Evaluating selection criteria for optimized excitation coils in magnetorelaxometry imaging.

OBJECTIVE Magnetorelaxometry imaging is an experimental imaging technique applicable for noninvasive, qualitative and quantitative imaging of magnetic nanoparticles. Accurate reconstructions of nanoparticle distributions are crucial for several novel treatment methods employing magnetic nanoparticles such as magnetic drug targeting or magnetic hyperthermia therapy. Hence, it is desirable to design magnetorelaxometry imaging setups such that the reconstruction accuracy is maximized for a given set of design parameters. Several attempts exist in literature that focus on the improvement of magnetorelaxometry imaging and other related linear inverse problems with respect to various figures of merit. However, to date it remains unclear, which approach leads to the largest benefit for the reconstruction accuracy. Thus, the aim of this study is to compare the different figures of merit, thereby determining the most reliable and effective optimization approach for magnetorelaxometry setups. APPROACH In the present simulation study, we translate these figures of merit to various cost functions, allowing us to optimize the electromagnetic coil positions and radii of two distinct magnetorelaxometry imaging setups with an adapted tabu search algorithm. Multiple artificial magnetic nanoparticle phantoms are reconstructed employing the optimized setups and the resulting imaging qualities are subsequently compared. MAIN RESULTS The extensive amount of generated synthetic data unprecedented in previous magnetorelaxometry imaging studies identifies the condition number as the most reliable indicator for good imaging results. This is the case for both the qualitative as well as the quantitative reconstruction accuracies. SIGNIFICANCE The results of this study show that optimized coil configurations increase the reconstruction quality compared to the state-of-the-art. The insights obtained here can also be extended to other design parameters of magnetorelaxometry imaging setups, thus enabling more reliable reconstructions of magnetic nanoparticle ensembles which will ultimately render the aforementioned treatment methods safer and more efficient.