Sub-pT oscillatory magnetometric system using magnetoresistive sensor array for a low-field magnetic particle imaging

Implementing low ac excitation fields toward clinical magnetic particle imaging (MPI) system is critical to avoid magnetostimulation effects. However, low-field MPI scenario demands high sensitivity to probe the change in monotone magnetization response of magnetic nanoparticles. Here, we use an array of ultrasensitive MR sensors to detect sub-pT magnetic signal and obtain its spatial distribution. While each sensor is operated at 5 V, signal processing circuit rises its sensitivity to 20 mV pT(-1) at 10 kHz with 0.25 pT noise level. In evaluating sensor performance, we initially measured a 10-kHz magnetic field from a 40-turns coil with 1 mm in diameter. MR sensor recognizes magnetic signal of mini coil to be linear with the coil input current. We then recorded the signals simultaneously from a 6 x 6 sensor channels to map the fields at 0.2 kHz. While placing mini coil 50 mm apart from the array, we obtained high-contrast field image showing coil position and its change in field polarity. For practical nanoparticle detection, we later used a 3 x 3 array configuration for the 10 kHz oscillatory magnetometry while compensating the MR sensor magnetically from the ac excitation field. Despite a 20-pT noise floor associated with the field compensation circuit, we were able to map stray fields of a 37-mg(Fe) iron oxide nanoparticle sample distanced 100 mm from the array, under 12.4 mu T/mu(0) field amplitude. This result highlights usability of MR sensor array for low-field MPI system.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/9.0000387

Automated summary

Implementing low ac excitation fields in clinical magnetic particle imaging (MPI) system is critical to avoid magnetostimulation effects. In this study, an array of ultrasensitive MR sensors was used to detect sub-pT magnetic signal and obtain its spatial distribution. The sensitivity of each sensor was increased to 20 mV pT(-1) at 10 kHz with a 0.25 pT noise level. The MR sensor array demonstrated usability for low-field MPI system in mapping high-contrast field images and detecting stray fields of iron oxide nanoparticles.