Summary Magnetic Resonance (MR) is an exceptionally powerful and versatile measurement technique. The basic structure of an MR experiment has remained nearly constant for almost 50 years. Here we introduce a novel paradigm, Magnetic Resonance Fingerprinting (MRF) that permits the non-invasive quantification of multiple important properties of a material or tissue simultaneously through a new approach to data acquisition, post-processing and visualization. MRF provides a new mechanism to quantitatively detect and analyze complex changes that can represent physical alterations of a substance or early indicators of disease. MRF can also be used to specifically identify the presence of a target material or tissue, which will increase the sensitivity, specificity, and speed of an MR study, and potentially lead to new diagnostic testing methodologies. When paired with an appropriate pattern recognition algorithm, MRF inherently suppresses measurement errors and thus can improve accuracy compared to previous approaches.

These nanoconstructs are composed of amphiphilic block copolymers with distinct hydrophobic and hydrophilic segments that can self-assemble into supramolecular core±shell structures (usually 10 to 100 nm) in aqueous solution. The hydrophobic micelle core provides an ideal carrier compartment for hydrophobic agents, and the shell consists of a protective corona that stabilizes the nanoparticles. Many hydrophobic drugs such as paclitaxel and doxorubicin have been successfully loaded inside the micelle core to improve drug solubility and pharmacokinetics. [2,3,6,7] In addition to therapeutic applications, polymeric micelles have also received increasing attention in diagnostic imaging applications. When incorporated into micelles, different types of contrast agents have achieved longer blood half-life, improved biocompatibility, and better contrast.[1]In this communication, we report the development of superparamagnetic polymeric micelles as a new class of magnetic resonance imaging (MRI) probes with remarkably high spin± spin (T 2 ) relaxivity and sensitivity. Superparamagnetic iron oxide (SPIO) nanoparticles such as magnetite (FeO´Fe 2 O 3 ) are known to have a strong effect on T 2 . Better detection sensitivity and slower kidney clearance of SPIO nanoparticles make them advantageous over Gd-based small molecular contrast agents. Currently, most T 2 contrast agents are composed of hydrophilic magnetite nanoparticles dispersed in a dextran matrix. [8,9] In contrast, our micelle design consists of a cluster of hydrophobic magnetite particles encapsulated inside the hydrophobic core of polymeric micelle whose surface is stabilized by a poly(ethylene glycol) (PEG) shell. This unique core±shell composite design has allowed us to achieve an ultrasensitive MRI detection limit of 5.2 lg mL ±1 (~5 nM), a sensitivity that promises to expand the ªtool boxº of MR probes for molecular imaging and image-visible drug-delivery applications.We used an amphiphilic diblock copolymer of poly(e-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) for the micelle formation (Fig. 1). This copolymer was synthesized by a ringopening polymerization of e-caprolactone using monomethoxy-terminated PEG (5 kDa; 1 Da .

To generate real-time, nongated, free-breathing cardiac images, the undersampled radial trajectory combined with parallel imaging in the form of radial GRAPPA has shown promise. However, this method starts to fail at high undersampling factors due to the assumptions that must be made for the purposes of calibrating the GRAPPA weight sets. In this manuscript, a novel through-time radial GRAPPA calibration scheme is proposed which greatly improves image quality for the high acceleration factors required for real-time cardiac imaging. This through-time calibration method offers better image quality than standard radial GRAPPA, but it requires many additional calibration frames to be acquired. By combining the through-time calibration method proposed here with the standard through-k-space radial GRAPPA calibration method, images with high acceleration factors can be reconstructed using few calibration frames. Both the throughtime and the hybrid through-time/through-k-space methods are investigated to determine the most advantageous calibration parameters for an R 5 6 in vivo short-axis cardiac image. Once the calibration parameters have been established, they are then used to reconstruct several in vivo real-time, freebreathing cardiac datasets with temporal resolutions better than 45 msec, including one with a temporal resolution of 35 msec and an in-plane resolution of 1.56 mm 2 . Magn Reson Med 65:492-505,