exchange during the entire operation.

14. A cryosurgical system of claim 6 wherein the apparatus are constructed for containing a plurality of existing designed cryoprobes each of the said cryoprobes being placed inside the patient for freezing tumour tissue.

A cryosurgical equipment as in claim 6 wherein the pressure manifold is fitted with cryogenic valves, connected in-line with the cryoprobes and electrically connected to the controller for the purpose of automatically cutting off or turning on of LN2.

16. A cryosurgical equipment as in claim 6 wherein the pressure manifold is fitted with cryogenic valve connected in line to a low pressure or vacuum Dewar for the purpose of the LN2.

17. A cryosurgical equipment as in claim 6 wherein the pressure manifold is fitted with thermocouple to monitor the quality of the LN2 giving feedback to the controller to open the expansion valve (cryogenic valve).