System and method for generating computed tomography (CT) images of a subject at a predetermined breathing state

Abstract

A method for generating computed tomography (CT) images of a subject at a predetermined breathing state includes receiving CT image data, including slice images, for a plurality of slice locations from a plurality of free-breathing CT scans. The method further includes receiving breathing surrogate data for the subject including a breathing amplitude for the CT image data associated with each slice location, and receiving a predetermined breathing amplitude. For each slice location, the method further includes determining an amplitude for each slice image associated with the slice location based on the breathing surrogate data, and selecting one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image associated with the slice location. The method further includes generating a CT image at the predetermined breathing amplitude based on the selected slice image for each slice location.

Description

SYSTEM AND METHOD FOR GENERATING COMPUTED TOMOGRAPHY (CT) IMAGES OF A SUBJECT AT A PREDETERMINED BREATHING STATECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on, claims priority to, and incorporates herein by reference in its entirety U.S. Serial No. 63 / 654,920 filed May 31, 2024 and entitled “System And Method for Generating Computer Tomography (CT) Images of a Subject at a Predetermined Breathing State.'’BACKGROUND

[0002] Radiation therapy of the lung and upper abdomen has to manage breathing motion, including having 3D images of a tumor and normal organs at different respiratory states to measure tumor motion. The only commercial solution to this is called four-dimensional computed tomography (4DCT). 4DCT was developed in the early 2000s as a modification of cardiac imaging. For 4DCT, a breathing surrogate is measured during CT scanning to define the breathing state for retrospective analysis of the CT data. The CT data can be sorted using 1) a phase-angle-based approach, where data from similar parts of the breathing cycle (e.g., inhalation or exhalation), are selected to define a common respiratory state, or 2) an amplitude-based approach, where CT data with similar breathing surrogate values comprise a respiratory state. All commercial 4DCT systems acquire the CT data slowly from one end to the other of the user-selected imaging extents (e.g., head-to-foot or foot-to-head directions). 4DCT systems can use either a) low-pitch helical or b) sequential cine scanning. In low-pitch helical scanning, low-pitch helical scans are helical CT scans with very low pitches, typically 0.06 or 0.10. The pitch is defined as the amount of couch motion per CT gantry rotation divided by the imaging detector craniocaudal extent. Modem commercial systems analyze the patient's respiratory7surrogate signal and select a pitch that allows for enough adequate time to acquire CT data throughout a breath. The CT data are sorted and multiple volumetric images at different respiratory states are reconstructed. Sequential cine scanning is more straightforward. For sequential cine scanning, the couch does not move as the CT scans are acquired; multiple CT scans are acquired for a duration that assures that at least one complete breath takes place. Once this is done, the couch is moved to the abutting position and the next set of scans are acquired. This is repeated until images have been acquired throughout the user’s desired anatomical coverage.

[0003] The main problem with the current commercial 4DCT approaches is that each location within the patient is scanned for only approximately one breathing period, so if thepatient breathes irregularly, then each successive couch position will have acquired data at different sets of breathing amplitudes. For phase-angle 4DCT, the system ignores this variation, so it will reconstruct images at the user-specified states, such as, e.g., inhalation, although each inhalation depth is different. Amplitude-based 4DCT avoids this problem but suffers from a lack of image data near breathing extremes and poorly manages patients with baseline breathing amplitude drift.

[0004] It would be desirable to provide systems and methods that overcome the challenges of prior 4DCT techniques.SUMMARY

[0005] In accordance with an embodiment, a method for generating computed tomography (CT) images of a subject at a predetermined breathing state includes receiving CT image data for a plurality of slice locations from a plurality of free-breathing CT scans of the subject, wherein the CT image data for each CT scan comprises a slice image for each slice location in the plurality of slice locations and the plurality of CT scans are acquired using a CT imaging system, receiving breathing surrogate data for the subject, the breathing surrogate data comprising a breathing amplitude for the CT image data associated with each slice location in each CT scan and receiving a predetermined breathing amplitude. For each slice location, the method further includes determining an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data, and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location. The method further includes generating a CT image at the predetermined breathing amplitude based on the selected slice image for each slice location.

[0006] In accordance with another embodiment, a system for generating computed tomography (CT) images of a subject at a predetermined breathing state includes a processor device, and a non-transitory computer readable memory storing instructions executable by the processor device. The instructions, when executed by the processor device cause the system to receive CT image data for a plurality of slice locations from a plurality of free-breathing CT scans of the subject, wherein the CT image data for each CT scan comprises a slice image for each slice location in the plurality of slice locations and the plurality of CT scans are acquired using a CT imaging system, receive breathing surrogate data for the subject, the breathing surrogate data comprising a breathing amplitude for the CT image data associated with each slice location in each CT scan, and receive a predetermined breathing amplitude.For each slice location, the instruction further cause the system to determine an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data, and select, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location. The instructions further cause the system to generate a CT image at the predetermined breathing amplitude based on the selected slice image for each slice location.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0008] FIG. 1 A is an illustration of an example of an x-ray computed tomography (CT) system in accordance with an embodiment;

[0009] FIG. IB is a block diagram of the example x-ray system of FIG. 1 A in accordance with an embodiment;

[0010] FIG. 2 illustrates a method for generating computed tomography (CT) images of a subject at a predetermined breathing state;

[0011] FIG. 3 illustrates a method for generating a four dimensional CT image of a subject for at least a portion of a respiratory' cycle in accordance with an embodiment; and

[0012] FIG. 4 is a block diagram of an example computer system in accordance with an embodiment.DETAILED DESCRIPTION

[0013] FIGs. 1 A and IB show an example of a computed tomography (CT) system 100 that may be used to perform the methods described herein. The CT system 100 includes a gantry' 102, to which at least one x-ray source 104 is coupled. The x-ray source 104 projects an x- ray beam 106, which may be a fan-beam or cone-beam of x-rays, towards a detector array 108 on the opposite side of the gantry' 102. The detector array 108 includes a number of x- ray detector elements 110. Together, the x-ray detector elements 110 sense the projected x- rays 106 that pass through a subject 112, such as a medical patient or an object undergoing examination, that is positioned in the CT system 100. Each x-ray detector element 110 produces an electrical signal that may represent the intensity of an impinging x-ray beam and, hence, the attenuation of the beam as it passes through the subject 112. In some configurations, each x-ray detector 110 is capable of counting the number of x-ray photons that impinge upon the detector 110. During a scan to acquire x-ray projection data, thegantry 102 and the components mounted thereon rotate about a center of rotation 114 within the CT system 100.

[0014] The CT system 100 also includes an operator workstation 116, which typically includes a display 118; one or more input devices 120, such as a keyboard and mouse; and a computer processor 122. The computer processor 122 may include a commercially available programmable machine running a commercially available operating system. The operator workstation 116 provides the operator interface that enables scanning control parameters to be entered into the CT system 100. In general, the operator workstation 116 is in communication with a data store server 124 and an image reconstruction system 126. By way of example, the operator workstation 116, data store server 124, and image reconstruction system 126 may be connected via a communication system 128, which may include any suitable network connection, whether wired, wireless, or a combination of both. As an example, the communication system 128 may include both proprietary or dedicated networks, as well as open networks, such as the internet. In some embodiments, a breathing surrogate (not shown), for example, a bellows-based breathing surrogate, may be used to monitor the breathing cycle of the subject 112 and may be in communication with the operator workstation 116. The breathing surrogate may provide breathing surrogate data (e.g., breathing amplitude) to the operator workstation 116.

[0015] The operator workstation 116 is also in communication with a control system 130 that controls operation of the CT system 100. The control system 130 generally includes an x-ray controller 132, a table controller 134, a gantry controller 136, and a data acquisition system (DAS) 138. The x-ray controller 132 provides power and timing signals to the x-ray source 104 and the gantry controller 136 controls the rotational speed and position of the gantry 102. The table controller 134 controls a table 140 to position the subject 112 in the gantry 102 of the CT system 100.

[0016] The DAS 138 samples data from the detector elements 110 and converts the data to digital signals for subsequent processing. For instance, digitized x-ray data is communicated from the DAS 138 to the data store server 124. The image reconstruction system 126 then retrieves the x-ray data for a scan from the data store server 124 and reconstructs one or more slices (or images) therefrom. The image reconstruction system 126 may include a commercially available computer processor, or may be a highly parallel computer architecture, such as a system that includes multiple-core processors and massively parallel, high-density computing devices. Optionally, image reconstruction can also be performed on the processor 122 in the operator workstation 116. Reconstructedslices (or images) for a scan can then be communicated back to the data store server 124 for storage or to the operator workstation 116 to be displayed to the operator or clinician.

[0017] The CT system 100 may also include one or more networked workstations 142, by way of example, a networked workstation 142 may include a display 144, one or more input devices 146, such as a keyboard or mouse, and a processor 148. The networked workstation 142 may be located within the same facility as the operator workstation 116, or a different faci 1 i ty, such as a different healthcare institution or clinic.

[0018] The networked workstation 142, whether within the same facility or in a different facility as the operator workstation 116, may gain remote access to the data store server 124 and / or the image reconstruction system 126 via the communication system 128. Accordingly, multiple networked workstations 142 may have access to the data store server 124 and / or image reconstruction system 126. In this manner, x-ray data, reconstructed slices (or images), or other data may be exchanged between the data store server 124, the image reconstruction system 126, and the networked workstations 142, such that the data or slices may be remotely processed by a networked workstation 142. This data may be exchanged in any suitable format, such as in accordance with the transmission control protocol ("TCP"), the internet protocol ("IP"), or other known or suitable protocols.

[0019] The present disclosure describes an alternative approach to 4DCT, which may be referred to herein as “pseudo-4DCT.” In some embodiments, the disclosed systems and methods can acquire CT image data using fast helical free-breathing CT (FHFBCT) scans, acquire the CT image data by scanning repeatedly for a plurality of scans (e.g., back and forth in alternating directions), and simultaneously acquiring breathing surrogate measurements with the plurality of CT scans (and the CT image data). Each CT scan can acquire CT image data for a plurality of slice location (or couch location) in a region of interest of the subject. The CT image data for each CT scan can include a slice image for each slice location. One or more desired breathing amplitudes can be selected, for example, by a user or operator, and can be referred to herein as a predetermined breathing amplitude. To generate a three- dimensional volumetric image for a user selected breathing state by selecting one of the slice images from one of the CT scans for each slice location. First, an amplitude can be determined for each slice image in a CT scan based on the acquired breathing surrogate data. An amplitude can be determined for each slice image from each CT scan. The slice image for each slice location for a particular breathing amplitude can be selected by determining which slice image from the different CT scans best represents the predetermined breathingamplitude at the slice location. In some embodiments, the slice image that best represents the predetermined breathing amplitude at the slice location can be determined by comparing the predetermined breathing amplitude to the determined slice image amplitude for each slice image at the slice location for each of the CT scans. Once one of the slice images from one of the CT scans has been selected for each slice location, a three-dimensional (3D) volumetric CT image can be generated based on the selected slice images for each slice location for the predetermined breathing amplitude, for example, by stacking the selected image slices for each slice location. If more than one predetermined breathing amplitude has been selected, the process for generating a volumetric CT image can be repeated for each predetermined breathing amplitude. A four-dimensional (4D) CT image can then be generated based on the generated volumetric CT images for each breathing amplitude, for example, a 4DCT image of a respirator}' cycle or a portion of a respiratory cycle.

[0020] In other words, a pseudo-CT scan according to the disclosed systems and methods, starts as a set of empty CT images at the slice location (or couch locations) for some or all of the slice locations existing in the acquired CT scans (e.g., FHFBCT scans). Each slice location (or a localized set of slice locations) can be selected to be '■filled” with CT image data (e.g., slice images). In some embodiments, for each slice location (or set of slice locations) a selected predetermined breathing amplitude can be compared to the slice image amplitudes determined for the slice images of each of the CT scans at the corresponding slice location (or couch position) or locations. In some embodiments, for example, the slice image or slice images that best represents the selected predetermined breathing amplitude at a particular slice location (or couch position) can be determined by finding the minimum difference between the selected amplitude and the set of determined amplitudes of the slice images of the CT scans at the slice location. In some embodiments, consideration can also be made for the breathing direction as well as the predetermined breathing amplitude, for example, a user or operator can also select a desired breathing direction, for example, inhalation or exhalation, which can be referred to herein as a predetermined breathing direction. For example, a predetermined breathing direction can be compared to a breathing direction associated with the slice image at the slice location. In some embodiments, the breathing direction for each slice image in each CT scan can be determined using the breathing surrogate data. Once the slice image(s) that best represent the selected predetermined breathing amplitude (and predetermined breathing direction, if appropriate) at each slice location are selected, a volumetric CT image can be generated for the predetermined breathing amplitude and inserted into the pseudo-4DCT corresponding to thepredetermined breathing amplitude and, if appropriate, predetermined breathing direction. The process can be repeated for all user selected predetermined breathing amplitudes and, if appropriate, breathing directions to generate a 4DCT image for a respiratory cycle or a portion of a respiratory cycle.

[0021] As mentioned, the disclosed systems and methods can generate CT images at the one or more user-selected breathing amplitudes (or predetermined breathing amplitude) and, if appropriate, user-selected breathing directions (or predetermined breathing directions). In some embodiments, a user or operator may want to either interpolate or extrapolate to other breathing amplitudes (or states). In such embodiments, the disclosed systems and methods for generating CT images of a subject at a predetermined breathing state can be used with deformable image registration to characterize, for example, tumor or normal organ motion as a function of the breathing surrogate. For example, one of the generated CT images (e.g., a volumetric CT image or a 4DCT image) can be selected as a reference image and the motion characterization characterized by the deformable image registration can be used to deform the reference image to a breathing amplitude (or state) different from the predetermined breathing amplitudes used on the pseudo-4DCT process.

[0022] FIG. 2 illustrates a method for generating computed tomography (CT) images of a subject at a predetermined breathing state. Although the blocks of the processes of FIG. 2 are illustrated in a particular order, in some embodiments, one or more blocks may be executed in a different order than illustrated in FIG. 2, or may be bypassed.

[0023] At block 202, CT image data for a plurality of slice locations (or couch positions) from a plurality of free-breathing CT scans of a region of interest of the subject may be received from, for example, a CT system (e.g., CT system 100 shown in FIGs. 1A and IB). Each CT scan (or CT scan dataset) in the plurality of free-breathing CT scans can acquire signals for each slice location (e.g., a slice image) during the scan. The plurality of CT scans can be acquired in alternating directions. In some embodiments, the retrieved CT image data can include one or more of the acquired signals and reconstructed slice images. In some embodiments, the CT image data from the plurality of free-breathing CT scans can be received in real-time from the CT system (e.g., from the data store 124 or image reconstruction system 126 of CT system 100 shown in FIG. IB), for example, the CT system 100 may acquire CT signals for each CT scan and reconstruct a slice image for each slice location for the CT scan using known reconstruction methods. Accordingly, a set of slice images corresponding to the plurality of slice locations can be reconstructed for each CT scan. In some embodiments, the CT image data from the plurality’ of free-breathing CT scansmay be retrieved or retrieved from data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0024] In some embodiments, the free-breathing CT scans can advantageously be acquired using a fast helical free-breathing CT (FHFBCT) acquisition protocol. In some embodiments, FHFBCT scans can use parameters such as one of the fastest CT gantry rotation times and highest useful pitch. Accordingly, FHFBCT scans can employ a gantry rotation speed and pitch that provide the maximum couch speed available from the CT system. Repeated FHFBCT scans can allow acquisition of image data at each couch position (or slice location) spread out over may seconds to minutes, depending on the amount of time between successive FHFBCT scans, distributing the acquired image data over multiple breaths (or respiratory cycles) and improving the chances that the image data are acquired at a representative range of breathing amplitudes and rates. As used herein, the term free- breathing is intended as a general description of the subject not holding their breath. Free- breathing may include coached breathing or mechanical ventilation or other method of modifying or controlling the breathing cycle. As mentioned, the pitch can be defined as the amount of couch motion per CT gantry rotation divided by the imaging detector craniocaudal extent. In some embodiments, the plurality of CT scans can include a series of low-dose CT scans with an initial higher dose CT scan that can be used as a reference scan. For example, in some embodiment, 25 FHFBCT scans of the subject can be acquired that include an initial higher dose CT scan and a series of 24 low dose CT scans. As mentioned, in some embodiments, the FHFBCT scans in the plurality of FHFBCT scans can be acquired in alternating directions.

[0025] At block 204, breathing surrogate data may be received from, for example, a breathing surrogate. In some embodiments, the breathing surrogate is measured externally. For example, an abdominal pneumatic bellows may be used as a real-time breathing surrogate to monitor and record the breathing (e.g., a breathing state or phase) of the subject simultaneously with the acquisition of the free-breathing CT scans. In another example, the breathing surrogate can be created using patient abdomen and / or thorax optical imaging that measures or characterizes the abdominal and / or chest expansion and contraction during breathing. In some embodiments, the breathing surrogate may be obtained or extracted from the image data (e.g., from the free-breathing CT scans) itself. In some embodiments, the breathing surrogate data includes an amplitude. The breathing amplitude may be derived from the breathing surrogate. In some embodiments, the breathing surrogate data can alsoinclude a breathing direction and / or a breathing rate (e.g., a time derivative of the breathing amplitude). The breathing surrogate may be synchronized with the CT scan acquisition so that an amplitude can be assigned to each CT slice image and slice location in the scan as related to the CT slice acquisition time. In some embodiments, a breathing direction and / or breathing rate may also be assigned to each slice image and slice location in a CT scan. In some embodiments, the breathing surrogate data can be received in real time from the breathing surrogate. In some embodiments, the breathing surrogate data may be received from data storage of the breathing surrogate, or data storage of other computer system (e g., storage device 416 of computer system 400 show n in FIG. 4).

[0026] At block 206, a predetermined breathing amplitude may be received, for example, a user-selected breathing amplitude. In some embodiments, the predetermined breathing amplitude can be selected or provided by a user using an input device of a CT system or another computer system, for example, input devices 120 of CT system 100 shown in FIG. IB or input devices 420 of computer system 400 shown in FIG. 4. In some embodiments, the predetermined breathing amplitude can be received from data storage of an imaging system (e.g.. data storage of CT system 100 shown in FIGs. 1A and IB) or other computer systems (e g., storage device 416 of computer system 400 shown in FIG. 4). In some embodiments, a predetermined breathing direction (e.g., during inhalation or during exhalation) may also be received. In some embodiments, the selected breathing amplitude can represent and define a selected breathing state for the CT image(s) to be generated. In some embodiments, the selected breathing amplitude and the selected breathing direction (e.g., during inhalation or during exhalation) can represent and define a selected breathing state. In some embodiments, as an example, the predetermined breathing amplitude can be defined by percentiles of the amplitudes using the breathing amplitudes throughout each acquired CT scan (e.g.. determined using the breathing surrogate data). For example, a user may select to create a CT image with an amplitude of the 10thpercentile or may select to create a CT image with an amplitude of the 30thpercentile when the subject is inhaling. In other embodiments, the selected breathing state for the CT images to be generated can be defined using, for example, an amplitude-based approach, a phase-angle approach, or other method of quantifying the breathing or respiratory cycle.

[0027] At block 208, an amplitude can be determined for each slice image at each slice location (or couch position) for each acquired CT scan using, for example, the breathing surrogate data from block 204. In some embodiments, the determined slice image amplitudes for each CT scan can be stored in data storage of an imaging system (e.g., data storage of CTsystem 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4). At block 210, for each slice location, one of the slice images associated with the slice location can be selected from one of the CT scans based on a comparison of the predetermined breathing amplitude and the determined slice image amplitudes for each slice image of each CT scan associated with the slice location. In some embodiments, the slice image from the CT scan that best represents the predetermined breathing amplitude at the slice location (e.g., the slice image at the slice location that has the nearest breathing amplitude) can be selected. For example, in some embodiments, the slice image from the CT scan that best represents the predetermined breathing amplitude at the slice location can be selected by determining the difference between the predetermined breathing amplitude and the determined slice image amplitude for each slice image in each CT scan associated with the slice location and selecting the slice image that has the minimum difference between the predetermined breathing amplitude and determined slice image amplitude for the slice image. As mentioned above, in some embodiments, a predetermined breathing direction may also be considered, for example, during inhalation or during exhalation. For example, a predetermined breathing direction can be compared to a breathing direction associated with each of the slice images associated with the slice location. For example, for mid-inhalation or mid-exhalation scans, the slice image can also be selected that has the same inhale or exhale status. Once each slice location has been processed, each slice location will have a selected slice image from one of the CT scans for the predetermined breathing amplitude. In some embodiment, the selected slice image for each slice location can be stored in data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0028] At block 212, a CT image may be generated at the predetermined breathing amplitude (and, if appropriate, breathing direction), e.g., the predetermined breathing state, based on the selected slices images for each slice location for the predetermined breathing amplitude (and, if appropriate, breathing direction). The CT image can be a three-dimensional volumetric image at the predetermined breathing amplitude (and. if appropriate, breathing direction) generated using known methods, such as, for example, stacking the selected slice images from block 210. At block 214, the generated CT image (e.g., a 3D volumetric CT image) may be stored in data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1 A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0029] As mentioned above, more than one predetermined breathing amplitude (and. if appropriate, breathing direction) can be selected by a user and a CT image (e.g., a 3D volumetric CT image) can be generated for each predetermined breathing amplitude using the process in FIG. 3 described above and the CT images for each predetermined breathing amplitude can then be used to generate a 4DCT image (i.e., pseudo-4DCT). FIG. 3 illustrates a method for generating a four dimensional CT image of a subject for at least a portion of a respiratory cycle in accordance with an embodiment. Although the blocks of the processes of FIG. 3 are illustrated in a particular order, in some embodiments, one or more blocks may be executed in a different order than illustrated in FIG. 3, or may be bypassed.

[0030] At block 302, CT image data for a plurality of slice locations (or couch positions) from a plurality of free-breathing CT scans of a region of interest of the subject may be received from, for example, a CT system (e.g., CT system 100 shown in FIGs. 1A and IB). Each CT scan (or CT scan dataset) in the plurality of free-breathing CT scans can acquire signals for each slice location (e.g., a slice image) during the scan. The plurality of CT scans can be acquired in alternating directions. In some embodiments, the retrieved CT image data can include one or more of the acquired signals and reconstructed slice images. In some embodiments, the CT image data from the plurality of free-breathing CT scans can be received in real-time from the CT system (e.g., from the data store 124 or image reconstruction system 126 of CT system 100 shown in FIG. IB), for example, the CT system 100 may acquire CT signals for each CT scan and reconstruct a slice image for each slice location for the CT scan using known reconstruction methods. Accordingly, a set of slice images corresponding to the plurality of slice locations can be reconstructed for each CT scan. In some embodiments, the CT image data from the plurality of free-breathing CT scans may be retrieved or retrieved from data storage of an imaging system (e.g., data storage of CT system 100 show n in FIGs. 1 A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4). As discussed above with respect to block 202 of FIG. 2, in some embodiments, the free-breathing CT scans can advantageously be acquired using a fast helical free-breathing CT (FHFBCT) acquisition protocol. In some embodiments, the plurality of CT scans can include a series of low-dose CT scans with an initial higher dose CT scan that can be used as a reference scan. For example, in some embodiment, 25 FHFBCT scans of the subject can be acquired that include an initial higher dose CT scan and a series of 24 low- dose CT scans. As mentioned, in some embodiments, the FHFBCT scans in the plurality of FHFBCT scans can be acquired in alternating directions.

[0031] At block 304, breathing surrogate data may be received from, for example, a breathing surrogate. As discussed above with respect to block 204 of FIG. 2, in some embodiments the breathing surrogate data can be acquired with an external breathing surrogate such as, for example, a pneumatic bellows and abdomen and / or thorax optical imaging. In some embodiments, the breathing surrogate data may be obtained or extracted from the image data (e g., from the free-breathing CT scans) itself. As discussed above with respect to block 204 of FIG. .2, the breathing surrogate data can include, for example, an amplitude, a breathing direction, and / or a breathing rate. In some embodiments, the breathing surrogate data may be received from data storage of the breathing surrogate, or data storage of other computer system (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0032] At block 306, a plurality of predetermined breathing amplitudes may be received, for example, a set of user-selected breathing amplitudes. In some embodiments, the plurality of predetermined breathing amplitudes can be selected or provided by a user using an input device of a CT system or another computer system, for example, input devices 120 of CT system 100 shown in FIG. IB or input devices 420 of computer system 400 shown in FIG. 4. In some embodiments, the plurality of predetermined breathing amplitude can be received from data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1A and IB) or other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4). As mentioned abive, in some embodiments, a predetermined breathing direction (e.g., during inhalation or during exhalation) for one or more of the predetermined breathing amplitudes may also be received. In some embodiments, the predetermined breathing amplitudes can represent and define one or more selected breathing states for the CT images to be generated. In some embodiments, the selected breathing amplitudes and the selected breathing directions (e.g.. during inhalation or during exhalation) can represent and define one or more selected breathing states. In some embodiments, as an example, the predetermined breathing amplitudes can be defined by percentiles of the amplitudes using the breathing amplitudes throughout each acquired CT scan (e.g., determined using the breathing surrogate data). For example, a user may select to create 8 CT images with amplitudes of the 10th, 30th. 50th, 70th, and 90th percentiles, and may limit the 30th, 50th. and 70thpercentiles to times when the subject is inhaling, and then repeating this percentiles when the subject is exhaling. In other embodiments, the selected breathing state for the CT images to be generated can be defined using, for example, an amplitude-based approach, a phase-angle approach, or other method of quantifying the breathing or respiratory cycle.

[0033] At block 308, one of the predetermined beating amplitudes (and, if appropriate, predetermined breathing directions) can be selected from the plurality of predetermined breathing amplitudes. For example, the 30thpercentile amplitude during inhalation. Then, for the selected predetermined breathing amplitude, at block 310 an amplitude can be determined for each slice image at each slice location (or couch position) for each acquired CT scan using, for example, the breathing surrogate data from block 304. In some embodiments, the determined slice image amplitudes for each CT scan can be stored in data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 show n in FIG. 4). At block 312, for each slice location, one of the slice images associated with the slice location can be selected from one of the CT scans based on a comparison of the predetermined breathing amplitude selected at block 308 and the determined slice image amplitudes for each slice image of each CT scan associated with the slice location. In some embodiments, the slice image from the CT scan that best represents the predetermined breathing amplitude at the slice location (e.g., the slice image at the slice location that has the nearest breathing amplitude) can be selected. For example, in some embodiments, the slice image from the CT scan that best represents the predetermined breathing amplitude at the slice location can be selected by determining the difference between the predetermined breathing amplitude and the determined slice image amplitude for each slice image in each CT scan associated with the slice location and selecting the slice image that has the minimum difference between the predetermined breathing amplitude and determined slice image amplitude for the slice image. As mentioned above, in some embodiments, a predetermined breathing direction may also be considered, for example, during inhalation or during exhalation. For example, a predetermined breathing direction can be compared to a breathing direction associated with each of the slice images associated with the slice location. For example, for mid-inhalation or mid-exhalation scans, the slice image can also be selected that has the same inhale or exhale status. Once each slice location has been processed, each slice location will have a selected slice image from one of the CT scans for the predetermined breathing amplitude. In some embodiment, the selected slice image for each slice location for the predetermined breathing amplitude can be stored in data storage of an imaging system (e.g., data storage of CT system 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 show n in FIG. 4).

[0034] At block 314, a CT image may be generated at the predetermined breathing amplitude selected at block 308 (and, if appropriate, breathing direction), e.g., the predeterminedbreathing state, based on the selected slices images for each slice location for the predetermined breathing amplitude (and, if appropriate, breathing direction). The CT image can be a three-dimensional volumetric image at the predetermined breathing amplitude (and, if appropriate, breathing direction) generated using known methods, such as, for example, stacking the selected slice images from block 210. The generated CT image (e.g., a 3D volumetric CT image) may be stored in data storage of an imaging system (e g., data storage of CT system 100 shown in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0035] At block 316, it can be determined whether the last predetermined breathing amplitude from the plurality of predetermined breathing amplitudes from block 304 has been reached (or processed). If the last predetermined breathing amplitude has not been reached, the process can return to block 308 and a different predetermined breathing amplitude can be selected. The process of blocks 310-314 can then be repeated for the next predetermined breathing amplitude in the plurality of predetermined breathing amplitudes. The process of blocks 308-314 can be repeated for each predetermined breathing amplitude in the plurality of predetermined breathing amplitudes.

[0036] At block 316, if the last predetermined amplitude has been processed, the process moves to block 318. At block 318, each CT image (e.g., a 3D volumetric CT image) generated for each predetermined breathing amplitude (and, if appropriate, predetermined breathing direction) can be used to generate a 4DCT image, for example, representing a portion of the respiratory (or breathing) cycle or the entire respiratory cycle. Known methods for generating a 4DCT image from a plurality of 3D volumetric images of different breathing amplitudes (and, if appropriate, breathing directions) may be used. The generated 4DCT image may be stored in data storage of an imaging system (e.g., data storage of CT system 100 show n in FIGs. 1A and IB) or data storage of other computer systems (e.g., storage device 416 of computer system 400 shown in FIG. 4).

[0037] As mentioned above, the disclosed systems and methods (e.g., as described with respect to FIGs. 2 and 3) can generate CT images at the one or more predetermined breathing amplitudes (e.g.. user-selected breathing amplitudes) and. if appropriate, or predetermined breathing directions (e g., user-selected breathing directions). In some embodiments, a user or operator may w ant to either interpolate or extrapolate to other breathing amplitudes (or states). In such embodiments, the methods described above with respect to FIGs. 2 and 3 for generating CT images of a subject at a predetermined breathing state can be used with deformable image registration to characterize, for example, tumor or normal organ motion asa function of the breathing surrogate. For example, one of the generated CT images (e.g., a volumetric CT image or a 4DCT image) can be selected as a reference image and the motion characterization characterized by the deformable image registration can be used to deform the reference image to a breathing amplitude (or state) different from the predetermined breathing amplitudes used on the pseudo-4DCT process.

[0038] FIG. 4 is a block diagram of an example computer system in accordance with an embodiment. Computer system 400 may be used to implement the systems and methods described herein. In some embodiments, the computer system 400 may be a workstation, a notebook computer, a tablet device, a mobile device, a multimedia device, a network server, a mainframe, one or more controllers, one or more microcontrollers, or any other general- purpose or application-specific computing device. The computer system 400 may operate autonomously or semi-autonomously, or may read executable software instructions from the memory or storage device 416 or a computer-readable medium (e.g., a hard drive, a CD- ROM, flash memory), or may receive instructions via the input device 420 from a user, or any other source logically connected to a computer or device, such as another networked computer or server. Thus, in some embodiments, the computer system 400 can also include any suitable device for reading computer-readable storage media.

[0039] Data, such as data acquired with an imaging system (e.g., a CT imaging system) may be provided to the computer system 400 from a data storage device 416, and these data are received in a processing unit 402. In some embodiment, the processing unit 402 includes one or more processors. For example, the processing unit 402 may include one or more of a digital signal processor (DSP) 404, a microprocessor unit (MPU) 406, and a graphics processing unit (GPU) 408. The processing unit 402 also includes a data acquisition unit 410 that is configured to electronically receive data to be processed. The DSP 404, MPU 406, GPU 408, and data acquisition unit 410 are all coupled to a communication bus 412. The communication bus 412 may be, for example, a group of wires, or a hardware used for switching data between the peripherals or between any component in the processing unit 402.

[0040] The processing unit 402 may also include a communication port 414 in electronic communication with other devices, which may include a storage device 416, a display 418, and one or more input devices 420. Examples of an input device 420 include, but are not limited to, a keyboard, a mouse, and a touch screen through which a user can provide an input. The storage device 416 may be configured to store data, which may include data such as, for example, acquired CT image data, breathing surrogate data, generated CT images, etc., whether these data are provided to, or processed by, the processing unit 402. The display 418may be used to display images and other information, such as CT images, patient health data, and so on.

[0041] The processing unit 402 can also be in electronic communication with a network 422 to transmit and receive data and other information. The communication port 414 can also be coupled to the processing unit 402 through a switched central resource, for example the communication bus 412. The processing unit can also include temporary storage 424 and a display controller 426. The temporary storage 424 is configured to store temporary information. For example, the temporary storage 424 can be a random access memory.

[0042] Computer-executable instructions for generating computed tomography (CT) images of a subject at a selected breathing state according to the above-described methods may be stored on a form of computer readable media. Computer readable media includes volatile and nonvolatile, removable, and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer readable media includes, but is not limited to, random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), flash memory or other memory technology, compact disk ROM (CD-ROM), digital volatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired instructions and which may be accessed by a system (e.g., a computer), including by internet or other computer network form of access.

[0043] The present disclosure has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.

Claims

CLAIMS:

1. A method for generating computed tomography (CT) images of a subject at a predetermined breathing state, the method comprising: receiving CT image data for a plurality of slice locations from a plurality of free- breathing CT scans of the subject, wherein the CT image data for each CT scan comprises a slice image for each slice location in the plurality of slice locations and the plurality of CT scans are acquired using a CT imaging system; receiving breathing surrogate data for the subject, the breathing surrogate data comprising a breathing amplitude for the CT image data associated with each slice location in each CT scan; receiving a predetermined breathing amplitude; for each slice location: determining an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data; and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location; and generating a CT image at the predetermined breathing amplitude based on the selected slice image for each slice location.

2. The method according to claim 1, wherein comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location comprises determining a slice image amplitude that is nearest to the predetermined breathing amplitude.

3. The method according to claim 2, wherein determining a slice image amplitude that is nearest to the predetermined breathing amplitude comprises determining a minimum difference between the predetermined beathing amplitude and the determined slice image amplitude for each slice image at the slice location.

4. The method according to claim 1, wherein the plurality of free-breathing CT scans are acquired using a fast helical free-breathing CT (FHFBCT) acquisition.

5. The method according to claim 1, wherein the plurality of free-breathing CT scans for includes a reference scan and a plurality of low-dose scans.

6. The method according to claim 1, wherein the predetermined breathing amplitudes are defined as a percentile.

7. The method according to claim 1, wherein the predetermined breathing amplitude has an associated predetermined breathing direction and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location further comprises comparing the predetermined breathing direction to a breathing direction associated with each slice image.

8. The method according to claim 1, wherein the generated CT image at the predetermined breathing amplitude is a three-dimensional (3D) volumetric CT image.

9. The method according to claim 1, further comprising: receiving a plurality of predetermined breathing amplitudes; for each predetermined breathing amplitude, generating a CT image at the predetermined breathing amplitude based on a slice image selected for each slice location by: determining an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data; and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location; and generating a four-dimensional (4D) CT image of the subject based on the CT image generated at each predetermined breathing amplitude.

10. The method according to claim 9, wherein the predetermined breathing amplitude has an associated predetermined breathing direction and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location further comprises comparing the predetermined breathing direction to a breathing direction associated with each slice image.

11. The method according to claim 9, wherein comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location comprises determining a slice image amplitude that is nearest to the predetermined breathing amplitude.

12. The method according to claim 11, wherein determining a slice image amplitude that is nearest to the predetermined breathing amplitude comprises determining a minimum difference between the predetermined beathing amplitude and the determined slice image amplitude for each slice image at the slice location.

13. A system for generating computed tomography (CT) images of a subject at a predetermined breathing state, the method comprising: a processor device; and a non-transitory computer readable memory storing instructions executable by the processor device, wherein the instructions, when executed by the processor device cause the system to: receive CT image data for a plurality of slice locations from a plurality of free- breathing CT scans of the subject, wherein the CT image data for each CT scan comprises a slice image for each slice location in the plurality of slice locations and the plurality of CT scans are acquired using a CT imaging system; receive breathing surrogate data for the subject, the breathing surrogate data comprising a breathing amplitude for the CT image data associated with each slice location in each CT scan; receive a predetermined breathing amplitude; for each slice location: determine an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data; and select, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location; and generate a CT image at the predetermined breathing amplitude based on the selected slice image for each slice location.

14. The system according to claim 13, wherein comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location comprises determining a slice image amplitude that is nearest to the predetermined breathing amplitude.

15. The system according to claim 14, wherein determining a slice image amplitude that is nearest to the predetermined breathing amplitude comprises determining a minimum difference between the predetermined beathing amplitude and the determined slice image amplitude for each slice image at the slice location.

16. The system according to claim 13. wherein the plurality of free-breathing CT scans are acquired using a fast helical free-breathing CT (FHFBCT) acquisition.

17. The system according to claim 13, wherein the plurality of free-breathing CT scans for includes a reference scan and a plurality of low-dose scans.

18. The system according to claim 13, wherein the predetermined breathing amplitudes are defined as a percentile.

19. The system according to claim 13. wherein the predetermined breathing amplitude has an associated predetermined breathing direction and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location further comprises comparing the predetermined breathing direction to a breathing direction associated with each slice image.

20. The system according to claim 13, wherein the generated CT image at the predetermined breathing amplitude is a three-dimensional (3D) volumetric CT image.

21. The system according to claim 13. wherein the instructions, when executed by the processor device, further cause the system to: receive a plurality7of predetermined breathing amplitudes; for each predetermined breathing amplitude, generate a CT image at the predetermined breathing amplitude based on a slice image selected for each slice location by:determining an amplitude for each slice image of each CT scan associated with the slice location based on the breathing surrogate data; and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location by comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location; and generate a four-dimensional (4D) CT image of the subject based on the CT image generated at each predetermined breathing amplitude.

22. The system according to claim 21, wherein comparing the predetermined breathing amplitude and the determined slice image amplitude for each slice image of each CT scan associated with the slice location comprises determining a slice image amplitude that is nearest to the predetermined breathing amplitude.

23. The system according to claim 22, wherein determining a slice image amplitude that is nearest to the predetermined breathing amplitude comprises determining a minimum difference between the predetermined beathing amplitude and the determined slice image amplitude for each slice image at the slice location.

24. The system according to claim 21. wherein the predetermined breathing amplitude has an associated predetermined breathing direction and selecting, from one of the plurality of CT scans, one of the slice images associated with the slice location further comprises comparing the predetermined breathing direction to a breathing direction associated with each slice image.

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