FIELD OF THE INVENTION

This invention relates generally to an apparatus for obtaining an X-ray image having a composite field of view. Also discussed is an X-ray imaging system, a method for obtaining an X-ray image having a composite field of view, a computer program element, and a computer-readable medium.

BACKGROUND OF THE INVENTION

The configuration of the field of view (FOV) for radiographic exposures such as lung radiographs, is a non-trivial task requiring the attention of a trained radiographer to operate an X-ray imager. A field of view which is set erroneously before an exposure means that a subsequent full X-ray image must be taken, because important anatomical detail could be missing from the first image. A patient might even need to be recalled for a second visit. Such occurrences are undesirable, leading to inefficiency in radiological departments, and leading to an increase in the X-ray dose absorbed by a patient. US 2015/0228071 A1 discusses an apparatus and method for automatically or semi-automatically controlling a collimator of an X-ray imager. However, such methods can be further improved.

SUMMARY OF THE INVENTION

Therefore, according to a first aspect, there is provided an apparatus for obtaining an X-ray image having a composite field of view. The apparatus comprises:a processing unit.

The processing unit is configured to obtain first X-ray image data of a portion of a region of interest of an object using an X-ray imager, wherein the first X-ray image data is obtained from an X-ray imager having an adjustable field of view set to an initial field of view state, to compare the first X-ray image data to an anatomical model, to define a boundary error region contiguous to the first X-ray image data based on the comparison of the first X-ray image data to the anatomical model, to generate an updated field of view state based on the location of the boundary error region in the region of interest, to transmit the updated field of view state to an X-ray imager, to obtain second X-ray image data of the region of interest of the object using the X-ray imager when set to the updated field of view state, and to combine the first X-ray image data and the second X-ray image data to obtain an output image of the region of interest having a composite field of view.

Accordingly, an apparatus may be provided capable of controlling an X-ray imager which identifies an acquisition deficiency in a first X-ray image. Settings are generated which can be used to adjust the field of view of the X-ray imager, providing a further X-ray image which completes the imaging of the region of interest. The updated field of view may, for example, be smaller in area than the initial field of view. In this case, a patient would be subjected, upon the retake of the X-ray image, to a lower dose of X-ray radiation, compared to the first X-ray image exposure. Such an apparatus enables a reduction in the total X-ray dose delivered to a patient.

Optionally, in the apparatus according to the first aspect, the anatomical model comprises a probabilistic anatomical atlas representing a plurality of anatomical elements. The processing unit is further configured to compare portions of the first X-ray image to anatomical elements in the probabilistic anatomical atlas.

Accordingly, an accurate impression of a boundary error region in the first X-ray image may be derived to enable a second X-ray image to be obtained.

Optionally, in the apparatus according to first aspect, the processing unit is configured to identify an expected element, or portion of an expected element, in the anatomical model and/or probabilistic anatomical atlas, which is missing from the first X-ray image data. The processing unit is further configured to define a boundary error region in the X-ray image data based on an extrapolation of the anatomical model and/or probabilistic anatomical atlas out of the portion of the region of interest.

Accordingly, the extent of the error in the field of view of the first X-ray image may be identified using accurate anatomical data.

Optionally, the apparatus of the first aspect in which the processing unit is further configured to generate an image completion metric of the first X-ray image data based on a characteristic of the boundary error region. The second X-ray image data is obtained by the processing unit when the image completion metric surpasses an image completion condition.

Accordingly, for example, following a comparison with the anatomical model, it could be found that a lung element in the first X-ray image data is 95% complete, with only a small degree of the edge of a lung missing from the first X-ray image data. In this case, a second X-ray image would not be needed, thus saving the patient an unnecessary extra X-ray exposure.

Optionally, an apparatus according to the first aspect is provided, wherein the processing unit is further configured to combine the first X-ray image data and the second X-ray image data using an image stitching algorithm.

Thus, an image discontinuity between the first X-ray image data and the second X-ray image data in the image may be hidden from a medical professional.

Optionally, an apparatus according to the first aspect is provided, wherein the processing unit is configured to choose the updated field of view state to provide second X-ray image data which is contiguous to the first X-ray image data in the region of interest.

Accordingly, the updated field of view state provides an updated field of view which is as small as possible, because it does not overlap with the field of view of the first X-ray image data. Thus, exposure of the patient to unnecessary X-ray radiation may be further reduced.

Optionally, the apparatus according to the first aspect is provided, wherein the processing unit is configured to choose the updated field of view state to provide second X-ray image data which overlaps the first X-ray image data over at least a portion of the region of interest.

Accordingly, the second X-ray image data contains image information which, at least to an extent, is already present in the first X-ray image data. Thus, it is possible to combine the first X-ray image data and the second X-ray image data at a region of the image which is less relevant for forming a clinical diagnosis. For example, the overlap point could track down the spine of the patient, an area of the field of view which, in a specific patient imaging case, might not have relevance to a diagnosis of a disease mainly at the edges of the lobes of the lung, for example.

Optionally, the apparatus according the first aspect is provided, wherein the processing unit is further configured to identify an image combination region in the first X-ray image data using the anatomical model and/or the probabilistic anatomical atlas, to generate the updated field of view state based additionally on the image combination path, and wherein the first X-ray image data and the second X-ray image data are combined along the image combination region.

Accordingly, anatomical information provided a priori is used to define the updated field of view state, leading to a more accurate image combination region being defined.

Optionally, an apparatus according to the first aspect is provided with a processing unit which is further configured to add an artificial combination region marker to the output image, based on the initial and/or updated field of view state, wherein the combination region marker illustrates to a user possible regions of distortion in the output image.

Accordingly, an end user may be warned that regions of the composite output image are not suitable for forming a medical diagnosis.

Optionally, according to an apparatus of the first aspect, the processing unit is further configured to receive 3D optical image data of the object from a 3D camera, and wherein the initial and/or the updated field of view states are additionally based on the location of the object in the 3D optical image data.

Accordingly, initial or updated fields of view may be defined using the position of a patient in the field of view as captured by, for example, a camera. This enables the initial field of view to be set accurately, as well as the updated field of view, further reducing unnecessary X-ray exposure of the patient.

Optionally, the apparatus of the first aspect is provided, wherein the processing unit is further configured to receive a repeat exposure command from an input device, and wherein the processor is configured not to obtain the second X-ray image data until the repeat exposure command has been received from the input device.

Accordingly, the apparatus can be configured to wait for an operator command before activating an X-ray source which performs the second exposure of the patient, thus enhancing the safety of the apparatus.

Optionally, an apparatus is provided according to the first aspect, wherein the X-ray imager comprises an adjustable collimator, the initial field of view state comprises a first adjustable collimator setting, and wherein the processing unit is configured to generate the updated field of view state by using the processing unit to generate a second adjustable collimator position setting, and the processing unit is further configured to adjust the field of view of the X-ray imager by transmitting the second adjustable collimator position setting to the adjustable collimator of the X-ray imager.

Accordingly, X-ray collimator settings may be used to vary the field of view state.

According to a second aspect, an X-ray imaging system is provided.

The X-ray imaging system comprises:an X-ray source having an adjustable field of view towards a target location;an apparatus for obtaining an X-ray image having a composite field of view as claimed in the first aspect, or any of its optional embodiments, andan X-ray detector arranged behind the target location to receive X-rays emitted from the X-ray source.

The X-ray imaging system is configured to provide a first X-ray image data to the apparatus, and the apparatus is configured to provide the updated field of view state to the X-ray source, to enable the field of view of the target location to be adjusted, and wherein the X-ray imaging system is configured to provide second X-ray image information to the apparatus for generating an X-ray image, which is configured to provide an output image of the region of interest having a composite field of view. Accordingly, the field of view of an X-ray imaging system may be automatically adjusted to capture elements of a region of interest of an imaged patient which were emitted from the first X-ray image.

According to a third aspect, a method for obtaining an X-ray image having a composite field of view is provided. The method comprises the steps of:a) obtaining first X-ray image data of a portion of a region of interest of an object using an X-ray imager, wherein the X-ray image data is obtained using an X-ray imager having an adjustable field of view set to an initial field of view state;b) comparing the X-ray image data to an anatomical model;c) defining a boundary error region contiguous to the first X-ray image data based on the comparison of the first X-ray image data to the anatomical model;d) generating an updated field of view state based on the location of the boundary error region in the region of interest;e) transmitting the updated field of view state to an X-ray imager;f) obtaining second X-ray image data of the region of interest of the object using the X-ray imager when set to the transmitted field of view state;g) combining the first X-ray image data and the second X-ray image data to obtain an output image of the region of interest having a composite field of view.

Accordingly, a method is provided for generating an X-ray image which contains all of the relevant elements in a region of interest of a patient, with a lower amount of X-ray radiation exposure produced than would be the case if the field of view state of the second X-ray is set so as to encompass all relevant elements which were already encompassed within the first X-ray.

According to a fourth aspect, a computer program element is provided for controlling an apparatus and/or an X-ray system as described in the first or second aspects, which, when the computer program element is executed by the processor and/or system, is adapted to perform the method of the third aspect.

According to a fifth aspect, a computer-readable medium having stored the computer program element of the fourth aspect is provided.

In the following specification, the term “X-ray image data” refers to a data structure containing an array of pixels, wherein each pixel represents the intensity of a received X-ray at a specific pixel following the traversal of that X-ray through a region of interest of a patient. When assembled into a two-dimensional image, the intensity values provide an additive image representing the integral of the X-ray absorption at each pixel location.

In the following specification, the term “X-ray source” refers to an X-ray source containing, for example, a rotating anode X-ray tube. This emits X-ray radiation towards a region of interest of a patient to be imaged. The X-ray radiation traverses the patient at the region of interest, and is received by an X-ray detector, which may also be considered to be part of an X-ray imaging system. The X-ray imager may comprise automatically settable field of view parameters, such as, for example, an adjustable collimator arrangement, adjustable pan or tilt servomotors, adjustable height or x-y coordinate setting. In addition, the X-ray detector may be translated vertically or horizontally.

In the following specification, the term “field of view” refers to a portion of the region of interest that an X-ray imager may capture during a typical exposure. The field of view is generically defined by the distance of an X-ray imager from the X-ray detector and/or patient, and the size of the X-ray detector's aperture. The field of view may be translated across the region of interest by moving the X-ray imager in an x-z plane. The field of view may also be changed by panning or tilting the X-ray imager. The field of view may be cropped or enlarged by adjusting a collimator shutter, or shutters, of an X-ray source. Therefore, it will be appreciated that there are many ways to adjust the field of view of an X-ray imager.

In the following specification, the term “anatomical model” refers to a data structure, typically stored and executed on a processing means such as a computer. The anatomical model contains information defining the location and shape of common anatomical features of patients. A typical anatomical model defines a section of a generic patient body. The anatomical model contains a representation of structures such as lungs, rib bones, a spine, for example, and the likelihood that a certain anatomical element is present in a certain position. The anatomical model may be designed to allow anatomical elements to be identified from incomplete portions of an image of an organ.

The term “boundary error region” defines an unanatomical region in the X-ray image data. It will be appreciated that in this case of an incorrect collimation of the field of view, the boundary error region will appear to be cropped. For example, the extreme left or extreme right hand portions of a lung lobe may be missing from the X-ray image data. However, in this case of a field of view which is incorrectly set owing to a poor pan or tilt setting, a boundary error region may be defined by an anatomical element which is present, but warped, for example, into a “keystone shape”. In other words, a boundary error region of the X-ray image data defines an area of the image which is not a faithful, or accurate reproduction of the anatomy of the patient.

Thus, it is a basic idea of the present specification to provide an automated method for robustly checking an initial X-ray image for problems with the field of view, automatically resetting the field of view to enable a second acquisition of anatomical regions not exposed within the initial exposure, and thereby to complete the full field of view using an image combination method. In this way, erroneous initial exposures may be utilized to complete a second exposure which has a smaller field of view, enabling a reduction in radiation exposure of a patient, compared to the radiation exposure that would be needed to undertake two complete images.

Although this application discusses the concept in terms of lung imaging based on the posterior-anterior view, it will be appreciated that the techniques discussed herein have wide applicability in radiography, wherever an initial X-ray image has missing boundary elements.

