We propose a 3-D-printed breast phantom for use in preclinical experimental microwave imaging studies. The phantom is derived from an MRI of a human subject; thus, it is anthropomorphic, and its interior is very similar to an actual distribution of fibroglandular tissues. Adipose tissue in the breast is represented by the solid plastic (printed) regions of the phantom, while fibroglandular tissue is represented by liquid-filled voids in the plastic. The liquid is chosen to provide a biologically relevant dielectric contrast with the printed plastic. Such a phantom enables validation of microwave imaging techniques. We describe the procedure for generating the 3-D-printed breast phantom and present the measured dielectric properties of the 3-D-printed plastic over the frequency range 0.5–3.5 GHz. We also provide an example of a suitable liquid for filling the fibroglandular voids in the plastic.

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 To characterize the effects of concomitant gradients (CGs) on chemical shift encoded (CSE)-based estimation of B0 field map, proton density fat fraction (PDFF), and R2*. Theory A theoretical framework was used to determine the effects of CG-induced phase errors on CSE-MRI data. Methods Simulations, phantom experiments, and in vivo experiments were conducted at 3T to assess the effects of CGs on quantitative CSE-MRI techniques. Correction of phase errors attributable to CGs was also investigated to determine if these effects could be removed. Results Phase errors due to CGs introduce errors in the estimation of B0 field map, PDFF, and R2*. Phantom and in vivo experiments demonstrated that CGs can introduce estimation errors greater than 30 Hz in the B0 field map, 10% in PDFF, and 16 s−1 in R2*, 16 cm off isocenter. However, CG phase correction before parameter estimation was able to reduce estimation errors to less than 10 Hz in the B0 field map, 1% in PDFF, and 2 s−1 in R2*. Conclusion CG effects can impact CSE-MRI, leading to inaccurate estimation of B0 field map, PDFF, and R2*. However, correction for phase errors caused by CGs improve the accuracy of quantitative parameters estimated from CSE-MRI acquisitions.

Purpose: The purpose of this work is to characterize the magnitude and variability of B 0 and B 1 inhomogeneities in the liver in large cohorts of patients at both 1.5 T and 3.0 T. Methods: Volumetric B 0 and B 1 maps were acquired over the liver of patients presenting for routine abdominal MRI. Regions of interest were drawn in the nine Couinaud segments of the liver, and the average value was recorded. Magnitude and variation of measured averages in each segment were reported across all patients. Results: A total of 316 B 0 maps and 314 B 1 maps, acquired at 1.5 T and 3.0 T on a variety of GE Healthcare MRI systems in 630 unique exams, were identified, analyzed, and, in the interest of reproducible research, de-identified and made public. Measured B 0 inhomogeneities ranged (5th-95th percentiles) from −31.7 Hz to 164.0 Hz for 3.0 T (−14.5 Hz to 81.3 Hz at 1.5 T), while measured B 1 inhomogeneities (ratio of actual over prescribed flip angle) ranged from 0.59 to 1.13 for 3.0 T (0.83 to 1.11 at 1.5 T). Conclusion: This study provides robust characterization of B 0 and B 1 inhomogeneities in the liver to guide the development of imaging applications and protocols. Field strength, bore diameter, and sex were determined to be statistically significant effects for both B 0 and B 1 uniformity. Typical clinical liver imaging at 3.

Purpose To develop and validate a T1‐corrected chemical‐shift encoded MRI (CSE‐MRI) method to improve noise performance and reduce bias for quantification of tissue proton density fat‐fraction (PDFF). Methods A variable flip angle (VFA)‐CSE‐MRI method using joint‐fit reconstruction was developed and implemented. In computer simulations and phantom experiments, sources of bias measured using VFA‐CSE‐MRI were investigated. The effect of tissue T1 on bias using low flip angle (LFA)‐CSE‐MRI was also evaluated. The noise performance of VFA‐CSE‐MRI was compared to LFA‐CSE‐MRI for liver fat quantification. Finally, a prospective pilot study in patients undergoing gadoxetic acid‐enhanced MRI of the liver to evaluate the ability of the proposed method to quantify liver PDFF before and after contrast. Results VFA‐CSE‐MRI was accurate and insensitive to transmit B1 inhomogeneities in phantom experiments and computer simulations. With high flip angles, phase errors because of RF spoiling required modification of the CSE signal model. For relaxation parameters commonly observed in liver, the joint‐fit reconstruction improved the noise performance marginally, compared to LFA‐CSE‐MRI, but eliminated T1‐related bias. A total of 25 patients were successfully recruited and analyzed for the pilot study. Strong correlation and good agreement between PDFF measured with VFA‐CSE‐MRI and LFA‐CSE‐MRI (pre‐contrast) was observed before (R2 = 0.97; slope = 0.88, 0.81–0.94 95% confidence interval [CI]; intercept = 1.34, −0.77–1.92 95% CI) and after (R2 = 0.93; slope = 0.88, 0.78–0.98 95% CI; intercept = 1.90, 1.01–2.79 95% CI) contrast. Conclusion Joint‐fit VFA‐CSE‐MRI is feasible for T1‐corrected PDFF quantification in liver, is insensitive to B1 inhomogeneities, and can eliminate T1 bias, but with only marginal SNR advantage for T1 values observed in the liver.