Off‐resonance spin locking for MR imaging

Santyr, Giles; Fairbanks, E. Jeffrey; Kelcz, Frederick; Sorenson, James A.

doi:10.1002/mrm.1910320107

Cited by 76 publications

(89 citation statements)

References 19 publications

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“…The phantom consisted of three 0.8-cm tubes of varying concentrations (2.0, 3.1, and 4.8%) of agar bound together with nonmagnetic tape, surrounded by distilled water, and encased in a 2.6-cm-inner-diameter tube. Agar was chosen because it was known to exhibit T 1 contrast varying with concentration (6,25,26) as well as T 1 relaxation times similar to those of biological tissues (26,27). All phantom images are single-slice images, consisting of 800 equal angle radial views, with 256 pointsper-view regridded to 512 2 for reconstruction then cropped for display.…”

Section: Methodsmentioning

confidence: 99%

T1? imaging using magnetization-prepared projection encoding (MaPPE)

Nugent

Johnson

2000

Magn. Reson. Med.

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Section: Methodsmentioning

confidence: 99%

T1? imaging using magnetization-prepared projection encoding (MaPPE)

Nugent

Johnson

2000

Magn. Reson. Med.

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“…In biological tissues, off-resonance RF pulse, in addition to spin-locking, also leads to 'magnetization transfer' effect (162) which may complicate the analysis of T off 1r . The details of off-resonance experiments can be found in the literature (163)(164)(165). However, for the rest of the sections we restrict ourselves to describing T 1r in the on-resonance condition.…”

Section: T 1r Mrimentioning

confidence: 99%

Sodium and T_1ρ MRI for molecular and diagnostic imaging of articular cartilage

et al. 2006

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In this article, both sodium magnetic resonance (MR) and T 1r relaxation mapping aimed at measuring molecular changes in cartilage for the diagnostic imaging of osteoarthritis are reviewed. First, an introduction to structure of cartilage, its degeneration in osteoarthritis (OA) and an outline of diagnostic imaging methods in quantifying molecular changes and early diagnostic aspects of cartilage degeneration are described. The sodium MRI section begins with a brief overview of the theory of sodium NMR of biological tissues and is followed by a section on multiple quantum filters that can be used to quantify both bi-exponential relaxation and residual quadrupolar interaction. Specifically, (i) the rationale behind the use of sodium MRI in quantifying proteoglycan (PG) changes, (ii) validation studies using biochemical assays, (iii) studies on human OA specimens, (iv) results on animal models and (v) clinical imaging protocols are reviewed. Results demonstrating the feasibility of quantifying PG in OA patients and comparison with that in healthy subjects are also presented. The section concludes with the discussion of advantages and potential issues with sodium MRI and the impact of new technological advancements (e.g. ultra-high field scanners and parallel imaging methods). In the theory section on T 1r , a brief description of (i) principles of measuring T 1r relaxation, (ii) pulse sequences for computing T 1r relaxation maps, (iii) issues regarding radio frequency power deposition, (iv) mechanisms that contribute to T 1r in biological tissues and (v) effects of exchange and dipolar interaction on T 1r dispersion are discussed. Correlation of T 1r relaxation rate with macromolecular content and biomechanical properties in cartilage specimens subjected to trypsin and cytokineinduced glycosaminoglycan depletion and validation against biochemical assay and histopathology are presented. Experimental T 1r data from osteoarthritic specimens, animal models, healthy human subjects and as well from osteoarthritic patients are provided. The current status of T 1r relaxation mapping of cartilage and future directions is also discussed. Copyright # 2006 John Wiley & Sons, Ltd. KEYWORDS: cartilage; arthritis; spin-lock; T1rho; sodium; MRI OSTEOARTHRITIS Osteoarthritis (OA) affects more than half of the population above the age of 65 (1,2) and has a significant negative impact on the quality of life of elderly individuals (3). The economic costs in the USA from OA have been estimated to be more than 1% of the gross domestic product (4). OA is now increasingly viewed as a metabolically active joint disorder of diverse etiologies. The biochemistry of the disease is characterized by the following changes in cartilage: reduced proteoglycan (PG) concentration, possible changes in the size of collagen fibril and aggregation of PG, increased water content and increased rate of synthesis and degradation of matrix macromolecules. The earliest changes in the cartilage due to OA result in a partial breakdown in the proteoglyc...

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“…SL technique has been implemented also for human imaging at higher field strengths (Dixon et al 1996, Ulmer et al 1996, Semple et al 1998, Ulmer et al 1998. By using suitable imaging parameters and off-resonance technique the exceeding of SAR limits has been avoided (Santyr et al 1994). Higher SNR combined with even enhanced T1ρ contrast (due to longer T1 values of tissues) makes multiple slice SL technique an attractive method for tissue characterization and contrast enhancement also for high field strengths.…”

Section: Future Prospectsmentioning

confidence: 99%