Saline bolus for negative contrast perfusion imaging in magnetic particle imaging

Abstract

Objective. Magnetic particle imaging (MPI) is capable of high temporal resolution measurements of the spatial distribution of magnetic nanoparticles and therefore well suited for perfusion imaging, which is an important tool in medical diagnosis. Perfusion imaging in MPI usually requires a fresh bolus of tracer material to capture the key signal dynamics. Here, we propose a method to decouple the imaging sequence from the injection of additional tracer material, without further increasing the administered iron dose in the body with each image. Approach. A bolus of physiological saline solution without any particles (negative contrast) diminishes the steady-state concentration of a long-circulating tracer during passage. This depression in the measured concentration contributes to the required contrast dynamics. The presence of a long-circulating tracer is therefore a prerequisite to obtain the negative contrast. 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. Every acquired perfusion image thus requires a new bolus of tracer with a sufficiently large iron dose to be visible above the background. Main results. Perfusion parameters are calculated based on the time response of the proposed 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. Significance. 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.

System characterization of a human-sized 3D real-time magnetic particle imaging scanner for cerebral applications

“…A specifically tailored MPI tracer, which could be clinically approved in the future, would increase the measurement signal leading to a lower iron dose per bolus. A complementary approach could make use of negative boli to increase the total number of administrable boli 56 .…”

“…The definitions and the post-processing script that handles the data are based on the work by ref. 56 , which provides more details.…”

Solving the MPI reconstruction problem with automatically tuned regularization parameters

“…Thus, a high concentrated tracer circulating constantly through the body for a longer time period is not suitable. New concepts like negative contrast perfusion try to tackle this problem (Mohn et al 2023). This underlines the importance of getting good reconstruction results on preferably low iron concentrations and thus the relevance of finding a good amount of regularization at each stage of a bolus.…”