Quantitative 2D Magnetorelaxometry Imaging of Magnetic Nanoparticles using Optically Pumped Magnetometers For biomagnetical applications exploiting physical properties of magnetic nanoparticles (MNP), e.g., magnetic hyperthermia, knowledge about the quantitative spatial MNP distribution is crucial, which can be extracted by magnetorelaxometry (MRX) imaging. In this paper, we present quantification, quantitative 1D reconstruction, and quantitative 2D imaging of MNP by exploiting optically pumped magnetometers for MRX. While highlighting the potential of commercially available optically pumped magnetometers (OPM) for MRXI, we discuss current limitations of the used OPM. We show, that with our OPM setup, MNP can be precisely quantified with iron amounts down to     xe2x89x88 6 g    , which can be improved easily. With a 1Dreconstruction setup, pointlike and complex MNP phantoms can be reconstructed quantitatively with high precision and accuracy. We show that with our developed 2D MRX imaging setup, which measures 12   c      m    by 8   c      m   , pointlike MNP distributions with clinically relevant iron concentrations can be reconstructed precisely and accurately. Our 2D setup has the potential to be easily extended to a tomography styled (and thus sliceselective) 3D scanner, by adding a mechanical axis to the phantom.

WARF: A WeightedSum Approach to Radial MRI Image Reconstruction With a Rotating RF Coil The recently developed singleelement surface rotating radiofrequency coil (RRFC) for magnetic resonance imaging (MRI) is able to acquire signals from around the subject in the manner of a multicoil array, while exhibiting simplified construction and no coil size restrictions. Herein, we present a novel image reconstruction algorithm for data acquired with the RRFC, which we label WARF (a weightedsum approach to radial MRI image reconstruction with a rotating RF coil). The algorithm approaches the reconstruction problem by considering each image pixel to be a weighted sum of all acquired kspace data, which is already the case implicitly in several established methods. The problem is thus posed as one of solving for the appropriate weights directly. The theory underlying WARF is presented, and several measures to improve the computational efficiency of a practical implementation are considered. We note that while still computationally expensive, the calculation of the weights themselves would not necessarily need to be repeated each time the algorithm is applied. MR data are simulated for imaging schemes involving the rotating RF coil with both ideal and variable angular velocities, and for the case where the kspace locations of the radial trajectory are deviated from their intended positions. The WARF reconstruction algorithm is applied to each simulated data set, and compared with reconstructions from existing methods, where it is seen to demonstrate a robustness to velocity variation and the suppression of artefacts arising from a deviated trajectory. Finally, WARF is applied to experimental rotating RF coil data, where it is shown to yield good quality images.