WO2004076989A1

WO2004076989A1 - Ultrasound power sensor

Info

Publication number: WO2004076989A1
Application number: PCT/GB2004/000736
Authority: WO
Inventors: Adam Shaw
Original assignee: The Secretary Of State For Trade And Industry
Priority date: 2003-02-25
Filing date: 2004-02-25
Publication date: 2004-09-10
Also published as: EP1599707A1; GB0304281D0

Abstract

An HIFUS transducer (1) is situated above a tumour (2) in a patient (3) and coupled to the patient by a bag (4) filled with water (5) or any other suitable liquid or fluid. A PVDF membrane or in-line power sensor (6) of thickness approximately (50) µm mounted on a ring (7) is inserted between the transducer and the patient. The ring (6) is poled to be pyroelectrically active and is constructed with electrodes so that any charge generated by the membrane (6) can be measured. When the HIFUS transducer (1) is energised, an ultrasound wave (10) is generated which propagates through the membrane (6). A small part of the ultrasound energy is absorbed by the membrane (6), resulting in a change of temperature which will vary from point to point across the membrane (6). Thus, power can be measured or monitored without dismantling the HIFUS system, thus reducing equipment downtime. Power can be measured immediately before or during every patient treatment, thus ensuring accurate dosimetry.

Description

ULTRASOUND POWER SENSOR

The present invention relates to an ultrasound power sensor, preferably an in-line ultrasound power sensor. The preferred embodiment provides for the determination of the amount of ultrasound power generated by a High Intensity Focused Ultrasound Surgery (HIFUS) system. The preferred embodiment can be used to measure the ultrasound power generated by other medical and non-medical ultrasound systems.

The use of ultrasound for ablative surgical procedures deep in the body (for instance for the removal of tumours) is undergoing rapid development and appears to have a strong future. In these procedures, the surgical site is not exposed and cannot be seen by the surgeon. Effective treatment requires that the tissue reaches an adequate temperature and this requires that the ultrasound transducer generates at least the amount of power which is anticipated. Safe treatment requires that the output power does not exceed the expected level.

There currently appears to be no method that allows the applied power to be measured during treatment. Methods for measuring the generated power prior to treatment are also not proven. It is also known that more general therapeutic ultrasound equipment is of relatively poor quality in the sense that the output may be substantially higher or lower than anticipated and may even be zero.

It is possible to measure the electrical power to the transducer, and this is done on most HIFUS systems. With some HIFUS systems, it is possible to measure the ultrasound power using a radiation force balance. However, this cannot be done while the patient is being treated.

Generally, HIFUS systems are complex (often with integrated imaging systems) and it is extremely difficult to measure the acoustic output without disassembling the system, which the user is not normally able to do. Even when this is possible, the strongly focused, very high intensity, ultrasound fields cannot be measured accurately with conventional ultrasound quality assurance equipment. Instead, the electrical drive to the transducer is monitored in an attempt to detect changes in the expected output level. This method has a large margin for error and is very indirect for such a safety critical application.

The present invention seeks to provide improved sensing of radiated power.

According to an aspect of the present invention, there is provided apparatus for measuring the power emitted during operation by a radiating system including a sensing transducer located in the radiation field to sense power generated during radiation by the system, the transducer being substantially non-absorbing of the radiation beam.

, Advantageously, the sensing transducer is located substantially in-line with the path of emitted radiation. Preferably, the transducer includes a membrane substantially transparent to ultrasound located within the emission path of the system.

The preferred embodiment provides a nearly acoustically transparent membrane

(either permanently or temporarily) in the beam of the ultrasound transducer and provides sensing apparatus operable to determine the amount of heating caused by ultrasonic absorption in the membrane. The amount of heating can be related quantitatively to the ultrasound power. It is preferred that the membrane will be minimally perturbing to the transmitted ultrasound field.

The prime task of the preferred embodiment is to ensure that the correct amount of ultrasound power is delivered to a patient during treatment with HIFUS.

According to another aspect of the present invention, there is provided a surgery system including apparatus as specified herein.

According to another aspect of the present invention, there is provided a method of measuring the power emitted during operation by a radiating system including providing a sensing transducer located to sense power generated during radiation by the system, the transducer being substantially non-absorbing of the radiation beam. The method may be used to monitor the power from chemical reaction chambers, cleaning baths, material treatment and processing stations, ultrasonic welders, to monitor the power radiated by transducer arrays for underwater acoustics; for medical diagnostic ultrasonic devices including imaging scanners and others; and/or to indicate that an ultrasound device is functioning or to monitor stability or changes in power output.

Reference is made to the applicant's earlier-filed International patent application no. PCT/GB02/004852 which discloses another ultrasonic power measuring system.

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawing, in which Figure 1 shows an embodiment of in-line power sensor.

Referring to Figure 1, in one preferred implementation an HIFUS transducer 1 is situated above a tumour 2 in a patient 3 and coupled to the patient by a bag 4 filled with water 5 or any other suitable liquid or fluid.

In this embodiment, it is preferred to obtain a measure of the power generated by the whole of the radiating beam 10 and for this purpose there is provided a PVDF membrane or in-line power sensor 6 of thickness approximately 50 μm mounted on a ring 7 which is inserted between the radiating transducer 1 and the patient 3 and held in position by any suitable mechanism.^" The ring 7 may be mechanically connected to the membrane 6 and it may be oriented so that it is not perpendicular to the axis of the ultrasound beam.

During construction, the membrane 6 is poled to be pyroelectrically active and is constructed with electrodes so that any charge generated by the membrane 6 can be measured. The electrodes are connected to an electronic circuit 8 which may be of different specifications as required. In this specific implementation, the circuit 8 is configured such that the charge generated by the membrane 6 is converted to a voltage which is proportional or nearly proportional to the rate of change of temperature averaged across the part of the membrane which is provided with electrodes. This voltage signal is digitised and presented to the user along with relevant numeric information on display 9.

When the HIFUS transducer 1 is energised, an ultrasound wave 10 is generated which propagates through the membrane 6. A small part of the ultrasound energy is absorbed by the membrane 6, resulting a change in temperature of the membrane which will vary from point to point across the membrane. The charge generated by the change in temperature of the membrane 6 is collected by the electronic circuit 8 via the electrodes as a voltage. In this configuration, the voltage reaches a maximum very soon after the transducer 1 is energised and decays with time until the membrane reaches its equilibrium temperature, when the voltage will be close to zero, which is expected to be after less than one second. There will be a similar but inverted voltage signal when the transducer is de-energised.

The membrane 6 is substantially non-absorbing of the radiating beam. By this it is meant that the membrane 6, or other sensor placed in the beam 10, still allows the beam 10 to perform its intended function, in the example shown in Figure 1 to treat the tumour 2 with substantially the same intensity as without any sensor.

The membrane 6 provides a measure of the intensity of the entire beam 10, in effect summing individual areas of the radiation beam 10. In some embodiments, it may be desired to measure only parts of the beam 10, in which case the membrane could take a different form, such as a grid of wires or could instead be one or more sensors occupying a small area of the beam 10. The skilled person will appreciate what sensors would be suitable from the teachings herein.

Thus, the precise location of the sensor relative to the beam may be changed and the properties of the membrane (material, dimensions, thickness, protective coatings and so on) may be varied to produce the required sensitivity to the propagating ultrasound field. For example, the sensor may be made partially or totally absorbing; the sensor may be used for off-line testing and be removed from the beam during treatment; the sensor may be located away from the usual axis of the beam and a reflector used to direct the beam at the sensor as required; the sensor may intercept only part of the beam thus giving an indication of a more localised power integral; the sensor may placed in contact with the patient; the sensor may be placed on or incorporated into the ultrasound transducer; the sensor may contain layers or coatings for protection or other purposes.

The system could potentially be used in any application where there is a technical or economic advantage in being able to measure ultrasound power in the normal operating environment of the ultrasound device. Wider applications may include: the sensor being used to monitor the power from non-medical devices including chemical reaction chambers, cleaning baths, material treatment and processing stations, ultrasonic welders and others; to measure the power radiated by transducer arrays for underwater acoustics; for medical diagnostic ultrasonic devices including imaging scanners and others; and/or simply to indicate that an ultrasound device is functioning or to monitor stability or changes in power output (without necessarily arriving at traceable values for power).

The sensor may also be used for any of these primary or secondary applications with non-ultrasound devices that produce a heating effect including lasers and others.

The main advantages of the preferred embodiment include: (a) that power can be measured or monitored without dismantling the HIFUS system, thus reducing equipment downtime; (b) that power can be measured immediately before or during every patient treatment, thus ensuring accurate dosimetry; (c) that power can be measured at the output levels used for treatment (whereas a radiation force balance fitted with an absorbing target would probably be damaged by overheating); (d) that power can be measured with equal accuracy irrespective of the amount of focusing applied to the ultrasound beam (whereas a radiation force balance fitted with an conical reflecting target exhibits substantial and increasing systematic errors in more focused fields).

The method uses components which are robust and simple to use compared to radiation force balances or hydrophone scanning systems. The disclosures in British patent application no. 0304281.9, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims

1. Apparatus for measuring the power emitted during operation by a radiating system including a sensing transducer located in the radiation field to sense power generated during radiation by the system, the transducer being substantially non-absorbing of the radiation beam.

2. Apparatus according to claim 1, wherein the sensor is operable to sense heat produced by the radiating system.

3. Apparatus according to claim 1 or 2, sensor includes a sensing membrane.

4. Apparatus according to claim 3, wherein the membrane is substantially transparent to ultrasound.

5. Apparatus according to claim 3 or 4, wherein the membrane is formed form PVDF.

6. Apparatus according to any one of claims 3 to 5, wherein the membrane has a thickness of the order of 50 μm.

7. Apparatus according to any one of claims 3 to 6, wherein the membrane is pyroelectrically active.

8. Apparatus according to any one of claims 3 to 7, wherein the membrane is provided with electrodes.

9. Apparatus according to claim 8, wherein the electrodes are connected to a measuring device.

10. Apparatus according to claim 9, wherein the measuring device is configured such that the charge generated by the membrane is converted to a voltage which is substantially proportional to the rate of change of temperature averaged across the part of the membrane.

11. Apparatus according to any one of claims 3 to 10, including a support element operable to support the membrane.

12. Apparatus according to claim 11, wherein the support element is mechanically connected to the membrane.

13. Apparatus according to claim 11 or 12, wherein the support element is orientable so as not to be perpendicular to the axis of the radiating beam.

14. Apparatus according to any one of claims 3 to 13, wherein the membrane is located in an amount of fluid.

15. Apparatus according to claim 14, wherein the fluid is water.

16. Apparatus according to claim 14 or 15, wherein at least a part of the radiation system can be located within the fluid such that the radiation beam is generated within the fluid.

17. Apparatus according to any preceding claim, wherein the sensor is located substantially in-line with the path of emitted radiation.

18. Apparatus according to any preceding claim, wherein the radiating system is an ultrasonic radiating system and the sensor is operable to measure ultrasonic radiation.

19. Apparatus according to any preceding claim, wherein the radiating system is provided with a high intensity focused ultrasound surgery system.

20. A surgery system including apparatus according to any preceding claim.

21. A surgery system according to claim 20, wherein the surgery system is a high intensity focused ultrasound surgery system.

22. A method of measuring the power emitted during operation by a radiating system including providing a sensing transducer located to sense power generated during radiation by the system, the transducer being substantially non-absorbing of the radiation beam.

23. A method according to claim 22, wherein the method measures heat generated by the system.

24. A method according to claim 22 or 23, including the step of providing a sensing membrane for sensing the generated radiation.

25. A method according to claim 24, wherein the membrane is formed to be pyroelectrically active.

26. A method according to any one of claims 22 to 25, wherein the method is used to monitor the power from chemical reaction chambers, cleaning baths, material treatment and processing stations, ultrasonic welders, to monitor the power radiated by transducer arrays for underwater acoustics; for medical diagnostic ultrasonic devices including imaging scanners and others; and/or to indicate that an ultrasound device is functioning or to monitor stability or changes in power output.