Efficiency of paramagnetic relaxation enhancement in off-resonance rotating frame

Zhang, Huiming; Xie, Yang

doi:10.1016/j.jmr.2006.05.005

Cited by 4 publications

(63 citation statements)

References 30 publications

(44 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In consistent with our previous studies [1,2,7], the imaging sequence used in this study contains a long off-resonance pulse in the preparation, followed by a routine spin echo imaging sequence for the spatial encoding. The RF amplitude (ω 1 ) and the frequency offset (Δ) for this long pulse are sufficiently large to overcome the magnetization dephase induced by B 0 inhomogeneities (Δω 0 ).…”

Section: Introductionmentioning

confidence: 65%

“…The MWCO of the membrane of the dialysis tube was 0.1, 2, 10 and 15 kDa respectively. Following the formation of the gels, the dialysis tube was placed into a 10 mm glass tube containing aqueous (Gd-DTPA) 30 -BSA (Mw∼85 kDa) at 1 mM Gd(III), which was synthesized as reported elsewhere [1].…”

Section: In Vitro Phantomsmentioning

confidence: 99%

“…The paramagnetic relaxation enhancement in off-resonance rotating frame can increase the relaxivitiy and detection sensitivity of paramagnetic agents at magnetic fields higher than 3T [1]. The enhanced relaxation rate constant depends on several factors, including the hydration number q, the rotational correlation timeτ R and the diffusion correlation time τ D of T 1 -type agents, and the nano-particles' diameter d of T 2 -type agents [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…The enhanced relaxation rate constant depends on several factors, including the hydration number q, the rotational correlation timeτ R and the diffusion correlation time τ D of T 1 -type agents, and the nano-particles' diameter d of T 2 -type agents [1,2]. These factors are critical to the smart labeling of molecular MR imaging.…”

Section: Introductionmentioning

confidence: 99%

“…This method can be further extended to quantify the alterations of other factors such as q, τ D and d, and to distinguish the small difference between the relaxation rate constants for T 1 /T 2 type agents. Since the paramagnetic relaxation enhancement increases as the square of magnetic field strength [1], high sensitivity is expected for the detection of paramagnetic agents at high magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

Zhang

Xie

2007

Journal of Magnetic Resonance

Self Cite

View full text Add to dashboard Cite

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T 1ρ can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields. However, the in vivo detectable dimension for labeled cell clusters/tissues in T 1ρ -weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/ in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide submillimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment, and intravascular agents (Gd-DTPA) 30 -BSA were administrated into the compartment via bolus injections. Both in vitro and in vivo results demonstrate that the paramagnetic relaxation enhancement is predominant in the T 1ρ -weighted imaging in the presence of water diffusion exchange. The T 1ρ contrast has substantially higher sensitivity than the conventional T 1 contrast in detecting paramagnetic agents, especially at low paramagnetic agent volumetric fractions, low paramagnetic agent concentrations, and low RF amplitudes. Short pulse duration, short pulse recycle delay and efficient paramagnetic relaxation can reduce the influence of water diffusion-exchange on the paramagnetic enhancement. This study paves the way for the design of off-resonance rotating experiments to detect labeled cell clusters/tissue compartments in vivo at a sub-millimeter scale.

show abstract

Section: Introductionmentioning

confidence: 65%

Section: In Vitro Phantomsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

Zhang

Xie

2007

Journal of Magnetic Resonance

Self Cite

View full text Add to dashboard Cite

show abstract

In vitro Gd‐DTPA relaxometry studies in oxygenated venous human blood and aqueous solution at 3 and 7 T

Kalavagunta

Michaeli

Metzger

2014

Contrast Media & Molecular

View full text Add to dashboard Cite

In-vitro T1 and T2* relaxivities (r1 and r2*) of Gd-DTPA (GaD) in oxygenated human venous blood (OVB) and aqueous solution (AS) at 3T and 7T were calculated. GaD concentrations ([GaD]) in OVB and AS were prepared in the range 0–5 mM. All measurements were acquired at 37±2 °C. At both 3T and 7T, a linear relationship was observed between [GaD] and R1 in both AS and OVB. At 7T, r1 in AS decreased by 7.5% (p = 0.045) while there was a negligible change in OVB. With respect to R2*, a linear relationship with [GaD] was only observed in AS, while a more complex relationship was observed in OVB; quadratic below and linear above 2 mM at both field strengths. There was a significant increase of over four-fold in r2* with GaD in OVB at 7T (for [GaD] above 2mM, p ≪0.01) as compared to 3T. Furthermore, in comparison to r1, r2* in AS was less than two-fold higher at both field strengths while in OVB it was ~twenty-fold and ~ninety-fold higher at 3T and 7T, respectively. This observation emphasizes the importance of r2* knowledge at high magnetic fields, ≥3T. The comparison between r1 and r2* presented in this work is crucial in the design and optimization of high field MRI studies making use of paramagnetic contrast agents. This is especially true in multiple compartment systems such as blood where r2* dramatically increases while r1 remains relatively constant with increasing magnetic field strength.

show abstract

Dynamics of paramagnetic agents by off-resonance rotating frame technique

Zhang

Xie

2006

Journal of Magnetic Resonance

Self Cite

View full text Add to dashboard Cite

Off-resonance rotating frame technique offers a novel tool to explore the dynamics of paramagnetic agents at high magnetic fields (B0 > 3T). Based on the effect of paramagnetic relaxation enhancement in the off-resonance rotating frame, a new method is described here for determining the dynamics of paramagnetic ion chelates from the residual z-magnetizations of water protons. In this method, the dynamics of the chelates are identified by the difference magnetization profiles, which are the subtraction of the residual z-magnetization as a function of frequency offset obtained at two sets of RF amplitude omega(1) and pulse duration tau. The choices of omega(1) and tau are guided by a 2-D magnetization map that is created numerically by plotting the residual z-magnetization as a function of effective field angle theta and off-resonance pulse duration tau. From the region of magnetization map that is the most sensitive to the alteration of the paramagnetic relaxation enhancement efficiency R(1rho)/R1, the ratio of the off-resonance rotating frame relaxation rate constant R(1rho) verse the laboratory frame relaxation rate constant R(1), three types of difference magnetization profiles can be generated. The magnetization map and the difference magnetization profiles are correlated with the rotational correlation time tauR of Gd-DTPA through numerical simulations, and further validated by the experimental data for a series of macromolecule conjugated Gd-DTPA in aqueous solutions. Effects of hydration water number q, diffusion coefficient D, magnetic field strength B0 and multiple rotational correlation times are explored with the simulations of the magnetization map. This method not only provides a simple and reliable approach to determine the dynamics of paramagnetic labeling of molecular/cellular events at high magnetic fields, but also a new strategy for spectral editing in NMR/MRI based on the dynamics of paramagnetic labeling in vivo.

show abstract

Efficiency of paramagnetic relaxation enhancement in off-resonance rotating frame

Cited by 4 publications

References 30 publications

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

In vitro Gd‐DTPA relaxometry studies in oxygenated venous human blood and aqueous solution at 3 and 7 T

Dynamics of paramagnetic agents by off-resonance rotating frame technique

Contact Info

Product

Resources

About