Modeling Magnetization Transfer Using a Three-Pool Model and Physically Meaningful Constraints on the Fitting Parameters

Ceckler, Toni L.; Maneval, James E.; Melkowits, Brian

doi:10.1006/jmre.2001.2326

Cited by 25 publications

(28 citation statements)

References 58 publications

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“…It is similar in concept to the three-pool models developed by Tessier (19) for describing multipool MT and Woessner who studied PARACEST agents with multiple labile groups (20). Although some cases necessitate the inclusion of more than one MT pool (19,(21)(22)(23)), we chose here to limit the number of MT pools to one as it is sufficient to describe MT effects in agar (17). The framework of the model used in this article is illustrated in Fig.…”

Section: Theorymentioning

confidence: 99%

Understanding quantitative pulsed CEST in the presence of MT

Desmond

Stanisz

2011

Magnetic Resonance in Med

134

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Phantom experiments in agar and ammonium chloride were performed to evaluate a three-pool model of magnetization transfer and chemical exchange saturation transfer (CEST) in a pulsed saturation transfer experiment. The utility of the pulsed CEST method was demonstrated by varying the pH of the phantoms and observing the effect upon the CEST spectra both with and without the solid agar (the magnetization transfer pool), while fitting the spectra to the Bloch equation model with exchange. Pulsed CEST could be used to robustly quantify parameters related to CEST, including the exchange rate constant describing proton exchange with free water and the concentration of exchanging protons. Furthermore, the exchange rate constant and the CEST pool offset frequency of the ammonium chloride remained unchanged in the presence of a magnetization transfer pool. The logarithm of the fitted exchange rate constant was linearly related to pH: this relationship was maintained in the presence of magnetization transfer. Magn Reson Med 67:979-990,

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Section: Theorymentioning

confidence: 99%

Understanding quantitative pulsed CEST in the presence of MT

Desmond

Stanisz

2011

Magnetic Resonance in Med

134

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“…[15][16][17][18][19][20][21][22] We hypothesize that if the physical basis of empirically useful biexponential decay analyses is two distinct water compartments with widely disparate diffusion coefficients, then it would reasonably follow that the two compartments might have substantially different magnetization transfer ratios. [23][24][25][26] For example, within the context of an intra-vs extracellular water compartmentation model, the intracellular water molecules responsible for the 'slow' diffusion component might reasonably be expected to experience more interactions with macromolecules, intracellular organelles, etc, than those responsible for the 'fast' diffusion component within the extracellular matrix. This in turn would lead to a larger 'bound' water fraction and so an enhanced MTR for the slow vs the fast tissue water diffusion component.…”

Section: Introductionmentioning

confidence: 99%

Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain

et al. 2005

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Magnetization transfer (MT) properties of the fast and slow diffusion components recently observed in the human brain were assessed experimentally. One set of experiments, performed at 1.5 T in healthy volunteers, was designed to determine whether the amplitudes of fast and slow diffusion components, differentiated on the basis of biexponential fits to signal decays over a wide range of b-factors, demonstrated a different or similar magnetization transfer ratio (MTR). Another set of experiments, performed at 3 T in healthy volunteers, was designed to determine whether MTRs differed when measured from high signal-to-noise images acquired with b-factor weightings of 350 vs 3500 s/mm2. The 3 T studies included measurements of MTR as a function of off-resonance frequency for the MT pulse at both low and high b-factors. The primary conclusion drawn from all the studies is that there appears to be no significant difference between the magnetization transfer properties of the fast and slow tissue water diffusion components. The conclusions do not lend support to a direct interpretation of the 'components' of the biexponential diffusion decay in terms of the 'compartments' associated with intra- and extracellular water.

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“…24 into Eq. 12, we obtain: [25] where g͑ d Ϫ ,T 2d ͒ represents the line-shape function (Lorentzian) and is commonly replaced with a gaussian or super-Lorentzian line-shape function to model the MT effect of macromolecule-bound water (30,31). In the current work, Eq.…”

Section: Appendixmentioning

confidence: 99%

“…The underlying mechanism of MT has been described successfully using a two-pool or three-pool model, including a pool of free protons and one or more pools of bound protons (27)(28)(29)(30)(31). To describe the MT effect in tissue, the line shape of the macromolecular component is best described using a super-Lorentzian or gaussian line shape in the Bloch equations rather than a Lorentzian line shape (29)(30)(31).…”

mentioning

confidence: 99%

“…To describe the MT effect in tissue, the line shape of the macromolecular component is best described using a super-Lorentzian or gaussian line shape in the Bloch equations rather than a Lorentzian line shape (29)(30)(31). We have previously presented a four-pool model to describe how the inherent MT effect can affect the in vivo off-resonance detection sensitivity of PARACEST agents (23,32).…”

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confidence: 99%

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Optimized MRI contrast for on‐resonance proton exchange processes of PARACEST agents in biological systems

Suchý

Jones

et al. 2009

Magnetic Resonance in Med

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Image contrast associated with paramagnetic chemical exchange saturation transfer agents can be generated by off-resonance irradiation of agent-bound water or amide protons or on-resonance irradiation of bulk water. Previously, a four-pool model was developed to describe an in vivo system. The model incorporated the magnetization transfer effect from macromolecules when using off-resonance irradiation. In the current study, this four-pool model is modified to describe the in vivo system when using on-resonance irradiation. The influences of pulse power, pulse duration, the chemical shift of bound water, the proton exchange rate between bulk water and bound water, and agent concentration on the on-resonance paramagnetic agent chemical exchange effects were simulated using a WALTZ-16 pulse train in the absence and presence of the macromolecule pool. The results demonstrated that while contrast increases with pulse duration in aqueous solution, there is an optimal pulse duration that maximizes on-resonance paramagnetic agent chemical exchange effects contrast in vivo. Diamagnetic and paramagnetic chemical exchange saturation transfer (PARACEST) (1-12) agents have many possible medical and biologic applications, including the measurement of tissue pH based on the pH dependence of the exchange rate of amide protons with bulk water protons (13-15), the measurement of tissue temperature using the linear dependence of the bound water chemical shift on temperature (16,17), enzymatic activity (18), and metabolite levels (19-21). The CEST detection sensitivity (or CEST effect) is defined as the change in the bulk water signal intensity of the agent solution following irradiation of the exchangeable protons. The PARACEST effect and the chemical shift of bound protons can be modified using different metals in the lanthanide series or ligands (22). Currently, the most efficient PARACEST agents are europium (Eu 3ϩ ) based, with a bound water chemical shift around 45 parts per million (ppm) and visible CEST contrast from millimolar concentrations.Despite the large chemical shift of the bound water and amide protons associated with PARACEST agents, the relatively high saturation power needed for in vivo PARAC-EST imaging results in the simultaneous observation of inherent magnetization transfer (MT) from macromolecule-bound protons (17,23). Though dysprosium-, thulium (Tm 3ϩ )-, and ytterbium-based PARACEST agents have bound water chemical shifts beyond the MT effect range, the fast proton exchange between the bound water of these compounds and the bulk water results in an undetectable CEST signal within specific absorption rate power limits. However, the irradiation of bulk water (on-resonance) in solutions with fast proton exchange between bound water and bulk water may also produce contrast due to chemical exchange (24).The detected effect of a PARACEST agent based on the radiofrequency (RF) excitation of bulk water was previously described as the on-resonance paramagnetic agent chemical exchange effect (OPARACHEE) to differe...

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Modeling Magnetization Transfer Using a Three-Pool Model and Physically Meaningful Constraints on the Fitting Parameters

Cited by 25 publications

References 58 publications

Understanding quantitative pulsed CEST in the presence of MT

Understanding quantitative pulsed CEST in the presence of MT

Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain

Optimized MRI contrast for on‐resonance proton exchange processes of PARACEST agents in biological systems

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