Design, construction and validation of a magnetic particle imaging (MPI) system for human brain imaging.

Magnetic Particle Imaging (MPI) was introduced in 2005 as a promising, tracer-based medical imaging modality with the potential for high sensitivity and spatial resolution. Since then, numerous preclinical devices have been built but only a few human-scale devices, none of which targeted functional neuroimaging. In this work, we probe the challenges of scaling the technology to meet the needs of human functional neuroimaging with sufficient sensitivity for detecting the hemodynamic changes following brain activation with a spatio-temporal resolution comparable to current functional Magnetic Resonance Imaging (fMRI) approaches. Approach: We built a human brain-scale MPI system using a mechanically-rotated, permanent-magnet-based field-free-line (1.1 T/m) with a water-cooled, 26 kHz drive coil producing a field of up to 7 mT, and receive coil that can fit over a human head. Images are acquired continuously at a temporal resolution of 5 sec/image, controlled by in-house LabView-based acquisition software with online reconstruction. We used a dilution series to quantify the detection limit, a series of parallel-line phantoms to assess the spatial resolution, and a large 'G' shaped phantom to demonstrate the human-scale field-of-view. Main results: The imager has a sensitivity of about 1 μg Fe over an imaging field of view of 181 mm (132 pixels) diameter in a 5 sec image. Depending on the image reconstruction used, the spatial resolution defined by 50% contrast between adjacent lines was 5-7 mm. Significance: This proof-of-concept system demonstrates a pathway for human MPI functional neuroimaging with the potential for an order of magnitude increase of sensitivity compared to the other human hemodynamic imaging methods. It demonstrates the successful transition of the field-free-line based MPI architecture from the rodent to human scale and identifies areas which could benefit from further work.