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.