Patent Description:
Ultrasound is the modality of choice for fetal screening as it is able to show fetal anatomy in sufficient detail, while at the same being cost effective with no known adverse effects. Fetal screening allows for detecting abnormalities at an early gestational age, such that therapeutically suitable interventions can be planned and performed as required. Currently, there is a trend towards using 3D ultrasound, since a 3D image contains much more spatial information about the location of several organs with respect to each other and it allows for a variety of workflow optimizations.

A major part of the fetal examination is performed at <NUM> to <NUM> weeks gestational age with specific recommended standard measurements, for example as outlined in <NPL>.

These measurements are related to the size of certain bones and structures and provide an insight into the fetal growth. Furthermore, structures are qualitatively investigated to detect anomalies.

One of these structures is the fetal spine. Standard views are required, for instance the ossification centers are best visible in sagittal views, abnormal curvature can be detected in sagittal and coronal views, and in axial (transverse) planes each vertebra can be investigated.

<CIT> for example discloses a method for detecting deformation of a spine.

Searching for optimal view planes for investigating the fetal spine is a demanding and time-consuming task. It requires an optimal manual positioning of the ultrasound probe and needs to be repeated in case the fetus is moving. Furthermore, due to the curvature of the spine, it is not always possible to find a plane which contains the whole spine. In such a case, a sweep through a range of neighboring view planes is required to cover the whole spine. Such an investigation requires several minutes to be performed completely.

There is a need for an improved way to obtain standard fetal ultrasound images.

According to examples in accordance with an aspect of the invention, there is provided a computer-implemented fetal imaging method comprising:.

This method displays the shape of the spine in the sagittal and coronal planes, by detecting the spine centerline so that projections of the spine image may be performed using the centerline as a representation of the spine location. If there is significant curvature out of the sagittal plane, a projection of the spine image may be provided onto the sagittal plane. The spine image is projected onto the coronal plane since the spine does not lie within a coronal plane.

The method thus provides an automatic generation of view planes of interest. The spine centerline is obtained using an image processing algorithm and from this sagittal and coronal views are obtained which each contain a whole view of the spine, from the two orthogonal directions. Thus, a three dimensional spine shape can quickly be assessed from automatically generated views.

The first plane is for example the mid-sagittal plane.

In this way, if the spine is not contained in a single sagittal plane, a projection of the spine image is made onto the sagittal plane, using the spine centerline to define the projection transformation, thereby to project the image of the spine onto the first plane. In this way, a view is ensured containing the whole spine. Presenting such automatically generated standard views to the physician can significantly speed up the investigation time. A manual view plane selection typically requires several minutes, whereas the automated approach enables views to be generated in less than one minute.

The method avoids the needs for manually positioning the ultrasound probe.

If the measure of fit error is above a second threshold, an output may be provided indicating high spine curvature (out of the sagittal plane). This provides automated detection of spine curvature problems.

The method may comprise deriving a measure of fit error of the spine centerline to the second plane, wherein if the measure of fit error is above a third threshold, providing an output indicating high spine curvature. This provides automated detection of spine curvature problems out of the coronal plane.

The method may further comprise deriving a sequence of planes perpendicular to the spine centerline. Thus, a sweep of axial views can also be computed automatically.

The method for example comprises implementing a user interface allowing a user to sweep though the sequence in order to view each vertebra in an axial view. Thus, a user can sweep through standard axial views.

The method may further comprise defining a volume of interest around the spine and performing volume rendering.

The invention also provides a controller for controlling the processing of a 3D fetal ultrasound image, wherein the controller is adapted to implement the method as defined above.

The invention also provides an ultrasound system, the system comprising:.

The invention provides a fetal imaging method which involves detecting a spine centerline in a 3D ultrasound image, and determining a first plane which is a sagittal plane of best fit through the spine centerline. The first plane and the image of the spine in the first plane and/or a projection of the image of the spine onto the first plane are displayed. A second, coronal plane, is also determined, and the image of the spine is projected onto the second plane, and the second plane and the projection of the spine onto the second plane are displayed.

<FIG> shows an illustration of the 3D volume data obtained by a 3D ultrasound scan. From the 3D scan, the spin centerline <NUM> is detected.

An example of an algorithm for detecting the spine centerline is applied for example as described in <NPL>. The result is a sequence of points located in the spinal canal.

A first plane is then defined, which is a sagittal plane of best fit through the spine centerline. In particular, the mid-sagittal plane S is defined as that plane where the quadratic sum q of the distances of spine centerline points to the plane is minimal.

This sum q serves as a measure of fit error of the spine centerline to the first plane. If the measure of fit error q is below a threshold, the first plane and the spine image are displayed as shown in <FIG>. In particular, if q is below a pre-defined threshold, it means the spine centerline points are nearly contained in the plane S. Hence the plane S can be displayed together with the image along the spine centerline.

If the measure q of fit error is not below the threshold, the spine image is projected onto the first plane, and the plane is then displayed with the projected spine image. The image will again be as shown in <FIG>. Thus, if q exceeds the threshold, then the image along the spine centerline needs to be projected onto the plane S, yielding the projected view of the 3D data set.

<FIG> shows the spine centerline <NUM> or projected spine centerline <NUM> for illustrative purposes. In practice, the practitioner wishes to view the actual spine image, and the centerline does not need to be displayed. The spine centerline, as obtained from the analysis of the 3D ultrasound volume, is used to create the transformation of the 3D volume data so that the spine image is projected onto the first plane. Thus, the spine centerline is used for the purposes of defining the mid-sagittal plane and creating the mapping to enable the spine image data in the 3D data volume to be projected onto a 2D plane.

If the measure q of fit error exceeds a further clinically relevant threshold, it could indicate an abnormally high spine curvature, corresponding for instance to scoliosis. The visualizations can then be flagged accordingly, potentially indicating regions of high deviation.

A second plane is also determined, perpendicular to the first plane, which is a coronal plane of best fit to the spine centerline. The coronal plane C is thus defined as being perpendicular to S and as having the minimal quadratic sum of distances to the spine centerline points. This plane normally does not contain all spine centerline points, hence the spine image is projected onto the plane C, yielding a projected view of the 3D data set.

<FIG> shows this second, coronal, plane. The spine is projected onto the second plane, and the second plane and the projected spine image are displayed. Again, the projected spine centerline <NUM> is shown for illustration purposes and in clinical practice it would not be shown since it could distract the physician and may hide important details.

The quadratic sum may also be considered as a measure of fit error of the spine centerline to the second plane. This may also be used as a measure of spine curvature out of the coronal plane. Thus spine curvatures in the two orthogonal directions may be assessed automatically based on the fitting of the spine centerline to the two planes.

If required, a sequence of planes perpendicular to the spine centerline may be computed. The investigating physician can sweep through these planes in order to investigate each vertebra in an axial view.

Similarly, if required, a slab like volume of interest can be defined around the spine, to allow a direct volume rendering of the spine anatomy. Such a volume of interest is shown in <FIG>.

<FIG> shows a computer-implemented fetal imaging method.

In step <NUM>, a 3D ultrasound image is obtained.

In step <NUM>, a spine centerline is detected in the 3D ultrasound image.

In step <NUM>, a first plane which is a sagittal plane of best fit through the spine centerline is determined.

In step <NUM>, the first plane is displayed with the image of the spine or a projection of the image of the spine onto the first plane. In particular, in accordance with the invention, a measure of fit error of the spine centerline to the first plane is derived. If the measure of fit error is below a threshold, the first plane and the image of the spine is displayed. If the measure of fit error is not below the threshold, the image of the spine image is projected onto the first plane, and the first plane and the projected image of the spine is displayed.

In step <NUM>, a second plane, perpendicular to the first plane, which is a coronal plane of best fit to the spine centerline is determined.

In step <NUM>, the second plane is displayed with a projection of the image of the spine onto the second plane.

Of course, the steps of the method may be performed in a different order. For example, both planes can be derived (in either order) before any display of information.

For completeness, the general operation of an exemplary ultrasound diagnostic imaging system will first be described, with reference to <FIG>, and with emphasis on the signal processing function of the system since this invention relates to the processing of the signals measured by the transducer array.

The system comprises an array transducer probe <NUM> which has a CMUT transducer array <NUM> for transmitting ultrasound waves and receiving echo information. The transducer array <NUM> may alternatively comprise piezoelectric transducers formed of materials such as PZT or PVDF. The transducer array <NUM> is a two-dimensional array of transducers <NUM> capable of scanning in three dimensions for 3D imaging.

The transducer array <NUM> is coupled to a microbeamformer <NUM> in the probe which controls reception of signals by the CMUT array cells or piezoelectric elements. Microbeamformers are capable of at least partial beamforming of the signals received by sub-arrays (or "groups" or "patches") of transducers as described in <CIT>), <CIT>), and <CIT>).

Note that the microbeamformer is entirely optional. The examples below assume no analog beamforming.

The microbeamformer <NUM> is coupled by the probe cable to a transmit/receive (T/R) switch <NUM> which switches between transmission and reception and protects the main beamformer <NUM> from high energy transmit signals when a microbeamformer is not used and the transducer array is operated directly by the main system beamformer. The transmission of ultrasound beams from the transducer array <NUM> is directed by a transducer controller <NUM> coupled to the microbeamformer by the T/R switch <NUM> and a main transmission beamformer (not shown), which receives input from the user's operation of the user interface or control panel <NUM>.

The transducer controller <NUM> can be coupled to control a DC bias control <NUM> for the CMUT array. The DC bias control <NUM> sets DC bias voltage(s) that are applied to the CMUT cells.

In the reception channel, partially beamformed signals are produced by the microbeamformer <NUM> and are coupled to a main receive beamformer <NUM> where the partially beamformed signals from individual patches of transducers are combined into a fully beamformed signal. For example, the main beamformer <NUM> may have <NUM> channels, each of which receives a partially beamformed signal from a patch of dozens or hundreds of CMUT transducer cells or piezoelectric elements. In this way the signals received by thousands of transducers of a transducer array can contribute efficiently to a single beamformed signal.

The signal processor <NUM> can process the received echo signals in various ways, such as band-pass 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 micro-bubbles. The band-pass filter in the signal processor can be a tracking filter, with its pass band 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.

In Fig. <NUM> only the receiver beamformers <NUM>, <NUM> are shown, for simplicity.

However, the bandwidth that the transmission pulses occupy can vary depending on the transmission beamforming that has been used. The reception channel can capture the whole transducer bandwidth (which is the classic approach) or by using bandpass processing it can extract only the bandwidth that contains the useful information (e.g. the harmonics of the main harmonic).

The processed signals are coupled to a B mode (i.e. brightness mode, or 2D imaging mode) processor <NUM> and a Doppler processor <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 as described in <CIT>) and <CIT>) The Doppler processor <NUM> 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 <NUM> 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.

The structural and motion signals produced by the B mode and Doppler processors are coupled to a scan converter <NUM> and a multi-planar 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 multi-planar reformatter will convert echoes which are received from points in a common plane in a volumetric region of the body into an ultrasound image of that plane, as described in <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>, multi-planar reformatter <NUM>, and volume renderer <NUM> to an image processor or controller <NUM> for further enhancement, buffering and temporary storage for display on an image display <NUM>. 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>, and for audio output from the display device <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 user interface <NUM>, such as patient name. The user interface is also 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 and the ultrasound system. The transmit control function of the controller <NUM> is only one of the functions performed. The controller <NUM> also takes account of the mode of operation (given by the user) and the corresponding required transmitter configuration and band-pass configuration in the receiver analog to digital converter. The controller <NUM> can be a state machine with fixed states.

The image processing functions described above may for example be performed by the image processor <NUM>.

In accordance with a further aspect of the invention, a computer program product comprises instructions (software) for the image processor or controller <NUM> to implement the method of the invention. The computer program product may be software that can be downloaded from a server. Alternatively, the computer program product may be a data carrier (e.g. a CD or DVD) comprising the software.

Claim 1:
A computer-implemented fetal imaging method, the method comprising:
obtaining (<NUM>) a 3D ultrasound image;
detecting (<NUM>) a spine centerline in the 3D ultrasound image;
determining (<NUM>) a first plane which is a sagittal plane of best fit through the spine centerline;
determining (<NUM>) a second plane, perpendicular to the first plane, which is a coronal plane of best fit to the spine centerline; and
displaying (<NUM>) the second plane and a projection of the image of the spine onto the second plane; characterized by
deriving a measure of fit error of the spine centerline to the first plane;
if the measure of fit error is below a threshold,
displaying (<NUM>) the first plane and the image of the spine;
if the measure of fit error is not below the threshold,
projecting the image of the spine image onto the first plane, and
displaying (<NUM>) the first plane and the projected image of the spine.