Abstract
A method of performing a heat treatment of blood vessels (6), such as varicose veins, in order to coagulate the vessel walls (2). Bubbles (4) are selectively created in the blood (3), such that the formation of blood coagula is avoided during the treatment due to cavitation (5).
Claims
1.-15. (canceled)
16. A method for treating a patient by thermal ablation of blood vessels (6) by HIFU, wherein the treatment is carried by a sonication with at least one HIFU pulse (8), characterized in that the characteristics of at least one of said pulses (8) is chosen such as to create bubbles (4) within the blood (3) inside the vessel (6) and such as to thermally coagulate at least part of the wall (2) of the targeted vessel.
17. The method according to claim 16, wherein the characteristics of at least one pulse (8) are adapted such as to create bubbles (4) at blood temperatures that do not cause thermal coagulation in the blood (3.
18. The method according to claim 16, Wherein the intensity of at least one HIFU pulse (8) is such that the blood is heated to a blood temperature that would cause thermal coagulation in the absence of bubbles.
19. The method according to claim 16, wherein the intensity of the at least one pulse (8) is such that cavitation (5) is constantly present.
20. The method according to claim 16, wherein the mechanical index of the at least one HIFU pulse (8) is kept above 1.9 during the whole treatment.
21. The method according to claim 16, wherein the creation of bubbles (4) during the at least one HIFU pulse is, intermittently or continuously, triggered by at least one of amplitude modulation and frequency modulation.
22. The method according to claim 16, further comprising a monitoring step performed by a monitoring means (56) that is adapted to image the area to be treated.
23. The method according to claim 16, wherein the intensity of the at least one pulse is chosen based on a manual control or automatic feedback loop from the monitoring means (56) such as to create bubble activity.
24. The method according to claim 16, wherein the sonication is delivered on an incompletely collapsed vessel (6).
25. The method according to claim 24, wherein the sonication is delivered on a collapsed vessel (6) of size smaller than a focal spot size (1) of the at least one HIFU pulse (8) along an axis of main propagation of the ultrasound.
26. The method according to claim 24, wherein the sonication is delivered on a vessel (6) of a size comprised between 100 μm and 200% of a focal spot size (1) of the at least one pulse (8) along an axis of main propagation of the ultrasound.
27. The method according to claim 16, wherein the focal spot (1) of the at least one HIFU pulse (8) is moved during the sonication.
28. The method according to claim 16, wherein an acceptable size or position of the lumen of the vessel (7) along the main ultrasound propagation axis is overlaid on a realtime monitoring images.
29. The method according to claim 16, wherein the intensity of the at least one HIFU pulse is such that cavitation (5) is only triggered inside the vessel lumen (7) and not in the surrounding soft tissues.
30. The method according to claim 16, wherein the intensity of the at least one HIFU pulse is such that bubble activity (5) is triggered inside the vessel lumen (7) and in the surrounding soft tissues.
Description
[0070] In the following, the invention is described in detail by reference to the following figures, showing:
[0071] FIG. 1: Schematic drawing of a vein that is treated by HIFU according to the claimed method.
[0072] FIG. 2: schematic illustration of an embodiment of a device according to the invention.
[0073] FIG. 3: schematically a bubble cloud with a first and second zone.
[0074] FIGS. 4a-4c: schematically a treatment of a first location.
[0075] FIGS. 5a-5c: schematically different treatments of a second location.
[0076] FIG. 1 schematically shows a vein 6 that is being treated by a HIFU pulse 8. The focal spot 1 is chosen such that it is larger than the vein 6 along the main propagation axis of the ultrasound. In particular, this enables the treatment of both sides of the vein wall 2. Inside the vein lumen 7, the sonication creates bubbles 4 in the blood 3. The creation of a plurality of bubbles leads to micro-streaming 5, which prevents the formation of a blood coagulum.
[0077] FIG. 2 shows schematically a device 50 that is adapted to perform the method according to the invention to treat a patient with HIFU. The device 50 comprises a probe head 51 with a treatment transducer 55. The transducer is adapted to deliver ultrasound waves focused onto a target 54 in an object 53. In the present embodiment, the treatment head 51 further comprises a monitoring means 56, for example an ultrasound imaging device. The treatment head further comprises a compression unit 52, here in the form of a membrane 64 that is mounted onto the probe head 51 and forms a cavity for receiving a fluid. The fluid in the cavity is circulated by a pumping system 63. The device further comprises an actuator 60 that is connected to the probe head 51 by an arm 57 and that is adapted to move the treatment head 51. The device also comprises a controller unit 61 that is operatively connected to the transducer 55, the compression unit 52 and the actuator 60, in the present example by means of a cable 62. In particular, the controller unit 61 is adapted to control the intensity of an emitted HIFU pulse.
[0078] FIG. 3 schematically shows a bubble cloud 4 caused by a HIFU beam in a tissue. For clarity, no particular tissue is shown here, but it will be understood that the described principle could be applied to any tissue or tissue structure, in particular a tissue structure as shown in FIG. 1 or 2. The HIFU beam was focused on and delivered a HIFU dose to a target location 100. A first zone 101 is defined such as to have a substantially elliptical shape. The target location 100 is positioned within the first zone 101 and substantially coincides with a center of the first zone 101. A second zone 102 is defined such as to fully encompass the first zone 101. The second zone 102 has an elliptical shape, wherein the first and second zones 101,102 are displaced along a treatment axis 105 to reflect a common occurrence where larger HEMs are formed closer to the transducer. As a consequence, a first distance 104′ between the circumferences of the first and second zones 101,102 in a direction parallel to the treatment axis is larger than a second distance 104″. Here, the bubble cloud 4 has a size smaller to the first zone 101. However, the bubble cloud 4 forms a hyperechoic mark and is shifted in a direction opposite of the treatment axis 105. Therefore, the hyperechoic mark is partially positioned outside the first zone 101. The hyperechoic mark does not extend outside the second zone 102. For example, if a first criterion required a hyperechoic mark with a size equal to or larger than the first zone 101, the first condition would not be met. Alternatively, a first criterion may require that the hyperechoic mark extends over a delimitation 106 of the first zone 101 in a direction opposite of the treatment axis 105 (i.e. towards a treatment head), which would presently be met. Similarly, if a second criterion required that no hyperechoic mark extends beyond the second zone 102, the second criteria would presently be fulfilled.
[0079] FIGS. 4a-4c schematically show a treatment of a first treatment location. For clarity, no tissue is shown. A first and second zone 101,102 is defined basically as shown in FIG. 3. However, the first and second zones 101,102 are presently co-centered.
[0080] FIG. 4a shows a treated area with the first and second zones 101,102 after delivery of a first HIFU dose. Here, the HIFU dose comprised one pulse with an energy of 100 J. The treatment characteristics were chosen such as to not create a significant bubble activity. Thus, no hyperechoic mark is visible. Thus a next dose with is delivered with an increased energy of 125 J.
[0081] FIG. 4b shows the same tissue area as FIG. 4a after delivery of a second HIFU dose. The treatment characteristics, here the energy delivered with the pulse, were increased. As a consequence, a bubble cloud 4 forms that is visible as a hyperechoic mark 107. Here, a first criterion was defined according to which the entire the hyperechoic mark 107 needs to have a surface area at least as large as the first zone 101. Presently, the first condition is thus not fulfilled and the energy is further increased for delivery of a next HIFU dose.
[0082] FIG. 4c shows the tissue area of FIGS. 4a and 4b after delivery of a third HIFU dose. The bubble cloud 4 forms a hyperechoic mark 107 that presently fulfills the first criterion because the hyperechoic mark has a larger surface area than the first zone 101. Thus, the treatment at the shown location is terminated and the treatment head is moved to a next location. The treatment characteristics used for the third HIFU dose are saved and used for a first HIFU dose at a next treatment location.
[0083] FIGS. 5a-5c show the second treatment location with different possible outcomes of after delivery of a first HIFU dose at the second location.
[0084] FIG. 5a shows a situation where the hyperechoic mark 107 formed by the bubbles 4 is smaller than the corresponding hyperechoic mark at the first treatment location (FIG. 4c). Thus, the first criterion is not fulfilled as the hyperechoic mark is smaller than the first zone. This indicates that the delivered HIFU energy was insufficient for the desired treatment effect. Thus, a further HIFU dose may be delivered at the same treatment location with adjusted treatment characteristics, for example a higher power and/or a higher number of pulses, such as to increase the size of the hyperechoic mark.
[0085] FIG. 5b shows a situation where the bubble cloud 4 and consequently the hyperechoic mark 107 are larger than the first zone 101, but smaller than the second zone 102. Thus, the first criterion and the second criterion are fulfilled and treatment and this treatment location may be terminated. FIG. 5b corresponds to FIG. 4c for a second treatment location.
[0086] FIG. 5c shows a situation where the delivered HIFU energy was larger than intended and expected at a second treatment location. The bubbles 4 and the hyperechoic mark 107 extend over the second zone 102. Thus, the first criterion is fulfilled, but the second one is not. Therefore, the treatment at this location may be terminated and the treatment head is moved to a third location. However, a next HIFU dose at the third location would be delivered with treatment characteristics which lead to less bubble activity. Alternatively, the procedure as shown in FIGS. 4a-4c may be initiated at the third location.
