CT scanner and scanning method for performing a brain scan

Abstract

A CT scanner for performing a brain scan performs a low-dose 3D scan in a first field of view. By analyzing the low-dose 3D scan, for example using landmark detection, a proposed field of view for a full-dose 3D brain scan is obtained. A representation of the proposed field of view is displayed and a final field of view is generated as the proposed field of view or an updated version of the proposed field of view provided by a user of the CT scanner.

Description

Technical Field

[0001] The present invention relates to a CT scanner and a scanning method for performing a brain scan.

Background Art

[0002] CT image medical imaging is becoming an increasingly important tool in the accurate analysis and evaluation of subjects / patients.

[0003] Proper patient positioning is one of the most important considerations in medical imaging, particularly CT imaging, to ensure a high-quality scan. In head CT imaging (head CT), quality is related to the diagnostic modality of the scan, e.g., diagnostic utility, and preferably the dose exposure to the patient, which is minimized or reduced.

[0004] When performing a CT scan of the human brain, the operator's task is to position the patient and plan the scan so that the entire brain is within the field of view of the scan, while at the same time, the eyes are optimally shielded from direct radiation. Some CT scanners, in particular, enable tilting of the gantry of the CT system to support an optimal scan of the patient in situations where the patient's condition does not allow tilting the head in the required direction.

[0005] Another task is to ensure that the resulting scan is reformatted into a standard view that is easy for a radiologist to read. Official standards for medical imaging techniques such as head CT provide guidelines for proper medical scans, for example, to generate clinically useful and reproducible medical images. Non-compliance with the guidelines may result in a decrease in the quality of the images generated by the scan procedure and may lead to unnecessary radiation exposure to anatomical features such as high-risk organs or the lens of the eye. Similarly, compliance with the guidelines generates high-quality images, and the guidelines typically ensure that the images contain diagnostically sensitive or useful structures.

[0006] These guidelines are typically defined with respect to a series of anatomical landmarks. For example, one set of guidelines for head CT published by the American Association of Physicists in Medicine defines the recommended scan angle as "parallel to the line generated by the supraorbital ridge and the inner table of the posterior margin of the foramen magnum." Figure 1 shows, for example, the position of the maxilla of the occipital bone (this is the midpoint of the posterior margin of the foramen magnum), and the points on the supraorbital ridges of the left (le) and right (re) eyes relative to the skull, as well as the corresponding CT image of the subject. Summary of the Invention Problems to be Solved by the Invention

[0007] Planning a CT scan of the brain is particularly difficult because there is a small margin during cropping of the lower part of the brain that includes the eye orbits within the field of view. None of these should be done in an optimal scan, but to ensure complete brain coverage, most technicians add a margin to the field of view and accept partial or complete irradiation of the eyes (in violation of the guidelines) during the scan planning. This situation is complicated by the fact that currently the scan planning is based on a 2D scout scan (usually a lateral projection).

[0008] Therefore, there is a need for an improved scan procedure that enables reducing the radiation exposure of the eyes during a brain scan. Means for Solving the Problems

[0009] This invention is defined by the claims.

[0010] According to an embodiment according to one aspect of the present invention, a CT scanner for performing a brain scan of a patient, a gantry, an X-ray tube and a detector within the gantry, a camera system for detecting the position and orientation of the patient's head with respect to the CT scanner, A display, and a controller, wherein the controller derives a first field of view from the detected head position and orientation; controls the CT scanner to perform a low-dose 3D scan in the derived first field of view; analyzes the result of the low-dose 3D scan to derive a proposed field of view for a full-dose 3D brain scan; displays a representation of the proposed field of view; determines a final field of view as the proposed field of view or an updated version of the proposed field of view provided by the user of the CT scanner; and is configured to perform the above steps, a controller; A CT scanner having the above components is provided.

[0011] This scanner uses a low-dose 3D scan (i.e., a so-called scout scan or service scan) to enable adjustment of the field of view for a final full / regular-dose scan. The low-dose 3D scan enables adjustment of the field of view so that the desired brain region is covered without irradiating the eyes.

[0012] The system performs an automatic analysis of the low-dose scan to provide a recommended field of view that can be accepted or modified by the operator. The recommended field of view is the result of a specific patient position, gantry position, and scan plan.

[0013] The availability of a 3D low-dose scan (for creating a 3D service image) enables detection of anatomical landmarks in this low-dose 3D image so that the head orientation can be determined. The complete 3D orientation of the head can be determined not only by rotation around one axis, as can be achieved with a 2D lateral service image.

[0014] For example, the low dose is achieved with an X-ray tube current of about 2 mAs and a corresponding radiation intensity CTDI-vol of about 0.2 mGy. For example, the full / regular dose is achieved with an X-ray tube current of about 300 mAs and a corresponding radiation intensity CTDI-vol of about 50 to 60 mGy. Thus, the low dose has, for example, a tube current in the range of 0.2 to 5% of the full / regular dose and a radiation intensity in the range of 0.1% to 2% of the full / regular dose.

[0015] By incorporating a camera system for detecting the position and orientation of a patient's head relative to a CT scanner and appropriately configuring a controller, a first field for a low-dose scan can be derived from the detected head position and orientation. This first field of view for the low dose can already be aimed at excluding the eyes. Thus, the camera system enables a two-step approach starting from a rough estimate of the head orientation derived from an optical camera image and then refined based on a 3D CT scout image.

[0016] In addition to avoiding eye radiation, the analysis may be used (e.g., based on AI) to detect foreign metal objects. The gantry can then be tilted or the plane of the axial slice reconstruction can be adapted so that foreign objects are avoided in a given axial field of view.

[0017] The proposed field of view is part of the overall scan plane. The scan plan includes a definition of the scan length defined by the initial and final table positions. It also includes a definition of a box around the target anatomical structure that defines the field of view used for reconstruction.

[0018] The first field of view includes, for example, the brain and eyes, and the final field of view excludes the eyes. Thus, the low-dose plan is used when the eyes are (e.g., partially) within the field of view but the final field of view excludes the eyes.

[0019] The controller is configured to determine the final field of view, for example, by setting the gantry tilt angle. In the case of a scanner with an adjustable gantry angle, this is one of the parameters that can be selected based on the analysis of a low-dose scan. The gantry tilt in such cases can also be considered as part of the scan plan for the purposes of this application.

[0020] If the scanner is not equipped with a gantry tilt function, or if the patient's position (direction of the head) does not allow fixing the eye problem within the field of view even with gantry tilt, there may be an alternative solution to warn the operator to reposition the patient's head.

[0021] The controller is configured to analyze the results of a low-dose 3D scan, for example, to identify landmarks on the skull. These landmarks identify the positions of different regions of the head within the initial field of view and can be used to determine the direction of the head. Image detection methods (using regular dosages) for detecting landmarks on the skull are known.

[0022] The landmarks can include the upper edges of the left and right eye sockets, the position of the occipital bone, and the top of the skull.

[0023] The upper edges of the eye sockets and the occipital bone make it possible to determine the direction and position of the head. The plane defined by these landmarks establishes the lowest axial slice of an optimally planned brain scan. The top of the skull makes it possible to determine the necessary limits of the field of view.

[0024] The controller is configured to derive a proposed field of view in the form of a rectangular 3D box that surrounds the brain. This box is intended to avoid irradiating the eyes. The controller is, a box having axes parallel to the CT scanner coordinate system, or a box tilted around one axis compared to a box having axes parallel to the CT scanner coordinate system configured to derive a rectangular 3D box as described above.

[0025] These different box definitions are suitable for different scanners, for example, with or without the ability to provide gantry tilt.

[0026] The controller may be configured to freely rotate the box in 3D space compared to a box having axes parallel to the CT scanner coordinate system in order to generate a diagnostic standard view representation. The box freely rotated in 3D space can be used, for example, to provide a modified representation of the scan as preferred by a radiologist for diagnostic reading.

[0027] The controller is further configured to generate, for example, images of axial up-slices and axial down-slices for the final field of view from a low-dose 3D scan.

[0028] These images obtained from a low-dose scan typically do not show sufficient information for diagnostic purposes. However, considering the high contrast between bone and soft tissue, they show fairly well the gross anatomical structure. The user can, for example, view these images to verify that the anatomical structure is included as expected by a radiologist. The axial view is a common representation used for diagnostic reading.

[0029] The present invention also relates to a method for preparing a patient for a CT brain scan, comprising controlling a camera system to detect the head position and orientation of the patient with respect to the CT scanner; deriving a first field of view from the detected head position and orientation; controlling the CT scanner to perform a low-dose 3D scan in the derived first field of view; analyzing the results of the low-dose 3D scan to derive a proposed field of view for a full-dose 3D brain scan; displaying the proposed field of view to a user of the CT system; determining a final field of view as the proposed field of view or an updated version of the proposed field of view provided by the user; also provides a method having.

[0030] The method can further include analyzing the results of a low-dose 3D scan to identify landmarks on the skull such as the upper edges of the left and right eye sockets, the occipital bone position, and the top of the skull.

[0031] The method may comprise deriving the proposed field of view in the form of a rectangular 3D box surrounding the brain, the method being a box having axes parallel to the CT scanner coordinate system, or a box tilted about one axis as compared to a box having axes parallel to the CT scanner coordinate system having the step of deriving a rectangular 3D box such as.

[0032] The method can include freely rotating the box in 3D space as compared to a box having axes parallel to the CT scanner coordinate system to generate a diagnostic standard view representation.

[0033] The method may include controlling a camera system to detect the position and orientation of a patient's head relative to the CT scanner, the controller being further configured to derive a first field of view from the detected head position and orientation.

[0034] The invention also provides a computer program comprising computer program code adapted when the program is run on a computer to perform the method as defined above.

[0035] Another concept is a CT scanner for performing a brain scan,

[0036] a gantry, and

[0037] the X-ray tube and detector within the gantry,

[0038] a camera system for detecting the position and orientation of the patient's head relative to the CT scanner,

[0039] a display,

[0040] a controller, the controller being configured to

[0041] analyze the position and orientation of the head to determine a required field of view and / or movement of the patient's head that may be required, use the display to output to the user a representation of the required field of view and / or required movement of the patient's head, and execute, a CT scanner having a controller.

[0042] The camera system is, for example, an overhead 2D or 3D (depth) camera mounted on the patient's bed, or one or more cameras integrated with the gantry. This is used to predict the desired tilt of the head and guide the operator in optimal examination preparation. This can be achieved by tilting the CT gantry or by guiding the operator to orient the patient's head according to a calculated tilt. In both cases, the brain plane and the CT gantry axis are parallel, and the field of view of the brain scan can be determined to exclude the eyes for both the low-dose scan and the actual scan, or to avoid the need for a low-dose scan altogether.

[0043] These and other aspects of the invention will be apparent from, and will be elucidated with reference to, the embodiments described hereinafter.

[0044] To better understand the present invention and to more clearly show how it may be practiced, reference is now made, by way of example only, to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 4c

Figure 5

Figure 6

Figure 7a

Figure 7b

Mode for Carrying Out the Invention

[0046] The present invention will be described with reference to the drawings.

[0047] The detailed description and specific examples illustrate exemplary embodiments of apparatus, systems, and methods and are for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems, and methods of the present invention will be better understood from the following description, the appended claims, and the accompanying drawings. It is to be understood that the figures are merely schematic and are not drawn to scale. Also, it is to be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0048] The present invention provides a CT scanner and method for performing a brain scan. A low-dose 3D scan is performed in a first field of view. By analyzing the low-dose 3D scan, for example, using landmark detection, a proposed field of view is obtained for a full (i.e., regular) dose 3D brain scan. A representation of the proposed field of view is displayed and a final field of view is generated as an updated version of the proposed field of view provided by the user of the proposed field of view or the CT scanner.

[0049] Accordingly, the present invention provides an automated analysis of head anatomical structures from low-dose 3D scans, preferably resulting in an automated scan plan based on a proposed field of view in the form of a 3D scan box. In the case of a CT scanner having gantry tilt control, the proposed scan plan includes guidance regarding the gantry tilt angle of the CT system for an optimal scan.

[0050] Before the modified functions provided by the present invention are described, the basic well-known components of a CT scanner are first described.

[0051] FIG. 2 schematically shows a known CT system 100 including a CT scanner 102. The CT scanner 102 generally includes a stationary gantry 104 and a rotating gantry 106 rotatably supported by the stationary gantry 104 and rotating about the z-axis around an examination region 108. A subject support 110, such as a treatment table, supports an object or subject within the examination region 108.

[0052] A radiation source 112 such as an X-ray tube is rotatably supported by a rotating gantry 106, rotates together with the rotating gantry 106, and emits radiation that traverses the examination region 108.

[0053] The radiation-sensitive detector array 114 defines a range of an angular arc on the opposite side of the radiation source 112 across the examination region 108. The radiation-sensitive detector array 114 detects radiation traversing the examination region 108 and generates an electrical signal (s) (projection data) indicative thereof.

[0054] The detector array 114 can include a single-layer detector, a direct conversion photon counting detector, and / or a multi-detector. The direct conversion photon counting detector can include a conversion material such as CdTe, CdZnTe, Si, Ge, GaAs, or other direct conversion materials. An example of a multi-layer detector includes a double-decker detector such as the double-decker detector described in U.S. Patent No. 7,968,853 B2, filed Apr. 10, 2006, and titled "double Decker Detector for Spectral CT".

[0055] The reconstructor 116 of the imaging system 102 receives projection data from the detector array 114 and reconstructs one or more CT images from the projection data. The reconstructed CT images can include one or more 2D or 3D images. The mechanism for reconstructing one or more CT images from projection data is well established in the art.

[0056] The controller 118 is configured to process the CT images generated by the imaging system 102. The controller 118 can include a processor 120 (e.g., a microprocessor, a controller, a central processing unit, etc.) and a computer-readable storage medium 122 including a transient medium such as a physical memory device, excluding non-transient media.

[0057] The computer-readable memory medium 122 may include instructions 124 for processing an image as described below, including detecting landmarks in a low-dose (survey) scan and executing a scan plan. The processor 120 is configured to execute the instructions 124. The processor 120 may further be configured to execute one or more computer-readable instructions carried by a carrier wave, a signal, and / or other transient media.

[0058] However, instead of the processor 120 executing instructions for performing the methods described herein, the processor may alternatively comprise a fixed-function circuit (such as, for example, a properly programmed FPGA) for performing the methods described.

[0059] In some examples, the controller may also function as an operator console. The controller 118 includes a human-readable output device such as a monitor and an input device such as a keyboard, a mouse, etc. Software resident on the controller 118 enables an operator to interact with and / or operate the scanner 102 via a graphical user interface (GUI) or otherwise.

[0060] In a variant, a separate controller (not shown) may function as an operator console and may comprise the aforementioned related operator console elements.

[0061] FIG. 2 also shows a camera 130 (discussed below) and a display 132 for presenting the scan results, as well as the scan plan results (so-called survey or scout scan results) to the operator.

[0062] FIG. 3 shows a method 300 for preparing a patient for a CT brain scan, for example using the system of FIG. 2.

[0063] The first step in the application of the present invention is the acquisition of a low-dose (or ultra-low-dose) 3D scan of the patient at step 302. This is performed in a first field of view. The first field of view may be permitted to include irradiation of the patient's eyes due to the ultra-low dose, but measures may be taken to prevent irradiation of the patient's eyes even in the low-dose field of view, as described below.

[0064] For example, a low dose is achieved with an X-ray tube current of about 2 mAs and a corresponding radiation intensity CTDI-vol of about 0.2 mGy. For example, a full / regular dose is achieved with an X-ray tube current of about 300 mAs and a corresponding radiation intensity CTDI-vol of about 50 to 60 mGy. Thus, the low dose has, for example, a tube current in the range of 0.2 to 5% of the full dose and a radiation intensity in the range of 0.1% to 2% of the full dose.

[0065] At step 304, the results of the low-dose 3D scan are analyzed, and in particular, a proposed field of view for a full-dose 3D brain scan is derived. Analysis of the low-dose scan enables analysis of the anatomical structure of the head. This can be done by various known medical image analysis techniques. One example is the detection of landmarks on the skull as shown in FIG. 1 (the upper margins of the left and right eye sockets and the upper jaw of the occipital bone).

[0066] The analysis at step 304 includes, for example, the detection of these three landmarks. This is sufficient for analysis of the 3D rotational state of the head.

[0067] Examples of approaches for landmark detection are described, for example, in Hrishikesh Deshpande, Axel Saalbach, Tim Harder, Stewart Young, Thomas Buelow, ”Deep learning for detection of landmarks in head CT images and automatic qual” (SPIE 11596, Medical Imaging 2021: Image Processing, 115960N (February 15, 2021); https: / / doi.org / 10.1117 / 12.2581810.). Landmark detection is also described in WO2022 / 023228.

[0068] The plane defined by these three landmarks establishes the lowest axial slice of an optimally planned brain scan. To define the scan plan, preferably, in step 304, additional landmarks at the top of the skull are also detected.

[0069] Based on the derived anatomical structure of the head, in step 306, a rectangular 3D box surrounding the brain is derived. This rectangular box can be considered to represent the proposed field of view for the final full-dose scan.

[0070] The proposed field of view is displayed to the user of the CT system in step 306. In this way, based on the scan box and the 3D low-dose scan, the operator receives a visual representation of the scan plan in step 308. This visual representation shows the expected scan results when the scan is performed using the current patient position, gantry tilt (if adjustable), and other parameters of the scan plane defining the field of view (the shape of the scan box). The expected results are presented in real time so that the user can manipulate the scan box. This manipulation can be achieved by a graphical user interface.

[0071] Next, in step 310, the final field of view is derived. It may be the proposed field of view (if approved by the user), or an updated version of the proposed field of view provided by the user.

[0072] As described above, a rectangular box is derived as the field of view. As shown in FIG. 4, two different box types can be derived.

[0073] FIG. 4a shows a box 400 having axes parallel to the scanner coordinate system. Such a box can be proposed for a system that does not allow gantry tilt.

[0074] FIG. 4b shows a box 402 tilted about one axis to optimize the tight enclosure of the brain. The single degree of freedom is selected to correspond to the gantry tilt angle. It corresponds to the angle at which the patient nods. It can be proposed for a system that allows gantry tilt. The tilt angle between the scan boxes 400 and 402 represents the proposed gantry tilt applied to the scanner hardware.

[0075] The rectangular box can also be manipulated to provide a standard view for diagnostic purposes. FIG. 4c shows a rectangular box 404 freely rotated in 3D space to optimally capture the anatomical structure of the brain. This box represents a corrected representation of the final scan result preferred by a radiologist for diagnostic reading.

[0076] FIG. 5 shows a visual representation of the scan plan provided in step 308.

[0077] Box 500 (not tilted) and Box 502 (tilted) are overlaid on the 2D synthetic lateral scout scan. The synthetic scout scan is derived from the 3D low-dose scan. Starting from these scan box representations, the operator can determine whether a gantry tilt should be applied. Also, the starting and ending points (upper and lower positions of the scan box) can be adapted by the user.

[0078] In addition to the visual scan box representation shown in FIG. 5, the 3D low-dose scan enables the generation of axial slices representing the upper and lower slices of the expected final scan result, based on selections made by the operator.

[0079] These results can be adapted to the operator's scan selection without gantry tilt (Box 400), with gantry tilt (Box 402), and are presented in a reformatted manner for transfer to the radiologist (Box 404).

[0080] FIG. 6 shows examples of axial slices obtained from the 3D low-dose scan. FIG. 6a shows the simulation results of a scan performed according to scan box 400, FIG. 6b shows the simulation results of a scan performed using a tilted gantry according to scan box 402, and FIG. 6c shows the simulation results of a scan reformatted according to scan box 404.

[0081] Anatomically registered reformats of scans are clinically important for diagnostic radiography. Measurements such as aspect scores for rapid assessment of stroke severity rely on symmetric representations of the brain's anatomical structure. Manual reformatting requires valuable time for the radiologist.

[0082] As described above, the most accurate way to align the brain plane and the gantry is to tilt the gantry so that its axis is parallel to the head tilt measured during the 3D low-dose scan. However, not all CT devices provide the possibility to tilt the gantry. In the absence of this feature, the only opportunity to align the brain plane and the gantry is to manually change the position of the head, for example, by using a cushion or different types of head supports.

[0083] This manual procedure is mainly done by eye, without direct feedback regarding accurate alignment, and is mostly done before acquisition of the low-dose scan. To ensure that the new head tilt actually conforms to the gantry axis, for example, an additional low-dose scan is required, which again exposes the entire head, including the eyes, to radiation.

[0084] To prevent even the eyes from being irradiated during the low-dose scan, the correction utilizes a camera system to determine the field of view of the low-dose scan. In particular, an overhead depth camera, schematically shown as 130 in FIG. 2, may be mounted on the patient treatment table to predict the desired tilt of the head and guide the operator in optimal examination preparation.

[0085] This can be achieved by tilting the CT gantry if possible, or by guiding the operator to orient the patient's head according to the calculated tilt. In both cases, the brain plane and the CT gantry axis are parallel, and the field of view of the brain scan can be determined to exclude the eyes for both the low-dose scan and the actual scan.

[0086] The depth map collected by the depth camera provides information about the height of every part of the body. Usually, it is possible to detect different points on specific surface parts of the face, such as above the eyebrows, nose, lips, chin, etc., by using a landmark detection algorithm that operates on color, gray, depth, or IR images.

[0087] Standard 3D cameras typically offer the possibility to acquire both a color image and a depth image simultaneously. With appropriate calibration, surface landmarks detected from the color image can be mapped to the depth image as they are mostly unobstructed by the face for patient safety reasons and thus provide reliable information about the depth of these specific points. By comparing the depths of different landmarks with each other, the tilt of the entire head can be calculated.

[0088] Figures 7a and 7b show images of the head of an exemplary subject acquired with an overhead camera having respective landmarks marking the eyebrows, eyes, nose, lips, and the outline of the face. The detected landmarks are visualized, for example, as a color overlay (represented in black and white in Figures 7a and 7b) on the grayscale version of each image.

[0089] Different head nodding angles are shown in Figures 7a and 7b. For example, different colors are used to represent specific parts of the face. After mapping these points to the respective depth data, the depth values of these fixed points can be compared with each other. From this depth information, a previously learned digital 3D head model can be adapted to the landmarks that serve as a basis for calculating the angle of the brain plane and deriving the optimal tilt of the head.

[0090] Once fitted to the depth data, the head model automatically enables the calculation of the plane separating the eyes from the brain. For this purpose, the same landmarks above the eyes and below the skull derived from the low-dose scan described above can be used.

[0091] To reduce or avoid the exposure of the ocular lens, the scan angle should be parallel to the line generated by the supraorbital ridge and the inner table of the posterior margin of the foramen magnum. By comparing the tilt angle of the resulting plane with the axis of the gantry, the corrections that need to be made can be determined. If they are already parallel, the patient and the gantry can remain in their actual positions. If a distinct tilt angle is detected, there are two possibilities to correct it. If the CT apparatus tilts the gantry, the gantry can be moved so that both the head and the gantry are perfectly aligned. If no gantry tilt is provided, the head needs to be manually moved, for example, by replacing the cushion or the headrest.

[0092] Visual guidance on how to orient the head to match the desired tilt can be provided to the operator in real time by a computer display placed in the vicinity of the gantry. In another setup, the head can be automatically repositioned by moving the actuator that holds the headrest or by inflating or deflating an inflatable cushion under the patient's head until the position is correct.

[0093] Since the face landmark detection and fitting of the digital head model operate in real time, it is possible to instantaneously check the accuracy of the position. Thus, the head can be moved until the system indicates an appropriate tilt angle. In this way, real-time guidance can be provided to the operator. When the orientation of the head matches the gantry axis, the defined plane can be used to define the end of the scan range so that the entire eye, rather than the entire brain, is part of the field of view.

[0094] In another example, the head direction is derived directly from the relative positions of landmarks in the color image without the need for depth data. This can be achieved, for example, by learning the inclination of the brain plane from images taken in different head directions. Due to the camera's projection geometry, the relative positions of face landmarks in the color image depend on the current head direction.

[0095] Accordingly, the camera system starts with a rough estimate of the head direction derived from the optical camera image, enabling a two-step approach, which is then refined based on the 3D CT scout image. Alternatively, the 3D scout image can be replaced with a 2D scout image.

[0096] The camera image is used to analyze the direction of the patient's head. This information can often be used to reposition the patient. However, in many cases, for example, in trauma patients, optimal patient positioning is not possible. Therefore, based on the head direction estimated by the camera system, the optimal gantry tilt angle is calculated and applied to the scanner. Based on the optical camera image, this first tilt is a rough approximation of the tilt angle applied to the clinical scan. Since this step does not involve the application of ionizing radiation, the operator can stay with the patient in the scanner room and ensure the patient's safety while the gantry is being tilted.

[0097] The 3D low-dose scan is only performed after the application of the gantry tilt. Also, the scan range of the low-dose scan can be restricted based on the anatomical structure analysis from the optical camera image. This helps to avoid exposing the eyes to ionizing radiation during the low-dose scan.

[0098] After the low-dose scan is acquired, the resulting 3D scout image can be analyzed to derive a more accurate estimate of the patient's head anatomical structure. Based on the 3D scout, the gantry tilt can be refined before the acquisition of the clinical scan.

[0099] The provision of the camera system also enables additional features to be implemented to better enable 3D low-dose scans.

[0100] (i) The shape and size of the body can be evaluated to provide an optimized dose level and dose modulation profile for 3D low-dose scans.

[0101] (ii) The start and end positions of the 3D low-dose scan can be defined, not only for the head region and tilt.

[0102] (iii) The optimal treatment table height for 3D low-dose scans can also be derived to place the target anatomical structure as close as possible to the isocenter for optimal image quality.

[0103] The above example of the camera system still utilizes an initial low-dose scan. However, alternative embodiments of the camera system can completely avoid low-dose scans by using only optical analysis to determine the required field of view.

[0104] In an additional enhancement, an AI model for the detection of foreign metal objects can be applied to 3D low-dose scans. The results can be used to change the plane of axial image acquisition. Axial slices of the head's anatomical structure - and other anatomical structures - are acquired in the patient's clinical routine. If a foreign object is detected in such a case, the availability of 3D information using 3D scout images can facilitate the generation of a 3D model of the foreign object present in the field of view. Taking this information into account, the gantry can be tilted, or the plane of axial slice reconstruction can be adapted so that the foreign object is avoided in a given axial field of view. Thus, the radiologist can view the anatomical structure of interest with the least possible amount of artifacts resulting from the foreign object.

[0105] With additional enhancements, the accuracy of the scan plan and patient positioning can be aggregated over a number of scans and collected in a database. This information can be presented on a dashboard for educational and training purposes to enable technicians to gain insights into the most common positioning and scan plan issues.

[0106] Variations to the disclosed embodiments can be understood and effected by persons skilled in the art in carrying out the claimed invention, from a study of the drawings, disclosure, and appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0107] Functions implemented by a controller can be implemented by a single processor or by a plurality of discrete processing units that may be considered to make up a "controller". Such processing units may in some cases be remote from each other and may communicate with each other in a wired or wireless manner.

[0108] The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used advantageously.

[0109] A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless electrical communication systems.

[0110] It should be noted that when the term "adapted to" is used in the claims or description, the term "adapted to" is intended to be equivalent to the term "configured to". When the term "apparatus" is used in the claims or description, the term "apparatus" is intended to be equivalent to the term "system" and vice versa.

[0111] No reference signs in the claims shall be construed as limiting the scope.

Claims

1. A CT scanner for performing a brain scan of a patient, comprising: a gantry, an X-ray tube and a detector within the gantry, a camera system for detecting the position and orientation of the patient's head relative to the CT scanner, a display, a controller, the controller being configured to: derive a first field of view from the detected head position and orientation; control the CT scanner to perform a low-dose 3D scan in the derived first field of view; analyze the results of the low-dose 3D scan to derive a proposed field of view for a full-dose 3D brain scan; display a representation of the proposed field of view; and determine a final field of view as the proposed field of view or an updated version of the proposed field of view provided by a user of the CT scanner. A controller configured to perform the above steps, and A CT scanner having the same.

2. The scanner according to claim 1, wherein the first field of view includes the brain and eyes, and the final field of view excludes the eyes.

3. The scanner according to claim 1 or 2, wherein the controller is configured to determine the final field of view by setting an angle relative to the tilt of the gantry.

4. The scanner according to any one of claims 1 to 3, wherein the controller is configured to analyze the results of the low-dose 3D scan to identify landmarks on the skull.

5. The scanner according to any one of claims 1 to 4, wherein the controller is configured to derive a proposed field of view in the form of a rectangular 3D box surrounding the brain.

6. The controller is configured to derive a rectangular 3D box such as: a box having axes parallel to the CT scanner coordinate system, or a box tilted around one axis compared to a box having axes parallel to the CT scanner coordinate system. The scanner according to claim 5.

7. The scanner according to claim 6, wherein the controller is configured to freely rotate the box in 3D space compared to a box having axes parallel to the CT scanner coordinate system to generate a diagnostic standard view representation.

8. The scanner according to any one of claims 1 to 7, wherein the controller is further configured to generate images of axial slices and axial down slices for the final field of view from the low-dose 3D scan.

9. A method of preparing a patient for a CT brain scan, comprising: Controlling a camera system to detect the head position and orientation of the patient with respect to a CT scanner; Deriving a first field of view from the detected head position and orientation; Controlling the CT scanner to perform a low-dose 3D scan in the derived first field of view; Analyzing the results of the low-dose 3D scan to derive a proposed field of view for a full-dose 3D brain scan; Displaying the proposed field of view to a user of the CT system; Determining a final field of view as the proposed field of view or an updated version of the proposed field of view provided by the user. A method.

10. The method according to claim 9, further comprising analyzing the results of the low-dose 3D scan to identify craniofacial landmarks such as the upper edges of the left and right eye sockets, the occipital bone position, and the top of the skull.

11. The method includes deriving a proposed field of view in the form of a rectangular 3D box surrounding the brain, the method comprising: A box having axes parallel to the CT scanner coordinate system, or A box tilted about one axis compared to a box having axes parallel to the CT scanner coordinate system. The method according to claim 9 or 10, comprising deriving a rectangular 3D box such as.

12. A computer program comprising computer program code adapted to perform the method according to any one of claims 9 to 11 when the program is executed on a computer.

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