Magnetic resonance imaging of the spine to detect scoliosis

Abstract

In one aspect, the present invention is a method for detecting spinal abnormalities using magnet resonance imaging. The method comprises positioning a patient in an upright posture in an imaging volume of a magnet resonance imaging magnet with the spine of the patient adjacent to an antenna and capturing magnetic resonance imaging signals from a first portion of the patient's spine using the antenna with the patient positioned in a first position. The method may further comprise adjusting the patient position along a substantially vertical direction to a second position and capturing magnetic resonance imaging signals from a second portion of the patient's spine using the antenna with the patient positioned in the second position.

Claims

1. A magnetic resonance imaging system, comprising: a magnet defining a patient-receiving space and having a static magnetic field with a field vector in a substantially horizontal direction; a patient support having a support surface for a human body, said patient support being positioned within said patient-receiving space and being pivotable about a horizontal pivot axis; and a planar housing having— a phased array antenna coil assembly including a first portion and a second portion, each portion operable to receive magnetic resonance image signals, wherein the first portion is aligned with an upper portion of the patient's spine including the base of the patient's skull and the second portion is aligned with a lower portion of the patient's spine including the patient's coccyx, such that the phased array antenna coil assembly extends in the lengthwise axis from the base of the patient's skull to the patient's coccyx, and wherein the length of the antenna assembly in the lengthwise axis is greater than the length of an imaging volume of the magnet, such that the phased array antenna coil assembly extends out of the imaging volume; and active decoupling circuitry connected to the first and second portions and operable to selectively decouple either the first or second portions from receiving magnetic resonance image signals; and a patient support adjustment mechanism for adjusting the patient support device between: a first upright position such that the upper portion of the patient's spine and the first portion are in the imaging volume of the magnetic resonance imaging magnet, and the second portion is out of the imaging volume, and a second upright position such that the lower portion of the patient's spine and the second portion are in the imaging volume of the magnetic resonance imaging magnet, and the first portion is out of the imaging volume.

2. The system of claim 1, further comprising active decoupling circuitry connected to the first and second portions of the phased array antenna coil assembly, the decoupling circuitry being operable to selectively decouple either the first or second portions from receiving magnetic resonance image signals.

3. The system of claim 2, wherein each portion of the phased array antenna coil assembly is connected to a separate decoupling circuit of the decoupling circuitry.

4. The system of claim 3, wherein each decoupling circuit comprises at least one diode and a capacitor, whereby activation of the at least one diode detunes the portion of the phased array antenna coil assembly connected to said decoupling circuit.

5. The system of claim 1, further comprising a resonator coil located proximate the housing.

6. The system of claim 1, wherein: the first portion comprises a first quadrature coil arrangement having a first butterfly coil and a first loop coil disposed above the first butterfly coil, the second portion comprises a second quadrature coil arrangement having a second butterfly coil and a second loop coil disposed above the second butterfly coil, and the phased array antenna coil assembly further comprises a third loop coil arranged adjacent to and between the first and second loop coils.

7. The system of claim 1, wherein each portion of the phased array antenna coil assembly is adapted to capture magnetic resonance images of the patient's spine.

8. The system of claim 7, wherein the magnetic resonance images of the patient's spine are three-dimensional volume images.

9. The system of claim 1, wherein images obtained in the first and second upright positions are capable of being stitched together to form a magnetic resonance image from the base of the patient's skull to the patient's coccyx, whereby scoliosis of the patient may be determined based on the stitched image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustratively depicts a front view of an apparatus in accordance with an aspect of the present invention.

(2) FIG. 2 is a side view of the apparatus of FIG. 1.

(3) FIG. 3 is a side view of a patient and antenna assembly in accordance with an aspect of the present invention.

(4) FIG. 4 shows an antenna assembly in accordance with an aspect of the present invention.

(5) FIG. 5 shows an antenna assembly in accordance with an aspect of the present invention.

(6) FIGS. 6A, 6B and 6C show examples of images obtained in accordance with an aspect of the present invention.

(7) FIG. 7 is a schematic of a decoupling circuit in accordance with an aspect of the present invention.

DETAILED DESCRIPTION

(8) Turning to FIGS. 1 and 2, there is illustrated an apparatus 1 according to one embodiment of the present invention. The apparatus 1 includes a static field magnet having a frame 10 including a pair of poles 12 spaced apart from one another along a horizontal pole axis 14. Frame 10 further includes flux conducting and return members that, in the particular embodiment illustrated, include a pair of sidewalls 16 and columns 18 extending between the sidewalls 16. The particular frame depicted in FIGS. 1 and 2 is generally in accordance with the aforementioned U.S. Pat. No. 6,677,753, (hereinafter “the '753 patent”), although other configurations can be employed. The opposed poles define a patient-receiving space or gap 20 between them. The magnet further includes a source of magnetic flux adapted to direct into and out of the gap through poles 12 so as to form a static magnetic field having a field vector B.sub.0 in the horizontal direction, parallel to pole axis 14. In the particular embodiment illustrated, the flux source includes a pair of electromagnet coils 22 encircling poles 12. These coils may be superconductive or resistive coils. Alternate flux sources such as coils disposed at other locations along the ferromagnetic frame and permanent magnets also may be employed.

(9) The apparatus further includes a patient support assembly including a bed 24 defining an elongated patient supporting surface 26 having a lengthwise axis 25 and a platform 28 projecting from the supporting surface at a foot end of the bed. In addition, as best seen in FIG. 3, a seat may be mounted to supporting surface 26 to allow a patient to be positioned in a sitting position. The patient supporting assembly further includes a frame 30. Bed 24 is pivotably mounted to the frame 30 for movement about a generally horizontal pivot axis 32. Pivot axis 32 is substantially parallel to pole axis 14. Bed 24 can pivot between an upright position in which the lengthwise direction over the bed extends generally vertically as seen in FIG. 2 and a fully horizontal position, in which the lengthwise direction of the bed 24 extends horizontally. As further described in the '753 patent, bed 24 also may be mounted for vertical motion relative to frame 30 and hence relative to the static field magnet 10. Moreover, frame 30 can be mounted for horizontal movement relative to the static field magnet. Appropriate actuators and control devices (not shown) are provided for moving the bed and for moving support frame 30.

(10) The patient support assembly further includes an antenna assembly schematically depicted as a planar box 34 in FIGS. 1, and 2. As best seen in FIGS. 4 and 5, the antenna assembly generally includes a plurality of coils, including coils having a winding extending in a loop configuration and others that extend in butterfly or “FIG. 8” configuration. Each configuration may be provided with a conventional coupling to a separate coaxial cable or other output line for conveying signals to a receiver or receiving signals from a transmitter. Also, each loop may include a capacitor (not shown) in series and/or in parallel with the conductor forming the loop so as to define a resonant antenna circuit.

(11) The term “coil surface” as used herein refers to an imaginary surface defined by the central axis of the conductors constituting the coil or antenna. For example, as shown in FIG. 4, in the special case of a flat circular coil, the coil surface is the surface of the planar box 34. Each coil surface defines a coil vector V.sub.c normal to the coil surface itself (see FIGS. 2 and 4). In the case of a curved coil surface, the coil vector of the coil surface as a whole can be taken as the integral of the normal vector to the coil surface over the entire area of the coil surface inside the coil. In that regard, in some instances it may prove useful to have the surface of the box 34 contoured to more naturally match the shape of the human anatomy using some degree of curvature.

(12) FIG. 5 shows a plurality of loop coils configured in a phased array arrangement. These coils may also be placed in planar box 34. In this configuration, the surface of the box may also be continued to match the shape of the human anatomy.

(13) In the case of a substantially flat butterfly coil, each coil defines a coil vector V.sub.b is parallel to the surface in which the coil lies. As shown in FIGS. 2 and 4, these vectors are generally parallel to the surface of the planar box 34 in which the coils are disposed.

(14) Returning to FIG. 3, there is shown an embodiment of the present invention for monitoring and detecting scoliosis in patients P. As shown, the patient P is positioned in the sitting position in the magnet apparatus 1 shown in FIGS. 1 and 2. In addition, although FIG. 3 shows a patient in a setting position, the patient may be positioned in a standing position as shown in FIGS. 1 and 2. As a general matter, the patient may be positioned in an upright position to take the MRI images needed for monitoring and detecting scoliosis. Thus, the descriptions of the sitting or standing position herein are meant to limit the present invention. Rather, the patient may be positioned in an upright position. With respect to FIG. 3 and for clarity, only those portions of the apparatus 1 needed to discuss this aspect of the invention is shown. Those include the pole 12, the antenna assembly 34 and a resonator 108. In accordance with a method aspect of the present invention, the patient P is first positioned on the seat 104 in an upright posture. Ideally, the patient is positioned so that the lower lumbar area coincides with the center of the imaging volume, i.e., the sweet spot of the magnet. In general, however, as long as the region of interest is located within the imaging volume, imaging may proceed. In this first position, the patient's lower lumbar area is then imaged.

(15) In accordance with an aspect of the present invention, imaging is preferably done using a pulse sequence from which a three dimensional volume (3-D) volume image may be created. In addition, a pulse sequence lasting approximately three to four minutes may be used to obtain such images. Once imaging of the lower lumbar is completed, the patient is then lowered so that the upper part of the spine, i.e., the cervical spine, can be imaged. In this second position, as in imaging the lower spine, a pulse sequence from which 3D volume image can be reconstructed is preferably used. Likewise, imaging usually takes approximately three to four minutes to complete. Once both images are acquired and further processed they may be stitched together to form a full image of the spine as is illustrated in FIG. 6.

(16) Patients with scoliosis usually receive posterior to anterior (P-A) radiography every four to nine months and an additional lateral disclosure once a year. The orthopedic surgeon now has to make a judgment as to the degree of rotation of the vertebra. Using the P-A radiographs the orthopedist measures the extent of the curvature in the scoliosis, i.e., the Cobb angle. These measurements are usually done by hand, e.g., drawings lines onto the X-ray images by hand and then measuring the Cobb angle.

(17) As described above, using an upright MRI it is possible to complete a total examination in approximately 10 minutes. In this regard, examination includes data acquisition and patient positioning. Generally, it covers the time that the patient needs to be in the magnet. However, with complete automation even post-processing may take place contemporaneously with image acquisition. Therefore, the entire process may be completed in under 10 minutes. A total spine image in a standard solenoid MRI could take as much as 30 minutes and may under estimate the Cobb angle because the patient is in a supine posture. By keeping the exam time to a minimum the cost to the patient becomes competitive with radiography. In addition, with the patient in a standing or seated position, the results in the upright MRI are at least the same as with standard radiography.

(18) In general, the MRI exam should be setup so that the patient just has to stand-up or sit down. All alignments could be preset for a typical person. A single spine coil (such as those shown in FIGS. 4 and 5) placed along the back of the patient P could cover the total range of interest. The MRI technician may first perform a quick scout scan to confirm the patient's position and align the MRI slices to be taken.

(19) As discussed above, the preferred scanning technique is 3D volume acquisition. This would permit a doctor to do post-processing to produce views in the coronal (P-A radiograph), sagittal, or axial planes. The total spine could be scanned in two 3-D volume acquisitions. Each scan would take less than five minutes for a total scan time of ten minutes. The two scans could then be stitched together to form a single imaging volume set. Using a curved multi-planar reconstruction the doctor would produce an image of the spine in the coronal view. The image would show the spine from the base of the skull to the coccyx, as shown in FIG. 6. The images obtainable using this method also allow for better diagnosis. In addition, in accordance with another aspect of the present invention, the images obtained may be processed digitally to determine the Cobb angle. For example, a computer program may be written to detect the curvature in the spine and measure the Cobb angle automatically.

(20) Returning to FIG. 3, as shown, a resonator 108 may be attached to the planar box 34 housing the antenna assembly. In this regard, the present invention may be done without attaching the resonator. The resonator 108, when attached, uses means that allows it to be adjusted to accommodate patients of different sizes. In addition, aside from improving the reception of the signals received, it also assists in immobilizing the patient. In the preferred embodiment, the resonator is not electrically connected to the other coil assemblies. Rather, it is inductively coupled to the other antenna assemblies in the box 34. Specifically, the resonator 108 is connected around the patient's neck to passively pick-up extra resonance signals when imaging the upper spine of the patient. In essence, the resonator 108 addresses the issue of having the cervical spine being positioned away from the coils in the upper part of the assembly 34. It detects the extra signals passively as is discussed in more detail in U.S. Pat. No. 5,583,438, which is assigned to the assignee of the present application, and the disclosure of which is incorporated by reference herein.

(21) In one embodiment, the antenna assembly in the planar box 34 comprises the arrangement shown in FIG. 4. As shown, the antenna assembly 400 includes a pair of quadrature coils assemblies 404, 408. A quadrature coil antenna arrangement advantageously improves the signal-to-noise ratio by a factor up to √{square root over (2)}. As a practical matter, the quadrature coil arrangement reduces the measurement or MRI scanning time by approximately one-half. That is, a measurement that takes approximately two minutes using a quadrature coil antenna arrangement will take approximately four minutes using another antenna arrangement. This improvement in performance translates into increased efficiency at MRI facilities.

(22) Each assembly 404, 408 comprise a butterfly coil antenna 410.sub.1 and 410.sub.2 which are disposed beneath a loop coil antenna 420.sub.1 and 420.sub.2, respectively. Additional details regarding these types of antenna assemblies are discussed in U.S. patent application Ser. No. 10/998,395 entitled “COILS FOR HORIZONTAL FIELD MAGNETIC RESONANCE IMAGING,” the disclosure of which is incorporated by reference herein, and included with this application as an attachment. In addition, a third loop coil 430 is shown arranged adjacent to and overlapping both quad coil assemblies 404, 408. The loop coil 430 acts as a passive resonator to each of these assemblies to pick up extra signals during image acquisition.

(23) During image acquisition, an assembly 404, 408 may be selectively decoupled or turned off depending on the area of the spine being measured. For example, when the lower spine is being measured, quad assembly 404 (if positioned proximate the patient's cervical spine area) is decoupled from the magnetic circuit during imaging. This allows for better images to be acquired of the lower spine. Likewise, when imaging the cervical spine, the quad assembly proximate the lumbar spine area (e.g., quad assembly 408) is then decoupled from the circuit.

(24) Such decoupling may be accomplished using, for example, the circuit arrangement 700 shown in FIG. 7. As shown, the circuit 700 includes input ports 704.sub.1 and 704.sub.2 to which are applied a control voltage. The circuit 700 also includes output ports 708.sub.1 and 708.sub.2, which may be connected to a coil of the RF coil antenna assembly as shown in FIGS. 4 and 5. In the preferred embodiment, each quad coil 404,408 is connected to a separate one of circuit 700. In particular, one coil is connected to nodes 450, 452, while the other is connected to nodes 456, 458. The phase array is now preferred.

(25) As shown, a first diode 710 is connected to port 704.sub.1. A second diode 716 is connected to port 704.sub.2. Between the first and second diodes 710, 716 is a capacitor C1. In parallel with the capacitor C1 is an inductor L1, which is connected in series with pair of diodes 722, 724. During reception mode, a control voltage may be applied across the input ports 704.sub.1 and 704.sub.2. At a predetermined voltage, the diodes 710 and 716 will conduct and effectively detunes the capacitor C1. This, in turn, powers off the coil connected to the circuit 700.

(26) Conversely, during transmission mode, the coil exerts a voltage across the diodes 722 and 724, thereby allowing the diodes 722 and 724 to conduct. In this way, during transmission mode capacitor C1 is not part of RF coil circuit. During reception mode diodes 722 and 724 do not conduct and C1 is part of the RF coil circuit.

(27) According to one embodiment of the present invention, a decoupling circuit such as the circuit 700 may be connected to each coil in the RF coil antenna assembly. In this regard, different portions of the antenna may be selectively powered on and off. Thus, whereas a portion of the antenna that is positioned near a lower part of the spine may be powered on to receive images of the lower spine, a portion of the antenna near the upper spine may be powered off, and vice versa.

(28) FIG. 5 shows an alternative antenna assembly 500 which may be operated in a similar manner to the double quad arrangement of FIG. 4. As those skilled in the art may recognize, this antenna 500 comprises a phased array assembly and functions as is known in the art. The antenna 500 includes a plurality of loop coils 510, 512, 514 and 516 arranged so that the coils 512 and 514 are arranged to overlap two of the other coils. Like antenna 400, this antenna 500 is effective in providing a wide field of view and high signal-to-noise ratio resonance signals. The antenna 500 is preferably coupled to the circuits shown in FIG. 7, one each at nodes 520, 522 and 526,528.

(29) By using the antenna assemblies shown in FIGS. 4 and 5, imaging of the entire spine may take place using a single antenna assembly. This allows the process to take place by moving the patient in a substantially vertical direction without having to otherwise reposition the patient. For example, this avoids having to use two different antenna assemblies.

(30) Turning now to FIG. 6, there is shown images of a spine of a patient having scoliosis that was acquired using the methods described above. FIG. 6A shows a representative slice of a 3-dimensional sagittal image acquisition of the spine from which multiplanar reconstruction of both coronal and axial views are generated, as shown in FIGS. 6B and 6C, respectively. FIG. 6B shows a coronal view of the spine showing Cobb angles measured to be 22.6 degrees and 36.5 degrees. FIG. 6C shows axial views of the spine showing direct measurement of vertebral rotations, for example 8.8 degrees at T7, 24.3 degrees at T9 and 10.1 degrees at T10. As shown in FIG. 6B, the Cobb angles was measured at 22.6 and 36.5 degrees. This measurement of the Cobb angle was done using software. As may be appreciated, these images allow for better diagnosis of the condition. In this regard, the Cobb angle may be seen and measured more easily.

(31) In general, whereas in a radiograph, images of the spine are shadows in the presence of the other organs in the body, e.g., the ribs, heart, and other internal organs, MRI produces a single slice through the spine for all the MRI views: coronal, sagittal and axial. In FIG. 6 of the embodiment from a single 3D MRI exam all three views maybe obtained. The coronal view will indicate the severity of the scoliosis. The sagittal view will show the amount of Kyphosis and Lordosis in the spine. And, the axial views will indicate the severity of twisting in the spine and possible neurological complications of the scoliosis. Thus, MRI aids in making a better diagnosis and determining the severity of the scoliosis.

(32) Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.