Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-03-26
2001-02-06
Oda, Christine K. (Department: 2862)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S307000, C324S309000
Reexamination Certificate
active
06185447
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to magnetic resonance data acquisition and imaging, and more particularly the invention relates to a three-dimensional magnetic resonance sequence for acquiring volumetric data depicting a motion cycle.
Cardiac MRI can provide extremely accurate measures of chamber volumes, stroke volume, cardiac output and ejection fraction. The most commonly used methods are cine MR (described in U.S. Pat. No. 4,710,717, “Method for Fast Scan Cine NMR Imaging,” Norbert J. Pelc and Gary H. Glover, December, 1987), and segmented k-space techniques (described in U.S. Pat. No. 5,377,680, “MRI Cardiac Image Produced by Temporal Data Sharing,” Tsur Bernstein and Thomas K. Foo, January, 1995). Both of these techniques employ two-dimensional (2D) data acquisition strategies, and have limitations. For example, a cine scan with 128 phase-encodings can image 3 slices with a temporal resolution of approximately 60 ms in roughly 2 minutes, but the need for volumetric coverage increases the total scan time substantially. The segmented k-space methods reduce the scan time at the expense of temporal resolution. They image a single slice in a breath-hold with 80 ms temporal resolution. However, the rest periods between scans makes the total scan time for volumetric coverage comparable to that in cine. Both techniques produce 2D image sets, which must be concatenated for volumetric measurements. Thus, any subject movement during the scan can lead to slice registration errors, which in turn can affect the quality of the results. With both techniques, it may be difficult to obtain high spatial resolution in the slice direction. Further, both methods can suffer from insufficient contrast between the blood in the chambers and the myocardium, especially during flow stasis in diastole. This makes automatic volumetric analysis difficult, and manual analysis is tedious and introduces measurement variability.
MRI techniques produce images of individual slices by encoding spatial information. In the most commonly used method, often called 2DFT or “spin-warp”, location in one direction is encoded using selective excitation which generates signal only from a slice through the object. Location in a second direction is encoded by acquiring the signal in the presence of a magnetic field in that direction, thereby encoding position into the temporal frequency of the measured signal. Location in the third direction is encoded using a preparation “phase encoding gradient”. To form an image, the sequence of pulses that form the pulse sequence must be repeated many times using many values of this phase encoding gradient. The time between sequence repetitions is called the repetition time TR.
The method described above forms an image of a single plane. Many such images to cover a volume can be acquired either sequentially or in an interleaved manner. It is also possible to acquire data from a 3D volume simultaneously. For example, one can generate signal using an excitation pulse that excites a relatively thick slab. Position in the slice direction along the slab is encoded using a second phase encoding gradient.
Imaging techniques which are faster than those described above are known. One, called Echo Planar Imaging (EPI) is even capable of forming an image of an entire slice from data acquired during a single pulse sequence execution. However, the image quality using “single shot EPI” may not be acceptable for some applications. For these, it is possible to use multi-shot EPI. Other fast imaging methods, e.g. spiral k-space scanning, are also known.
SUMMARY OF THE INVENTION
The present invention provides a fast 3D imaging sequence for acquiring volumetric data in a cine mode whereby the entire volume, e.g. the heart, can be imaged in a time comparable to that of a single cine scan with the temporal resolution being similar to that in a segmented k-space 2D acquisition.
Briefly, a body with cyclical motion such as the heart is placed in a magnetic field (B
o
), and a plurality of data acquisition sequences are implemented using a common time marker, such as the heartbeat as determined by an electrocardiogram (ECG). The repetition time for each sequence is made very short. A phase encode rewinder gradient can be used to reduce artifacts, and RF spoiling and crusher gradients can be used to improve the suppression of static tissue.
In the preferred embodiment, data for different slice direction phase encode gradients are collected during each heart beat while the in-plane phase encode gradient remains constant.
The invention and objects and features thereof will be more readily apparent from the following description and appended claims when taken with the drawings.
REFERENCES:
patent: 4707658 (1987-11-01), Frahm et al.
patent: 4710717 (1987-12-01), Pelc et al.
patent: 5377680 (1995-01-01), Bernstein et al.
Thomas K. Foo, Ph.D., et al., “Improved Ejection Fraction and Flow Velocity Estimates with Use of View Sharing and Uniform Repetition Time Excitation with Fast Cardiac Techniques”, Radiology 1995; 195:471-478.
Dennis R. Wetter, MD et al., “Cardiac Echo-planar MR Imaging: Comparison of Single- and Multiple-shot Techniques”, Radiology 1995; 194:765-770.
Martin Unterweger, MS et al., “Comparison of Echoplanar and Conventional Cine-Magnetic Resonance Data-Acquistion Strategies”, vol. 29, No. 11, 994-1000.
Alley Marcus T.
Pelc Norbert J.
Fetzner Tiffany A.
Oda Christine K.
The Leland Stanford Junior University
Townsend and Townsend / and Crew LLP
Woodward Henry K.
LandOfFree
Method for temporally resolved, three-dimensional MR volume... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for temporally resolved, three-dimensional MR volume..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for temporally resolved, three-dimensional MR volume... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590354