Method for monitoring the PET readout position using MRI fiducials

Abstract

A method of measuring PET system position using MRI using an MRI coil and fiducials is described herein. This method provides a more flexible approach to automatic calibration than other methods. This position measurement method is useful in, for example, systems with mobile or removable PET readout board systems or with mobile or removable PET scintillator blocks.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 945,468, filed on December 9, 2019, entitled “Method for Monitoring PET Readout Positions using MRI Fiducials,” which is hereby incorporated by reference in its entirety for all purposes. Technical Field

[0003] The present application relates to a method for monitoring PET readout position using MRI fiducials. Background Art

[0004] Simultaneous PET and MRI systems can be designed as systems manufactured together as a single unit, or as systems in which the PET is inserted into the MRI at the customer's site and never removed, or as systems in which the PET is inserted into and removed from the MRI at the customer's site, with insertion and removal occurring daily or weekly. For all of these systems, calibration and image registration are necessary to account for performance differences that arise between the MRI and PET systems. More flexible and automated calibration and image registration procedures are particularly useful for combined simultaneous PET and MRI imaging systems in which the PET system is inserted and removed daily or weekly. These flexible and automated procedures can save customers time and money while also improving accuracy. One issue that can arise with PET insertion systems is the exact positioning of the PET system's scintillator blocks and readout plates. This is because, with PET insertion systems, the PET can be removed and replaced at the customer's site, meaning that the specific alignment may not be equivalent to the alignment used at the time of manufacture. The exact position of these readout plates must be known and maintained to achieve accurate reconstruction.

[0005] One way to achieve accurate positioning is through a manufacturing process in which the tolerances of the parts are maintained to achieve the tolerances required for the scintillator and readout system. This approach requires the added cost of manufacturing the parts and may not be very useful if the position of the parts changes due to maintenance or other factors, such as heating or cooling of the parts.

[0006] Prior art PET imaging systems have been designed to use fiducials to identify the location of an object.

[0007] For example, US 5,947,981 identifies a fiducial method for head and neck treatments. This patent is referenced by numerous other patents and patent applications, all of which appear to use fiducial methods in surgical or diagnostic imaging designs, but none of which use fiducials to measure the position of PET readout elements.

[0008] Specifically, the patent teaches attaching a graphical reference device to a horizontal arm. The graphical reference device can include horizontal bars and diagonal elements that provide graphical reference markers for image scans. This enables reference of scanned image data and the patient's anatomy relative to the horizontal arm.

[0009] Several other patents have been filed for using moving elements in PET systems to achieve various resolution and performance goals, including:

[0010] U.S. Patent No. 8,295,905, titled “Movable integrated scanner for surgical imaging applications,” filed in 2007;

[0011] “Apparatus for Improving Image Resolution and Apparatus for Super-Resolution Photography Using Wobble Motion and Point Spread Function (PSF), in Positron Emission Tomography,” filed as application US20110268334A1, in which a PET cylinder wobbles;

[0012] “Method for acquiring pet image with ultra-high resolution using movement of pet device”, this is an application, WO2013162172A1;

[0013] U.S. Patent 5,825,031A, issued in 1996, for a "Tomographic pet camera with adjustable diameter detector ring," in which the diameter of the PET cylinder can be changed; and

[0014] "Pet camera with individually rotatable detector modules and / orindividually movable shielding sections", US Patent 6,744,053.

[0015] None of these PET-related patents use fiducials to position PET components.

[0016] Instead, these system designs allow the detector elements to move radially to accommodate object size, axially to match the surgical procedure at the start of imaging, and in an oscillating motion to optimize line sampling response.

[0017] As will be appreciated by those skilled in the art, these types of removable insertion systems would benefit from methods of measuring the position of the PET element using MRI methods. Summary of the Invention

[0018] According to a first aspect of the present invention, there is provided a PET ring comprising at least one PET readout element marked with at least one MRI detectable fiducial.

[0019] According to another aspect of the present invention, in an MRI system comprising an MRI bore, there is provided:

[0020] A PET ring is inserted into the MRI bore, the PET ring including at least one PET read element marked with at least one MRI-detectable fiducial.

[0021] According to another aspect of the present invention, there is provided a BrainPET, comprising:

[0022] A PET ring comprising at least one PET readout element marked with at least one MRI-detectable fiducial

[0023] an MRI coil, located within the PET ring, and

[0024] A radio frequency shield is located outside the PET ring.

[0025] According to another aspect of the present invention, a method for co-registering an MRI image and a PET image is provided, comprising:

[0026] Provides a BrainPET, including:

[0027] a PET ring comprising at least one PET readout element, marked with at least one MRI-detectable fiducial,

[0028] An MRI coil, located inside the PET ring,

[0029] a radio frequency shield located outside the PET ring; and

[0030] a control unit including data acquisition, reconstruction and analysis software;

[0031] The MRI coil detects and locates at least one MRI-detectable fiducial on the at least one PET readout element;

[0032] Generate a PET scan of a patient using a PET ring;

[0033] generating an MRI scan of a patient using an MRI coil;

[0034] the data acquisition, reconstruction, and analysis software determining the position of the at least one PET readout element relative to the MRI coil based on the position of MRI detectable fiducials; and

[0035] The data acquisition, reconstruction, and analysis software co-registers the MRI scan and the PET scan based on the position of at least one PET readout element relative to the MRI coil.

[0036] According to another aspect of the present invention, a method for co-registering an MRI image and a PET image is provided, comprising:

[0037] Provided are: an MRI system comprising an MRI bore; a workstation comprising data acquisition, reconstruction, and analysis software; and a BrainPET inserted into the MRI bore, the BrainPET comprising:

[0038] a PET ring comprising at least one PET readout element, marked with at least one MRI-detectable fiducial,

[0039] an MRI coil, located within the PET ring, and

[0040] A radio frequency shield, located outside the PET ring;

[0041] The MRI coil detects and locates at least one MRI-detectable fiducial on the at least one PET readout element;

[0042] Generate a PET scan of a patient using a PET ring;

[0043] generating an MRI scan of a patient using an MRI coil;

[0044] the data acquisition, reconstruction, and analysis software determining the position of the at least one PET readout element relative to the MRI coil based on the position of MRI detectable fiducials; and

[0045] The data acquisition, reconstruction, and analysis software co-registers the MRI scan and the PET scan based on the position of at least one PET readout element relative to the MRI coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 An MRI, cart, and BrainPET scanner are shown.

[0047] Figure 2 Shown are the components of a PET scanner, including the head holder, Rx coil, Tx coil, and PET ring.

[0048] Figure 3 A cross-sectional view of the PET ring is shown with the coil in place.

[0049] Figure 4 A schematic diagram of the components of a BrainPET scanner. DETAILED DESCRIPTION

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned below are incorporated herein by reference.

[0051] Described herein is a method for co-registering MRI and PET scans by using MRI coils and MRI-detectable fiducials to measure the position of a PET system's readout element using MRI. This method provides a more flexible approach to automated calibration than other methods. This position measurement method is useful, for example, in systems with a movable or removable PET readout plate or a movable or removable PET scintillator block.

[0052] As will be appreciated by those skilled in the art, this arrangement can be used to co-register MRI and PET scans in any MRI / PET imaging system. As discussed herein, this approach is ideal for co-registering MRI and PET images, but of course this approach can also be used to register non-simultaneous images.

[0053] For example, assume a system comprising a BrainPET imaging system arranged to be inserted into an MRI system comprising at least:

[0054] Previously installed MRI,

[0055] A docking station,

[0056] a BrainPET insert that can be slid or placed into the MRI, and

[0057] A workstation installed in the MRI control room with appropriate data acquisition, reconstruction, and analysis software;

[0058] Part of this system is Figure 1 Specifically, Figure 1 FIG1 is a diagram of a BrainPET system showing a cart 12 behind a BrainPET scanner 11 and an MRI 13. The BrainPET scanner 11 is connected to the cart 12 via a copper cable 14 and a cable management system 17. In some embodiments, the copper cable 14 is 10 to 20 feet long, depending on the type of MRI being used. The scanner weighs between 50 and 100 pounds, so a scanner movement system 15 is required to lift the scanner and place it on the MRI bed 16. The diagram shows the cart, MRI, insert, and cable management method. The BrainPET workstation and the fiber optic connections to the workstation are not shown.

[0059] In one embodiment, a BrainPET scanner comprises:

[0060] an MRI coil within the PET ring, and

[0061] A PET ring having readout elements, such as scintillator and detector elements, includes at least one MRI-detectable fiducial positioned on at least one of the readout elements.

[0062] Figure 2 An embodiment of a BrainPET scanner is shown, showing a head holder 21, a PET ring 22, and Tx and Rx coils 23. The PET ring 22 and Tx and Rx coils 23 are connected together as a movable unit, sliding back and forth on a sliding platform 24. The PET ring 22 and Tx and Rx coils 23 have two locking positions, using a lock 25 on the side of the PET ring 22 to lock them in either the posterior or anterior position. Only one lock 25 is shown in this view. The Rx coil is located in the innermost position within the insert; the Tx coil is outside and adjacent to the Rx coil, and both the Rx coil and the Tx coil are within the PET ring 22. In some embodiments, the approximate dimensions of the scanner are an inner bore diameter of 26.5 cm, an Rx coil extending from 26.5 cm to 28 cm, a Tx coil extending from 28 cm to 32 cm, and a PET ring extending from 32 cm to 44 cm. As one skilled in the art will appreciate, these dimensions may vary in different specific designs and versions of MRI.

[0063] The BrainPET scanner or PET insert includes a head holder, an Rx coil, a Tx coil, and a PET ring. In this embodiment, the head holder, Rx coil, and Tx coil are removable from the PET ring for calibration purposes. This embodiment also shows a sliding portion that allows the scanner to be moved forward and backward and locked in place. Sliding capability is not required in all embodiments.

[0064] However, when replacing and / or reinserting coils, it is important to measure their position to ensure that the correct calibration meter is being used, which would indicate that the alignment of the components is incorrect or that a new calibration meter needs to be installed.

[0065] Figure 3 A schematic side view is shown showing a patient's head 31 positioned on a head holder 21 and a PET ring 22, within which is a Tx coil 35, and within which is an Rx coil 36. Four scintillator blocks 37 are positioned within the PET ring 22. The axial positioning of these scintillator blocks identifies or establishes the PET center of the field of view 38. In this example, an MRI fiducial 39 is shown positioned between scintillator blocks 2 and 3. As will be appreciated by those skilled in the art, in some embodiments, multiple fiducials may be placed on the scintillator and readout plate.

[0066] Figure 4 A "close-up" view of the scanner elements is shown, moving from the middle of the aperture to the outer edge. This includes, in increasing order, the center of the field of view 41, the inner plastic aperture of the scanner assembly 42, the Rx receive coil element 36, shown in this case as four circles indicating the Rx loop; the transmit element 35, shown as a single transmit line, although multiple transmit lines may exist, organized symmetrically around the circumference; the readout plate 32 and four scintillator blocks 37, with a fiducial 39 located on the plate; the RF shield 48, and the outer cover of the scanner 49. In one embodiment, the radii of these elements from the center of the aperture can be designed to be 13.25 cm from the center of the aperture to the inner plastic aperture of the scanner assembly, 14 cm from the center of the aperture to the start of the Tx assembly, 16 cm from the center of the aperture to the bottom of the scintillator, and 22 cm from the center of the aperture to the outer cover of the scanner 49. The scintillator is typically 2 cm thick, and the readout plate can be less than 1 cm thick. This allows for additional space between the readout board and the cover to provide adequate heat dissipation and wiring. Scintillators are typically blocks with an axial dimension of approximately 49 mm, with a typical gap between blocks of between 1 and 2 mm. This gap facilitates manufacturing, and the gap can be filled with material to ensure that the scintillator blocks do not contact each other during manufacturing and operation.

[0067] The readout board consists of SiPM pixels that convert light into electrical signals, readout board resistors and capacitors, optical glue or gel, reflective tape, and optical methods to allow readout or detection of scintillation events. MRI-detectable fiducials can be placed on this readout board.

[0068] MRI-detectable fiducials are commonly and previously used on patients during imaging and are used to identify "landmarks," e.g., anatomical sites or regions of a patient, during imaging. Suitable MRI-detectable fiducial materials include, but are not limited to, copper sulfate, iodine, and gold particles. Other suitable materials for MRI-detectable fiducials used in the present invention will be apparent to those skilled in the art.

[0069] Fiducials can be purchased from suppliers who specialize in their design. Typically, they are gel or liquid enclosed in a capsule and are approximately circular in shape.

[0070] Those skilled in the art will appreciate that due to manufacturing tolerances, the readout board cannot be misaligned by more than 2 mm. That is, any problematic readout board will be identified during the manufacturing process and / or during the manufacturing acceptance process. Specifically, if such a large misalignment occurs, the circuit board and assembly will never be shipped. However, even a misalignment of less than 2 mm is important when aligning or co-registering MR and PET images. However, the combination of fiducials arranged for fiducial positioning software and imaging software allows the images to be automatically aligned. As discussed herein, the combination of fiducials and software designed to detect the fiducials and align the scan based on the location of the fiducials and, therefore, the location of the PET readout element will adjust for fiducials that are off by 1 or 2 mm. In some embodiments, more than one fiducial can be placed on the corresponding readout element, preferably arranged in an asymmetrical manner on the readout element to facilitate alignment, thereby achieving a more precise alignment overall.

[0071] The location of the fiducials is mechanically controlled by the design of the board and is typically within 1mm of the desired location. Even if the fiducials are placed within 1mm of the desired location, the final accuracy of image alignment is better than 1mm when many fiducials need to be averaged.

[0072] As described herein, the readout plate is external to the RF shield that is part of the MRI coil system. Because the shield is external to the readout plate, the fiducials are within the field of view of the RX coil. With this arrangement, the MRI-detectable fiducials are visible to the MRI system. The MRI system can automatically align the fiducials, which are located at known positions and have known spatial orientations relative to the readout plate components, so that the positions of the fiducials, and therefore the readout plate and PET components, are known.

[0073] For a typical BrainPET system, there will be 16 or more readout plates arranged around the circumference of the PET ring. In some embodiments, each of these readout plates can have at least one MRI-detectable fiducial. It will be apparent to one skilled in the art that having more than one MRI-detectable fiducial, for example, two or more MRI-detectable fiducials, on a given PET readout element (e.g., a readout plate or scintillator block) can improve the accuracy of positioning the readout element. In this way, as described herein, the position of each readout element, for example, the position of each readout plate and / or scintillator element, can be calibrated and / or adjusted, or the co-registration of the images can be adjusted, if necessary.

[0074] In one aspect of the present invention, a PET ring is provided that includes at least one PET readout element marked with at least one MRI-detectable fiducial.

[0075] As will be appreciated by those skilled in the art, such a PET ring may be placed within an MRI bore and used to co-register PET and MRI scans or images using the methods described herein.

[0076] As discussed herein, at least one PET readout element is a readout plate or a scintillator block.

[0077] As discussed herein, at least one readout element can include two or more MRI-detectable fiducials that are asymmetrically arranged relative to each other. In particular, using two or more MRI-detectable fiducials can achieve more accurate co-registration.

[0078] In another aspect of the present invention, an MRI system is provided that includes an MRI bore; a PET ring that is inserted into the MRI bore, the PET ring including at least one PET read element marked with at least one MRI-detectable fiducial.

[0079] Those skilled in the art will appreciate that in these embodiments, the PET ring is inserted into the MRI bore. Such insertion may be temporary (i.e., the PET ring is removable) or permanent (i.e., the MRI system includes a PET ring in the bore or is modified to include a PET ring).

[0080] In another aspect of the invention, an MRI body coil may be used as the Tx coil, in which case only the PET ring and the Rx coil are designed to be close to the patient's head.

[0081] In some embodiments of the present invention, a BrainPET is provided, comprising: a PET ring including at least one PET readout element marked with at least one MRI detectable fiducial, an MRI coil inside the PET ring, and an RF shield outside the PET ring.

[0082] Although this arrangement is referred to as "BrainPET," it is important to note that this device can be used to perform simultaneous MRI and PET scans of body parts other than the brain, as will be apparent to those skilled in the art.

[0083] It should also be noted that as used herein, "simultaneously" with respect to PET and MRI scan generation does not necessarily mean that the scans are taken at exactly the same moment in time, but rather may mean taken within a sufficiently close time without moving the patient or the patient themselves.

[0084] According to another aspect of the present invention, a method for co-registering an MRI image and a PET image is provided, comprising:

[0085] Provides a BrainPET, including:

[0086] A PET ring comprising at least one PET readout element marked with at least one MRI-detectable fiducial

[0087] an MRI coil, located within the PET ring;

[0088] A radio frequency shield located outside the PET ring; and

[0089] A control unit including data acquisition, reconstruction and analysis software,

[0090] The MRI coil detects and locates at least one MRI-detectable fiducial on at least one PET readout element;

[0091] Generate a PET scan of a patient using a PET ring;

[0092] generating an MRI scan of a patient using an MRI coil;

[0093] The data acquisition, reconstruction, and analysis software determines the position of at least one PET readout element relative to the MRI coil based on the position of the MRI detectable fiducials; and

[0094] The data acquisition, reconstruction, and analysis software co-registers the MRI scan and the PET scan based on the position of at least one PET readout element relative to the MRI coil.

[0095] According to another aspect of the present invention, a method for co-registering an MRI image and a PET image is provided, comprising:

[0096] Provided are: an MRI system comprising an MRI bore; a workstation comprising data acquisition, reconstruction, and analysis software; and a BrainPET inserted into the MRI bore, the BrainPET comprising:

[0097] a PET ring comprising at least one PET readout element, the at least one PET readout element being marked with at least one MRI-detectable fiducial;

[0098] an MRI coil located within the PET annulus; and

[0099] A radio frequency shield, located outside the PET ring;

[0100] The MRI coil detects and locates at least one MRI-detectable fiducial on at least one PET readout element;

[0101] Generate a PET scan of a patient using a PET ring;

[0102] generating an MRI scan of a patient using an MRI coil;

[0103] The data acquisition, reconstruction, and analysis software determines the position of at least one PET readout element relative to the MRI coil based on the position of the MRI detectable fiducials; and

[0104] The data acquisition, reconstruction, and analysis software co-registers the MRI scan and the PET scan based on the position of at least one PET readout element relative to the MRI coil.

[0105] It will be apparent to those skilled in the art that an MRI coil performs two separate and distinct functions.

[0106] Specifically, the MRI coil scans the patient in a first plane or direction, ie, below the MRI coil, but also detects MRI-detectable fiducials on the PET readout element in a second directional plane, ie, above the MRI coil.

[0107] That is, in use, the receive coils of the MRI coil receive images from the entire volume within the RF shield. Therefore, by placing the shield outside the PET readout plate, the PET readout plate is now in the field of view of the MRI coil. Therefore, by placing the MR fiducials on the readout plate, the fiducials are visible even if the MRI technician can see the image, i.e., the image that will be presented by the imaging software will only be the MRI scan of the patient. Therefore, although the technician does not necessarily see the fiducials, the MRI system, i.e., the control unit or workstation, "sees" the entire image or the entire volume within the RF shield. As described above, once the MRI system or control unit or workstation sees all of the MRI-detectable fiducials, the PET and MRI images are aligned based on the relative positions of the MRI coil and the PET readout element marked by the MRI-detectable fiducials.

[0108] Notably, as described herein, MRI-detectable fiducials may be detected by the RF coils before a patient is scanned, e.g., before the patient enters the scanning area or apparatus, or may be detected by the RF coils generally while a PET scan and an MRI scan are being performed.

[0109] While preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made therein, and the appended claims are intended to cover all such modifications that may fall within the spirit and scope of the invention.

Claims

1. A method for jointly registering an MRI image and a PET image, the method comprising: A BrainPET insertion device is provided that can be slid or placed in an MRI and includes: a PET ring comprising a PET readout plate and a scintillator block for scanning a patient and generating a PET image of the patient, wherein a plurality of MRI-detectable fiducials are disposed on the scintillator block and / or the PET readout plate; an MRI system including an MRI coil located within the PET ring for scanning a patient and generating an MRI image of the patient; a radio frequency shield located outside the PET ring; and a control unit including data acquisition, reconstruction and analysis software; generating the PET image of the patient using the PET ring; generating an MRI image of the patient using the MRI coil; the MRI coil scanning the patient in a first plane, the first plane being below the MRI coil, and detecting the MRI-detectable fiducials on the PET readout plate and / or scintillation block in a second plane, the second plane being above the MRI coil; The data acquisition, reconstruction, and analysis software determines the position of the PET readout plate and the scintillation block relative to the MRI coil based on the position of the MRI detectable fiducials; and When the MRI system detects all of the MRI-detectable fiducials, the PET image and the MRI image are aligned based on the relative positions of the MRI coil and the PET readout plate and / or scintillator marking the MRI-detectable fiducials.

2. The method according to claim 1, characterized in that At least one readout plate or scintillation block includes two or more MRI-detectable fiducials that are asymmetrically arranged relative to each other.

3. The method according to claim 1, characterized in that PET scans and MRI scans are done at the same time.

4. The method according to claim 1, characterized in that The MRI coil is part of the MRI system, which includes an MRI bore; and a workstation, which includes data acquisition, reconstruction and analysis software.

5. The method according to claim 1, wherein A combination of the MRI detectable fiducials and software designed to detect the fiducials and align images based on the position of the MRI detectable fiducials and therefore the position of the PET readout plate and / or scintillation block adjusts MRI detectable fiducials that are off by 1 mm or 2 mm.

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