Computed tomography perfusion phantom and method use thereof

A computed tomography perfusion phantom includes a scanned plane configured to align with an imaging plane of a CT device. A sample rod extends through the scan plane and includes a plurality of adjacent cells. The plurality of adjacent cells are each constructed of materials having predetermined CT numbers and the plurality of adjacent cells include cell of a plurality of CT numbers. A drive motor is coupled to the sample rod and the drive motor moves the sample rod through the scan plane. A method of calibrating a CT device with the perfusion phantom includes aligning the scan plane of the perfusion phantom with an imaging plane of the CT device. The drive motor moves the sample rod through the scan plane of the perfusion phantom. A plurality of CT number measurements of the sample rod are acquired through the scanned plane of the perfusion phantom.

BACKGROUND

The present disclosure is related to the configuration and calibration of a computed tomography (CT) device using a phantom. More specifically, the present disclosure is related to a perfusion phantom and a method of using the perfusion phantom for CT device calibration.

Bodies of material that represent a quantity of one or more body structures are known as phantoms. Phantoms represent one or more characteristics or properties (e.g. mass, composition, dimension, shape, magnetic, or radiation) of one of more body parts or structures. Such phantoms are used in the medical field for quality control of medical imaging and radiotherapy devices. Such testing can be a part of initial set up and calibration, or can be used as part of a routine quality assurance program to maintain optimal system performance. The American College of Radiology (ACR) offers a voluntary program of CT device quality assurance that includes the use of phantoms for CT device accreditation.

The human body is a dynamic subject that is constantly moving and moreover, many diagnostic imaging procedures rely upon the evaluation of dynamically changing conditions within a patient's body. One such technique that is used with CT imaging devices is to introduce a contrast agent to the patient, organ, or organ system that is to be imaged, and using the CT device to track the progression of the contrast agent through the region of interest (ROI).

Phantoms, which are typically static structures, are challenged in quality assurance and calibration applications for CT devices used to capture dynamically changing images.

DETAILED DISCLOSURE

Medical imaging applications seek to provide visual representations of bodily structures, organs, and organ systems. Computed tomography (CT) is one known platform for diagnostic imaging. While CT will exemplarily be used throughout the current description, it will be understood by one of ordinary skill in the art that medical imaging devices may include other modalities of imaging devices used in the medical field.

One type of procedure that may be performed with a CT device is a blood perfusion analysis. Perfusion analysis evaluates an organ or tissue-region for the flow and/or distribution of blood (perfusion) within the targeted organ, or tissue-region by examining the blood flow in the vessels feeding the organ or tissue-region.

In perfusion analysis, the patient is injected with a contrast material. Often, this contrast material is a radiopaque substance that stands out in radiographic images as compared to tissue and fluids commonly found in the body. As an example, the contrast material may be on iodinated compound. A region of interest (ROI) is scanned with the CT device multiple times in order to capture the distribution over time of the contrast material through the vessel, organ, or tissue-region being imaged.

As the perfusion analysis progresses, the amount of the contrast material first increases, then peaks, and is finally washed out of the vessel, organ, or tissue-region. This progression can be seen in the changing CT number for the ROI as obtained from an analysis of each of the progressive CT scans of the ROI.

Specific to each type of vessel, organ, or tissue-region selected to be the ROI for the perfusion analysis, the resulting time-density curve of the CT number of the ROI across progressive scans exhibit generalized graph curves or shapes that are associated with normal and abnormal perfusion through the vessel or tissue. Identified deviations from expected normal perfusion graph curves can provide diagnostic and therapeutic insight to trained healthcare professionals.

As disclosed herein, a CT perfusion phantom enables the calibration and continued quality assurance that the CT number time density curves obtained from a CT apparatus during a perfusion analysis are accurate.

FIG. 1depicts a medical imaging system10. The medical imaging system10includes a computed tomography (CT) device12. The CT device12includes one or more x-ray radiation sources (not depicted) that rotate about a defined path. The radiation sources are supported by a circular gantry14or a C-arm (not depicted).

The CT device12is communicatively connected to a computer16or another processing unit. In one embodiment, the computer16is integrated with the CT device12and in an alternative embodiment, the computer16is a separate component that is communicatively connected such as with wired or wireless communication platforms. The computer16executes computer readable code that is either stored locally or at a remote computer storage location, such as a server18that is communicatively connected to the computer16by wired or wireless communication networks.

The computer16executes the computer readable code to operate the CT device12in order to capture medical images in the manner directed by a clinician or other user through a user interface20. The user interface20comprises a graphical display22that presents one or more graphical user interfaces (GUI) that present captured medical images or user input prompts, other medical or patient information, or a combination thereof. The user input device20further includes a data entry device24that is exemplarily a keyboard, mouse, or touch screen, or any other of a variety of data entry devices as would be recognized by one of ordinary skill in the art. In alternative embodiments, the computer16, user interface20, graphical display22, and data entry device24can be integrated into any of a variety of devices, such as, but not limited to desktop computers, laptop computers, tablet computers, or mobile computers/smartphones.

The medical imaging system10further includes a movable gurney26. The movable gurney26is configured to support a patient or other subject for imaging by the CT device12. The movable gurney26translates along arrow28to position the subject within the gantry14. Additionally, the movable gurney26can be movable along additional axes, including but not limited to four degrees of freedom movement. The positioning of the subject within the gantry14on the gurney26aligns a particular region of interest (ROI) of the subject with an imaging plane of the one or more radiation sources of the CT device12. The one or more radiation sources of the CT device12each produce image slices through the subject along the imaging plane. The translation of the movable gurney26changes the ROI of the patient that is imaged by the CT device. An embodiment of the perfusion phantom30is depicted as being placed on the movable gurney26. While embodiments of the perfusion phantom30will be described in further detail herein, the perfusion phantom30includes a scan plane32. In use of the perfusion phantom30, the movable gurney26is translated generally along arrow28in order to align the scan plane32of the perfusion phantom30with the imaging plane of the radiation sources of the CT device12.

FIG. 2is a side view of an embodiment of a perfusion phantom. The perfusion phantom30includes a CT end34that extends between the scan plane32and a CT end handle36. The perfusion phantom30further includes a drive end38that extends between the scan plane32and a drive end handle40. In an embodiment, the perfusion phantom30is oriented on the gurney26(FIG. 1) in a manner such that the CT end34extends into the CT device12past the imaging plane of the CT device12. However, it is understood that these designations are used for descriptive purposes and it will be recognized by one of ordinary skill in the art that embodiments of the perfusion phantom30can be designed to have alternative orientations with respect to a CT device12.

The handles36and40facilitate the movement and proper placement of the phantom30on the gurney by a technician. The handles36and40further form the opposing ends of the perfusion phantom30. The handles36and40also provide structural support to the phantom30. A CT end outer tubular cover42extends from the CT end handle36to the scan plane32. A drive end outer tubular cover44extends from the drive end handle40to the scan plane32. The outer tubular covers42and44further provide structural integrity to the perfusion phantom30as well as protect the operational elements of the perfusion phantom30contained within. The outer tubular covers42and44define a CT end open interior46and a drive end open interior48(FIG. 4), respectively, on either side of the scan plane32between the scan plane32and a respective handle36or40. The outer tubular covers42and44may be visually transparent or opaque in construction, as outer covers42and44of a transparent material will permit the viewing of the elements within the perfusion phantom30by a user which may facilitate a basic user confirmation that the perfusion phantom30has been assembled correctly as disclosed in further detail herein.

FIG. 3is a cutaway slice view of an embodiment of the perfusion phantom30as taken along plane3ofFIG. 1and line3-3ofFIG. 2.FIG. 4is a cutaway view of the perfusion phantom30, as take along plane4ofFIG. 1and line4-4ofFIG. 2. It is understood that as the views of the perfusion phantom30inFIGS. 3 and 4are different views of the same embodiment, that like reference numerals betweenFIGS. 3 and 4identify the same structures and that the following description is in reference toFIGS. 3 and 4.

Referring specifically toFIG. 4, a rail50extends from either side of the scan plane32through the open interiors46and48. A rail50extends from the CT end handle36to the scan plane32. A rail50extends from a drive support52on the drive end38to the scan plane32. It is recognized that in embodiments, a plurality of rails50extending away from the scan plane32may be used.

A carriage54is defined between two opposed end plates56. Sample tubes that extend between the end plates56provide structural support and linear dimension to the carriage54. In the embodiment of the perfusion phantom30depicted, the carriage54includes at least one vessel sample tube58and at least one tissue sample tube60. In the embodiment of the perfusion phantom30depicted inFIGS. 3 and 4, there are two vessel sample tubes58and two tissue sample tubes60as can be best seen inFIG. 3. However, it is to be understood that alternative embodiments may include other numbers of sample tubes. In the embodiment depicted, the sample tubes58and60are circular in cross section and the vessel sample tubes58differ in dimension from the tissue sample tubes60. It will be recognized that in alternative embodiments, the sample tubes58and60may be constructed of alternative cross sectional shapes or sizes based upon material, necessity, or the specific tissue region, organ, or organ system to be modeled.

The carriage54is controllably positioned within the perfusion phantom30by a worm gear62that is driven by a motor64. A drive shaft66of the motor64is operationally connected to the worm gear62by a coupling68.

The motor64is exemplarily an electric motor that receives energization from a power supply70which is exemplarily a battery. Alternative embodiments include a power supply70that is a power cord coupling suitable to connect the perfusion phantom30to a suitable source of utility electricity. The motor64operates to turn the drive shaft66either in the clockwise or counterclockwise directions, such rotation is translated to the worm gear62, which through nut72in the end plate56, translates into linear motion of the carriage54in the direction of arrow74. The end76of the worm gear62is rotatably coupled to the scan plane32.

While the motor64has been described above as driving a worm gear62, it will be understood by persons of ordinary skill in the art in view of this disclosure, that a variety of other styles and configurations of motors and drives may be incorporated into embodiments of the phantom as disclosed herein. Non-limiting examples of such motors and configurations include, but are not limited to a linear motor, a cable drive, or a linear actuator.

Bearings78in the end plates56facilitate sliding engagement between the end plates56and the rails50. Thus, operation of the motor64can move the carriage54along the rail or rails50to move the carriage54between a first carriage position wherein a greater portion of the carriage54is located in the CT end34of the perfusion phantom30, and a second carriage position wherein a greater portion of the carriage54resides in the drive end38of the perfusion phantom30.

Limit switches80are respectively positioned on the drive support52and the scan plane32. Arrestor pads82positioned on the end plate56interact with a respective sensor84of each of the limit switches80. In one embodiment, the sensors84are pressure sensors that sense the impact of the arrestor pads82to indicate that the carriage54has reached one end of the translational path of the carriage54. While described above as being a pressure sensor, it will be understood that in alternative embodiments, the sensor84may be mechanical, magnetic, electrical, or another type of sensor known to one of ordinary skill in the art. The arrestor pad82would similarly be selected such as to facilitate interaction with the type of sensor84in the embodiment.

FIG. 5depicts an isometric view of an embodiment of the perfusion phantom30. Particularly,FIG. 5depicts the drive end handle40of the drive end38of the perfusion phantom30. The controls for the perfusion phantom30are located in the drive end handle40. A toggle switch130is operated by a clinician or technician between the positions of “forward”; “off”; and “reverse.” It is with the toggle switch130that the clinician or technician controls the direction of the movement of the carriage54(FIG. 3) within the perfusion phantom30. LED indicator lights132provide a visual feedback indication of the basic operation of the phantom, namely whether the carriage is being driven forward, reverse, or is off. Additional controls of the LED indicator lights132, exemplarily blinking, can be used in embodiments to indicate a low battery or other maintenance and/or warning conditions.

It is to be understood that alternative embodiments, a more complex user interface that exemplarily includes a number pad (not depicted) or other input device and/or LCD display (not depicted) or other graphical display may be used in some embodiments, particularly in embodiments of the perfusion phantom as disclosed herein with more complex and/or more detailed control over the operation of the perfusion phantom.

The drive end handle40further includes battery slots134that are configured to receive and retain one or more batteries which, in embodiments, may be used as a power source for the perfusion phantom30. The drive end handle40further includes a fuse slot136in which a fuse (not depicted) used for electrical isolation and protection of the components of the perfusion phantom is disposed.

Referring back to—FIGS. 2 and 4, the perfusion phantom30is modularly constructed such that the phantom30can be at least partially disassembled for adjustment and maintenance of the components within the phantom30. As such, the outer perimeter of the perfusion phantom30as defined by the handles36and40and the covers42and44are secured to the scan plane32and to the drive support52with the use of a plurality of fasteners86, which may, in an exemplary embodiment, be screws as shown inFIGS. 4-6. In one particular embodiment, one or more screws86can be removed to separate the CT end handle36and the CT end tubular cover42from the perfusion phantom30, thus exposing the CT end34of the components within the perfusion phantom30. As shown inFIGS. 3 and 4, the vessel sample tubes58and the tissue sample tubes60each have open ends88at the CT end34. The open ends88are configured such as to receive sample rods as will be described in further detail herein. As noted above, just as the vessel tubes58and the tissue sample tubes60may be of different sizes, shapes, or dimensions, the sample rods would similarly be constructed to a size, shape, and dimension to be received in one or more sample tubes. Specifically, vessel sample rods90are dimensioned to be received within the vessel sample tubes58and tissue sample rods92are dimensioned to be received within the tissue sample tubes60. Retaining clips94secure the sample rods within the sample tubes58and60. It is understood that while the retaining clips94have been depicted in the currently described embodiment, a person of ordinary skill in the art would recognize a variety of other suitable retaining solutions, including, but not limited to clips, clasps, friction fit, or screw fit retaining solutions that may also be used to secure the sample rods within the respective sample tubes58and60.

As will be disclosed in greater detail herein, after the sample rods are secured within the respective sample tubes, the CT end tubular cover42and CT end handle36can be re-assembled to close the phantom30into a condition for use.

As will be described in further detail herein, the perfusion phantom30further includes a tube that can accept an ion chamber96that extends through the CT end34of the perfusion phantom30and at least partially through the scan plane32. More specifically, the ion chamber96, when within the holder, extends at least through a center line98of the scan plane32. As will be described in further detail herein, the ion chamber96when inserted into the holder provides the functionality to the perfusion phantom30of the measurement of radiation dose during a calibration or quality assurance procedure with a CT device. This measurement of radiation dose during a calibration procedure can be used to tailor a procedure to minimize radiation dose delivered to a patient.

FIG. 6is a sectional view of an embodiment of a perfusion phantom30without the CT and tubular cover42, taken along line6-6ofFIG. 5.FIG. 6depicts in an isometric relation many of the features previously depicted and described with respect toFIGS. 3 and 4above. In particular,FIG. 6shows the tissue sample rods92disposed within the tissue sample tubes60and the vessel sample rod90that is disposed within the vessel sample tubes58. As shown inFIG. 6, one of the vessel sample rods90can represent a vein while the other sample rod90represents an artery. The isometric view ofFIG. 6further helps to show the relationship of the fixed structures within the phantom30, such as the ion chamber96, scan plan32, and the rail50in relation to the movable components of the carriage54that include the end plate56, vessel sample tubes58, and tissue sample tubes60.

FIG. 7depicts an exemplary embodiment of a sample rod as disclosed above with respect to the embodiment of the perfusion phantom30. The sample rod depicted inFIG. 7is exemplarily a tissue sample rod92. However, it will be understood that the disclosure herein with respect to the tissue sample rod92is equally applicable to a vessel sample rod90. The tissue sample rod92has a measurement region100which is defined by a plurality of sample cells101-116. While the embodiment of the tissue sample rod92depicted inFIG. 7includes sixteen sample cells, it is to be understood that this number of cells is merely exemplary and alternative embodiments of sample rods may include more or fewer sample cells. Each of the sample cells are constructed of a material with a CT number that is selected independently from the CT numbers of the other sample cells. Similarly, the CT numbers selected for the sample cells will depend upon whether the sample rod92is designed to represent a vessel such as an artery or a vein, or organ tissue, and further which organ or organ structure is to be represented by the sample rod. In exemplary embodiments, the tissue sample rod92represents a sample area of the brain.

The CT number of each of the sample cells101-116is selected to create a model perfusion graph when each of the cells101-116are sequentially scanned by a CT device. Thus, the change in the CT number across a sequential scan of the sample cells101-116represents the wash in and wash out of the contrast agent into the tissue, artery, or vein represented by the sample rod. In an embodiment, the sample rod is constructed of an epoxy material and the CT number is achieved in each of the cells by varying concentrations of additive substances to the epoxy. Two such additives are iodine and calcium. Increased concentrations of these materials within the cell will result in a cell that produces a higher CT scan result when imaged by a CT device.

In a still further embodiment, the shape, size, or diameter of the sample rod, or the sample cells within the sample rod, are designed to achieve a designated CT number or characteristic.

Table 1 provides exemplary CT numbers for exemplary sample cells for sample rods representing tissue, artery, or vein of a patient. The CT numbers are provided in Hounsfield units (HU).

FIG. 8is a graph120that represents the CT number results of an exemplary CT scan of each of the sample rods represented in the table above. In the embodiment that resulted in the graph ofFIG. 8, each of the sample cells101-116of the sample rod92is approximately one centimeter in length and the perfusion phantom30as described above moves the sample cells of the sample rod through the scan plane at a constant exemplary speed of 0.24 centimeters per second. Arrow118inFIG. 7represents the direction of movement of the sample rod92through the scan plane. In an embodiment, the CT number detected by the CT device is a moving average of the CT number detected across a group of scans. It is to be understood that in modern CT devices, multiple scans are simultaneously performed on the subject. In two non-limiting examples, the CT device can simultaneously perform three scans or five scans of the subject with slightly different alignments within the scan plane.

Referring to the graph120ofFIG. 8, the graph120depicts the measured CT number for a scan of each of the tissue sample rod122, artery sample rod124, and vein sample rod126. As will be described in further detail herein, ideal results for the result graphs122,124, and126are known based upon the design of the specific sample rod used in the perfusion phantom30and the operational settings of the perfusion phantom30. Therefore, the actual results obtained with the CT device can be compared to the known ideal scan results and adjustment or calibrations can be made to the CT device in order to achieve the known ideal scan result as the actual result. Particular deviations from the idealized graphs can be informative to skilled clinicians/technicians or analysis software in identifying the adjustment and/or correction that is required to calibrate the CT device in order to achieve the desired results.

In still further embodiments, the model CT perfusion graphs can be representative of a “normal” expected result of the perfusion of the contrast agent through the artery, vein, or tissue of the patient. The actual results performed in a CT perfusion procedure can be compared to the model graphs as obtained from a pre-procedure scan of the perfusion phantom in order to identify deviations from the actual results obtained from the patient in comparison to the model or normal expected results. This application can further assist a clinician in identifying areas of concern or abnormal perfusion procedure results.

FIG. 9is a flow chart that depicts an embodiment of a method200of testing and/or calibrating a CT device for performance of a perfusion analysis procedure.

At202, at least one sample rod is selected for use in the method200. As disclosed above, the sample rods are constructed to each represent different vessels, tissues, organs, or organ systems to be scanned in the CT perfusion analysis procedure. Additionally, different sample rods are constructed to represent different types and concentrations of contrast agent delivered to the patient, or to represent the results of varying patient pathologies.

At least one sample rod is inserted into the perfusion phantom at204. The perfusion phantom, as disclosed above, may include a plurality of sample tubes to receive a plurality of sample rods selected at202. The sample tubes of the phantom may be arranged in a variety of layouts or orientations, and may exhibit different shapes, sizes, or dimensions in order to receive varying shapes, sizes, or dimensions of sample rods. Some or all of the sample tubes of the phantom may be used simultaneously as disclosed herein.

At206, the motor controls for the perfusion phantom are set. As disclosed above, a motor in the perfusion phantom moves the carriage containing the sample rods through the scan plane of the phantom. In the exemplary embodiment above, the motor operates to drive the carriage at the rate of 0.24 centimeters per second. It is understood that in alternative embodiments, the clinician or technician performing the method200can control the motor of the phantom to drive the carriage at any of a variety of rates. In an alternative embodiment, the motor controls may be established to operate the motor at a variety of speeds, such that the carriage moves the sample rods through the scan plane of the phantom at varying speeds throughout the procedure, as defined in the motor controls. In a still further embodiment, the motor controls operate the motor to move the carriage such that the sample rods move back and forth through the scan plane. By adjustment of the motor controls, such as through varying routines or procedures, further bodily conditions can be represented with the perfusion phantom.

At208, the clinician or technician aligns the perfusion phantom with the CT device. The perfusion phantom can be aligned with the CT device as disclosed above by securing the phantom to a movable gurney and operating the movable gurney to locate the perfusion phantom within the CT device. The alignment of the perfusion phantom with the CT device may include embodiments of aligning a CT imaging ROI with the perfusion phantom scan plane.

At210, both the CT scanning procedure and the movement of the perfusion phantom carriage are initiated. In an exemplary embodiment, a coordination of the motor controller and the CT device controller is used to initiate the CT scan and the carriage movement simultaneously. In still a further embodiment, the CT scan and carriage movement are initiated in rapid succession, while in still further embodiments, a delay is incorporated into the initiation of one or more of the CT scan and carriage movement.

As disclosed above in embodiments, the CT scan is a perfusion analysis procedure which is stored as a functionality of the CT device that is carried out by operating the CT device according to stored computer programs or modules of the CT device, as disclosed above.

The CT scan of the perfusion phantom is performed at212. If the perfusion phantom includes a plurality of sample rods as discussed above with reference to202and204, the clinician or technician identifies an ROI for each of the sample rods in the captured CT images and the CT device determines a CT number of each of the ROIs in the successive CT images captured by the CT device in performing the scan of the perfusion phantom.

At214, the resulting graph of the CT numbers for each of the sample rods is compared to a model graph that is specific to each of the sample rods and motor control settings used in the perfusion phantom. The comparison between the acquired CT numbers and the CT numbers of the model graph associated with the sample rod can be compared in a variety of ways, including, but not limited to statistical or morphological analysis of the differences between the acquired and modeled CT number graphs.

The CT device is adjusted or calibrated to correct for any identified deviation between the actual and model CT number graphs at216. In an alternative embodiment, identification of particular deviations between the actual and model CT number graphs will indicate the need for CT device service or other condition in which the CT device should not be used for a perfusion analysis procedure. With the completion of the adjustment or calibration of the CT device216, some embodiments of the method200are completed. In other embodiments, the method200continues to222where additional CT perfusion procedure scans of the perfusion phantom are performed to check and/or to recheck the adjustments or calibrations made to the CT device before the use of the CT device to perform a perfusion analysis procedure on a patient.

In another embodiment, radiation exposure from the performed CT scan is studied at218. The radiation exposure is measured with the ion chamber included in embodiments of the perfusion phantom disclosed above. Since CT perfusion analysis procedures are a type of CT exam where one small portion of the patient's anatomy is studied over multiple scans, the target area has the potential to receive a high radiation dose. Therefore, a study of the radiation exposure at step218as measured by the ion chamber of the perfusion phantom enables the clinician or technician at step220to adjust the CT device settings to reduce or minimize radiation exposure from the perfusion procedure. The addition of the radiation exposure information as a result of conducting a CT scan of the perfusion phantom enables the clinician or technician to experiment with procedure protocols or CT device settings in order to identify or establish a protocol to deliver a minimized radiation dose while still achieving desirable CT results as identified through the comparison of the actual and model CT number graphs at214.

Finally, at222, additional CT perfusion procedure scans of the perfusion phantom are performed to check and/or to recheck the adjustments or calibrations made to the CT device before the use of the CT device to perform a perfusion analysis procedure on a patient.

While the invention has been described with reference to a preferred embodiment, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made without departing from the spirit thereof. Accordingly, the foregoing description is meant to be exemplary only and should not be deemed limitative on the scope of the invention set forth with the following claims.