阅读说明：本技术 用于生成血管内超声图像的超声图像生成系统 (Ultrasound image generation system for generating intravascular ultrasound images ) 是由 T·维塞尔 F·M·韦伯 于 2018-11-13 设计创作，主要内容包括：本发明涉及血管内超声(IVUS)成像的领域。提供血管(6)的IVUS图像,所述IVUS图像已经基于在沿着所述血管的长度的不同采集位置(9、10)处并且在不同采集时间处采集的IVUS信号来确定。此外,提供压力值,所述压力值指示在所述采集时间处所述血管内的所述压力,其中,组合IVUS图像通过组合已经基于在所述压力值与参考压力值相差小于预定义的偏差阈值的采集时间处采集的IVUS信号被确定的所提供的IVUS图像来生成。血管内的压力作为用于组合IVUS图像的选择准则的这种使用能够确保仅对应于相同血管壁运动状态的IVUS图像被组合,由此减少组合IVUS图像中的伪影。(The present invention relates to the field of intravascular ultrasound (IVUS) imaging. An IVUS image of a blood vessel (6) is provided, which IVUS image has been determined based on IVUS signals acquired at different acquisition positions (9, 10) along the length of the blood vessel and at different acquisition times. Furthermore, a pressure value is provided, the pressure value being indicative of the pressure within the vessel at the acquisition time, wherein a combined IVUS image is generated by combining provided IVUS images that have been determined based on IVUS signals acquired at acquisition times at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold. This use of intravascular pressure as a selection criterion for combining IVUS images can ensure that only IVUS images corresponding to the same vessel wall motion state are combined, thereby reducing artifacts in the combined IVUS images.)

1. An ultrasound image generation system for generating intravascular ultrasound images, wherein the ultrasound image generation system (1) comprises:

an ultrasound image providing unit (4, 5) for providing intravascular ultrasound images of a blood vessel (6), which have been determined based on intravascular ultrasound signals acquired at different acquisition positions (9, 10) along the length of the blood vessel (6) and at different acquisition times,

an acquisition position providing unit (18) for providing the different acquisition positions at which the intravascular ultrasound signals have been acquired,

a pressure value providing unit (4) for providing an intravascular pressure value indicative of the pressure within the blood vessel (6) at the acquisition time (11, 12),

an ultrasound image combination unit (14) for generating a combined ultrasound image by combining, according to the acquisition location (9, 10), provided intravascular ultrasound images which have been determined based on intravascular ultrasound signals acquired at acquisition times (11, 12) at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold.

2. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image combination unit (14) is adapted to combine the provided intravascular ultrasound images which have been determined based on intravascular ultrasound signals acquired at acquisition times (11, 12) differing by less than a predefined upper time deviation threshold.

3. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image combination unit (14) is adapted to combine the provided intravascular ultrasound images which have been determined based on intravascular ultrasound signals acquired at acquisition times (11, 12) differing by more than a predefined lower time deviation threshold.

4. Ultrasound image generation system as claimed in claim 3, wherein the ultrasound image generation system (1) further comprises a cardiac period value providing unit (15) for providing a cardiac period value indicative of a temporal length of a cardiac cycle, wherein the lower time deviation threshold is predefined such that it is equal to or larger than the temporal length of the cardiac cycle indicated by the provided cardiac period value.

5. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image combination unit (14) is adapted to combine the provided intravascular ultrasound images which have been determined based on intravascular ultrasound signals acquired at acquisition positions (9, 10) differing by less than a predefined spatial deviation threshold.

6. Ultrasound image generation system as claimed in claim 5, wherein the ultrasound image combination unit (14) is adapted to provide a morphology of the blood vessel (6) and to modify the predefined spatial deviation threshold in accordance with the provided morphology.

7. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image combination unit (14) is adapted to combine temporally adjacent intravascular ultrasound images.

8. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image generation system (1) further comprises a controller (5) for controlling the ultrasound signal acquisition unit (7) for acquiring the intravascular ultrasound signals when the ultrasound signal acquisition unit (7) is moved within the blood vessel (6) and to different positions along the length of the blood vessel (6) by using a moving unit (17), wherein the pressure value providing unit (4, 5) is adapted to provide a pressure value indicative of a current pressure within the blood vessel (6) when the ultrasound signal acquisition unit (7) is moved, wherein the controller (5) is adapted to control the ultrasound signal acquisition unit (7) such that for determining intravascular ultrasound images an intravascular ultrasound image is acquired in case a difference between the current pressure value and the reference pressure value is smaller than the predefined pressure deviation threshold value An acoustic signal, the reference pressure value being a pressure value provided within a last acquisition time for determining that an intravascular ultrasound signal of a previous intravascular ultrasound image has been acquired, wherein the ultrasound image providing unit is adapted to provide the intravascular ultrasound image by determining the intravascular ultrasound image based on the acquired ultrasound signal.

9. Ultrasound image generation system as claimed in claim 8, wherein the controller (5) is adapted to control the ultrasound signal acquisition unit (7) and also the movement unit (17) such that the ultrasound signals are acquired at acquisition positions (9, 10) having a predetermined spatial resolution.

10. Ultrasound image generation system as claimed in claim 9, wherein the controller (5) is adapted to control a) the moving unit (17) such that after an intravascular ultrasound signal has been acquired at an acquisition location, the ultrasound signal acquisition unit (7) is moved to a next acquisition location corresponding to the predetermined spatial resolution, and b) the ultrasound signal acquisition unit (7) such that an intravascular ultrasound signal is acquired at the next acquisition location if a current pressure differs from the reference pressure value by less than the predefined deviation threshold, the reference pressure value being a pressure value measured when the intravascular ultrasound signal was acquired at the previous acquisition location.

11. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image combination unit (14) is adapted to generate several combined ultrasound images for different reference pressure values, wherein for generating the respective combined ultrasound images the provided intravascular ultrasound images which have been determined based on the intravascular ultrasound signals acquired at acquisition times (11, 12) at which the pressure values differ from the respective reference pressure values by less than a predefined deviation threshold are combined in accordance with the acquisition positions (9, 10).

12. Ultrasound image generation system as claimed in claim 1, wherein the pressure value providing unit (4) is adapted to provide the intravascular pressure values such that they are indicative of the pressure within the blood vessel (6) at the acquisition location (9, 10).

13. Ultrasound image generation system as claimed in claim 1, wherein the ultrasound image providing unit (4, 5) and the pressure value providing unit (4) are integrated in a single unit.

14. An ultrasound image generation method for generating an intravascular ultrasound image, wherein the ultrasound image generation method comprises:

providing, by an ultrasound image providing unit (4, 5), intravascular ultrasound images of a blood vessel (6), which have been determined based on intravascular ultrasound signals acquired at different acquisition times (11, 12) and at different acquisition positions (9, 10) along the length of the blood vessel (6),

providing the different acquisition positions at which the intravascular ultrasound signals have been acquired by an acquisition position providing unit (18),

providing an intravascular pressure value by a pressure value providing unit (4), the intravascular pressure value being indicative of the pressure within the blood vessel (6) at the acquisition time (11, 12),

generating a combined ultrasound image by an ultrasound image combining unit (14) by combining, according to the acquisition location (9, 10), the provided intravascular ultrasound images which have been determined based on the intravascular ultrasound signals acquired at acquisition times (11, 12) at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold.

15. A computer program for generating an intravascular ultrasound image, the computer program comprising program code means for causing an ultrasound image generation system as defined in claim 1 to carry out the steps of the ultrasound image generation method as defined in claim 14, when the computer program is run on a computer controlling the ultrasound image generation system.

Technical Field

The present invention relates to an ultrasound image generation system, a method and a computer program for generating intravascular ultrasound images.

Background

US2010/0030061a1 discloses an image guided navigation system comprising an imaging device, a tracking device, a controller and a display. The imaging device generates an image of a region of the patient and the tracking device tracks a position of the instrument within the region of the patient, wherein the controller superimposes an icon representing the instrument onto the image based on the tracked instrument position. The display ultimately displays the image with the superimposed icons.

US2008/0051660a1 discloses a catheter device comprising a nozzle system having exit holes around its periphery, said nozzle system being adapted to guide a jet of a medicament through a hole close to, next to or in close proximity to a portion of the vessel wall of a vessel to be imaged. The catheter device further comprises a conduit connecting the nozzle system to an external or internal medicament reservoir and an electro-dynamic flow controller and/or injector adapted to control the flow of medicament from the reservoir to exit the bore through the conduit to the nozzle system. The catheter device further comprises an intravascular ultrasound probe connected to the IVUS imaging unit and an IVUS digital or analog processing unit adapted to receive and analyze IVUS data before, during and/or after the ejection of the medicament.

The Rodriguez-Granillo et al article "In-vivo, cardiac-cycle related assessment of coronary plaque assessed by 3-D ECG-gated intramyocardial infarction:" The International Journal of coronary Imaging, Vol.22, pp.147 to 152 (2006)) discloses The use of (electrocardiographic) ECG gated IVUS Imaging for The detection of coronary plaque.

Ultrasound image generation systems are known which acquire several cross-sectional IVUS images of a blood vessel during pullback of an ultrasound signal acquisition element, which use an ECG for selecting cross-sectional IVUS images that have been acquired at the same cardiac phase, and which combine adjacent selected cross-sectional IVUS images for generating a longitudinal IVUS view of the blood vessel. Since ECG is not a good measure for the movement of the vessel wall, the combined IVUS images may correspond to different vessel wall motion states, which can cause image artifacts in longitudinal IVUS views of the vessel.

Disclosure of Invention

It is an object of the present invention to provide an ultrasound image generation system, a method and a computer program which allow to generate a longitudinal IVUS view of a blood vessel with improved image quality.

In a first aspect of the present invention an ultrasound image generation system for generating intravascular ultrasound images is presented, wherein the ultrasound image generation system comprises:

an ultrasound image providing unit for providing IVUS images of a blood vessel, the IVUS images having been determined based on IVUS signals acquired at different acquisition positions and at different acquisition times along a length of the blood vessel,

an acquisition position providing unit for providing the different acquisition positions at which the IVUS signals have been acquired,

a pressure value providing unit for providing an intravascular pressure value indicative of the pressure within the vessel at the acquisition time,

an ultrasound image combination unit for generating a combined ultrasound image by combining, according to the acquisition location, the provided IVUS images that have been determined based on the IVUS signals acquired at acquisition times at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold.

Since the ultrasound image combination unit is adapted to generate a combined ultrasound image by combining provided IVUS images which have been acquired at acquisition times where the pressure values differ from the reference pressure value by less than a predefined deviation threshold, i.e. since IVUS images corresponding to similar pressure values are combined, and since intravascular pressure is a good measure for the motion state of the blood vessel wall, the combined IVUS images correspond to the same motion state of the blood vessel wall, thereby reducing artifacts or even eliminating artifacts in the resulting combined IVUS images (i.e. in the resulting longitudinal IVUS view of the blood vessel), which artifacts may typically be caused by combining IVUS images corresponding to different motion states of the blood vessel wall. Furthermore, since there is no need to use ECG for selecting IVUS images to be combined, the manipulation of the image generation procedure can be simplified, as there is no need to equip the patient with ECG electrodes.

The ultrasound image providing unit can be a storage unit in which IVUS images of the blood vessel are stored and from which IVUS images can be retrieved for providing IVUS images. Furthermore, the ultrasound image providing unit can be a receiving unit for receiving IVUS images from the intravascular ultrasound image generation unit and providing the received IVUS images. Furthermore, the ultrasound image providing unit can be adapted to receive ultrasound signals from the ultrasound signal acquisition unit, to determine an IVUS image based on the received ultrasound signals, and to provide the generated IVUS image. The ultrasound image providing unit can further include an ultrasound signal acquisition unit. The IVUS images provided are preferably cross-sectional IVUS images of the blood vessel at the respective acquisition locations.

The acquisition location providing unit can be a storage unit in which different acquisition locations are stored and from which the different acquisition locations are retrieved for providing the different acquisition locations. The acquisition position providing unit can also be a receiving unit for receiving different acquisition positions from, for example, an acquisition position measuring unit and for providing the received acquisition positions. Furthermore, the acquisition position providing unit can also be the acquisition position measuring unit itself. The acquisition position providing unit can be adapted to provide as acquisition positions either absolute positions or relative positions, wherein a relative position is preferably a position along the length of the blood vessel relative to a previous position at which an ultrasound image has been provided, which position fulfils one or more of the pressure-related conditions described above and optionally (i.e. depending on the respective embodiment) the temporal and spatial conditions described below. The preferred relative position can also be defined as a position along the length of the blood vessel relative to a previous position at which an ultrasound image has been provided for combination with other provided ultrasound images.

Furthermore, the pressure value providing unit can be a memory unit, wherein in this case the memory unit is adapted to store intravascular pressure values and to provide the stored intravascular pressure values. The pressure value providing unit can also be a receiving unit for receiving intravascular pressure values from the pressure value measuring unit and for providing received intravascular pressure values. Furthermore, the pressure value providing unit can also be a pressure value measuring unit.

Preferably, the ultrasound image combination unit is adapted to combine provided IVUS images that have been determined based on IVUS signals acquired at acquisition times differing by less than a predetermined large time deviation threshold. This enables to determine that relatively slow changes in the movement of the vessel wall have no or only a limited effect on the pressure value. The pressure value can thus be a further improved measure for the vessel wall motion state, which can lead to a further improved quality of the combined ultrasound image.

Furthermore, it is preferred that the ultrasound image combination unit is adapted to combine provided intravascular ultrasound images that have been determined based on IVUS signals acquired at acquisition times differing by more than a predefined lower time deviation threshold. In particular, the ultrasound image generation system further comprises a cardiac period value providing unit for providing a cardiac period value indicative of a temporal length of a cardiac cycle, wherein the lower time deviation threshold is predefined such that it is equal to or larger than the temporal length of the cardiac cycle as indicated by the provided cardiac period value. The lower time deviation threshold can also be greater than the length of time of several cardiac cycles. Since the vessel wall motion is mainly caused by heart motion, by combining IVUS images that have been acquired at acquisition times that differ by more than the time length of the cardiac cycle, it can be ensured that the combined IVUS images correspond to different vessel wall motion periods rather than to the same vessel wall motion period, thereby determining that the combined IVUS images correspond to the same vessel wall motion state in different vessel wall motion periods. This can lead to a further improved image quality of the resulting combined IVUS image, i.e. the longitudinal view of the blood vessel.

The cardiac period value is preferably predefined and stored in a cardiac period value providing unit, wherein the cardiac period value providing unit is adapted to provide the stored cardiac period value. Thus, preferably, no measurements such as electrocardiograms are required when acquiring IVUS signals for providing cardiac phase values. The cardiac period value can be a previous measurement of the length of time of the cardiac cycle based on an estimate and/or based on a particular patient or a group of patients similar to the particular patient with respect to a predetermined criterion like age, gender, etc.

It is further preferred that the ultrasound image combination unit is adapted to combine provided IVUS images that have been determined based on IVUS signals acquired at acquisition positions differing by less than a predetermined spatial deviation threshold. This can significantly reduce the likelihood of pressure variations being largely caused by varying vessel morphology along the length of the vessel, rather than by vessel wall motion, thereby further increasing the likelihood that IVUS images corresponding to the same vessel wall motion state are combined, which can lead to further increased image quality of the longitudinal view of the vessel.

The ultrasound image combination unit can be adapted to provide a morphology of the blood vessel and to modify the predetermined spatial deviation in accordance with the provided morphology. In particular, the lower temporal deviation ultrasound image combination unit can be adapted to determine a gradient of the open cross section of the blood vessel along the length of the blood vessel, wherein the spatial deviation threshold can be modified (i.e. determined) based on the gradient at the current position of the blood vessel, e.g. of the ultrasound signal acquisition unit. For this determination and thus modification of the spatial deviation threshold, an assignment between gradients and the spatial deviation threshold or a modification of gradients and the spatial deviation threshold can be used, which can be defined during a calibration procedure and/or by simulations. The morphology of the blood vessel may already be known from previous measurements of the blood vessel with IVUS or another imaging modality, wherein the ultrasound image combination unit can adapt to this already known morphology.

Preferably, the ultrasound image combination unit is adapted to combine temporally adjacent IVUS images. Therefore, the ultrasound image combination unit is preferably adapted to combine the IVUS images in pairs. The ultrasound image combination unit can thus be adapted to combine, for example, a) a first IVUS image in time with a second IVUS image in time, wherein for two IVUS images the above-described pressure-related condition and optionally (i.e. depending on the respective embodiment) one or more of the other above-described conditions are fulfilled, b) the second IVUS image in time and the third IVUS image in time, wherein for two IVUS images the above-described pressure-related condition and optionally one or more of the other above-described conditions are fulfilled, c) a temporally third IVUS image and a temporally fourth IVUS image, wherein the above-described pressure-related condition and optionally one or more of the other above-described conditions are fulfilled for both IVUS images, and so on, in order to generate a combined IVUS image showing the length of the blood vessel covering different acquisition locations. In other words, preferably, the expression "temporally adjacent" merely refers to a set of IVUS images that fulfill one or more conditions that should be fulfilled in the respective embodiment, wherein a temporally first IVUS image of the set is combined with a temporally second IVUS image of the set, the temporally second IVUS image of the set is combined with a temporally third IVUS image of the set, and so on. The process of combining the two IVUS images is preferably a collage process, wherein the two IVUS images are simply collaged together. In an embodiment, the ultrasound image combination unit can be further adapted to register the two IVUS images before being combined and to stitch the registered IVUS images together. The registration is preferably based on registration of features detectable in the IVUS images to be combined.

In one embodiment, the ultrasound image generation system further comprises a controller for controlling the ultrasound signal acquisition unit for acquiring the IVUS signal when the ultrasound signal acquisition unit is moved within the blood vessel and to different positions along the length of the blood vessel by using a moving unit, wherein the pressure value providing unit is adapted to provide a pressure value indicative of the current pressure within the blood vessel when the ultrasound signal acquisition unit is moved, wherein the controller is adapted to control the ultrasound signal acquisition unit such that, for determining an IVUS image, an IVUS signal is acquired if a difference between a current pressure value and the reference pressure value for a pressure value provided within a last acquisition time for determining that an IVUS signal of a previous IVUS image has been acquired is smaller than the predetermined pressure deviation threshold, wherein the ultrasound image providing unit is adapted to provide the IVUS image by determining the IVUS image based on the acquired ultrasound signals. Thus, the controller can be adapted to control the ultrasound signal acquisition unit such that the acquired IVUS signals, and thus the provided IVUS images, already fulfill the condition that they should correspond to similar pressure values. The controller can be further adapted to control the ultrasound signal acquisition unit such that only ultrasound signals are acquired if one or more of the other above-mentioned conditions are also fulfilled. Thus, the controller can be adapted to control the ultrasound signal acquisition unit such that only IVUS signals are acquired if the currently measured pressure is similar to the pressure corresponding to IVUS signals acquired at the last acquisition position and optionally a) if the current time differs from the last acquisition time at which IVUS signals have been acquired by less than a predetermined large time deviation threshold and/or b) if the current time differs from the last acquisition time at which IVUS signals have been acquired by more than a predefined lower time deviation threshold and/or c) if the current position of the ultrasound signal acquisition unit differs from the last acquisition position at which IVUS signals have been acquired by less than a predetermined spatial deviation threshold. The pressure measurements and optionally the time and position measurements can thus be used to control the acquisition of IVUS signals and thus the determination and provision of IVUS images. However, it is also possible that the acquisition of the IVUS signals is not controlled in this way, and that IVUS signals are also acquired and corresponding IVUS images are determined which do not fulfill the above mentioned conditions. The selection of IVUS images to be combined such that the above mentioned conditions are fulfilled is then performed by the ultrasound image combination unit. Thus, instead of gated acquisition, it is also possible to use retrospective gating.

The reference pressure value can be a pressure value that has been measured at the acquisition time at which the IVUS signal has been acquired. For example, it can be a pressure value that has been measured at the earliest of the acquisition times corresponding to IVUS measurements performed during pullback movement of the IVUS acquisition unit in the vessel. The reference pressure value can also be adjusted during IVUS acquisition. For example, the reference pressure value can be a pressure value that has been measured when the IVUS signal for the last IVUS image that satisfies the pressure condition described above, and preferably the time and position condition described above, has been acquired.

The controller and the ultrasound image providing unit are preferably integrated such that the controller is also adapted to determine an IVUS image based on the acquired IVUS signals. However, the controller and the ultrasound image providing unit can also be different units. Furthermore, in a preferred embodiment, the controller is adapted to control the ultrasound signal acquisition unit and the moving unit such that the ultrasound signals are acquired at acquisition positions having a predetermined spatial resolution. In particular, the controller is adapted to control a) the moving unit such that after an IVUS signal has been acquired at an acquisition location, the ultrasound signal acquisition unit is moved to a next acquisition location corresponding to the predetermined spatial resolution, and b) the ultrasound signal acquisition unit such that an IVUS signal is acquired at the next acquisition location if a current pressure differs from the reference pressure value being a pressure value measured when acquiring the IVUS signal at the previous acquisition location by less than the predefined deviation threshold and optionally if one or both of the above-described time conditions are fulfilled. By determining a combined ultrasound image with a predetermined (in particular constant) spatial resolution, the image quality of the combined ultrasound image can be further improved.

In an embodiment, the ultrasound image combination unit is adapted to generate several combined ultrasound images for different reference pressure values, wherein, for generating a respective combined ultrasound image, the provided IVUS images, which have been determined based on IVUS signals acquired at acquisition times at which the pressure values differ from the respective reference pressure values by less than a predefined deviation threshold, are combined according to the acquisition positions. Thus, different combined ultrasound images showing the length of the vessel can be generated for different states of vessel wall motion, wherein these several combined ultrasound images form a time-combined ultrasound image showing the motion of the vessel wall.

The pressure value providing unit is preferably adapted to provide the intravascular pressure values such that they are indicative of the pressure within the blood vessel at the collection location. Therefore, preferably, the pressure value is measured directly at the acquisition location. This can further increase the quality of the pressure value with regard to its suitability for selecting which IVUS images should be combined in order to generate a combined ultrasound image showing the vessel length. This can lead to a further increased image quality of the combined ultrasound image.

Further, preferably, the ultrasound image providing unit and the pressure value providing unit are integrated in a single unit. For example, the ultrasound image providing unit can comprise an ultrasound signal acquisition unit, which can comprise a catheter with an ultrasound transducer for acquiring IVUS signals, wherein the ultrasound transducer can also be used for measuring pressure and thus for generating pressure values, or wherein an additional sensor can be used for measuring pressure, wherein this additional sensor can also be attached to the catheter. By using the same unit for providing ultrasound images and for providing pressure values, the manipulation of the ultrasound image generation system can be simplified for the user.

In a further aspect of the present invention, an ultrasound image generation method for generating an intravascular ultrasound image is presented, wherein the ultrasound image generation method comprises:

providing, by an ultrasound image providing unit, intravascular ultrasound images of a blood vessel, which have been determined based on intravascular ultrasound signals acquired at different acquisition times and at different acquisition positions along the length of the blood vessel,

providing the different acquisition positions at which the intravascular ultrasound signals have been acquired by an acquisition position providing unit,

providing, by a pressure value providing unit, an intravascular pressure value indicative of the pressure within the vessel at the acquisition time,

generating, by an ultrasound image combination unit, a combined ultrasound image by combining, according to the acquisition position, provided intravascular ultrasound images that have been determined based on intravascular ultrasound signals acquired at acquisition times at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold.

In particular, the ultrasound image providing unit provides the ultrasound image combining unit with the determined intravascular ultrasound image by transmitting the determined intravascular ultrasound image to the ultrasound image combining unit. Furthermore, the acquisition position providing unit provides the ultrasound image combination unit with different acquisition positions at which intravascular ultrasound signals have been acquired, preferably by transmitting these different acquisition positions to the ultrasound image combination unit. Furthermore, the pressure value providing unit provides the ultrasound image combination unit with an intravascular pressure value indicative of the pressure within the vessel at the acquisition time (which intravascular pressure value has been acquired when the intravascular ultrasound signal has been used for determining the intravascular ultrasound image has been acquired), preferably by transmitting these intravascular pressure values to the ultrasound image combination unit.

In a further aspect of the present invention a computer program for generating an intravascular ultrasound image is presented, wherein the computer program comprises program code means for causing an ultrasound image generation system as defined in claim 1 to carry out the steps of the ultrasound image generation method as defined in claim 14, when the computer program is run on a computer controlling the ultrasound image generation system.

It shall be understood that the ultrasound image generation system according to claim 1, the ultrasound image generation method according to claim 14 and the computer program according to claim 15 have similar or identical preferred embodiments, in particular, as defined in the dependent claims.

It shall be understood that preferred embodiments of the invention can also be any combination of the dependent claims or the above embodiments with the respective independent claims.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

Drawings

In the following drawings:

figure 1 schematically and exemplarily shows an embodiment of an ultrasound image generation system for generating intravascular ultrasound images,

figure 2 shows schematically and exemplarily the distal end of a catheter with an intravascular ultrasound transducer of an ultrasound image generation system,

FIG. 3 shows an example of intravascular pressure measurement, an

Fig. 4 shows a flow chart exemplarily illustrating an embodiment of an ultrasound image generation method for generating an intravascular ultrasound image.

Detailed Description

Fig. 1 schematically and exemplarily shows an embodiment of an ultrasound image generation system for generating intravascular ultrasound images. The ultrasound image generation system 1 comprises a catheter 4 adapted to be introduced into a blood vessel of a person 3 lying on a support means 2, like a patient table. After the catheter 4 has been introduced into the blood vessel of the person 3 and moved to the desired position within the blood vessel, the catheter 4 can be pulled back manually or by using the moving unit 17. The moving unit 17 is an automatic pull-back device that pulls the catheter 4 back and out of the blood vessel within the person 3. The moving unit 17 can also be adapted to move the catheter 4 in a forward direction within a blood vessel in the person 3, i.e. to move the catheter 4 further into the person 3. However, the forward movement can also be performed manually.

A distal portion of the catheter 4 is schematically and exemplarily illustrated in fig. 2. The catheter 4 comprises an IVUS transducer 7 which is movable in a pull-back direction 30 via the catheter 4 by using a moving unit 17. Fig. 2 also shows schematically and exemplarily a blood vessel 6 with a stenosis 8. The IVUS transducer 7 is adapted to transmit and receive ultrasound waves for generating ultrasound signals which can be used for determining cross-sectional IVUS images at the respective positions of the IVUS transducer 7. The acquired ultrasound signals are then sent to the controller 5 via the catheter 4, wherein the controller 5 is adapted to generate cross-sectional IVUS images at different positions along the length of the blood vessel 6 when the IVUS transducer 7 is moved in the pullback direction 30. The catheter 4 with the IVUS transducer 7 and the controller 5 thus provides IVUS images of the blood vessel 6 that have been determined based on IVUS signals acquired at different locations along the length of the blood vessel 6 and at different acquisition times. The catheter 4 with the IVUS transducer 7 and the controller 5 can thus be seen as a component of the ultrasound image providing unit.

In this embodiment, the IVUS transducer 7 is further adapted to measure the pressure within the blood vessel at the respective position of the IVUS transducer 7, wherein the measured pressure is sent to the controller 5 via the catheter 4. The catheter 4 with the IVUS transducer 7 thus also provides an intravascular pressure value indicative of the pressure within the blood vessel. The catheter 4 with the IVUS transducer 7 can thus also be shown as a pressure value providing unit.

Thus, in this embodiment, the same device (i.e. the catheter 4 with the IVUS transducer 7) is used for providing cross-sectional IVUS images and for providing pressure values, wherein the pressure values can be measured directly at a location along the length of the blood vessel 6 at which the IVUS signal is also measured. In another embodiment, it is also possible that an additional sensor, preferably also integrated with the catheter 4, is used to measure the pressure close to the location of the IVUS transducer 7.

The ultrasound image generation system further comprises a position measurement sensor 18 arranged at the mobile unit 17, wherein the position measurement sensor 18 is adapted to measure at the mobile unit 17 how far the IVUS transducer 7 has been moved within the blood vessel 6, wherein this information is used to determine the respective position of the IVUS transducer 7 along the length of the blood vessel 6. The determined position is preferably a relative position, i.e. a position relative to the last acquisition position at which IVUS signals have been acquired and for which the corresponding IVUS image has been determined based on these IVUS signals. The position measurement sensor 18 can also be adapted to measure a position relative to another position along the length of the blood vessel (i.e. for example relative to the furthest position of the IVUS transducer 7 that is moved forward into the blood vessel 6 before the pullback procedure is started). Since the position measurement sensor 18 is adapted to measure the position of the IVUS transducer 7 within the blood vessel 6 and since these measured positions also include the position at which IVUS signals for determining the cross-sectional IVUS images are acquired, the position measurement unit 18 can be regarded as an acquisition position providing unit for providing different acquisition positions for acquiring IVUS signals for determining the cross-sectional IVUS images. The position measuring sensor 18 can be, for example, an incremental encoder. However, other means can be used to provide the acquisition position. For example, the acquisition position providing unit can be adapted to provide the acquisition position based on an angiogram (i.e. a vessel based image).

The ultrasound image generation system 1 further comprises a cardiac period value providing unit 15 for providing a cardiac period value indicative of the temporal length of the cardiac cycle. In this embodiment, the cardiac period value providing unit 15 is a memory unit in which a cardiac period value is stored which is indicative of a typical length of time of a cardiac cycle of the person 3 lying on the examination table 2. For example, a heart rate indicating the time length of a cardiac cycle can be stored in the cardiac period value providing unit 15. In another embodiment, the cardiac period value providing unit 15 may be a measuring unit for measuring a length of time of a cardiac cycle of the person 3, like an electrocardiograph. However, in a further embodiment, the cardiac period value providing unit 15 can also be absent. In fact, in another embodiment, the ultrasound image generation system 1 does not necessarily need the cardiac period value providing unit 15.

When the moving unit 17 pulls back the catheter 4 with the IVUS transducer 7, the position of the IVUS transducer 7 and the pressure at the respective position are continuously measured. Also, the time is continuously measured by, for example, the controller 5 or by another component capable of measuring time. The controller 5 is adapted to control the IVUS transducer 7 such that it only acquires IVUS signals if the following conditions are met: a) a difference between the current pressure value and a reference pressure value, which is a pressure value provided within a last acquisition time for determining that an IVUS signal of a previous IVUS image has been acquired, is less than a predetermined pressure deviation threshold, b) a difference between the current time and a previous acquisition time for determining that an IVUS signal of an IVUS image has been acquired before is less than a predetermined larger time deviation threshold, c) the time difference is greater than a predefined lower time deviation threshold, and d) a difference between the current position and a previous acquisition position for determining that an IVUS signal of a previous cross-sectional IVUS image has been acquired is less than a predetermined spatial deviation threshold. The controller 5 is therefore adapted to continuously check whether these conditions are met, wherein, if this is the case, the IVUS signal is next acquired and used to determine the next cross-sectional IVUS image.

The ultrasound image generation system 1 further comprises an ultrasound image combination unit 14 for generating a combined ultrasound image by combining the provided IVUS images according to the respective acquisition positions. Preferably, the ultrasound image combination unit 14 is adapted to tile together temporally adjacent IVUS images to generate a combined ultrasound image showing a longitudinal ultrasound image of the blood vessel 6 along its length. In particular, cross-sectional IVUS images corresponding to different acquisition locations along the length of the blood vessel 6 are tiled together in pairs in order to generate a combined ultrasound image. For this combining or collaging process, known registration-based algorithms can be used, like for example the algorithms disclosed in the article "raised and elastic registration for social areas IVUSimages" (technical and Health Care, Vol.2, pages 455 to 463 (2016)) by Z.Sun et al, which is incorporated herein by reference. The collage process can also be performed without registering the IVUS images to be combined, i.e. the respective two IVUS images can simply be collaged together. The collage process may also be considered a stacking process, in which two IVUS images are stacked together.

In fig. 2, the acquisition positions satisfying the above described conditions and the IVUS signals for determining the corresponding cross-sectional IVUS images are indicated by lines 9 and 10. Fig. 3 schematically and exemplarily illustrates pressure measurements over time and thus over position along the length of the blood vessel 6, as the IVUS transducer 7 is moved out of the blood vessel 6 in the pull-back direction 30. The acquisition times corresponding to the acquisition positions 9, 10 are indicated in fig. 3 by small dots 11, 12, respectively.

The predetermined larger temporal deviation threshold, the predetermined spatial deviation threshold and the predefined lower temporal deviation threshold define a temporal-spatial association window, i.e. a window having temporal and spatial aspects, or in other words a temporal window and a spatial window. In fig. 3, reference numeral "13" schematically and exemplarily indicates a temporal aspect of the temporal-spatial association window, or in other words, the temporal window. If the difference between the current pressure value and a reference pressure value, which is a pressure value provided during the last acquisition time for determining that the IVUS signal of the previous IVUS image has been acquired, is less than a predetermined pressure deviation threshold and if the current position of the IVUS transducer and the current time are within a spatio-temporal correlation window, then the IVUS signal is acquired and used to determine the next cross-sectional IVUS image.

The controller 5 can be further adapted to control the IVUS transducer 7 and the moving unit 17 such that the ultrasound signals are acquired at acquisition positions 9, 10 having a constant spatial resolution, wherein the spatial resolution may be selectable by a user via the input unit 16 (like a keyboard, a computer mouse, a touch pad, etc.). In particular, the controller 5 is adapted to control a) the moving unit 17 such that after the IVUS signal has been acquired at the acquisition position 9, the IVUS transducer 7 is moved to a next acquisition position 10 corresponding to a desired constant spatial resolution, and b) the IVUS transducer 7 such that the ultrasound signal is acquired at this next acquisition position 10 if the above described conditions regarding pressure and time are fulfilled. After the IVUS signals have been acquired at this next acquisition position 10, the moving unit 17 moves the IVUS transducer 7 to a further acquisition position still corresponding to the desired constant spatial resolution, where the IVUS signals are also acquired if the above described conditions with respect to pressure and time are fulfilled. This process can be performed until a desired number of cross-sectional ultrasound images have been acquired. The constant spatial resolution preferably corresponds to a distance between adjacent acquisition positions that is less than a predetermined spatial deviation threshold.

The acquisition of the ultrasound signal is a gated acquisition only if the above-described conditions are fulfilled. Instead of or in addition to gating already during acquisition, in an embodiment the ultrasound image combination unit can also be adapted to provide retrospective gating. For example, when the IVUS transducer 7 is pulled back from the blood vessel 6, IVUS signals can be acquired, corresponding cross-sectional IVUS images can be determined based on these acquired IVUS signals, the position of the IVUS transducer 7, the pressure values and the time at these positions of the IVUS transducer 7 can be measured, and the non-gated information can be provided to an ultrasound image combination unit, wherein the ultrasound image combination unit can determine which of the cross-sectional IVUS images fulfill the above described conditions with respect to pressure values, acquisition time and acquisition position, and then only combine these cross-sectional IVUS images fulfilling these conditions.

Hereinafter, an embodiment of an ultrasound image generation method for generating IVUS images will be exemplarily described with reference to a flowchart shown in fig. 4.

In step 101, the moving unit 17 pulls the catheter 4 with the IVUS transducer 7 in the pull-back direction 30 within the blood vessel 6, while the position measurement sensor 18 measures the position of the IVUS transducer 7, the IVUS transducer 7 is used to measure the pressure at the respective position, and the time is measured. Furthermore, still in step 101, if the above described conditions regarding position, time and pressure are fulfilled, the IVUS signals are acquired at the respective positions (i.e. at the respective acquisition positions), and the IVUS images are determined based on the IVUS signals for the respective acquisition positions.

In step 102, the ultrasound image combination unit 14 combines IVUS images that have been acquired at different acquisition positions according to the different acquisition positions in order to generate a combined ultrasound image showing the blood vessel 6 along its length.

Since the acquisition of IVUS signals and the corresponding determination of IVUS images in step 101 are gated with respect to the above described conditions, the ultrasound image combination unit 14 combines only IVUS images that fulfill these conditions. If in another embodiment the acquisition of IVUS signals and the corresponding determination of IVUS images are not gated with respect to the above described conditions for pressure values, position and time, in step 102 the ultrasound image combination unit 14 will check which IVUS images fulfill these conditions and then only combine these IVUS images.

In step 103, the combined ultrasound image is displayed on the display 19.

Ultrasound image generation systems and methods are particularly useful for diagnosing coronary artery disease. For example, they are very useful for assessing coronary plaque burden or for characterizing stenosis. Ultrasound image generation systems and methods can also be very useful as an imaging support in the context of stenting.

IVUS images, which are preferably cross-sectional IVUS images and recorded during the pullback procedure, are joined together such that temporally adjacent IVUS images that should be combined are aligned. The resulting combined ultrasound image is a longitudinal ultrasound view, i.e. a view along the blood vessel.

If the combined IVUS image is not gated by using the conditions described above, the combined ultrasound image will show artifacts due to movement of the vessel wall caused by the beating heart and intra-vascular pressure changes. These artifacts would be, for example, jagged image artifacts. To avoid these artifacts, the ultrasound image generation systems and methods described above use pressure, location, and time based conditions for gating. However, ultrasound image generation systems and methods do not use electrocardiogram gating for the following reasons.

Electrocardiographic gating would require the recording of electrocardiographic signals, which adds effort to the clinical workflow and inconvenience to the person to be examined during the invasive procedure. Furthermore, electrocardiographic recording can be a source of error related to the human operator, where corresponding errors can relate to electrode placement, contact impedance, and the like. This source of error associated with the human operator can compromise the longitudinal representation of the final combined ultrasound image. Furthermore, poor quality longitudinal views of blood vessels resulting from inappropriate electrocardiographic recording can generally only be noticed retrospectively when options for correction are limited. Furthermore, the electrocardiogram provides only a general electrocardiogram signal and is not related to the respective blood vessel or a specific location at the respective blood vessel along, preferably, the coronary arteries. One example for a non-systematic source of error is the delay interval between the QRS complex of the electrocardiogram signal and the mechanical contraction of the heart, where the delay interval may vary over time. The use of an electrocardiogram as a representation for, for example, coronary artery movements is therefore often not very accurate, especially in persons suffering from cardiac dysfunction. The ultrasound image generation system and method described above with reference to fig. 1 to 4 thus make use of an alternative measurement, i.e. a pressure value provided closer to the site of interest, and no external electrocardiogram measurement, i.e. no additional effort as mentioned before, is required.

Ultrasound image generation systems and methods are adapted to gate IVUS recordings by intravascular blood pressure measurements in respective vessels, preferably coronary arteries. For measuring the intravascular blood pressure, a capacitive sensor in the IVUS transducer 7 itself may be used. However, it is also possible to use one or several additional sensors attached to e.g. the catheter 4, which are adapted to measure only the intravascular blood pressure. In addition to this pressure measurement, the ultrasound image generation system and method is preferably adapted to require feedback of time and relative catheter position to define a spatiotemporal correlation window for the pressure signal, wherein the spatiotemporal correlation window is defined by the upper and lower temporal deviation thresholds and the spatial deviation threshold described above.

Information about the catheter position can be obtained by automatically pulling back one or several sensors at the device. In particular, the position measurement sensor 18 described above can be used to provide the required information about the catheter position, in particular about the position of the IVUS transducer 7. If the mobile unit 17 (which may be an automatic pullback device or another unit like the controller 5) knows how much of the catheter 4 has been pulled back at a particular time, additional sensors for determining the respective position may not be needed and the position may be provided directly by, for example, the mobile unit or the controller 5. In this case, the mobile unit or the controller, respectively, may be regarded as an acquisition position providing unit for providing acquisition positions at which IVUS signals have been acquired. The ultrasound image generation systems and methods described above with reference to fig. 1 to 4 incorporate and correlate time, position and pressure information to obtain information about when the desired IVUS signal is to be acquired, and thus determine the desired IVUS image, and monitor whether the current pressure is still within the spatio-temporal limits that allow for direct comparison of pressure values recorded by, for example, a capacitive sensor in the IVUS transducer 7.

Considering a pressure measurement at a certain position of the length of the blood vessel and at a certain time, it is assumed that the pressure signal will approximately return to the pressure measurement in the subsequent cardiac cycle, which can be considered as defining a reference pressure value. The IVUS images, preferably cross-sectional images, recorded in these corresponding points are used to tile together the longitudinal views of the blood vessel. The challenge for this assumption is that the pressure signal is non-stationary. This means that it depends not only on the heartbeat, i.e. on the contraction and expansion of the heart system, but also on the morphology of the vessels (in particular the coronary arteries) at the current catheter position and on the long-term hemodynamics of the vascular system. The latter can be affected by many external factors, such as excitement or relaxation. Since pressure signals are subject to these misleading and non-informative variations, the above described conditions are preferably used, which are time and location dependent and which can be considered as defining a spatio-temporal correlation window. The window can ensure that the catheter (i.e. the IVUS transducer 7 at the tip of the catheter) does not move significantly along the vessel centerline so that pressure variations are not also affected to a large extent by the changing vessel morphology. The limiting case of such a pressure change caused by the stenosis 8 is illustrated in fig. 2.

As shown in fig. 2 in connection with fig. 3, when the IVUS transducer 7 is pulled back along the blood vessel 6, a pressure signal p is continuously recorded, wherein this pressure signal p depends on the time t and, therefore, on the corresponding position x along the length of the blood vessel 6 as the catheter 4 with the IVUS transducer 7 is moved in the pull-back direction 30. The pressure signal p exhibits a superposition of pressure variations over time (i.e. e.g. across the cardiac cycle) and due to long-term hemodynamics. Also, the pressure drop along the vessel caused by the stenosis 8 is illustrated in fig. 3.

The spatial variation of the pressure p follows a certain decay pattern, which is, however, locally more or less stable. The pressure recording at the first time 11 and corresponding first position 9 has a certain temporal spatial neighborhood, wherein the pressure will still return to about the same level again, which is indicated in fig. 2 and 3 by reference numerals 10 and 12. The cross-sectional views (i.e. IVUS images) acquired at these two points can be selected as adjacent cross-sectional views to be combined into a longitudinal view. The associated window moves with the pull back and may vary in length depending on the anatomy. In particular, the ultrasound image combination unit 14 can be adapted to provide a morphology of the blood vessel and to modify the predetermined spatial deviation threshold and thus the length of the spatial aspect of the correlation window in accordance with the provided morphology. For example, the ultrasound image combination unit 14 can be adapted to determine a gradient of an open cross section (i.e. an internal cross section or lumen) of the blood vessel along the length of the blood vessel, wherein the spatial deviation threshold can be modified (i.e. determined) based on the gradient at the current position of the blood vessel of the IVUS transducer 7. For this determination and thus modification of the spatial deviation threshold, an assignment between gradients and the spatial deviation threshold or a modification of gradients and the spatial deviation threshold can be used, which can be defined during a calibration procedure and/or by simulations. The morphology of the blood vessel may already be known from previous measurements of the blood vessel with IVUS or another imaging modality, wherein the ultrasound image combination unit 14 can adapt to this already known morphology. However, if retrospective gating is used, the acquired non-gated IVUS images can also be used to determine morphology, i.e. for example, the non-gated IVUS can be collaged together and the vessels can be segmented in the resulting non-gated IVUS overall image in order to determine morphology.

The spatiotemporal correlation window is preferably defined temporally such that the measured pressure values fall within a certain time interval since the pressure value associated with the last cross-sectional IVUS image was recorded. If this is the case, long-term (i.e. slowly varying) hemodynamics have only a limited effect on the pressure signal, and only the much faster heart beats that are subject to the gating process may have an effect.

By using the conditions described above, the ultrasound image generation system and method determines that the comparison between the reference pressure value of the last cross-sectional IVUS image and the newly acquired pressure value is valid only within the correlation window. Thus, the most similar (i.e. in the best case equal) pressure values can be ensured and the position along the length of the vessel is selected for acquiring the next cross-sectional IVUS image still within the window. The reference pressure value is preferably always updated to the pressure value of the last acquisition position (i.e. the last selected cross-sectional IVUS image), wherein this allows for a slower change of the baseline signal than the heartbeat.

The above described mobile unit 17 can be adapted to provide a continuous automatic pullback, wherein the associated window internally defines the active acquisition context. During pullback, the pressure signal is recorded, i.e. the pressure value is measured by using the pressure measurement sensor 18, and a new acquisition is triggered when the current pressure signal is similar to the reference of the previously acquired cross-sectional IVUS image and the recording is valid according to the associated window. If a heart beat rate of about 1 to 2Hz and a pull back speed between 0.5 and 1mm/s is assumed, the heart beat will always contain a certain distance, which may be 1mm in case of a heart beat rate of 1Hz and a pull back speed of 1 mm/s. This distance is then the lower limit of spatial resolution along the centerline. The temporal aspect of the association window, here the lower time deviation threshold, always exceeds the duration of at least one heartbeat, but preferably comprises several heartbeats, i.e. exceeds the duration of several heartbeats. In this example, the spatial resolution is only approximate, not guaranteed, since it depends on the heart rate and the exact pressure variations. Only images deemed eligible by the gating process are acquired or, if they have already been acquired, used to generate a combined ultrasound image.

In yet another example, a certain spatial resolution can be ensured, which may be constant. In particular, the clinician is able to define a desired spatial resolution along the vessel centerline by using, for example, the input unit 16. The pullback device 17 (i.e. the mobile unit) can then be required to proceed at varying speeds or discrete spatial steps in case of pullback, wherein for this procedure a feedback back can be used. In backward feedback, the ultrasound imaging process can signal whenever an ultrasound acquisition with an appropriate pressure level and still within the bounds of the associated window constraints can proceed, where in this case, a gap is given to the pullback device to advance to the next sample point according to the desired spatial resolution. Thus, the controller can control the pullback device such that the IVUS transducer 7 is moved to the next sampling point when IVUS images have been acquired according to the pressure, time and position conditions described above. This means that the pullback speed can be adjusted online according to the current heart rate to achieve approximately equidistant sampling of the IVUS image along the cross section of the vessel. Also in this example, the described pressure measurement provides a more direct feedback than other measurements (like electrocardiographic measurements), i.e. the feedback is much less delayed and more closely related to the region of interest. Therefore, intravascular pressure measurements are well suited for such "control loops" for pullback devices.

As explained above, the ultrasound image generation system and method can also be configured to be used retrospectively. The cross-sectional IVUS images and pressure values can be acquired simultaneously at different locations along the length of the vessel without gating, wherein thereafter during off-line processing the ultrasound images can be stored according to the vessel wall motion state which may correspond to a pressure-defined cardiac phase, in order to provide different longitudinal views for different vessel wall motion states or different cardiac phases, respectively. Moreover, such retrospective intravascular pressure-based gating still does not require, for example, electrocardiographic recording, and does not rely on retrospectively computed image mutual similarity measures.

The ultrasound image generation system and method can be used for plaque burden or lesion monitoring, for example, for Acute Coronary Syndrome (ACS) or stable angina. The ultrasound image generation system and method can also be adapted to be used in the context of stent placement and/or subsequent imaging. In these applications, the described ultrasound image generation system and method can increase the value of the longitudinal overview across the entire vessel segment and improve the examination of the vessel or treatment characteristics that continue along the vessel. The ultrasound image generation system and method can allow for more realistic, equidistant, and controllable sampling along a blood vessel.

Although in the above described embodiments the determination of IVUS images to be combined as ultrasound images comprises, in addition to the comparison of intravascular pressure values with reference pressure values, a comparison of a difference between a current acquisition time and a previous acquisition time with a temporal deviation threshold or other criteria like a difference between a current acquisition position and a previous acquisition position with a spatial deviation threshold, IVUS images to be combined for generating combined ultrasound images may also be determined by determining IVUS images which have been determined based on IVUS signals acquired at acquisition times where the pressure values differ from the reference pressure values by less than a predefined deviation threshold, without taking into account other criteria.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality.

A single processing unit or device may fulfill the functions of several items recited in the claims. Although specific measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage.

The procedures performed by one or several units or devices, like providing IVUS images, providing acquisition locations, providing pressure values, generating combined ultrasound images, etc., can be performed by any other number of units or devices. These programs and/or the control of the ultrasound image generation system according to the ultrasound image generation method can be implemented as program code means of a computer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

Any reference signs in the claims shall not be construed as limiting the scope.

The present invention relates to the field of IVUS imaging. Providing IVUS images of a blood vessel, the IVUS images having been determined based on IVUS signals acquired at different acquisition locations along a length of the blood vessel and at different acquisition times. Furthermore, a pressure value is provided, the pressure value being indicative of the pressure within the vessel at the acquisition time, wherein a combined IVUS image is generated by combining provided IVUS images that have been determined based on IVUS signals acquired at acquisition times at which the pressure value differs from a reference pressure value by less than a predefined deviation threshold. This use of intravascular pressure as a selection criterion for combining IVUS images can ensure that only IVUS images corresponding to the same vessel wall motion state are combined, thereby reducing artifacts in the combined IVUS images.