Optimization of the design of a single-sided magnetic resonance magnet array for improved T2 estimation accuracy

Single-sided magnetic resonance (SSMR) technology has a compact structure and great potential for use in mobile and nondestructive detection of large aqueous materials. As the detection depth increases, the magnetic field gradient generated by the magnetic resonance magnet placed on one side weakens, leading to a large distortion of T2, thereby significantly impeding accurate estimation of the pore size distribution within the detection target. In this study, to address this problem, the distortion in the region of interest (ROI) is significantly reduced by optimizing the size and arrangement of the SSMR magnet array. First, to evaluate the T2 distortion within the ROI, we developed a T2 distortion loss function based on alpha and theta, which are key parameters of the spin echo (SE) signal. We then combined the nonlinear constraints with the loss function to form a Lagrangian function, which was solved via the Newton iteration method to obtain the magnet array parameters. The magnet array is called the AT magnet array. The T2 distortion was quantitatively evaluated by calculating the SE signal generated by the AT magnet array in the ROI. Furthermore, we compared the detection results obtained with the AT and the semi-annular (SA) magnet array. The results showed that within the 3 cm x 3 cm target range of a 10 cm depth, the AT magnet array had a smaller T2 distortion of only 1.3%. After the ROI was expanded to 5 cm x 5 cm, the T2 distortion of the SE signal measured by the AT magnet array was 6%, which met the SSMR detection accuracy requirements in this range. Therefore, the optimized design of the magnet array based on alpha and theta provides a theoretical basis for obtaining SE signals with low T2 distortion at large depths and over large areas via SSMR.