Objectives To determine the relaxation properties of ferumoxytol, an off-label alternative to gadolinium based contrast agents (GBCA), under physiological conditions at 1.5T and 3.0T. Materials and Methods Ferumoxytol was diluted in gradually increasing concentrations (0.26–4.2 mM) in saline, human plasma and human whole blood. MR relaxometry was performed at 37˚C at 1.5T and 3.0T. Longitudinal and transverse relaxation rate constants (R1, R2, R2*) were measured as a function of ferumoxytol concentration and relaxivities (r1, r2, r2*) were calculated. Results A linear dependence of R1, R2 and R2* on ferumoxytol concentration was found in saline and plasma with lower R1 values at 3.0T and similar R2 and R2* values at 1.5T and 3.0T (1.5T: r1saline = 19.9 ± 2.3 s−1mM−1, r1plasma = 19.0 ± 1.7 s−1mM−1; r2saline = 60.8 ± 3.8 s−1mM−1; r2plasma = 64.9 ± 2.3 s−1mM−1; r2*saline = 60.4 ± 1.3 s−1mM−1; r2*plasma = 64.4 ± 0.3 s−1mM−1; 3.0T: r1saline = 10.0 ± 0.3 s−1mM−1, r1plasma = 9.5 ± 0.2 s−1mM−1; r2saline = 62.3 ± 3.7 s−1mM−1; r2plasma = 65.2 ± 1.8 s−1mM−1; r2*saline = 57.0 ± 3.6 s−1mM−1; r2*plasma = 55.7 ± 4.4 s−1mM−1). The dependence of relaxation rates on concentration in blood was nonlinear. Formulas from 2nd order polynomial fittings of the relaxation rates were calculated to characterize the relationship between R1blood and R2 blood with ferumoxytol. Conclusions Ferumoxytol demonstrates strong longitudinal and transverse relaxivities. Awareness of the nonlinear relaxation behavior of ferumoxytol in blood is important for ferumoxytol-enhanced MRI applications and for protocol optimization.

Purpose We propose a new acquisition to minimize the per-excitation encoding duration and improve the imaging capability for short T2* species. Method In the proposed ramped hybrid encoding (RHE) technique, gradients are applied before the RF pulse as in pointwise encoding time reduction with radial acquisition (PETRA) and Zero TE (ZTE) imaging. However, in RHE, gradients are rapidly ramped after RF excitation to the maximum amplitude to minimize encoding duration. To acquire central k-space data not measured during RF deadtime, RHE utilizes a hybrid encoding scheme similar to PETRA. A new gradient calibration method based on single-point imaging was developed to estimate the k-space trajectory and enable robust and high quality reconstruction. Result RHE enables a shorter per-excitation encoding time and provides the highest spatial resolution among ultrashort T2* imaging methods. In phantom and in vivo experiments, RHE exhibited robust imaging with negligible chemical shift or blurriness caused by T2* decay and unwanted slice selection. Conclusion RHE allows the shortest per-excitation encoding time for ultrashort T2* imaging, which alleviates the impact of fast T2* decay occurring during encoding, and enables improved spatial resolution.

Purpose To validate a fully automated adipose segmentation method with magnetic resonance imaging (MRI) fat fraction abdominal imaging. We hypothesized that this method is suitable for segmentation of subcutaneous adipose tissue (SAT) and intra‐abdominal adipose tissue (IAAT) in a wide population range, easy to use, works with a variety of hardware setups, and is highly repeatable. Materials and Methods Analysis was performed comparing precision and analysis time of manual and automated segmentation of single‐slice imaging, and volumetric imaging (78–88 slices). Volumetric and single‐slice data were acquired in a variety of cohorts (body mass index [BMI] 15.6–41.76) including healthy adult volunteers, adolescent volunteers, and subjects with nonalcoholic fatty liver disease and lipodystrophies. A subset of healthy volunteers was analyzed for repeatability in the measurements. Results The fully automated segmentation was found to have excellent agreement with manual segmentation with no substantial bias across all study cohorts. Repeatability tests showed a mean coefficient of variation of 1.2 ± 0.6% for SAT, and 2.7 ± 2.2% for IAAT. Analysis with automated segmentation was rapid, requiring 2 seconds per slice compared with 8 minutes per slice with manual segmentation. Conclusion We demonstrate the ability to accurately and rapidly segment regional adipose tissue using fat fraction maps across a wide population range, with varying hardware setups and acquisition methods. J. Magn. Reson. Imaging 2015;41:233–241. © 2014 Wiley Periodicals, Inc.