Focused small field of view magnetic particle imaging for the detection and quantification of tumour associated macrophages

Tumour Associated Macrophages (TAMs) play a crucial role in breast cancer progression and have the potential to be used as a biomarker for patient prognosis. Magnetic particle imaging (MPI) is an emerging modality which can detect cells labelled with superparamagnetic iron oxide (SPIO) nanoparticles and can be used for non-invasive TAM assessment. However, MPI TAM detection is limited by its effective dynamic range. This limitation occurs when SPIO nanoparticles injected intravenously accumulate in the liver resulting in a large MPI signal which shadows regions of interest with lower signals (i.e the tumour) preventing their isolation and quantification. In this study we test an advanced reconstruction algorithm which allows us to prescribe a small focused field of view (FOV) on lower signals of interest. We then demonstrate the success of this method with an in vivo tumour model and show enhanced image quality and successful quantification of TAMs in mouse mammary tumours with different metastatic potentials (4T1 and E0771). Utilizing in vivo MPI, we did not see significant differences in the MPI signal for 4T1 tumours compared to E0771. These findings highlight the potential of MPI for in vivo TAM quantification offering a promising avenue for broader applications in cancer research and potentially overcoming constraints of MPI in other in vivo imaging contexts.