[Show abstract][Hide abstract] ABSTRACT: Both magnetic relaxometry and magnetic resonance imaging (MRI) can be used to detect and locate targeted magnetic nanoparticles, noninvasively and without ionizing radiation. Magnetic relaxometry offers advantages in terms of its specificity (only nanoparticles are detected) and the linear dependence of the relaxometry signal on the number of nanoparticles present. In this study, detection of single-core iron oxide nanoparticles by superconducting quantum interference device (SQUID)-detected magnetic relaxometry and standard 4.7 T MRI are compared. The nanoparticles were conjugated to a Her2 monoclonal antibody and targeted to Her2-expressing MCF7/Her2-18 (breast cancer cells); binding of the nanoparticles to the cells was assessed by magnetic relaxometry and iron assay. The same nanoparticle-labeled cells, serially diluted, were used to assess the detection limits and MR relaxivities. The detection limit of magnetic relaxometry was 125 000 nanoparticle-labeled cells at 3 cm from the SQUID sensors. T(2)-weighted MRI yielded a detection limit of 15 600 cells in a 150 µl volume, with r(1) = 1.1 mm(-1) s(-1) and r(2) = 166 mm(-1) s(-1). Her2-targeted nanoparticles were directly injected into xenograft MCF7/Her2-18 tumors in nude mice, and magnetic relaxometry imaging and 4.7 T MRI were performed, enabling direct comparison of the two techniques. Co-registration of relaxometry images and MRI of mice resulted in good agreement. A method for obtaining accurate quantification of microgram quantities of iron in the tumors and liver by relaxometry was also demonstrated. These results demonstrate the potential of SQUID-detected magnetic relaxometry imaging for the specific detection of breast cancer and the monitoring of magnetic nanoparticle-based therapies.
[Show abstract][Hide abstract] ABSTRACT: Nuclear Magnetic Resonance Images (MRIs) of the velocity of water droplets and velocity of the suspending gas, hexafluoroethane, are presented for a vertical and horizontal mist pipe flow. In the vertical flow, the upward velocity of the droplets is clearly slower than the upward velocity of the gas. The average droplet size calculated from the average falling velocity in the upward flow is larger than the average droplet size of mist drawn from the top of the pipe measured with a multi-stage aerosol impactor. Vertical flow concentrates larger particles because they have a longer transit time through the pipe. In the horizontal flow there is a gravity-driven circulation with high-velocity mist in the lower portion of the pipe and low-velocity gas in the upper portion. MRI has the advantages that it can image both phases and that it is unperturbed by optical opacity. A drawback is that the droplet phase of mist is difficult to image because of low average spin density and because the signal from water coalesced on the pipe walls is high. To our knowledge these are the first NMR images of mist.
Journal of Magnetic Resonance 02/2012; 216:88-93. · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report progress toward the development of a targeted contrast agent for specific MRI detection of human prostate cancer. Here we investigate antibodies against prostate specific membrane antigen (PSMA) conjugated to two different types (Dynabeads and MACS) of commercial superparamagnetic iron oxide nanoparticles (SPIONs). Biotinylated anti-PSMA monoclonal antibodies (3C6 or J591) were conjugated to the streptavidin-labeled SPIONs and used in an MRI study of two of the cell lines: LNCaP cells (PSMA-positive) and DU-145 cells (control). After labeling with anti-PSMA-conjugated SPIONs, the cells, suspended in agarose gel, were imaged using several different MRI methods. For the LNCaP cells, the presence of the Dynabead-conjugated antibodies resulted in significant dark contrast in spin-echo (T2-weighted) and gradient-echo (T2*-weighted) images, as expected. The presence of the MACS-conjugated antibodies resulted in strong bright contrast in T1-weighted images, which is surprising, as bright contrast is typically not observed from SPION contrast agents. In the case of the DU-145 cells, comparitively weak contrast was observed using either agent due to the lack of specific binding. The observed contrast is explained based on the measured relaxivities (r1 and r2) of the SPIONs. Images of xenograft tumor-bearing mice, injected with MACS-conjugated antibodies, also demonstrate that bright contrast can be achieved in vivo for relevant intra-tumoral SPION concentrations.
64th American Chemical Society Southwest Regional Meeting; 11/2009
[Show abstract][Hide abstract] ABSTRACT: We describe a direct simulation method that effectively determines the appropriate hindered settling behavior of polydisperse particle suspensions. Our method allows adequate representation of the hydrodynamic interactions as well as system specific colloidal interactions. Simulation results are in good agreement with experimental data obtained by MRI imaging. Our results demonstrate the importance of hydrodynamic diffusion and Brownian diffusion in the hindered settling suspensions.