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Background: Phase-contrast (PC) MRI is a feasible and valid noninvasive technique to measure renal artery blood flow, showing potential to support diagnosis and monitoring of renal diseases. However, the variability in measured renal blood flow values across studies is large, most likely due to differences in PC-MRI acquisition and processing. Standardized acquisition and processing protocols are therefore needed to minimize this variability and maximize the potential of renal PC-MRI as a clinically useful tool., Purpose: To build technical recommendations for the acquisition, processing, and analysis of renal 2D PC-MRI data in human subjects to promote standardization of renal blood flow measurements and facilitate the comparability of results across scanners and in multicenter clinical studies., Study Type: Systematic consensus process using a modified Delphi method., Population: Not applicable., Sequence Field/strength: Renal fast gradient echo-based 2D PC-MRI., Assessment: An international panel of 27 experts from Europe, the USA, Australia, and Japan with 6 (interquartile range 4-10) years of experience in 2D PC-MRI formulated consensus statements on renal 2D PC-MRI in two rounds of surveys. Starting from a recently published systematic review article, literature-based and data-driven statements regarding patient preparation, hardware, acquisition protocol, analysis steps, and data reporting were formulated., Statistical Tests: Consensus was defined as ≥75% unanimity in response, and a clear preference was defined as 60-74% agreement among the experts., Results: Among 60 statements, 57 (95%) achieved consensus after the second-round survey, while the remaining three showed a clear preference. Consensus statements resulted in specific recommendations for subject preparation, 2D renal PC-MRI data acquisition, processing, and reporting., Data Conclusion: These recommendations might promote a widespread adoption of renal PC-MRI, and may help foster the set-up of multicenter studies aimed at defining reference values and building larger and more definitive evidence, and will facilitate clinical translation of PC-MRI., Level of Evidence: 1 TECHNICAL EFFICACY STAGE: 1., (© 2020 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC. on behalf of International Society for Magnetic Resonance in Medicine.)

Background: Lung T 1 is a potential translational biomarker of lung disease. The precision and repeatability of variable flip angle (VFA) T 1 mapping using modern 3D ultrashort echo time (UTE) imaging of the whole lung needs to be established before it can be used to assess response to disease and therapy., Purpose: To evaluate the feasibility of regional lung T 1 quantification with VFA 3D-UTE and to investigate long- and short-term T 1 repeatability in the lungs of naive mice., Study Type: Prospective preclinical animal study., Population: Eight naive mice and phantoms., Field Strength/sequence: 3D free-breathing radial UTE (8 μs) at 4.7T., Assessment: VFA 3D-UTE T 1 calculations were validated against T 1 values measured with inversion recovery (IR) in phantoms. Lung T 1 and proton density (S 0 ) measurements of whole lung and muscle were repeated five times over 1 month in free-breathing naive mice. Two consecutive T 1 measurements were performed during one of the imaging sessions., Statistical Tests: Agreement in T 1 between VFA 3D-UTE and IR in phantoms was assessed using Bland-Altman and Pearson 's correlation analysis. The T 1 repeatability in mice was evaluated using coefficient of variation (CV), repeated-measures analysis of variance (ANOVA), and paired t-test., Results: Good T 1 agreement between the VFA 3D-UTE and IR methods was found in phantoms. T 1 in lung and muscle showed a 5% and 3% CV (1255 ± 63 msec and 1432 ± 42 msec, respectively, mean ± SD) with no changes in T 1 or S 0 over a month. Consecutive measurements resulted in an increase of 2% in both lung T 1 and S 0 ., Data Conclusion: VFA 3D-UTE shows promise as a reliable T 1 mapping method that enables full lung coverage, high signal-to-noise ratio (∼25), and spatial resolution (300 μm) in freely breathing animals. The precision of the VFA 3D-UTE method will enable better design and powering of studies., Level of Evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018., (© 2018 International Society for Magnetic Resonance in Medicine.)

Purpose: To assess the feasibility of multiple-bolus dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in the pancreas; to optimize the analysis; and to investigate application of the method to a glucose challenge in type 2 diabetes., Materials and Methods: A 4-bolus DCE-MRI protocol was performed on five patients with type 2 diabetes and 11 healthy volunteers during free-breathing. Motion during the dynamic time series was corrected for using a model-driven nonlinear registration. A glucose challenge was administered intravenously between the first and second DCE-MRI acquisition in all patients and in seven of the healthy controls., Results: Image registration improved the reproducibility of the DCE-MRI model parameters across the repeated bolus-acquisitions in the healthy controls with no glucose challenge (eg, coefficient of variation for K(trans) improved from 38% to 28%). Native tissue T(1) was significantly lower in patients (374 +/- 68 msec) compared with volunteers (519 +/- 41 msec) but there was no significant difference in any of the baseline DCE-MRI parameters. No effect of glucose challenge was observed in either the patients or healthy volunteers., Conclusion: Multiple bolus DCE-MRI is feasible in the pancreas and is improved by nonlinear image registration but is not sensitive to the effects of an intravenous glucose challenge.

Purpose: To fully automate intra-abdominal (IAT) and total adipose tissue (TAT) segmentation in mice to replace tedious and subjective manual segmentation., Materials and Methods: A novel transform codes each voxel with the radius of the narrowest passage on the widest possible three-dimensional (3D) path to any voxel in the target object to select appropriate IAT seed points. Then competitive region growing is performed on a distance transform of the fat mask such that competing classes meet at narrow passages effectively segmenting the IAT and subcutaneous adipose compartments. Fully automatic segmentations were conducted on 32 3D mouse images independent to those used for algorithm development., Results: Automatic processing worked on all 32 images and took 28 s on a 3.6 GHz Pentium computer with 2.0 GB RAM. Manual segmentation by an experienced operator typically took 1 h per 3D image. The correlation coefficients between manual and automated segmentation of TAT and IAT were 0.97 and 0.94, respectively., Conclusion: The fully automatic method correlates well with manual segmentation and dramatically speeds up segmentation allowing MRI to be used in the anti-obesity drug discovery pipeline.

Purpose: To evaluate the lipopolysaccharide (LPS) model of chronic obstructive pulmonary disease (COPD) in mouse with (1)H and hyperpolarized (HP) (3)He MR imaging., Materials and Methods: Axial slices of the lung volume were acquired with HP (3)He and (1)H MRI at 4, 24, and 48 h after LPS exposure. A quantitative ventilation index was calculated from two HP (3)He acquisitions. A bronchoalveolar lavage (BAL) for a cell count was performed following magnetic resonance imaging (MRI)., Results: The LPS exposure resulted in a significant increase of cells in BAL, with maximum at 48 h. Lesions on (3)He images were characterized by ventilation defects, whereas lesions on (1)H images were hyperintense and were attributed to edema. The number of lesions was at maximum at 48 h. At this time point, and for both (3)He and (1)H MRI, the volume of the lesions was significantly higher for LPS-exposed mice compared to controls. At 4, 24, and 48 h the ventilation index from the (3)He data was significantly smaller for the LPS-exposed animals compared to controls., Conclusion: The time point 48 h after LPS exposure was advantageous for MRI evaluation. Functional read-out with (3)He MRI seems to be more sensitive than conventional (1)H MRI.

Purpose: To evaluate whether MRI signal and T2* measurements of lung tissue acquired at ultrashort detection times (tds) can detect emphysematous changes in lungs., Materials and Methods: MR signal intensity of in vivo mouse lungs was measured at 4.7 T at tds of 0.2 and 0.4 msec using single-point imaging (SPI). T2* was calculated from the measurements obtained at the two tds. Two groups of 8- and 30-week-old Tight Skin (TS) and aged-matched CB57BL/6 mice were examined. The TS mice spontaneously developed emphysema-like alveolar enlargement. In vivo micro-computed tomography (microCT) scanning and histology were used as reference methods., Results: MR signal and T2* were significantly lower in the lungs of TS mice than in controls. There were no significant differences between the different age groups. MR signal in lung parenchyma correlated linearly (P < 0.0001, r = 0.89) with microCT mass density, and T2* correlated linearly (P < 0.0001, r = -0.91) with the alveoli size (mean linear intercept [MLI])., Conclusion: The MR signal intensity and T2* measured at short tds can be used as imaging biomarkers to characterize parenchyma density and alveolar size, respectively.

Global forebrain ischemia in the Mongolian gerbil is a common animal model for use in stroke research. We produced lesions of graded severity in gerbil brains (after prescreening by MR imaging) by performing 6-minute bilateral carotid artery occlusions while monitoring pericranial temperature with a temporalis muscle thermocouple probe and maintaining the temperature at 32 degrees C, 36 degrees C, or 40 degrees C. Lesion severity was scored 4 days after occlusion from findings on spin-echo images acquired at 7 T and from histologic scores. Statistically significant correlation was observed between the MR imaging score and brain temperature and between the MR imaging score and the area of the CA region of the hippocampus measured by histology. In addition, because prescreening with MR imaging revealed abnormalities in the hippocampus of some of the animals, and these animals were rejected from the study, the statistical significance of the result could be strengthened.