System and method for collimator screening in computed tomography systems - Patents.com

Abstract

To provide a method for verifying aperture positions of a pre-patient collimator of a computed tomography (CT) imaging system.SOLUTION: The method includes obtaining data collected by an X-ray measurement device having detector elements subjected to X-rays emitted from an X-ray source of the CT imaging system with the pre-patient collimator at an expected aperture position, calculating a measured collimator aperture position for the pre-patient collimator on the basis of the obtained data, comparing the measured collimator aperture position to a system specification for the expected aperture position for the CT imaging system, and generating an output on the basis of the comparison of the measured collimator aperture position to the system specification.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The subject matter disclosed herein relates to medical imaging systems, and more particularly, to collimator screening. [Background technology]

[0002] In computed tomography (CT), x-rays are propagated through a subject of interest, such as a patient, and portions of the x-rays impinge on a detector where image data is collected. In digital x-ray systems, photodetectors generate signals that represent the amount or intensity of radiation that impinges on discrete pixel areas of the detector surface. These signals can then be processed to form images that can be displayed for review. Images generated by such systems may enable internal structures and organs within the patient's body to be identified and examined. In CT systems, as the gantry is displaced about the patient, a detector array, which includes a series of detector elements or sensors, generates similar signals through various positions, allowing a volumetric reconstruction to be obtained. Summary of the Invention [Problem to be solved by the invention]

[0003] CT imaging systems may include a pre-patient collimator to ensure that the subject of interest receives the intended dose. The collimator blades of the pre-patient collimator are adjusted in front of the x-ray source to form the appropriate opening or aperture to transmit the x-rays for the scan as set by the operator. It is important that the collimator blades open correctly and with precision to the intended aperture because even slight misalignment can result in substantial dose mismatch to the subject of interest. [Means for solving the problem]

[0004] Summarized below are some embodiments that are consistent with the scope of the originally claimed subject matter. These embodiments are not intended to limit the scope of the claimed subject matter, but are merely intended to provide a brief summary of possible forms of the subject matter. Indeed, the subject matter may encompass a variety of forms, which may be similar to or different from the embodiments set forth below.

[0005] In one embodiment, a method for verifying an aperture position of a pre-patient collimator of a computed tomography (CT) imaging system is provided. The method includes obtaining data collected by an x-ray measurement device having detector elements exposed to x-rays emitted from an x-ray source of the CT imaging system with the pre-patient collimator positioned at an expected aperture position. The method also includes calculating an actual collimator aperture position for the pre-patient collimator based on the obtained data. The method further includes comparing the actual collimator aperture position against a system specification for expected aperture positions for the CT imaging system. The method also includes generating an output based on the comparison of the actual collimator aperture position against the system specification.

[0006] In another embodiment, a method for verifying an aperture position of a pre-patient collimator of a CT imaging system including an x-ray source and a radiation detector is provided. The method includes acquiring air scan data by emitting x-rays from an x-ray source toward a radiation detector with the pre-patient collimator positioned at various expected aperture positions. The method also includes calculating respective widths of respective normalized intensity distribution profiles for the pre-patient collimator at the various expected aperture positions based on the acquired air scan data. The method further includes converting the respective widths to respective doses using a transfer function. The method includes determining respective dose error estimates at the various expected aperture positions based on the respective doses. The method further includes comparing the respective dose error estimates against respective acceptable dose thresholds for the various expected aperture positions. The method further includes generating an output based on the comparison of the respective dose error estimates against the respective acceptable dose thresholds.

[0007] In yet another embodiment, a CT imaging system is provided. The system includes an X-ray source configured to emit X-rays during operation. The system also includes a radiation detector configured to receive the X-rays. The system further includes a pre-patient collimator disposed between the X-ray source and the radiation detector and configured to shape a beam of X-rays through an aperture. The system further includes a processing circuit configured to perform operations. The operations include acquiring air scan data by emitting X-rays from the X-ray source toward the radiation detector with the pre-patient collimator positioned at various expected aperture positions. The operations also include calculating respective widths of respective normalized intensity distribution profiles for the pre-patient collimator at the various expected aperture positions based on the acquired air scan data. The operations further include converting the respective widths to respective doses using a transfer function. The operations include determining respective dose error estimates at the various expected aperture positions based on the respective doses. The operations also include comparing the respective dose error estimates against respective acceptable dose thresholds for the various expected aperture positions. The operations further include generating an output based on a comparison of each dose error estimate against a respective acceptable dose threshold. [Brief description of the drawings]

[0008] These and other features, aspects, and advantages of the disclosed subject matter will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which like characters represent like parts throughout.

[0009] [Figure 1] FIG. 1 is a combination schematic and block diagram of a computed tomography (CT) imaging system as discussed in this document. [Diagram 2] 1 is a schematic diagram (eg, viewed in the XY plane) of an X-ray source and a multi-row X-ray detector according to aspects of the present disclosure. [Diagram 3] 1 is a schematic diagram (eg, viewed in the YZ plane) of an X-ray source and a multi-row X-ray detector according to aspects of the present disclosure. [Figure 4] 1A-1C are schematic diagrams of collimator blades of a collimator according to aspects of the present disclosure, with both blades correctly positioned (left) and with one of the collimator blades incorrectly positioned (right). [Diagram 5] 1 is a schematic diagram of how collimator blade placement in accordance with aspects of the present disclosure affects the scanned area on a patient. [Figure 6] 1 is a flow diagram of a method for verifying an aperture position of a pre-patient collimator (eg, of the CT imaging system of FIG. 1) according to aspects of the present disclosure. [Figure 7] 2 is a block diagram of a method for verifying an aperture position of a pre-patient collimator (such as that of the CT imaging system of FIG. 1) according to aspects of the present disclosure. [Figure 8A] FIG. 1 is a graphical representation of data from one stage of validation of aperture position of a pre-patient collimator according to aspects of the present disclosure. [Figure 8B] 13A-13C are graphical representations of data at different stages of validation of aperture position of a pre-patient collimator according to aspects of the present disclosure. [Figure 8C] FIG. 13 is a graphical representation of data at different stages of validation of aperture position of a pre-patient collimator according to aspects of the present disclosure. [Figure 8D] FIG. 13 is a graphical representation of data at yet another different stage of validation of aperture position of a pre-patient collimator according to aspects of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] One or more specific embodiments are described below. In an attempt to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It will be appreciated that in the development of any such actual implementation, as with any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific goals, such as adhering to system-related and business-related constraints that may vary from implementation to implementation. It will also be appreciated that such development efforts may be complex and time-consuming, but are nevertheless routine undertakings of design, manufacturing, and commercialization for those of ordinary skill in the art having the benefit of this disclosure.

[0011] When describing elements of various embodiments of the present subject matter, terms such as "a," "an," "the," and "said" are intended to mean that there are one or more of the elements in question. Also, the terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, 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.

[0012] Although aspects of the following discussion may be presented in the context of medical imaging, it should be appreciated that the present approach is not limited to such a medical context. Indeed, the illustrative and descriptive description of such a medical context is merely to facilitate discussion by providing examples of real-world implementations and applications. However, the present approach may also be used in other contexts, such as industrial computed tomography (CT) for non-destructive testing of manufactured parts or articles (i.e., quality control or quality screening applications) and / or non-invasive testing of parcels, boxes, baggage, and the like (i.e., security or screening applications). In general, the present approach may be useful in any imaging or screening context, or in the field of image processing, where a collimator is used to control the dimensions of an x-ray beam.

[0013] The present disclosure provides systems and methods for performing collimator screening in a CT imaging system. In particular, these systems and methods enable verification of the aperture position of a pre-patient collimator. The disclosed embodiments include obtaining data (e.g., air scan data or calibration) via air scans at various aperture positions of the pre-patient collimator. The data may be obtained by a detector of the CT imaging system or by other x-ray measurement devices separate or independent of the CT imaging system. From the obtained data, actual collimator aperture positions may be determined for various expected (e.g., intended or predetermined) aperture positions or settings. The measured aperture positions may be compared against system specifications of the CT imaging system to determine whether the measured (i.e., actual) aperture positions deviate from the expected aperture positions by any amount. In some embodiments, a normalized intensity distribution profile may be calculated from the obtained data. The width of the normalized distribution profile (which is a measure of the aperture position) can be converted to dose, and this dose can be compared against the expected dose for the expected aperture position to determine a dose error estimate. The dose error estimate can then be compared against a tolerance dose threshold for the expected aperture position. This analysis of the aperture position may be reported to a user and / or stored.

[0014] The disclosed embodiments provide a safety check to ensure that the collimator blades are correctly positioned. Additionally, the disclosed embodiments may be used as a stand-alone tool or integrated with a daily update calibration process to routinely enable verification of the collimator blades' functioning. In some embodiments, the collimator parameters (i.e., aperture position analysis) can be remotely monitored (in the case of a connected CT imaging system) for preventative maintenance. The disclosed embodiments provide a holistic approach combining system hardware and software for calculations and analysis to validate the functioning of a critical hardware component (i.e., pre-patient collimator) used in a CT imaging system to avoid excessive radiation dose to the patient if the pre-patient collimator malfunctions (e.g., has a larger aperture opening than expected).

[0015] With the above in mind, and referring to FIGURE 1, a CT imaging system 10 is shown by way of example. The CT imaging system includes a gantry 12 having an x-ray source 14 that projects a beam of x-rays 16 toward a detector assembly 15 on the opposite side of the gantry 12. The x-ray source 14 projects the beam of x-rays 16 through a pre-patient collimator or collimator assembly 13 that determines the dimensions of the beam of x-rays 16. The detector assembly 15 includes a collimator assembly 18 (or post-patient collimator assembly), a number of detector modules 20 (e.g., detector elements or sensors), and a data acquisition system (DAS) 32. The multiple detector modules 20 detect the projected x-rays that have passed through a patient 22, and the DAS 32 converts the data into digital signals for further processing. Each detector module 20 in a conventional system produces an analog electrical signal that represents the intensity of an incident x-ray beam and hence the attenuated x-ray beam as it passes through the patient 22. During a scan to acquire x-ray projection data, the gantry 12 and the components mounted to it rotate about a center of rotation 25 (e.g., an isocenter) so as to collect attenuation data from multiple view angles relative to the imaged volume.

[0016] Rotation of gantry 12 and operation of x-ray source 14 are controlled by a control mechanism 26 of CT system 10. Control mechanism 26 includes an x-ray controller 28, which provides power and timing signals to x-ray source 14, a collimator controller 29, which controls the width of the aperture of pre-patient collimator 13 (and thus the size of x-ray beam 16), and a gantry motor controller 30, which controls the rotational speed and position of gantry 12. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed reconstruction. The reconstructed image is applied as an input to computer 36, which stores the image in mass storage device 38. Computer 36 also receives commands and scanning parameters from an operator via console 40. An associated display 42 allows the operator to observe the reconstructed image, and other data from computer 36. Operator provided commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray control 28, collimator control 29, and gantry motor controller 30. In addition, computer 36 operates a table motor controller 44, which in turn controls a motorized table 46 to position patient 22 and gantry 12. Specifically, table 46 moves portions of patient 22 through a gantry opening or bore 48.

[0017] With the above discussion of the overall imaging system 10 in mind, turning to FIGS. 2 and 3, an example of an x-ray source 14 and detector assembly 15 (e.g., an x-ray detector having multiple rows 50) is shown in the XY plane (FIG. 2) and the YZ plane (FIG. 3), respectively. For ease of illustration, the rotating gantry 12 along with the x-ray source 14 is rotated (+Y direction) from the position shown in FIG. 1 to the apex of the gantry. As shown, the pre-patient collimator 13 is disposed between the x-ray source 14 and the detector assembly 15 to determine the shape of the x-ray beam 52. Specifically, an opening or aperture 54 (as shown in FIG. 3) between a pair of collimator blades 56 of the pre-patient collimator 13 shapes the x-ray beam 52. Also shown are the field of view 24 and the beam width 58, which correspond to the dimensions of the x-ray beam 52 intended for the patient scan. Correct placement of the collimator blades 56 is important to ensure that the patient receives the correct radiation dose and that the correct area is scanned. The shape of the blades 56 is shown in different orientations in Figures 2 and 3. By way of example, the blades 56 are generally curved in the XY plane, with a circular leading edge in the YZ plane that determines the beam dimensions. There are many other possible blade shapes in the XY plane, including flat and angled, and the leading edge shape in the YZ plane may also be rectangular or triangular, for example.

[0018] FIG. 4 is a schematic diagram of the collimator blades 56 of the pre-patient collimator 13 with both blades 56 (e.g., blades A and B) correctly positioned (left side) and one of the collimator blades 56 (blade B) incorrectly positioned (right side). As shown in FIG. 5, with the correct positioning of the collimator blades 56 (as seen in the left view of FIG. 4), the correct and desired region 60 (shown in solid lines) of the patient 22 is scanned. As shown in the right view of FIG. 4, blade B is incorrectly positioned relative to the desired or correct location 62. With the incorrect positioning of blade B as shown in the right view of FIG. 4, the incorrect and undesired region 64 (shown in dashed lines) of the patient 22 is scanned (shown in FIG. 5). In accordance with the present disclosure, systems and methods are provided for checking or verifying the positioning of the collimator blades 56 of a pre-patient collimator to ensure that the patient 22 receives the proper dose and the correct region is scanned.

[0019] 6 is a flow diagram of a method 66 for verifying an aperture position of a pre-patient collimator (e.g., of the CT imaging system of FIG. 1). One or more steps of the method 66 may be performed by one or more components (e.g., processing circuitry) of the CT imaging system of FIG. 1 or may be performed by a device separate or remote from the CT imaging system. The method 66 includes initiating a calibration scan or air scan (e.g., a scan with no object present in the bore of the gantry) for the CT imaging system at various expected (e.g., intended or predetermined) aperture positions or settings (e.g., 5 millimeters [mm], 10 mm, etc.) of the pre-patient collimator (block 68).

[0020] The method 66 also includes acquiring or obtaining data (e.g., calibration scan data or air scan data) using an x-ray measurement device having detector elements (block 70). In some embodiments, the x-ray measurement device is a detector assembly of a CT imaging system. In other embodiments, the x-ray measurement device may be a device separate or independent from the CT imaging system. Some examples of a separate x-ray measurement device include analog-type methods, such as x-ray sensitive film, or digital-type methods, such as a CCD camera coupled to an x-ray scintillator. The separate x-ray device may be capable of determining a measurement of spatial resolution (e.g., half-width).

[0021] The method 66 further includes calculating or computing the actual collimator aperture position based on the acquired data at each of the various expected aperture positions (block 72). In some embodiments (e.g., when the data is acquired via a detector assembly of a CT imaging system), the acquired data may be processed (e.g., normalized and removed bad pixel data, etc.) to determine respective normalized intensity distribution profiles at the various expected aperture positions, from which the actual collimator aperture position (e.g., width of each normalized intensity distribution profile) may be obtained. These calculations (and subsequent calculations) may occur within the software of the CT imaging system. In some embodiments (e.g., when the data is acquired via a separate or external x-ray measurement device), the calculations may occur in software of a device separate from the CT imaging system (e.g., using a finite element method spreadsheet or computer programming of a numerical method).

[0022] The method 66 further includes comparing the respective measured aperture positions for each of the expected aperture positions against system specifications of the CT imaging system for each expected aperture position (block 74). The system specifications may be respective acceptable dose thresholds for each expected aperture position or expected widths for the expected aperture positions. In some embodiments, the comparison may be performed at the CT imaging system. In some embodiments, the comparison may be performed separately or remotely from the CT imaging system.

[0023] The method 66 further includes generating an output based on a comparison of each actual collimator position to the system specifications for each expected aperture position (block 76). In some embodiments, generating the output includes generating a report that may be provided to a user / operator or may be stored internally in the CT imaging system. In some embodiments, generating the output includes generating a user-perceivable notification (e.g., on a graphical user interface screen of the CT imaging system device or a device remote from the CT imaging system (e.g., computer, smartphone, etc.). In some embodiments, the notification may include a warning that the pre-patient collimator needs or will soon need replacement. In some embodiments, the parameters (i.e., analysis of aperture positions) can be remotely monitored (in the case of a connected CT imaging system) for preventive maintenance of the collimator.

[0024] FIG. 7 is a block diagram of a method 78 for verifying an aperture position of a pre-patient collimator (e.g., of the CT imaging system of FIG. 1). One or more steps of the method 78 may be performed by one or more components (e.g., processing circuitry) of the CT imaging system of FIG. 1. The method 70 includes initiating air scans (e.g., scans with no object present in the gantry bore) for the CT imaging system at various expected (e.g., intended or predetermined) aperture positions or settings (e.g., 5 millimeters [mm], 10 mm, etc.) of the pre-patient collimator (block 80), either as a stand-alone process or integrated with an update calibration scan process. As shown, a scan 82 (e.g., scan 1) is associated with a minimum aperture width (W1) and a maximum aperture width (W2) is associated with a minimum aperture width (W3). n A predetermined number of scans may be performed, up to scan 84 at .

[0025] The method 78 also includes processing the acquired scan data at the various expected aperture positions (block 86). The processing includes normalizing the acquired scan data, removing bad pixel data, and obtaining a channel average. For example, as shown by block 90, the average 88 of the scan data obtained from the scan associated with the smallest aperture width (W1) is calculated as the average 88 of the scan data obtained from the scan associated with the largest aperture width (W2). n ) can be normalized with respect to the average scan data associated with the smallest aperture width (W1). The normalized scan data associated with the smallest aperture width (W1) can also be examined for any bad pixels, as indicated by block 92, and the bad pixel data can be removed. Once the bad pixel data has been removed, a channel average can be obtained for the normalized scan data associated with the smallest aperture width (W1), as indicated by block 94.

[0026] Various expected aperture positions (maximum aperture width (W n ) except for the scan data associated with W n-1Similar processing occurs for all of the acquired scan data from the aperture width W n-1 The average of the scan data obtained from the scans associated with the maximum aperture width (W n ) and as indicated by block 100, the aperture width W n-1 The normalized scan data associated with the aperture width W may be inspected for any bad pixels, and the bad pixel data may be removed. Once the bad pixel data has been removed, the aperture width W may be removed, as indicated by block 102. n-1 A channel average can be obtained for the normalized scan data associated with

[0027] The method 78 includes further processing of the normalized acquired scan data (block 104). The further processing may include calculating a normalized intensity distribution profile for the normalized scan data associated with each expected aperture position. For example, calculating the normalized intensity distribution profile may occur for the channel-averaged (at block 94) normalized scan data associated with the smallest aperture width (W1), as shown in block 106. Similarly, calculating the normalized intensity distribution profile may occur for the channel-averaged (at block 94) normalized scan data associated with the smallest aperture width (W1), as shown in block 108. n-1 A similar process may occur for the channel-averaged (at block 102) normalized scan data associated with W1 and W n-1 The width of the normalized intensity distribution profile is equivalent to the actual measurement of the aperture or opening of the collimator (i.e., the measured aperture position).

[0028] Further processing also includes fitting the normalized intensity distribution profile data (e.g., to a fitting function such as a Gaussian function) and then measuring the width of the actual normalized intensity distribution across the open aperture for each expected aperture position. For example, as indicated by block 110, the normalized intensity distribution profile associated with the smallest aperture width (W1) can be fitted to measure the width. Similarly, as indicated by block 112, the aperture width W n-1 The width can be measured by fitting the normalized intensity distribution profile associated with W1 and W2. n-1 This may occur for all of the normalized scan data associated with all aperture widths between .

[0029] The method 78 further includes converting each width of the measured normalized intensity distribution for each expected aperture position to a respective dose using a transfer function (block 114). The transfer function may be a linear conversion function that converts widths or measured intensity values ​​to dose.

[0030] The method 78 also includes determining a dose error estimate for each expected aperture position (block 116). Determining the dose error estimate may include comparing the dose derived from the width of the normalized intensity distribution to a respective expected dose associated with each expected aperture position.

[0031] The method 78 further includes comparing each respective dose error estimate against a respective acceptable dose threshold (e.g., acceptable dose range) for the various expected aperture locations (block 118). The comparison allows a determination to be made as to whether the respective dose error estimate is within or outside the respective acceptable dose threshold (i.e., pass or fail) for each expected aperture location.

[0032] The method 78 further includes generating an output based on the comparison. For example, the method 78 includes recording or storing the results of the comparison in a memory internal to the CT imaging system or in a memory at a remote location (block 120). As mentioned above, in a connected CT imaging system, the recorded information may be provided to a remote location for monitoring purposes for preventive maintenance of the collimator. The results or analysis may be recorded or stored regardless of the outcome (i.e., pass or fail). The method 78 also includes providing a user-perceivable notification to a user / operator (block 122). For example, a notification may be provided that the pre-patient collimator requires or will soon require replacement if one or more of the dose error estimates fall outside of a respective acceptable dose threshold. The user-perceivable notification may be provided on a graphical user interface screen of the CT imaging system device or a device remote from the CT imaging system (e.g., computer, smart phone, etc.).

[0033] 8(A) through 8(D) are graphical representations of data at various stages of verification of the aperture position of the pre-patient collimator. Specifically, these graphical representations show data obtained at various stages of the data processing described in method 78 of FIG. 7. FIG. 8(A) shows a graphical representation 124 of view averaged scan data (e.g., for scan 1 at W1 as shown in block 88 of FIG. 7). FIG. 8(B) shows a graphical representation 125 of view averaged data (e.g., for scan 2 at W1 as shown in block 96 of FIG. 7). n FIG. 8(C) shows a graph 128 of normalized scan data (e.g., normalized scan 1 at W1 as shown in block 98). The normalized scan in FIG. 8(C) shows a graph 129 of the view average data for scan 1 at W1 compared to the view average data for scan 1 at W1. n8(D) is derived by normalizing with respect to the view average data for scan n at 100 nm (e.g., as shown in block 90 of FIG. 7). FIG. 8(D) shows a graphical representation 130 of the intensity distribution profile of the normalized data (e.g., as shown in block 106 of FIG. 7). The intensity distribution profile of FIG. 8(D) may be data fitted (e.g., to a fitting function such as a Gaussian function) to obtain the width of the profile from which dose can be derived (e.g., via a transfer function).

[0034] Technical effects of the disclosed subject matter include providing systems and methods for performing collimator screening in CT imaging systems. Specifically, these systems and methods enable verification of the aperture position of a pre-patient collimator. The disclosed embodiments provide a safety check to ensure that the collimator blades are correctly positioned (e.g., regardless of collimator style or design). Additionally, the disclosed embodiments may be used as a stand-alone tool or may be integrated with a daily update calibration process to routinely enable verification of collimator blade function. In some embodiments, parameters (i.e., aperture position analysis) can be remotely monitored (in the case of a connected CT imaging system) for preventive maintenance of the collimator. Routine monitoring of collimator blade position allows preventive maintenance to be performed on demand, allowing for reduced downtime of the CT imaging system. The disclosed embodiments demonstrate the operation of a critical hardware component used in CT imaging systems (i.e., the pre-patient collimator) and provide a holistic approach combining system hardware and software for calculations and analysis to avoid excessive radiation dose to the patient in the event the pre-patient collimator malfunctions (e.g., has an aperture opening larger than expected).

[0035] The techniques presented and claimed herein have been applied to materials and examples that have utility in demonstrating improvements to the art, and as such are not abstract, intangible, or mere theory. Moreover, if any claim appended hereto contains one or more elements designated as "means for performing such and such an action" or "step for performing such and such an action," such elements shall be construed under 35 U.S.C. § 112(f). However, for any claim containing an element designated in any other manner, such elements shall not be construed under 35 U.S.C. § 112(f).

[0036] This written description uses examples to disclose the subject matter, including the best mode, and to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The scope of patentable subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are considered to be within the scope of the claims if they have structural elements that do not differ from the written language of the claims, or if they include equivalent structural elements that have insubstantial differences from the written language of the claims. [Explanation of symbols]

[0037] 10. CT Imaging System 12 Gantry 13 (Pre-Patient) Collimator Assembly 14 X-ray source 15 Detector Assembly 16 X-ray beam 18 Post-Patient Collimator Assembly 20 Detector Module 22 patients 24 Field of View 25 Rotation Center 26 Control Mechanism 32 Data Acquisition System (DAS) 42 Display 46 Table 48 Bore 50 rows 52 X-ray beam 54 Aperture 56 Collimator Blade 58 Beam Width 60 Correct and desired location of patient 22 62 Desired or correct position of collimator blade B 64 Unauthorized and Unwanted Areas of Patient 22 66 How to Verify the Aperture Position of a Pre-Patient Collimator 78 How to Verify the Aperture Position of a Pre-Patient Collimator 80 Steps to start air scanning 86 Processing the acquired scan data 104 Further processing of normalized scan data Graphical representation of 124 view average scan data (scan 1 at W1) 126 Views Average Scan Data Graph (W n Scanning in 128 Graph of normalized scan data (normalized scan 1 on W1) 130 Graphical representation of the intensity distribution profile of normalized data

Claims

1. 1. A method for verifying an aperture position of a pre-patient collimator in a computed tomography (CT) imaging system, comprising: an operation of obtaining data collected by an X-ray measurement device having detector elements exposed to X-rays emitted from an X-ray source of the CT imaging system while the pre-patient collimator is placed at an expected aperture position; calculating a measured collimator aperture position for the pre-patient collimator based on the obtained data; comparing the measured collimator aperture positions against a system specification for the expected aperture positions for the CT imaging system; and generating an output based on the comparison of the measured collimator aperture position to the system specification. A method, wherein the system specification is a tolerance dose threshold for an expected aperture position or an expected width for an expected aperture position.

2. The method of claim 1 , wherein the X-ray measurement device is separate from the CT imaging system.

3. The method of claim 1 , wherein the X-ray measurement device comprises a detector of the CT imaging system.

4. The method of claim 1 , wherein the data comprises air scan data obtained during an air scan.

5. obtaining the data collected by the X-ray measurement device having detector elements exposed to X-rays emitted from the X-ray source of the CT imaging system with the pre-patient collimator positioned at a plurality of expected aperture positions; calculating actual collimator aperture positions for each of the pre-patient collimators at the plurality of expected aperture positions based on the obtained data; comparing each of the measured collimator aperture positions against the system specifications for each of the plurality of expected aperture positions for the CT imaging system; generating respective outputs based on said comparison of said respective measured collimator aperture positions against said system specifications; 2. The method of claim 1, comprising:

6. The method of claim 1 , wherein the output includes storing the results of the comparison in a memory of the CT imaging system or a memory of a remote device.

7. The method of claim 1 , wherein the act of generating an output includes providing a user-perceivable notification of a result of the comparison.

8. 1. A method for verifying an aperture position of a pre-patient collimator of a computed tomography (CT) imaging system including an x-ray source and a radiation detector, comprising: acquiring air scan data by emitting X-rays from the X-ray source toward the radiation detector with the pre-patient collimator positioned at various expected aperture positions; calculating respective widths of respective normalized intensity distribution profiles for the pre-patient collimator at the various expected aperture positions based on the obtained air scan data; converting said respective widths to respective doses using a transfer function; determining respective dose error estimates at the various expected aperture positions based on the respective doses; comparing said respective dose error estimates for said various expected aperture positions against respective tolerance dose thresholds; generating an output based on the comparison of each dose error estimate against the respective tolerance dose threshold; The method according to claim 1,

9. 9. The method of claim 8, wherein the act of calculating the respective widths comprises processing the obtained air-scan data to calculate respective normalized intensity distribution profiles at the various expected aperture positions.

10. 10. The method of claim 9, wherein the act of processing the acquired air scan data includes normalizing the acquired air scan data to remove bad pixel data prior to calculating the respective normalized intensity distribution profiles.

11. 10. The method of claim 9, wherein the act of calculating the respective widths comprises fitting the respective normalized intensity distribution profiles to a fitting function prior to calculating the respective widths.

12. 9. The method of claim 8, wherein the act of determining the respective dose error estimates comprises comparing the respective doses at the different expected aperture positions against respective expected doses at the different expected aperture positions.

13. 9. The method of claim 8, wherein the act of generating an output includes storing the results of the comparison in a memory of the CT imaging system.

14. 10. The method of claim 8, wherein the act of generating an output includes providing a user-perceivable notification when one of the respective dose error estimates falls outside a tolerance dose threshold for a respective expected aperture position.

15. 9. The method of claim 8 used as a stand-alone tool or during a daily calibration process.

16. 1. A computed tomography (CT) imaging system comprising: an x-ray source configured to emit x-rays during operation; a radiation detector configured to receive the x-rays; a pre-patient collimator disposed between the x-ray source and the radiation detector and configured to shape the beam of x-rays through an aperture; Processing circuit and The processing circuitry comprises: acquiring air scan data by emitting X-rays from the X-ray source toward the radiation detector with the pre-patient collimator positioned at various expected aperture positions; calculating respective widths of respective normalized intensity distribution profiles for the pre-patient collimator at the various expected aperture positions based on the obtained air scan data; converting said respective widths to respective doses using a transfer function; determining respective dose error estimates at the various expected aperture positions based on the respective doses; comparing said respective dose error estimates for said various expected aperture positions against respective tolerance dose thresholds; generating an output based on the comparison of each dose error estimate against the respective tolerance dose threshold; 1. A computed tomography (CT) imaging system configured to perform:

17. 17. The CT imaging system of claim 16, wherein the operation of calculating the respective widths comprises processing the obtained air-scan data to calculate respective normalized intensity distribution profiles at the various expected aperture positions.

18. 20. The CT imaging system of claim 17, wherein the operation of processing the acquired air scan data includes normalizing the acquired air scan data to remove bad pixel data prior to calculating the respective normalized intensity distribution profiles.

19. 17. The CT imaging system of claim 16, wherein the operation of determining the respective dose error estimates comprises comparing the respective doses at the different expected aperture positions against respective expected doses at the different expected aperture positions.

20. 17. The CT imaging system of claim 16, wherein the act of generating an output includes providing a user-perceivable notification when one of the respective dose error estimates falls outside a tolerance dose threshold for a respective expected aperture position.

Images