WO2015011690A2

WO2015011690A2 - Imaging system for generating an image of a living object

Info

Publication number: WO2015011690A2
Application number: PCT/IB2014/063435
Authority: WO
Inventors: Shyam Bharat; Ehsan DEHGHAN MARVAST; Steven Antonie Willem Fokkenrood
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-07-26
Filing date: 2014-07-25
Publication date: 2015-01-29
Also published as: WO2015011690A3

Abstract

The invention relates to an imaging system for generating an image of a living object (11) like an image from a prostate during a brachytherapy. A first ultrasound data generating unit (40) like a TRUS probe generates first ultrasound data of a field of view (52) including the object and a second ultrasound data generating unit (50), which might be an ultrasound transducer on a brachytherapy catheter (12), generates second ultrasound data of at least a part of the field of view, wherein a segmented ultrasound image, in which the object is segmented, is generated based on the ultrasound data. In particular, spatial regions, which are not sensible by the first ultrasound data generating unit due to shadows (53), may be sensible by the second ultrasound data generating unit, which may allow for an augmentation of the first ultrasound data and finally for a segmented image having an improved quality.

Description

Imaging system for generating an image of a living object

FIELD OF THE INVENTION

The invention relates to an imaging system, an imaging method and an imaging computer program for generating an image of a living object, particularly during a brachytherapy procedure. The invention relates further to a brachytherapy system comprising the imaging system and to a brachytherapy catheter to be used together with the imaging system.

BACKGROUND OF THE INVENTION

High dose rate (HDR) brachytherapy is a form of cancer therapy that utilizes high doses of ionizing radiation delivered over a short period of time, for instance in some minutes, directly at or near the target. Since the delivered doses are relatively high, only a very small margin of error regarding dwell locations, where the doses are applied, and dwell times defining the time periods of applying the doses at the dwell locations is acceptable. It is therefore essential to be able to develop an accurate treatment plan, which defines the dwell locations and the dwell times, and to accurately deliver radiation according to this treatment plan. The treatment plan is generally developed based on a segmented ultrasound image in which the target is segmented. For developing a very accurate treatment plan it is therefore required to very accurately segment the target in the ultrasound image. However, the inherent ultrasonic contrast between the target and its surrounding is often relatively low, which leads to a not very accurate segmentation of the target in the ultrasound image.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an imaging system, an imaging method and a computer program for generating an image of a living object, which allows for an improved segmentation of the object in the image. It is a further object of the present invention to provide a brachytherapy system comprising the imaging system and a brachytherapy catheter to be used with the imaging system.

In a first aspect of the present invention an imaging system for generating an image of a living object is presented, wherein the imaging system comprises: a first ultrasound data generating unit for being located at a first location and for generating first ultrasound data of a field of view of the first ultrasound data generating unit, wherein the field of view includes the object,

a second ultrasound data generating unit for being located at a second location, which is different to the first location, and for generating second ultrasound data of at least a part of the field of view,

an ultrasound image generating unit for generating a segmented ultrasound image, in which the object is segmented, based on the first and second ultrasound data.

Since first and second ultrasound data are generated by first and second ultrasound data generating units, which are located at different locations, wherein the second ultrasound data generating unit generates ultrasound data of at least a part of the field of view of the first ultrasound generating unit, i.e. since the first and second ultrasound data generating units have at least partly overlapping field of views, which are ultrasonically sensed from different locations, parts of the object, which are not very well ultrasonically sensible by one of the first and second ultrasound data generating units, may be better ultrasonically sensible by the other of the first and second ultrasound data generating units. Thus, for instance, parts of the living object like a certain part of a boundary of the living object, which is not detectable in, for example, the first ultrasound data, may be detectable in the second ultrasound data. In particular, parts of the living object, which are not detectable in the first ultrasound data because of shadowing effects, may be detectable in the second ultrasound data and in this way the second ultrasound data may augment the first ultrasound data. Since the ultrasound image generating unit can generate the segmented ultrasound image based on the augmented ultrasound data, i.e. since the segmentation can be based on ultrasound data in which more parts of the living object may be well detectable, the segmentation of the living object in the ultrasound image can be improved.

The imaging system is preferentially adapted to be used during a brachytherapy, wherein the living object is the target object to which radiation should be applied. The first and second ultrasound data generating units are therefore preferentially adapted to generate first and second ultrasound data of the target object and the image generating unit is preferentially adapted to generate a segmented ultrasound image, in which the target object is segmented. The target object is preferentially the prostate or another organ of a person or an animal.

The first and second ultrasound data generating units are preferentially different ultrasound data generating units which have ultrasound transducers in different housings that are arranged at different locations. Preferentially, the first ultrasound data generating unit is a transrectal ultrasound (TRUS) probe and the second ultrasound data generating unit is formed by single element ultrasound transducers arranged on

brachytherapy catheters used during the brachytherapy. During the brachytherapy the first ultrasound data generated by the TRUS probe can comprise shadowing regions caused by the brachytherapy catheters arranged in the field of view of the TRUS probe. However, the corresponding missing spatial information in the first ultrasound data can be provided by the second ultrasound data generated by the single element ultrasound transducers on the brachytherapy catheters such that a generation of a segmented ultrasound image, in which the target object is segmented, can be improved, if in addition to the TRUS ultrasound data the second ultrasound data are used for the segmentation.

In an embodiment the first ultrasound data generating unit is adapted to generate the first ultrasound data at multiple times and/or the second ultrasound generating unit is adapted to generate the second ultrasound data at multiple times, wherein the ultrasound image generating unit is adapted to generate several segmented ultrasound images for the multiple times based on the first and second ultrasound data. Thus, the segmentation in the ultrasound image can be updated at the respective time based on the actually generated first ultrasound data and/or second ultrasound data. For instance, the first ultrasound data and/or the second ultrasound data can be continuously generated, wherein an actual updated segmented ultrasound image can be generated based on the actually present ultrasound data. In particular, only the first ultrasound data or the second ultrasound data may be continuously updated, wherein the segmented ultrasound image, in particular, the segmentation in the ultrasound image, may be updated based on the continuously generated first or second ultrasound data and based on the other of the first and second ultrasound data, which have been generated before. Based on the segmented ultrasound image, which is continuously updated, in particular, in real-time, the actual dimensions of the living object, which may change during a brachytherapy due to edema, i.e. due to swelling, can be monitored and the brachytherapy can be adapted to the actual dimensions of the living object. This can lead to an improved brachytherapy procedure.

In a further embodiment the ultrasound image generating unit is adapted to generate a first ultrasound image of the object based on the first ultrasound data, to generate the segmented ultrasound image by segmenting the object in the first ultrasound image and to amend the segmentation of the object in the segmented ultrasound image based on the second ultrasound data. The second ultrasound data generating unit may be adapted to generate the second ultrasound data at multiple times, wherein the ultrasound image generating unit is adapted to amend the segmentation of the object in the segmented ultrasound image multiple times based on the second ultrasound data generated at the multiple times. In particular, the ultrasound image generating unit can be adapted to update the segmentation in real-time based on actually generated second ultrasound data. For instance, the ultrasound image generating unit can be adapted to generate a B-mode image from the first ultrasound data as the first ultrasound image of the object, wherein firstly the object can be segmented in the B- mode image and this segmentation can then be amended in real-time, i.e. corrected, by using M-mode ultrasound data as the second ultrasound data.

The ultrasound image generating unit can be adapted to replace a part of the first ultrasound data by at least a part of the second ultrasound data for generating combined ultrasound data, to generate the ultrasound image based on the combined ultrasound data and to segment the object in the generated ultrasound image for generating the segmented ultrasound image. In particular, the ultrasound image generating unit can be adapted to determine a part of the first ultrasound data having ultrasound data values being smaller than a predefined threshold and to replace the determined part of the first ultrasound data.

Moreover, also in this embodiment the second ultrasound data generating unit may be adapted to generate the second ultrasound data at multiple times, wherein the ultrasound image generating unit may be adapted to, for each of the multiple times, replace a part of the first ultrasound data by at least a part of the second ultrasound data for generating combined ultrasound data, to generate the ultrasound image based on the combined ultrasound data and to segment the object in the generated ultrasound image for generating the segmented ultrasound image.

The second ultrasound data generating unit can be adapted to generate second ultrasound data of different spatial regions within the field of view, wherein the ultrasound image generating unit can be adapted to detect a boundary of the object within the different spatial regions based on the second ultrasound data and to generate the segmented ultrasound image based on the detected boundary and the first ultrasound data. In particular, the ultrasound image generating unit can be adapted to determine an interpolated boundary of the object in spatial regions, for which the second ultrasound data have not been generated, based on the boundary detected within the spatial regions, for which second ultrasound data have been generated, and to generate the segmented ultrasound image based on the detected boundary, the interpolated boundary and the first ultrasound data. For example, the ultrasound image generating unit can be adapted to generate a B-mode image from the first ultrasound data, wherein the detected and interpolated boundary of the object can be added to the B-mode image for generating the segmented ultrasound image. Also in this case the second ultrasound data can be provided in real-time, for instance, they can be M-mode ultrasound data, wherein the real-time second ultrasound data can be used to determine the boundary of the object in real-time by detecting the boundary in the spatial regions, for which the real-time second ultrasound data are generated, and by determining an interpolated boundary of the object in real-time in spatial regions, for which the second ultrasound data have not been generated. This real-time boundary can be shown on the B-mode image generated from the first ultrasound data. In another embodiment, the boundary in the spatial regions, for which the second ultrasound data have not been generated, can also be determined in another way. For instance, a prostate model, which models the boundary of the prostate, can be adapted to be in conformance with the positions of the boundary detected in the spatial regions for which the second ultrasound data have been generated, wherein the positions of the boundary in the spatial regions, for which the second ultrasound data have not been generated, can be determined from the adapted prostate model. The prostate model may initially be determined based on a B-mode image of the prostate, which may have been generated, before the brachytherapy catheters are inserted into the prostate.

The ultrasound image generating unit can also be adapted to detect a boundary of the object in spatial regions, for which the second ultrasound data have not been generated, based on the first ultrasound data and to generate the segmented ultrasound image based on the boundary detected in the different spatial regions. For instance, the ultrasound image generating unit can be adapted to generate a B-mode image from the first ultrasound data and to detect in the B-mode image within the spatial regions, for which the second ultrasound data have not been generated, the boundary of the object, wherein this detected boundary together with the boundary detected in the spatial regions, for which the second ultrasound data have been generated, can be shown on the B-mode image for providing the segmented ultrasound image.

In an embodiment the second ultrasound data generating unit comprises an ultrasound transducer adapted to be arranged within the urethra. In particular, the ultrasound transducer of the second ultrasound data generating unit may be arranged on a urethra catheter adapted to be introduced into the urethra, wherein the urethra catheter is

preferentially a Foley catheter. Also if the ultrasound transducer of the second ultrasound data is arranged within the urethra, it can generate second ultrasound data, which can provide spatial information about the living object, which may not be detectable in the generated first ultrasound data, thereby also allowing for an improved segmentation of the living object in the ultrasound image. Moreover, since the Foley catheter is relatively large, in particular, larger than a brachytherapy catheter, more ultrasound transducers may be arranged on the Foley catheter, thereby allowing for an increased field of view of the second ultrasound data generating unit, which can further improve the segmentation of the living object in the segmented ultrasound image.

In another aspect of the present invention a brachytherapy system for applying a brachytherapy to a living object is presented, wherein the brachytherapy system comprises:

a brachytherapy catheter to be inserted into the object, wherein the brachytherapy catheter is adapted to receive a radiation source for applying the

brachytherapy,

an imaging system as defined in claim 1.

The brachytherapy system preferentially further comprises a treatment plan determination unit for determining a treatment plan defining a dwell location and a dwell time of the radiation source within the object and a catheter pose and shape providing unit for providing the pose and shape of the catheter within the object, wherein the treatment plan determination unit is adapted to determine the treatment plan based on the segmented image and the provided pose and shape of the catheter. Preferentially, the brachytherapy system further comprises a brachytherapy application unit for applying the brachytherapy in accordance with the treatment plan, wherein the brachytherapy application unit is adapted to position the radiation source within the brachytherapy catheter in accordance with the treatment plan.

In a preferred embodiment, the first ultrasound data generating unit is adapted to generate the first ultrasound data at multiple times and/or the second ultrasound data generating unit is adapted to generate the second ultrasound data at multiple times during the brachytherapy, wherein the ultrasound image generating unit is adapted to generate several segmented ultrasound images for the multiple times based on the first and second ultrasound data and wherein the treatment plan determination unit is adapted to determine multiple treatment plans for the multiple times based on the multiple segmented images. In particular, the first ultrasound data generating unit and/or the second ultrasound data generating unit are adapted to generate ultrasound data in real-time and the ultrasound image generating unit is adapted to generate the segmented ultrasound image in real-time such that the treatment plan can be adapted to the actual dimensions of the living object, which may change during the brachytherapy due to edema, wherein the brachytherapy application unit can be adapted to apply the brachytherapy in accordance with the actual treatment plan, thereby improving the quality of the brachytherapy procedure.

In another aspect of the present invention a brachytherapy catheter to be used with the imaging system as defined in claim 1 is presented, wherein the brachytherapy catheter is equipped with an ultrasound transducer of the second ultrasound data generating unit.

In a further aspect of the present invention an imaging method for generating an image of a living object is presented, wherein the imaging method comprises:

generating first ultrasound data of a field of view of a first ultrasound data generating unit located at a first location by using the first ultrasound data generating unit, wherein the field of view includes the object,

generating second ultrasound data of at least a part of the field of view by a second ultrasound data generating unit located at a second location,

generating a segmented ultrasound image, in which the object is segmented, based on the first and second ultrasound data by an ultrasound image generating unit.

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

It shall be understood that the imaging system of claim 1, the brachytherapy system of claim 10, the brachytherapy catheter of claim 13, the imaging method of claim 14, and the computer program of claim 15 have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims.

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings:

Fig. 1 shows schematically and exemplarily an embodiment of a brachytherapy system, Fig. 2 shows schematically and exemplarily a placing unit of the brachytherapy system,

Fig. 3 shows schematically and exemplarily several brachytherapy catheters of the brachytherapy system inserted into the prostate of a person,

Fig. 4 schematically and exemplarily illustrates an arrangement of the placing unit with a TRUS probe with respect to the person,

Figures 5 to 7 show different views of an embodiment of a brachytherapy catheter equipped with a single element ultrasound transducer,

Fig. 8 schematically illustrates an arrangement during an ultrasound data acquisition procedure,

Fig. 9 shows schematically and exemplarily an embodiment of a tracking device within a brachytherapy catheter,

Fig. 10 shows a flowchart exemplarily illustrating an embodiment of a brachytherapy method,

Fig. 11 shows a flowchart exemplarily illustrating an embodiment of an imaging method,

Fig. 12 exemplarily illustrates an ultrasound acquisition procedure,

Fig. 13 exemplarily shows first ultrasound data and second ultrasound data,

Fig. 14 exemplarily shows a combination of the first and second ultrasound data illustrated in Fig. 13, and

Fig. 15 schematically and exemplarily illustrates a brachytherapy catheter having several single element ultrasound transducers.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 schematically and exemplarily shows an embodiment of a brachytherapy system for applying a brachytherapy to a living object. In this embodiment the brachytherapy system 1 is adapted to apply a brachytherapy to a prostate 11 of a person 2 lying on a table 3. The brachytherapy system 1 comprises a placing unit 5 for being partly inserted into the person 2 and for placing radiation sources close to or within the prostate 11 for directing radiation emitted by the radiation sources to the prostate 11. The placing unit 5 is exemplarily and schematically shown in more detail in Fig. 2.

The placing unit 5 comprises several brachytherapy catheters 12 for being inserted into the person 2. The placing unit 5 further comprises several navigation

elements 13 being wires to which the radiation sources 10 are attached, wherein a respective wire 13 can be moved within a respective brachytherapy catheter 12 for placing a respective radiation source 10 at a desired dwell position. The brachytherapy catheters 12 with the wires 13 are attached to a motor unit 14 comprising several motors for moving the wires 13 in a forward direction and in a backward direction for placing the radiation sources 10 at desired dwell positions. The radiation sources 10 are preferentially radioactive radiation sources emitting radioactive radiation like Ir-192. However, other radioactive sources can also be used for performing the brachytherapy.

The brachytherapy catheters 12 may be flexible or rigid. They have a central hollow channel through which the radiation sources 10 can be moved. In particular, a brachytherapy catheter may be a plastic flexible hollow device having, for instance, an outer diameter of about 2 mm, an inner diameter of about 1.5 mm and a length of approximately 25 cm. The brachytherapy catheters 12 preferentially have a flat opening at one end through which the radiation sources 10 can be introduced. The other end of the brachytherapy catheters 12 is preferentially closed in the form of a beveled tip. This is to ensure that the radiation sources 10 do not come in direct contact with the tissue.

The placing unit 5 further comprises a template 19, which can be used for inserting the brachytherapy catheters 12 in a more uniform configuration into the person 2. The brachytherapy catheters 12 are held in openings 29 in the template 19, which are arranged in a rectangular grid. Fig. 3 shows schematically and exemplarily a possible arrangement of the brachytherapy catheters 12 of the placing unit 5 within the prostate 11.

A first ultrasound data generating unit 40 for being located at a first location and for generating first ultrasound data of the prostate 11 is attached to the placing unit 5. In this embodiment the first ultrasound data generating unit 40 is a TRUS probe 40. The arrangement of the placing unit 5 with the TRUS probe 40 during the brachytherapy is schematically and exemplarily illustrated in Fig. 4. The TRUS probe 40 and the placing unit 5 are held by a holding element 41.

The TRUS probe 40 is connected to an ultrasound image generating unit 42, which is located in a processing and control device 7, for generating a segmented ultrasound image, in which the prostate 11 is segmented, based on the first ultrasound data obtained from the TRUS probe 40 and based on second ultrasound data obtained from a second ultrasound data generating unit 50 located at a second location, which is different to the first location where the TRUS probe 40 is located. The second ultrasound data generating unit is formed by single element ultrasound transducers 50 arranged on the outside of at least some of the brachytherapy catheters 12. A possible arrangement of a single element ultrasound transducer 50 on a brachytherapy catheter 12 is schematically and exemplarily illustrated in Figs. 5 to 7, wherein Fig. 5 shows a side view, Fig. 6 a cross-sectional view and Fig. 7 a top view. The single element ultrasound transducer 50 is connected to the ultrasound image generating unit 42 via a wire 51 running along the length of the brachytherapy catheter 12.

In this embodiment the ultrasound image generating unit 42 is adapted to generate a B-mode image as a first ultrasound image of the prostate 11 based on the first ultrasound data obtained from the TRUS probe 40, to generate the segmented ultrasound image by segmenting the prostate 11 in the B-mode image and to amend the segmentation of the prostate 11 in the B-mode image based on the second ultrasound data, which are, in this embodiment, M-mode data. The M-mode data are used to continuously update the segmentation of the prostate 11 in the B-mode image such that an updated segmented ultrasound image can be provided in real-time.

Fig. 8 shows schematically and exemplarily the arrangement of the TRUS probe 40 and the single element ultrasound transducers 50. A subset of the brachytherapy catheters 12 comprises the single element transducers 50, which acquire second ultrasound data along the lines 55, in order to provide ultrasound data being indicative of boundary positions 54 arranged within shadows 53. The shadows 53 are shadows caused by the respective brachytherapy catheters 12 due to a shadowing of the ultrasound waves emitted by the TRUS probe 40 within a field of view 52. Although in Fig. 8 the shadows 53 are shown only for the brachytherapy catheters 12 equipped with the single element ultrasound transducers 50, also the other brachytherapy catheters 12 generate shadows, which are not shown in Fig. 8 for clarity reasons.

The brachytherapy catheters 12 equipped with the single element ultrasound transducers 50 are preferentially arranged further away from the TRUS probe 40 than the brachytherapy catheters 12 not being equipped with the single element ultrasound transducers 50. Depending on the orientation of the single element ultrasound transducers 50 on the brachytherapy catheters 12 respective locations 54 of the prostatic boundary are imaged. These points on the prostatic boundary are preferentially known at all times during the brachytherapy procedure, which is, in this embodiment, a HDR brachytherapy procedure. This information can be used to augment image information directly available from the TRUS probe 40. Since the M-mode ultrasound data from the single element ultrasound transducers 50 are available in real-time, these data can be used to provide continuous updates of an original segmentation, which may be initially generated in a B-mode image produced from the first ultrasound data obtained from the TRUS probe 40. These continuous updates afford the ability to accurately track and monitor edema of the prostate 11 during the brachytherapy procedure. The updated segmentation may be shown on a display 30. The TRUS probe 40, the single element ultrasound transducers 50 and the ultrasound image generating unit 42 can be regarded as forming an imaging system for generating an image of the prostate 11.

The brachytherapy system 1 further comprises a treatment plan determination unit 39 for determining a treatment plan defining dwell locations and dwell times of the radiation sources 10 within the prostate 11, wherein the treatment plan determination unit 39 is adapted to determine the treatment plan based on the segmented image and the poses and shapes of the brachytherapy catheters 12. In particular, the treatment plan determination unit 39 is adapted to determine the pose and shape of the prostate 11 from the segmented image and to determine the treatment plan based on the pose and shape of the prostate 11 and the poses and shapes of the brachytherapy catheters 12. The determination of the poses and shapes of the brachytherapy catheters 12 will be described further below. The dwell locations define where the radiation sources 10 are to be placed and the dwell times define when and how long the respective radiation source 10 is to be placed at the respective dwell position.

The brachytherapy system 1 further comprises a placing control unit 15 for controlling the placing unit 5 depending on the determined treatment plan. Alternatively, the placing unit 5 may be used manually in accordance with the determined treatment plan, wherein a user may move the radiation sources 10 via the wires 13 within the catheters 12 in accordance with the treatment plan. The placing unit 5 and the placing control unit 15 can be regarded as forming a brachytherapy application unit for applying the brachytherapy in accordance with the treatment plan.

Before introducing the radiation sources 10 into the brachytherapy catheters 12, the three-dimensional poses and shapes of the brachytherapy catheters 12 within the person 2 are determined, i.e. the three-dimensional spatial run of each brachytherapy catheter 12 within the person 2 is determined. For this determination procedure the brachytherapy system 1 further comprises a tracking device 16 for being sequentially introduced into the brachytherapy catheters 12 and for being moved to different locations within the respective brachytherapy catheter 12, wherein a tracking device position providing unit 6 provides positions of the tracking device 16 at the different locations within the respective brachytherapy catheter 12. The brachytherapy system 1 further comprises a brachytherapy catheter pose and shape determination unit 44 for determining the poses and shapes of the brachytherapy catheters 12 from the tracked positions of the tracking device 16. The tracking device 16, the tracking device position providing unit 6 and the brachytherapy catheter pose and shape determination unit 44 can be regarded as forming a catheter pose and shape providing unit for providing the pose and shape of the respective brachytherapy catheter 12 within the prostate 11.

In this embodiment the tracking device position providing unit 6 is an electromagnetic (EM) tracking unit, which cooperates with the tracking device 16 being an electromagnetic sensing element arranged at the tip of a guidewire 60 as schematically and exemplarily illustrated in Fig. 9. In other embodiments the tracking device position providing unit can also be adapted to track the positions of the tracking device by using other tracking technologies like a fiber optic shape sensing and localization (FOSSL) technology.

For determining the position of the grid 19 in a coordinate system defined by the tracking system the tracking device 16 can be arranged at the grid 19, while the position of the tracking device 16 is determined by the tracking system. After the position of the grid 19 has been determined in the coordinate system defined by the tracking system, the poses and shapes of the brachytherapy catheters 12 are known with respect to the grid 19, because the poses and shapes of the brachytherapy catheters 12 have been determined based on tracking information obtained from the tracking system. Preferentially, the TRUS probe 40 and the grid 19 are fixed to each other such that the spatial relation between the grid 19 and the TRUS probe 40 is known. If in another embodiment the spatial relation between the TRUS probe 40 and the grid 19 is not a priori known, it can be determined by placing the tracking device 16 also at one or several locations at the TRUS probe 40 and by determining the position of the tracking device at these locations, or the TRUS probe can be equipped by a further tracking device, which is also trackable by the tracking device position providing unit 6. For example, also the TRUS probe can be equipped with an EM tracking element.

Since this spatial relation is known and since the poses and shapes of the brachytherapy catheters 12 relative to the grid 19 are also known, the pose and shape of the prostate 11 obtained from the segmented ultrasound image is known relative to the poses and shapes of the brachytherapy catheters 12 such that the treatment plan determination unit 39 can determine the treatment plan defining the dwell locations and the dwell times of the radiation sources 10 depending on the spatial relationship between the pose and shape of the prostate 11 and the poses and shapes of the brachytherapy catheters 12. For planning the different dwell positions and dwell times known planning techniques can be used like the planning technique disclosed in the article "Optimization of HDR brachytherapy dose distributions using linear programming with penalty costs" by Ron Alterovitz et al., Medical Physics, volume 33, number 11, pages 4012 to 4019, November 2006, which is herewith incorporated by reference.

Since the poses and shapes of the brachytherapy catheters 12 are known with respect to the grid 19, since the position of the respective single ultrasound transducer 50 relative to the respective brachytherapy catheter 12 is also known, for instance, from a pre- interventional measurement, and since the position of the TRUS probe 40 is also known relative to the grid 19, the grid 19 serves as a reference to which all imaging and tracking modalities are registered. In particular, if a coordinate system is defined, wherein the x and y axes of the coordinate system are within a plane defined by the grid 19 and the z axis is perpendicular to the plane defined by the grid 19, due to the above described registration procedure the x and y coordinates of the respective brachytherapy catheter are known at different z positions, wherein this information together with the a priori known information about the location of the respective single element transducer 50 along the length of the respective brachytherapy catheter 12 and together with the known spatial relation between the TRUS probe 40 and the grid 19 provides the location of the respective single element transducer 50 relative to the TRUS probe 40. The rotational position of the single element transducer 50 can be known, for instance, because the respective brachytherapy catheter has been introduced into the prostate such that the single element transducer 50 is at a known rotational position, for example, vertically upward or downward looking. Moreover, the location of the wire 51 or another marker at the end of the respective brachytherapy catheter, which is opposite to the end of the brachytherapy catheter that has been introduced into the prostate, may be used to determine the rotational position of the single element transducer 50. The rotational position of the single element transducer 50 may be observed by the user and input in the processing and control device 7 via an input unit like a keyboard, a computer mouse, a touch screen, et cetera. In this way the first ultrasound data generating unit and the second ultrasound data generating unit can be registered to each other. However, in another embodiment the first and second ultrasound data generating units can also be registered in another way.

Since the TRUS probe 40 and the single element ultrasound transducers 50 are registered with respect to each other, the ultrasound data provided by the TRUS probe, i.e. the first ultrasound data, and the ultrasound data provided by the single element ultrasound transducers 50, i.e. the second ultrasound data, can together be used for generating the segmented ultrasound image. For instance, the ultrasound image generating unit 42 can be adapted to generate a B-mode image based on the first ultrasound data obtained from the TRUS probe 40, wherein parts in the B-mode image, which are also imaged by the single element ultrasound transducers 50, can be replaced by the imaging information provided by the second ultrasound data. The segmentation can then be based on the resulting combined ultrasound image, in order to generate the segmented ultrasound image.

The second ultrasound data are preferentially M-mode data such that the second ultrasound data are generated at multiple times during the brachytherapy. The ultrasound image generating unit 42 is preferentially adapted to continuously update the segmented ultrasound image, i.e. to generate several segmented ultrasound images, based on the M-mode ultrasound data. Thus, the parts of the original B-mode image, which correspond to regions within the person 2, which are also imaged by the single element ultrasound transducers 50, are replaced by image information from the actually acquired M-mode ultrasound data, in order to continuously update the segmented ultrasound image. The treatment plan determination unit 39 is preferentially adapted to correspondingly update the treatment plan based on the actually updated segmented ultrasound image showing the segmented prostate 11. Thus, at different times different treatment plans can be determined based on the respective segmented ultrasound image generated for the respective time, wherein the brachytherapy is preferentially performed based on the respective actual treatment plan.

Real-time segmentation updates can therefore be fed back to the treatment plan determination unit 39 to enable an adaptive brachytherapy workflow. For example, if edema occurs in the anterior part of the prostate during the HDR brachytherapy, the treatment plan can be reoptimized to increase the dwell times of radiation sources in the brachytherapy catheters located in the region of the edema. Alternatively, additional dwell positions may be suggested in these brachytherapy catheters. The updated treatment plan may also recommend inserting additional brachytherapy catheters in the region of the edema.

In the following an embodiment of a brachytherapy method will be explained with reference to a flowchart shown in Fig. 10.

After the brachytherapy catheters 12 have been inserted into the prostate 11 of the person 2, for instance, under guidance of an ultrasound image generated by the ultrasound image generating unit 42 based on ultrasound data received from the TRUS probe 40, in step 101 the TRUS probe 40 generates first ultrasound data and the single element ultrasound transducers 50 generate second ultrasound data, which are used by the ultrasound image generating unit 42 for generating a segmented ultrasound image, in which the prostate 11 is segmented. In step 102 the poses and shapes of the brachytherapy catheters 12 are determined by using, for instance, the EM sensing elements 16 at the tip of the guidewire 60. Based on the segmented ultrasound image generated in step 101 and based on the poses and shapes of the brachytherapy catheters 12 determined in step 102, in step 103 an initial treatment plan is determined defining dwell locations and dwell times of the radiation sources 10 within the brachytherapy catheters 12. In step 104 the brachytherapy application unit applies the brachytherapy in accordance with the treatment plan, i.e. it places the radiation sources 10 within the brachytherapy catheters 12 in accordance with the dwell locations and dwell times defined by the treatment plan, wherein in parallel in step 105 the single element ultrasound transducers 50 further measure the second ultrasound data, i.e. in this embodiment M-mode ultrasound data, which are used by the ultrasound generating unit 42 to update the segmented ultrasound image, particularly to update the segmentation of the prostate 11. Also in parallel to the brachytherapy performed in step 104, in step 106 the treatment plan determination unit 39 updates the treatment plan based on the segmented ultrasound image updated in step 105, wherein the updated treatment plan is provided to the brachytherapy application unit, in order to allow the brachytherapy application unit to consider the updated treatment plan in step 104. Steps 105 and 106 are carried out in a loop such that continuously second ultrasound data are acquired and used to update the segmentation of the prostate 11 in the ultrasound image, wherein the updated treatment plan is continuously fed to the brachytherapy application unit for adaptively applying the brachytherapy in accordance with the actual treatment plan. After the brachytherapy has been performed in accordance with the treatment plan, the brachytherapy method ends in step 107.

The imaging method performed in steps 101 and 105 can be illustrated by the flowchart shown in Fig. 11.

In accordance with the embodiment of the imaging method illustrated in Fig. 11, in step 201 first ultrasound data of the prostate 11 are generated by the TRUS probe 40 and in step 202 the single element ultrasound transducers 50 generate second ultrasound data being preferentially M-mode ultrasound data. In step 203 the ultrasound image generating unit 42 generates a segmented ultrasound image, in which the prostate 11 is segmented, based on the first and second ultrasound data. Steps 202 and 203 may be performed in a loop such that the second ultrasound data are continuously acquired and continuously used to update the segmented ultrasound image.

In known ultrasound-based clinical work flows manual or semi-automated methods are used to segment the prostate on ultrasound images of a TRUS probe. The inherent ultrasonic contrast between the prostate and its surrounding anatomy is rather low. Additionally, in HDR brachytherapy procedures, since there are many brachytherapy catheters implanted in the prostate, for instance, ten to twenty brachytherapy catheters, shadowing artifacts from these brachytherapy catheters render it even more difficult to see the distal boundaries of the prostate. This can lead to inaccuracies in prostate segmentation.

The brachytherapy system described above with reference to, for instance, Fig. 1 is therefore preferentially adapted to reinforce/build confidence in existing prostate segmentations by providing additional data points. In cases where catheter- induced shadowing artifacts are present, the segmentation accuracy can be improved by providing prostatic boundary information that is unavailable, if the TRUS probe is used only.

The brachytherapy system preferentially comprises single element ultrasound transducers to augment information obtained from the TRUS probe, which may also be regarded as being a TRUS array. These single element ultrasound transducers are integrated with the brachytherapy catheters and utilized to augment TRUS images, resulting in organ segmentations with improved quality and accuracy. The single element ultrasound transducers can be forward-looking transducers and/or radial transducers. Moreover, the ultrasound image generating unit is preferentially adapted to combine M-mode information, from each single element ultrasound transducer with B-mode images from the TRUS probe, wherein the different ultrasound imaging devices are registered to each other by using, for instance, EM tracking functionality. The treatment plan determination unit provides an adaptive treatment planning technique to utilize real-time segmentation updates to iteratively improve the treatment plan.

Although in the embodiment described above with reference to Fig. 8 it has been described that in shadow regions 53 of a B-mode image generated by using the TRUS probe 40 M-mode data are used for improving the quality of the B-mode image, which is finally used for segmenting the prostate 11, in other embodiments the first and second ultrasound data can also be combined in another way for finally generating a segmented ultrasound image, in which the prostate is segmented. For instance, the ultrasound image generating unit 42 can be adapted to replace a part of the first ultrasound data by at least a part of the second ultrasound data for generating combined ultrasound data, wherein an ultrasound image can be generated based on the combined ultrasound data and wherein the prostate 11 can be segmented in the ultrasound image for generating the segmented ultrasound image. In particular, the ultrasound image generating unit 42 can be adapted to determine a part of the first ultrasound data having ultrasound data values being smaller than a predefined threshold and to replace the determined part of the first ultrasound data by corresponding second ultrasound data. This replacement procedure will in the following be explained in more detail with reference to Figs. 11 to 13.

Fig. 12 schematically and exemplarily shows exemplarily a certain location 71 at which ultrasound transducers of the TRUS probe 40 measure first ultrasound data 56 along the line 70, wherein the entire array of ultrasound transducers of the TRUS probe 40 has the indicated field of view 52. The ultrasound waves are strongly attenuated by the

brachytherapy catheter 12 with the single element ultrasound transducer 50, thereby generating a shadow region 53. Within the shadow region 53 second ultrasound data 57 are generated by using the single element ultrasound transducer 50. In particular, the single element ultrasound transducer 50 sends and receives ultrasound waves along the broken line 55 for sensing the boundary location 54, which points substantially in the same direction as the line 70 along which the first ultrasound data 56 are measured. The first ultrasound data 56 and the second ultrasound data 57 are exemplarily illustrated in Fig. 13. As can be seen in Fig. 13, in a region 59 the first ultrasound data being, in this example, RF data are weak due to the shadow region 53. The first ultrasound data 56 in this weak region 59 can be replaced by the corresponding second ultrasound data 57 being, in this example, also RF data, in order to generate combined ultrasound data 58 exemplarily illustrated in Fig. 14. Combined ultrasound data of this kind can be generated for different ultrasound transducers of the array of ultrasound transducers of the TRUS probe 40, wherein these combined ultrasound data can then be used to reconstruct an ultrasound image, in which the prostate 11 can be segmented. Thus, received RF data from the TRUS probe can be enhanced by using the RF data from the single element ultrasound transducer, wherein the enhanced RF data can be used to generate an improved ultrasound image, in which the prostate can be segmented for providing the segmented ultrasound image. Since the second ultrasound data are preferentially M-mode ultrasound data, they are generated at multiple times. The ultrasound image generating unit 42 can therefore be adapted to, for each of the multiple times, replace a part of the first ultrasound data by at least a part of the second ultrasound data for generating combined ultrasound data, to generate the ultrasound image based on the combined ultrasound data and to segment the prostate 11 in the generated ultrasound image for generating the segmented ultrasound image. Thus, the combined ultrasound data can be continuously updated based on the actually acquired M-mode ultrasound data, wherein an updated segmented ultrasound image can be generated based on the updated combined ultrasound data. Although in Fig. 12 exemplarily only a single brachytherapy catheter with a single element ultrasound transducer and a single location on the array of ultrasound transducers of the TRUS probe are shown for illustrative purposes, in reality several brachytherapy catheters with single element ultrasound transducers are preferentially inserted into the prostate and several corresponding locations on the array of ultrasound transducers of the TRUS probe can be present.

In an embodiment the ultrasound image generating unit is adapted to detect the boundary of the prostate in the spatial regions within the field of view of the TRUS probe, for which the second ultrasound data have been generated, and to determine the boundary of the prostate in intermediate spatial regions, which are located in between the spatial regions for which the second ultrasound data have been determined, by interpolation. This interpolation is preferentially based on the positions of the boundary detected within the spatial regions, for which the second ultrasound data have been generated, by using the generated second ultrasound data. The boundary in the spatial regions, for which the second ultrasound data have not been generated, can also be determined in another way. For instance, in these regions the first ultrasound data may be used for detecting the boundary, or a prostate model, which models the boundary of the prostate, can be adapted, i.e., for instance, the size of the prostate model can be modified without or with only slightly modifying the shape of the prostate model, to be in conformance with the positions of the boundary detected in the spatial regions for which the second ultrasound data have been generated, wherein the positions of the boundary in the spatial regions, for which the second ultrasound data have not been generated, can be determined from the adapted prostate model. The prostate model may initially be determined based on a B-mode image of the prostate, which may have been generated, before the brachytherapy catheters are inserted into the prostate. The boundaries determined in the different spatial regions can form a segmentation of the prostate, which can be shown on a B-mode or another kind of ultrasound image generated from the first ultrasound data received from the TRUS probe.

Although in above described embodiments a brachytherapy catheter 12 comprises only one single element ultrasound transducer 50, in another embodiment the brachytherapy catheters 12 may also comprise more than one single element ultrasound transducer as schematically and exemplarily illustrated in Fig. 15. In the example shown in Fig. 15 the brachytherapy catheter 12 comprises a forward-looking ultrasound transducer 75 and several radial ultrasound transducers 50, which are all electrically connected with the ultrasound image generating unit 42 via electrical connections 51 like wires. It is known a priori where each single element ultrasound transducer 50, 75 is arranged along the length of the respective brachytherapy catheter 12, in order to allow for a determination of the locations of the single element transducers 50, 75 with respective to the TRUS probe 40.

Although in above described embodiments an EM tracking system is used for registering the different components of the brachytherapy system with respect to each other, in particular, for registering the single element ultrasound transducers with the TRUS probe 40, in other embodiments also other tracking techniques can be used for registering the single element ultrasound transducers with the TRUS probe 40. For instance, a position encoder can be used to register TRUS images to the grid and a manual ultrasound based catheter identification procedure can be used to determine the x and y coordinates of the

brachytherapy catheters. The a priori known information about the location of the respective single element ultrasound transducer along the length of the respective brachytherapy catheter and the insertion depth of the respective brachytherapy catheter can provide the z coordinate of the respective single element ultrasound transducer with respect to the grid. The insertion depth of the respective brachytherapy catheter may also be determined by using a position encoder, by visually detecting depth markers on the outside of the respective brachytherapy catheter or by another means. The rotation information can be obtained as described further above.

As a further example, the single element ultrasound transducers may also be registered with the TRUS probe by coupling the single element ultrasound transducers with the ultrasound transducers of the TRUS probe such that the single element ultrasound transducers receive RF waves emitted by the transducers of the TRUS probe. In particular, the ultrasound signals received by a respective single element ultrasound transducer from the TRUS probe as the beam of the TRUS probe sweeps the field of view can be analyzed for determining the distance of the respective single element ultrasound transducer to the TRUS probe based on the time of arrival of the received ultrasound signals and to determine the angular dimension based on the amplitude of the received ultrasound signals as a function of an imaging beam steering angle of the TRUS probe. In this way the positions of the single element ultrasound transducers can be tracked in the frame of reference of the TRUS probe.

Although in above described embodiments the first ultrasound data generating unit is a TRUS probe and the second ultrasound data generating unit is formed by single element ultrasound transducers on brachytherapy catheters, in other embodiments also another first ultrasound data generating unit located at a first location and/or a second ultrasound data generating unit located at a second location can be used. For instance, the brachytherapy catheters can be equipped with ultrasound transducer arrays such that the ultrasound data of a single brachytherapy catheter can be used for providing a B-mode ultrasound image in real-time. The ultrasound transducer array of a first brachytherapy catheter may be regarded as being a first ultrasound data generating unit at a first location and an ultrasound transducer array of a second brachytherapy catheter may be regarded as being a second ultrasound data generating unit at a second location, wherein the ultrasound data generated by these ultrasound data generating units can be used by the ultrasound image generating unit for generating a segmented ultrasound image, in which the prostate is segmented. In this case the first images provided by the TRUS probe may only be used for guiding the implementation of the brachytherapy catheters, wherein further steps of the brachytherapy procedure like the planning and adjustment steps may be performed based on the ultrasound images provided by the ultrasound transducer arrays of the brachytherapy catheters.

Although in above described embodiments the brachytherapy catheters are equipped with ultrasound transducers, in other embodiments, alternatively or in addition, ultrasound transducers can also be arranged on or within other components used during the brachytherapy for providing ultrasound data, which can be used to generate the segmented ultrasound image. For instance, ultrasound transducers can be arranged on a Foley catheter, which may be introduced into the urethra during a brachytherapy procedure. The ultrasound transducers on the Foley catheter can be regarded as forming a second ultrasound data generating unit for generating second ultrasound data, which are combined with first ultrasound data generated by the TRUS probe for generating a segmented ultrasound image of the prostate.

The brachytherapy system can comprise one or several first ultrasound data generating units and one or several second ultrasound data generating units, which are arranged at different locations, for generating first and second ultrasound data, which are used for generating a segmented ultrasound image.

Although in the above described embodiments the first and second ultrasound data generating units and the ultrasound image generating unit are adapted to generate a segmented ultrasound image of a prostate, in which the prostate is segmented, in other embodiments the first and second ultrasound data generating units and the ultrasound image generating unit can also be adapted to generate a segmented ultrasound image of another object or of a part of an object. The other object is, for instance, another organ, a tumor, et cetera. Moreover, the part of the object may be a target region within the object, which should be treated. The target region within the object is, for instance, a cancerous region of the object.

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 indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Procedures like the generation of an ultrasound image based on the first ultrasound data and/or the second ultrasound data, the segmentation of an object in the ultrasound image, the determination of the treatment plan, et cetera performed by one or several units or devices can also be performed by any other number of units or devices. These procedures and/or the control of the imaging system in accordance with the imaging method and/or the control of the brachytherapy system in accordance with the brachytherapy 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 should not be construed as limiting the scope.

The invention relates to an imaging system for generating an image of a living object like an image from a prostate during a brachytherapy. A first ultrasound data generating unit like a TRUS probe generates first ultrasound data of a field of view including the object and a second ultrasound data generating unit, which might be an ultrasound transducer on a brachytherapy catheter, generates second ultrasound data of at least a part of the field of view, wherein a segmented ultrasound image, in which the object is segmented, is generated based on the ultrasound data. In particular, spatial regions, which are not sensible by the first ultrasound data generating unit due to shadows, may be sensible by the second ultrasound data generating unit, which may allow for an augmentation of the first ultrasound data and finally for a segmented image having an improved quality.

Claims

CLAIMS:

1. An imaging system for generating an image of a living object, the imaging system comprising:

a first ultrasound data generating unit (40) for being located at a first location and for generating first ultrasound data of a field of view (52) of the first ultrasound data generating unit (40), wherein the field of view (52) includes the object (11),

a second ultrasound data generating unit (50) for being located at a second location, which is different to the first location, and for generating second ultrasound data of at least a part of the field of view (52),

an ultrasound image generating unit (42) for generating a segmented ultrasound image, in which the object (11) is segmented, based on the first and second ultrasound data.

2. The imaging system as defined in claim 1, wherein the ultrasound image generating unit (42) is adapted to generate a first ultrasound image of the object (11) based on the first ultrasound data, to generate the segmented ultrasound image by segmenting the object (11) in the first ultrasound image and to amend the segmentation of the object (11) in the segmented ultrasound image based on the second ultrasound data.

3. The imaging system as defined in claim 1, wherein the ultrasound image generating unit (42) is adapted to replace a part of the first ultrasound data by at least a part of the second ultrasound data for generating combined ultrasound data, to generate the ultrasound image based on the combined ultrasound data and to segment the object (11) in the generated ultrasound image for generating the segmented ultrasound image.

4. The imaging system as defined in claim 1, wherein the second ultrasound data generating unit is adapted to generate second ultrasound data of different spatial regions within the field of view, wherein the ultrasound image generating unit is adapted to detect a boundary of the object within the different spatial regions based on the second ultrasound data and to generate the segmented ultrasound image based on the detected boundary and the first ultrasound data.

5. The imaging system as defined in claim 4, wherein the ultrasound image generating unit is adapted to determine an interpolated boundary of the object in spatial regions, for which the second ultrasound data have not been generated, based on the boundary detected within the spatial regions, for which second ultrasound data have been generated, and to generate the segmented ultrasound image based on the detected boundary, the interpolated boundary and the first ultrasound data.

6. The imaging system as defined in claim 4, wherein the ultrasound image generating unit is adapted to detect a boundary of the object in spatial regions, for which the second ultrasound data have not been generated, based on the first ultrasound data and to generate the segmented ultrasound image based on the boundary detected in the different spatial regions.

7. The imaging system as defined in claim 1, wherein the first ultrasound data generating unit (40) is a transrectal ultrasound imaging unit.

8. The brachytherapy system as defined in claim 1, wherein the second ultrasound data generating unit (50) comprises an ultrasound transducer arranged on a brachytherapy catheter (12).

9. The imaging system as defined in claim 1, wherein the second ultrasound data generating unit (50) comprises an ultrasound transducer adapted to be arranged within the urethra.

10. A brachytherapy system for applying a brachytherapy to a living object (11), the brachytherapy system comprising:

a brachytherapy catheter (12) to be inserted into the object (11), wherein the brachytherapy catheter (12) is adapted to receive a radiation source (10) for applying the brachytherapy,

an imaging system as defined in claim 1.

11. The brachytherapy system as defined in claim 10, wherein the brachytherapy system (1) further comprises a treatment plan determination unit (39) for determining a treatment plan defining a dwell location and a dwell time of the radiation source (10) within the object (11) and a catheter pose and shape providing unit (6, 16, 44) for providing the pose and shape of the catheter (12) within the object (11), wherein the treatment plan

determination unit (39) is adapted to determine the treatment plan based on the segmented image and the provided pose and shape of the catheter (12).

12. The brachytherapy system as defined in claim 11, wherein the first ultrasound data generating unit (40) is adapted to generate the first ultrasound data at multiple times and/or the second ultrasound data generating unit (50) is adapted to generate the second ultrasound data at multiple times during the brachytherapy, wherein the ultrasound image generating unit (42) is adapted to generate several segmented ultrasound images for the multiple times based on the first and second ultrasound data and wherein the treatment plan determination unit (39) is adapted to determine multiple treatment plans for the multiple times based on the multiple segmented images.

13. A brachytherapy catheter (12) to be used with the imaging system as defined in claim 1, wherein the brachytherapy catheter (12) is equipped with an ultrasound transducer of the second ultrasound data generating unit (50).

14. An imaging method for generating an image of a living object (11), the imaging method comprising:

generating first ultrasound data of a field of view (52) of a first ultrasound data generating unit (40) located at a first location by using the first ultrasound data generating unit (40), wherein the field of view (52) includes the object (11),

generating second ultrasound data of at least a part of the field of view (52) by a second ultrasound data generating unit (50) located at a second location,

generating a segmented ultrasound image, in which the object (11) is segmented, based on the first and second ultrasound data by an ultrasound image generating unit (42).

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