KR20090039855A - Mri-pet-ct hybrid imaging system and method - Google Patents

Abstract

An MRI(Magnetic Resonance Imaging)-PET(Positron Emission Tomography)-CT(Computed Tomography) hybrid imaging system and an imaging method thereof are provided to correct spatial distortion phenomenon of the MRI image by using a CT image as a reference image. An imaging system(100) includes a first scanner(110), a second scanner(120), and a movable table(130). The first scanner obtains the first information. The first information includes the first anatomical information, the molecular information and the functional information. The second scanner obtains the second information. The second information includes the second anatomical information having the resolution different from the first anatomical information. The movable table moves between the first scanner and the second scanner. The movable table supports the subject.

Description

MRI-PET-CT hybrid imaging system and method {MRI-PET-CT HYBRID IMAGING SYSTEM AND METHOD}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to imaging systems and methods for non-invasive acquisition of images containing information about biological tissues, and in particular, Positron Emission Tomography (PET), Computed Tomography (Computed Tomography). Integrated imaging system and method that integrates Tomography (CT) and Magnetic Resonance Imaging (MRI) to provide high resolution images that include not only functional and molecular information but also anatomical information within human tissue It is about.

Medical images used for the diagnosis of patients are generally classified into structural images and functional images. The structural image refers to the structure and anatomical image of the human body, and the functional image is to image functional information about the human body's cognition, sensory function, etc. directly or indirectly. Structural imaging techniques include CT and MRI, and PET is widely used as a technique for imaging functional information by observing physiological / biochemical effects of the human body.

PET is a powerful biological imaging tool that quantifies non-invasive human function, injects biological probe molecules labeled with radioactive positron emitting isotopes into the body, and then reconstructs the distribution of radioactivity by tomography. Imaging can quantify the physiological and biochemical responses within each organ of the human body. Functional / molecular information on the structure of the human body, such as the brain and organs, provided by PET can be usefully used for studying the pathogenesis of diseases, determining the prognosis of the disease, and monitoring the progress after chemotherapy. However, since images obtained by PET have a lower anatomical resolution than images obtained by MRI or CT, it is difficult to determine the exact anatomical position of the lesion site or the relationship with surrounding organs. In addition, accurate gamma-ray attenuation correction is required to obtain accurate quantitative results in PET, and calculation of accurate attenuation constants is required for this.However, when the resolution and sensitivity of the transmission images using nuclides are low Since the attenuation constant cannot be extracted, the accuracy of the PET image is inevitably deteriorated.

CT is a diagnostic test equipment that reconstructs the structure of the human body into cross sections using X-rays and computers.It is a good test method for observing the location and shape of lesions because it reflects anatomical changes of human organs relatively easily and accurately. In addition, it has been difficult to characterize and early diagnose the lesion, and to evaluate the change of the lesion after treatment. The disadvantage of CT is that the patient is exposed to radiation and that a drug called contrast agent, which is often used to photograph blood vessels or to characterize tissues, may be dangerous for patients with renal failure or drug hypersensitivity.

MRI, which is the most widely used in clinical and research as an anatomical image, detects anatomical changes of human body using Nuclear Magnetic Resonance (NMR), unlike CT, so it is not exposed to radiation. It is harmless and provides anatomical information with high resolution compared to other imaging equipment. Because of this, MRI is very useful for imaging soft tissues such as muscles, ligaments, brain nervous system, and tumors. Recently, MRI has been widely used to determine the extent of soft tissue cancers such as breast cancer, liver cancer, ovarian cancer and cervical cancer. As mentioned, because MRI is an imaging device that provides anatomical imaging, it does not provide direct molecular / functional information such as that obtained through PET.

In view of the properties of PET, CT, and MRI as described above, attempts have been made in the art to combine the advantages of these PET, CT, and MRI. For example, by combining the existing PET to check the metabolic abnormalities of the body and the CT to check the structural abnormality of the body to obtain the functional and molecular information of the PET and the anatomical information of the CT at the same time, the diagnosis of diagnostic than the conventional PET A PET-CT system with increased accuracy has been developed, and a PET / MRI system is being developed that replaces CT with MRI in PET-CT in order to overcome the harmful effects of CT. .

In particular, Patent Application No. 2006-0051013 entitled "PET-MRI Hybrid System" (Application Date: September 5, 2005, Priority Date: September 6, 2004), PET, CT, MRI combined PET / CT-MRI imaging hybrid system is disclosed. The conventional PECT / CT-MRI system is a form in which CT is added to an existing PET / MRI system, and it is possible to simultaneously acquire functional and anatomical information from PET and MRI. The PET / CT-MRI imaging system includes an MRI scanner, an RF shield, a PET / CT scanner, a patient stand, a transport rail and an imaging processor. In this imaging system, an MRI scanner and a PET / CT scanner are placed at a considerable distance and an RF shield is formed between them in order to protect PET, which is easily damaged by magnetic fields, from the magnetic field from the MRI scanner. The pedestal for supporting the patient is sequentially transported in the direction of the MRI scanner and the PET / CT scanner along a transfer rail placed between the MRI scanner and the PET / CT, whereby images from each scanner are obtained in turn.

However, in the conventional PET / CT-MRI system, the moving table must be frequently moved along the transfer rail between the spatially separated MRI scanner and the PET / CT scanner for shielding, which causes the MRI scanner and the PET / CT scanner. There is a drawback that the image fusion combining may be difficult because the information obtained through the time-space is not exactly matched. That is, in a conventional system, when transferring a patient between an MRI scanner and a PET / CT scanner along a transfer rail, it is difficult not only to maintain exactly the same coordinates for the subject under each scanner, but also to obtain images from the MRI and PET / CT. Obtained at these different locations (different environments / conditions) and times (possibly metabolic changes during that time), test conditions change and thus there is room for inconsistency between the two images. Therefore, there is a need for an imaging system that can provide highly accurate functional / molecular image information and high resolution anatomical images, and further improve image fusion by allowing these images to be optimally synchronized temporally and spatially in the same environment. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a PET-CT-MRI hybrid imaging system and a method for implementing the same, wherein the anatomical and molecular information of human tissue is optimally synchronized temporally and spatially within a single image.

Another object of the present invention is to perform accurate attenuation correction on a PET image using information from a CT to improve accuracy in quantitative aspects of a fused PET image, and to correct spatial distortion of an MRI image. To provide a PET-CT-MRI hybrid imaging system.

According to an embodiment of the present invention, an imaging system for providing an image including anatomical information, molecular information, and functional information about a subject is provided, the system comprising: first anatomical information, molecular information And a first scanner for acquiring first information including functional information, a second scanner for acquiring second information including second anatomical information having a different resolution from the first anatomical information, and the first scanner. A moving table movable between the first scanner and the second scanner and for supporting the subject, wherein the first scanner comprises: means for obtaining the first anatomical information and the molecular information and the functional information; Means for obtaining are made integrally formed.

According to another embodiment of the present invention, there is provided a method for providing an image including anatomical information, molecular information, and functional information about a subject, the method, the first anatomical Moving to a first scanner acquiring information, molecular information and functional information, protecting the first scanner from an external RF field, at the first scanner the first anatomical information, the molecular information and the Acquiring functional information, moving the subject under test to a second scanner acquiring second anatomical information having a different resolution than the first anatomical information; and at the second scanner, the second anatomical information Obtaining a step.

The MRI-PET-CT hybrid system of the present invention has various effects as follows.

(1) Providing a more synchronous image of anatomical and molecular functional information

Since the system of the present invention is composed of MRI and PET as a single body, a high-resolution MRI image and a PET image that provides molecular function information can provide a fusion image in which time and space are optimally synchronized.

(2) Increased quantitative accuracy of PET images

As described above, contrast on hard materials such as bone can be used to extract accurate attenuation constants from the best CT images among medical imaging devices and use this attenuation constants to perform accurate attenuation correction on PET images. By doing so, it is possible to improve the accuracy in the quantitative aspect of the PET image to be fused.

(3) Correction of spatial distortion of MRI image

MRI is designed to classify spatial information by gradient magnetic field in MRI. However, this spatial information is likely to be distorted depending on the uniformity of the magnetic field in the MRI. Moreover, the degree of distortion becomes more severe as the magnetic field gets higher, and depends greatly on the pulse sequence and parameters used in the MRI, so no matter how physically matching the MRI and PET systems are, The two images may be spatially displaced. To correct this, an accurate reference image is required, but since the PET image has a very different resolution from the MRI image, there is a large error due to the difference in resolution between the two images. Therefore, by using a CT image having almost no such error as a reference image, accurate spatial information with high resolution without distortion can be obtained.

(4) Additional Information from CT

In addition, from a clinical point of view, CT can be combined with an integrated PET / MRI system to further improve imaging accuracy. Combining the same system means that images of PET, MRI and CT will all share the same coordinate system. In general, MRI is very well suited for differentiating between soft tissues, while CT is very well suited for differentiating hard tissues such as bones and tissues with density differences, such as soft tissues. For example, in the case of calcification caused by tumors, information by CT plays a very important role. Therefore, additional information not obtained from PET or MRI can be obtained by CT, thereby obtaining excellent clinical performance.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, advantages and features of the present invention will become apparent from the following detailed description, which is disclosed with reference to the accompanying drawings which illustrate certain embodiments of the present invention.

1A and 1B show an MRI-PET-CT hybrid imaging system according to an embodiment of the present invention. 1A is a side view of one embodiment of an MRI-PET-CT hybrid system, and FIG. 1B shows a front view of one embodiment. In this embodiment, the system 100 includes a PET / MRI scanner 110, a CT scanner 120, and a movement table 130. PET / MRI scanner 110 is made of a single PET and MRI, the CT scanner 120 is disposed in close proximity to the PET / MRI scanner 110. As shown in FIG. 1A, the movement table 130 may be configured to be connected to the PET / MRI scanner 110 via the CT scanner 120, but alternatively, the CT table may be configured via the PET / MRI scanner 110. 120). FIG. 1B shows a configuration in which the moving table 130 is connected to the CT scanner 120 through the PET / MRI scanner 110 in the latter case.

The PET / MRI scanner 110 is a combination of a PET using a radionuclide that emits positrons and an MRI using a high frequency magnetic field in order to provide various anatomical information in high resolution as well as functional images of human tissue. As shown in FIG. 1B, the PET / MRI scanner 110 includes a magnet and gradient coil 140 for MRI, an RF coil 150 and a non-magnetic detector 160 for PET. Include. MRI uses magnetic fields generated by magnetic gradient coils to resonate the nuclei of hydrogen in the human body, thereby imaging the distribution of the nucleus and the inherent physical and chemical changes in the tissue containing the nucleus, thus affecting the magnetic field. When the PET is easily integrated with the MRI, it is difficult to guarantee the normal operation of the PET. Therefore, in the PET / MRI scanner 110 according to the present invention, the PMT (Photo-Multiplier Tube) part, which is a device affected by the magnetic field in the detector of PET, is not affected by the magnetic field, such as Avalanche Photo-Diode (APD). A nonmagnetic PET detector 160 is used, which is replaced with a non-volatile device.

The CT scanner 120 records the minute changes in the amount of X-ray absorption at various angles around the body of the patient on the moving table 130 using the X-rays, and combines them to reconstruct the image.

The moving table 130 supports the patient and is movable between the PET / MRI scanner 110 and the CT scanner 120. The movement table 130 may be driven in such a way that the same coordinates are maintained for the patient between the two scanners, for example driven by a drive means (not shown) including a roller or the like.

Since PET and MRI are integrally coupled within the PET / MRI scanner 110, the PET / MRI scanner 110 provides a precise time and space matching PET and MRI image, and also PET / MRI scanner. Since the 110 and the CT scanner 120 are disposed in close proximity, the image acquisition origin of both scanners can also be maintained fairly accurately when the movement table 130 is moved between both scanners.

If the MRI in the PET / MRI scanner 110 has an active shielding function to prevent the magnetic field from leaking, the CT 120 and the PET / MRI scanner 110 are shown in FIG. 1A. ) Is arranged at a predetermined distance (? D). The predetermined distance? D may be determined according to the performance of the active shielding and the strength of the magnetic field. On the contrary, when the MRI of the PET / MRI scanner 110 does not have an active shielding function and it is difficult to shield the magnetic field only by a predetermined distance, the CT scanner 120 and the PET / MRI scanner 110 may be used to protect the CT scanner 120 from the MRI magnetic field. A separate magnetic shield may be installed between the MRI scanners 110.

2 shows a system 200 in which a magnetic shield 240 is installed between PET / MRI 210 and CT scanner 220. Additional RF shield (not shown) between PET / MRI scanner 210 and CT scanner 220 to ensure that MRI blocks within PET / MRI scanner 210 are not affected by RF fields from external or CT scanners. You can also place The magnetic field shield 240 and the RF shield may include an openable shutter 250 that is configured to open only when the moving table passes. Alternatively, instead of placing the RF shield, RF shielding may be implemented by controlling the power supply of the CT scanner 220 or the PET / MRI scanner 210. For example, while MRI imaging is performed in the PET / MRI scanner 210, the CT scanner 220 is powered off to block the RF signal emission from the electronic circuit inside the CT, and CT imaging immediately after the MRI imaging is completed. By only applying power to the CT scanner 220 and cutting off the power of the PET / MRI scanner 210, the RF signal emitted from the CT scanner 220 interferes with MRI operation or PET / MRI scanner. The magnetic field from 210 can be prevented from affecting the CT scanner 220.

Although not shown, the imaging systems 100 and 200 according to the present invention provide image processing means for performing algorithms necessary for fusing PET, MRI and CT images, such as Fourier Transformation and three-dimensional reconstruction. Include. The algorithm also includes various mathematical transformations, such as geometric error calibration and correction required to combine MRI and PET images. The image processing means may extract an accurate attenuation constant for the gamma ray of the PET from the images obtained from the CT scanners 120 and 220, and perform accurate attenuation correction on the PET image by using the same.

As mentioned above, in order to obtain accurate quantitative results in PET, accurate attenuation correction is required, which requires accurate calculation of the attenuation constant. However, the existing PET system obtains the attenuation constant through the transmission images captured using nuclides such as Ge-68 or Cs-137.However, since such images have very low sensitivity as well as the resolution, the accurate attenuation constant is obtained. Can't extract Recently, since the scattering correction of PET is performed based on the attenuation information, the accuracy of extraction of the attenuation constant is becoming more important. The CT scanners 120 and 220 are not only used for obtaining the anatomical position of molecular images because the contrast to the bone is the best among medical imaging devices and the images can be obtained at high resolution. It can be used to accurately extract the attenuation constants of hard materials such as bones. Therefore, the image processing means can greatly improve the quantitative accuracy of the fused PET image by extracting an accurate attenuation constant from the CT image and performing accurate attenuation correction on the PET image using the same.

3 is a flowchart of a method for providing a fused image in an exemplary MRI-PET-CT hybrid imaging system with an RF shield in accordance with the present invention. First, the method begins with RF shielding the PET / MRI scanners 110 and 210 prior to acquiring the PET / MRI image in step 310. In this step, the patient is fixed on the moving tables 130, 230, and the moving tables 130, 230 move in the direction of the PET / MRI scanners 110, 210. When the moving tables 130 and 230 approach the RF shield by a predetermined distance, the shutters installed therein start to open. If the patient's foot passes completely through the shutter, the shutter is then closed. The moving tables 130 and 230 continue to move in the direction of the PET / MRI scanners 110 and 210 until the patient's head is positioned inside the RF coil.

In operation 320, the PET / MRI scanners 110 and 210 photograph PET and MRI images. First, RF field and gradient are applied to the part of the patient to obtain anatomical information, and the RF pulse signal is emitted. In general, each nuclide constituting body tissue has its own Lamor frequency when located within a constant magnetic field. Thus, the body tissue to which the RF pulse signal is applied emits magnetic resonance (MR) signals corresponding to the upper lamore frequency. These MR signals are collected by the RF coil 150 of the PET / MRI scanners 110 and 210 and transmitted to the image processing means. The image processing means generates an MRI image by performing signal processing such as Fourier transform on the received information. The PET / MRI scanners 110 and 210 then begin to detect gamma rays (annihilation positrons) by examining the same site of the patient to produce a PET image. Some of the atoms of the positron emitting isotopes labeled on the biological detector molecules and injected into the human body spontaneously decay, releasing positrons and neutrinos for a period of time. However, positrons are released in gamma-ray form as they collide with electrons in the tissue and lose energy and are annihailed with these electrons within a very short distance of less than 2 mm. In this extinction process, a pair of gamma rays (extinction photons) are generated 180 degrees in the opposite direction because the momentum must be preserved. Due to this extinction characteristic, the detectors 150 are arranged in a circle in the PET / MRI scanners 110 and 210 so that a pair of detectors in opposite directions detect a pair of gamma rays at the same time. This detection means that there was a collision of positrons and electrons somewhere on the line connecting the two receiving detectors, and this line is called the response line. Thus, a number of matching reaction lines are obtained in the PET / MRI scanners 110 and 210 and undergo a mathematical reconstruction of the image processing means to produce a cross-sectional image. The PET and MRI imaging mentioned above may perform PET imaging after the MRI imaging is completed, or may simultaneously perform these imaging.

In step 330, the moving tables 130 and 230 move in the direction of the CT scanners 120 and 220 to obtain a CT image. As described above, when the moving table 230 approaches the magnetic field shield 240 (or the RF shield) by a predetermined distance, the shutter 250 installed thereon starts to open. When the moving table 230 passes completely through the shutter 250, the shutter 250 is closed again.

In operation 340, when the moving tables 130 and 230 arrive inside the CT scanners 120 and 220, the CT scanners 120 and 220 take an image using X-rays.

In operation 350, the image processing unit fuses three images (ie, MRI image, PET image, and CT image) to obtain an optimally synchronized fusion image in terms of time and space. In order to fusion the PET / MRI and CT images as accurately as possible, the moving tables 130 and 230 are fixed and precisely maintained to meet the required geometric and mechanical accuracy.

4 is a flowchart of a method for providing a fusion image in an exemplary MRI-PET-CT hybrid system without an RF shield in accordance with the present invention.

First, in step 410, prior to acquiring the MRI image in the PET / MRI scanner 110, 210, the power of the CT scanner 120, 220 is cut off.

In step 420, the PET / MRI scanners 110 and 210 apply the RF field and gradient to the part of the patient whose anatomical information is to be obtained, and then collect the magnetic field collected by the RF coil 150. Resonance signals are transmitted to the image processing means. In addition, the same region of the patient is examined to generate a PET image. It should be noted that MRI and PET imaging may be performed simultaneously.

In step 430, the moving tables 130 and 230 are moved toward the CT scanners 120 and 220, and power is applied to the CT scanners 120 and 220 in step 440.

When the moving tables 130 and 230 arrive inside the CT scanners 120 and 220, in step 450, the CT scanners 120 and 220 take a CT image by using an X-ray.

In step 460, the image processing means fuses three images (ie, MRI image, PET image and CT image) to obtain a fused image that is optimally synchronized in terms of time and space.

Although the present invention has been described in connection with specific embodiments with reference to the accompanying drawings, the above embodiments are not intended to limit the present invention, but are merely examples to make the present invention easier to understand. It is apparent that various changes, modifications, and modifications can be made to the present invention without departing from the spirit and scope of the present invention as defined by the claims by those skilled in the art.

1A is a side view of an MRI-PET-CT hybrid system in accordance with an embodiment of the present invention.

1B is a front view of an MRI-PET-CT hybrid system according to one embodiment of the present invention.

2 is a diagram showing a system configuration in which a magnetic shield is installed between a CT scanner and a PET / MRI scanner.

3 is a flow diagram of a method for providing a fusion image in an exemplary MRI-PET-CT hybrid imaging system with an RF shield in accordance with the present invention.

4 is a flow chart of a method for providing a fusion image in an exemplary MRI-PET-CT hybrid system without an RF shield in accordance with the present invention.

<Description of the reference numerals for the main parts of the drawings>

110: PET / MRI Scanner

120: CT scanner

130: moving table

140: magnetic gradient coil for MRI

150: RF coil

160: nonmagnetic detector for PET

Claims (18)

An imaging system for providing an image including anatomical, molecular and functional information about a subject, A first scanner for acquiring first information comprising first anatomical information, molecular information and functional information; A second scanner for acquiring second information including second anatomical information having a different resolution than the first anatomical information; And A moving table movable between the first scanner and the second scanner and supporting the inspected object Including, And said first scanner is formed integrally with means for obtaining said first anatomical information and means for obtaining said molecular information and said functional information. The method of claim 1, And the first scanner and the second scanner are spaced a predetermined distance apart. The method of claim 1, And an RF shield for protecting the first scanner from an external RF field. The method of claim 1, And a magnetic shield for protecting the second scanner from the magnetic field from the first scanner. The method of claim 1, And an image processor configured to process the first information obtained by the first scanner and the second information obtained by the second scanner to form a fused image. The method according to any one of claims 1 to 5, The first scanner is a PET / MRI scanner, the means for acquiring the first anatomical information in the first scanner and the means for acquiring the molecular information and the functional information correspond to MRI and PET, respectively. And the second scanner is CT. The method of claim 6, And the PET comprises a nonmagnetic detector that is not affected by magnetic fields. The method of claim 7, wherein And the nonmagnetic detector comprises an Avalanche Photo-Diode (APD). The method of claim 6, The image processor extracts the attenuation constant using the second anatomical information obtained by the CT, and the molecular information and the functional information obtained by the PET of the PET / MRI scanner using the attenuation constant. Imaging system for performing attenuation correction. The method according to claim 3 or 4, The magnetic field shield and the RF shield include a shutter, the shutter configured to open only when the moving table passes. A method for providing an image including anatomical information, molecular information, and functional information about a subject, Moving the subject under test to a first scanner for acquiring first anatomical, molecular and functional information; Protecting the first scanner from an external RF field; Acquiring the first anatomical information, the molecular information, and the functional information at the first scanner; Moving the subject under test to a second scanner for obtaining second anatomical information having a different resolution than the first anatomical information; And Acquiring the second anatomical information from the second scanner Including, the method. The method of claim 11, Protecting the second scanner from an external magnetic field prior to performing the step of obtaining the second anatomical information at the second scanner. The method of claim 11, Acquiring first anatomical information, the molecular information, and the functional information in the first scanner includes sequentially obtaining the first anatomical information, the molecular information, and the functional information. . The method of claim 11, Acquiring the first anatomical information, the molecular information, and the functional information in the first scanner includes acquiring the first anatomical information, the molecular information, and the functional information simultaneously and in parallel. , Way. The method of claim 11, Extracting attenuation constants using second anatomical information, and performing attenuation correction of the molecular information and the functional information using the attenuation constants. The method of claim 11, Protecting the first scanner from an external RF field comprises using an RF shield. The method of claim 11, Protecting the first scanner from an external RF field includes powering off the second scanner, And applying power to the second scanner before performing the step of obtaining the second anatomical information at the second scanner. The method according to any one of claims 11 to 17, Wherein the first scanner is a PET / MRI scanner in which an MRI for acquiring the first anatomical information and a PET for acquiring the molecular information and the functional information are integral, and the second scanner is a CT scanner.

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