Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2000-03-14
2004-04-06
Fulton, Christopher W. (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S309000, C324S318000
Reexamination Certificate
active
06717406
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to magnetic resonance imaging and, more particularly, to a method and corresponding apparatus for capturing and providing MRI data suitable for use in a multi-dimensional imaging processes.
BACKGROUND OF THE INVENTION
Magnetic resonance imaging (MRI) is a well known method of non-invasively obtaining images representative of internal physiological structures. In fact, there are many commercially available approaches and there have been numerous publications describing various approaches to MRI. Although MRI will be described herein as applying to a person's body, it may be applied to visualize the internal structure of other objects as well, and the invention is not limited to application of MRI in a human body.
A conventional MRI system is schematically illustrated in FIG.
1
. As shown in
FIG. 1
, an MRI system
10
includes a static magnet assembly, gradient coils, and transmit RF coils collectively denoted
12
under control of a processor
14
, which typically communicates with an operator via a conventional keyboard/control workstation
16
. These devices generally employ a system of multiple processors for carrying out specialized timing and other functions in the MRI system
10
. Accordingly, as depicted in
FIG. 1
, an MRI image processor
18
receives digitized data representing radio frequency nuclear magnetic resonance responses from an object region under examination and, typically via multiple Fourier transformation processes well-known in the art, calculates a digitized visual image (e.g., a two-dimensional array of picture elements or pixels, each of which may have different gradations of gray values or color values, or the like) which is then conventionally displayed, or printed out, on a display
18
a.
A plurality of surface coils
20
a,
20
b
. . .
20
i
may be provided to simultaneously acquire NMR signals for simultaneous signal reception, along with corresponding signal processing and digitizing channels.
A conventional MRI device establishes a homogenous magnetic field, for example, along an axis of a person's body that is to undergo MRI. This magnetic field conditions the interior of the person's body for imaging by aligning the nuclear spins of nuclei, in atoms and molecules forming the body tissue, along the axis of the magnetic field. If the orientation of the nuclear spin is perturbed out of alignment with the magnetic field, the nuclei attempt to realign their nuclear spins with an axis of the magnetic field. Perturbation of the orientation of nuclear spins may be caused by application of a radiofrequency (RF)—pulses. During the realignment process, the nuclei precess about the axis of the magnet field and emit electromagnetic signals that may be detected by one or more coils placed on or about the person.
It is known that the frequency of the nuclear magnetic radiation (NMR) signal emitted by a given precessing nucleus depends on the strength of the magnetic field at the nucleus' location. Thus, as is well known in the art, it is possible to distinguish radiation originating from different locations within the person's body simply by applying a field gradient to the magnetic field across the person's body. For sake of convenience, this will be referred to as the left-to-right direction. Radiation of a particular frequency can be assumed to originate at a given position within the field gradient, and hence at a given left-to-right position within the person's body. Application of a such a field gradient is referred to herein as frequency encoding.
The simple application of a field gradient does not allow two dimensional resolution, however, since all nuclei at a given left-to-right position experience the same field strength, and hence emit radiation of the same frequency. Accordingly, application of a frequency-encoding gradient, alone, does not make it possible to discern radiation originating from the top vs. radiation originating from the bottom of the person at a given left-to-right position. Resolution has been found to be possible in this second direction by application of gradients of varied strength in a perpendicular direction to thereby perturb the nuclei in varied amounts. Application of such additional gradients is referred to herein as phase encoding.
Frequency-encoded data sensed by the coils during a phase encoding step is stored as a line of data in a data matrix known as the k-space matrix. Multiple phase encoding steps must be performed to fill the multiple lines of the k-space matrix. An image may be generated from this matrix by performing a Fourier transformation of the matrix to convert this frequency information to spatial information representing the distribution of nuclear spins or density of nuclei of the image material.
MRI has proven to be a valuable clinical diagnostic tool for a wide range of organ systems and pathophysiologic processes. Both anatomic and functional information can be gleaned from the data, and new applications continue to develop as the technology and techniques for filling the k-space matrix improve. As technological advances have improved achievable spatial resolution, for example, increasingly finer anatomic details have been able to be imaged and evaluated using MRI.
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 MRI, 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 may not have the resolution necessary to trace the course and patency of coronary arteries.
Imaging time is largely a factor of the speed with which the MRI device can fill the k-space matrix. In conventional MRI, the k-space matrix is filled one line at a time. Although many improvements have been made in this general area, the speed with which the k-space matrix may be filled is limited by, e.g., the intervals necessary to create, switch or measure the magnetic fields or RF signals involved in data acquisition, as well as physiological limits on the maximum strength and variation of magnetic fields and RF signals the human body is able to withstand.
To overcome these inherent limits, several techniques have been developed to simultaneously acquire multiple lines of data for each application of a magnetic field gradient. These techniques, which may collectively be characterized as “parallel imaging techniques,” use spatial information from arrays of RF detector coils to substitute for encoding which would otherwise have to be obtained in a sequential fashion using field gradients and RF pulses. The use of multiple effective detectors has been shown to multiply imaging speed, without increasing gradient switching rates or RF power deposition.
The first in vivo images using the parallel MR imaging approach were obtained using the SMASH (SiMultaneous Acquisition of Spatial Harmonics) technique. The history of parallel imaging in general and of the SMASH technique in particular is described in greater detail in U.S. Pat. No. 5,910,728, the content of which is hereby incorporated by reference. An alternative strategy for parallel imaging, known as “subencoding”, had been described earlier using phantom images only. A technique closely related to subencoding—the SENSE (SENSitivity Encoding) technique—has recently been described and applied to in vivo imaging. The SENSE technique is discussed in more detail in International Publication Number WO 99/54746, the content of which is hereby incorporated by reference.
Parallel imaging techniques have tended to fall into one of two general categories, as exemplified by the SMASH and the subencoding/SENSE methods, respectively. SMASH operates primarily on the k-space matrix and is referred to herein as o
Beth Israel Deaconess Medical Center Inc.
Fetzner Tiffany A.
Fulton Christopher W.
Wolf Greenfield & Sacks P.C.
LandOfFree
Parallel magnetic resonance imaging techniques using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Parallel magnetic resonance imaging techniques using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Parallel magnetic resonance imaging techniques using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3269800