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Purpose To investigate the heating induced by (pseudo)-continuous arterial spin labeling ((p)CASL) sequences in vivo at 9.4T and to evaluate the benefit of a dedicated labeling coil. Methods Temperature was measured continuously in the brain, neck, and rectum of 9 rats with fiber-optic temperature probes while running pCASL-EPI and CASL-EPI sequences, with labeling B1 amplitudes (B1ave ) of 3, 5, and 7 μT and using a dedicated labeling RF coil or a volume coil. From the temperature time courses, the corresponding specific absorption rate (SAR) was computed. A trade-off between SAR and labeling quality was determined based on measured inversion efficiencies. Results ASL experiments with standard parameters (B1ave = 5 µT, Tacq = 4 min, labeling with volume coil) lead to a brain temperature increase due to RF of 0.72 ± 0.46 K for pCASL and 0.25 ± 0.17 K for CASL. Using a dedicated labeling coil reduced the RF-induced SAR by a factor of 10 in the brain and a factor of 2 in the neck. Besides SAR due to RF, heat from the coil decoupling circuits produced significant temperature increases. When labeling with a dedicated coil, this mechanism was the dominant source of brain heating. At equivalent RF-SAR, CASL provided slightly superior label efficiency to pCASL and is therefore the preferred sequence when an ASL coil is available. Conclusion B1ave = 4-5 µT provided a good compromise between label efficiency and SAR, both for pCASL and CASL. The sensitivity of animals to heating should be taken into account when optimizing preclinical ASL protocols and may require reducing scan duration or lowering B1ave .

International audience; Aim: To determine whether non-steroidal mineralocorticoid receptor (MR) antagonists oppose metabolic syndrome-related end-organ, i.e. cardiac, damage. Materials and methods: In Zucker fa/fa rats, a rat model of metabolic syndrome, we assessed the effects of the non-steroidal MR antagonist finerenone (oral 2 mg/kg/day) on left ventricular (LV) function, haemodynamics and remodelling (using echocardiography, magnetic resonance imaging and biochemical methods). Results: Long-term (90 days) finerenone modified neither systolic blood pressure nor heart rate, but reduced LV end-diastolic pressure and LV end-diastolic pressure-volume relationship, without modifying LV end-systolic pressure and LV end-systolic pressure-volume relationship. Simultaneously , long-term finerenone reduced both LV systolic and diastolic diameters, associated with reductions in LV weight and LV collagen density, while proteinuria and renal nGAL expression were reduced. Short-term (7 days) finerenone improved LV haemodynamics and reduced LV systolic diameter, without modifying LV diastolic diameter. Moreover, short-term finerenone increased myocardial tissue perfusion and reduced myocardial reactive oxygen species, while plasma nitrite levels, an indicator of nitric oxide (NO) bio-availability, were increased. Conclusions: In rats with metabolic syndrome, the non-steroidal MR antagonist finerenone opposed metabolic syndrome-related diastolic cardiac dysfunction and nephropathy. This involved acute effects, such as improved myocardial perfusion, reduced oxidative stress/ increased NO bioavailability, as well as long-term effects, such as modifications in the myocar-dial structure. K E Y W O R D S animal pharmacology, cardiovascular disease, diabetes complications, drug development, experimental pharmacology, type 2 diabetes

International audience; Magnetic Resonance Imaging (MRI) appears as a good surrogate to Computed Tomography (CT) scan as it does not involve radiation. In this context, a 3D anatomical and perfusion MR imaging protocol was developed to follow the evolution of bone regeneration and the neo-vascularization in femoral bone defects in rats. For this, three different biomaterials based on Pullulan-Dextran and containing either Fucoidan or HydroxyApatite or both were implanted. In vivo MRI, ex vivo micro-CT and histology were performed 1, 3 and 5 weeks after implantation. The high spatially resolved (156 × 182 × 195 µm) anatomical images showed a high contrast from the defects filled with biomaterials that decreased over time due to bone formation. The 3D Dynamic Contrast Enhanced (DCE) imaging with high temporal resolution (1 image/19 s) enabled to detect a modification in the Area-Under-The-Gadolinium-Curve over the weeks post implantation. The high sensitivity of MRI enabled to distinguish which biomaterial was the least efficient for bone regeneration, which was confirmed by micro-CT images and by a lower vessel density observed by histology. In conclusion, the methodology developed here highlights the efficiency of longitudinal MRI for tissue engineering as a routine small animal exam.

Purpose To develop a fast three-dimensional (3D) k-space encoding method based on spiral projection imaging (SPI) with an interleaved golden-angle approach and to validate this novel sequence on small animal models. Methods A disk-like trajectory, in which each disk contained spirals, was developed. The 3D encoding was performed by tilting the disks with a golden angle. The sharpness was first calculated at different T2* values. Then, the sharpness was measured on phantom using variable undersampling ratios. Finally, the sampling method was validated by whole brain time-of-flight angiography and ultrasmall superparamagnetic iron oxide (USPIO) enhanced free-breathing liver angiography on mouse. Results The in vitro results demonstrated the robustness of the method for short T2* and high undersampling ratios. In vivo experiments showed the ability to properly detect small vessels in the brain with an acquisition time shorter than 1 min. Free-breathing mice liver angiography showed the insensitivity of this protocol toward motions and flow artifacts, and enabled the visualization of liver motion during breathing. Conclusions The method implemented here allowed fast 3D k-space sampling with a high undersampling ratio. Combining the advantages of center-out spirals with the flexibility of the golden angle approach could have major implications for real-time imaging. Magn Reson Med 77:1831-1840, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

International audience; Introduction: The purpose of this paper is to develop an easy method to generate both fat signal and banding artifact free 3D balanced Steady State Free Precession (bSSFP) images at high magnetic field.Methods: In order to suppress fat signal and bSSFP banding artifacts, two or four images were acquired with the excitation frequency of the water-selective binomial radiofrequency pulse set On Resonance or shifted by a maximum of 3/4TR. Mice and human volunteers were imaged at 7T and 3T, respectively to perform whole-body and musculoskeletal imaging. “Sum-Of-Square” reconstruction was performed and combined or not with parallel imaging.Results: The frequency selectivity of 1-2-3-2-1 or 1-3-3-1 binomial pulses was preserved after (3/4TR) frequency shifting. Consequently, whole body small animal 3D imaging was performed at 7T and enabled visualization of small structures within adipose tissue like lymph nodes. In parallel, this method allowed 3D musculoskeletal imaging in humans with high spatial resolution at 3T. The combination with parallel imaging allowed the acquisition of knee images with ~500μm resolution images in less than 2min. In addition, ankles, full head coverage and legs of volunteers were imaged, demonstrating the possible application of the method also for large FOV.Conclusion: In conclusion, this robust method can be applied in small animals and humans at high magnetic fields. The high SNR and tissue contrast obtained in short acquisition times allows to prescribe bSSFP sequence for several preclinical and clinical applications.

Background: Enhanced heart rate observed in metabolic syndrome (MS) contributes to the deterioration of left ventricular (LV) function via impaired LV filling and relaxation, increased myocardial O2 consumption, and reduced coronary perfusion. However, whether heart rate reduction (HRR) opposes LV dysfunction observed in MS is unknown. Methods: We assessed in Zucker fa/fa rats, a rat model of MS, the cardiovascular effects of HRR induced by the If current inhibitor S38844 (3 mg·kg−1·d−1). Results: Delayed short-term (4 days) and long-term (90 days) HRR induced by S38844 reduced LV end-diastolic pressure and LV end-diastolic pressure–volume relation, increased myocardial tissue perfusion, decreased myocardial oxidized glutathione levels, and preserved cardiac output, without modifying LV end-systolic pressure and LV end-systolic pressure–volume relation, although only long-term S38844 opposed LV collagen accumulation. Long-term S38844 improved flow-induced endothelium-dependent dilatation of mesenteric arteries, while metabolic parameters, such as plasma glucose levels, and Hb1c, were never modified. Conclusions: In rats with MS, HRR induced by the If inhibitor S38844 improved LV diastolic function and endothelium-dependent vascular dilatation, independent from modifications in metabolic status. Moreover, this improvement in cardiac function involves not only immediate effects such as improved myocardial perfusion and reduced oxidative stress but also long-term effects such as modifications in the myocardial structure.