Method of magnetic resonance imaging

Details Method of magnetic resonance imaging Method of magnetic resonance imaging

2000-05-19

2002-04-16

Arana, Louis (Department: 2862)

Electricity: measuring and testing

Particle precession resonance

Using a nuclear resonance spectrometer system

C324S307000

Reexamination Certificate

active

06373250

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to magnetic resonance imaging and, more particularly, to a method of slice selective multiple quantum magnetic resonance imaging of, for example, connective tissues.
Connective tissues, such as ligaments, tendons and cartilage appear in standard magnetic resonance (MR) images with low signal-to-noise (S/N) ratio (SNR) due to the water short T
2
relaxation times. Images performed with short echo time (TE), result in a significant loss of contrast. In addition to the need to enhance the nuclear magnetic resonance (NMR) signal of connective tissues, it is also important to increase the contrast between the different compartments within a specific tissue and between adjacent tissues.
Methods developed to meet these requirements include heavily T, weighted imaging [R. J. Scheck, A. Romagnolo, R. Biemer, T. Pfluger, K. Wilhelm, K. HEran, The carpal ligaments in MR arthrograpby of the wrist: correlation with standard MRI and wrist arthroscopy, J. Magn. Reson. Imag. 1999; 9:468-474] magnetization transfer [T. D. Scholz, R. F. Eyot, J. R. DeLeornardis, T. L. Ceckler, R. S. Balaban, Water-macromolecular proton magnetization transfer in infarcted myocardium: a method to enhance magnetic resonance image contrast, Magn. Reson. Med 1995; 33:178-184; M. L. Gray, D. Burstein, L. M. Lesperance, L. Gehrke, Magnetization transfer in cartilage and its constituent macromolecules, Magn. Reson. Med. 1995; 34: 319-325; R. M. Henkelman, X. Huang, Q.-S. Xiang, G. J. Staniz, S. D. Swanson, M. J. Bronskill, Quantitative interpretation of magnetization transfer, Magn. Reson. Med. 1993; 29:759-766], fat suppression [C. G. Peterfy, S. Majumdar, P. Lang, C. F. van Dijke, K. Sack, H. K. Ganant, MR Imaging of the artitic knee: improved discrimination of cartilage, synovium, and effusion with pulsed saturation transfer and fat-suppressed T
1
-weighted sequences, Radiology 1994; 191:413-419], diffusion weighted imaging [Y. Xia, T. Farquhar, N. Burton-Wurster, E. Ray, L. Jelinski, Diffusion and relaxation mapping of cartilage-bone plugs and excised disk using micromagnetic resonance imaging, Magn. Reson. Med. 1994; 31:273-282] and projection reconstruction techniques that achieve much shorter echo time than conventional methods [G. E. Gold, J. M. Pauly, A. Macovsky, R. J. Herfkens, MR spectroscopic imaging of collagen: tendons and knee menisci, Magn. Reson. Med. 1995; 34:647-6543].
While these approaches do increase the MR signal of connective tissues and the contrast between connective and adjacent tissues, the results are not yet optimal for diagnostic purposes.
It has recently been demonstrated by the inventors of the present invention that proton double quantum filtered (DQF) NIRI produces a new type of contrast and may serve as a good modality for the imaging of ordered biological tissues [Y. Sharf, Y. Seo, U. Eliav, S. Akselrod, G. Navon, Mapping strain exerted on blood vessel walls using deuterium double quantum filtered MRI, PNAS 1998; 95:4108-4112; L. Tsoref, H. Shinar, G. Navon, Observation of a
1
H double quantum filtered signal of water in biological tissues, Magn. Reson. Med. 1998;
39:11-17; Tsoref, H. Shinar, Y. Seo, U. Eliav, G. Navon, Proton Double Quantum Filtered MRI—A New Method for Imaging Ordered Tissues, Magn. Reson. Med. 1998; 40:720-726].
The contrast in DQF MRI stems from the fact that only water molecules associated with ordered structures are detected, and signals originating from molecules in isotropic tissues are suppressed. The
1
H DQF signal intensity is sensitive to the magnitude of the residual dipolar interaction and the proton exchange rate between the water molecules [U. Eliav, G. Navon, A study of dipolar interactions and dynamic processes of water molecules in tendon by
1
H and
2
H homonuclear and heteronuclear multiple-quantum-filtered NMR spectroscopy, J. Magn. Reson. 1999; 137:295-310].
Previous studies of
1
H and
23
Na multiple quantum imaging [Tsoref, H. 35 Shinar, Y. Seo, U. Eliav, G. Navon, Proton Double Quantum Filtered MR—A New Method for Imaging Ordered Tissues, Magn. Reson. Med. 1998; 40:720-726; M. D. Cockman, L. W. Jelinski, Double-quantum-filtered sodium imaging, J. Magn. Reson. 1990; 90:9-18] did not employ slice selection, and hence were limited to samples that are uniform along one axis.
3-D imaging techniques [R. Kemp-Harper, P. Styles, S. Wimperis, Three-dimensional triple-quantum filtration
23
Na NMR imaging, J. Magn. Reson. B. 1995; 108:280-2841] may to some extent solve this problem but are highly time consuming. Thus, for clinical applications a DQF slice selective sequence must be developed.
The short relaxation times of tendons and ligaments poses a particular problem in a straightforward application of slice-selection to the previous DQF MRI pulse sequences [Tsoref, H. Shinar, Y. Seo, U. Eliav, G. Navon, Proton Double Quantum Filtered MRI—A New Method for Imaging Ordered Tissues, Magn. Reson. Med. 1998; 40:720-726].
There is thus a widely recognized need for, and it would be highly advantageous to have, a methods of MR imaging of connective tissue devoid of the above limitations. While reducing the present invention to practice solutions to the above problems were obtained and novel protocols for multiple quantum filtered (MQF) slice selective imaging were developed. It was found that
1
H DQF images changed dramatically during the heating process of injured tissues and were more informative than standard MR images. It was further found that although
1
H DQF imaging requires high gradient slew-rates, by using composite RF-pulses one can apply
1
H multiple quantum techniques with a commercial clinical spectrometer. The quality of the DQF images was evaluated by comparing their SNR and the contrast to noise ratio (CNR) to standard gradient-recalled-echo (GRE) images.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of magnetic resonance imaging of an object, the method comprising the steps of (a) applying a radiofrequency pulse sequence selected so as to select a coherence of an order n to the object, wherein n is zero, a positive or a negative integer other than ±1; (b) applying magnetic gradient pulses to the object, so as to select a slice of the object to be imaged and create an image; and (c) acquiring a radiofrequency signal resulting from the object, so as to generate a magnetic resonance slice image of the object.
According to further features in preferred embodiments of the invention described below, the coherence is selected from the group consisting of double quantum filter (DQF), where n equals ±2 and triple quantum filter (TQF), where n equals ±3.
According to still further features in the described preferred embodiments the coherence is selected by phase cycling or gradient selection.
According to still further features in the described preferred embodiments the radiofrequency is selected so as to enable imaging of an atomic nucleus selected from the group consisting of
1
H,
2
H and
23
Na.
According to still further features in the described preferred embodiments the radiofrequency pulse sequence is selected so as to optimize imaging of the atomic nucleus.
According to still further features in the described preferred embodiments the radiofrequency signal is derived from an atomic nucleus selected from the group consisting of
1
H,
2
H and
23
Na.
According to still further features in the described preferred embodiments a creation time of the radiofrequency pulse sequence is selected so as to maximize the radiofrequency signal or to obtain a desired contrast.
According to still further features in the described preferred embodiments a time to echo as controlled by the magnetic gradient pulses is selected so as to maximize the radiofrequency signal or to obtain a desired contrast.
According to still further features in the described preferred embodiments a repetition time of the radiofrequency pulse s

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