Magnetic resonance imaging is an important technique for identifying different types of tissues in a body or spatial information about composite materials. Because temperature is a fundamental parameter reflecting the biological status of the body and individual tissues, it would be helpful to have temperature maps superimposed on spatial maps. Here we show that small ferromagnetic particles with a strong temperature-dependent magnetization, can be used to produce temperature-dependent images in magnetic resonance imaging with an accuracy of about 1 °C. This technique, when further developed, could be used to identify inflammation or tumours, or to obtain spatial maps of temperature in various medical interventional procedures such as hyperthermia and thermal ablation. This method could also be used to determine temperature profiles inside nonmetallic composite materials.

We investigate the use of ${\mathrm{Cu}}_{1-x}{\mathrm{Zn}}_x{\mathrm{Fe}}_2{\mathrm{O}}_4$ ferrites ($0.60<x<0.76$) as potential sensors for magnetic-resonance-imaging thermometry. Samples are prepared by a standard ceramic technique. Their structural and magnetic properties are determined using x-ray diffraction, scanning electron microscopy, superconducting quantum-interference device magnetometry, and Mössbauer and 3-T nuclear-magnetic-resonance spectroscopies. We use the mass magnetization of powdered ferrites and transverse relaxivity $r_2^{*}$ of water protons in Ringer’s-solution-based agar gels with embedded micron-sized particles to determine the best composition for magnetic-resonance-imaging (MRI) temperature sensors in the (280–323)-K range. A preclinical 3-T MRI scanner is employed to acquire $T_2^{*}$ weighted temperature-dependent images. The brightness of the MRI images is cross-correlated with the temperature of the phantoms, which allows for a temperature determination with approximately $1°\mathrm{C}$ accuracy. We determine that the composition of $0.65<x<0.70$ is the most suitable for MRI thermometry near human body temperature.

We investigate the use of Cu_0.35Zn_0.65Fe₂O₄ particles as temperature-dependent sensors in magnetic resonance imaging (MRI). This material has a Curie temperature near 290 K, but in the large magnetic fields found in MRI scanners, there is a significant temperature-dependent magnetic moment near body temperature; 310 K. When the ferrite particles are doped into an agar gel, the temperature-dependent magnetic moment leads to a temperature-dependent broadening of the NMR linewidth for water protons and to a temperature-dependent image intensity for MRI, allowing one to make temperature maps within objects. The temperature resolution is about 1.3 K.

Superparamagnetic ferrite nanoparticles coated with a polymer layer are widely used for biomedical applications. The objective of this work is to design nanoparticles as a magnetic resonance imaging (MRI) temperature-sensitive contrast agent. Copper-zinc ferrite nanoparticles coated with a poly(ethylene glycol) (PEG) layer are synthesized using a one-step thermal decomposition method in a polymer matrix. The resulting nanoparticles are stable in water and biocompatible. Using Mössbauer spectroscopy and magnetometry, it was determined that the grown nanoparticles exhibit superparamagnetic properties. Embedding these particles into an agarose gel resulted in significant modification of water proton relaxation times T ₁, T ₂, and T ₂* determined by nuclear magnetic resonance measurements. The results of the spin-echo T ₂-weighted MR images of an aqueous phantom with embedded Cu_0.08Zn_0.54Fe_2.38O₄ nanoparticles in the presence of a strong temperature gradient show a strong correlation between the temperature and the image intensity. The presented results support the hypothesis that CuZn ferrite nanoparticles can be used as a contrast agent for MRI thermometry.

The aim of this project is to fabricate hydrogen-rich silicone doped with magnetic nanoparticles for use as a temperature change indicator in magnetic resonance imaging-guided (MRIg) thermal ablations. To avoid clustering, the particles of mixed MnZn ferrite were synthesized directly in a medical-grade silicone polymer solution. The particles were characterized by transmission electron microscopy, powder X-ray diffraction, soft X-ray absorption spectroscopy, vibrating sample magnetometry, temperature-dependent nuclear magnetic resonance relaxometry (20 °C to 60 °C, at 3.0 T), and magnetic resonance imaging (at 3.0 T). Synthesized nanoparticles were the size of 4.4 nm ± 2.1 nm and exhibited superparamagnetic behavior. Bulk silicone material showed a good shape stability within the study’s temperature range. Embedded nanoparticles did not influence spin–lattice relaxation, but they shorten the longer component of spin–spin nuclear relaxation times of silicone’s protons. However, these protons exhibited an extremely high r₂^* relaxivity (above 1200 L s⁻¹ mmol⁻¹) due to the presence of particles, with a moderate decrease in the magnetization with temperature. With an increased temperature decrease of r₂^*, this ferro–silicone can be potentially used as a temperature indicator in high-temperature MRIg ablations (40 °C to 60 °C).