Patent Application
20120078089
The subject matter disclosed herein relates generally to imaging systems, and more particularly, to an apparatus and method for generating medical images.
Multi-modality imaging systems exist that scan using different modalities, for example, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), and Single Photon Emission Computed Tomography (SPECT). During operation, the image quality of conventional imaging systems may be affected by the motion of the object being imaged. In particular, motion of the imaged object can degrade the image quality. More specifically, image artifacts are produced by movement of the object during image acquisition. Respiratory motion is a common source of involuntary motion in mammals (e.g., people and animals) encountered in medical imaging systems. The respiratory motion may lead to errors during image review, such as when a physician is determining the size of a lesion, determining the location of the lesion, or quantifying the lesion.
To correct for motion related imaging artifacts, at least one conventional imaging system utilizes various techniques to correct for motion related imaging artifacts. However, the quantity of data produced by utilizing the various motion correction techniques is typically relatively large. Specifically, the various known techniques generate more data than is typically required by a physician to assess the medical condition from the imaged object. Accordingly, the physician is required to view all the data, including the motion-corrected data, to determine which portions of the data best represent the medical condition being diagnosed.
In one embodiment, a method for generating a hybrid imaging volume is provided. The method includes acquiring a Positron Emission Tomography (PET) imaging dataset of an object using a PET imaging system, the PET imaging dataset including at least one motion affected portion and at least one non-motion affected portion, identifying a motion affected portion of the PET imaging dataset, motion correcting the identified portion of the PET imaging dataset to generate a hybrid portion, and constructing a hybrid PET image volume using the hybrid portion and the at least one non-motion affected portion.
In another embodiment, a method of improving the quality of a medical image is provided. The method includes generating a plurality of gated Positron Emission Tomography (PET) images, motion correcting the gated PET images using a PET reference gate to generate a hybrid PET series of images, selecting at least one Computed Tomography (CT) image having the same respiratory phase as the gated PET images stored in the PET reference bin, and constructing at least one PET image volume using the hybrid PET series of images.
In a further embodiment, a multi-modality imaging system is provided. The imaging system includes a first modality unit, a second modality unit, and a computer operationally coupled to the first and second modality units. The is programmed to acquire a Positron Emission Tomography (PET) imaging dataset of an object using a PET imaging system, the PET imaging dataset including at least one motion affected portion and at least one non-motion affected portion, identify the motion affected portion of the PET imaging dataset, motion correct the identified portion of the PET imaging dataset to generate a hybrid portion, and construct a hybrid PET image using the hybrid portion and the at least one non-motion affected portion.
The foregoing summary, as well as the following detailed description of various embodiments, will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of the various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or a block of random access memory, hard disk, or the like) or multiple pieces of hardware. Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional elements not having that property.
Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated, but a viewable image is not. Therefore, as used herein the term “image” broadly refers to both viewable images and data representing a viewable image. However, many embodiments generate, or are configured to generate, at least one viewable image.
Various embodiments described herein provide a multi-modality imaging system 10 as shown in
Referring to
The gantry 18 includes an x-ray source, 26 that projects a beam of x-rays toward a detector array 28 on the opposite side of the gantry 18. The detector array 28 is formed by a plurality of detector rows (not shown) including a plurality of detector elements which together sense the projected x-rays that pass through the patient 16. Each detector element produces an electrical signal that represents the intensity of an impinging x-ray beam and hence allows estimation of the attenuation of the beam as the beam passes through the patient 16. During a scan to acquire x-ray attenuation data, the gantry 18 and the components mounted thereon rotate about a center of rotation. Additionally, the PET imaging system includes a detector (not shown) that is configured to acquire emission data.
The imaging system 10 also includes at least one motion sensor 30 that is adapted to detect and transmit information that is indicative of the motion of the patient 16. In one embodiment, the motion sensor 30 may be embodied as a belt-type motion sensor 32 that is adapted to extend at least partially around the patient 16. Optionally, the motion sensor 30 may be embodied as a motion sensor 34 that is adapted to be secured to a predetermined position on the patient 16. It should be realized that although two different motion sensors are described, that the imaging system 10 may include other types of motions sensors to generate motion related information of the patient 16.
The imaging system 10 also includes an operator workstation 40. During operation, the motorized table 24 moves the patient 16 into the central opening 22 of the gantry 18 and/or 20 in response to one or more commands received from the operator workstation 40. The workstation 40 then operates the first and second modalities 12 and 14 to both scan the patient 16 and acquire attenuation and/or emission data of the patient 16. The workstation 40 may be embodied as a personal computer (PC) that is positioned near the imaging system 10 and hard-wired to the imaging system 10 via a communication link 42. The workstation 40 may also be embodied as a portable computer such as a laptop computer or a hand-held computer that transmits information to, and receives information, including motion information, from the imaging system 10. Optionally, the communication link 42 may be a wireless communication link that enables information to be transmitted to or from the workstation 40 to the imaging system 10 wirelessly. In operation, the workstation 40 is configured to control the operation of the imaging system 10 in real-time. The workstation 40 is also programmed to perform medical image diagnostic acquisition and reconstruction processes described herein.
The operator workstation 40 includes a central processing unit (CPU) or computer 44, a display 46, and an input device 48. As used herein, the term “computer” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), field programmable gate array (FPGAs), logic circuits, and any other circuit dr processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer”. In the exemplary embodiment, the computer 44 executes a set of instructions that are stored in one or more storage elements or memories, in order to process information received from the first and second modalities 12 and 14. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element located within the computer 44.
The set of instructions may include various commands that instruct the computer 44 as a processing machine to perform specific operations such as the methods and processes of the various embodiments described herein. The set of instructions may be in the form of a software program. As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.
The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to user commands, or in response to results of previous processing, or in response to a request made by another processing machine.
The computer 44 connects to the communication link 42 and receives inputs, e.g., user commands, from the input device 48. The input device 48 may be, for example, a keyboard, mouse, a touch-screen panel, and/or a voice recognition system, etc. Through the input device 48 and associated control panel switches, the operator can control the operation of the CT imaging system 12 and the PET imaging system 14 and the positioning of the patient 16 for a scan. Similarly, the operator can control the display of the resulting image on the display 46 and can perform image-enhancement functions using programs executed by the computer 44.
At 102 at least one scout scan of the patient 16 is performed to generate a scout scan image 150 shown in
At 104, a scan range that includes a volume of interest to be motion corrected is selected. In one embodiment, an exemplary volume of interest 152 (shown in
Referring again to
However, as discussed above, the selected volume of interest 152 has been predetermined to be more likely affected by motion, thus the selected volume of interest 152 may be scanned using a second different scanning protocol. For example, the selected volume of interest 152 may be scanned at a higher resolution and/or over a longer time duration and/or with respiratory gating to generate additional more information than is acquired using the first scanning protocol. It should be realized that although the selected volume of interest 152 is shown as being axially located between the second and third volumes of interest 154 and 156, the selected volume of interest 152 may be located anywhere within the overall volume of interest produced by the scanning procedure. Moreover, although only one volume of interest 152 is shown, it should be realized that multiple of volumes of interest, each affected by motion, may be selected.
At 108, a signal indicative of motion of the selected volume of interest 152 of the patient 16 is obtained. The motion signal may be obtained during the CT imaging scan at 106, during a related PET imaging scan, or during any other medical imaging system scanning procedure. Optionally, the motion signal may be obtained from a database of previous medical examination procedures. In the exemplary embodiment, the motion signal is obtained using the motion sensor 30 shown in
At 110, the CT scanning of patient 16 is completed. As a result of the scanning procedure described at 106, an initial CT imaging dataset 160 (shown in
At 112, in the exemplary embodiment, the CT imaging dataset 160 acquired at 106 is reconstructed. For example, the helical cine CT images for portions 164 and 166, that are not affected by motion, e.g. acquired from volumes of interest 154 and 156, may be reconstructed to form a portion of the hybrid image 170. Thereafter, at 114, the information acquired at 106 may be utilized directly to construct the hybrid CT image 170 that includes the 3D information for portions 164 and 166 and a hybrid portion 172 that represents the portion 162 after motion correction is performed on the portion 162. The method of performing the motion correction on the portion 162 to generate the hybrid portion 172 is discussed in more detail below.
At 116, the patient 16 is scanned using the PET imaging system 14 to acquire emission data of the patient 16. In the exemplary embodiment, the selected volume of interest 152 is again utilized to perform the scanning procedure at 116. For example, as discussed above, only a portion of the information acquired at 106 is typically affected by motion. Thus, in the exemplary embodiment, scanning at 116 includes scanning the patient 16 using more than one scanning protocol. For example,
However, as discussed above, a selected volume of interest 182, which typically is at the same axial location as the selected volume of interest 152 in the CT imaging dataset, has been predetermined to be more likely affected by motion, thus the selected volume of interest 182 may be scanned using a second different imaging protocol. For example, the selected volume of interest 182 may be scanned at a higher resolution and/or over a longer time period and/or with respiratory gating to generate more information than the first imaging protocol. It should be realized that although the selected volume of interest 182 is shown as being axially located between the second and third volumes of interest 184 and 186, the selected volume of interest 182 may be located anywhere within the overall volume of interest produced by the scanning procedure. Moreover, although only one volume of interest 182 is shown, it should be realized that multiple of volumes of interest, each affected by motion, may be selected.
In various embodiments, a portion of the emission data acquired during the scanning at 116 may be acquired in a list of events, a mode commonly referred to as list mode. Further, another portion of, the emission data may be acquired in a sinogram mode. The list mode generally refers to an acquisition mode in which each annihilation event is stored sequentially in a list mode file. The sinogram mode generally refers to an acquisition mode in which annihilation events, optionally having an identical Time-of-Flight (TOF), are stored in sinograms in an (radius from axis, angle) format. In one embodiment, a portion of the emission data may be acquired in the list mode for regions outside the selected volume of interest 182 and a portion of emission data is acquired in the sinogram mode for other portions, such as for example, the second and third regions of interest 184 and 186. In another embodiment, a portion of the emission data may be acquired in the list mode for regions outside the volume of interest. Further, a portion of the emission data may be acquired simultaneously, or concurrently, both in list mode, and sinogram mode for the volume of interest. In yet another embodiment of the invention, a portion of the emission data may be acquired in the list mode for every x annihilation event, where x is a positive number greater than one.
Referring again to
For example,
At 120, in the exemplary embodiment, a portion of the initial PET imaging dataset 190 acquired at 116 is utilized to reconstruct un-gated PET images 190 of the patient 16. For example, the emission information for portions 194 and 196, that are not affected by motion, e.g. volumes of interest 184 and 186, may be reconstructed to form a portion of the hybrid image 200. Thereafter, at 122, the information acquired at 116 may be utilized directly to construct the hybrid PET image 200 (shown in
Referring again to
For example, assuming that the total length of the PET scan to acquire emission data for the region 182 is three minutes, then the resulting portion of emission data 192 representing the region of interest 182 covers three minutes. Moreover, assuming that the emission data portion 192 is gated into six bins, then each respective bin includes approximately 30 seconds of emission data from the region of interest 182. Thus a first portion 320 of the emission data portion 192 is gated into the gate 300, a second portion 322 of the emission data portion 192 is gated into the gate 302, a third portion 324 of the emission data portion 192 is gated into the gate 304, a fourth portion 326 of the emission data portion 192 is gated into the gate 306, a fifth portion 328 of the emission data portion 192 is gated into the gate 308, and a sixth portion 330 of the emission data portion 192 is gated into the gate 310.
In the exemplary embodiment, the emission data acquired for the portion 192 is gated into a respective bin based on the motion state of the patient 16. Information to determine the motion state of the patient 16 may be acquired from, for example, the motion sensor 30. For example, the bin 300 may include emission data acquired at the beginning of the respiration phase (inspiration), and the bin 310 may include emission data acquired at the end of the respiration phase (expiration). Moreover, each intervening bin, e.g. bins 302, 304, 306, and 308 may include emission data that represents a motion state between inspiration and expiration. More specifically, each of the bins 300, 302, 304, 306, 308, and 310 are adapted to receive emission data that was acquired over a plurality of breathing cycles. Moreover, each of the bins 300, 302, 304, 306, 308, and 310 are adapted to receive emission data that represents approximately the same point in the patient's breathing cycle. Accordingly, each of the bins 300, 302, 304, 306, 308, and 310 include emission data representing a certain motion state of the patient 16. Thus, in the exemplary embodiment, the motion information acquired from the motion sensor 30 is utilized to divide the emission data 192 into six substantially equal portions and store the substantially equal portions in a respective bin 300, 302, 304, 306, 308, and 310.
In another exemplary embodiment, the information that represents emission data within the PET portion 192 may be binned or gated using a Quiescent Period Gating (QPG) algorithm or method. Quiescent as used herein refers to a respiratory state of relative inactivity, repose, and/or tranquility. The QPG algorithm may be implemented using, for example, the computer 44. The QPG algorithm performs quiescent period gating on the data subset 192 to account for the motion of a region of interest of the patient 16 based on a motion signal received from the motion sensor 30 shown in
In operation, the QPG algorithm determines at least one quiescent period of at least a portion of the motion signal received from the motion sensor 30. The QPG algorithm utilizes the determined quiescent period to perform quiescent gating. For example, in one embodiment, the QPG algorithm utilizes the determined quiescent period to perform a displacement histogram-based gating of the image data subset 192. Specifically, the QPG algorithm divides the motion signal into intervals based on the displacement of the motion signal. The image data subset 192 is then gated into respective bins based on the displacement of the motion signal. Optionally, the QPG algorithm utilizes the determined quiescent period to perform a cycle-based gating of the image data subset 192. During operation, the QPG algorithm is configured to, extract image data from the image data subset 192 that corresponds to periods where, for each cycle, the motion signal is below or less than a predetermined threshold.
Referring again to
At 128, a reference gate is selected to further perform the motion correction 130 on the portion 192 to generate the hybrid PET portion 202. The reference gate may be selected manually by the operator. Optionally, the reference gate may be selected automatically by the computer 44. For example, the reference gate may be determined to be the bin 310 including information generated at the end of the respiration phase where the patient's diaphragm is at a highest point and the patient's lunge volume is a lowest point.
At 130, the gated PET images formed at 126 are corrected to substantially reduce or eliminate the effects of motion of the portion 192. In the exemplary embodiment, the motion correction is performed by registering the bins shown in
In another embodiment, a non-rigid, or elastic, registration procedure may be utilized to perform the motion correction on the portion 192. In operation, the non-rigid registration includes non-rigid transformations. These non-rigid transformations allow local warping of image features and provide registrations that account for local deformations. Non-rigid transformation approaches include, for example, polynomial warping, interpolation of smooth basis functions (thin-plate splines and wavelets), and physical continuum models (viscous fluid models and large deformation diffeomorphisms), among others. The non-rigid registration is performed using the PET images forming the portion 192. The non-rigid registration may include, for example, warping of points or landmarks and providing a best fit along a contour with interpolation and correlation of the points or landmarks. Alternatively, a blending process may be performed that compares image voxels and blends corresponding regions. In general, the local non-rigid registration includes any type of elastic deformation model that allows for variations or movements in the different image sets. After the rigid or non-rigid registration process is completed, all of the bins 300 . . . 310 are averaged together. Specifically, the bins may be averaged together because each of the bins now represents the same spatial distribution of the counts. For example, a lesion that was in one location in a first gate and a second location in a second different gate, now appear to be in the same location in both gates.
As discussed above, the motion correction procedures are performed on the portion 192 to generate a hybrid portion 202 that is motion corrected. Thus, the hybrid portion represents motion-corrected or gated. PET images. As shown in
Referring again to
In operation, the CT scan at 106 is performed by first identifying the location of potential motion in the patient 16. The area or areas having motion then may be scanned using a different protocol than areas not aftected by motion. In areas where motion is detected, the table 24 may be held in the same axial imaging position for a predetermined period of time. For example, on average it takes approximately 5 seconds per respiratory cycle. Accordingly, the table 24 may remain in the same position for 5-6 seconds to capture images at all parts of the cycle. This procedure may be accomplished for multiple table imaging positions. As a result of the CT imaging procedure, a relatively large quantity of CT images are generated. In the exemplary embodiment, at 132, the large quantity of CT images are sorted based on the breathing phase of the patient 16. More specifically, at least a portion of the CT images acquired at 106 are selected to be gated into bins based on the motion state of the patient 16. Information to determine the motion state of the patient 16 may be acquired from for example, the motion sensor 30.
In the exemplary embodiment, the reference gate selected at 128 is utilized to identify the gate of the CT images that are utilized to generate the hybrid CT portion 172. More specifically, the PET reference gate includes PET information acquired at a specific point or phase in the patient's breathing cycle. Moreover, the PET images at other gates are each motion corrected using the reference gate selected at 128. Therefore, the CT information acquired during the same respiration phase as information stored in the PET reference gate is utilized to form the CT hybrid portion 172. Thus, the reference gate 128 is utilized to select the portion of the CT imaging dataset that is affected by motion, e.g. portion 162. At 114, the motion selected CT information, e.g. the hybrid portion 172 formed at 132 is then reinserted or combined with the un-gated data to construct the hybrid CT image 170 that includes both 3D information for portions 164 and 166 and the hybrid portion 172 that represents the portion 162 after motion selection is performed.
A technical effect of the various embodiments described herein is to provide a fully or partially automatic steamlined 4D PET-CT workflow to generate a hybrid image volume or volumes. Various embodiments perform respiratory motion correction on PET-CT images utilizing gated 4D PET and gated 4D CT optionally with phase-match of the CT for PET attenuation correction. The 4D PET data is then input to a global non-rigid registration algorithm such that (N−1) gates are registered to the Nth gate, e.g. the reference gate. As a result, the quantity of respiratory motion induced blur in the PET images may be reduced and the quantification, as well as lesion detectability, is increased. Various embodiments are configured to generate the most clinically relevant information in a substantially automated manner, thus reducing the quantity of user interactions required and increasing the clinical efficiency.
Various embodiments described herein provide a tangible and non-transitory machine-readable medium or media having instructions recorded thereon for a processor or computer to operate an imaging apparatus to perform an embodiment of a method described herein. The medium or media may be any type of CD-ROM, DVD, floppy disk, hard disk, optical disk, flash RAM drive, or other type of computer-readable medium or a combination thereof.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments, they are by no means limiting and are merely exemplary. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose the various embodiments, including the best mode, and also to enable any person skilled in the art to practice the various embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if the examples have structural elements that do, not differ from the literal language of the claims, or the examples include equivalent structural elements with insubstantial differences from the literal language of the claims.
