Incorporation of saturation transfer into the formalism for rotating-frame spin-lattice NMR relaxation in the presence of an off resonance-irradiation field

Caines, G. Herbert; Schleich, Thomas

doi:10.1016/0022-2364(91)90161-l

Cited by 12 publications

(6 citation statements)

References 15 publications

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“…Further experiments to elucidate the underlying mechanisms are necessary. In particular, these processes have to be characterized quantitatively in terms of rate constants using either the Bloch formalism or the formalism of off-resonance rotating-frame spinlattice relaxation with incorporated magnetization transfer (15,16). Possible spatial differences in the magnetization transfer effects of Cr/PCr within the healthy brain as well as between healthy and diseased brain tissue should be measured using spectroscopic imaging techniques (17,18).…”

Section: Discussionmentioning

confidence: 99%

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

Dreher

Norris

Leibfritz

1994

Magnetic Resonance in Med

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The effect of off-resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatine/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between +/- 10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a long T2 relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off-resonance preirradiation. Possible interpretations of these results are discussed.

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Section: Discussionmentioning

confidence: 99%

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

Dreher

Norris

Leibfritz

1994

Magnetic Resonance in Med

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“…There are two pools: a liquid and a semisolid pool with Lorentzian NMR line shapes characterizing each pool. This was the first model used to extract information on the rate of exchange between the two pools for systems such as agar (11), lipid bilayers (12), rat muscle (13), calf lens homogenate (14), heat denatured egg albumin (15), and cross-linked bovine serum albumin (16). However, in all the above systems only one off-resonance irradiation power was used and, as was eventually realized, this is not sufficient for uniquely determining the model parameters or drawing any conclusions about the validity of the model (17).…”

Section: Introductionmentioning

confidence: 99%

A Model for Magnetization Transfer in Tissues

Morrison

1995

Magnetic Resonance in Med

269

365

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Magnetization transfer in several tissues is measured and successfully modeled using a two-pool model of exchange. The line shape for the semi-solid pool is characterized by a superLorentzian and the liquid pool by a Lorentzian. The tissues investigated were white and gray matter, optic nerve, muscle, and liver. All tissues the authors studied are characterized by the same model but differ in the parameter values of the model. Blood and cerebral spinal fluid (CSF) were also investigated. The two-pool model with a Lorentzian line shape for both the semi-solid and liquid pools modeled the magnetization transfer in blood. In CSF, as expected, there is no measurable exchange of magnetization. The T2B associated with the semi-solid pool was short (approximately 10 microseconds) for all tissues indicating a fairly rigid semi-solid pool. In addition characterization of the line shape as superLorentzian indicates molecules such as integral membrane proteins or lipids in membranes are likely molecules participating in the exchange. Conversely, in blood large globular proteins are indicated due to the Lorentzian nature of the semi-solid pool and a T2B approximately 300 microseconds.

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“…The situation in tissue becomes complex because considerable distribution of water spin lifetimes pre vails, and consequently, relaxation dispersion is inevitably broadened. Additional factors influencing T I I' values include (I) saturation transfer effects close-to-resonance resulting from saturation of spins by the locking pulse(Caines and Schleich, 1991), and (2) contribution of broadened macromolecular lines as the spin-lock field approaches internal magnetic fields of immobile proteins(Brown and Koenig, 1992).Consequently, our reported figures for Tip have inherent contributions from several processes. Physical modeling of these factors exceeds the scope of this work; consequently, we have analyzed dis persion of Tip (ms) as a function of spin-lock field (B I' G)…”

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confidence: 99%

Early Detection of Irreversible Cerebral Ischemia in the Rat Using Dispersion of the Magnetic Resonance Imaging Relaxation Time, T_1ρ

Gröhn

Kettunen

Mäkelä

et al. 2000

J Cereb Blood Flow Metab

129

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The impact of brain imaging on the assessment of tissue status is likely to increase with the advent of treatment methods for acute cerebral ischemia. Multimodal magnetic resonance imaging (MRI) demonstrates potential for selecting stroke therapy patients by identifying the presence of acute ischemia, delineating the perfusion defect, and excluding hemorrhage. Yet, the identification of tissue subject to reversible or irreversible ischemia has proven to be difficult. Here, the authors show that T1 relaxation time in the rotating frame, so-called T1rho, serves as a sensitive MRI indicator of cerebral ischemia in the rat. The T1rho prolongs within minutes after a drop in the CBF of less than 22 mL 100 g(-1) min(-1). Dependence of T1rho on spin-lock amplitude, termed as T1rho dispersion, increases by approximately 20% on middle cerebral artery (MCA) occlusion, comparable with the magnitude of diffusion reduction. The T1rho dispersion change dynamically increases to be 38% +/- 10% by the first 60 minutes of ischemia in the brain region destined to develop infarction. Following reperfusion after 45 minutes of MCA occlusion, the tissue with elevated T1rho dispersion (yet normal diffusion) develops severe histologically verified neuronal damage; thus, the former parameter unveils an irreversible condition earlier than currently available MRI methods. The T1rho dispersion as a novel MRI index of cerebral ischemia may be useful in determination of the therapeutic window for acute ischemic stroke.

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Incorporation of saturation transfer into the formalism for rotating-frame spin-lattice NMR relaxation in the presence of an off resonance-irradiation field

Cited by 12 publications

References 15 publications

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

A Model for Magnetization Transfer in Tissues

Early Detection of Irreversible Cerebral Ischemia in the Rat Using Dispersion of the Magnetic Resonance Imaging Relaxation Time, T_1ρ

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Incorporation of saturation transfer into the formalism for rotating-frame spin-lattice NMR relaxation in the presence of an off resonance-irradiation field

Cited by 12 publications

References 15 publications

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

Magnetization transfer affects the proton creatine/phosphocreatine signal intensity: In vivo demonstration in the rat brain

A Model for Magnetization Transfer in Tissues

Early Detection of Irreversible Cerebral Ischemia in the Rat Using Dispersion of the Magnetic Resonance Imaging Relaxation Time, T1ρ

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Product

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Early Detection of Irreversible Cerebral Ischemia in the Rat Using Dispersion of the Magnetic Resonance Imaging Relaxation Time, T_1ρ