Modeling of Thermal Magnetic Fluctuations in Nanoparticle Enhanced Magnetic Resonance Detection

TL;DR

This paper models the magnetization dynamics and thermal magnetic noise of nanoparticles to evaluate and improve the signal-to-noise ratio in MRI detection, suggesting simple system modifications for better imaging performance.

Contribution

It extends previous analyses by numerically evaluating thermal magnetic noise effects on MRI SNR using the Landau-Lifshitz-Gilbert model for anisotropic nanoparticles.

Findings

Nanoparticle shape and configuration influence SNR enhancement.

Narrow band filtering can reduce thermal noise impact.

Simple modifications can improve MRI detection in modest magnetic fields.

Abstract

We present a systematic numerical modeling investigation of magnetization dynamics and thermal magnetic moment fluctuations of single magnetic domain nanoparticles in a configuration applicable to enhancing inductive magnetic resonance detection signal to noise ratio (SNR). Previous proposals for oriented anisotropic single magnetic domain nanoparticle amplification of magnetic flux in MRI coil focused only on the coil pick-up voltage signal enhancement. Here we extend the analysis to the numerical evaluation of the SNR by modeling the inherent thermal magnetic noise introduced into the detection coil by the insertion of such anisotropic nanoparticle-filled coil core. We utilize the Landau-Lifshitz-Gilbert equation under the Stoner-Wohlfarth single magnetic domain (macrospin) assumption to simulate the magnetization dynamics in such nanoparticles due to AC drive field as well as thermal noise. These simulations are used to evaluate the nanoparticle configurations and shape effects on enhancing SNR. Finally, we explore the effect of narrow band filtering of the broadband magnetic moment thermal fluctuation noise on the SNR. Our results provide the impetus for relatively simple modifications to existing MRI systems for achieving enhanced detection SNR in scanners with modest polarizing magnetic fields.