The present invention relates to a method of treating varicose veins by application of High-Intensity Focused Ultrasound (HIFU) comprising the features of the independent claim.

HIFU treatments enable the non-invasive ablation of anatomical targets in the body. They are usually guided based on an imaging modality such as ultrasonography, in particular B-mode imaging.

In several devices, an ultrasonography imaging transducer is em bedded in the "treatment head" subsystem which also comprises a therapy transducer as described e.g. in WO 2006/129045.

For treating varicose veins, it is known to use Radio Frequency Ablations (RFA) or Endovenous Laser Ablations (EVLA) . These pro cedures generally rely on treating the vein from the sapheno- femoral junction (with a safety distance of a few centimetres) up to the knee or the ankle.

Treating such a length with HIFU may take a long time. HIFU is therefore sometimes considered less suitable for treatment of varicose veins. Indeed, HIFU treatments generally require pauses between the pulses, for example to avoid skin burns, which can lead to treatment durations exceeding an hour for long veins such as the Great Saphenous Vein (GSV) . In addition, the supply of energy to the vein system can be painful for a patient. Thus, current HIFU treatments of vein systems can cause severe discom fort for the treated patient.

It is known in the prior art to treat varicose veins by closing parts of veins with the goal of selectively changing the blood flow. This method, commonly referred to as CHIVA method, re quires anesthesia and involves surgical treatment of the leg and the varicose veins.

It is the object of the present invention to overcome the disad vantages of the prior art, in particular to provide a method which allows to non-invasively treat a vein with HIFU and in particular avoid a time-consuming treatment and pain, stress and discomfort for the patient.

This and other objects are solved by the present invention and the method according to independent claim.

As will be clear to a person skilled in the art, the treatment described herein can of course be combined with other treatment methods. As such, any description herein should not be under stood as a limitation to a treatment exclusively with HIFU.

In the method according to the invention, first, at least one first section of the vein to be treated is identified. A first section is treated by applying HIFU emitted from a treatment head to the first section. An area neighbouring the section is not treated with HIFU. In other words, the method according to the invention is based on performing a sectional treatment. It has been surprisingly found that it is not necessary to treat the vein along its entire length but that the treatment of at least one section is sufficient. Typically, the treatment can occur in only one section but also in a plurality of sections (e.g. at least two sections) spaced from each other along the vein .

A section in the context of the present invention means a part of a vein, in particular a part of a vein within a single vein system. Herein, vein system refers to the vein to be treated and every vein directly connected to the vein to be treated, in par ticular every vein directly connected to the vein to be treated in an upstream direction. Unless otherwise indicated and/or specified, a plurality of sections shall refer to sections with in the same vein system. A section can refer to a portion of a vein or a vein system representing a percentage of said vein or vein system. It can also refer to a portion of a vein or vein system with a defined total length. A section can also generi- cally refer to a portion of a vein or a vein system that is ad jacent to at least one other portion of the same vein or vein system that was treated differently from the section.

Preferably, the at least one section is part of segment of the vein that is non-functional. At least a second section of the segment may not be treated with HIFU. The treated section is preferably completely occluded.

Methods known in the prior art typically identify veins, vein systems, or more generally non-functional segments of vein sys tems that have lost their healthy functionality. For example, a portion of a varicose vein may be dilated and the valves can no longer stop backflow of blood. Such segments are then treated in their entirety. If a HIFU treatment were envisioned, for exam ple, methods known in the art would treat the entire segment with HIFU.

By contrast, the method according to the invention may prefera bly be used to only treat a section of such a segment. Particu larly preferably, at least two sections of a continuous non- healthy segment are treated, wherein the at least two sections are separated by a section that is not treated. It is also pos sible to only treat one section of a segment. The treated section may be adjacent to a healthy, functional segment of a vein. Alternatively, the section may be located within the non-functional segment such as to be adjacent to non- healthy, non-functional vein parts.

In a preferred variant of the method according to the invention, the treated section is completely occluded. In particular, the power of a HIFU pulse, the duration of the treatment, and the number of pulses may be chosen such as to completely occlude the treated section.

Thus, the method particularly preferably includes a step of identifying a section to be treated, wherein the section is part of a non-healthy, non-functional segment. A length of the sec tion, measured along the longitudinal axis of the vein, is shorter than the length of the segment.

The method may also include a step of occluding the section com pletely.

In the context of the present application, a section is typical ly, but not necessarily, a section of the vein or a vein segment which has a length of less than 200 mm and/or 50% of the total length of the vein or vein segment.

In particular, unless otherwise indicated and/or specified, treating a section refers to treating at least 50% for a circum ference of at least one layer of a vein wall. For example, it can refer to treating 50% of a circumference of the tunica inti- ma, the tunica media, and/or the tunica adventitia.

In particular, a section can be a portion of a vein or a vein system that is to be treated by HIFU and is adjacent to a por- tion that is not to be treated by HIFU, or is to be treated with substantially different treatment characteristics (for example, power, pulse duration, and/or frequency) . Substantially differ ent treatment characteristics shall denominate differences greater than a standard deviation, in particular greater than normal fluctuations caused by precision limits of a device. Ad ditionally or alternatively, substantially different treatment characteristics shall include characteristics that do not cause a treatment effect.

For example, in a first section, three or four pulses are deliv ered in all treated cross-sections, resulting in a mean of 3.5 pulses delivered per cross-section and a standard deviation of 0.2 pulses in this section, while, in the second section, only two pulses are delivered in all treated cross-sections, which is smaller than the mean (3.5) minus the standard deviation (0.2) and/or differences in the parameters inducing different signifi cantly different biological effects (for example, thermal abla tion versus mechanical ablation) .

Furthermore, numbered sections, such as "first section", shall not denominate an order of treatment, but shall be used to iden tify different sections. For example, a second section may be treated before a first section. For example, the "first section" may refer to the most proximal section.

Distal, in the context of the present invention, shall refer to the direction opposite to the normal direction of flow in the vein and further away from the heart. Proximal shall refer to the normal direction of flow in the vein and closer to the heart . The treated sections can be arranged depending on the specific vein which is treated. Typically, if the refluxing vein extends in the thigh and in the calf (e.g. the GSV) , the sections are preferably mainly or only located in the thigh, since the sensi tive structures are generally closer to the vein under the knee.

For example, in the case of a treatment of a GSV, one may begin the treatment at the sapheno-femoral junction.

If several tributaries are connected to the refluxing vein, the sectional approach described hereinabove can be adapted to ac count for the location of these tributaries. In this context, the tributary refers to a smaller vein that leads to a larger vein .

In particular, one and preferably multiple HIFU pulses can be emitted to the section to be treated. The HIFU pulses can be targeted at one spot or different spots within the same section.

The treatment head preferably comprises a conventional HIFU transducer or phased-array transducer.

In a preferred embodiment, the first section is treated without substantially moving the treatment head and/or the transducer.

It is, however, also possible to move the head along the section during the treatment.

In a one embodiment of the present invention, only the first section is treated with HIFU.

In a preferred embodiment, the treatment step is repeated at least once for a second section distanced from the first sec- tion . In preferred embodiment, the method is carried out to treat the GSV or the Anterior Accessory Saphenous Vein (AASV) as a reflux ing vein. In this case, the first section begins close to the sapheno-femoral junction, preferably at a distance that is smaller than 2 cm.

In a preferred embodiment, the length of the treated section is greater than 5 cm, or greater than 10 cm.

In an alternative embodiment, the sum of the lengths of the treated sections is greater than 5 cm, preferably greater than 10 cm.

The length of the first section to be treated can in particular be chosen such as to not reach the level of the knee.

In an alternative preferred embodiment, the refluxing vein to be treated is a perforator vein. In this case the first section is located close to the fascia and preferably has a length smaller than 2 cm, or smaller than 1 cm.

In another preferred embodiment, the first section can be treat ed with different parameters than any other section. Typically, at least one of a.) the length of the treated section b.) the delivered energy, c.) the linear endovenous energy density, d.) the fluence, e.) the power, is substantially larger for the first, in particular the most proximal, section (which is pref erably at a distance smaller than 2 cm from the sapheno-femoral junction, most preferably at the sapheno-femoral junction) than for at least one, preferably all, other sections.

In yet another preferred embodiment, at least one of the length and spacing of the sections is chosen such that sensitive sur- rounding structures that could be damaged by HIFU, for example nerves, possibly present along the vein are not subjected to HI FU.

In a preferred embodiment, the treated sections are spread all along the vein or the vein system, preferably in a regular pat tern .

In an alternative preferred embodiment, the sections are ar ranged only in a predefined part of the vein or the vein system.

If the refluxing vein to be treated extends in the thigh and in the calf, the sections are located preferably mainly and more preferably only in the thigh.

In a preferred embodiment, the number, length, and/or location of the sections that are to be treated and/or a characteristic value of the Linear Endovenous Energy Density (LEED, W/cm) and/or the treatment power and/or the fluence, for each section is defined prior to the treatment, in particular prior to the emission of the first HIFU pulse. The characteristic value may be constant or may vary within a range. For example some charac teristics of the sections can be defined based on a preliminary examination using ultrasound imaging.

In alternative preferred embodiment, the number, length, and/or location of the sections that are to be treated and/or a value of the LEED and/or the treatment power and/or the fluence for each section is adjusted or adjustable during the treatment, in particular after the first HIFU pulse has been emitted. For ex ample, they can be adjusted based on the response of the vein to the treatment that may be determined by the presence or absence of flow in color Doppler) . In alternative preferred embodiment, at least one of the number, length and location of the sections is defined prior to the treatment, in particular after the first HIFU pulse has been emitted. Then, at least one of the number, length and location of the sections that are to be treated is adjusted or adjustable during the treatment, in particular, after the first HIFU pulse has been emitted. For example, for the treatment of a Great Sa phenous Vein (GSV) , based on the location of the tributaries (e.g. assessed by ultrasound imaging), it can be decided to place one section at the junction with at least one of the trib utaries and one section at the Sapheno-Femoral junction. Then, during treatment, the length of the sections and/or a character istic value of the LEED and/or of the power and/or of the flu- ence can be adjusted based on color Doppler information. For ex ample, the length of the sections can be increased at least un til no flow is visible in the section to be treated.

In a particularly preferred embodiment, the length of a treated section is reduced during the treatment if and when the vein be comes less visible due to heat-induced shrinkage of its wall. Preferably, in dependence of the reduced visibility of the vein, the treatment head is moved distally. At the new distal loca tion, a new section is treated.

For example, if the vein becomes less visible, the treatment of the section can be aborted and a next section, in particular in a distal direction, is treated next.

Alternatively, if the vein becomes barely visible on the moni toring mean due to the heat-induced shrinkage of its wall, the treatment head is moved during the treatment, in particular along a direction parallel to the treated section, such that the treated vein or vein system is more easily visible. This process can be repeated until treatment completion.

For example, the vein may become barely visible during the treatment. Instead of continuing the current section, it may be decided to stop the treatment of the current segment, to move (e.g. more distally) , and to deliver another section at this new location. Note that this second section was maybe already planned (in this case, the first section is simply interrupted, but no other section is added) . Alternatively, the second sec tion was not planned. Alternatively, the second section was planned but some characteristics are changed due to this event (for example, its length is increased to compensate for the first section being shorter than expected) .

In a preferred embodiment, the treatment is controlled or stopped on the basis of at least one of the level of total de livered energy, absence of detectable flow in the vein, treat ment duration, total treated length, a predefined number of sec tions treated, and/or vein shrinkage. Typically, treatment will be stopped if certain treatment completion criteria defined by these parameters are fulfilled.

In a preferred embodiment, the sections are treated from the proximal side of the vein to the distal side of the vein. This is particularly advantageous if cavitation is used for achieving a treatment effect, since a proximal occlusion of the vein will block some blood distally and inflate the vein, thus letting enough blood to initiate cavitation.

Alternatively, especially if the vein is big and/or if only thermal pulses are used and/or if no tumescence is used, the treatment can start on the distal side to decrease the blood flow into the vein and to avoid the distal inflation. Alterna tively, the order and direction of treatment of the sections are free .

In another preferred embodiment, at least one section is placed, in particular adapted in its length and position, to target a junction with a tributary.

In a preferred embodiment, the occlusion of the junctions in cludes one of i.) treating only the vein at said junction, ii.) treating the vein and the tributary at said junction, and iii.) treating only the tributary at the junction.

In another preferred embodiment, at least one tributary, in par ticular a tributary that is connected to the same vein, is treated away from the junction.

Additionally to a sectional HIFU treatment, an additional treat ment with at least one other modality can be performed to treat at least part of the same vein system.

These modalities include, but are not limited to Radio Frequency Ablation, Endovenous Laser Ablation, Micro-wave ablation, heat ing with a hot catheter, mechanical damage of the endothelium, Glue, and/or Sclerotherapy or a combination of modalities. Pref erably, Sclerotherapy is used to avoid the invasiveness related to the insertion of a catheter. Alternatively, the other treat ment is performed with HIFU. In particular, the additional treatment is performed distally from the most proximal section treated with HIFU. In a particularly preferred embodiment, the method according to the invention further comprises a step of treating the vein with sclerotherapy .

Sclerotherapy is a known treatment of varicose veins wherein a sclerosant is injected into a vein, causing occlusion of said vein. However, sclerosants may have undesired side effects and it is therefore advantageous if the treatment with a sclerosant can be as localized as possible.

To this end, a section of a non-healthy segment may be located at a downstream end of the segment, for example directly adja cent to a healthy, functional segment. Non-healthy segments may in particular not be able to properly prevent reflux of blood, i.e. flow of blood against the natural flow direction, which is one of the functions of veins. Downstream is understood here with respect to flow direction of blood. The section is occluded by means of HIFU. Subsequently, a sclerosant can be injected in the segment at an upstream position of the section. The occlu sion of the section at the downstream end of the segment reduces or prevents passage of the sclerosant into the blood stream. Therefore, side effects of the sclerosants are reduced.

Preferred sclerosants are dodecylpolyethyleneglycolether

(polidocanol ) , iodine, sodium tetradecyl sulfate, sodium

salycilate, chromated glycerin and other ethers.

The other treatment, preferably sclerotherapy, can be performed during the same or another session, before or preferably after the HIFU treatment. Preferably, it targets at least part of the untreated part of the vein, most preferably the entire untreated part of the vein. The additional treatment may be performed on a partially or to tally occluded vein, in particular to avoid recanalisation. Par tially occluded shall be understood as exhibiting signs of oc clusion but still allowing for some blood flow.

Additionally or alternatively, it may also target some part of the vein(s) which was already treated by HIFU. In case sclero therapy is used, it is preferably used when the vein is occluded to avoid the systemic (neurological etc.) side-effects related to the sclerosant being released in the blood circulation.

In another embodiment, at least one of the targeted veins is the Great Saphenous Vein or the Anterior Accessory Saphenous Vein and at least one section treated by HIFU is close to the Saphe- no-Femoral Junction at the at least one additional treatment targets at least a more distal part of the vein.

Additionally or alternatively, the sum of all treatment deliv ered substantially corresponds to the length of the vein from the Sapheno-Femoral Junction to the level of the knee.

Additionally or alternatively, the sum of all treatments deliv ered substantially corresponds to the length of the vein from the Sapheno-Femoral Junction.

For example, it can be long to treat the whole Great Saphenous Vein with HIFU, thus, only one section is treated from the sa- phenofemoral junction, but durability of the occlusion might not be as good as if the whole GSV would be treated. Thus, during a control session, preferably after the occlusion has been ob served, a sclerotherapy is performed distally to the treated section to occlude at least some (preferably all) the distal part of the GSV. The invention further relates to a device. The device according to the invention comprises a memory unit, a display, a control unit, and a treatment head with a transducer. The control unit is adapted to control the treatment head and the transducer, in particular such that different sections can be treated with dif ferent treatment characteristics, for example pulse length, num ber of pulses, power, LEED, fluence, length of the sections, number of sections, and/or others. Furthermore, the display is adapted to display the treatment characteristics for each sec tion. In particular, the display may display the treatment char acteristics as a table or as a graphic representation, for exam ple with color codes overlaid over a B-mode image. The control unit is further adapted to compute characteristic values from the treatment characteristics, such as mean and median values. These values may be displayed on the display as well.

In the following, the present invention is described with refer ence to the figures and preferred embodiments, showing:

Fig. la: schematically the concept of a sectional treatment with several sections.

Fig. lb: schematically the concept of a sectional treatment with one section.

Fig. 2a: schematically the treatment of a vein without par ticularly adjusting the sections with respect to the tributaries .

Fig. 2b: schematically a sectional treatment of a vein where in both the vein and the tributaries are treated. Fig. 2c: schematically a sectional treatment of a vein where in only the tributaries are treated.

Fig. 2d: schematically a sectional treatment of a vein where- in only the tributaries are treated at the junc- tions .

Fig. 2e: schematically a sectional treatment of a vein where in only the tributaries are treated.

Fig. 3: schematically a device for carrying out the present invention .

Fig. 4: schematically by means of a flow chart the steps of a method according to the invention.

Figs. 5a-5b: a detailed view of a sectional treatment.

Fig. la shows schematically a method according to the invention, wherein several sections 6a, 6b, 6c, and 6d are treated along a vein system 1,2. Here, the refluxing vein 2 is the Great Saphe nous Vein (GSV) or the Anterior Accessory Saphenous Vein (AASV) one treated section 6d begins as close as possible to the saphe- no-femoral junction 8, preferably at a distance dl smaller than 2 cm. The length LI of the treated section 6d neighbouring the sapheno femoral junction 8 is bigger than the other treated sec tions. Alternatively, this section could also have the same size but the delivered energy could be higher, or the linear endove- nous energy density could be higher than for the other sections 6a, 6b, and 6c. In the shown embodiment, the treated sections have equal spacings si, but could also be of unequal spacing and/or lengths. In between the sections 6c and 6b, a nerve 7 is close to the refluxing vein 2. The position, length, and/or spacing of the treated sections is thus adjusted to avoid expos ing and/or harming the nerve 7, which is a sensitive structure.

However, in the shown embodiment, the sections are not specifi cally arranged with respect to the junctions 4 between the trib utaries 3 and the refluxing vein 2. Thus, one section 6b lies at a junction 4, while the other sections 6a, 6c, and 6d do not.

The sections 6a, 6b, 6c, and 6d are spread equally along the treated vein 2. Here, the treatment is started with proximal section 6d, while an area neighboring the section 9 is not treated. Alternatively, the treatment can be started with a dis tal section 6a.

Fig. lb shows a vein system with a vein 1, and an insufficient vein 2 fed by smaller veins 3. According to the embodiment of the invention shown in Fig. lb, only one section 6e of the vein 2 is treated.

Here, the refluxing vein 2 is the Great Saphenous Vein (GSV) (or alternatively the Anterior Accessory Saphenous Vein (AASV) ) . The treated section begins as close as possible to the sapheno- femoral junction 8, preferably at a distance d2 smaller than 2 cm. The length L2 of the treated section is larger than 5 cm, most preferably larger than 10 cm, but does not reach the level of the knee (not shown in Fig. lb) .

Figs. 2a-2e show several other embodiments of the method accord ing to the invention where the vein 2 to be treated has several tributaries 3.

In Fig. 2a, a treatment of a refluxing vein 2 with several trib utaries 3 is schematically shown. The sectional treatment ap proach is applied independently from the location of the tribu- taries 3, but the treatment is begun at the sapheno-femoral junction 8. The sections 6f, 6g, 6h, and 6j are spread uniformly along the treated vein 2 and are adapted in the lengths L3 and spacing s3 irrespective of the position of the tributaries 3. Thus, in this particular embodiment, section 6g is located at a junction 4 between the refluxing vein 2 and a tributary 3, while the other sections 6f, 6h, and 6j are not. In this embodiment, only the vein 2 is treated even if a section 6g lies at a junc tion 4, meaning that the tributary 3 is not treated.

Fig. 2b shows schematically an embodiment of the method accord ing to the invention, where sections 6k and 61 are placed to target the junctions 4 with the tributaries 3. This allows for avoiding a recanalization due to the blood inflow or a bypass of the treated sections which would transmit the increased pressure to the bottom of the leg. Both the vein 2 and the tributaries 3 are treated in the junction areas 4. Furthermore, in the shown embodiment, the sections have a length, spacing, and placement irrespective of the distance d3 to the sapheno-femoral junction 8 and the vein 1. However, the sections 6k, 61 are located such that they coincide with the junctions 4 and are thus not neces sarily spread uniformly along the treated vein 2.

Fig. 2c shows schematically another embodiment of the method ac cording to the invention where only the tributaries 3 close to the junctions 4 are treated. The sections 6m and 6n lie on the tributaries 3, while the refluxing vein 2 itself is not treated.

Fig. 2d shows schematically an embodiment of the method accord ing to the invention, where at each junction area 4a, 4b, 4c, and 4d, only the tributary portion of the junction is treated.

As such, only the part of the refluxing vein 2 that is directly adjacent to the vein 1 is treated and section 6p is placed ac cordingly. Similarly, the sections 6q, 6r, and 6s are placed such that the tributaries 3a, 3b, and 3c are treated at the junction area 4b, 4c, and 4d where they are connected to the re fluxing vein 2. In contrast to Fig. 2c, the refluxing vein 2 is also treated with a section 6p at the junction 4a between the vein 1 and the refluxing vein.

Fig. 2d corresponds to a preferred method of treatment of a GSV or an AASV. This embodiment includes treatment of at least one section at the sapheno-femoral junction 8 and occlusion of some of, preferably all, the tributaries 3 upstream to or at the junctions with the GSV or AASV.

Preferably, the length 15 of the treated section 6p at the sa- pheno-femoral junction 8 is larger and/or the delivered energy is higher, and/or the linear endovenous energy density is higher for the other sections 6q, 6r, and 6s.

Similarly, if a tributary 3a is larger than the other tributar ies 3b and 3c, the length L6 of the treated section 6q at the junction 4b is preferably larger and/or the delivered energy is preferably higher, and/or the linear endovenous energy density is preferably higher than for the sections 6r and 6s at the sec tions 4c and 4d.

Fig 2e schematically shows another preferred embodiment of the method according to the invention, wherein only the tributaries 3 are treated. The sections 6t, 6u, and 6v are located at a dis tance d4, d5, and d6, from the junction areas 4, respectively.

Fig. 3 shows schematically a device 42 which can be used to per form the method according to the invention, wherein a patient 31 is treated by HIFU. The device comprises a treatment head 34 which is placed on the patient's leg 32 below his knee 41. Here, some of the treated sections lie in the calf and thus, some are as below the knee are treated. It is possible, however, to only treat sections in the thigh. In this particular embodiment of the device, the treatment head 34 comprises a balloon 36 that is in contact with the patient's leg 32 and enables acoustic cou pling. The treatment head 34 comprises a transducer 35 for emit ting ultrasound waves. A control unit 40 controls the emission of HIFU pulses. A memory unit (not shown) saves the number of sections and at least some of the treatment characteristics for each section. In this exemplary embodiment, the memory unit saves the number of sections that were treated along with their location and pulse power, pulse length, and the number of puls es. In this particular case, other treatment characteristics are not of interest, but it is clear to a person skilled in the art that the memory may also save other treatment characteristics as required. The treatment head 34 is connected to the control unit 40 through a robotic arm 33. The arm 33 comprises mechanical joints 39 in order to perform a controlled movement 38 of the arm. In this embodiment, the device comprises a user interface in the form of a display 37. The display displays to a user the treatment characteristics that were saved in the memory. Here, this happens in the form of a schematic diagram which shows the location of the sections on a dedicated part of the screen. In addition, the control unit also computes the average pulse power and the standard deviation, which is classified into ranges as sociated to a color. The different sections on the displays are thus colored, wherein each color represents a pulse power range. The other treatments characteristics are displays as alphanumer ical digits on the display. They may, however, also be displayed symbolically by, for example, a number of dots in the sections, the thickness of a line, or others. Treatment parameters for the sections Include, but are not lim ited to, frequency, number of pulses, energy, pulse spacing, du ration, LEED (W/cm), and fluence (W/cm ² ) .

Fig. 4 shows schematically, by way of a flow chart, the steps of a method according to the invention. In a first step 51, a sec tion to be treated is identified and the treatment parameters are determined. Here, the treatment parameters include the fre quency, number of pulses, and total delivered energy for all sections to be treated. Other parameters can be included in ad dition or as an alternative to the parameters used here. A treatment step 52, comprising the emission of a HIFU pulses with the pre-determined frequency is performed subsequently without moving the treatment head. Alternatively, multiple HIFU pulses can be emitted in one treatment step. A further step consists in comparing the treatment with a pre-determined stopping condition 58. Here, the treatment a section shall be terminated upon de livery of a total amount of energy. Alternatively, stopping pa rameters could total number of HIFU pulses, total length of the treated section, duration of the treatment, and others. If the condition for stopping 53 is not met, the visibility of the treated vein is checked 54. If is well visible 56, the treatment is continued by performing another treatment step 52. If the vein is not visible 57, the treatment head is moved, preferably distally, in a movement step 55, for example to treat another section. Subsequently, the treatment is continued with another treatment step 52. If and when the stopping condition 53 is met 58, the treatment of section is stopped 59. If another section is planned to be treated 60, the procedure is repeated 62 with another treatment step 52 for the new section. In this embodi ment, the treatment parameters are pre-defined for the next sec tion and another planning and identifying step 51 can be omit ted. However, it would also be possible to identify a section and/or determine the treatment parameters after a section has already been treated. If no new section is to be treated, the procedure is finished 61. Fig. 5a shows schematically a varicose vein 100 before a treat ment. In healthy parts of the vein IOI',IOI'', the vein 100 com prises valves 102 that are functional and prevent the flow of blood in a direction opposite the natural direction of flow 105 of blood. The vein 100 has a varicose segment 103 where a diame- ter of the vein is extended and the vein 100 dilated. The valves 105 do not close in the varicose segment 103. Therefore, blood may flow against the normal direction 105.

Fig. 5b schematically shows the vein 100 after a treatment ac- cording the invention. A section 104' at a distal end, i.e. at a downstream end of the segment 103, has been treated with HIFU and is completely occluded as a result. A second section 104 adjacent to the first section 104' is untreated. The occlusion of first section 104' is sufficient to restore the functionality of the vein system. Additionally, it would be possible to treat at least a part of the second section 104 with a sclerosant.