Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-03-30
2001-11-20
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S309000
Reexamination Certificate
active
06320378
ABSTRACT:
BACKGROUND
1. Field of the Invention
The invention generally relates to magnetic resonance imaging techniques. More particularly, the invention relates to magnetic resonance imaging techniques useful in situations in which gross transient motion and/or magnetic field inhomogeneities are present within the field of view.
2. Summary of the Prior Art
Magnetic resonance imaging is the optimal imaging modality for surgical applications primarily because of its ability to elucidate a wide variety of lesions. Stereotactic systems employing magnetic resonance imaging steadily have been enhanced, thereby improving a surgeon's ability to safely and efficaciously operate. The latest step in this evolution has been the ability to provide intraoperative updates of previously obtained magnetic resonance images of tissues of interest in a manner that allows the surgeon to track changes therein throughout the course of a particular surgical procedure.
Unfortunately, the phase sensitivity of conventional two and three-dimensional Fourier transform magnetic resonance image scans to motion and varying magnetic field inhomogeneities causes problems. Specifically, it has been found that when there is motion within the imaging field of view during such conventional magnetic resonance imaging, undesirable artifacts are created in the resulting image. Similarly, varying magnetic field inhomogeneities in the imaging field of view also cause undesired artifacts in the resulting images. Accordingly, it presently is necessary to halt the surgical procedure, and to clear the surgical field of all metal operating instruments and the like, each time a conventional Fourier type magnetic resonance image is to be taken. Obviously, this is not a satisfactory requirement.
Besides multi-shot phase encoded, two-dimensional or three-dimensional Fourier imaging, the technique of so-called “line-scan imaging” also is known in the art. Generally speaking, line scan imaging sequentially acquires the individual lines of a magnetic resonance image in multiple independent single shots. Phase encoding is not used in line-scan imaging. Instead, only the magnitude of the Fourier-transformed signal is used. Known and established single-shot techniques, by their nature, do not have shot-to-shot phase encoding, although they generally have phase encoding within each shot. Therefore, a line-scan imaging sequence is immune to the phase encoding errors mentioned above that are encountered in conventional Fourier magnetic resonance imaging methods.
Typically, however, line-scan generated image signals demonstrate smaller signal-to-noise ratios than are present in conventional imaging techniques. This results in less distinct resultant images. In addition, line-scan imaging basically eliminates ghosting artifacts caused by gross transient motion-related shot-to-shot phase variations. Nevertheless, signal losses within each of the isolated lines still may occur due to non-uniform motion and/or magnetic field phenomena during the acquisition of the individual lines.
Accordingly, a technique for magnetic resonance imaging useful during the course of a surgical procedure or the like, without the requirement of a cessation of the procedure and/or a clearing of the field of view to be imaged, would be a significant advance in, and beneficial to, the art.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an apparatus for, and method of, acquiring magnetic resonance images during the course of a surgical procedure or the like which does not require the procedure be stopped during the imaging process.
Also, it is an object of the invention to provide an apparatus for, and a method of, acquiring intra-operative magnetic resonance images in which there is no necessity to remove metallic surgical instruments or the like from the field of view during the imaging period.
Further, it is an object of the present invention to utilize basic averaging concepts in a novel way to overcome the shortcomings of line-scan magnetic resonance imaging during ongoing surgical procedures and the like.
Still further, it is an object of the present invention to provide an apparatus for, and method of, detecting, and correcting for, or supplying, images or image portions which are missing and/or deteriorated by isolated transient motion or displacement effects in line-scan magnetic resonance imaging.
Yet another object of the present invention is to provide an apparatus for, and method of, displaying a moving average of line-scan derived magnetic resonance images during the course of surgical procedures and the like.
These and other objects of the present invention are accomplished by the provision of an apparatus and a method that utilize line-scan techniques for creating magnetic resonance images of invasive surgical fields of view. This is accomplished without a requirement to either temporarily terminate the surgical procedure, or to clear the surgical site, as required in the prior art.
The invention proceeds from the concept that magnetic resonance images obtained using line-scan techniques are not dependent upon phase encoding. This results in magnetic resonance images that are immune to the phase errors induced in Fourier type magnetic resonance signals by gross transient field inhomogeneities such as those caused by the motion of metal surgical instruments in the magnetic field. It also results in images immune to gross transient motion induced phase errors.
Further, the present invention takes advantage of the fact that the signal-to-noise ratio of any magnetic resonance image is partially determined by the number of signals that are averaged in the course of the creation of each pixel of the final image. Commonly, this means that a significant number of signals are generated within a short time period, such that for all practical purposes the signals were all generated at the same time. The average value of the signals of each so generated group of signals then is used as the single “signal point” for the particular measurement involved. This technique has been found to be acceptable as a way of acquiring high signal-to-noise ratios for individual signals of an individual image.
The present invention expands upon this concept by the acquisition of magnetic resonance images using a line-scan technique at time intervals such that the various signals making up each image cannot be said to have been acquired essentially simultaneously. The advantages made possible by the implementation of this concept are significant. First, a display of the moving average of a time series of images so acquired is characterized by a signal-to-noise ratio determined by the number of images included in the average. Typically, this is significantly greater than the signal-to-noise ratio of each line-scan generated image.
Second, averaging images created from signals generated at spaced out intervals tends to minimize the effect of short-term transient gross displacements and varying magnetic field inhomogeneities within the field of view. Accordingly, distortions arising as a result of motion and/or field inhomogeneities in the field of view tend to be averaged out of an image representing an average of a significant number of images of the field of view taken at intervals over a given period of time.
Third, averaging as described herein permits the time history of displacement that occurs within the target object to be displayed as a single image. Further, any portion of that time history may be selected for use at any time. Therefore, comparisons of a target object may be made from different portions of a procedure, or to previously acquired images. Similarly, a running moving average of the target object may be continuously viewed during the course of the procedure, or thereafter. Still further, selected portions of the slice and/or volume scanned may be updated more frequently than other portions thereof. Similarly, such selected portions also may be provided at different resolutions and/or at different image contrasts. This allow
Jolesz Ferenc A.
Kacher Daniel F.
Maier Stephan E.
Brigham & Women's Hospital
Dike Bronstein Roberts & Cushman IP Group
Fetzner Tiffany A.
Neuner George W.
Patidar Jay
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