Quantitative Magnetic Resonance Imaging of Cellular Density with TurboSPI

Abstract

Magnetic Resonance Imaging can now detect cells that are labeled with contrast agents such as superparamagnetic iron oxide (SPIO). Quantitative monitoring, which is desirable for evaluating cellular therapies, remains challenging. In this work, an MRI technique called TurboSPI is implemented for quantitative cellular imaging. TurboSPI acquires maps of the relaxation rate R2', which is directly related to SPIO concentration. Quantification of R2' is demonstrated using micron-sized iron oxide particles and SPIO-labeled cells. To explain experimental results that deviated from predicted behavior, an extended analytical description of MRI signal relaxation near SPIO was developed. This model compares well to Monte Carlo simulations and experimental data, and may allow improved quantification. The slow imaging speed of TurboSPI is overcome using a signal processing technique called compressed sensing to reconstruct undersampled data, enabling in vivo animal imaging with TurboSPI. Such images demonstrate detection of iron with improved specificity and good potential for quantification.