Effective Néel relaxation time constant and intrinsic dipolar magnetism in a multicore magnetic nanoparticle system

2021 ◽  
Vol 130 (6) ◽  
pp. 064302
Author(s):  
Suko Bagus Trisnanto ◽  
Yasushi Takemura
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Magnetic Nanoparticle ◽  
Relaxation Time Constant ◽  
Nanoparticle System ◽  
Néel Relaxation

Regarding the Néel relaxation time constant in magnetorelaxometry

2014 ◽  
Vol 116 (16) ◽  
pp. 163914 ◽  
Author(s):  
J. Leliaert ◽  
A. Coene ◽  
G. Crevecoeur ◽  
A. Vansteenkiste ◽  
D. Eberbeck ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Relaxation Time Constant ◽  
Néel Relaxation

scholarly journals Calculation of Left Ventricular Relaxation Time Constant-Tau in Patients With Aortic Regurgitation by Continuous-Wave Doppler

2008 ◽  
Vol 2 (1) ◽  
pp. 28-30 ◽  
Author(s):  
Bai Xufang
Keyword(s):  
Relaxation Time ◽  
Aortic Regurgitation ◽  
Time Constant ◽  
Continuous Wave ◽  
Left Ventricular ◽  
Simple Method ◽  
Relaxation Time Constant ◽  
Left Ventricular Relaxation ◽  
Ventricular Relaxation ◽  
Continuous Wave Doppler

Left ventricular relaxation time constant, Tau, is the best index to evaluate left ventricular diastolic function. The measurement is only available traditionally in catheter lab. In Echo lab, several methods of non-invasive measurement of Tau have been tried since 1992, however almost all the methods are still utilizing the same formula to calculate Tau as in catheter lab, which makes them inconvenient, time-consuming and sometimes not very accurate. A simple method to calculate Tau in patients with mitral regurgitation has been developed just based on Weiss’ formula and simplified Bernoulli’s equation. Similarly, formulas are developed here by pure mathematical derivative to calculate Tau by continuous-wave Doppler in patients with aortic regurgitation.

scholarly journals Calculation of Left Ventricular Relaxation Time Constant-Tau in Humans by Continuous-Wave Doppler

2008 ◽  
Vol 2 (1) ◽  
pp. 9-11 ◽  
Author(s):  
Xufang Bai
Keyword(s):  
Relaxation Time ◽  
Time Constant ◽  
Continuous Wave ◽  
Left Ventricular Diastolic Function ◽  
Left Ventricular ◽  
Simple Method ◽  
Relaxation Time Constant ◽  
Left Ventricular Relaxation ◽  
Ventricular Relaxation ◽  
Continuous Wave Doppler

Left ventricular relaxation time constant, Tau, is the best index to evaluate left ventricular diastolic function, but the measurement is only available traditionally in catheter lab. In Echo lab, several methods of non-invasive measurement of Tau have been tried since 1992, however almost all the methods are still utilizing the same formula to calculate Tau as in catheter lab, which makes them inconvenient, time-consuming and sometimes not very accurate. Based on Weiss’ formula and simplified Bernoulli’s equation, a simple method is developed by pure mathematical derivative to calculate Tau by continuous-wave Doppler in patients with mitral regurgitation.

scholarly journals An adapted Coffey model for studying susceptibility losses in interacting magnetic nanoparticles

2015 ◽  
Vol 6 ◽  
pp. 2173-2182 ◽  
Author(s):  
Mihaela Osaci ◽  
Matteo Cacciola
Keyword(s):  
Relaxation Time ◽  
Magnetic Fields ◽  
Biomedical Applications ◽  
Tumor Therapy ◽  
Linear Response Theory ◽  
Orientation Model ◽  
Specific Loss Power ◽  
Acceptable Range ◽  
Nanoparticle System ◽  
Néel Relaxation

Background: Nanoparticles can be used in biomedical applications, such as contrast agents for magnetic resonance imaging, in tumor therapy or against cardiovascular diseases. Single-domain nanoparticles dissipate heat through susceptibility losses in two modes: Néel relaxation and Brownian relaxation. Results: Since a consistent theory for the Néel relaxation time that is applicable to systems of interacting nanoparticles has not yet been developed, we adapted the Coffey theoretical model for the Néel relaxation time in external magnetic fields in order to consider local dipolar magnetic fields. Then, we obtained the effective relaxation time. The effective relaxation time is further used for obtaining values of specific loss power (SLP) through linear response theory (LRT). A comparative analysis between our model and the discrete orientation model, more often used in literature, and a comparison with experimental data from literature have been carried out, in order to choose the optimal magnetic parameters of a nanoparticle system. Conclusion: In this way, we can study effects of the nanoparticle concentration on SLP in an acceptable range of frequencies and amplitudes of external magnetic fields for biomedical applications, especially for tumor therapy by magnetic hyperthermia.

Load-sensitive diastolic relaxation in hypertrophied left ventricles

1998 ◽  
Vol 274 (2) ◽  
pp. H609-H615 ◽  
Author(s):  
Wataru Hayashida ◽  
Julian Donckier ◽  
Henri Van Mechelen ◽  
André A. Charlier ◽  
Hubert Pouleur
Keyword(s):  
Relaxation Time ◽  
Angiotensin Ii ◽  
Time Constant ◽  
Left Ventricular ◽  
Control Group ◽  
Relaxation Time Constant ◽  
Significant Prolongation ◽  
Wide Range ◽  
Diastolic Relaxation

We studied effects of enalaprilat and L-158,809, an angiotensin II type-1 receptor antagonist, on left ventricular (LV) diastolic relaxation in 11 normal control dogs and 16 LV hypertrophied (LVH) dogs with perinephritic hypertension. At baseline, LV systolic and end-diastolic pressures and end-systolic elastance were increased in the LVH group (all P < 0.01 vs. the control group). LV relaxation time constant was also prolonged ( P < 0.01), suggesting impaired LV diastolic relaxation in this model of LVH. Before and after the administration of enalaprilat (0.25 mg/kg) and L-158,809 (0.30 mg/kg), LV relaxation was assessed over a wide range of LV loading conditions during vena caval occlusion. LV relaxation time constant was insensitive to load reduction in the control group, which was not affected by enalaprilat or L-158,809. In contrast, LV unloading caused a significant prolongation of the relaxation time constant in the LVH group. This load-sensitive LV relaxation abnormality was significantly improved by enalaprilat or L-158,809. These results support the concept that angiotensin II is involved in the pathogenesis of diastolic dysfunction in pressure-overloaded LVH and also suggest that angiotensin-converting enzyme inhibitors and angiotensin II type-1 receptor antagonists are potentially beneficial in the treatment of the hypertrophied heart.

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