Characterization and Relaxation Properties of a Series of Monodispersed Magnetic Nanoparticles

Magnetic iron oxide nanoparticles are relatively advanced nanomaterials, and are widely used in biology, physics and medicine, especially as contrast agents for magnetic resonance imaging. Characterization of the properties of magnetic nanoparticles plays an important role in the application of magnetic particles. As a contrast agent, the relaxation rate directly affects image enhancement. We characterized a series of monodispersed magnetic nanoparticles using different methods and measured their relaxation rates using a 0.47 T low-field Nuclear Magnetic Resonance instrument. Generally speaking, the properties of magnetic nanoparticles are closely related to their particle sizes; however, neither longitudinal relaxation rate r 1 nor transverse relaxation rate r 2 changes monotonously with the particle size d . Therefore, size can affect the magnetism of magnetic nanoparticles, but it is not the only factor. Then, we defined the relaxation rates r i ′ (i = 1 or 2) using the induced magnetization of magnetic nanoparticles, and found that the correlation relationship between r 1 ′ relaxation rate and r 1 relaxation rate is slightly worse, with a correlation coefficient of R 2 = 0.8939, while the correlation relationship between r 2 ′ relaxation rate and r 2 relaxation rate is very obvious, with a correlation coefficient of R 2 = 0.9983. The main reason is that r 2 relaxation rate is related to the magnetic field inhomogeneity, produced by magnetic nanoparticles; however r 1 relaxation rate is mainly a result of the direct interaction of hydrogen nucleus in water molecules and the metal ions in magnetic nanoparticles to shorten the T 1 relaxation time, so it is not directly related to magnetic field inhomogeneity.

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In Vivo Quantification of Cerebral R2*-Response to Graded Hyperoxia at 3 Tesla

Journal of Clinical Imaging Science ◽

10.4103/2156-7514.150439 ◽

2015 ◽

Vol 5 ◽

pp. 1 ◽

Cited By ~ 2

Author(s):

Grigorios Gotzamanis ◽

Roman Kocian ◽

Pinar S. Özbay ◽

Manuel Redle ◽

Spyridon Kollias ◽

...

Keyword(s):

Magnetic Resonance ◽

Relaxation Rate ◽

Tumor Therapy ◽

Cerebrovascular Reactivity ◽

Oxygen Intake ◽

Transverse Relaxation Rate ◽

Dependent Manner ◽

Relaxation Rates ◽

Transverse Relaxation ◽

Arterial Blood

Objectives: This study aims to quantify the response of the transverse relaxation rate of the magnetic resonance (MR) signal of the cerebral tissue in healthy volunteers to the administration of air with step-wise increasing percentage of oxygen. Materials and Methods: The transverse relaxation rate (R2*) of the MR signal was quantified in seven volunteers under respiratory intake of normobaric gas mixtures containing 21, 50, 75, and 100% oxygen, respectively. End-tidal breath composition, arterial blood saturation (SaO2), and heart pulse rate were monitored during the challenge. R2* maps were computed from multi-echo, gradient-echo magnetic resonance imaging (MRI) data, acquired at 3.0T. The average values in the segmented white matter (WM) and gray matter (GM) were tested by the analysis of variance (ANOVA), with Bonferroni post-hoc correction. The GM R2*-reactivity to hyperoxia was modeled using the Hill's equation. Results: Graded hyperoxia resulted in a progressive and significant (P < 0.05) decrease of the R2* in GM. Under normoxia the GM-R2* was 17.2 ± 1.1 s-1. At 75% O2 supply, the R2* had reached a saturation level, with 16.4 ± 0.7 s-1 (P = 0.02), without a significant further decrease for 100% O2. The R2*-response of GM correlated positively with CO2 partial pressure (R = 0.69 ± 0.19) and negatively with SaO2 (R = -0.74 ± 0.17). The WM showed a similar progressive, but non-significant, decrease in the relaxation rates, with an increase in oxygen intake (P = 0.055). The Hill's model predicted a maximum R2* response of the GM, of 3.5%, with half the maximum at 68% oxygen concentration. Conclusions: The GM-R2* responds to hyperoxia in a concentration-dependent manner, suggesting that monitoring and modeling of the R2*-response may provide new oxygenation biomarkers for tumor therapy or assessment of cerebrovascular reactivity in patients.

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A nuclear magnetic resonance study of water in aggrecan solutions

Royal Society Open Science ◽

10.1098/rsos.150705 ◽

2016 ◽

Vol 3 (3) ◽

pp. 150705 ◽

Cited By ~ 8

Author(s):

Richard J. Foster ◽

Robin A. Damion ◽

Thomas G. Baboolal ◽

Stephen W. Smye ◽

Michael E. Ries

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Relaxation Rate ◽

Activation Energies ◽

Proton Nuclear Magnetic Resonance ◽

Water Molecules ◽

Transverse Relaxation Rate ◽

Relaxation Rates ◽

Transverse Relaxation ◽

Nuclear Magnetic

Aggrecan, a highly charged macromolecule found in articular cartilage, was investigated in aqueous salt solutions with proton nuclear magnetic resonance. The longitudinal and transverse relaxation rates were determined at two different field strengths, 9.4 T and 0.5 T, for a range of temperatures and aggrecan concentrations. The diffusion coefficients of the water molecules were also measured as a function of temperature and aggrecan concentration, using a pulsed field gradient technique at 9.4 T. Assuming an Arrhenius relationship, the activation energies for the various relaxation processes and the translational motion of the water molecules were determined from temperature dependencies as a function of aggrecan concentration in the range 0–5.3% w/w. The longitudinal relaxation rate and inverse diffusion coefficient were approximately equally dependent on concentration and only increased by upto 20% from that of the salt solution. The transverse relaxation rate at high field demonstrated greatest concentration dependence, changing by an order of magnitude across the concentration range examined. We attribute this primarily to chemical exchange. Activation energies appeared to be approximately independent of aggrecan concentration, except for that of the low-field transverse relaxation rate, which decreased with concentration.

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