Patent Description:
Digital X-ray imaging systems are becoming increasingly widespread for producing digital data which can be reconstructed into useful radiographic images. In current digital X-ray imaging systems, radiation from a source is directed toward a subject, typically a patient in a medical diagnostic application. A portion of the radiation passes through the patient and impacts a detector that is divided into a matrix of discrete elements, e.g., pixels. The detector elements are read out to generate output signals based upon the quantity or intensity of the radiation impacting each pixel region. The signals may then be processed to generate an image that may be displayed for review.

In certain contexts, a mobile X-ray imaging system may employ a portable detector that is not fixed in position or orientation with respect to the X-ray source. In such contexts, a technician may position the patient and/or portable detector to image the anatomy of interest. In certain circumstances the patient being imaged may be difficult to move or should not be disturbed. Examples of such situations include imaging of newborns or infants in a neonatal intensive care unit (NICU) or of other patients in a critical care type setting, such as a burn unit or intensive care unit (ICU).

In such situations, a mobile imaging system having a portable detector (e.g., a detector that is freely movable relative to the X-ray source) may be employed so that the patient does not have to be moved, and instead the imaging equipment is brought to, and positioned with respect to, the patient. The detector, in such a situation, may be positioned below the patient, such as on a shelf below the patient support surface (e.g., bed) and a single-exposure X-ray image may then be obtained.

In such an approach, only a coarse patient alignment is needed to ensure that the target anatomy is projected onto the detector active area, and will therefore appear in the X-ray image. This coarse alignment may be accomplished based on operator estimation of the placement of the detector based upon a light box shined on the patient during positioning. That is, the path from the X-ray tube head to the projected light box informs the operator about the path of the X-rays and the operator can approximately extrapolate this path to the detector plane.

While this approach may be sufficient for a single-exposure imaging procedure, it is typically not suitable for a tomographic X-ray scan, in which a sequence of offset images are acquired. Such a tomographic scan allows a three-dimensional (3D) view of the patient anatomy to be generated by acquiring this sequence of images (e.g., <NUM>, <NUM>, <NUM>, <NUM> images) from different views over a limited angular range (e.g., <NUM>°, <NUM>°, <NUM>°, <NUM>°, and so forth). Such a tomographic scan requires additional precise position and orientation information about the source focal spot and detector. However, in contexts where the detector is freely positionable it may not be readily determined if the detector is well-positioned, particularly where the detector is occluded by a table, the patient, blankets covering the patient, or other surface on which the patient is resting cannot be moved.

<CIT> describes a method for positioning a mobile X-ray image with an X-ray source with respect to an X-ray detector, using a marker image acquired with an optical sensor.

<CIT> describes a method for positioning an X-ray detector with respect to an X-ray source as well as an X-ray device and a positioning aid for carrying out the method. The method has a step of arranging a positioning aid with the X-ray detector under a patient. In a further step, a predetermined position of a position marker is specified as a function of a predetermined position of the X-ray detector. In another step, the predetermined position of the position marker is compared with a current position of the position marker and, in a further step, a relative position of the patient couch with respect to the X-ray source is corrected with the positioning aid such that the current position of the position marker is essentially equal to the predetermined position of the position.

In a first aspect, a method for determining an X-ray scan geometry according to claim <NUM> is provided. In a second aspect, a mobile X-ray imager according to claim <NUM> is provided.

Various features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:.

When introducing elements of various embodiments of the present embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

As discussed herein, various imaging contexts may exist where the patient is not to be moved or disturbed, such as a newborn in a neonatal intensive care unit (NICU) or other patients in intensive care units (ICUs) or burn units. To image such patients a mobile imaging system may be employed, including systems having a portable detector that is detached from the primary imaging base station and generally freely movable with respect to the imager and patient. In such instances, during imaging the detector may be placed below the patient in a compartment of the table or patient support (as opposed to being placed between the patient and patient support surface) and positioned by the operator based on a visual extrapolation of the X-ray path.

While such crude estimation may be sufficient for single exposure images, it is not typically sufficient for tomographic acquisitions, where a series (e.g., <NUM>, <NUM>, <NUM>, <NUM>) of images are acquired of a limited angular range (e.g., <NUM>°, <NUM>°, <NUM>°, <NUM>°, and so forth) so as to all three-dimensional (3D) reconstruction. A reconstruction algorithm creates an accurate 3D view of patient anatomy from data acquired at precisely known locations. In particular, such tomographic imaging processes typically need precise position and orientation information about the source focal spot and detector. The positions and orientations are either precisely controlled motion during acquisition, or are otherwise precisely determined as a result of a registration process. However, simple placement of the detector beneath the patient support surface typically does not provide sufficient position and orientation information for tomosynthesis imaging, potentially missing the anatomy of interest in some number of the views acquired from different angles.

In accordance with the present approach, to address these issues arising from the use of portable detectors in a tomography context, a compartment or chamber is provided beneath a patient support surface (such as a bed surface or table surface) on which the patient rests such that the patient support surface is between the patient and the detector. The compartment is configured to interface or dock with the portable detector such that the detector position with respect to landmarks on the support and the source-detector geometry is thereby determinable or known when the detector is in place. By way of example, in one implementation, housing landmarks are employed to register the position and orientation of the portable detector when docked in the compartment, such as via a provided docking mechanism or structure. In this manner, the problem of occlusion of the detector from camera views is handled by placing the detector and patient anatomy in coordination with the compartment or chamber in which the detector is docked. For example, ArUco markers can be applied on the patient support structure and served as optical landmarks viewed by a camera. Otherwise, methods known in the art of object recognition within images by utilizing color, shape, texture of the patient support can be used to determine the source-detector geometry. Landmarks may incorporate radiopaque materials so that the registration accuracy may benefit from analysis of the features cast in the acquired X-ray images.

With the preceding discussion of the present approach in mind, <FIG> depicts an imaging system that may be suitable for implementation of the present approach. In particular an X-ray system is represented and referenced generally by reference numeral <NUM>. In the illustrated embodiment, the X-ray system <NUM> is a digital X-ray system, such as an X-ray system. The depicted X-ray system <NUM> is designed both to acquire original image data and to process image data for display in accordance with present techniques. The X-ray system <NUM> may be a radiographic imaging system, including a system used to image a patient region from multiple angles, such as along a limited angular range so as to generate a three-dimensional representation.

In the embodiment illustrated in <FIG>, the X-ray system <NUM> is a mobile imaging system <NUM> that may be moved to a patient recovery room, an emergency room, a surgical room, a neonatal ward, or any other space to enable imaging of a patient <NUM> without transporting the patient <NUM> to a dedicated (i.e., fixed) X-ray imaging room. For the purpose of illustrating the present approach and to provide a real-world context, the present examples primarily focus on mobile X-ray imaging systems employing portable detectors for tomosynthesis imaging, although it should be understood that other imaging approaches using non-mobile systems and/or non-tomosynthesis applications may benefit from the present approach.

In the depicted example, the X-ray system <NUM> includes a mobile imager or mobile X-ray base station <NUM> and a portable digital X-ray detector <NUM> that is freely positionable with respect to the base station <NUM>. In the depicted example, an X-ray base station <NUM> of the mobile imaging system <NUM> has a wheeled base <NUM> to facilitate movement of the station <NUM>.

In the depicted example, a support arm <NUM> is provided in conjunction with a support column <NUM> to facilitate positioning of a radiation source <NUM> and collimator <NUM> with respect to the patient <NUM>. By way of example, one or both of the support arm <NUM> and support column <NUM> may be configured to allow rotation or movement of the radiation source <NUM> about one or more axes and/or along the lateral extent of the support arm <NUM>, such as to acquire images at different view angles relative to the patient <NUM>. The X-ray source <NUM> may be provided as an X-ray tube and may be provided in conjunction with a collimator <NUM> that may be automatically adjusted to shape or limit the X-ray beam incident on the patient <NUM> and detector <NUM>.

In a mobile imaging context, as discussed herein, the patient <NUM> may be located on a bed <NUM> (or gurney, table or any other support) between the X-ray source <NUM> and the portable detector <NUM> and subjected to X-rays that pass through the patient <NUM>. During an imaging sequence, the detector <NUM> receives X-rays that pass through the patient <NUM> and transmits imaging data to the base station <NUM>. The portable detector <NUM> in this example is in wireless communication with the base unit <NUM>, though in other examples communication may be completely or partially via a tethered (i.e., cable) connection. The base station <NUM> houses electronic circuitry <NUM> that acquires readout signals from the detector <NUM> and that may be processed to generate diagnostically useful images. In addition, the electronic circuitry <NUM> may provide and/or and control power to one or both of the X-ray source <NUM> (i.e., controlling activation and operation of the source <NUM>) and the wheeled base <NUM> (i.e., a movement system). In the depicted example, the base station <NUM> also has an operator workstation <NUM> and display <NUM> that facilitates user operation of the X-ray system <NUM>. The operator workstation <NUM> may include a user interface to facilitate operation of the X-ray source <NUM> and detector <NUM>. In one embodiment, the workstation <NUM> may be configured to function communicate on or through a network <NUM> of the medical facility, such as HIS, RIS, and/or PACS. In certain embodiments, the workstation <NUM> and/or detector <NUM> may wirelessly communicate with the network <NUM>. Algorithmic computations resulting in determination of source-detector geometry can be done all or in part on the workstation or other server nodes on the network.

As shown in the depicted example the patient support <NUM> includes a defined docking compartment <NUM> in which the detector <NUM> is positioned during imaging. In certain embodiments, the portable detector <NUM> engages with one or more tracks or docking mechanisms within the compartment <NUM> (or other docking framework) such that the engagement of the detector <NUM> within the docking framework rigidly secures the detector <NUM> in a known position (e.g., x, y, z - coordinates, polar coordinates, or other reference frame data) and/or orientation (e.g., roll, pitch, azimuth) with respect to one or more landmarks <NUM> (e.g., crosshairs, optical patterns, LED lights, and so forth) that may be visible on the patient facing surface of the support <NUM>. Thus, in this example, the detector <NUM> is not positioned between the support <NUM> and patient <NUM> but under a surface of the support <NUM>, with the position of the detector <NUM> when so engaged being determinable from the visible landmarks <NUM> that have a known spatial relationship to the docked detector <NUM>.

While <FIG> illustrates schematically aspects of the operation of a mobile X-ray imaging system <NUM>, <FIG> diagrammatically illustrates certain components of such a system and their interrelationship.

In the depicted example, the imager system <NUM> includes the X-ray source <NUM> connected to a power supply <NUM> that furnishes both power and control signals for examination sequences. In addition, in mobile imaging systems the power supply <NUM> may furnish power to a mobile drive unit <NUM> of the wheeled base <NUM>. The power supply <NUM> is responsive to signals from a system controller <NUM>. In general, the system controller <NUM> commands operation of the imaging system to execute examination protocols, such as tomosynthesis examination protocols, and to process acquired image data. In the present context, the system controller <NUM> also includes signal processing circuitry, typically based upon a general purpose or application-specific circuitry, associated memory circuitry for storing programs and routines executed by the computer, as well as configuration parameters and image data, interface circuits, and so forth. The system controller <NUM> may include or may be responsive to a processor <NUM>. The processor <NUM> receives image data from the detector <NUM> and processes the data to reconstruct an image of a subject. In addition, the processor <NUM> is configured to calculate or estimate a source-detector geometry (e.g., relative position and orientation), which may be relevant to image acquisition or reconstruction, based on visual sensor inputs and landmarks <NUM> corresponding to a docked detector <NUM>. With this in mind, the processor <NUM>, in accordance with the present approach may receive inputs from one or more visual sensor(s) <NUM> (e.g., cameras) of the imager system <NUM> to facilitate determination of a detector position and/or orientation relative to the source <NUM>, such as during a sequence of image acquisitions for tomosynthesis. In addition, as discussed herein, based upon the relative position of the source and the detector, the processor <NUM> is configured to control or adjust the radiation source <NUM> and/or collimator <NUM> over the course of a sequential X-ray image acquisition, such as may occur in tomosynthesis imaging.

In the implementation shown, the processor <NUM> is linked to a wireless communication interface <NUM> that allows wireless communication with the detector <NUM>, e.g., a portable detector. Further, the processor <NUM> may be linked to a wired communication interface <NUM> that allows communication with the detector <NUM> via a tether (e.g., a multi-conductor cable). The imager system <NUM> may also be in communication with a server providing part or all of the algorithmic computations leading to determination of the source-detector geometry. The processor <NUM> is also linked to a memory <NUM>, an input device <NUM>, and the display <NUM>. The memory <NUM> stores configuration parameters, calibration files received from the detector <NUM>, and lookup tables used for image data processing. The input device <NUM> may include a mouse, keyboard, or any other device for receiving user input, as well as to acquire images using the imager system <NUM>. The display <NUM> allows visualization of output system parameters, images, and so forth.

The detector <NUM> includes a wireless communication interface <NUM> for wireless communication with the imager system <NUM>, as well as a wired communication interface <NUM>, for communicating with the detector <NUM> when it is tethered to the imager system <NUM>. The detector <NUM> may also be in communication with a server. It is noted that the wireless communication interface <NUM> may utilize any suitable wireless communication protocol, such as an ultra wideband (UWB) communication standard, a Bluetooth communication standard, or an <NUM> communication standard, or any other suitable wireless communication standard. Moreover, the detector <NUM> is coupled or includes a detector controller <NUM> which coordinates the control of the various detector functions. For example, the detector controller <NUM> may execute various signal processing and filtration functions, such as for initial adjustment of dynamic ranges, interleaving of digital image data, and so forth. The detector controller <NUM> is responsive to signals from the system controller <NUM>, as well as the detection circuitry <NUM>. The detector controller <NUM> is linked to a processor <NUM> that in turn is linked to a memory <NUM>. The processor <NUM>, the detector controller <NUM>, and all of the circuitry receive power from a power supply <NUM>. The power supply <NUM> may include a battery. In some embodiments, the detector <NUM>, including the power supply <NUM>, may receive power from the power supply <NUM> when tethered to the imager system <NUM>.

In the depicted example the processor <NUM> is linked to detector interface circuitry <NUM>. In one embodiment, the detector <NUM>, which may be used in radiographic, fluoroscopic, tomographic, or other imaging operations, converts X-ray photons incident on its surface to lower energy (e.g., optical light) photons. The detector <NUM> includes a detector array <NUM> that includes an array of photodetector elements that generate responsive electrical signals in response to the light photons generated in this manner such that the electrical signals are representative of the number of photons or the intensity of radiation impacting individual pixel regions of the detector surface. Alternatively, the detector <NUM> may convert the X-ray photons directly to electrical signals (i.e., a direct conversion type detection mechanism). These electrical signals are converted to digital values by the detector interface circuitry <NUM>, which provides the values to the processor <NUM> to be converted to imaging data and sent to the imager system <NUM> to reconstruct an image of the features within a subject. Alternatively, the imaging data may be sent from the detector <NUM> to a server to process the imaging data.

With the preceding discussion of an imaging system <NUM> in mind, in accordance with the present approach a portable detector <NUM> is positioned and oriented with respect to a patient anatomy of interest and an X-ray emission source <NUM> of a mobile system X-ray imager <NUM> using a docking compartment <NUM> associated with externally visible landmark features. Aspects of this approach are depicted graphically in <FIG>. In the depicted example, the mobile imaging system <NUM> is configured for a tomosynthesis acquisition. As such, the X-ray source <NUM> is shown as being movable (here linearly displaced) between a series of view positions <NUM>, each at a different respective view position (i.e., angle) with respect to the patient <NUM> and detector <NUM>.

A patient <NUM> to be imaged, here a neonate, is depicted in an incubator <NUM>. In this example, it is undesirable to move the neonate, patient <NUM>, from the incubator for imaging. Likewise, this example illustrates an instance where it may be undesirable to move the patient <NUM> so as to position a detector <NUM> between the patient <NUM> and the support surface. Instead, as discussed herein, a docking compartment <NUM> is provided in which the detector <NUM> can be positioned without disturbing the patient. The docking compartment <NUM> may be configured or structured to mechanically register the detector <NUM> in a particular manner, such that when inserted properly, the detector <NUM> is rigidly fixed or held in a known orientation and position. Examples of mechanical structures that may be employed to mechanically register the detector <NUM> within the compartment include, but are not limited to, the geometry or shape of the compartment <NUM>, one or more guide rails or positioning features within the compartment <NUM>, and/or one or more engagement features or structures (e.g., complementary mating or engagement features <NUM>,<NUM>) provided by detector <NUM> and compartment <NUM>. Electronic or optical limit switches and/or sensors can inform the system controller <NUM> that detector engagement is complete. As a result, when the detector <NUM> is properly fitted in the compartment <NUM>, the detector position and orientation is known with respect to the patient support surface.

In the depicted example an optical sensor <NUM> (e.g., a camera), which may be provided on the mobile X-ray imaging system <NUM> as shown, views an alignment feature (e.g., landmark(s) <NUM>, such as cross hairs, LED lights, reflectors, and so forth) on the incubator <NUM>. The optical sensor <NUM> is mounted to the support column <NUM> with a known geometry relative to the X-ray source <NUM>. Multiple source locations <NUM> may be calculated from encoder values of the drive mechanism which translates the source <NUM>. Alternatively the optical sensor <NUM> may be provided separate from the system but so as to have a view of both the source <NUM> and landmarks <NUM>. Regardless of the location of the optical sensor(s) <NUM>, the sensor <NUM> has a view of the source <NUM> and/or landmarks from a calibrated vantage point that is known or determinable.

As discussed herein, based on the image data acquired from the optical sensor <NUM>, the relative position of the source <NUM> and the landmark(s) <NUM> is determined for a given tomographic image acquisition sequence. Likewise, the position and orientation of the patient <NUM> may be determined from such optical data. Due to the known relationship between the landmarks <NUM> and the position and orientation of the detector <NUM>, when the detector <NUM> is docked within the compartment <NUM> the relative position and orientation of the source <NUM> and the detector <NUM>, including the angle of the detector plane relative to the emission focal spot/ detector center axis, is also determinable.

For example, in accordance with one embodiment the known vantage of the optical sensor <NUM> allows relevant tomographic coordinates to be calculated during a scan of the patient <NUM> through application of one or more monocular or stereoscopic vision analysis routines or algorithms. In other implementations, additional robustness and accuracy may be provided by use of additional cameras, radiopaque markers or other depth sensing sensors. Thus, in these approaches, monocular or stereoscopic analysis of a series of camera image frames allows the source (e.g., tube) focal spot position and the landmark(s) <NUM> to be registered. Alternately, the camera is in known geometric relationship to the source by virtue of the mounting positions and encoder values of the tomographic drive mechanism.

Thus, in certain implementations, there is a relative position (i.e., three coordinates, x, y, and z) and orientation (i.e., three angles) of the tube focal spot, and compartment relative to some origin point defined for the scan. In addition, as noted above, the patient position may also be observed and, based on the relative source and detector position and orientation, it may be determined if an X-ray projection will fall onto the detector <NUM> when a directed-tomographic scan is initiated.

In one embodiment, a tomographic scan may be performed that utilizes the positional coordinates determined in this manner configure or adjust the radiation source and collimator opening, thereby allowing X-rays to be incident on the patient anatomy of interest and on the detector's active area. Each sequential exposure in the tomographic scan may be actuated in turn through this mechanism, i.e., collimation may be adapted for each image acquisition to accommodate the relative position and orientation of the source and detector. In addition, the position and orientation data may also be provided to the image reconstruction algorithm to improve or facilitate reconstruction of a 3D view of the patient anatomy.

Technical effects of the invention include the use of a spatially registered detector docking compartment to determine source and detector alignment in a patient imaging context. In certain implementations, sensors and/or cameras provide visual data that may be analyzed to determine a spatial relation between an X-ray source and landmarks provided on a patient support surface, where the landmarks have a known spatial relationship to a detector positioned beneath the patient support surface. This position and orientation information may, in turn be used to control collimation of the X-ray source during a tomographic scan.

Claim 1:
A method for determining an X-ray scan geometry comprising:
positioning a portable detector (<NUM>) within a docking compartment (<NUM>) provided in a patient support structure (<NUM>);
positioning a mobile X-ray imager (<NUM>) with respect to the patient support structure (<NUM>), wherein the mobile X-ray imager comprises an X-ray source (<NUM>) in a known geometric relationship to an optical sensor (<NUM>), and wherein the mobile X-ray imager is configured to move the X-ray source so as to acquire a sequence of images at different views during an image acquisition sequence;
analyzing a visual image generated by the optical sensor (<NUM>) of one or more landmarks (<NUM>) provided on a patient-facing surface of the patient support structure (<NUM>);
determining a source-detector geometry based on a known spatial relationship between the one or more landmarks (<NUM>) and the docking compartment; and
based on the source-detector geometry, controlling operation of a collimator (<NUM>) of the mobile X-ray imager (<NUM>) during the image acquisition sequence.