Purpose:To develop a center-out echo planar imaging (COEPI) acquisition technique to increase SNR through minimizing the TE. Methods: In single-shot COEPI, the phase-encoding starts from the center (k y = 0) toward both sides of k-space to substantially shorten the TE compared to the conventional single-shot EPI. The phase-encoding gradient waveform is partially overlapped with the frequency-encoding gradient waveform to keep the echo spacing constant during the echo train readout. A reconstruction pipeline was developed to correct for phase and off-resonance errors in COEPI. Gradient-recalled echo (GRE), spin echo (SE), and DWI COEPI were obtained in phantoms and healthy brains at 1.5 tesla (T) and 3.0T. The SNR in COEPI and single-shot partial k y EPI was compared. Results: Acquisition matrix of 128 × 80 (16 overscan lines) was obtained in both COEPI and EPI. At 1.5T/3.0T, a minimum TE of 3 ms/4 ms in GRE-COEPI, 11 ms/12 ms in SE-COEPI, and 40 ms in DWI-COEPI (3.0T only, maximum b value = 2000 s/mm 2 ) was achieved, compared to a minimum TE of 18 ms/16 ms in GRE-EPI, 37 ms/34 ms in SE-EPI, and 66 ms in DWI-EPI, respectively. Image blurring and Nyquist ghost appear in COEPI and were substantially reduced after corrections. At 1.5T/3.0T, a SNR increase of 27.7% ± 6.9%/20.7% ± 7.0% in GRE-COEPI and 37.7% ± 5.7%/28.2% ± 1.3% in SE-COEPI was observed in white matter of human brains, compared to GRE-EPI and SE-EPI, respectively. At 3.0T, a SNR increase of 41.2% ± 4.1% in DWI-COEPI was observed in white matter of 5 subjects at 5 b values (0~2000 s/mm 2 ), compared to DWI-EPI. Conclusion: The feasibility of COEPI and its SNR benefit were demonstrated in this study. K E Y W O R D Scenter-out, diffusion imaging, echo planar imaging, SNR, T 2 effect 788 | CHEN Et al.

Objectives: To assess the feasibility of ferumoxytol-enhanced MRI in pregnancy with a nonhuman primate model. Materials and methods:In this prospective study, eleven pregnant rhesus macaques at day 98 ± 5 of gestation were divided into three groups, untreated control (UC) (n = 3), saline control (SC) (n = 4) and interleukin 1 beta (IL-1β) treated (IT) (n = 4), which were administered with either saline or IL-1β into the amniotic fluid. All animals were imaged at multiple time points before and after ferumoxytol administration (4 mg/kg). Longitudinal R2* and susceptibility of tissues were obtained using region-of-interest analysis and the longitudinal changes were assessed using linear mixed models and Student's t-test. Results:In fetuses, a slope of 0.3s −1 /day (P = 0.008), 0.00ppm/day (P = 0.699) and −0.2s −1 /day (P = 0.023) was observed in liver R2*, liver susceptibility, and lung R2*, respectively. In

Ferumoxytol is a superparamagnetic iron oxide nanoparticle used off-label as an intravascular magnetic resonance imaging (MRI) contrast agent. Additionally, ferumoxytol-uptake by macrophages facilitates detection of inflammatory sites by MRI through ferumoxytol-induced image contrast changes. Therefore, ferumoxytol-enhanced MRI holds great potential for assessing vascular function and inflammatory response, critical to determine placental health in pregnancy. This study sought to assess the fetoplacental unit and selected maternal tissues, pregnancy outcomes, and fetal well-being after ferumoxytol administration. In initial developmental studies, seven pregnant rhesus macaques were imaged with or without ferumoxytol administration. Pregnancies went to term with vaginal delivery and infants showed normal growth rates compared to control animals born the same year that did not undergo MRI. To determine the impact of ferumoxytol on the maternal–fetal interface (MFI), fetal well-being, and pregnancy outcome, four pregnant rhesus macaques at ~100 gestational day underwent MRI before and after ferumoxytol administration. Collection of the fetoplacental unit and selected maternal tissues was performed 2–3 days following ferumoxytol administration. A control group that did not receive ferumoxytol or MRI was used for comparison. Iron levels in fetal and MFI tissues did not differ between groups, and there was no significant difference in tissue histopathology with or without exposure to ferumoxytol, and no effect on placental hormone secretion. Together, these results suggest that the use of ferumoxytol and MRI in pregnant rhesus macaques does not negatively impact the MFI and can be a valuable experimental tool in research with this important animal model.

Purpose To propose a motion‐robust chemical shift‐encoded (CSE) method with high signal‐to‐noise (SNR) for accurate quantification of liver proton density fat fraction (PDFF) and R2∗. Methods A free‐breathing multi‐repetition 2D CSE acquisition with motion‐corrected averaging using nonlocal means (NLM) was proposed. PDFF and R2∗ quantified with 2D CSE‐NLM were compared to two alternative 2D techniques: direct averaging and single acquisition (2D 1ave) in a digital phantom. Further, 2D NLM was compared in patients to 3D techniques (standard breath‐hold, free‐breathing and navigated), and the alternative 2D techniques. A reader study and quantitative analysis (Bland‐Altman, correlation analysis, paired Student’s t‐test) were performed to evaluate the image quality and assess PDFF and R2∗ measurements in regions of interest. Results In simulations, 2D NLM resulted in lower standard deviations (STDs) of PDFF (2.7%) and R2∗ (8.2  s-1) compared to direct averaging (PDFF: 3.1%, R2∗: 13.6  s-1) and 2D 1ave (PDFF: 8.7%, R2∗: 33.2  s-1). In patients, 2D NLM resulted in fewer motion artifacts than 3D free‐breathing and 3D navigated, less signal loss than 2D direct averaging, and higher SNR than 2D 1ave. Quantitatively, the STDs of PDFF and R2∗ of 2D NLM were comparable to those of 2D direct averaging (p>0.05). 2D NLM reduced bias, particularly in R2∗ (−5.73 to −0.36  s-1) that arises in direct averaging (−3.96 to 11.22  s-1) in the presence of motion. Conclusions 2D CSE‐NLM enables accurate mapping of PDFF and R2∗ in the liver during free‐breathing.