Patent Description:
The present invention further relates to an ultrasound system including such an ultrasound image processing apparatus.

The present invention further relates to a computer-implemented method to render a volumetric ultrasound image from a <NUM>-D ultrasound image and control a display apparatus to display said rendered image.

The present invention further relates to a computer program product for implementing such a method on an ultrasound imaging processing apparatus.

Ultrasound plays an essential role in many diagnostic imaging techniques including but not limited to fetal imaging. Ultrasonic imaging is routinely used during pregnancy to assess the development of a fetus in the mother's womb, for example to detect structural anomalies in the fetus. The traditional way for a clinician to acquire an image of each required view of the fetus is to manipulate an ultrasound probe while in acoustic contact with the abdomen of the mother until a desired anatomical orientation is in the plane of the <NUM>-D imaging probe. If multiple views are to be generated with such a procedure, there is a risk of missed abnormalities because obtaining and analyzing these views requires high skill (e.g. fetal echocardiography is very operator-dependent) whilst in addition the fetus may be moving during the procedure, requiring the clinician to reorient himself or herself with the fetus each time the fetus moves.

With the advent of three dimensional (<NUM>-D) ultrasound image acquisition, it is now possible to capture a large volume of the fetus and to perform computed rendering of <NUM>-D views at any point in time, e.g. even after the patient (the fetus) is released. The <NUM>-D acquisition procedure may be conducted by making a slow sweep of the <NUM>-D image plane over the fetus (mechanical steering) or by electronically steering the ultrasound beams over the fetus. User-directed image processing may then be used for evaluation of the captured image volume, i.e. to evaluate the fetal anatomy. As such, <NUM>-D ultrasound image acquisition is less operator-dependent and facilitates evaluation of the image volume along different views, for example to answer different diagnostic questions following the examination of the fetus.

Of particular interest to analyse the development of the fetus are so-called biometry measurements, which are used to check if the fetus is developing correctly, e.g. within expected tolerances. However, due to the complexity of the interpretation of <NUM>-D ultrasound images, such as in volume rendering mode in which a <NUM>-D volume of the fetus is imaged on a display device of the ultrasound imaging system, many clinicians prefer to perform such biometric measurements on <NUM>-D ultrasound images, as they have greater confidence in the reliability of such measurements when obtained from <NUM>-D images because it is more straightforward to obtain a visualization of the anatomical feature of interest in a desired plane, e.g. a plane along such a feature, despite the evidence provided by <NPL> in which they demonstrate that <NUM>-D ultrasound in volume rendering mode can produce biometric measurement accuracy comparable with <NUM>-D ultrasound imaging with good inter-operator reproducibility. For example, a clinician may be concerned that an incorrect biometric measurement is obtained through effects such as foreshortening of an anatomical feature of interest, e.g. a fetal bone or the like due to the measurement being performed in a volumetric view in which the clinician is unaware of the fact that an anatomical feature of interest is visualized under an angle, causing an underestimation of its dimensions obtained through measurement by the clinician.

Consequently, <NUM>-D (and <NUM>-D) ultrasound imaging at present is largely used to provide the expecting parents with realistic images of their developing child, i.e. the fetus. This hampers the penetration of such <NUM>-D and <NUM>-D ultrasound imaging systems into medical facilities, given the investment required for such systems may be considered unjustifiable if the system is not routinely being used for diagnostic purposes. Hence, there exists a need to facilitate the evaluation of volume rendered <NUM>-D images by a clinician.

<CIT> discloses an ultrasound diagnosis apparatus including a display configured to display a first ultrasound image showing an object, a user input device configured to receive a user input for selecting first and second depths in the first ultrasound image and setting different three-dimensional (3D) rendering properties with respect to the first and second depths; and a controller configured to generate a second ultrasound image showing a 3D volume of the object based on the set 3D rendering properties, wherein the display is further configured to display the generated second ultrasound image. In particular, opacity values, a color, a shape of an ROI or a degree of focus may be set by the user according to a depth.

The present invention discloses an ultrasound image processing apparatus for obtaining biometric measurements from a volume rendered ultrasound image according to claim <NUM>.

The present invention further discloses a computer-implemented method for obtaining biometric measurements from a volume rendered ultrasound image according to claim <NUM>.

Finally the present invention discloses a computer program product for implementing such a method on an ultrasound imaging processing apparatus.

Hence, an ultrasound image processing apparatus is provided in which a user can specify a number of points, e.g. two or more points on the display apparatus, for example by touching the screen of the display apparatus in case of a touchscreen display apparatus or by using any suitable user interface such as a mouse, trackball, or the like to highlight an anatomical feature of interest within the volumetric ultrasound image, which user-specified points are interpreted by the ultrasound image processing apparatus in the context of the rendered volumetric ultrasound image to identify a <NUM>-D path in the image, based on which the processor arrangement may perform one or more of a number of operations based on the determined <NUM>-D path. For example, the processor arrangement may determine the length of the <NUM>-D path, which for example may be useful where the user has specified two (or more) points to obtain a measurement of an anatomical feature of interest identified by these points, where the <NUM>-D path is typically mapped onto the anatomical feature of interest, thereby providing an accurate measurement of the dimension, e.g. length, of this anatomical feature. Alternatively, the <NUM>-D path may be used to reorient the rendered volumetric ultrasound image such that the <NUM>-D path is aligned with the viewing angle or perpendicular to the viewing angle along the rendered volumetric ultrasound image, thereby providing the user with an option to reorient the volumetric ultrasound image inner intuitive manner, e.g. to obtain a view of an anatomical feature of interest identified of the user-specified points on which the <NUM>-D path is based. A particularly preferred processing option is that a (reformatted) <NUM>-D image slice is extracted from the volumetric ultrasound image and displayed on the display apparatus to facilitate interpretation of the anatomical feature of interest by the user. Preferably, the <NUM>-D image slice is generated such that the anatomical feature of interest, or at least a substantial part thereof, lies in the plane of the image slice, thereby reducing the risk of incorrect biometric measurement of the anatomical feature of interest by the user in case the user wishes to manually perform such a measurement.

The various examples of the present disclosure have in common that they are based on the insight that a volumetric ultrasound image typically includes depth information, e.g. in the form of a certain intensity iso-surface as obtained through texture rendering or depth information obtained using the viewing angle of the user in conjunction with the user-specified point based on which a view ray through the volumetric ultrasound image may be estimated, which view ray may be used to obtain image information along this view in order to find the depth in the volumetric ultrasound image having the highest contribution to the pixel intensity of the display apparatus pixel coinciding with the user-defined point. In this manner, the <NUM>-D path may be accurately created along a surface contour of the anatomical structure of interest captured within the volumetric ultrasound image, which <NUM>-D path may be utilized in further processing operations performed on the volumetric ultrasound image as explained above.

In an example, the processor is adapted to generate the <NUM>-D ultrasound image from a sequence of <NUM>-D ultrasound images, which sequence for example may be captured through mechanical or electronic beam steering, or through manual migration of an ultrasound probe along a trajectory such as a body contour of a patient.

In an example, the processor arrangement is adapted to generate a <NUM>-D image slice based on the defined <NUM>-D path by fitting a plurality of tangential planes to different regions of the defined <NUM>-D path; selecting the tangential plane having the best fit with the defined <NUM>-D path; and generating the <NUM>-D image slice in accordance with the selected tangential plane. In this manner, the <NUM>-D image slice of the volumetric ultrasound image can be accurately aligned with the <NUM>-D path.

Optionally, the selected tangential plane is further based on a current view orientation of the rendered volumetric ultrasound image. For example, the best fitting plane within a defined range of view orientations around the current view orientation may be selected in order to avoid a sudden large change in the view orientation of the rendered volumetric ultrasound image, which may be confusing to the user of the ultrasound image processing apparatus.

In a further example, the processor arrangement further is adapted to perform the biometric measurement on an anatomical feature of interest visible within the generated <NUM>-D image slice; and control the display apparatus to display a result of the performed biometric measurement in order to provide a fully automated procedure to obtain such a biometric measurement. The processor arrangement may be adapted to control the display apparatus to display a result of the performed biometric measurement by controlling the display apparatus to display the generated <NUM>-D image slice together with said result.

In order to obtain the biometric measurement, the processor arrangement may be adapted to perform the biometric measurement on an anatomical feature of interest visible within the generated <NUM>-D image slice by defining a volume of interest associated with the defined <NUM>-D path; and identifying the anatomical feature of interest within the volume of interest. This is a robust manner to identify the anatomical feature of interest associated with the user-specified points.

In such an automated biometric measurement, the anatomical feature of interest may be a priori known, for example because the user has specified which anatomical feature of interest the user is looking for, in which case of the anatomical feature of interest may be identified in the defined volume of interest in a straightforward manner, e.g. using an image filter and/or segmentation algorithm in order to identify the known anatomical feature of interest within the volume of interest. However, in a scenario in which it is not known which anatomical feature of interest the user is looking for, the processor arrangement may be adapted to identify the anatomical feature of interest within the volume of interest by applying a plurality of image filters to the volume of interest; and identifying the anatomical feature of interest based on the filter results obtained by said applying. In this manner, the anatomical feature of interest may be identified in an automated manner by using those filter results that result in the recognition of an anatomical feature with the highest degree of confidence, for example.

According to another aspect, there is provided an ultrasound imaging system comprising the ultrasound image processing apparatus of any of the herein described embodiments and an ultrasound probe for providing the ultrasound image processing apparatus with the <NUM>-D ultrasound image data. Such an ultrasound probe typically is an ultrasound probe for capturing <NUM>-D ultrasound images, i.e. by capturing the sequence of <NUM>-D ultrasound images from which the <NUM>-D ultrasound image can be rendered through mechanical or electronic steering.

According to yet another aspect, there is provided a computer-implemented method. As explained above in the context of the ultrasound image processing apparatus, such a computer-implemented method facilitate interpretation of the volumetric ultrasound image by a user such as a clinician or sonographer by allowing the user to obtain a biometric measurement, reorient the rendered volumetric image or select a <NUM>-D image slice in which an anatomical feature of interest lies in the plane of the slice in an intuitive and straightforward manner, e.g. by specifying the points through a user interface such as a touchscreen, mouse, trackball or the like. As explained above, in this manner a <NUM>-D path may be constructed that accurately follows a feature such as a contoured surface within the volumetric ultrasound image.

The method may further comprise generating the <NUM>-D ultrasound image from a sequence of <NUM>-D ultrasound images, as explained above.

Generating a <NUM>-D image slice based on the defined <NUM>-D path may comprise fitting a plurality of tangential planes to different regions of the defined <NUM>-D path; selecting the tangential plane having the best fit with the defined <NUM>-D path; and generating the <NUM>-D image slice in accordance with the selected tangential plane in order to obtain a good match between the defined <NUM>-D path and the <NUM>-D image slice to be displayed on the display apparatus as explained above. Such generating optionally comprises selecting the best fitting plane within a defined range of view orientations around the current view orientation of the rendered volumetric image in order to avoid a sudden large change in the view orientation of the rendered volumetric ultrasound image, which may be confusing to the user of the ultrasound image processing apparatus.

In an example, the computer-implemented method further comprises performing the biometric measurement on an anatomical feature of interest visible within the generated <NUM>-D image slice; and controlling the display apparatus to display a result of the performed biometric measurement, optionally wherein controlling the display apparatus to display a result of the performed biometric measurement comprises controlling the display apparatus to display the generated <NUM>-D image slice together with said result, thereby providing a fully automated method of obtaining accurate biometric measurements from a rendered volumetric ultrasound image.

Performing the biometric measurement on an anatomical feature of interest visible within the generated <NUM>-D image slice may comprise defining a volume of interest associated with the defined <NUM>-D path; and identifying the anatomical feature of interest within the volume of interest in order to reliably identify the anatomical feature of interest as explained above.

Identifying the anatomical feature of interest within the volume of interest may comprise applying a plurality of image filters to the volume of interest; and identifying the anatomical feature of interest based on the filter results obtained by said applying in order to recognize an unknown anatomical feature of interest as explained above.

According to yet another aspect, there is provided a computer program product comprising a computer readable storage medium having computer readable program instructions embodied therewith for, when executed on a processor arrangement of an ultrasound image processing apparatus of any of the herein described embodiments, cause the processor arrangement to implement the method of any of the herein described embodiments.

Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein:.

<FIG> shows a schematic illustration of an ultrasound imaging system <NUM> according to an example embodiment. The ultrasound imaging system <NUM> is applied to inspect a volumetric region of an anatomical site, in particular an anatomical site of a patient <NUM> including a fetus <NUM>. The <NUM>-D image of such a volumetric region will also be referred to as the imaging volume, whilst a <NUM>-D slice of such a <NUM>-D image will also be referred to as a volume slice.

The ultrasound imaging system <NUM> comprises an ultrasound probe <NUM> having at least one transducer array having a multitude of transducer elements for transmitting and/or receiving ultrasound waves. The transducer elements are preferably arranged in a two-dimensional (2D) array, which is constructed to electronically steer ultrasound beams within the volumetric region such that a three-dimensional ultrasound image frame of said region is provided. Alternatively, the array may be a one-dimensional array (1D) constructed to be mechanically steered through the volumetric region in order to provide a three-dimensional ultrasound image frame. The probe <NUM> is adapted to transmit ultrasound waves in a particular direction and to receive ultrasound waves from a particular direction which forms a field of view <NUM> for a given 3D image frame of the ultrasound probe <NUM>. Such <NUM>-D imaging is well-known per se and will therefore not be explained in further detail for the sake of brevity only.

In the embodiment shown in <FIG>, the patient <NUM> is a pregnant person, wherein an anatomical entity to be inspected is a fetus <NUM>, at least part of which is disposed in the field of view <NUM>.

The ultrasound imaging system <NUM> further comprises an ultrasound image processing apparatus <NUM> such as a control unit, which typically comprises a processor arrangement <NUM> including one or more processing elements, and controls the provision of an ultrasound image via the ultrasound system <NUM>. As will be explained further below, the ultrasound image processing apparatus <NUM> may receive ultrasound image data from the transducer array of the ultrasound probe <NUM> and provides a compounded three-dimensional (3D) ultrasound image, i.e. a volume rendered image, derived from the different ultrasound data sets of the fetus <NUM> in a volume rendering mode of the ultrasound system <NUM>.

The ultrasound imaging system <NUM> further comprise a display device <NUM> for displaying the ultrasound image received from the ultrasound image processing apparatus <NUM>. Still further, a user interface <NUM> is provided that may comprise any combination of keys or a keyboard and inputting devices and may be connected to the display device <NUM> and/or directly to the ultrasound image processing apparatus <NUM>. Such inputting devices for example may include a mouse, trackball, or the like. Other suitable inputting devices will be immediately apparent to the skilled person. In the context of the present application, a user may convey a translation instruction to the ultrasound image processing apparatus <NUM> by moving an input device such as a trackball or mouse, by clicking a key, and so on. It should be understood that a translation instruction in some embodiments equates to the movement of an input device such as a trackball or mouse by the user. A particular example for a three-dimensional ultrasound system <NUM> may be the CX40 Compact Xtreme ultrasound system sold by the applicant. In general, matrix transducer systems as found on Philips iE33 systems or mechanical 3D/4D transducer technology as found, for example, on the Philips iU22 and HD15 systems may be applied in conjunction with the current invention.

An example embodiment of the ultrasound image processing apparatus <NUM> is provided in more detail in <FIG>, in which the ultrasound image processing apparatus <NUM> comprises at least a processor arrangement <NUM> and a data storage arrangement <NUM>. The display device <NUM> may be separate to the ultrasound image processing apparatus <NUM> or may form part of the ultrasound image processing apparatus <NUM>. Similarly, at least part of the user interface <NUM> may be separate to the ultrasound image processing apparatus <NUM> or may form part of the ultrasound image processing apparatus <NUM>.

The processor arrangement <NUM> may include an ultrasound image processor adapted to process digital echo signals by spatial compounding in an ultrasound image processor, such as the ultrasound image processor <NUM> in the example embodiment of the ultrasound imaging system as schematically depicted in <FIG>, which will be described in more detail below. The data storage arrangement <NUM> may comprise one or more memory devices, which may be discrete memory devices or may form part of the processor arrangement <NUM>. For example, the data storage arrangement <NUM> may include a compound image memory unit, which may form part of the ultrasound image processor or may be separate to the ultrasound image processor. The compound image memory may be implemented as a 3D frame storage buffer and may be implemented as a dual port memory which can be written to and read from simultaneously. The use of such a R/W memory enables newly acquired 3D ultrasound image frames by the transducer array of the ultrasound probe <NUM> and the beamformer (to be described in more detail below) to be written into one area of the R/W memory while the data of other 3D image frames previously stored in the memory is read out and analyzed. The writing of new slice image data into the memory may be controlled by a write address controller while the reading of slice image data from other locations in the memory may be under the control of a read address controller, thereby facilitating real time image analyses and compounding. Of course, such a compound image memory unit equally may be used for evaluation of the imaging volume upon completion of its acquisition, e.g. after investigation of the patient.

<FIG> schematically depicts an example embodiment of an ultrasound imaging system <NUM> in which the ultrasound image processing apparatus <NUM> is provided as a user console to which the ultrasound probe <NUM> comprising an ultrasound transducer array <NUM> is communicatively coupled, e.g. using an appropriate cable or the like. It should however be understood that at least parts of the ultrasound imaging system <NUM> may be distributed, e.g. provided as a remote service, in particular those elements for which the skilled person will understand that these elements are deployed for the processing of the sonographic data captured with the ultrasound transducer array <NUM>.

In particular, <FIG> schematically depicts a block diagram of an example embodiment of the electronics that may be deployed to interface with and control the ultrasound transducer array <NUM> for the generation of ultrasound waves, e.g. ultrasound pulses, and reception of ultrasound echoes, e.g. pulse echoes, e.g. for diagnostic imaging purposes. At least part of these electronics may be embodied by the processor arrangement <NUM>. Therefore, it should be understood that although these electronics are identified by different reference numerals, this does not necessarily mean that these electronics are distinct to the processor arrangement <NUM>.

The ultrasound transducer array <NUM> may be coupled to a microbeam former <NUM>, which may be located in the ultrasound probe <NUM> in some embodiments, which controls transmission and reception of signals by the ultrasound transducer cells <NUM> of the ultrasound transducer array <NUM>. Microbeam formers are capable of at least partial beam forming of the signals received by groups or "patches" of transducer element tiles for instance as described in US patents <CIT>), <CIT>), and <CIT>) The microbeam former <NUM> may be coupled by a probe cable, e.g. coaxial wire, to a terminal, e.g. an ultrasound image processing apparatus <NUM> such as a user console device or the like, which apparatus may comprise a transmit/receive (T/R) switch <NUM> which switches between transmission and reception modes and protects the main beam former <NUM> from high energy transmit signals when a microbeam former is not present or used and the transducer array is operated directly by the main system beam former <NUM>.

The transmission of ultrasonic beams from the ultrasound transducer array <NUM> under control of the microbeam former <NUM> may be directed by a transducer controller <NUM> coupled to the microbeam former by the T/R switch <NUM> and the main system beam former <NUM>, which receives input from the user's operation of the user interface <NUM> through control panel <NUM>. The transducer controller <NUM> may be coupled to control a voltage source <NUM> for the ultrasound transducer array <NUM>. For instance, the voltage source <NUM> may set the DC and AC bias voltage(s) that are applied to CMUT (capacitive micro-machined ultrasound transducer) elements <NUM> of a CMUT array <NUM>, e.g. to operate the CMUT elements in collapse mode, as is well-known per se although it should be understood that embodiments of the present invention are not limited to CMUT-based ultrasound probes <NUM> and that any suitable ultrasound probe may be used in the ultrasound imaging system <NUM> of the present invention. The transducer controller <NUM> may be further adapted to control the voltage supply <NUM> such as to switch the ultrasound transducer cells <NUM> to a low-power mode, e.g. in response to a temperature sensor signal indicative of the ultrasound transducer cells <NUM> reaching a critical temperature.

The partially beam-formed signals produced by the microbeam former <NUM> may be forwarded to the main beam former <NUM> where partially beam-formed signals from individual patches of transducer elements are combined into a fully beam-formed signal. For example, the main beam former <NUM> may have <NUM> channels, each of which receives a partially beam-formed signal from a patch of dozens or hundreds of ultrasound transducer cells <NUM> and/or from the individual ultrasound transducer elements of such ultrasound transducer cells <NUM>. In this way the signals received by thousands of transducer elements of an ultrasound transducer array <NUM> can contribute efficiently to a single beam-formed signal.

The beam-formed signals are coupled to a signal processor <NUM>, which may form part of the processor arrangement <NUM> as previously explained. The signal processor <NUM> can process the received echo signals in various ways, such as bandpass filtering, decimation, I and Q component separation, and harmonic signal separation which acts to separate linear and nonlinear signals so as to enable the identification of nonlinear (higher harmonics of the fundamental frequency) echo signals returned from tissue and microbubbles. The signal processor <NUM> optionally may perform additional signal enhancement such as speckle reduction, signal compounding, and noise elimination. The bandpass filter in the signal processor <NUM> may be a tracking filter, with its passband sliding from a higher frequency band to a lower frequency band as echo signals are received from increasing depths, thereby rejecting the noise at higher frequencies from greater depths where these frequencies are devoid of anatomical information.

The processed signals may be forwarded to a B-mode processor <NUM> and optionally to a Doppler processor <NUM>, each of which may form part of the processor arrangement <NUM>. The B-mode processor <NUM> employs detection of an amplitude of the received ultrasound signal for the imaging of structures in the body such as the tissue of organs and vessels in the body. B-mode images of structure of the body may be formed in either the harmonic image mode or the fundamental image mode or a combination of both for instance as described in US Patents <CIT>) and <CIT>).

The Doppler processor <NUM>, if present, processes temporally distinct signals from tissue movement and blood flow for the detection of the motion of substances, such as the flow of blood cells in the image field. The Doppler processor typically includes a wall filter with parameters which may be set to pass and/or reject echoes returned from selected types of materials in the body. For instance, the wall filter can be set to have a passband characteristic which passes signal of relatively low amplitude from higher velocity materials while rejecting relatively strong signals from lower or zero velocity material.

This passband characteristic will pass signals from flowing blood while rejecting signals from nearby stationary or slowing moving objects such as the wall of the heart. An inverse characteristic would pass signals from moving tissue of the heart while rejecting blood flow signals for what is referred to as tissue Doppler imaging, detecting and depicting the motion of tissue. The Doppler processor may receive and process a sequence of temporally discrete echo signals from different points in an image field, the sequence of echoes from a particular point referred to as an ensemble. An ensemble of echoes received in rapid succession over a relatively short interval can be used to estimate the Doppler shift frequency of flowing blood, with the correspondence of the Doppler frequency to velocity indicating the blood flow velocity. An ensemble of echoes received over a longer period of time is used to estimate the velocity of slower flowing blood or slowly moving tissue. The structural and motion signals produced by the B-mode (and Doppler) processor(s) are coupled to a scan converter <NUM> and a multiplanar reformatter <NUM>. The scan converter <NUM> arranges the echo signals in the spatial relationship from which they were received in a desired image format. For instance, the scan converter may arrange the echo signal into a two dimensional (2D) sector-shaped format, or a pyramidal three dimensional (3D) image.

The scan converter can overlay a B-mode structural image with colors corresponding to motion at points in the image field with their Doppler-estimated velocities to produce a color Doppler image which depicts the motion of tissue and blood flow in the image field. The multiplanar reformatter <NUM> will convert echoes which are received from points in a common plane in a volumetric region of the body into an ultrasonic image of that plane, for instance as described in US Patent <CIT>). A volume renderer <NUM> converts the echo signals of a 3D data set into a projected 3D image as viewed from a given reference point as described in <CIT>).

The 2D or 3D images are coupled from the scan converter <NUM>, multiplanar reformatter <NUM>, and volume renderer <NUM> to an image processor <NUM> for further enhancement, buffering and temporary storage for display on an image display <NUM>. The image processor <NUM> may form a part of the processor arrangement <NUM> and may further be adapted to control the visualization of volume slices as explained above. In addition to being used for imaging, the blood flow values produced by the Doppler processor <NUM> and tissue structure information produced by the B-mode processor <NUM> are coupled to a quantification processor <NUM>. The quantification processor produces measures of different flow conditions such as the volume rate of blood flow as well as structural measurements such as the sizes of organs and gestational age. The quantification processor may receive input from the user control panel <NUM>, such as the point in the anatomy of an image where a measurement is to be made.

Output data from the quantification processor is coupled to a graphics processor <NUM> for the reproduction of measurement graphics and values with the image on the display <NUM>. The graphics processor <NUM> can also generate graphic overlays for display with the ultrasound images. These graphic overlays can contain standard identifying information such as patient name, date and time of the image, imaging parameters, and the like. For these purposes the graphics processor receives input from the control panel <NUM>, such as patient name.

The user interface <NUM> may be coupled to the transmit controller <NUM> to control the generation of ultrasound signals from the transducer array <NUM> and hence the images produced by the transducer array <NUM> and the ultrasound system <NUM>. The user interface <NUM> also may be coupled to the multiplanar reformatter <NUM> for selection and control of the planes of multiple multiplanar reformatted (MPR) images which may be used to perform quantified measures in the image field of the MPR images. At least parts of the above described functionality of the ultrasound imaging system <NUM> may be implanted with the processor arrangement <NUM> as will be immediately apparent to the skilled person.

In accordance with embodiments of the present invention, the processor arrangement <NUM> of the ultrasound image processing apparatus <NUM> is adapted to implement the method <NUM>, a flow chart of which is depicted in <FIG>. In other words, the method <NUM> is a computer-implemented method in the sense that the method is implemented on an apparatus comprising computational capability, such as the ultrasound image processing apparatus <NUM>.

In accordance with embodiments of the present invention, an operator of the ultrasound image processing apparatus <NUM> may operate the apparatus in the so-called volume rendering mode, in which the apparatus renders a volumetric image for display on the display apparatus <NUM> from the <NUM>-D ultrasound image or <NUM>-D image slices captured with the ultrasound probe <NUM> of the ultrasound system <NUM>, which image slices may have captured using an ultrasound probe <NUM> deploying mechanical or electronic steering as previously explained. The rendered volumetric image typically comprises an anatomical object of interest, such as a fetus <NUM>, although it should be understood that the teachings of the present invention are not limited to fetal ultrasound but may be applied to the ultrasound imaging of any anatomical object of interest onto which a clinician may wish to perform a diagnostic evaluation such as a biometric measurement of a feature of interest of the anatomical object, such as for example an organ of interest of a patient <NUM> under investigation, such as the heart, the brain or the like of such a patient.

In an embodiment, the processor arrangement <NUM> receives a <NUM>-D ultrasound image or a sequence of <NUM>-D ultrasound images in operation <NUM> of the method <NUM>, which data may be received in real time from the ultrasound probe <NUM> or alternatively may be retrieved from the data storage arrangement <NUM>, e.g. in the case of off-line evaluation of the ultrasound image data captured with the ultrasound probe <NUM>, such as upon completion of an examination of a patient <NUM>. The processor arrangement <NUM> next processes this image data in operation <NUM> of the method <NUM> in order to render a volumetric ultrasound image. This may be preceded by generating a <NUM>-D ultrasound image from the received sequence, in case of a sequence of <NUM>-D ultrasound image frames having been generated with the probe <NUM>. Any suitable type of volume rendering such as direct volume rendering, surface rendering, maximum or minimum intensity projection rendering and so on may be deployed. As such rendering techniques are well-known per se, they will not be explained in further detail for the sake of brevity only. The processor arrangement <NUM> controls the display apparatus <NUM> to display the rendered volumetric ultrasound image <NUM>. Again, such control is entirely routine to the skilled person and will therefore not be explained in further detail for the sake of brevity only.

<FIG> depicts an image of such a volume rendered image <NUM>, in which an anatomical object of interest, here a fetus <NUM>, has been captured. The user may be interested in obtaining a view of a particular feature of the anatomical object of interest, e.g. a part of the anatomy of this object, in <NUM>-D mode, for example to evaluate the anatomical feature of interest in an optimal view and/or to perform a biometric measurement of the anatomical feature of interest. To this end, the user may wish to generate a <NUM>-D slice of the rendered volumetric ultrasound image <NUM> in which the anatomical feature of interest or at least a substantial part thereof, e.g. a cross-section thereof, lies in the plane of this generated <NUM>-D slice. However, it is not straightforward for the user to obtain such a <NUM>-D slice from such a rendered volumetric ultrasound image <NUM>.

In embodiments of the present invention, the user may specify a number of points <NUM> in the volumetric ultrasound image <NUM> to highlight the anatomical feature of interest, or at least a view expected to align with this feature, as schematically depicted in <FIG>, with the dashed line connecting the user-specified points <NUM> indicating this anatomical feature or view. The user may specify the two or more points <NUM> in any suitable manner. Particularly preferred for ease of use and intuitive interaction with the display apparatus <NUM> is that the display apparatus <NUM> comprises a touchscreen onto which the volumetric ultrasound image <NUM> is displayed, such that the user can simply touch the touchscreen in order to specify the two or more points <NUM>, for example by running a finger across a desired trajectory on the touchscreen or by tapping discrete points on the touchscreen. However, alternative ways of specifying the points <NUM> equally may be contemplated. For example, the user may move a cursor, crosshairs or other suitable location identifier across the screen of the display apparatus <NUM> using a controller such as a mouse, trackball or the like, in which case the user may specify the two or more points <NUM> by providing a point selection command with the location identifier in the location of the point to be selected, which point selection command may be provided in any suitable manner, e.g. through a button or the like on the controller or on a separate user interface such as a keyboard or the like. It should be understood that any suitable manner in which the user can select the points <NUM> may be deployed.

In operation <NUM> of the method <NUM>, the processor arrangement <NUM> receives the user-selected points <NUM>, e.g. through communication with the display apparatus <NUM> and/or with a user interface such as the user interface <NUM> used by the user to select the points <NUM>, with the processor arrangement <NUM> processing the user-selected points <NUM> to link each of these points to a particular location within the volume rendered ultrasound image <NUM>. In the volume rendered ultrasound image <NUM>, each pixel of the image of the rendering result displayed on the display apparatus <NUM> is typically associated with depth information regarding the volume rendered image <NUM>, e.g. a depth map. For example, the volume rendered image <NUM> may depict an iso-surface <NUM>, which may have been derived from pixel intensity information in the <NUM>-D image slices that have been processed to generate the volume rendered image <NUM>, such that it will be known at which depth within the volume rendered image <NUM> a user's viewing angle or view ray of the image will coincide with the iso-surface <NUM>. Alternatively, in scenarios where a transfer table is being used, integration of the image information along such a view path can be used to estimate the depth value mostly contributing to the pixel coinciding with that view path.

In operation <NUM> of the method <NUM>, the processor arrangement <NUM> uses this depth information to define a <NUM>-D path <NUM> in the volumetric ultrasound image <NUM>, as schematically depicted in <FIG>, in which non-limiting example the <NUM>-D path <NUM> follows the outer contours of part of the leg of the fetus <NUM>, which has been derived from a number of points <NUM> defined by the user of the ultrasound image processing apparatus <NUM> as previously explained, with the processor arrangement <NUM> of this apparatus mapping each of the user-specified points <NUM> onto a location at a determined depth within the volumetric ultrasound image <NUM> as explained above. The processor arrangement <NUM> may be adapted to deploy any suitable algorithms to identify the <NUM>-D path <NUM>, such as for example regression or outlier suppression algorithms to obtain meaningful <NUM>-D curves in noisy volumetric images or in volumetric images containing artefacts.

In an embodiment, the processor arrangement <NUM> is adapted to control the display apparatus <NUM> such that the <NUM>-D path <NUM> is displayed within the volume rendered ultrasound image <NUM>, thereby giving the user visual feedback based on which user may decide if the <NUM>-D path <NUM> has been appropriately defined by the processor arrangement <NUM>, in which case the method may proceed to operation <NUM>, or based on which the user may decide that refinement of the <NUM>-D path <NUM> is required, at which point the user may interact with the display apparatus <NUM> to adjust the positioning of the <NUM>-D path <NUM>, e.g. by altering one or more of the previously defined points <NUM> or in any other suitable manner.

At this point, two main embodiments of the present invention will be explained in more detail. This is depicted in <FIG> by the operation <NUM> in which one of the two main embodiments is chosen. It should be understood however that operation <NUM> has been included for the sake of clarity only and that it is by no means necessary to decide with main embodiment to follow after operation <NUM>. It is for example equally feasible to decide which main embodiment is followed before invoking the method <NUM> or at any suitable point in time during execution of the method <NUM>.

In the first main embodiment, the user may wish to rely on the processor arrangement <NUM> to perform an automated biometric measurement of an anatomical feature of interest associated with the <NUM>-D path <NUM>. This is checked in operation <NUM>, and if it is the case that the user wishes to rely on such an automated biometric measurement, the method <NUM> proceeds to operation <NUM> in which the processor arrangement <NUM> defines a volume of interest <NUM> associated with the <NUM>-D path <NUM>. Such a volume of interest <NUM> may be defined around the <NUM>-D path <NUM>. In some embodiments, the volume of interest <NUM> may not be centred around the <NUM>-D path <NUM> but may be defined from the <NUM>-D path <NUM> and extend from this path into a volume portion of the volumetric ultrasound image <NUM>, which for instance may increase the likelihood of detecting an anatomical feature of interest <NUM> within the volume of interest <NUM> in case the <NUM>-D path <NUM> delimits a (body) surface of the anatomical object of interest. The volume of interest <NUM> may have any suitable shape such as for example a tubular shape having a circular cross-section, which tubular shape follows the <NUM>-D path <NUM> as previously explained. Other shapes of the volume of interest <NUM> may be equally contemplated as will be apparent to the skilled person.

Upon definition of the volume of interest <NUM>, the volume of interest <NUM> may be investigated by the processor arrangement <NUM> in order to identify the anatomical feature of interest <NUM> within this volume in operation <NUM>. This for example may be achieved using an appropriate image filter or segmentation algorithm adapted to identify such an anatomical feature of interest <NUM>. Such image filters and segmentation algorithm are well-known to the skilled person and are therefore not explained in further detail for the sake of brevity only. In the remainder, where reference is made to an image filter, it should be understood that this is intended to also cover segmentation algorithms.

When it is clear what anatomical feature <NUM> the user is interested in, the appropriate image filter for detecting this anatomical feature <NUM> within the volume of interest <NUM> may be deployed. For example, where the user has identified the anatomical feature of interest <NUM>, such as a fetal femur length, the image filter for fetal femur detection may be deployed by the processor arrangement <NUM>. Alternatively, where it is prima facie unknown what anatomical feature <NUM> the user is interested in, the processor arrangement <NUM> may deploy a plurality of image filters to detect different anatomical features <NUM> and select the filtering result in which an anatomical feature <NUM> was identified with the highest degree of confidence, which is indicative of a best match between the applied image filter and the anatomical feature <NUM>.

If no anatomical feature <NUM> can be identified in the volume of interest <NUM>, the volume of interest <NUM> may be rescaled, e.g. its cross-sectional size increased, after which operation <NUM> is repeated. If after a defined number of such iterations the anatomical feature <NUM> still cannot be identified, the user may be presented with a warning signal or message, e.g. a message is displayed on the display apparatus <NUM>. Once the anatomical feature of interest <NUM> has been identified, the processor arrangement <NUM> may perform a biometric measurement on the identified anatomical feature of interest <NUM> in operation <NUM> in any suitable manner. Such automated biometric measurements are well-known per se and are therefore not explained in further detail for the sake of brevity only. This may be any suitable biometric measurement such as a length, thickness or cross-section measurement of the anatomical feature of interest <NUM>.

Following the completion of the biometric measurement, or alternatively following the second main embodiment in which the user has indicated that a manual biometric measurement of an anatomical feature of interest is to be performed such that the aforementioned operations <NUM>, <NUM> and <NUM> are omitted, the method <NUM> proceeds to operation <NUM> in which the processor arrangement <NUM> generates a <NUM>-D image slice <NUM> based on the constructed <NUM>-D path <NUM> as schematically depicted in <FIG>, with the processor arrangement <NUM> adapted to control the display apparatus <NUM> to display the generated <NUM>-D image slice <NUM> in operation <NUM>. The <NUM>-D image slice <NUM> preferably is arranged tangentially to the <NUM>-D path <NUM> such that an anatomical feature of interest <NUM> (if present) lies in the plane of the <NUM>-D image slice <NUM>. In other words, the processor arrangement <NUM> generates an optimal viewing plane of such an anatomical feature of interest <NUM> based on which the user may perform manual biometric measurements of the anatomical feature of interest <NUM> as indicated by the double arrow in <FIG> with a minimal risk of such measurements being inaccurate, e.g. due to foreshortening of the anatomical feature of interest <NUM> by viewing this feature under a non-optimal angle in which the feature appears shorter as explained in more detail above.

Where such biometric measurements have been performed in accordance with the first main embodiment of the present invention, the processor arrangement <NUM> may be further adapted to display the biometric measurement results on the display apparatus <NUM> in operation <NUM>. The processor arrangement <NUM> preferably displays the biometric measurement results together with the generated <NUM>-D image slice <NUM>, e.g. as an overlay of this image slice, adjacent to this image slice, and so on, although in an alternative embodiment of the first main embodiment of the present invention the processor arrangement <NUM> may simply display the biometric measurement results on their own, i.e. without displaying the <NUM>-D image slice <NUM>, in which case operation <NUM> may be skipped.

The <NUM>-D image slice <NUM> may be generated by the processor arrangement <NUM> in any suitable manner. In a particularly advantageous embodiment, a best fitting tangential plane to the <NUM>-D path <NUM> is estimated, for example by fitting a plurality of tangential planes to the <NUM>-D path <NUM> and selecting the plane having the best fit with this path. The view geometry may be changed in accordance with the selected tangential plane such that the view direction is now parallel to the normal of this plane. This may be refined by selecting the plane having the best fit with this path within a range of view orientations around the current view orientation of the rendered volumetric image such as to limit the change in view orientation relative to the rendered volumetric image, as large changes in such view orientation may be experienced as confusing by the user.

At this point, it is noted that the <NUM>-D path <NUM> derived from the depth information associated with the pixels of the volumetric image corresponding to the user-specified points <NUM> is not necessarily leveraged to generate a <NUM>-D image slice <NUM>. In alternative embodiments of the method <NUM> (not explicitly shown), the processor arrangement <NUM> may use the <NUM>-D path in further processing operations.

A first example processing operation is the determination of the length of the <NUM>-D path <NUM>, which may provide an accurate biometric measurement of an anatomical feature of interest in an automated fashion, which for example is useful where a user has sufficient confidence in such an automated biometric measurement. In such a scenario, the generation of the <NUM>-D image slice <NUM> may not be required in order to obtain the desired biometric measurement.

A second example processing operation is the reorientation of the rendered volumetric image (rather than the generation of <NUM>-D image slice <NUM>) based on the <NUM>-D path <NUM>, in which a main direction of the path (i.e. an anatomical feature of interest associated with the path) is oriented perpendicular to the viewing angle of the rendered volumetric image such that the anatomical feature of interest extends across the screen of the display apparatus <NUM>, which facilitates the evaluation of the anatomical feature of interest by the user of the apparatus. Other reorientations, e.g. a reorientation in which the main direction of the path <NUM> is oriented parallel to the viewing angle of the rendered volumetric image may of course also be contemplated.

The above described embodiments of the method <NUM> may be realized by computer readable program instructions embodied on a computer readable storage medium having, when executed on a processor arrangement <NUM>, cause the processor arrangement to implement the method <NUM>. Any suitable computer readable storage medium may be used for this purpose, such as for example an optically readable medium such as a CD, DVD or Blu-Ray disc, a magnetically readable medium such as a hard disk, an electronic data storage device such as a memory stick or the like, and so on. The computer readable storage medium may be a medium that is accessible over a network such as the Internet, such that the computer readable program instructions may be accessed over the network. For example, the computer readable storage medium may be a network-attached storage device, a storage area network, cloud storage or the like. The computer readable storage medium may be an Internet-accessible service from which the computer readable program instructions may be obtained. In an embodiment, the ultrasound image processing apparatus <NUM> is adapted to retrieve the computer readable program instructions from such a computer readable storage medium and to create a new computer readable storage medium by storing the retrieved computer readable program instructions in the data storage arrangement <NUM>, e.g. in a memory device or the like forming part of the data storage arrangement <NUM>.

Claim 1:
An ultrasound image processing apparatus (<NUM>) for obtaining a biometric measurement of an anatomical feature of interest from a <NUM>-D ultrasound image, comprising a display apparatus (<NUM>) communicatively coupled to a processor arrangement (<NUM>) adapted to:
render a volumetric ultrasound image (<NUM>) along a viewing angle from the <NUM>-D ultrasound image and control the display apparatus to display said rendered image, wherein the volume rendered ultrasound image depicts an intensity iso-surface (<NUM>);
receive a plurality of user inputs (<NUM>) highlighting the anatomical feature of interest, each input corresponding to a user-specified point (<NUM>) on the display apparatus and corresponding to a pixel of the displayed volumetric image (<NUM>);
mapping each of the user-specified points (<NUM>) to a location within the volume rendered image (<NUM>) with the depth being determined from a user's view ray coinciding with the iso-surface (<NUM>);
define a <NUM>-D path (<NUM>) in the volumetric ultrasound image based on the received user inputs along said determined depths;
perform a processing operation based on the defined <NUM>-D path; and control the display apparatus to display the processing operation result, wherein the processing operation based on the defined <NUM>-D path comprises
a measurement of a length of the <NUM>-D path (<NUM>), and at least one of:
a reorientation of the rendered volumetric ultrasound image (<NUM>) such that the <NUM>-D path is aligned with the viewing angle along the rendered volumetric ultrasound image or perpendicular to a viewing angle along the rendered volumetric ultrasound image; and
a generation of a <NUM>-D image slice (<NUM>) of the <NUM>-D ultrasound image based on the defined <NUM>-D path.