Excitation frequency dependence of temperature resolution in magnetic nanoparticle temperature imaging with a scanning magnetic particle spectrometer

This paper investigates the dependence of temperature resolution in magnetic nanoparticle (MNP) temperature imaging on the frequency of an applied ac magnetic field with a custom-built scanning magnetic particle spectrometer (SMPS). The fundamental f₀ and 3f₀ harmonics are measured with the SMPS while the amplitude ratio of the 3f₀ to f₀ harmonics is used to determine the spatial distribution of temperatures. Experiments on a three-line phantom filled with a MNP sample are performed in different-frequency ac magnetic fields with a constant strength of 8 mT. The standard deviation of measured temperatures is used to characterize the temperature resolution. Experimental results show that the temperature resolution improves from 0.9 K to 0.2 K with increasing the excitation frequency from 600 Hz to 5 kHz, which is mainly caused by a higher signal-to-noise ratio due to Faraday's law and by a higher temperature sensitivity of the 3f₀ to f₀ harmonic ratio.