X-ray systems and methods

Abstract

An x-ray system comprising first and second x-ray sources; and first and second x-ray detectors having first and second detector surfaces configured to detect x-rays. X-rays emitted by the first and second x-ray sources are detected by the second and first x-ray detectors respectively. The first x-ray source and the second x-ray source are configured to illuminate with x-rays a target volume between the first x-ray source and the second x-ray source for exposing of an object within the target volume to x-rays. X-rays emitted by the first x-ray source pass through the first detector surface before reaching the target volume; and x-rays emitted by the second x-ray source pass through the second detector surface of the second x-ray detector before reaching the target volume.

Description

[0001] X-RAY SYSTEMS AND METHODS

[0002] The present disclosure relates to x-ray systems and x-ray methods such as for obtaining x-ray measurements, for example for medical x-ray imaging, or for generally deploying x-rays.

[0003] X-ray systems have wide application in medical diagnostics and image guidance, industrial inspection, quality control and metrology, and security. X-ray measurements, such as X-ray imaging, are based on the fact that different materials have different X-ray absorption coefficients.

[0004] Conventional X-ray imaging has been known since the 19thCentury and produces a single two-dimensional (2D) projection of a three-dimensional (3D) object onto an X-ray detector plate. Computerized Axial Tomography (CT) is a more advanced imaging technique that generates a large number of cross-sectional images of an object by collecting a series of 2D images of the same object viewed from different angles. From these multiple 2D images, a 3D image of the object can be reconstructed. This can be used to reveal the internal structure of the object.

[0005] In conventional CT scanners, such as those commonly used for medical imaging, a single X-ray source (such as an X- ray tube) and an opposing x-ray detector array rotate around an object (such as a patient) positioned in the bore of a gantry supporting the x-ray source and detector. Hundreds of 2D projections are taken such that a 3D volume can be reconstructed.

[0006] Although these devices are effective at reconstructing 3D structure, conventional x-ray scanners are large machines that are expensive to manufacture and maintain. They also produce high doses of radiation that pose a risk to operators and patients. Spatial resolution is limited due to the detector construction, and the need to move parts of the detector causes image reconstruction artefacts and slow acquisition times. The latter is particularly a problem for CT scanners used in industrial inspection, where rapid throughput is desired. In addition, the object or person to be imaged needs to be brought to the imaging device, which may be inconvenient.

[0007] Alternatively, a CT scanner may have a fixed ring of x-ray detectors and rotate the x ray source around the gantry to capture the plural 2D images. This is used for some devices such as breast tomography systems. Although these systems have some advantages over the rotating source / detector pair arrangement, the moving parts still cause image artefacts, and the source to detector distance needs to be relatively large to achieve the multiple views required for 3D image reconstruction. High doses of radiation are produced with uneven x ray coverage of the object. Typically, a heavy thermionic radiation source is used.

[0008] US7634045B2 describes a further alternative arrangement for acquiring CT images in which an electron beam generator generates an electron beam that is electromagnetically directed to a series of focus points on an anode ring positioned around the patient from which x-rays can be generated. The x rays are directed to detectors positioned concentrically around the system axis. This avoids the need for moving parts, which reduces some image artefacts. However, the source to detector distance still needs to be large to achieve the multiple views required for 3D image reconstruction, and the x ray coverage of tissue is still uneven.

[0009] There is therefore still a need for x-ray systems and methods that address some or all of these drawbacks.

[0010] According to a first aspect, there is provided an x-ray system comprising: a first x-ray source configured to emit x-rays; and a first x-ray detector having a first detector surface configured to detect x-rays, wherein the system is configured such that at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface.

[0011] This arrangement allows for the detector and source to be overlaid on one another, so that a compact, combined detector / source device can be provided with no moving parts. This has significant advantages in portability and flexibility of taking x-ray measurements and images.

[0012] Optionally, the first emission direction is perpendicular to the first detector surface. This provides a clear orientation of the detection area and x-ray emission. Optionally, the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays. Optionally, the first emission direction is towards the target volume. This allows for measurements and images of the object within the target volume to be obtained.

[0013] Optionally, x-rays emitted by the first x-ray source pass through the first detector surface before reaching the target volume. This means that the x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0014] According to a second aspect, there is provided an x-ray system comprising: a first x-ray source configured to emit x- rays; and a first x-ray detector having a first detector surface configured to detect x-rays, wherein: the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays; and x-rays emitted by the first x-ray source pass through the first detector surface before reaching the target volume.

[0015] This arrangement allows for the detector and source to be overlaid on one another, so that a compact, combined detector / source device can be provided with no moving parts. The x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0016] Optionally, the system is configured such that a) signals from the first x-ray detector due to x-rays emitted by the first x- ray source are disregarded, and / or b) the first x-ray detector does not generate signals in response to x-rays emitted by the first x-ray source and passing through the first detector surface. This ensures that the x-ray detector is not affected by x-rays passing through the detector surface from the x-ray source, improving detector performance.

[0017] Optionally, wherein the system comprises a plurality of first x-ray sources. This can improve x-ray illumination of the object to be measured.

[0018] Optionally, the first x-ray sources are selectively controllable. Optionally, each first x-ray source is individually selectively controllable. This allows for different parts of the object to be illuminated at different times, which can be used, for example, to construct CT images.

[0019] Optionally, the system is configured to selectively control the first x-ray sources such that a maximum power consumption of the plurality of first x-ray sources is below a predetermined power threshold during the emission of x-rays by the first x-ray sources. This allows the power requirements of the system to be limited so that it can be operated using readily available power sources or even battery systems. This in turn improves portability and flexibility of use.

[0020] Optionally, the first x-ray source is provided in an emitter layer, and the first detector surface is provided in a detector layer. This provides a defined layered structure to the device, which may be advantageous in improving ease of manufacturing.

[0021] Optionally, the detector layer is adjacent to or adjoins the emitter layer. This provides a well-defined spatial relationship between the detectors and sources and improves compactness.

[0022] Optionally, the system comprises a plurality of first x-ray sources uniformly distributed across the emitter layer. Uniform distribution ensures that the illumination of an object to be measured is more uniform.

[0023] Optionally, the first x-ray source is configured to emit x-rays through the detector layer. This means that the x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0024] Optionally, wherein the emitter layer and the detector layer are flat and / or parallel. This provides a well-defined emission and detection orientation of the system.

[0025] Optionally, the system further comprises a filtering element configured to absorb x-rays emitted by the first x-ray source having an energy below a predetermined threshold. Low-energy x-rays may be emitted by some types of x-ray source. These low-energy x-rays are unsuitable for high-quality measurements, but can still introduce unwanted noise in detected signal. Filtering these therefore improves measurement quality.

[0026] Optionally, the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays; and the system further comprises a shielding element configured to absorb x-rays that have passed through the first detector surface in a direction away from the target volume. This reduces leakage of x-rays from the target volume, thereby reducing the radiation exposure of operators and other nearby people and equipment.

[0027] Optionally, the system comprises a plurality of first x-ray detectors. This can allow for detection from multiple angles and positions, improving imaging resolution and allowing for CT reconstruction of 3D images.

[0028] Optionally, the first detector surfaces of the plurality of first x-ray detectors are co-planar. This provides a uniform distance and arrangement of the detectors so that measurements can easily be combined for analysis.

[0029] Optionally, a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at most 40cm, optionally at most 30 cm, optionally at most 25cm. This contributes to the compactness of the system that allows for high portability and flexibility of use.

[0030] Optionally, a minimum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at least 5cm, optionally at least 10 cm. This ensures a minimum area for good-quality measurements in some applications such as medical imaging.

[0031] Optionally, the system comprises a plurality of first x-ray sources; and a maximum total extent of the first x-ray sources is equal to or less than a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x- ray detectors. This ensures the x-ray sources are within the extent of the detectors so that the system overall remains compact.

[0032] Optionally, the x-ray system further comprises: a second x-ray source configured to emit x-rays; and a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; and x-rays emitted by the second x-ray source are detected by the first x-ray detector. Including a second x-ray source and detector allows for detection of x-rays after they have passed through the target volume, potentially in different directions, allowing for more complete measurements and for imaging applications.

[0033] Optionally, at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction towards the first x-ray source. This means that the x-ray sources illuminate the object from different directions.

[0034] According to a third aspect, there is provided an x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray source configured to emit x-rays; and a first x-ray detector having a first detector surface configured to detect x- rays; a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; x-rays emitted by the second x-ray source are detected by the first x-ray detector; at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction towards the first x-ray source.

[0035] This arrangement of opposed sources and detectors allows for a compact system that can provide high-resolution measurements and CT images with no moving parts.

[0036] Optionally, at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction; and the second emission direction is parallel and opposite to the first emission direction. This provides a well-defined opposing orientation of the first and second x-ray sources.

[0037] According to a fourth aspect, there is provided an x-ray system comprising: a first x-ray source configured to emit x- rays; a second x-ray source configured to emit x-rays; and a first x-ray detector having a first detector surface configured to detect x-rays; a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; x-rays emitted by the second x-ray source are detected by the first x-ray detector; at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction; and at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction parallel and opposite to the first emission direction.

[0038] This provides a well-defined opposing orientation of the first and second x-ray sources. This arrangement also allows for a compact system that can provide high-resolution measurements and CT images with no moving parts.

[0039] Optionally, the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources. This can improve x-ray illumination of the object to be measured.

[0040] Optionally, the system is configured such that the first x-ray detector detects x-rays emitted by two or more second x- ray sources. Optionally, the system is configured such that the second x-ray detector detects x-rays emitted by two or more first x-ray sources. This can allow measurement of an object from different angles and orientations.

[0041] Optionally, the system is configured to selectively control the second x-ray sources to emit x-rays sequentially, such that x-rays emitted by different second x-ray sources are detected at different times by the first x-ray detector. Optionally, the system is configured to selectively control the first x-ray sources to emit x-rays sequentially, such that x-rays emitted by different first x-ray sources are detected at different times by the second x-ray detector. This allows for separation of signals from different sources, which can provide for applications such as CT reconstruction.

[0042] Optionally, the system comprises a plurality of first x-ray detectors; and each first x-ray detector is configured to detect x-rays emitted by a different subset of the second x-ray sources. Optionally, the system comprises a plurality of second x-ray detectors; and each second x-ray detector is configured to detect x-rays emitted by a different subset of the first x-ray sources. This can allow for detection from multiple angles and positions, improving imaging resolution and allowing for CT reconstruction of 3D images.

[0043] Optionally, the first x-ray source and / or the second x-ray source is / are configured to illuminate with x-rays a target volume between the first x-ray source and the second x-ray source for exposing of an object within the target volume to x-rays. This allows for measurements and images of the object within the target volume to be obtained. The provision of the volume between the sources allows for illumination from multiple directions.

[0044] Optionally, the system is configured to obtain x-ray images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object within the target volume, optionally wherein the object comprises mammalian tissue. This allows detailed structure of the object to be determined, for example for medical purposes.

[0045] Optionally, x-rays emitted by the second x-ray source pass through the second detector surface of the second x-ray detector before reaching the target volume. This means that the second x-ray source will not obstruct x-rays arriving at the second detector surface from the target volume, improving detection performance.

[0046] Optionally, a largest linear extent of the target volume is at least 50% of a distance between the first x-ray source and the second x-ray source, optionally at least 70%, optionally at least 80%. Optionally, a smallest linear extent of the target volume is at least 10% of a distance between the first x-ray source and the second x-ray source, optionally at least 20%, optionally at least 40%. Ensuring that the target volume occupies a large proportion of the space between the sources improves compactness relative to the size of the object to be measured.

[0047] Optionally, a smallest linear extent of the target volume is at least 5cm, optionally at least 10 cm. This ensures the target volume is large enough to accommodate common types of objects for measurement.

[0048] Optionally, the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources, and one or both of: a) a largest linear extent of the target volume is at least 25% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 50%, optionally at least 70%, optionally at least 80%; and b) a smallest linear extent of the target volume is at least 10% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 20%, optionally at least 40%. Ensuring that the target volume occupies a large proportion of the space between the sources improves compactness relative to the size of the object to be measured.

[0049] Optionally, the arrangement of the first x ray sources and the second x ray sources is such that, when all of the first x- ray sources and the second x-ray sources are simultaneously activated, at least part of the target volume is illuminated by x-rays emitted by at least two different first x-ray sources or second x-ray sources. This allows measurements from different angles that provide more information about the object, and can allow for CT reconstruction.

[0050] Optionally, the at least two different first x-ray sources or second x-ray sources comprise at least one first x-ray source and at least one second x-ray source. Taking measurements using x-rays travelling in opposing directions is particularly advantageous for improving uniformity of exposure and the measurements taken.

[0051] Optionally, the system comprises a first x-ray detector having a first detector surface configured to detect x-rays, and a second x-ray detector having a second detector surface configured to detect x-rays; and the first detector surface of the first x- ray detector and the second detector surface of the second x-ray detector are flat and parallel to one another. This provides a well-defined opposing orientation of the first and second x-ray detectors.

[0052] Optionally, a distance between the first x-ray source and the second x-ray source is at most 40cm, optionally at most 30cm, optionally at most 22cm. The ensures the system remains compact to improve portability and ease of use.

[0053] Optionally, a distance between the first x-ray source and the second x-ray source is at least 5cm, optionally at least 10cm, optionally at least 15cm. This ensures the spacing is large enough to accommodate common types of objects for measurement.

[0054] Optionally, the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources; the system comprises a plurality of first x-ray detectors and a plurality of second x-ray detectors; the first detector surfaces of the first x-ray detectors and the second detector surfaces of the second x-ray detectors are arranged such that a cross-section through the first detector surfaces and the second detector surfaces forms a regular polygon having an even number of sides; the first x-ray sources and the second x-ray sources are located around the circumference of the regular polygon; each first x-ray detector is configured to detect x-rays emitted by second x-ray sources located on an opposite side of the regular polygon to a side on which the first x-ray detector is located; each second x-ray detector is configured to detect x-rays emitted by first x-ray sources located on an opposite side of the regular polygon to a side on which the second x-ray detector is located. Optionally, the regular polygon has at least four sides, optionally at least six sides. Optionally, the regular polygon has at least eight sides. This allows the object to be imaged from a greater range of angles and orientations, to further improve the detail of measurements and quality of imaging performance.

[0055] Optionally, the system comprises a support body configured to support the first x-ray source and the first x-ray detector; and the support body is configured to fixably engage with a frame for holding an object to be exposed to x-rays, optionally wherein the frame is a stereotactic head frame. This ensures a fixed spatial relationship between the x-ray source, x- ray detector, and the object so that accurate relative positions of the frame and the object can be obtained.

[0056] According to a fifth aspect, there is provided an x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray detector having a second detector surface configured to detect x-rays emitted by the first x-ray source; and a support body configured to support the first x-ray source and the second x-ray detector, wherein: the support body is configured to fixably engage with a frame for taking a measurement of a brain, the frame being a stereotactic head frame; and a distance between the first x-ray source and the second x-ray detector is at most 40cm.

[0057] This provides for an x-ray system that is compact enough to be head-mounted on a stereotactic frame. This has significant advantages for imaging in preparation for brain surgery, which can be made more comfortable for the patient and easier to set up and perform for attending clinicians.

[0058] Optionally, the support body is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the support body is engaged with the frame. This allows for accurate relative positions of the frame and structures identified in x-ray measurements to be obtained.

[0059] Optionally, the support body comprises one or more coupling features configured to engage with corresponding attachment features of the frame. This allows for easy and convenient coupling and decoupling of the x-ray system from the frame. According to a sixth aspect, there is provided a system for preparing a surgical instrument configured to engage with a stereotactic head frame, the system comprising: the x-ray system of the fifth aspect; and a processor configured to determine a setting of the surgical instrument based on a measurement taken using the x-ray system.

[0060] The frame-mounted x-ray system can allow a fixed spatial relationship between the x-ray source, x-ray detector, and the object so that accurate relative positions of the frame and the object can be obtained. In the case of surgical instruments, this can allow for automatic determination of settings such as positions and trajectories of surgical devices that are otherwise complicated and time-consuming to determine manually.

[0061] According to a seventh aspect, there is provided a radiotherapy system comprising: the x-ray system of the third or fourth aspect; a processor configured to: obtain a measurement of a subject using the x-ray system; locate a target structure within the subject based on the measurement; and control the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a first intensity during the obtaining of the measurement; the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

[0062] This allows real-time tracking of the sub-region to which the therapeutic dose of radiation is to be applied, and corresponding adjustment of the location at which the therapeutic dose of radiation is applied. This improves the effectiveness of the treatment and reduces radiation applied to nearby, healthy regions of the body.

[0063] Optionally, the system is portable, optionally human-portable. This allows for improved ease of use of the system and patient comfort.

[0064] Optionally, the first x-ray source and the first x-ray detector are stationary during exposing of an object using the system. This reduces mechanical complexity and improves measurement quality.

[0065] Optionally, the first x-ray source is configured to emit x rays with controllable energies. This allows for adjusting the energy for different applications, such as measuring objects comprising different materials.

[0066] Optionally, the first x-ray source is configured to emit cone beams of x-rays. This is a readily available configuration of x-ray source that allows for coverage of a large area.

[0067] Optionally, the system comprises a collimation element configured to shape beams of x-rays emitted by the first x-ray source. Optionally, the collimation element is configured to shape the beams into rectangular beams, optionally square beams. This allows for greater control over the volume illuminated by x-rays.

[0068] Optionally, the first x ray source comprises a cold cathode field emission electron source, for example carbon nanotube layers, graphene multilayer structures, bulk graphene, or a Spindt-type emitter. These x-ray sources are advantageous for having compact design and low power requirements relative to more traditional x-ray sources such as x-ray tubes.

[0069] Optionally, the first x-ray source comprises transmissive x-ray targets, optionally comprising tungsten, tantalum, or molybdenum. These targets convert high-energy electrons to x-rays within the x-ray source that can be used for measurements.

[0070] Optionally, the first x-ray detector is a digital x-ray detector, for example an organic photodetector (OPD), organic- inorganic hybrid semiconductor, or low-gain avalanche diode (LGAD). These detectors are compact and easily integrated into digital systems.

[0071] Optionally, the x-ray system is an x-ray imaging system. This is a particularly desirable application, for example in medical imaging or industrial monitoring.

[0072] According to an eighth aspect, there is provided a method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object, wherein at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from a first detector surface of a first x-ray detector and such that a line along the first emission direction intersects the first detector surface; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector.

[0073] This arrangement allows for the detector and source to be overlaid on one another, so that a compact, combined detector / source device can be provided with no moving parts. This has significant advantages in portability and flexibility of taking x-ray measurements and images.

[0074] Optionally, at least a portion of x-rays emitted by the first x-ray source pass through the first detector surface of the first x-ray detector before reaching the target volume. This means that the x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0075] According to a ninth aspect, there is provided a method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object, wherein at least a portion of x-rays emitted by the first x-ray source pass through a first detector surface of a first x-ray detector before reaching the target volume; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector.

[0076] This means that the x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0077] Optionally, at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface. This arrangement allows for the detector and source to be overlaid on one another, so that a compact, combined detector / source device can be provided with no moving parts.

[0078] Optionally, the method further comprises: emitting x-rays from a second x-ray source to illuminate the target volume; and detecting x-rays from the second x-ray source at the first detector surface. Including a second x-ray source allows for detection of x-rays after they have passed through the target volume, potentially in different directions, allowing for more complete measurements and for imaging applications.

[0079] Optionally, at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction, the second emission direction being away from the second detector surface and such that a line along the second emission direction intersects the second detector surface.

[0080] Optionally, at least a portion of x-rays emitted by the second x-ray source pass through the second detector surface before reaching the target volume. This means that the x-ray sources will not obstruct x-rays arriving at the detector surface from the target volume, improving detection performance.

[0081] According to a tenth aspect, there is provided a method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object; emitting x-rays from a second x-ray source to illuminate the target volume, wherein at least a portion of x-rays emitted by the second x-ray source propagate towards the first x-ray source; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector; and detecting x-rays from the second x-ray source at a first detector surface of a first x-ray detector. This means that the x-ray sources illuminate the object from different directions.

[0082] According to an eleventh aspect, there is provided a method of obtaining x-ray measurements of an object comprising: emitting x-rays in a first emission direction from a first x-ray source to illuminate a target volume containing the object; emitting in a second emission direction x-rays from a second x-ray source to illuminate the target volume; and detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector, detecting x-rays from the second x-ray source at a first detector surface of a first x-ray detector; wherein the second emission direction is parallel and opposite to the first emission direction. This provides a well-defined opposing orientation of the x-rays from the first and second x-ray sources.

[0083] According to a twelfth aspect, there is provided a method of preparing a device to interact with an object, the method comprising: obtaining a measurement of the object using the x-ray system of any of the first to seventh aspects; and determining a setting of the device based on the measurement. Automatically determining settings of devices can simplify processes, for example in industrial manufacturing, that rely on x-ray measurements for feedback or monitoring.

[0084] According to a thirteenth aspect, there is provided a method of preparing a surgical instrument configured to engage with a stereotactic head frame, the method comprising: engaging a support body of an x-ray system with the stereotactic head frame while the stereotactic head frame is attached to a head of a patient; obtaining a measurement of at least a part of the head of the patient using the x-ray system; and adjusting a setting of the surgical instrument based on the measurement.

[0085] The frame-mounted x-ray system can allow a fixed spatial relationship between the x-ray source, x-ray detector, and the object so that accurate relative positions of the frame and the object can be obtained. In the case of surgical instruments, this can allow for automatic determination of settings such as positions and trajectories of surgical devices that are otherwise complicated and time-consuming to determine manually.

[0086] Optionally, the x-ray system comprises a first x-ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays; the support body of the x-ray system is configured to support the first x-ray source and the first x-ray detector; and the support body of the x-ray system is configured to engage with the stereotactic head frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the stereotactic head frame when the x-ray system is engaged with the frame. This allows for accurate relative positions of the frame and structures identified in x-ray measurements to be obtained.

[0087] Optionally, the first x-ray source and the first x-ray detector are stationary relative to the stereotactic head frame during the taking of the measurement. This reduces artefacts from movement of the sources and detectors, which in turn improves measurement quality.

[0088] Optionally, the setting of the surgical instrument comprises a position of at least part of the surgical instrument relative to the head of the patient when the surgical instrument is engaged with the stereotactic head frame. These settings are commonly determined manually in current procedures, which is time-consuming and inefficient.

[0089] Optionally, obtaining a measurement comprises taking a plurality of images sufficient for two-dimensional and / or three- dimensional tomographic reconstruction of the head of the patient. This allows detailed structure of the head to be determined, for example for planning brain surgery.

[0090] Optionally, adjusting the setting comprises determining a trajectory from an exterior of the head to a target structure within the head based on the tomographic reconstruction of the head. Trajectory planning is a time-consuming aspect of planning brain surgery, which can be improved in efficiency by the additional automation provided by the method.

[0091] Optionally, adjusting the setting comprises determining a location of the target structure within the head using the predetermined positions of the first x-ray source and the first x-ray detector. The predetermined positions relative to the head frame make it possible to determine target locations accurately.

[0092] Optionally, determining the location does not comprise using one or more fiducial markers in the images. Fiducial markers are commonly used in present methods, but are time consuming to arrange and configure. The present method eliminates the need for markers due to the predetermined positions of the source and detector.

[0093] According to a fourteenth aspect, there is provided a method of locating a structure within an object comprising: engaging a support body of an x-ray system with a frame attached to the object, the x-ray system comprising a first x-ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays, and the support body configured to support the first x-ray source and the first x-ray detector; obtaining a measurement of the object using the x- ray system; and determining a location of the structure within the object based on the measurement, wherein: the x-ray system is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the x-ray system is engaged with the frame; and the location of the structure is defined by coordinates relative to the frame. This method allows for accurate relative positions of the frame and structures identified in x-ray measurements to be obtained.

[0094] Optionally, the first x-ray source and the first x-ray detector are stationary relative to the frame during the taking of the measurement. This reduces artefacts from movement of the sources and detectors, which in turn improves measurement quality.

[0095] Optionally, the object is an animal and the structure is an anatomical structure. This is an important application of x- ray systems, for example for medical purposes.

[0096] Optionally, the object is a human head and the frame is a stereotactic head frame. This allows the use of the method for applications such as planning brain surgery.

[0097] Optionally, obtaining a measurement comprises taking a plurality of images sufficient for two-dimensional and / or three- dimensional tomographic reconstruction of the object. This allows detailed structure of the object to be determined.

[0098] Optionally, determining the location comprises using the predetermined positions of the first x-ray source and the first x-ray detector. The predetermined positions relative to the head frame make it possible to determine target locations accurately.

[0099] Optionally, determining the location does not comprise using one or more fiducial markers in the images. Fiducial markers are commonly used in present methods, but are time consuming to arrange and configure. The present method eliminates the need for markers due to the predetermined positions of the source and detector.

[0100] According to a fifteenth aspect, there is provided a method of radiotherapy comprising: obtaining a measurement of a subject using the x-ray system of the third or fourth aspect; locating a target structure within the subject based on the measurement; and controlling the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a first intensity during the obtaining of the measurement; the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

[0101] This allows real-time tracking of the target structure to which the therapeutic dose of radiation is to be applied, and corresponding adjustment of the location at which the therapeutic dose of radiation is applied. This improves the effectiveness of the treatment and reduces radiation applied to nearby, healthy regions of the body.

[0102] Embodiments of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:

[0103] Fig. 1 shows an x-ray system;

[0104] Fig. 2 shows an x-ray system with emitter and detector layers;

[0105] Fig. 3 shows the system of Fig. 1 illuminating a target volume;

[0106] Fig. 4 shows an alternative x-ray system;

[0107] Fig. 5 shows an x-ray system comprising plural x-ray sources and x-ray detectors;

[0108] Fig. 6 shows an example arrangement of x-ray sources and x-ray detectors;

[0109] Fig. 7 shows an alternative example arrangement of x-ray sources and x-ray detectors;

[0110] Fig. 8 shows an x-ray system with first and second x-ray sources and first and second detectors;

[0111] Fig. 9 shows an x-ray system with plural first and second x-ray sources and plural first and second detectors;

[0112] Fig. 10 shows a prior art x-ray system;

[0113] Fig. 11 shows a prior art x-ray system with a larger number of x-ray sources;

[0114] Fig. 12 shows x-ray illumination of an object by an x-ray system of the type shown in Fig. 9;

[0115] Fig. 13 shows x-ray illumination of an object by an x-ray system of the type shown in Fig. 9 having a larger number of x-ray sources than the system of Fig. 12;

[0116] Fig. 14 shows a system in which first and second x-ray sources and detectors are arranged in a square; Fig. 15 shows a system in which first and second x-ray sources and detectors are arranged in a hexagon;

[0117] Fig. 16 shows a system in which first and second x-ray sources and detectors are arranged in an octagon and selective control of the x-ray sources is used to obtain measurements of part of a target object;

[0118] Fig. 17 shows an implementation of the system of Fig. 15 for medical imaging;

[0119] Fig. 18 shows an implementation of the system of Fig. 15 for x-ray fluorescence measurements;

[0120] Fig. 19 shows a system in which the x-ray sources and x-ray detectors are support by a support body;

[0121] Fig. 20 shows a system in which the support body is configured to engage with a stereotactic head frame;

[0122] Fig. 21 shows the system of Fig. 20 engaged with the stereotactic head frame;

[0123] Fig. 22 is a flowchart of a method of obtaining x-ray measurements; and

[0124] Fig. 23 is a flowchart of a method of preparing a device or locating a structure.

[0125] To address various limitations of existing x-ray systems such as those described above, the present disclosure provides an x-ray system 1 such as shown in Fig. 1. The x-ray system 1 may be an x-ray imaging system, for example being configured to capture two-dimensional images.

[0126] The x-ray system 1 may be portable, optionally human-portable. The size and weight of the x-ray system 1 may be such that it can be carried or moved by two humans, optionally only one human, without mechanical assistance. The x-ray system 1 may be configured to be worn or carried by a human. This is optional and the size of the x-ray system 1 in a particular implementation will depend on the requirements of the specific application. For example, an implementation of the x-ray system 1 intended for medical imaging of a brain, such as discussed further below, may be significantly smaller than an implementation intended for industrial inspection of large components.

[0127] The x-ray system 1 comprises a first x-ray source 3 configured to emit x-rays. The first x-ray source 3 may be configured to emit x-rays having a wavelength between 10nm and 10pm. The first x-ray source 3 may be configured to emit x rays with controllable energies or wavelengths. In other words, the energies or wavelengths of the x-rays emitted by the first x- ray source 3 may be controllable. This can allow for spectral x-ray measurements, where measurements at multiple different wavelengths are taken of the object to obtain different information.

[0128] The first x-ray source 3 may be configured to emit x rays with controllable intensity. This can allow the emitted x-ray power to be varied while keeping the wavelength of the x-rays constant. Controllable intensity may be achieved in any suitable manner, for example by reducing a continuous output of the first x-ray source 3, or by varying a duty cycle of the first x-ray source 3.

[0129] The first x ray source 3 may comprise any suitable type of known x-ray source. Most common x-ray sources comprise a cathode configured to emit an electron beam (i.e. an electron source), and an anode onto which the electron beam is directed (the x-ray target). The high-energy electrons impacting the anode cause the emission of x-rays.

[0130] Preferably, the first x-ray source 3 comprises a cold cathode field emission electron source. Field emission electron sources rely on high electric fields applied to a cathode having a high aspect ratio shape that causes enhancement of the electric field at a tip of the cathode. This causes emission of electrons without the need for high cathode temperatures. The cathode of the first x-ray source 3 may not be heated above 100°C, optionally not above 50°C during the emission of x-rays by the first x-ray source 3. This is compared to typical temperatures of above 2500°C for traditional hot cathode x-ray tubes. This type of electron source is advantageous with respect to providing compactness and reduced power requirements of the x-ray system compared to traditional x-ray sources. For example, the first x-ray source 3 may comprise carbon nanotube layers, graphene multilayer structures, bulk graphene, or a Spindt-type emitter.

[0131] The first x-ray source 3 may comprise a transmissive x-ray target. The x-ray target is typically metallic. For example, the x-ray target may comprise tungsten, tantalum, or molybdenum.

[0132] The first x-ray source 3 may be configured to emit cone beams of x-rays. The cone beams may have a cone angle of at most 60 degrees, optionally at most 30 degrees, optionally at most 20 degrees, optionally at most 12 degrees, optionally at most 5 degrees.

[0133] The x-ray system 1 may comprise a collimation element configured to shape beams of x-rays emitted by the first x-ray source 3. The shape used may depend on the intended application and the area or volume to be illuminated with x-rays. For example, a collimation element comprising small circular apertures may be used to obtain cone beams. The collimation element may alternatively be configured to shape the beams into rectangular beams, optionally square beams.

[0134] The x-ray system 1 further comprises a first x-ray detector 5 having a first detector surface 7 configured to detect x- rays. The first x-ray detector 5 may be any suitable detector capable of detecting x-rays. Preferably, the first x-ray detector 5 comprises a digital x-ray detector, for example an organic photodetector (OPD), organic-inorganic hybrid semiconductor, or low- gain avalanche diode (LGAD).

[0135] The first x-ray source 3 and the first x-ray detector 5 may be stationary during exposing of an object to x-rays using the x-ray system 1. This is preferable to avoid mechanical complexity and image artefacts such as discussed above that can be caused by motion of the x-ray source and / or detector in known systems.

[0136] As shown in Fig. 2, the first x-ray source 3 may be provided in an emitter layer 9, and the first detector surface 7 may be provided in a detector layer 11. The emitter layer 9 may comprise other elements of the x-ray system 1 for supporting the function of the first x-ray source 3, such as control electronics, electrical wiring, or heat sinks. Similarly, the detector layer 11 may comprise elements for supporting the function of the first x-ray detector 5.

[0137] The detector layer 11 may be adjacent to or adjoin the emitter layer 9. This provides a well-defined spatial relationship between the first x-ray source 3 and the first x-ray detector 5. This may also simplify manufacturing concerns, for example by allowing the detector layer 11 and emitter layer 9 to be manufactured separately and assembled together. The emitter layer 9 and the detector layer 11 may be flat and / or parallel to one another.

[0138] The x-ray system 1 may further comprise a filtering element 13 such as that shown in Fig. 2. The filtering element 13 is configured to absorb x-rays (or other electromagnetic radiation) emitted by the first x-ray source 3 having an energy below a predetermined threshold. This can help to reduce noise at a detector from low-energy radiation that is insufficient to provide high-quality measurements or images. The filtering element 13 may also be configured to absorb x-rays (or other electromagnetic radiation) having an energy above a predetermined threshold. This helps to limit the x-rays used for measurements to a known range. The filtering element 13 may be provided as part of the detector layer 11 , or the detector layer 11 itself may be configured to provide the filtering effect. In the latter case, no separate filtering element 13 may be provided within the structure of the detector layer 11. The material of the detector layer 11 itself, such as the material of the first detector surface 7, will absorb some of the x-rays emitted by the first x-ray source 3. This provides a filtering effect without requiring a separate filtering element 13.

[0139] The x-ray system 1 is configured such that at least a portion of x-rays emitted by the first x-ray source 3 propagate in a first emission direction 15. The first emission direction 15 may be away from the first detector surface 7. The first emission direction 15 may be perpendicular to the first detector surface 7, as shown in Fig. 1 , although this is not essential.

[0140] As shown in Fig. 3, the x-ray system 1 may further comprise a shielding element 19 configured to absorb x-rays that have passed through the first detector surface 7 in a direction away from the target volume 17. The shielding element 19 may be behind both the first x-ray source 3 and the first x-ray detector 5 along the first emission direction. This helps to prevent x-rays from passing entirely through the x-ray system 1 , thereby reducing the risk and radiation dose to operators of the x-ray system 1.

[0141] Where a collimation element is used, the collimation element may already be sufficient to block x-rays that have passed through the first detector surface 7 in a direction away from the target volume 17. By design, the collimation element absorbs x rays emitted from the first x ray source 3 except for x-rays that are emitted along the desired trajectories. Therefore, the collimation element will also absorb x rays travelling in the opposite direction towards the first x-ray source 3 that do not align exactly with the desired trajectories. Even x-rays that pass through the collimation element towards the first x-ray source 3 will likely impact part of the first x-ray source 3 itself, such as the anode, and be absorbed. This will provide shielding in both directions and limit external exposure for operators. This may reduce the size and weight of the separate shielding element 19 or eliminate the need for the shielding element 19 entirely.

[0142] As shown in Fig. 3, the first x-ray source 3 may be configured to illuminate with x-rays a target volume 17 for exposing of an object within the target volume 17 to x-rays. The first emission direction 15 may be towards the target volume 17. The x- rays that illuminate the target volume 17 will interact with the object within the target volume 17. For example, a proportion of the x-rays may be absorbed by the object. The interaction of the x-rays with the object will provide information about the object’s properties when the x-rays leaving the target volume 17 after interaction with the object are detected.

[0143] The x-rays leaving the target volume 17 after interaction with the object may be detected by the first x-ray detector 5 in some applications. For example, x-rays may be reflected from and / or scattered by the object, or x-rays may be detected by the first x-ray detector 5 that are generated from other interactions of the x-rays emitted by the first x-ray source 3 with the object, such as fluorescence. Alternatively or additionally, the x-rays may be detected by another detector other than the first x-ray detector 5.

[0144] However, it is sometimes desirable to avoid detecting x-rays emitted by the first x-ray source 3 using the first x-ray detector 5. Optionally, the x-ray system 1 is a non-backscatter system that does not rely on backscattered x-rays, which may be reflected from or scattered by the object in the target volume 17. In this case, the x-ray system 1 may disregard, ignore, or not measure backscattered x-rays. For example, x-rays emitted by the first x-ray source 3 may be ignored, disregarded, or not measured by the first x-ray detector 5. Instead, the x-ray system 1 may only measure x-rays emitted from the first x-ray source 3 that are transmitted through the object in the target volume 17 and / or are scattered by less than 90 degrees, optionally less than 45 degrees. X-rays emitted from the first x-ray source 3 may be measured by an x-ray detector other than the first x-ray detector 5, for example the second x-ray detector 25 discussed further below.

[0145] The x-ray system 1 may be configured such that such that a line along the first emission direction 15 intersects the first detector surface 7. The line is a hypothetical line along the first emission direction 15 and can be extended to any length. The line should intersect the first detector surface 7 itself, i.e. a part of the x-ray system 1 configured to detect x-rays, and not merely intersect a plane parallel to the first detector surface 7.

[0146] This configuration can be achieved in two main ways. The first is illustrated in Fig. 1 , where the first x-ray source 3 is situated behind the first x-ray detector 5 along the first emission direction 15, such that at least a portion of the x-rays emitted by the first x-ray source 3 pass through the first detector surface 7. Where the first x-ray source 3 illuminates a target volume 17, at least a portion of the x-rays emitted by the first x-ray source 3 therefore pass through the first detector surface 7 before reaching the target volume 17.

[0147] Where the x-ray system 1 comprises a detector layer 11 , the first x-ray source 3 may be configured to emit x-rays through the detector layer 11. The detector layer 11 may be configured to reduce absorption of x-rays emitted by the first x-ray source 3. For example, the detector layer 11 may be configured such that electronics of the first x-ray detector 5 are located away from regions of the detector layer 11 through which x-rays emitted by the first x-ray source 3 will pass. The electronics of the first x-ray detector 5 may include control electronics for control of the first x-ray detector 5 and / or measurement electronics for detecting signals generated by x-rays passing through the first detector surface 7. The electronics may be located so that x- rays emitted by the first x-ray source 3 do not pass through the electronics before reaching the target volume 17.

[0148] The second alternative configuration is shown in Fig. 4. In this situation, the first x-ray source 3 is situated in front of the first x-ray detector 5 along the first emission direction 15, such that x-rays emitted by the first x-ray source 3 do not pass through the first detector surface 7. This configuration is possible, but usually not preferred as there is a chance that the first x- ray source may affect x-rays arriving at the first x-ray detector 5. In the configuration of Fig. 1 in which at least a portion of the x-rays emitted by the first x-ray source 3 pass through the first detector surface 7, x-rays emitted by the first x-ray source 3 may be detected by the first detector 5 before they have interacted with an object to obtain a measurement. This may be undesirable and produce spurious measurements. To avoid this, x-ray system may be configured such that signals from the first x-ray detector 5 due to x-rays emitted by the first x-ray source 3 are disregarded. Additionally, or alternatively, the first x-ray detector 5 may not generate signals in response to x-rays emitted by the first x-ray source 3 and passing through the first detector surface 7.

[0149] As discussed above, this functionality can also be used to disregard backscattered x-rays. The x-ray system 1 can thus be a transmissive system in that the x rays measured by the x-ray system 1 are those that have passed through the target volume 17 from an x-ray source to an x-ray detector, without being back-scattered, i.e. without being scattered by more than 90 degrees and / or while being scattered by less than 90 degrees.

[0150] The first x-ray detector 5 is mounted in front of the first x-ray source 3 with respect to the first emission direction 15, but the first x-ray detector 5 preferably does not in operation use the first x-ray detector 5 and first x-ray source 3 together, i.e. x-rays emitted by the first x-ray source are not intended for detection by the first x-ray detector 5. Rather, the x-ray system 1 uses the first x-ray detector 5 to detect transmitted x-rays from another x-ray source, such as the second x-ray source 23 discussed below, and uses the first x-ray source 3 to emit x-rays towards another detector, such as the second x-ray detector 25 discussed below.

[0151] Where it is desirable to detect backscattered x-rays, x-rays emitted by the first x-ray source 3 may be disregarded or no signals generated only in a predetermined time period. The predetermined time period may be a period in which the first x- ray source 3 is emitting x-rays and / or a predetermined length of time after the first x-ray source 3 has stopped emitting x-rays. Signals from the first x-ray detector 5 due to x-rays emitted by the first x-ray source 3 may still be regarded or generated if the signals are a result of x-rays emitted by the first x-ray source 3 that have interacted with an object in the target volume before the signals are or would be generated. This allows for measurements to be obtained from x-rays emitted by the first x-ray source 3 and reflected by an object in the target volume, or x-rays generated from other interactions of the x-rays emitted by the first x-ray source 3 with the object, such as fluorescence.

[0152] As shown in Fig. 5, the x-ray system 1 may comprise a plurality of first x-ray sources 3. In Fig. 5, the x-ray system 1 comprises six first x-ray sources 3, but it is not limited thereto. The x-ray system 1 may comprise at least 10 first x-ray sources 3, optionally at least 20 first x-ray sources 3, optionally at least 30 first x-ray sources 3. Where an emitter layer 9 is provided, the plurality of first x-ray sources 3 may be uniformly distributed across the emitter layer 9. The first x-ray sources 3 may be arranged along a line, for example along a single axis. Alternatively, the first x-ray sources 3 may be arranged in a two- dimensional arrangement, such as a grid or array extending along two perpendicular axes. Fig. 6 shows an example arrangement in which the first x-ray sources 3 are arranged in a square grid. Fig. 7 shows an example arrangement in which the first x-ray sources 3 are arranged in a triangular grid.

[0153] Each of the first x-ray sources 3 may be substantially the same in performance. Alternatively, the first x-ray sources 3 may differ in performance and / or characteristics. For example, one or more of the first x-ray sources 3 may be configured to emit x-rays having a first wavelength, and one or more of the first x-ray sources may be configured to emit x-rays having a second wavelength. This could be achieved, for example, by using x-ray sources having targets comprising different materials.

[0154] The first x-ray sources 3 may be selectively controllable. Optionally, each first x-ray source 3 may be individually selectively controllable. For example, different subsets of the first x-ray sources 3 can be caused to emit x-rays at different times. This can be used to allow for measuring x-rays that have passed through different parts of the target volume. Where the first x-ray sources 3 are configured to emit x rays with controllable energies, different subsets of the first x-ray sources 3 may be caused to emit x-rays having different energies.

[0155] The x-ray system 1 may be configured to selectively control the first x-ray sources 3 such that a maximum power consumption of the plurality of first x-ray sources 3 is below a predetermined power threshold during the emission of x-rays by the first x-ray sources 3. This can allow for the x-ray system 1 to operate with limited power requirements.

[0156] As further shown in Fig. 5, the x-ray system 1 may comprise a plurality of first x-ray detectors 5. In Fig. 5, the x-ray system 1 comprises three first x-ray detectors 5, but it is not limited thereto. The x-ray system 1 may comprise at least 5 first x- ray detectors 5, optionally at least 10 x-ray detectors 5, optionally at least 20 first x-ray detectors 5. The first x-ray detectors 5 may be arranged along a line, for example along a single axis. Alternatively, the first x-ray detectors 5 may be arranged in a two- dimensional arrangement, such as a grid or array extending along two perpendicular axes. The first detector surfaces 7 of the plurality of first x-ray detectors 5 may be co-planar. Fig. 6 and Fig. 7 shows arrangements in which the first x-ray detectors 5 are arranged in a square grid.

[0157] A maximum total extent of the first detector surfaces 7 of the first x-ray detectors 5 in the plane of the first x-ray detectors 5 may be at most 40cm, optionally at most 30 cm, optionally at most 25cm. A minimum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors may be at least 5cm, optionally at least 10 cm. These sizes are suitable for some particularly advantageous medical imaging applications such as discussed further below. However, in general, the extent of the first x-ray detectors 5 will be determined by the particular application for which it is intended and may be larger or smaller than these exemplary values.

[0158] Where the x-ray system 1 comprises both a plurality of first x-ray sources 3 and a plurality of first x-ray detectors 5, a maximum total extent of the first x-ray sources 3 may be equal to or less than a maximum total extent of the first detector surfaces 7 of the first x-ray detectors 5 in the plane of the first x-ray detectors 5. This limits the area covered by emitted x-rays, thereby reducing x-ray dosage outside of the intended detecting area.

[0159] The x-ray system 1 as described so far is suitable for measurements in which x-rays emitted by the first x-ray source 3 are reflected by an object in the target volume and returned to the first x-ray detector 5. Other suitable measurements include fluorescence measurements in which x-rays are generated from interactions of the x-rays emitted by the first x-ray source 3 with the object and returned to be detected by the first x-ray detector 5. However, in other types of measurements, including many medical imaging applications, it is desirable to also be able to perform x-ray transmission measurements of objects.

[0160] An x-ray system 1 for providing this type of capability is shown in Fig. 8. The x-ray system 1 further comprises a second x-ray source 23 configured to emit x-rays, and a second x-ray detector 25 having a second detector surface 27 configured to detect x-rays.

[0161] The second x-ray source 23 and the second x-ray detector 25 may be substantially the same as the first x-ray source 3 and the first x-ray detector 5, or may be of a different type from the first x-ray source 3 and first-x-ray detector 5. Any of the features described above for the first x-ray source 3 and the first x-ray detector may be applied as appropriate to the second x- ray source 23 and the second x-ray detector 25 respectively. For example, the second x-ray source 23 may comprise any of the types of cathode described above, the second x-ray source 23 may be configured to emit x rays with controllable energies, and so forth.

[0162] The x-ray system 1 is configured such that x-rays emitted by the first x-ray source 3 are detected by the second x-ray detector 25, and x-rays emitted by the second x-ray source 23 are detected by the first x-ray detector 5.

[0163] As discussed above, the x-ray system 1 may be a non-backscatter system that does not rely on backscattered x-rays, which may be reflected from or scattered by the object in the target volume 17. In this case, x-rays emitted by the second x-ray source 23 may be ignored, disregarded, or not measured by the second x-ray detector 25. Instead, the x-ray system 1 may only measure x-rays emitted from the second x-ray source 23 that are detected by the first x-ray detector 5 after being transmitted through the object in the target volume 17 and / or being scattered by less than 90 degrees, optionally less than 45 degrees.

[0164] This arrangement of two x-ray sources and two x-ray detectors allows for very flexible measurement configurations for a wide range of objects. It allows for images to be taken by transmission. It also allows for measurements of various types to be taken for different angles and orientations of the object without requiring either the x-ray source or the x-ray detector to move during the measurements

[0165] The x-ray system of Fig. 8 can be used to carry out a method of obtaining x-ray measurements of an object such as that shown in Fig. 20. The method comprises emitting S1 x-rays from the first x-ray source 3 to illuminate a target volume 17 containing the object. As described above, at least a portion of x-rays emitted by the first x-ray source 3 may propagate in the first emission direction 15 away from the first detector surface 7 of the first x-ray detector 5 and such that a line along the first emission direction 15 intersects the first detector surface 7. Alternatively or additionally, at least a portion of x-rays emitted by the first x-ray source 3 may pass through the first detector surface 7 of the first x-ray detector 5 before reaching the target volume 17.

[0166] The method further comprises detecting S3 x-rays from the first x-ray source 3 at the second detector surface 27 of the second x-ray detector 25.

[0167] The method may further comprise emitting S5 x-rays from the second x-ray source 23 to illuminate the target volume 17, and detecting S7 x-rays from the second x-ray source 23 at the first detector surface 7.

[0168] Although the steps of the method are shown in a particular order in Fig. 20, this ordering is not essential. The steps may be carried out in any order, and the steps may even be carried out simultaneously. The only constraints on the ordering of steps is that the step of detecting S3 x-rays from the first x-ray source 3 cannot precede the step of emitting S1 x-rays from the first x-ray source 3, and the step of detecting S7 x-rays from the second x-ray source 23 cannot precede the step of emitting S5 x-rays from the second x-ray source 23. In practice it may be preferable that x-rays are emitted at different times from the first x- ray source 3 and the second x-ray source 23 so that the detection of x-rays from each source can be easily separated by a temporal difference. However, this may not be necessary, for example if the x-rays emitted by the first x-ray source 3 and the second x-ray source 23 have different wavelengths.

[0169] At least a portion of x-rays emitted by the second x-ray source 23 propagate in a second emission direction 35. The second emission direction 35 may be towards the first x-ray source 3. The second emission direction 35 may be away from the second detector surface 27. The second emission direction 35 may be parallel and opposite to the first emission direction 15.

[0170] Analogously to the first emission direction 15, the second emission direction 35 may be such that a line along the second emission direction 35 intersects the second detector surface 27. As shown in Fig. 8, at least a portion of x-rays emitted by the second x-ray source 23 may pass through the second detector surface 27 before reaching the target volume 17. The second x-ray source 3 in this case is situated behind the first x-ray detector 5 along the second emission direction 35. Alternatively, the second x-ray source 23 and the second x-ray detector 25 may be configured analogously to the configuration of the first x-ray source 3 and the first x-ray detector 5 shown in Fig. 4, such that the second x-ray source 23 is situated in front of the second x-ray detector 25 along the second emission direction 35

[0171] The first detector surface 7 of the first x-ray detector 5 and the second detector surface 27 of the second x-ray detector 25 may be flat and parallel to one another. However, this is not essential, and the first detector surface 7 and the second detector surface 27 may be inclined to one another as long as it is still the case that x-rays emitted by the first x-ray source 3 are detected by the second x-ray detector 25, and x-rays emitted by the second x-ray source 23 are detected by the first x-ray detector 5.

[0172] A distance between the first x-ray source 3 and the second x-ray source 23 may be at most 40cm, optionally at most 30cm, optionally at most 22cm. These dimensions are particularly suited for brain scanning and provide a compact and easily portable x-ray system 1. A distance between the first x-ray source 3 and the second x-ray source 23 may be at least 5cm, optionally at least 10cm, optionally at least 15cm. This ensures that there is sufficient space to place an object to be measured between the first x-ray source 3 and the second x-ray source 23.

[0173] As shown in Fig. 9, the x-ray system 1 may comprise a plurality of first x-ray sources 3 and a plurality of second x-ray sources 23. In Fig. 9, the x-ray system 1 comprises six second x-ray sources 23, but it is not limited thereto. The x-ray system 1 may comprise at least 10 second x-ray sources 23, optionally at least 20 second x-ray sources 23, optionally at least 30 second x-ray sources 23. The second x-ray sources 23 may be arranged with respect to each other and the second x-ray detector 25 in any suitable manner, such as those described in relation to the first x-ray source 3 above.

[0174] The x-ray system 1 may be configured such that the first x-ray detector 5 detects x-rays emitted by two or more second x-ray sources 23. This can allow for different measurements of the object by x-rays that have arrived at the first x-ray detector 5 along different paths.

[0175] The x-ray system 1 may be configured to selectively control the second x-ray sources 23 to emit x-rays sequentially, such that x-rays emitted by different second x-ray sources 23 are detected at different times by the first x-ray detector 5. This allows for easy temporal separation of x-rays that have taken different paths to reach the first x-ray detector 5 and therefore will encode different information about the object. Alternatively or additionally, the x-ray system 1 may be configured to control the second x-ray sources 23 to emit x-rays of different wavelengths. Where the second x-ray sources 23 have controllable energies, this may comprise controlling each second x-ray source 23 to emit x-rays of plural different wavelengths. Alternatively, whether or not the second x-ray sources 23 have controllable energies, this may comprise controlling different ones of the second x-ray sources 23 to emit x-rays of different wavelengths. This can be used for separation of x-rays from different second x-ray sources 23, or to perform spectral x-ray measurements by taking measurements at multiple different wavelengths.

[0176] As shown in Fig. 9, the x-ray system 1 may comprise a plurality of first x-ray detectors 5. Each first x-ray detector 5 may be configured to detect x-rays emitted by a different subset of the second x-ray sources 23. This is demonstrated in Fig. 9, where the leftmost first x-ray detector 5 detects x-rays from the leftmost two second x-ray sources 23, while the rightmost first x- ray detector 5 detects x-rays from the rightmost two second x-ray sources 23.

[0177] Similarly, the x-ray system 1 may be configured such that the second x-ray detector 25 detects x-rays emitted by two or more first x-ray sources 3. The x-ray system 1 may be configured to selectively control the first x-ray sources 3 to emit x-rays sequentially, such that x-rays emitted by different first x-ray sources 3 are detected at different times by the second x-ray detector 25. As for the first x-ray sources 3, the system may also be configured to control the first x-ray sources 3 to emit x-rays of different wavelengths, as described above for the first x-ay sources 3.

[0178] As in Fig. 9, the x-ray system 1 may comprise a plurality of second x-ray detectors 25. Each second x-ray detector 25 may be configured to detect x-rays emitted by a different subset of the first x-ray sources 3.

[0179] The first x-ray source 3 and the second x-ray source 23 are configured to illuminate the target volume 17 with x-rays as described above. This allows for exposing of an object within the target volume to x-rays such that measurements of the object can be made. The target volume 17 is between the first x-ray source 3 and the second x-ray source 23.

[0180] The x-ray system 1 is configured to obtain x-ray images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object within the target volume 17. The object may comprise, for example, an industrial component for quality inspection, or mammalian tissue such as a human brain. Obtaining x-ray images sufficient for tomographic reconstruction may comprise obtaining a plurality of images of the object, where each image is each taken from a different angle. For example, at least 5 images may be taken, optionally at least 10 images, optionally at least 20 images, optionally at least 50 images.

[0181] The target volume 17 ideally comprises most or all of the space between the first x-ray sources 3 and the second x-ray sources 23, and / or between the first detector surface 7 and the second detector surface 27, depending on the configuration of the system. This maximises the size of object that can be measured relative to the size of the x-ray system 1 , improving compactness. A cross-sectional area of the target volume 17 may comprise at least 50%, optionally at least 70%, optionally at least 80% of the cross-sectional area of a volume between the first x-ray sources 3 and the second x-ray sources 23, and / or between the first detector surface 7 and the second detector surface 27. A smallest linear extent of the target volume is at least 5cm, optionally at least 10 cm.

[0182] A largest linear extent of the target volume 17 may be at least 50% of a distance between the first x-ray source 3 and the second x-ray source 23, optionally at least 70%, optionally at least 80%. A smallest linear extent of the target volume 17 may be at least 10% of a distance between the first x-ray source 3 and the second x-ray source 23, optionally at least 20%, optionally at least 40%. Where the x-ray system 1 comprises a plurality of first x-ray sources 3 and a plurality of second x-ray sources 23, a largest linear extent of the target volume 17 may be at least 25% of a largest distance between any first x-ray source 3 and any second x-ray source 23, optionally at least 50%, optionally at least 70%, optionally at least 80%. A smallest linear extent of the target volume 17 may be at least 10% of a largest distance between any first x-ray source 3 and any second x-ray source 23, optionally at least 20%, optionally at least 40%.

[0183] These constraints may also be defined based on the distances between the first detector surface(s) 7 and the second detector surface(s) 27. A largest linear extent of the target volume 17 may be at least 50% of a distance between the first detector surface 7 and the second detector surface 27, optionally at least 70%, optionally at least 80%. A smallest linear extent of the target volume 17 may be at least 10% of a distance between the first detector surface 7 and the second detector surface 27, optionally at least 20%, optionally at least 40%. Where the x-ray system 1 comprises a plurality of first detectors 5 and a plurality of second detectors 25, a largest linear extent of the target volume 17 may be at least 25% of a largest distance between any first detector surface 7 and any second detector surface 27, optionally at least 50%, optionally at least 70%, optionally at least 80%. A smallest linear extent of the target volume 17 may be at least 10% of a largest distance between any first detector surface 7 and any second detector surface 27, optionally at least 20%, optionally at least 40%.

[0184] The arrangement of the first x ray sources 3 and the second x ray sources 23 may be such that, when all of the first x- ray sources 3 and the second x-ray sources 23 are simultaneously activated, at least part of the target volume 17 is illuminated by x-rays emitted by at least two different first x-ray sources 3 or second x-ray sources 23, optionally at least four, optionally at least six. The at least two different first x-ray sources 3 or second x-ray sources 23 may comprise at least one first x-ray source 3 and at least one second x-ray source 23. This ensures different angles of measurement can be taken. The arrangement of the first x ray sources 3 and the second x-ray sources 23 may be such that, when all of the first x-ray sources 3 and the second x-ray sources 23 are simultaneously activated, at least part of the target volume 17 is illuminated by x-rays emitted by the same number of first x-ray sources 3 or second x-ray sources 23. The at least part of the target volume 17 may comprise at least 50% of the target volume, optionally at least 70% of the target volume, optionally at least 80% of the target volume.

[0185] The x-ray imaging system 1 including first x-ray sources 3 and second x-ray sources 23 has advantages compared to prior art systems in allowing for adequate and even exposure of an object with a compact setup and avoiding excessive radiation exposure. The latter point is particular advantageous in medical imaging applications.

[0186] Fig. 10 illustrates a prior art x-ray system 101 comprising a plurality of x-ray sources 103 emitting cone beams with a typical 12-degree cone angle. The x-rays pass through the object 141 to form an image on the detector 105. As show, the coverage of the left-hand side of the object 141 is poor, and no x-rays pass through a significant portion of the object 141. This will prevent adequate imaging and reconstruction of this part of the object 141.

[0187] Fig. 11 illustrates a solution to this problem in which a larger number of more closely-spaced x-ray sources 103 are used. However, this leads to highly variable x-ray dosing of the object 141 , with the right-hand side of the object 141 receiving a significantly higher dose of x-rays than is necessary to achieve adequate imaging.

[0188] As demonstrated in Fig. 12, the present x-ray system 1 solves this problem by allowing the object 41 to be illuminated from opposing directions. In Fig. 12, the object 41 is illuminated evenly with x-rays sufficient for imaging, without unnecessarily high dosages being applied to any part of the object 41. In Fig. 13, the number of first x-ray sources 3 and second x-ray sources 23 is increased so that each part of the object is illuminated by at least two different x-ray sources, such that tomographic reconstruction is possible. The arrangement of the first x ray sources 3 and the second x-ray sources 23 may be such that, when all of the first x- ray sources 3 and the second x-ray sources 23 are simultaneously activated, at least part of the target volume 17 is illuminated by a substantially uniform flux density of x-rays. The at least part of the target volume 17 may comprise at least 50% of the target volume, optionally at least 70% of the target volume, optionally at least 80% of the target volume.

[0189] The arrangement of the first x ray sources 3 and the second x-ray sources 23 may be such that, when all of the first x- ray sources 3 and the second x-ray sources 23 are simultaneously activated, a flux density of x-rays in the target volume 17 is symmetrical along a line between the first detector surface 7 and the second detector surface 27. The line may be perpendicular to the first detector surface 7 and / or the second detector surface 27.

[0190] In the example of Fig. 9, a plurality of first x-ray sources 3 and a plurality of first detectors 5 are paired with a plurality of second x-ray sources 23 and a plurality of second x-ray detectors 25 in an opposing configuration. It is also possible to provide an x-ray system 1 in which further opposing pairs of first and second x-ray sources and x-ray detectors are provided.

[0191] Such an example is shown in Fig. 14. The first detector surfaces 7 of the first x-ray detectors 5 and the second detector surfaces 27 of the second x-ray detectors 25 are arranged such that a cross-section through the first detector surfaces 7 and the second detector surfaces 27 forms a regular polygon having an even number of sides. The first x-ray sources 3 and the second x-ray sources 23 are located around the circumference of the regular polygon.

[0192] Each first x-ray detector 5 is configured to detect x-rays emitted by second x-ray sources 23 located on an opposite side of the regular polygon to a side on which the first x-ray detector 5 is located, and each second x-ray detector 25 is configured to detect x-rays emitted by first x-ray sources 3 located on an opposite side of the regular polygon to a side on which the second x-ray detector 25 is located.

[0193] This arrangement allows for much greater detail in measurement and imaging of an object without significantly increasing the overall size of the x-ray system 1. In this system, the circumference of the target volume 17 may be defined by the first and second detector surfaces.

[0194] In Fig. 14, the regular polygon has four sides to form a square cross-section. However, larger number of pairs of opposing first and second x-ray sources and x-ray detectors are possible. The regular polygon may have at least four sides, optionally at least six sides, as shown in Fig. 15. The regular polygon may have at least eight sides, as shown in Fig. 16.

[0195] In the examples of Fig. 14 to Fig. 16, the first x-ray sources 3 and first x-ray detectors 5 are shown together on one half of the polygon, and the second x-ray sources 23 and the second x-ray detectors 25 are together on the half side. However, this is not essential, and the first and second x-ray sources and x-ray detectors may be arranged in any suitable manner, for example alternating around the sides of the polygon. The designations of first and second are merely conceptual labels to indicate pairs of sources and detectors that are related by the requirement mentioned above that x-rays emitted by the first x-ray source 3 are detected by the second x-ray detector 25, and x-rays emitted by the second x-ray source 23 are detected by the first x-ray detector 5.

[0196] Fig. 16 also illustrates how selective activation of the first x-ray sources 3 and second x-ray sources 23 can be used to image only a sub-region 43 of the object 41 within the target volume 17.

[0197] Selective activation of the first x-ray sources 3 and second x-ray sources 23 could also be used for radiotherapy applications. A radiotherapy system may comprise the x-ray system 1 and a processor. The processor may be configured to obtain a measurement of a subject (i.e. a patient) using the x-ray system 1 , locate a target structure within the subject based on the measurement, and control the x-ray system 1 to deliver a therapeutic x-ray dose to the target structure, for example a cancer tumour.

[0198] The processor may be configured to control the first x-ray source 3 and / or the second x-ray source 23 to emit x-rays at a first intensity during the obtaining of the measurement. The processor may be configured to control the first x-ray source 3 and / or the second x-ray source 23 to emit x-rays at a second intensity during the delivering of the therapeutic dose. The first intensity is different from, preferably lower than, the second intensity. The different intensities may be achieved by varying the intensity of x-rays emitted by each individual first x-ray source 3 and / or second x-ray source 23, as mentioned above. Alternatively or additionally, the different intensities may be achieved by varying the number of first x-ray sources 3 and second x-ray sources 23 that emit x-rays.

[0199] A problem with current radiotherapy is that the targeted region of the patient may move during the radiotherapy, for example due to the patient shifting position or breathing. An advantage of the present x-ray system 1 is that measurements, such as imaging, and therapeutic application of x-rays may be conducted simultaneously or alternately. This allows tracking of the target structure to which the therapeutic dose of radiation is to be applied, potentially in near real-time, and corresponding adjustment of the location at which the therapeutic dose of radiation is applied. This improves the effectiveness of the treatment and reduces radiation applied to nearby, healthy regions of the body.

[0200] Fig. 17 shows an application of the x-ray system of Fig. 15 to imaging of a patient by moving the patient through the bore of the x-ray system 1 to allow imaging along the length of the patient.

[0201] Fig. 18 shows an example application of the x-ray system 1 to fluorescence measurements. X-rays are shown being emitted by one of the first x-ray emitters 3. The x-rays emitted by the first x-ray emitter 3 interact with the object 41 , and the resulting x-rays are emitted in various directions from the object 41. X-rays emitted by the first x-ray source 3 and transmitted through the object 41 are detected at the opposing second detector 25. However, the resulting x-rays from the object 41 due to other interactions such as reflection or fluorescence are also detected at the first x-ray detectors 3. Such an arrangement could facilitate simultaneous performing of different types of measurements of the object 41 , which may be a living mammal. For example, CT imaging may be performed using the transmitted x-rays, and simultaneously quantification and spatial localisation of metals and metalloids in tissue using x-ray fluorescence may also be performed.

[0202] As shown in Fig. 19, the x-ray system 1 may comprise a support body 45 configured to support the first x-ray source 3. The support body 45 may be further configured to support the first x-ray detector 5. The support body may be further configured to support the second x-ray source 23 and / or the second x-ray detector 25, where present. The support body 45 allows the system to be situated around the object 41 to perform measurements,

[0203] As shown in Fig. 20, the support body 45 is configured to fixably engage with a frame 47 for holding an object 41 to be exposed to x-rays. In Fig. 20, the frame 47 is a stereotactic head frame, but this is not essential and other types of frame may be used depending on the object 41 to be exposed to x-rays. Where the frame is a stereotactic head frame, a distance between the first x-ray source 3 and the second x-ray detector 25 may be at most 40cm. This allows for the system to take measurements of the head while remaining compact. Fig. 21 shows a top-down view of the x-ray system when the support body 45 is engaged with the frame 47.

[0204] The support body 45 is configured to engage with the frame 47 such that the first x-ray source 3 and the first x-ray detector 5 adopt predetermined positions relative to the frame when the support body 45 is engaged with the frame 47. As discussed above, the x-ray system 1 may comprises a plurality of first x-ray sources 3 and first x-ray detectors 5, and / or one or more second x-ray sources 23 and second x-ray detectors 25. These may also be supported by the support body 45 and adopt predetermined positions relative to the frame 47 when the support body 45 is engaged with the frame 47.

[0205] This allows a three-dimensional coordinate system to be defined relative to the frame 47 in which the positions of the first x-ray source 3 and first x-ray detector 5 are known. This in turn allows the positions of features of the object 41 measured or imaged using the x-ray system 1 to be directly identified in the three-dimensional coordinate system relative to the frame 47. In other words, a direct correspondence is derivable between positions in an image captured using the x-ray system 1 and positions relative to the frame 47. The engagement of the x-ray system 1 with the frame co-registers 3D coordinates in the images captured by the x-ray system to the 3D coordinate system defined with reference to the frame 47.

[0206] The defining of the three-dimensional coordinate system may also be advantageous for applications such as industrial inspection. For industrial inspection, the expected dimensions of a manufactured object are likely to be known very precisely, for example if the object is manufactured using computer-aided design (CAD) and computer numerical control (CNC). This allows multiple objects to be sequentially and kinematically positioned relative to the x-ray system 1 using the frame 47 and support body 45. This in turn facilitates rapid inspection because the expected signal from each x-ray detector can be predicted and discrepancies (for example due to manufacturing inaccuracies or material flaws) can be identified rapidly without requiring complex image reconstruction.

[0207] As shown in Fig. 20 and Fig. 21 , the support body 45 may comprise one or more coupling features 49 configured to engage with corresponding attachment features 51 of the frame 47. The coupling features 49 may be kinematic coupling features that engage mechanically with the attachment features 51 . In Fig. 20, the coupling features 49 are provided by ballshaped features extending from the support body 45. The attachment features 51 are corresponding recesses in the frame 47 provided with camlocks to secure the coupling features. The attachment features 51 thereby provide points of reference to define the 3D coordinate system relative to the frame 47 and enabling measuring the location of any point in the object from x- ray images captured using the x-ray system 1. The three-dimensional coordinate system may be a Cartesian coordinate system such as is commonly used with stereotactic head frames.

[0208] The x-ray system 1 may be used to perform the method of preparing a device to interact with an object or locating a structure within an object shown in Fig. 21. The device may be a tool, for example a piece of industrial machinery such as a spray coater or a robotic arm. The object may be an object that is to be processed in some way using the device. The method comprises engaging S11 the support body 45 with the frame 47.

[0209] The method further comprises obtaining S13 a measurement of the object using the x-ray system 1. This can be achieved using the method shown in Fig. 20 and discussed above. For example, x-ray measurements may be used for quality control of components on an assembly line. The x-ray system 1 may be used to obtain the appropriate x-ray measurements, on which basis a parameter of the processing of the object can be determined. For example, a thickness of an applied coating could be determined, or a presence of fractures in a component detected. Obtaining S13 the measurement may comprise taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object. The first x- ray source 3 and the first x-ray detector 5 are preferably stationary relative to the frame 47 during the obtaining S13 of the measurement.

[0210] The method further comprises determining S15 a setting of the device based on the measurement or determining S15 a location of the structure within the object 41 based on the measurement.

[0211] Determining S15 the location may comprise using the predetermined positions of the first x-ray source 3 and the first x- ray detector 4. The location of the structure may be defined by coordinates relative to the frame 47. The object may be an animal, for example a human head, and the structure may be an anatomical structure, for example a region of the brain. The frame 47 may be a stereotactic head frame. Determining S15 the location may not comprise using one or more fiducial markers in the images.

[0212] The setting may be determined based on the parameter determined from the measurement. The setting could include settings such as a thickness of coating still to be applied to the object or a destination to move the object to using the robotic arm, e.g. to discard a defective component.

[0213] Many other examples are possible. In particular, the device may be a surgical instrument configured to engage with a stereotactic head frame, and the object a patient’s head to which the stereotactic frame is attached. On this basis, there may be provided a system for preparing a surgical instrument configured to engage with a stereotactic head frame. The system comprises the x-ray system 1 comprising the support body 45 and a processor configured to determine a setting of the surgical instrument based on a measurement taken using the x-ray system 1. The processor may be integrated with the x-ray system, for example also being supported by the support body 45. Alternatively, the processor may be provided separately to the x-ray system, and connected for exchange of data by any suitable connection, for example a wired or wireless connection.

[0214] The system can be used to perform a method of preparing a surgical instrument configured to engage with a stereotactic head frame. This is an example of the method shown in Fig. 21. The method comprises engaging S11 the support body 45 of the x-ray system 1 with the stereotactic head frame while the stereotactic head frame is attached to a head of a patient. The method further comprises obtaining S13 a measurement of at least a part of the head of the patient using the x-ray system 1. Preferably, the first x-ray source 3 and the first x-ray detector 5 are stationary relative to the stereotactic head frame during the obtaining S13 of the measurement. Obtaining S13 the measurement may comprise taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the head of the patient.

[0215] Finally, the method comprises adjusting a setting of the surgical instrument based on the measurement. The setting of the surgical instrument may comprise a position of at least part of the surgical instrument relative to the head of the patient when the surgical instrument is engaged with the stereotactic head frame. Adjusting the setting may comprise determining a trajectory from an exterior of the head to a target structure within the head based on the tomographic reconstruction of the head. Adjusting the setting may comprise determining a location of the target structure within the head using the predetermined positions of the first x-ray source 3 and the first x-ray detector 5, and optionally of the second x-ray source 23 and second x-ray detector 25.

[0216] As discussed above, the x-ray system 1 is able to register its x-ray images directly to the coordinate system of the stereotactic head frame, because the support body 45 of the x-ray system 1 is configured to engage with the stereotactic head frame such that the first x-ray source 3 and the first x-ray detector 5 adopt predetermined positions relative to the stereotactic head frame when the x-ray system 1 is engaged with the frame. This means that targets can be identified in the images and trajectories to the targets planned directly using the coordinate system of the x-ray images (which is also the coordinate system of the stereotactic head frame). Determined coordinates and settings can be directly transferred to the surgical instruments that engage with the stereotactic head frame.

[0217] This greatly simplifies the surgical process relative to existing methods where it is necessary to take multiple sets of images using different imaging modalities (e.g. MRI , x-ray etc.) and then perform complex registration techniques to align the images taken in different modalities using fiducial markers in the images. In the present method, determining the location may not comprise using one or more fiducial markers in the images.

[0218] As another application, the systems described herein could be used as part of a method of radiotherapy, as described in relation to Fig. 16. The method comprises obtaining a measurement of a subject using the x-ray system 1 , locating a target structure within the subject based on the measurement, and controlling the x-ray system 1 to deliver a therapeutic x-ray dose to the target structure.

[0219] The first x-ray source 3 and / or the second x-ray source 23 are controlled to emit x-rays at a first intensity during the obtaining of the measurement, and the first x-ray source 3 and / or the second x-ray source 23 are controlled to emit x-rays at a second intensity during the delivering of the therapeutic dose. The first intensity is preferably lower than the second intensity. The method may comprise tracking a location of the target structure over time, and adjusting a position at which the therapeutic dose is applied based on the location of the target structure. Tracking the location over time may comprise obtaining measurements of the subject using the x-ray system 1 at a plurality of times, and for each time locating the target structure based on the corresponding measurement. The method may comprise obtaining measurements of the subject and delivering the therapeutic dose simultaneously or alternately.

[0220] The different intensities may be achieved by varying the intensity of x-rays emitted by each individual first x-ray source 3 and / or second x-ray source 23, as mentioned above. Alternatively or additionally, the different intensities may be achieved by varying the number of first x-ray sources 3 and second x-ray sources 23 that emit x-rays.

[0221] The invention may also be characterised by the following numbered clauses. These are not the claims of the application, which follow under the heading “CLAIMS” below. 1. An x-ray system comprising: a first x-ray source configured to emit x-rays; and a first x-ray detector having a first detector surface configured to detect x-rays, wherein the system is configured such that at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface.

[0222] 2. The x-ray system of clause 1 , wherein the first emission direction is perpendicular to the first detector surface.

[0223] 3. The x-ray system of clause 1 or 2, wherein the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays.

[0224] 4. The x-ray system of clause 3, wherein the first emission direction is towards the target volume.

[0225] 5. The x-ray system of clause 3 or 4, wherein x-rays emitted by the first x-ray source pass through the first detector surface before reaching the target volume.

[0226] 6. An x-ray system comprising: a first x-ray source configured to emit x-rays; and a first x-ray detector having a first detector surface configured to detect x-rays, wherein: the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays; and x-rays emitted by the first x-ray source pass through the first detector surface before reaching the target volume.

[0227] 7. The x-ray system of any preceding clause, wherein the system is configured such that a) signals from the first x-ray detector due to x-rays emitted by the first x-ray source are disregarded, and / or b) the first x-ray detector does not generate signals in response to x-rays emitted by the first x-ray source and passing through the first detector surface.

[0228] 8. The x-ray system of any preceding clause, wherein the system comprises a plurality of first x-ray sources.

[0229] 9. The x-ray system of clause 8, wherein the first x-ray sources are selectively controllable, optionally wherein each first x-ray source is individually selectively controllable.

[0230] 10. The x-ray system of clause 9, wherein the system is configured to selectively control the first x-ray sources such that a maximum power consumption of the plurality of first x-ray sources is below a predetermined power threshold during the emission of x-rays by the first x-ray sources.

[0231] 11. The x-ray system of any preceding clause, wherein the first x-ray source is provided in an emitter layer, and the first detector surface is provided in a detector layer.

[0232] 12. The x-ray system of clause 11 , wherein the detector layer is adjacent to or adjoins the emitter layer.

[0233] 13. The x-ray system of clause 11 or 12, wherein the system comprises a plurality of first x-ray sources uniformly distributed across the emitter layer.

[0234] 14. The x-ray system of any of clauses 11 to 13, wherein the first x-ray source is configured to emit x-rays through the detector layer.

[0235] 15. The x-ray system of any of clauses 11 to 14, wherein the emitter layer and the detector layer are flat and / or parallel.

[0236] 16. The x-ray system of any preceding clause, wherein the system further comprises a filtering element configured to absorb x-rays emitted by the first x-ray source having an energy below a predetermined threshold.

[0237] 17. The x-ray system of any preceding clause, wherein: the first x-ray source is configured to illuminate with x-rays a target volume for exposing of an object within the target volume to x-rays; and the system further comprises a shielding element configured to absorb x-rays that have passed through the first detector surface in a direction away from the target volume.

[0238] 18. The x-ray system of any preceding clause, wherein the system comprises a plurality of first x-ray detectors.

[0239] 19. The x-ray system of clause 18, wherein the first detector surfaces of the plurality of first x-ray detectors are co-planar.

[0240] 20. The x-ray system of clause 18 or 19, wherein: a) a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at most 40cm, optionally at most 30 cm, optionally at most 25cm; and / or b) a minimum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at least 5cm, optionally at least 10 cm. 21. The x-ray system of any of clauses 18 to 20, wherein: the system comprises a plurality of first x-ray sources; and a maximum total extent of the first x-ray sources is equal to or less than a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors.

[0241] 22. The x-ray system of any preceding clause, wherein the x-ray system further comprises: a second x-ray source configured to emit x-rays; and a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; and x-rays emitted by the second x-ray source are detected by the first x-ray detector.

[0242] 23. The x-ray system of clause 22, wherein at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction towards the first x-ray source.

[0243] 24. An x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray source configured to emit x- rays; and a first x-ray detector having a first detector surface configured to detect x-rays; a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; x-rays emitted by the second x-ray source are detected by the first x-ray detector; at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction towards the first x-ray source.

[0244] 25. The x-ray system of clause 23 or 24, wherein: at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction; and the second emission direction is parallel and opposite to the first emission direction.

[0245] 26. An x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray source configured to emit x- rays; and a first x-ray detector having a first detector surface configured to detect x-rays; a second x-ray detector having a second detector surface configured to detect x-rays, wherein the system is configured such that: x-rays emitted by the first x-ray source are detected by the second x-ray detector; x-rays emitted by the second x-ray source are detected by the first x-ray detector; at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction; and at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction parallel and opposite to the first emission direction.

[0246] 27. The x-ray system of any of clauses 22 to 26, wherein the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources.

[0247] 28. The x-ray system of clause 27, wherein the system is configured such that the first x-ray detector detects x-rays emitted by two or more second x-ray sources.

[0248] 29. The x-ray system of clause 28, wherein the system is configured to selectively control the second x-ray sources to emit x-rays sequentially, such that x-rays emitted by different second x-ray sources are detected at different times by the first x-ray detector.

[0249] 30. The x-ray system of any of clauses 27 to 29, wherein: the system comprises a plurality of first x-ray detectors; and each first x-ray detector is configured to detect x-rays emitted by a different subset of the second x-ray sources.

[0250] 31. The x-ray system of any of clauses 27 to 30, wherein the system is configured such that the second x-ray detector detects x-rays emitted by two or more first x-ray sources.

[0251] 32. The x-ray system of clause 31 , wherein the system is configured to selectively control the first x-ray sources to emit x- rays sequentially, such that x-rays emitted by different first x-ray sources are detected at different times by the second x-ray detector.

[0252] 33. The x-ray system of any of clauses 27 to 32, wherein: the system comprises a plurality of second x-ray detectors; and each second x-ray detector is configured to detect x-rays emitted by a different subset of the first x-ray sources.

[0253] 34. The x-ray system of any of clauses 22 to 33, wherein the first x-ray source and / or the second x-ray source is / are configured to illuminate with x-rays a target volume between the first x-ray source and the second x-ray source for exposing of an object within the target volume to x-rays.

[0254] 35. The x-ray system of clause 34, wherein the system is configured to obtain x-ray images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object within the target volume, optionally wherein the object comprises mammalian tissue.

[0255] 36. The x-ray system of clause 34 or 35, wherein x-rays emitted by the second x-ray source pass through the second detector surface of the second x-ray detector before reaching the target volume.

[0256] 37. The x-ray system of any of clauses 34 to 36, wherein: a) a largest linear extent of the target volume is at least 50% of a distance between the first x-ray source and the second x-ray source, optionally at least 70%, optionally at least 80%; and / or b) a smallest linear extent of the target volume is at least 10% of a distance between the first x-ray source and the second x-ray source, optionally at least 20%, optionally at least 40%.

[0257] 38. The x-ray system of any of clauses 34 to 37, wherein a smallest linear extent of the target volume is at least 5cm, optionally at least 10 cm.

[0258] 39. The x-ray system of any of clauses 34 to 38 wherein the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources, and one or both of: a) a largest linear extent of the target volume is at least 25% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 50%, optionally at least 70%, optionally at least 80%; and b) a smallest linear extent of the target volume is at least 10% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 20%, optionally at least 40%.

[0259] 40. The x-ray system of any of clauses 34 to 39, wherein the arrangement of the first x ray sources and the second x ray sources is such that, when all of the first x-ray sources and the second x-ray sources are simultaneously activated, at least part of the target volume is illuminated by x-rays emitted by at least two different first x-ray sources or second x-ray sources, optionally wherein the at least two different first x-ray sources or second x-ray sources comprise at least one first x-ray source and at least one second x-ray source.

[0260] 41. The x-ray system of any of clauses 22 to 40, wherein: the system comprises a first x-ray detector having a first detector surface configured to detect x-rays, and a second x-ray detector having a second detector surface configured to detect x-rays; and the first detector surface of the first x-ray detector and the second detector surface of the second x-ray detector are flat and parallel to one another.

[0261] 42. The x-ray system of any of clauses 22 to 41 , wherein: a) a distance between the first x-ray source and the second x- ray source is at most 40cm, optionally at most 30cm, optionally at most 22cm; and / or b) a distance between the first x-ray source and the second x-ray source is at least 5cm, optionally at least 10cm, optionally at least 15cm.

[0262] 43. The x-ray system of any of clauses 22 to 42, wherein: the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources; the system comprises a plurality of first x-ray detectors and a plurality of second x-ray detectors; the first detector surfaces of the first x-ray detectors and the second detector surfaces of the second x-ray detectors are arranged such that a cross-section through the first detector surfaces and the second detector surfaces forms a regular polygon having an even number of sides; the first x-ray sources and the second x-ray sources are located around the circumference of the regular polygon; each first x-ray detector is configured to detect x-rays emitted by second x-ray sources located on an opposite side of the regular polygon to a side on which the first x-ray detector is located; each second x-ray detector is configured to detect x-rays emitted by first x-ray sources located on an opposite side of the regular polygon to a side on which the second x-ray detector is located.

[0263] 44. The x-ray system of clause 43, wherein the regular polygon has at least four sides, optionally at least six sides, optionally at least eight sides.

[0264] 45. The x-ray system of any preceding clause, wherein: the system comprises a support body configured to support the first x-ray source and the first x-ray detector; and the support body is configured to fixably engage with a frame for holding an object to be exposed to x-rays, optionally wherein the frame is a stereotactic head frame.

[0265] 46. An x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray detector having a second detector surface configured to detect x-rays emitted by the first x-ray source; and a support body configured to support the first x- ray source and the second x-ray detector, wherein: the support body is configured to fixably engage with a frame for taking a measurement of a brain, the frame being a stereotactic head frame; and a distance between the first x-ray source and the second x-ray detector is at most 40cm.

[0266] 47. The x-ray system of clause 45 or 46, wherein the support body is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the support body is engaged with the frame.

[0267] 48. The x-ray system of any of clauses 45 to 47, wherein the support body comprises one or more coupling features configured to engage with corresponding attachment features of the frame.

[0268] 49. A system for preparing a surgical instrument configured to engage with a stereotactic head frame, the system comprising: the x-ray system of any of clauses 45 to 48; and a processor configured to determine a setting of the surgical instrument based on a measurement taken using the x-ray system.

[0269] 50. A radiotherapy system comprising: the x-ray system of any of clauses 22 to 26, or any preceding clause dependent thereon; a processor configured to: obtain a measurement of a subject using the x-ray system; locate a target structure within the subject based on the measurement; and control the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a first intensity during the obtaining of the measurement; the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

[0270] 51. The x-ray system of any preceding clause, wherein the system is portable, optionally human-portable.

[0271] 52. The x-ray system of any preceding clauses, wherein the first x-ray source and the first x-ray detector are stationary during exposing of an object using the system.

[0272] 53. The x-ray system of any preceding clauses, wherein the first x-ray source is configured to emit x rays with controllable energies.

[0273] 54. The x-ray system of any preceding clause, wherein the first x-ray source is configured to emit cone beams of x-rays.

[0274] 55. The x-ray system of any preceding clause, wherein the system comprises a collimation element configured to shape beams of x-rays emitted by the first x-ray source, optionally wherein the collimation element is configured to shape the beams into rectangular beams, optionally square beams.

[0275] 56. The x-ray system of any preceding clause, wherein the first x ray source comprises a cold cathode field emission electron source, for example carbon nanotube layers, graphene multilayer structures, bulk graphene, or a Spindt-type emitter.

[0276] 57. The x-ray system of any preceding clause, wherein the first x-ray source comprises transmissive x-ray targets, optionally comprising tungsten, tantalum, or molybdenum.

[0277] 58. The x-ray system of any preceding clause, wherein the first x-ray detector is a digital x-ray detector, for example an organic photodetector (OPD), organic-inorganic hybrid semiconductor, or low-gain avalanche diode (LGAD).

[0278] 59. The x-ray system of any preceding clause, wherein the x-ray system is an x-ray imaging system.

[0279] 60. A method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object, wherein at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from a first detector surface of a first x-ray detector and such that a line along the first emission direction intersects the first detector surface; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector. 61. The method of clause 60, wherein at least a portion of x-rays emitted by the first x-ray source pass through the first detector surface of the first x-ray detector before reaching the target volume.

[0280] 62. A method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object, wherein at least a portion of x-rays emitted by the first x-ray source pass through a first detector surface of a first x-ray detector before reaching the target volume; and detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector.

[0281] 63. The method of clause 62, wherein at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface.

[0282] 64. The method of any of clauses 60 to 63, wherein the method further comprises: emitting x-rays from a second x-ray source to illuminate the target volume; and detecting x-rays from the second x-ray source at the first detector surface.

[0283] 65. The method of clause 64, wherein at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction, the second emission direction being away from the second detector surface and such that a line along the second emission direction intersects the second detector surface.

[0284] 66. The method of clause 64 or 65, wherein at least a portion of x-rays emitted by the second x-ray source pass through the second detector surface before reaching the target volume.

[0285] 67. A method of obtaining x-ray measurements of an object comprising: emitting x-rays from a first x-ray source to illuminate a target volume containing the object; emitting x-rays from a second x-ray source to illuminate the target volume, wherein at least a portion of x-rays emitted by the second x-ray source propagate towards the first x-ray source; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector; and detecting x-rays from the second x-ray source at a first detector surface of a first x-ray detector.

[0286] 68. A method of obtaining x-ray measurements of an object comprising: emitting x-rays in a first emission direction from a first x-ray source to illuminate a target volume containing the object; emitting in a second emission direction x-rays from a second x-ray source to illuminate the target volume; and detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector, detecting x-rays from the second x-ray source at a first detector surface of a first x-ray detector; wherein the second emission direction is parallel and opposite to the first emission direction.

[0287] 69. A method of preparing a device to interact with an object, the method comprising: obtaining a measurement of the object using the x-ray system of any of clauses 1 to 59; and determining a setting of the device based on the measurement.

[0288] 70. A method of preparing a surgical instrument configured to engage with a stereotactic head frame, the method comprising: engaging a support body of an x-ray system with the stereotactic head frame while the stereotactic head frame is attached to a head of a patient; obtaining a measurement of at least a part of the head of the patient using the x-ray system; and adjusting a setting of the surgical instrument based on the measurement.

[0289] 71. The method of clause 70, wherein; the x-ray system comprises a first x-ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays; the support body of the x-ray system is configured to support the first x-ray source and the first x-ray detector; and the support body of the x-ray system is configured to engage with the stereotactic head frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the stereotactic head frame when the x-ray system is engaged with the frame.

[0290] 72. The method of clause 71 , wherein the first x-ray source and the first x-ray detector are stationary relative to the stereotactic head frame during the taking of the measurement.

[0291] 73. The method of any of clauses 70 to 72, wherein the setting of the surgical instrument comprises a position of at least part of the surgical instrument relative to the head of the patient when the surgical instrument is engaged with the stereotactic head frame. 74. The method of any of clauses 70 to 73, wherein obtaining measurement comprises taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the head of the patient.

[0292] 75. The method of clause 74, wherein adjusting the setting comprises determining a trajectory from an exterior of the head to a target structure within the head based on the tomographic reconstruction of the head.

[0293] 76. The method of clause 75, wherein adjusting the setting comprises determining a location of the target structure within the head using the predetermined positions of the first x-ray source and the first x-ray detector.

[0294] 77. The method of clause 76, wherein determining the location does not comprise using one or more fiducial markers in the images.

[0295] 78. A method of locating a structure within an object comprising: engaging a support body of an x-ray system with a frame attached to the object, the x-ray system comprising a first x-ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays, and the support body configured to support the first x-ray source and the first x-ray detector; obtaining a measurement of the object using the x-ray system; and determining a location of the structure within the object based on the measurement, wherein: the x-ray system is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the x-ray system is engaged with the frame; and the location of the structure is defined by coordinates relative to the frame.

[0296] 79. The method of clause 78, wherein the first x-ray source and the first x-ray detector are stationary relative to the frame during the taking of the measurement.

[0297] 80. The method of clause 78 or 79, wherein the object is an animal and the structure is an anatomical structure.

[0298] 81. The method of any of clauses 78 to 80, wherein the object is a human head and the frame is a stereotactic head frame.

[0299] 82. The method of any of clauses 78 to 81 , wherein obtaining a measurement comprises taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object.

[0300] 83. The method of any of clauses 78 to 82, wherein determining the location comprises using the predetermined positions of the first x-ray source and the first x-ray detector.

[0301] 84. The method of any of clauses 78 to 83, wherein determining the location does not comprise using one or more fiducial markers in the images.

[0302] 85. A method of radiotherapy comprising: obtaining a measurement of a subject using the x-ray system of any of clauses 22 to 26, or any preceding system clause dependent thereon; locating a target structure within the subject based on the measurement; and controlling the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a first intensity during the obtaining of the measurement; the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

Claims

CLAIMS1. An x-ray system comprising: a first x-ray source configured to emit x-rays; and a second x-ray source configured to emit x-rays; a first x-ray detector having a first detector surface configured to detect x-rays, a second x-ray detector having a second detector surface configured to detect x-rays, wherein: x-rays emitted by the first x-ray source are detected by the second x-ray detector; x-rays emitted by the second x-ray source are detected by the first x-ray detector. the first x-ray source and the second x-ray source are configured to illuminate with x-rays a target volume between the first x-ray source and the second x-ray source for exposing of an object within the target volume to x-rays; x-rays emitted by the first x-ray source pass through the first detector surface of the first x-ray detector before reaching the target volume; and x-rays emitted by the second x-ray source pass through the second detector surface of the second x-ray detector before reaching the target volume.

2. The x-ray system of claim 1 , wherein at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface.

3. The x-ray system of claim 2, wherein the first emission direction is perpendicular to the first detector surface.

4. The x-ray system of claim 1 or 2, wherein the first emission direction is towards the target volume.

5. The x-ray system of any preceding claim, wherein the system is configured such that a) signals from the first x-ray detector due to x-rays emitted by the first x-ray source are disregarded, and / or b) the first x-ray detector does not generate signals in response to x-rays emitted by the first x-ray source and passing through the first detector surface.

6. The x-ray system of any preceding claim, wherein the system comprises a plurality of first x-ray sources.

7. The x-ray system of claim 6, wherein the first x-ray sources are selectively controllable, optionally wherein each first x- ray source is individually selectively controllable.

8. The x-ray system of claim 7, wherein the system is configured to selectively control the first x-ray sources such that a maximum power consumption of the plurality of first x-ray sources is below a predetermined power threshold during the emission of x-rays by the first x-ray sources.

9. The x-ray system of any preceding claim, wherein the first x-ray source is provided in an emitter layer, and the first detector surface is provided in a detector layer.

10. The x-ray system of claim 9, wherein the detector layer is adjacent to or adjoins the emitter layer.

11. The x-ray system of claim 9 or 10, wherein the system comprises a plurality of first x-ray sources uniformly distributed across the emitter layer.

12. The x-ray system of any of claims 9 to 11 , wherein the first x-ray source is configured to emit x-rays through the detector layer.

13. The x-ray system of any of claims 9 to 12, wherein the emitter layer and the detector layer are flat and / or parallel.

14. The x-ray system of any preceding claim, wherein the system further comprises a filtering element configured to absorb x-rays emitted by the first x-ray source having an energy below a predetermined threshold.

15. The x-ray system of any preceding claim, wherein the system further comprises a shielding element configured to absorb x-rays that have passed through the first detector surface in a direction away from the target volume.

16. The x-ray system of any preceding claim, wherein the system comprises a plurality of first x-ray detectors.

17. The x-ray system of claim 16, wherein the first detector surfaces of the plurality of first x-ray detectors are co-planar.

18. The x-ray system of claim 16 or 17, wherein: a) a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at most 40cm, optionally at most 30 cm, optionally at most 25cm; and / or b) a minimum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors is at least 5cm, optionally at least 10 cm.

19. The x-ray system of any of claims 16 to 18, wherein: the system comprises a plurality of first x-ray sources; and a maximum total extent of the first x-ray sources is equal to or less than a maximum total extent of the first detector surfaces of the first x-ray detectors in the plane of the first x-ray detectors.

20. The x-ray system of any preceding claim, wherein at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction towards the first x-ray source.

21. The x-ray system of claim 20, wherein: at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction; and the second emission direction is parallel and opposite to the first emission direction.

22. The x-ray system of any preceding claim, wherein the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources.

23. The x-ray system of claim 22, wherein the system is configured such that the first x-ray detector detects x-rays emitted by two or more second x-ray sources.

24. The x-ray system of claim 23, wherein the system is configured to selectively control the second x-ray sources to emit x-rays sequentially, such that x-rays emitted by different second x-ray sources are detected at different times by the first x-ray detector.

25. The x-ray system of any of claims 22 to 24, wherein: the system comprises a plurality of first x-ray detectors; and each first x-ray detector is configured to detect x-rays emitted by a different subset of the second x-ray sources.

26. The x-ray system of any of claims 22 to 25, wherein the system is configured such that the second x-ray detector detects x-rays emitted by two or more first x-ray sources.

27. The x-ray system of claim 26, wherein the system is configured to selectively control the first x-ray sources to emit x- rays sequentially, such that x-rays emitted by different first x-ray sources are detected at different times by the second x-ray detector.

28. The x-ray system of any of claims 22 to 27, wherein: the system comprises a plurality of second x-ray detectors; and each second x-ray detector is configured to detect x-rays emitted by a different subset of the first x-ray sources.

29. The x-ray system of any preceding claim, wherein the system is configured to obtain x-ray images sufficient for two- dimensional and / or three-dimensional tomographic reconstruction of the object within the target volume, optionally wherein the object comprises mammalian tissue.

30. The x-ray system of any preceding claim, wherein one or more of: a) a largest linear extent of the target volume is at least 50% of a distance between the first x-ray source and the second x-ray source, optionally at least 70%, optionally at least 80%; b) a smallest linear extent of the target volume is at least 10% of a distance between the first x-ray source and the second x-ray source, optionally at least 20%, optionally at least 40%; and c) a smallest linear extent of the target volume is at least 5cm, optionally at least 10 cm.

31. The x-ray system of any preceding claim, wherein the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources, and one or both of: a) a largest linear extent of the target volume is at least 25% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 50%, optionally at least 70%, optionally at least 80%; and b) a smallest linear extent of the target volume is at least 10% of a largest distance between any first x-ray source and any second x-ray source, optionally at least 20%, optionally at least 40%.

32. The x-ray system of any preceding claim, wherein the arrangement of the first x ray sources and the second x ray sources is such that, when all of the first x-ray sources and the second x-ray sources are simultaneously activated, at least part of the target volume is illuminated by x-rays emitted by at least two different first x-ray sources or second x-ray sources, optionally wherein the at least two different first x-ray sources or second x-ray sources comprise at least one first x-ray source and at least one second x-ray source.

33. The x-ray system of any preceding claim, wherein: the first detector surface of the first x-ray detector and the second detector surface of the second x-ray detector are flat and parallel to one another.

34. The x-ray system of any preceding claim, wherein: a) a distance between the first x-ray source and the second x-ray source is at most 40cm, optionally at most 30cm, optionally at most 22cm; and / or b) a distance between the first x-ray source and the second x-ray source is at least 5cm, optionally at least 10cm, optionally at least 15cm.

35. The x-ray system of any preceding claim, wherein: the system comprises a plurality of first x-ray sources and a plurality of second x-ray sources; the system comprises a plurality of first x-ray detectors and a plurality of second x-ray detectors; the first detector surfaces of the first x-ray detectors and the second detector surfaces of the second x-ray detectors are arranged such that a cross-section through the first detector surfaces and the second detector surfaces forms a regular polygon having an even number of sides; the first x-ray sources and the second x-ray sources are located around the circumference of the regular polygon; each first x-ray detector is configured to detect x-rays emitted by second x-ray sources located on an opposite side of the regular polygon to a side on which the first x-ray detector is located; each second x-ray detector is configured to detect x-rays emitted by first x-ray sources located on an opposite side of the regular polygon to a side on which the second x-ray detector is located.

36. The x-ray system of claim 35, wherein the regular polygon has at least four sides, optionally at least six sides, optionally at least eight sides.

37. The x-ray system of any preceding claim, wherein: the system comprises a support body configured to support the first x-ray source and the first x-ray detector; and the support body is configured to fixably engage with a frame for holding an object to be exposed to x-rays, optionally wherein the frame is a stereotactic head frame.

38. An x-ray system comprising: a first x-ray source configured to emit x-rays; a second x-ray detector having a second detector surface configured to detect x-rays emitted by the first x-ray source; and a support body configured to support the first x-ray source and the second x-ray detector, wherein: the support body is configured to fixably engage with a frame for taking a measurement of a brain, the frame being a stereotactic head frame; and a distance between the first x-ray source and the second x-ray detector is at most 40cm.

39. The x-ray system of claim 37 or 38, wherein the support body is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the support body is engaged with the frame.

40. The x-ray system of any of claims 37 to 39, wherein the support body comprises one or more coupling features configured to engage with corresponding attachment features of the frame.

41. A system for preparing a surgical instrument configured to engage with a stereotactic head frame, the system comprising: the x-ray system of any of claims 37 to 40; and a processor configured to determine a setting of the surgical instrument based on a measurement taken using the x- ray system.

42. A radiotherapy system comprising: the x-ray system of any preceding claim; a processor configured to: obtain a measurement of a subject using the x-ray system; locate a target structure within the subject based on the measurement; and control the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a first intensity during the obtaining of the measurement; the processor is configured to control the first x-ray source and / or the second x-ray source to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

43. The x-ray system of any preceding claim, wherein the system is portable, optionally human-portable.

44. The x-ray system of any preceding claims, wherein the first x-ray source and the first x-ray detector are stationary during exposing of an object using the system.

45. The x-ray system of any preceding claims, wherein one or both of: a) the first x-ray source is configured to emit x rays with controllable energies; and b) the first x-ray source is configured to emit cone beams of x-rays.

46. The x-ray system of any preceding claim, wherein the system comprises a collimation element configured to shape beams of x-rays emitted by the first x-ray source, optionally wherein the collimation element is configured to shape the beams into rectangular beams, further optionally square beams.

47. The x-ray system of any preceding claim, wherein the first x ray source comprises a cold cathode field emission electron source, for example carbon nanotube layers, graphene multilayer structures, bulk graphene, or a Spindt-type emitter.

48. The x-ray system of any preceding claim, wherein the first x-ray source comprises transmissive x-ray targets, optionally comprising tungsten, tantalum, or molybdenum.

49. The x-ray system of any preceding claim, wherein the first x-ray detector is a digital x-ray detector, for example an organic photodetector (OPD), organic-inorganic hybrid semiconductor, or low-gain avalanche diode (LGAD).

50. The x-ray system of any preceding claim, wherein the x-ray system is an x-ray imaging system.

51. A method of preparing a device to interact with an object, the method comprising: obtaining a measurement of the object using the x-ray system of any of claims 1 to 50; and determining a setting of the device based on the measurement.

52. A method of obtaining x-ray measurements of an object using an x-ray system comprising: emitting x-rays from a first x-ray source of the x-ray system to illuminate a target volume containing the object, wherein at least a portion of x-rays emitted by the first x-ray source pass through a first detector surface of a first x-ray detector of the x- ray system before reaching the target volume; detecting x-rays from the first x-ray source at a second detector surface of a second x-ray detector of the x-ray system; emitting x-rays from a second x-ray source of the x-ray system to illuminate the target volume, wherein at least a portion of x-rays emitted by the second x-ray source pass through the second detector surface before reaching the target volume; and detecting x-rays from the second x-ray source at the first detector surface, wherein the target volume is between the first x-ray source and the second x-ray source.

53. The method of claim 52, wherein at least a portion of x-rays emitted by the first x-ray source propagate in a first emission direction, the first emission direction being away from the first detector surface and such that a line along the first emission direction intersects the first detector surface.

54. The method of claim 52 or 53, wherein at least a portion of x-rays emitted by the second x-ray source propagate in a second emission direction, the second emission direction being away from the second detector surface and such that a line along the second emission direction intersects the second detector surface.

55. The method of any of claims 52 to 54, wherein at least a portion of x-rays emitted by the second x-ray source propagate towards the first x-ray source.

56. The method of any of claims 52 to 55, wherein x-rays emitted by the first x-ray source are emitted in a first emission direction; x-rays emitted by the second x-ray source are emitted in a second emission direction; and the second emission direction is parallel and opposite to the first emission direction.

57. A method of preparing a surgical instrument configured to engage with a stereotactic head frame, the method comprising: engaging a support body of an x-ray system with the stereotactic head frame while the stereotactic head frame is attached to a head of a patient; obtaining a measurement of at least a part of the head of the patient using the x-ray system; andadjusting a setting of the surgical instrument based on the measurement.

58. The method of claim 57, wherein; the x-ray system comprises a first x-ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays; the support body of the x-ray system is configured to support the first x-ray source and the first x-ray detector; and the support body of the x-ray system is configured to engage with the stereotactic head frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the stereotactic head frame when the x-ray system is engaged with the frame.

59. The method of claim 58, wherein the first x-ray source and the first x-ray detector are stationary relative to the stereotactic head frame during the taking of the measurement.

60. The method of any of claims 57 to 59, wherein the setting of the surgical instrument comprises a position of at least part of the surgical instrument relative to the head of the patient when the surgical instrument is engaged with the stereotactic head frame.

61. The method of any of claims 57 to 60, wherein obtaining measurement comprises taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the head of the patient.

62. The method of claim 61 , wherein adjusting the setting comprises determining a trajectory from an exterior of the head to a target structure within the head based on the tomographic reconstruction of the head.

63. The method of claim 62, wherein adjusting the setting comprises determining a location of the target structure within the head using the predetermined positions of the first x-ray source and the first x-ray detector.

64. The method of claim 63, wherein determining the location does not comprise using one or more fiducial markers in the images.

65. A method of locating a structure within an object comprising: engaging a support body of an x-ray system with a frame attached to the object, the x-ray system comprising a first x- ray source configured to emit x-rays and a first x-ray detector having a first detector surface configured to detect x-rays, and the support body configured to support the first x-ray source and the first x-ray detector; obtaining a measurement of the object using the x-ray system; and determining a location of the structure within the object based on the measurement, wherein: the x-ray system is configured to engage with the frame such that the first x-ray source and the first x-ray detector adopt predetermined positions relative to the frame when the x-ray system is engaged with the frame; and the location of the structure is defined by coordinates relative to the frame.

66. The method of claim 65, wherein the first x-ray source and the first x-ray detector are stationary relative to the frame during the taking of the measurement.

67. The method of claim 65 or 66, wherein the object is an animal and the structure is an anatomical structure.

68. The method of any of claims 65 to 67, wherein the object is a human head and the frame is a stereotactic head frame.

69. The method of any of claims 65 to 68, wherein obtaining a measurement comprises taking a plurality of images sufficient for two-dimensional and / or three-dimensional tomographic reconstruction of the object.

70. The method of any of claims 65 to 69, wherein determining the location comprises using the predetermined positions of the first x-ray source and the first x-ray detector.

71. The method of any of claims 65 to 70, wherein determining the location does not comprise using one or more fiducial markers in the images.

72. The method of any of claims 52 to 71 , wherein the x-ray system is the x-ray system of any of claims 1 to 50.

73. A method of radiotherapy comprising: obtaining a measurement of a subject using the x-ray system of any of claims 1 to 50; locating a target structure within the subject based on the measurement; and controlling the x-ray system to deliver a therapeutic x-ray dose to the target structure, wherein: the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a first intensity during the obtaining of the measurement; the first x-ray source and / or the second x-ray source are controlled to emit x-rays at a second intensity during the delivering of the therapeutic dose; and the first intensity is lower than the second intensity.

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