Note: article, openaccess

Abstract: Magnetic Particle Imaging is capable to measure the spatial distribution of magnetic nanoparticles with high temporal resolution. As a quantitative tracer based imaging method, the signal is linear in the tracer concentration for any location that contains nanoparticles and zero in the surrounding tissue which does not provide any intrinsic signal. After tracer injection, the concentration over time (positive contrast) can be utilized to calculate dynamic diagnostic parameters like perfusion parameters in vessels and organs, which are an important tool in medical diagnosis. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background. We propose a method, where a bolus of physiological saline solution without any particles (negative contrast) displaces the remaining steady state concentration which in turn contributes to the image contrast. Perfusion parameters are calculated based on the time response of this negative bolus and compared to a positive bolus. Results from phantom experiments show that normalized signals from positive and negative boli are concurrent and deviations of calculated perfusion maps are low. Our method opens up the possibility to increase the total monitoring time of a future patient by utilizing a positive-negative contrast sequence, while minimizing the iron dose per acquired image.