This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2017/063636, filed on Jun. 6, 2017, which claims the benefit of European Application Serial No. 16173091.6, filed Jun. 6, 2016. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to the field of medical ultrasound imaging. In particular, the present invention relates to a medical ultrasound image processing device for supporting reproducible acquisition of 2D ultrasound images. The present invention further relates to a corresponding method and ultrasound system. Still further, the present invention relates to a computer program comprising program code means for causing a computer to carry out the steps of said method.

BACKGROUND OF THE INVENTION

Medical ultrasound imaging is typically a dynamic examination wherein an ultrasound probe is manually moved over a region of interest by a physician. Hence, in contrast to imaging modalities such as CT or MRI, wherein a subject is positioned with a known orientation relative to the imaging system, an ultrasound examination strongly depends on the physician carrying out the examination. For example, one and the same structure, such as an organ or tumor, may be classified to have different sizes based on images taken by different physicians. In clinical practice, such measurements are typically performed based on 2D ultrasound images.

US 2006/0020204 A1 discloses a system and method for three-dimensional space management and visualization of ultrasound data. Instead of visualizing ultrasound images just as 2D images, it is suggested to visualize already acquired ultrasound images as positionally and orientally located slices within a particular 3D space.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device and method which support more consistent and/or reliable acquisition of 2D ultrasound images.

In a first aspect of the present invention a medical ultrasound image processing device is presented that comprises:

a first interface for receiving a first 3D scout ultrasound image and a first 2D ultrasound image of a volumetric region;

a second interface for receiving a second 3D scout ultrasound image of the volumetric region; and

a processing unit arranged to perform the steps of:determining an orientation of an image plane of the first 2D ultrasound image with respect to the first 3D scout ultrasound image;registration of the first 3D scout ultrasound image and the second 3D scout ultrasound image in a common coordinate frame;determining an orientation of the image plane of the first 2D ultrasound image with respect to said common coordinate frame based on said registration of the first and second 3D scout ultrasound images and the determined orientation of the image plane of the first 2D ultrasound image with respect to the first 3D scout ultrasound image; andproviding a control signal adapted to control an acquisition of a second 2D ultrasound image of the volumetric region by an ultrasound probe in accordance with the orientation of the image plane of the first 2D ultrasound image of the volumetric region,

wherein an orientation of an image plane of the second 2D ultrasound image corresponds to the determined orientation of the image plane of the first 2D ultrasound image of the volumetric region,

wherein the acquisition of the second 2D ultrasound image by the ultrasound probe is from either a same position as, or a tracked position with respect to, the position of the acquisition of the second 3D scout ultrasound image.

In a second aspect of the present invention a medical image processing method is presented, the method comprising the steps of:

obtaining (i.e., receiving or retrieving) a first 3D scout ultrasound image and a first 2D ultrasound image of a volumetric region;

obtaining (i.e., receiving or retrieving) a second 3D scout ultrasound image of the volumetric region;

determining an orientation of an image plane of the first 2D ultrasound image with respect to the first 3D scout ultrasound image;

registration of the first 3D scout ultrasound image and the second 3D scout ultrasound image in a common coordinate frame;

determining an orientation of the image plane of the first 2D ultrasound image with respect to said common coordinate frame based on said registration of the first and second 3D scout ultrasound images and the determined orientation of the image plane of the first 2D ultrasound image with respect to the first 3D scout image; and

providing a control signal adapted to control an acquisition of a second 2D ultrasound image of the volumetric region by an ultrasound probe in accordance with the orientation of the image plane of the first 2D ultrasound image of the volumetric region,

wherein an orientation of an image plane of the second 2D ultrasound image corresponds to the determined orientation of the image plane of the first 2D ultrasound image of the volumetric region,

wherein the acquisition of the second 2D ultrasound image by the ultrasound probe is from either a same position as, or a tracked position with respect to, the position of the acquisition of the second 3D scout ultrasound image.

In a further aspect of the present invention an ultrasound system for imaging a volumetric region is presented, the system comprising:

an ultrasound probe comprising an ultrasound transducer array arranged to acquire an ultrasound image of a subject;

the aforementioned medical ultrasound image processing device; and

a probe controller arranged to control the ultrasound probe to acquire the second 2D ultrasound image based on the control signal provided by said medical ultrasound image processing device from either a same position as, or at a tracked position with respect to, the position of the acquisition of the second 3D scout ultrasound image.

In yet further aspects of the present invention, there are provided a corresponding computer program which comprises program code means for causing a computer to perform the steps of the method disclosed herein when said computer program is carried out on a computer as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed.

Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed method, system, computer program and medium can have similar and/or identical preferred embodiments as the claimed device, in particular as defined in the dependent claims and as disclosed herein.

The present invention is based on the idea of using 3D scout ultrasound images for establishing a correspondence between a first and a second 2D ultrasound image. The solution presented herein is particularly advantageous for providing comparable 2D ultrasound images from a first, initial 2D ultrasound examination and a second, follow-up 2D ultrasound examination.

The first and the second 3D scout ultrasound images can be registered to determine their relative position and orientation. Hence, based on a relative position and orientation of the first 2D ultrasound image with respect to the first 3D scout ultrasound image, and further based the relative position and orientation of the first 3D scout ultrasound image with respect to the second 3D scout ultrasound image, a relative position and orientation for acquisition of the second 2D ultrasound image with respect to the second 3D scout ultrasound image can be calculated, such that the position and orientation of said second 2D ultrasound image corresponds to the position and orientation of the first 2D ultrasound image with respect to the examined volumetric region. In other words, a second, follow-up 2D ultrasound image with the same view as the initial 2D ultrasound image can be acquired.

In conventional 2D ultrasound systems, the acquisition of consistent and reproducible 2D ultrasound images is challenging and strongly depends on how the physician carrying out the examination positions the handheld ultrasound probe. Yet, if the view of follow-up examinations is not the same, also measurements may not be identical and comparisons between them are not reliable. In current clinical practice, small deviations between an initial and a follow-up ultrasound images are therefore often attributed to measuring inaccuracy. There is thus a need to enable more accurate measurements. For example, early detection of even small size changes of a lesion may change a therapy regime for the benefit of the patient.

To bypass this challenge it is proposed herein to employ a first and a second 3D scout ultrasound scan for alignment of a first 2D ultrasound image and a second 2D ultrasound image to be acquired. 3D ultrasound is feasible since it does not harm the patient and is acquired quickly, for example in 1/10thof a second. The first 3D scout ultrasound image and the first 2D ultrasound image can be stored together with information or data indicative of their relative position and/or orientation. This data can be received by the image processing device together with the first 3D scout ultrasound image and the first 2D ultrasound image. For example, the coordinates and orientation of the first 2D ultrasound image with respect to the first 3D scout ultrasound image can be stored. Alternatively or in addition, control parameters for acquisition of the first 2D ultrasound image and the first 3D scout ultrasound image with a 3D ultrasound probe may be stored. When a second, follow-up 2D ultrasound image with an identical view is required, a second 3D scout ultrasound scan be acquired and registered with the first, initial 3D scout ultrasound image. Through the knowledge of their correspondence and the relative orientation and/or position of the first, initial 2D ultrasound image with respect to the first 3D scout ultrasound image, the corresponding control signal for acquisition of the second, follow-up 2D ultrasound image can be deduced and the follow-up 2D ultrasound image with an identical view as the initial 2D ultrasound image can be acquired.

The proposed solution can thus support more consistent and/or reliable acquisition of 2D ultrasound images with an ultrasound system. By providing a control signal for acquisition of the second 2D ultrasound image in accordance with the orientation of the image plane of the first 2D ultrasound image of the volumetric region, the proposed medical image processing apparatus can thus enable the acquisition of 2D slices in a follow-up examination in accordance with the 2D slices in the previous examination.

As a further advantage, the time required by a physician for acquisition of a consistent follow-up ultrasound image may be reduced. Hence, instead of acquisition of an entire high resolution 3D ultrasound scan, it can be sufficient to acquire a 3D scout ultrasound image having a reduced resolution and then acquiring the specific follow-up 2D ultrasound image of interest which corresponds the initial, first 2D ultrasound image.

It should further be noted that in particular for time critical examinations such as an examination of a beating heart, a high resolution 3D scan may not be fast enough. In this case additional techniques such as gated acquisition would be required. A further advantage of the solution proposed herein can thus be a reduced complexity.

As a further advantage, a less trained physician may be supported in acquisition of comparable follow-up 2D ultrasound images. For example, the first 2D ultrasound image and the first 3D scout ultrasound image may have been acquired by a highly qualified specialist, whereas the follow-up ultrasound images may be acquired by an assistant.

Generally speaking, a first (scout) ultrasound image can refer to an initial examination and a second (scout) ultrasound image can refer to a follow-up examination. A follow-up examination may be carried out at a later point in time, for example a few weeks or months after the initial examination, to assess a healing process or progression of a disease. For example, the first 3D scout ultrasound image and the first 2D ultrasound image are acquired together at the initial examination, whereas the second 3D scout ultrasound image and the second 2D ultrasound image are subsequently acquired at the follow-up examination.

The first ultrasound images and the second ultrasound images can be images acquired with the same or a different ultrasound system. For example, the initial ultrasound images can be acquired at a hospital, whereas the second, follow-up ultrasound images are acquired in private practice. The first ultrasound images may be obtained, for example, from a database such as an electronic health record (EHR).

It shall be understood that the first interface and the second interface can be the same interface such as one single hardware interface or can also be different interfaces. For example, the first interface and the second interface can be one common data interface, i.e. an interface for receiving the first 3D scout ultrasound image, the first 2D ultrasound image and the second 3D scout ultrasound image of the volumetric region. In an embodiment, the first interface can be, for example, a data network interface for receiving the first 3D scout ultrasound image and the first 2D ultrasound image, whereas the second interface may be an interface for receiving data directly from an ultrasound acquisition unit. The first interface can be seen in a functional way as indicating data from an initial examination, whereas the second interface indicates data from a follow-up examination.

3D ultrasound images may be acquired by a mechanically steered array or electronically. Electronical steering can be enabled by a 2D ultrasound transducer array. Alternatively, mechanical steering of 1D ultrasound transducer array may be used to acquire a 3D ultrasound image.

A 3D scout ultrasound image as used herein refers to a 3D ultrasound image, in particular a 3D ultrasound image having a lower resolution than a 2D ultrasound image. Advantageously, lower resolution first and/or second 3D ultrasound images can be used to provide a fast acquisition time. This is particularly advantageous when imaging a moving organ such as the heart. The first and/or second 2D ultrasound images may be acquired with a higher resolution.

Image registration is a common term in medical imaging for determining a relative position and/or orientation of two 2D or 3D images relative to each other. Reference can be made to WO 2002/16963 A2 and the additional disclosures cited therein. For example, corresponding regions of images can be identified by edge detection and segmentation algorithms.

A common coordinate frame can refer to a coordinate frame of the first or second 3D scout ultrasound image or an arbitrarily oriented coordinate frame, in general any coordinate system which may serve as a reference. The relative orientation of the ultrasound images with respect to each other matters.

In an embodiment, the first 3D scout ultrasound image and the first 2D ultrasound image can be images acquired with a first 3D ultrasound probe from a first position. The second 3D scout ultrasound image can be an image acquired with a second 3D ultrasound probe from a second position, for example after repositioning the ultrasound probe or in a follow-up examination. The first 3D ultrasound probe and the second 3D ultrasound probe may thus refer to the same or different ultrasound probes. After acquisition of the second 3D scout ultrasound image, the control signal can then be provided for acquisition of the second 2D ultrasound image based on said control signal from said second position. Advantageously, the ultrasound probe is not moved substantially between the respective 3D scout ultrasound image and the corresponding 2D ultrasound image. Thereby, the first 3D scout ultrasound image and the first 2D ultrasound image are images acquired from the same, first position. Correspondingly, the second 3D scout ultrasound image and the second 2D ultrasound image will advantageously both be acquired from the second position. An advantage of this embodiment is that a position and/or orientation of the first 2D ultrasound image with respect to the first 3D scout ultrasound image can be determined based on system parameters of the ultrasound system for acquisition of said ultrasound images, such as for example beam steering parameters. It is thus not necessary to track a position of the ultrasound probe—even though this would also be possible in the alternative or in addition. Advantageously, for example when having a 3D ultrasound system with a matrix transducer, the position and/or orientation of the image plane for acquisition of the second 2D ultrasound image can be set electronically, i.e., via electronic beam steering. It is to be understood that the processing unit can be arranged accordingly. Generally speaking, the respective 2D and 3D ultrasound image have to be stored and will be received together with data indicative of their relative position and/or orientation with respect to each other.

In a refinement, for example, if the ultrasound probe was slightly moved between acquisition of the 3D scout ultrasound image and the 2D ultrasound image, the position and/or orientation of the 2D ultrasound image relative to the 3D scout ultrasound image may still be determined, e.g., by means of registration. Furthermore, such information can be stored for any subsequently acquired 2D ultrasound image in the vicinity. By this means, one 3D scout ultrasound image can serve as a basis for several 2D ultrasound images.

In an embodiment, the processing unit can be arranged to determine the orientation of the image plane of the first 2D ultrasound image with respect to the first 3D scout ultrasound image based on control parameters of the ultrasound probe for acquisition of the first 2D ultrasound image and the first 3D scout ultrasound image. Control parameters for acquisition of the respective 2D and 3D ultrasound images can be indicative of an orientation and/or position of said ultrasound images with respect the ultrasound probe. Provided that the ultrasound images are acquired from the same position, i.e. the ultrasound probe has not moved substantially, the relative position and/or orientation of the 2D ultrasound image and the 3D scout ultrasound image can thus be derived from the control parameters of the ultrasound probe. In particular, such control parameters may comprise beam steering parameters, in particular for electronic beam steering. Correspondingly, the control signal of the processing unit can provide one or more control parameters for acquisition of second 2D ultrasound image, such as beam steering parameters for acquisition of the second 2D ultrasound image at a desired orientation and/or position with respect to the second 3D scout ultrasound image and in correspondence with an orientation and/or position of the first 2D ultrasound image. Alternatively or in addition, the orientation and/or position of the image plane of the first 2D ultrasound image with respect to the first 3D scout ultrasound image can also be determined based on 2D to 3D registration. This is particularly helpful if the control parameter information is not available or insufficient. These techniques can also be combined to further improve the performance.

In an embodiment, at least one of the ultrasound images further can comprise metadata indicative of a control parameter of an ultrasound probe for acquisition of said ultrasound image, in particular indicative of at least one of an acquisition gain, focus, depth, zoom, position, orientation and beam steering parameter. An advantage of this embodiment is that said one or more control parameters can directly be stored together with the ultrasound image data. Alternatively or in addition, the medical image processing device may receive data regarding one or more control parameters (also referred to as system parameters) separately via an interface.

In an embodiment, the control signal provided by the processing unit can be indicative of at least one control parameter of the ultrasound probe for acquisition of the second 2D ultrasound image. For example, the control signal can be indicative of at least one of an acquisition gain, focus, depth, zoom, position, orientation and a beam steering parameter. Thereby, the ultrasound probe can be controlled to acquire a second 2D ultrasound image which provides a corresponding view as the first 2D ultrasound image. Alternatively, the control signal may also provide a control signal indicative of a relative position and/or orientation of the desired second 2D ultrasound image to be acquired with respect to the second 3D scout ultrasound image. The control parameters for the ultrasound probe, in particular for beam steering, can be calculated based thereon by an optional intermediate entity such as a probe or transducer controller.

In an embodiment, the step of registration can comprise an anatomy segmentation in said first and second 3D scout ultrasound images. A definition of said common coordinate frame can be based on said anatomy segmentation. An advantage of this embodiment is that anatomic features can be taken as a reference for determining the relative position and orientation of the first and second 3D scout ultrasound images.

In an embodiment, the registration of the second 3D scout ultrasound image with the first 3D scout ultrasound image can comprise a registration of an image content within field-of-view masks of said first 3D ultrasound image and said second 3D ultrasound image respectively. An advantage of this embodiment is, that not the entire ultrasound image is considered for the registration but only an image content within a relevant area as indicated by a field-of-view mask. Hence, the image content and not the field-of-view cones as such can be compared and registered. A field view cone can be the typical triangular or pyramidal view cone provided by an ultrasound probe.

In an embodiment, the registration can comprise determining an overlap between the first 3D scout ultrasound image and the second 3D scout ultrasound image, in particular determining whether there is a sufficient overlap of said 3D ultrasound images. Thereby, a sufficient overlap for registration of said 3D ultrasound images can be determined. A further advantage is that an alert signal can be generated by the image processing device if an insufficient overlap is determined. In consequence, an alert message can be provided via a user interface, for example via a separate or an already existing user interface of the ultrasound system, and the user may reposition the ultrasound probe accordingly. Advantageously, the user can be provided with guidance on how to position the ultrasound probe based on the determined overlap. For example, the user may be instructed to move or tilt the ultrasound probe in a certain direction. Such guidance can be provided, for example, by voice guidance with real-time feedback on how to position the probe and/or via a graphical user interface. The graphical user interface can advantageously show a current and a target position of the ultrasound probe and/or which probe displacements are required.

In a refinement, a sequence of 3D scout ultrasound images can be iteratively acquired until a sufficient overlap has been found. The image processing device can thus be arranged to provide a control signal for iterative acquisition of 3D scout ultrasound images. If a sufficient overlap has been detected, the user can be notified accordingly via a user interface.

In an embodiment, a resolution of the first and/or second 2D ultrasound image can be higher than a resolution of the first and/or second 3D scout ultrasound image. For example, the ultrasound system may be arranged to acquire the 2D ultrasound image with a higher resolution than the corresponding 3D scout ultrasound image. It has been found that a lower resolution 3D scout ultrasound image can be sufficient for registration. A higher resolution 2D ultrasound image may then be used for actual clinical diagnostics. An advantage of this embodiment is that in particular the first 3D scout ultrasound image may be quickly acquired in addition to the first 2D ultrasound image. For example, the acquisition of the 3D scout ultrasound image may only take 1/10thof a second. Hence, during a time when an operator of the ultrasound system freezes the screen for detailed analysis of a 2D ultrasound image, a background process for acquisition of a 3D scout ultrasound image having a reduced resolution may be performed, essentially without loss of time.

In an embodiment, the processing unit can be further arranged to determine a position of the first 2D ultrasound image with respect to the first 3D scout ultrasound image and/or the common coordinate frame and further arranged to provide a control signal adapted to control an acquisition of the second 2D ultrasound image by an ultrasound probe in accordance with the position of the first 2D ultrasound image of the volumetric region. It should be understood that a position and orientation of the second 2D ultrasound image may correspond to the position and orientation of the first 2D ultrasound image. Hence, the processing unit can be arranged to consider both the position and the orientation in each respective step. Advantageously, same structures are thus shown at the same position in the first and the second 2D ultrasound images.

In an embodiment, the medical image processing device, in particular the processing unit, can be arranged to provide guidance to a sonographer for acquisition of the second 2D ultrasound image based on said control signal via a user interface. In particular voice guidance or graphical guidance on how to position the ultrasound probe can be provided via the user interface to the sonographer based on the control signal for acquisition of the second 2D ultrasound image in accordance with the first 2D ultrasound image. For example, the sonographer can be provided with feedback via a human-machine-interface (HMI) on how to position the ultrasound probe for acquisition of the second 2D ultrasound image in correspondence with the first 2D ultrasound image. For example, guidance can be provided sonographer for the acquisition of the follow-up 2D ultrasound image by voice guidance, advantageously with real-time feedback, on how to position the probe and/or on a graphical display. Such guidance can advantageously indicate a current and a target position of the ultrasound probe and/or which probe displacements are required. For example, registration information indicative of the registration of the first 3D scout ultrasound image and the second 3D scout ultrasound image, such as position and/or orientation of the 3D scout ultrasound images with respect to each other, can be provided on a graphical user interface as a help for the sonographer to move the ultrasound probe in a way that the probe position and/or orientation corresponds better between the first and the second acquisition.

In an embodiment, the aforementioned method can further comprise the step of acquisition of the second 2D ultrasound image of the volumetric region with the ultrasound probe based on said control signal. Correspondingly, the method can further comprise the preceding steps of acquisition of the first 2D ultrasound image and the first 3D scout ultrasound image, for example in an initial first examination, as well as the step of acquiring the second 3D scout ultrasound image, for example immediately before acquisition of the second 2D ultrasound image based on said control signal, in a follow-up examination.

It is to be understood, that the acquired ultrasound images or more precisely the ultrasound image data can be obtained and processed by a processing unit. As used herein the term obtaining can refer to receiving or retrieving data. For example, ultrasound image data which has previously been acquired with an ultrasound probe is received by the medical ultrasound image processing device. It is also possible to actively retrieve such data from a storage unit or database such as an electronic health record (EHR), hospital information system (HIS) or picture archiving and communication system (PACS). Advantageously, the first 2D ultrasound image and the first 3D scout ultrasound image are stored in a database together with data indicative of their relative position and/or orientation. When performing a follow-up examination, this information can be accessed, received and used for determining the control signal for consistent and reliable acquisition of the second 2D ultrasound image.

