Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-03-30
2001-09-11
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S422000, C324S307000, C324S309000, C324S318000, C324S322000
Reexamination Certificate
active
06289232
ABSTRACT:
BACKGROUND AND TECHNICAL FIELD
This invention relates generally to magnetic resonance imaging (MRI) using nuclear magnetic resonance (NMR) phenomena. It is particularly directed to a method and corresponding apparatus for more efficiently capturing and providing MR data for use in multi-dimensional imaging processes.
MRI is a widely accepted, medically important and commercially viable technique for obtaining digitized video images representative of internal body tissue and structures. There are many commercially available systems and there have been numerous publications describing their operation and other approaches to MRI. Many of these use multi-dimensional Fourier transformation techniques which are now well-known to those skilled in this art.
In general, MRI devices establish a constant homogeneous magnetic field together with a specific additional bias field gradient in a known plane or region under consideration to orient nuclear spins, and apply a radiofrequency pulse or a sequence of pulses to further condition spins or perturb the nuclei. Those nuclei in a known region of the bias field gradient emit an RF signal in a specific band determined by the magnetic field distribution, and these RF emissions are detected by receiving coils and the received signals are stored as a line of information in a data matrix known as the k-space matrix. The full matrix is built up by successive cycles of conditioning the spins, perturbing them, and collecting RF emissions. An image is then generated from this matrix by Fourier transformation, which converts the frequency information present in the RF oscillations to spatial information representing the distribution of nuclear spins in the tissue.
Magnetic resonance imaging has proven to be a valuable clinical diagnostic tool in a wide range of organ systems and pathophysiologic processes. Both anatomic and functional information can be gleaned from the MR data, and new applications continue to develop with each improvement in basic imaging technique and technology. As technologic advances have improved achievable spatial resolution, for example, increasingly fine anatomic details have been amenable to MR imaging and evaluation. At the same time, fast imaging sequences have reduced imaging times to such an extent that many moving structures can now be visualized without significant motion artifacts.
Often, however, there is a tradeoff between spatial resolution and imaging time, since higher resolution images require a longer acquisition time. This balance between spatial and temporal resolution is particularly important in cardiac MR, where fine details of coronary artery anatomy, for example, must be discerned on the surface of a rapidly beating heart. A high-resolution image acquired over a large fraction of the cardiac cycle will be blurred and distorted by bulk cardiac motion, whereas a very fast image acquired in a shorter time may not have the resolution necessary to trace the course and patency of coronary arteries. Some of the fastest imaging sequences currently implemented, such as echo planar imaging (EPI), approach the goal of yielding images of reasonable resolution in a suitably short fraction of the cardiac cycle. Other approaches have also been tried to eliminate the effects of cardiac motion, including k-space segmentation, in which image acquisition is divided up over several cardiac cycles with ECG gating to ensure that the heart is in the same phase of systole or diastole during acquisition of each segment. Cine images of multiple cardiac phases may be pieced together with this technique, with partial acquisitions of the signal data for different phases occurring in each cardiac cycle. One problem with this class of techniques is that respiratory motion can change the position of the heart over the course of several cardiac cycles. Partial acquisitions will then be misregistered, and artifacts will result. In an attempt to eliminate or adjust for respiratory motion, breath holds, respiratory gating, and navigator echo gating techniques have all been tried, and each of these techniques has had some significant successes. Nevertheless, an imaging strategy which allowed high-resolution images to be acquired comfortably within one or two phases of the cardiac cycle would circumvent many of the difficulties and residual artifacts associated with these compensation techniques.
The speed with which magnetic resonance (MR) images may be acquired has already increased dramatically over the past decade. The improvements in speed may be traced to a combination of advances in the technologies of magnet construction and actuation, and innovations in imaging strategy. Strong, fast-switching magnetic field gradients and fast electronics have allowed the intervals between data collections to be reduced significantly. Meanwhile, fast gradient-echo and spin-echo sequences have reduced image acquisition time by allowing greater portions of k-space to be sampled quickly. Echo planar imaging (EPI), fast low-angle shot (FLASH), turbo spin echo (TSE), and spiral imaging techniques all allow very short intervals between acquisition of successive data points. The DUFIS, OUFIS, RUFIS, and BURST family of sequences further reduce image acquisition time by eliminating time delays incurred during gradient switching and echo formation. Details of the above-mentioned eight techniques may be found in the following papers: P. Mansfield,
Multi
-
planar image formation using NMR spin echoes. J Phys.
C. 10, L55-58 (1977); A. Haase, J. Frahm,
D. Mattaei, W. Hanicke, K. D. Merboldt,
FLASH imaging: rapid NMR imaging using low flip
-
angle pulses. J. Magn. Reson.
67, 256-266 (1986); J. L. Listerud, S. Einstein, E. Outwater, H. Y. Kressel,
First principles of fast spin echo. Magn. Reson. Q.
8, 199-244 (1992); C. Meyer, B. Hu, D. Nishimura, A. Macovski,
Fast spiral coronary artery imaging. Magn. Reson. Med.
28, 202-213 (1992); I. J. Lowe, R. E. Wysong,
DANTE ultrafast imaging sequence (DUFIS). J Magn. Reson.
Ser. B 101, 106-109 (1993); L. Zha, I. J. Lowe,
Optimized ultra-fast imaging sequence
(OUFIS).
Magn. Reson. Med
33, 377-395 (1995); D. P. Madio, I. J. Lowe,
Ultra
-
fast imaging using low flip angles and FIDs. Magn. Reson. Med
34, 525-529 (1995); and J. Hennig, M. Hodapp,
Burst imaging. MAGMA
1, 39-48 (1993).
Increasing the speed of MR imaging further is a challenging proposition, since the aforementioned fast imaging techniques have already achieved an impressive efficiency. All these techniques allow very short intervals between acquisition of successive data points, and hence do not waste much time in accumulating the data to fill the k-space matrix of a size required to generate a given image. In flow-encoded EPI images, for example, the entire complex k-space matrix is filled in a single spin excitation (which is followed by multiple spin conditioning cycles involving the application of multiple stepped field gradients), and the resulting image matrix is likewise “full,” with useful information stored in both the real and the imaginary channels. One common feature of nearly all the fast imaging techniques currently in common use, however, is that they acquire data in a sequential fashion. Whether the required data set, i.e., the k-space data matrix, is filled in a rectangular raster pattern, a spiral pattern, a rapid series of line scans, or some other novel order, it is acquired one point and one line at a time.
That is, the above-mentioned fast MR imaging has concentrated on increasing the speed of sequential acquisition by reducing the time intervals between scanned lines. Still, however, only a portion of k-space is acquired at a time, which sets a methodological upper limit to the achievable speed for data acquisition. Modifications to pulse sequences or to magnetic field gradients have yielded a gradual improvement in imaging speed by allowing faster sequential scanning of k-space, but these improvements face limits due to the length and number of the intervals necessary to create, switch or measure the magnetic fields o
Griswold Mark
Jakob Peter M.
Sodickson Daniel K.
Beth Israel Deaconess Medical Center Inc.
Lateef Marvin M.
Mantis Mercader Eleni
Morris James H.
Wolf Greenfield & Sacks P.C.
LandOfFree
Coil array autocalibration MR imaging does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coil array autocalibration MR imaging, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coil array autocalibration MR imaging will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492381