We have investigated the efficacy of superparamagnetic iron oxide nanoparticles (SPIONs) as positive T1contrast agents for low-field magnetic resonance imaging (MRI) at 64 millitesla (mT). Iron oxide-based agents, such as the FDA-approved ferumoxytol, were measured using a variety of techniques to evaluate T1contrast at 64 mT. Additionally, we characterized monodispersed carboxylic acid-coated SPIONs with a range of diameters (4.9–15.7 nm) in order to understand size-dependent properties of T1contrast at low-field. MRI contrast properties were measured using 64 mT MRI, magnetometry, and nuclear magnetic resonance dispersion (NMRD). We also measured MRI contrast at 3 T to provide comparison to a standard clinical field strength. SPIONs have the capacity to perform well as T1contrast agents at 64 mT, with measured longitudinal relaxivity (r1) values of up to 67 L mmol−1 s−1, more than an order of magnitude higher than corresponding r1values at 3 T. The particles exhibit size-dependent longitudinal relaxivities and outperform a commercial Gd-based agent (gadobenate dimeglumine) by more than eight-fold at physiological temperatures. Additionally, we characterize the ratio of transverse to longitudinal relaxivity, r2/r1and find that it is ~ 1 for the SPION based agents at 64 mT, indicating a favorable balance of relaxivities for T1-weighted contrast imaging. We also correlate the magnetic and structural properties of the particles with models of nanoparticle relaxivity to understand generation of T1contrast. These experiments show that SPIONs, at low fields being targeted for point-of-care low-field MRI systems, have a unique combination of magnetic and structural properties that produce large T1relaxivities.
Although imaging‐guided drug delivery represents a noninvasive alternative to both surgical resection and systemic methods, it has seen limited clinical use due to the potential toxicity and fast clearance of currently available imaging agents. Herein, we introduce theranostic biocompatible microcapsules as efficient contrast‐enhanced imaging agents that combine magnetic resonance imaging (MRI) with ultrasound‐triggered drug release for real‐time tracking and targeted delivery in vivo. The 3‐μm diameter capsules are assembled via layer‐by‐layer deposition of the natural polyphenol tannic acid and poly(
- NSF-PAR ID:
- 10062917
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Therapeutics
- Volume:
- 1
- Issue:
- 5
- ISSN:
- 2366-3987
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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