Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2003-03-14
2004-12-28
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S306000
Reexamination Certificate
active
06836114
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of magnetic resonance imaging (MRI). Specifically, the invention relates to spin-locking and T
1&rgr;
-weighted MRI pulse sequences.
BACKGROUND OF THE INVENTION
Magnetic resonance imaging (MRI) has become the modality of choice for imaging joints due to its excellent definition of ligaments, cartilage, bone, muscle, fat and superior soft tissue contrast (Smith,
Magn. Reson. Imaging Clin. N. Am.
3:229-248 (1995); Sofka, et al.,
Radiology
5:217-226 (2001)). For two decades, proton magnetic resonance imaging (MRI) has shown its efficacy in the noninvasive analysis of soft tissues, particularly in the diagnosis of tendinomuscular and osteoarticular diseases (Peterfy, et al.,
Radiol. Clin. North Am.
34:195 (1996); Peterfy,
Magn. Reson, Imaging Clin. N. Amer.
8:409-430 (2000)).
Articular cartilage is a connective tissue consisting of relatively few cells and a highly charged and hydrated extracellular matrix (ECM). The constituents of the ECM are proteoglycans (PG), collagen, and non-collagenous proteins and water (Grushko, et al.,
Conn. Tiss. Res.
19:149-176 (1989); Lohmander,
J. Anatomy
184:477-492 (1994); Mankin, et al.,
J. Bone Joint Surg
-
Am.
53:523-537 (1971)). Despite its remarkable durability, degeneration of articular cartilage can result from either noninflammatory processes, such as osteoarthritis (OA), or inflammatory processes, such as rheumatoid arthritis (RA). The early stage of OA is associated with loss of PG and changes in water content (Grushko, et al., 1989; Lohmander, 1994). Recent developments in chondroprotective therapies, cartilage grafting, gene therapy and tissue engineering have increased the demand for accurate and non-invasive techniques that will enable the detection of the early biochemical changes of cartilage degeneration in vivo.
Conventional proton MR techniques have been able to provide information about late stages of degeneration in which structural defects are present (Recht, et al.,
Am. J. Roent.
163:283-290 (1994); Peterfy, et al.,
Radiol. Clin. North Am.
32:291-311 (1994)). Recently, delayed gadolinium (Gd)-enhanced proton MRI of cartilage (dGEMRIC) (Bashir, et al.,
Magn. Reson. Med.
36:665-673 (1996); Burstein, et al.,
Magn. Reson. Med.
45:36-41 (2001); Mlynarik, et al.,
J. Magn. Reson. Imaging
10:497-502 (1999)), positively charged nitroxide based techniques (Lattanzio, et al., 25:1024 (2000), and sodium MRI (Reddy, et al.,
Magn. Reson. Med.
39:697-701 (1998); Shapiro, et al.,
J. Magn. Reson.
142:24-31; Shapiro, et al.,
Magn. Reson. Med.
47:284-291 (2002)) have been employed to measure PG changes in cartilage both in vivo and in vitro. However, these techniques have some practical limitations. In dGEMRIC, long waiting period between contrast agent injection and imaging and variation in intra tissue Gd-relaxivity may contribute to the errors in PG quantitation, thereby reducing the accuracy of this technique in the detection of OA. Although sodium MR imaging has high specificity towards proteoglycans, it has an inherently low sensitivity and requires special radio-frequency hardware modifications before it can be used with a routine clinical imaging unit.
Spin lattice relaxation time in the rotating frame (T
1&rgr;
) has been shown to be sensitive to changes in PG content of cartilage (Duvvuri, et al.,
Magn.Reson.Med.
38:863-867 (1997); Akella, et al.,
Magn. Reson. Med.
46:419-423 (2001)). It is well suited for probing macromolecular slow motions at high static fields without modifying MR system hardware (Sepponen, et al,
J, Computer Assisted Tomography
9:1007-1011 (1985); Santyr, et al.,
Magn. Reson. Med.
12:25-37 (1989)).
T
1&rgr;
provides an alternative contrast compared to conventional MRI methods. Since the first description by Redfield (
Phys. Rev.
98:1787 (1955)), spin-locking technique has been used extensively, to investigate the low frequency interactions between the macromolecules and bulk water. Several authors have investigated the T
1&rgr;
dispersion characteristics of biological tissues, including brain (Aronen, et al.,
Magn. Reson. Imag.
17:1001-1010 (1999); Rizi, et al.,
J Magn Reson Imaging
8:1090-1096 (1998)), tumors (Aronen, et al.,
Magn. Reson. Imag.
17:1001-1010 (1999); Markkola, et al.,
Radiology
200:369-375 (1996)), and articular cartilage (Mlynarik, et al., 1999; Akella, et al., 2001; Duvvuri, et al., 1997; Duvvuri, et al.,
Radiology
220:822-826 (2001)). These studies have demonstrated the potential value of T
1&rgr;
-weighting in evaluating various physiologic/pathologic states.
Although recent studies have demonstrated the potential role of T
1&rgr;
-weighted MRI in measuring cartilage degeneration, they all have been restricted to single slice imaging, and hence, are impractical for the imaging of a typical anatomic volume. The use of single slice techniques results from the problem in making the spin-locking pulse slice selective. A 2D multi-slice T
1&rgr;
MRI sequence has not been implemented since the use of a nonselective spin-lock (SL) pulse poses a challenge to slice-selective imaging. Multi-slice imaging requires the application of multiple radio frequency (RF) pulse trains within a sequence repetition time (TR) to excite several slices in a time efficient manner. Currently, T
1&rgr;
pulse sequences employ a non-selective RF pulse to spin-lock the magnetization in the transverse plane following the application of a non-selective &pgr;/2 pulse. As a result, using this method, the spin-lock pulse excites signals from the entire sample during each application, but the subsequent imaging sequence acquires data from only a single slice, wasting the information from the remainder of the volume. Accordingly, a need has remained until the present invention for a method to perform multi-slice T
1&rgr;
-weighted MRI.
Furthermore, in addition to the improved ability to image anatomic regions through 2D multi slice imaging, a 3D image provides even better contrast and faster acquisition than a 2D image. Even though a 3D, gradient-echo readout of a T
1&rgr;
-weighted MR signal has been used (Aronen, et al., 1999), that sequence was implemented on a low field magnet (0.1T) with a combination of adiabatic pulses, and RF spoiling alone was employed to destroy unwanted transverse coherence. The use of adiabatic pulses has certain drawbacks. Their long pulse lengths result in substantial decay of magnetization during the pulse period. These pulses cannot be easily calibrated on a clinical scanner, are more RF power intensive and may introduce specific absorption rate (SAR) issues. Moreover, any residual transverse magnetization resulting from incomplete restoration of the T
1&rgr;
-prepared magnetization to the longitudinal axis by the second adiabatic pulse will result in unwanted image artifacts.
The need has remained for a MR pulse sequence capable of performing 3D T
1&rgr;
-weighted MRI imaging on a high field clinical scanner. However, when using high field clinical scanners (greater than or equal to 1.5T), the SAR by the pulse sequence is significant, and imaging parameters must be chosen such that the energy deposition does not exceed the established SAR guidelines. Hence, determining the optimal sequence parameters has been necessary, so that the energy deposition by the radio frequency pulses in the sequence, measured as the SAR, does not exceed safety guidelines for imaging human subjects.
Additionally, significant artifacts arise in T
1&rgr;
-weighted imaging when nutation angles suffer small deviations from their expected values. These artifacts vary with spin-locking time and amplitude, severely limiting attempts to perform quantitative imaging or measurement of T
1&rgr;
relaxation times. As a result, a need has also remained for a “self-compensating” spin-locking pulse that dramatically reduces artifacts and provides a more robust implementation of T
1&rgr;
imaging despite spatial variations in nutation angles.
Finally, T
1&rgr;
-weighted MRI in volume coils has been employed to improv
Borthakur Ari
Charagundla Sridhar R.
Reddy Ravinder
Shapiro Erik M.
Arana Louis
Dilworth Paxson LLP
McConathy Evelyn H.
The Trustees of the University of Pennsylvania
LandOfFree
Pulse imaging sequences and methods for T1p-weighted MRI does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pulse imaging sequences and methods for T1p-weighted MRI, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulse imaging sequences and methods for T1p-weighted MRI will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3333443