Cervical vertebra angle measurement

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S. Provisional Patent Application Nos. 61/779,165 and 61/779,388, both filed Mar. 13, 2013, the disclosures of which are hereby incorporated herein by reference in their entirety.

BACKGROUND

The present application relates to magnetic resonance imaging systems and methods for using such systems.

In magnetic resonance imaging, an object to be imaged as, for example, a body of a human subject is exposed to a strong, substantially constant static magnetic field. The static magnetic field causes the spin vectors of certain atomic nuclei within the body to randomly rotate or precess around an axis parallel to the direction of the static magnetic field. Radio frequency excitation energy is applied to the body, and this energy causes the nuclei to “precess” in phase and in an excited state. As the precessing atomic nuclei relax, weak radio frequency signals are emitted; such radio frequency signals are referred to herein as magnetic resonance signals.

Different tissues produce different signal characteristics. Furthermore, relaxation times are the dominant factor in determining signal characteristics. In addition, tissues having a high density of certain nuclei will produce stronger signals than tissues with a low density of such nuclei. Relatively small gradients in the magnetic field are superimposed on the static magnetic field at various times during the process so that magnetic resonance signals from different portions of the patient's body differ in phase, amplitude, and/or frequency. If the process is repeated numerous times using different combinations of gradients, the signals from the various repetitions together provide enough information to form a map of signal characteristics versus location within the body. Such a map can be reconstructed by conventional techniques well known in the magnetic resonance imaging art, and can be displayed as a pictorial image of the tissues as known in the art.

The magnetic resonance imaging technique offers numerous advantages over other imaging techniques. MRI does not expose either the patient or medical personnel to X-rays and offers important safety advantages. Also, magnetic resonance imaging can obtain images of soft tissues and other features within the body which are not readily visualized using other imaging techniques. Accordingly, magnetic resonance imaging has been widely adopted in the medical and allied arts.

Despite the wide adoption of magnetic resonance imaging, X-ray detection continues to be the primary method used to detect certain abnormalities. One such abnormality is a rotation of a patient's cervical vertebra. Detecting and monitoring cervical vertebra rotation is important because such rotations can impact cerebral spinal fluid flow to and from the brain. If one of a patient's vertebrae is rotated improperly, it can significantly cut off flow of the cerebral spinal fluid, which can in turn create pressure buildup in the patient's brain. Monitoring a patient's cervical vertebra may require repeated exposure to x-rays. This repeated exposure, however, can cause damage to living tissue. It is, therefore, recommended that efforts to reduce exposure continue and that repeated X-ray exposure should be minimized.

MRI exams, by contrast, can be repeatedly done without health concerns, and can provide the same or better level of image detail as can X-ray imaging. In that regard, it is desirable to develop a method of detecting and monitoring cervical vertebra rotation using MRI.

With regard to the C1 and C2 (atlas and axis, respectively) cervical vertebrae, one difficulty in using MRI to monitor rotation of these two vertebrae is that they commonly lie on the boundary between head MRI scans (e.g., scans taken with a head coil) and cervical MRI scans (e.g., scans taken with a cervical belt coil). As such, neither the typical head or cervical MRI scan is adequate in diagnosing or monitoring these vertebrae. As such, it is desirable to generate an MRI image different from the typical head and back images normally generated for purposes of monitoring rotation of the C1 and C2 vertebrae.

SUMMARY

A method of measuring the axial rotation of a selected vertebra of a patient using a magnetic resonance (MR) image. The selected vertebra may be a cervical vertebra. The method may include: identifying, in the MR image, features of the selected vertebra; determining a first axis connecting the identified features of the vertebra; identifying, in the MR image, features of the patient's surrounding anatomy that are not the selected vertebra; determining a second axis connecting the identified surrounding anatomical features; measuring the angular difference between the first and second axes; and determining the axial rotation of the vertebra based on the measurement. In some examples of the disclosure, determining the axial rotation of the vertebra is based on the degree of perpendicularity between the first and second axes.

In some examples of the disclosure, the selected vertebra may be a C-2 vertebra and the MR image may show the C-2 vertebra along an axial plane of the patient. In such examples, the two or more features of the selected vertebra may include either anterior-most or posterior-most prominences of the cortical bone of the C-2 vertebra. Further, the surrounding anatomical features may include an anterior feature of the patient's anatomy, such as the nasal septum of the patient, and a relatively posterior feature of the patient's anatomy, such as the vertex of the uvula of the patient. These features may be visualized on an axial image of the cranio-cervical junction (foramen magnum, C1 and C2) and may extend along a sagittal plane of the patient. In some examples, the surrounding anatomical features may additionally or alternatively include a center of the axis of rotation of the C2 vertebra.

In other examples of the disclosure, the selected vertebra may be a C-1 vertebra and the MR image may show the C-1 vertebra along an axial plane of the patient. In such examples, the features of the selected vertebra may include the margins of the anterior-most or the posterior-most prominences of the cortical bone of the C-1 vertebra. Further, the surrounding anatomical features may include an anterior feature of the patient's anatomy, such as the nasal septum of the patient, and a relatively posterior feature of the patient's anatomy, such as the vertex of the uvula of the patient. Again, the features may be visualized on an axial image of the cranio-cervical junction (foramen magnum, C1 and C2) and may extend along a sagittal plane of the patient. In other examples, the surrounding anatomical features may additionally or alternatively include the dens center and/or spinal cord center of the patient.

The method may further include generating a scout MR image of the patient, the scout MR image showing a sagittal cross-section of the patient, and selecting an initial locating axis on the scout image. The initial locating axis defining an axial plane of the patient on which the selected vertebra is present or lies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sagittal scout magnetic resonance (MR) image of a patient in accordance with a first embodiment of the present disclosure.

FIG. 2 is another sagittal scout magnetic resonance (MR) image of a patient in accordance with a second embodiment of the present disclosure.

FIG. 3 is an axial MR image of a C1 vertebra in accordance with the first embodiment of the present disclosure.

FIG. 4 is an axial MR image of a C2 vertebra in accordance with the second embodiment of the present disclosure.

FIG. 5 illustrates a method according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is generally directed to methods using magnetic resonance imaging (MRI) to measure an angular rotation of a selected cervical vertebra of the patient. Specifically discussed in the disclosure are methods for measuring the atlas and axis of the cervical vertebrae (hereinafter C1 and C2, respectively). However, it will be appreciated by those skilled in the art that the methods described herein may be similarly applied to other vertebrae of the patient.

In its most general form, measuring angular rotation of a cervical vertebra using an MR image involves the following steps: (a) identifying, in the MR image, two or more features of the selected vertebra, (b) determining a first axis connecting the identified features, (c) identifying, in the MR image, two or more features of the patient's anatomy, (d) determining a second axis that would connect the identified anatomical features, and (e) measuring the angular difference between the first and second axes. The axial rotation of the cervical vertebra is then determined based on the angle measurement of step (e). It should be understood that these steps of the operation do not have to be performed in the precise order presented above. Rather, various steps can be performed in a different order, or simultaneously. Moreover, steps may be added and/or omitted.

Initially, identifying features of a vertebra and its surrounding anatomy in an MR image necessarily requires that those features be captured in the MR image. Thus, before step (a) can be performed for a selected vertebra, one must first set the MRI apparatus up to capture an image of the patient that includes each of the to-be-identified vertebral and surrounding anatomical features of the patient. Setting up the MRI apparatus involves aligning the patient within the apparatus such that each of the to-be-identified anatomical features lies or is present in a common plane that is transverse to a slice-select magnetic field gradient of the apparatus. Aligning the patient in such a manner may be performed by first generating a scout MR image of the patient and determining whether each of the to-be-identified anatomical features lies within a single slice perpendicular of the scout image. In the case of aligning a patient to image one of the patient's cervical vertebrae, the scout MR image may be a sagittal cross-section of the patient. The sagittal scout image of FIG. 1, for instance, depicts several lines 1-24 representing substantially axial image slices of the patient. For further example, the sagittal scout image of FIG. 2 depicts several lines 1-22, again representing substantially axial images of a patient. In a situation where the to-be-identified anatomical features do not lie on a common line 1-24 (of FIG. 1) or 1-22 (of FIG. 2), the patient may be rotated, translated, or otherwise repositioned in the MRI system. Such repositioning is hereinafter termed aligning an axis of the patient, and may be performed in the manner described below and in concurrently filed and commonly owned U.S. application entitled “Method and Apparatus for Magnetic Resonance Imaging of the Cranio-Cervical Junction,” the disclosure of which is hereby incorporated herein by reference in its entirety.

Using the scout image, a particular transverse imaging plane of the patient having the selected vertebra (and the to-be-identified anatomical features) may be selected. Again, to illustrate, in the sagittal scout image of FIG. 1, for instance, the imaging plane represented by line 2 may be selected for measuring angular rotation of the C1 vertebra since that plane lines up with the C1 vertebra. This axial imaging plane is shown in FIG. 3. For further example, in the sagittal scout image of FIG. 2, the axial imaging plane represented by line 9 may be selected for measuring angular rotation of the C2 vertebra since that axial plane lines up with the mid-point of the C2 vertebra. This imaging plane is shown in FIG. 4.

Turning now to steps (a)-(e) of the method presented above, for purposes of clarity, these steps will be described in turn first as a method for measuring the angular rotation of a C1 vertebra (in the context of FIG. 3), and second as a method for measuring the angular rotation of a C2 vertebra (in the context of FIG. 4). As stated above, these descriptions are meant merely as examples of the more general process described above, which will be understood to similarly apply to other vertebrae of the patient.

Turning first to measuring the angular rotation of a C1 vertebra, in step (a), once an MR image along an axial plane of the C1 vertebra (FIG. 3, which is the image taken along line 2 of FIG. 1) has been acquired, features of the vertebra and of the patient's surrounding anatomy may be identified in the MR image. In one embodiment of the disclosure, the identified features of the C1 vertebra may be the cortical bone margins of the leftmost anterior lateral prominence (310), and the cortical bone margins of the rightmost anterior lateral prominence (320) respectively. Alternatively, the identified features of the C1 vertebra may be the most posterior cortical bone prominence (330) and the lateral cortical bone prominence (340).

In step (b), a first axis connecting the identified features of the C1 vertebra is determined. In the example of FIG. 3, if features 310 and 320 were indentified in step (a), then line 301, which is not actually part of the MR image but rather superimposed for illustration purposes, is the first axis on which the identified features lie. Alternatively, if features 330 and 340 were identified in step (a), then superimposed line 302 is the first axis on which the identified features lie.

In step (c), features of the patient's surrounding anatomy (i.e., that are not features of the C1 vertebra) are identified. In some examples (including the example of FIG. 3), at least one relatively anterior feature and at least one relatively posterior feature (i.e., relative to the anterior feature) of the patient's anatomy may be identified, such that the features lie or extend along a sagittal plane of the patient. In the example of the C1 vertebra of FIG. 3, such features may be the nasal septum of the patient (350), the vertex of the uvula midline (360), the dens center (370), and the spinal cord center (380).

In step (d), a second axis connecting the identified surrounding anatomical features is determined. In the example of FIG. 3, superimposed line 303 illustrates the axis on which the identified non-rotatable anatomical features 350, 360, 370, and 380 lie.

Lastly, in step (e), the angular difference between the first and second axes is measured. Essentially, the first axis represents the actual orientation the patient's vertebra, whereas the second axis represents the sagittal plane of the patient. Under normal circumstances, the first axis of a healthy patient should be perpendicular to the second axis, meaning that the patient's vertebra is in proper rotational alignment (e.g., relative to the surrounding anatomical features). However, when the first and second axes are not perpendicular, that is an indication that the vertebra of the patient is not properly rotationally aligned relative to the surrounding anatomical features.

In the example of the C1 vertebra, the axis represented by line 303 may be measured against the axis represented by either line 301 or line 302. Since lines 301 and 302 are parallel with one another, the result of measuring line 303 against either line 301 or 302 should be virtually the same. If line 303 lies substantially perpendicular to lines 301 and 302, then the C1 vertebra of the patient is properly rotationally aligned. However, if the measured angle between the measured lines 303 and 301/302 is not 90 degrees (e.g., 74 degrees, 106 degrees, etc.,), then the C1 vertebra is out of its rotational alignment, and the degree of the malalignment may be determined. The difference between the measured angle and 90 degrees can indicate the severity of the vertebral axial rotation.

The above method may be similarly applied to measuring the angular rotation of a C2 vertebra. In step (a), once an MR image along an axial plane of the C2 vertebra (FIG. 4, which is the image taken along line 9 of FIG. 2) has been acquired, features of the vertebra and the patient's surrounding anatomy may be identified in the MR image. In one embodiment of the disclosure, the identified features of the C2 vertebra may be the cortical bone on the most anterior prominences shown in the MR image (410 and 420). Alternatively, the identified features of the C2 vertebra may be the cortical bone of the posterior prominences shown in the MR image (430 and 440).

In step (b), a first axis connecting the identified features of the C2 vertebra is determined. If features 410 and 420 were identified in step (a), then superimposed line 401 is the first axis. Alternatively, if features 430 and 440 were identified, then superimposed line 402 is the first axis. It may be preferable to use the second axis when the anterior heights of most anterior prominences 410 and 420 are unequal. Likewise, it may be preferable to use the first axis when the most posterior prominences 430 and 440 are of unequal height. In circumstances when both the most anterior prominences 410 and 420 and most posterior prominences 430 and 440 are of unequal height, it may instead be preferable to define the first axis as the horizontal midline through the central hypointensity of the C2 vertebra between the lateral prominences.

In step (c), features of the patient's surrounding anatomy are identified, including, in some examples (including the example of FIG. 4), at least one anterior feature and at least one relatively posterior feature. In the example of the C2 vertebra of FIG. 4, such features may be the nasal septum (450) the vertex of the uvula (460), and the center of the axis of rotation of the C2 vertebra (470). It should be noted that the center point of the axis of rotation of the C2 vertebra 470, although technically a feature of the C2 vertebra, may still be used as a surrounding anatomical feature for purposes of this disclosure, since it lies on the second axis even when the C2 vertebra is rotated.

In step (d), a second axis connecting the identified non-rotatable anatomical features is determined. In the example of FIG. 4, superimposed line 403 illustrates the second axis on which the identified surrounding features 450, 460 and 470 lie.

Lastly, in step (e), the angular difference between the first and second axes is measured. This step is essentially the same as for the C1 measurement, described above. As with the C1 measurement, both lines 401 and 402 are substantially parallel, and as such, comparing either line against line 403 results in substantially the same measurement.

FIG. 5 illustrates in a table format a summary of the general method described above and its application to axial rotation measurements of each the C1 and C2 vertebrae. The leftmost column of the table is illustrated as a flow chart having steps 501-506. Each of steps 501-505 generally corresponds to a respective step (a) through (e) of the above described method. In step 506, the axial rotation of the selected vertebra is determined based on the measurement of step 505. As described above, this determination is based on the degree of perpendicularity (or lack thereof) between the two measured axes. The middle and rightmost columns of the table summarize the specific application of the general steps 501-506 to each of the C1 and C2 measurements, respectively. Where application of a step is non-specific, the table is left blank.

The above described methods may be carried out using any MRI apparatus (e.g., bore-type, designs in which a patient is not upright, etc.), and preferably in any upright MRI apparatus, including the Fonar Upright® Multi-Position™ MRI. One such MRI apparatus having an MRI magnet subsystem and computing device for controlling the MRI magnet subsystem and generating images using the subsystem is described in greater detail in concurrently filed and commonly owned U.S. application Ser. No. 14/209,279 (now U.S. Pat. No. 9,766,310). The purpose of imaging a patient while upright is to gain a sense for the effect that gravity has on the vertebra of the patient. Moreover, a patient spends most of his or her time in an upright (standing or sitting) position. Thus although non-upright MRI systems and apparatuses may make use of the methods described herein, if the patient were imaged while lying down, the image may possibly not show the pressures (e.g., by gravity) or strains normally experienced by the vertebra of the patient. The upright apparatus may be positioned in a manner such that the patient is capable of standing or sitting on a pivoting base or platform (sometimes called a bed). The base may pivot forward or backward to change the orientation of the patient relative to the MRI magnet and/or imaging coils. In the method described above, the instruction provided to the bed to pivot, thereby reorienting the patient, is referred to as aligning an axis. The axis may be aligned by a user/operator of the apparatus by the user/operator viewing the anatomy of the patient on a screen and determining, based on the viewed image of the patient, whether (and how) the orientation of the patient should be changed, e.g., in order to place the anatomy of interest (i.e., a vertebra) in a single image slice or cross-section capable of being imaged by the apparatus.

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.