To our knowledge, this is the first time a chemical shift of the ultrashort-T brain component has been measured in vivo. This chemical shift, at around 1.7 ppm, is similar to the primary resonance of most lipids, indicating that much of the ultrashort-T component observed in vivo arises from bound protons in the myelin phospholipid membranes. Magn Reson Med 80:726-735, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetic resonance elastography (MRE) is a non invasive imaging modality, which holds the promise of absolute quantification of the mechanical properties of human tissues in vivo. MRE reconstruction with algebraic inversion of the Helmholtz equation upon the curl of the shear displacement field may theoretically be flawless. However, its performances are challenged by multiple experimental parameters, especially the frequency and the amplitude of the mechanical wave, the voxel size and the signal-to-noise ratio of the MRE acquisition. A point source excitation was simulated and realistic displacement fields were analytically computed to simulate MRE data sets in an isotropic, homogeneous, linearly-elastic, and half-space infinite medium. Acquisition and reconstruction methods were challenged and the joint influence of the aforementioned parameters was studied. For a given signal-to-noise ratio, the conditions on the number of voxels per wavelength were determined for optimizing voxel-wise accuracy and precision in MRE. It was shown that, once data are acquired, the reconstruction quality could even be improved by effective interpolation or decimation so data could eventually fulfill favorable conditions for mechanical characterization of the tissue. Finally, the overall outcome, which is usually computed from the three acquired motion-encoded directions, may further be improved by appropriate averaging strategies that are based on adapted curl of shear displacement field quality-weighting.

We report on local superficial blood flow monitoring in biological tissue from laser Doppler holographic imaging. In time-averaging recording conditions, holography acts as a narrowband bandpass filter, which, combined with a frequency-shifted reference beam, permits frequency-selective imaging in the radiofrequency range. These Doppler images are acquired with an off-axis Mach-Zehnder interferometer. Microvascular hemodynamic components mapping is performed in the cerebral cortex of the mouse and the eye fundus of the rat with near-infrared laser light without any exogenous marker. These measures are made from a basic inverse-method analysis of local first-order optical fluctuation spectra at low radiofrequencies, from 0 Hz to 100 kHz. Local quadratic velocity is derived from Doppler broadenings induced by fluid flows, with elementary diffusing wave spectroscopy formalism in backscattering configuration. We demonstrate quadratic mean velocity assessment in the 0.1-10 mm/s range in vitro and imaging of superficial blood perfusion with a spatial resolution of about 10 micrometers in rodent models of cortical and retinal blood flow.

Spirometry is today the gold standard technique for assessing pulmonary ventilatory function in humans. From the shape of a flow-volume loop measured while the patient is performing forced respiratory cycles, the Forced Vital Capacity (FVC) and the Forced Expiratory Volume in one second (FEV1) can be inferred, and the pulmonologist is able to detect and characterize common respiratory afflictions. This technique is non-invasive, simple, widely available, robust, repeatable and reproducible. Yet, its outcomes rely on the patient’s cooperation and provide only global information over the lung. With 3D Magnetic Resonance (MR) Spirometry, local ventilation can be assessed by MRI anywhere in the lung while the patient is freely breathing. The larger dimensionality of 3D MR Spirometry advantageously allows the extraction of original metrics that characterize the anisotropic and hysteretic regional mechanical behavior of the lung. Here, we demonstrated the potential of this technique on a healthy human volunteer breathing along different respiratory patterns during the MR acquisition. These new results are discussed with lung physiology and recent pulmonary CT data. As respiratory mechanics inherently support lung ventilation, 3D MR Spirometry may open a new way to non-invasively explore lung function while providing improved diagnosis of localized pulmonary diseases.

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Purpose Because of short signal lifetimes and respiratory motion, 3D lung MRI is still challenging today. Zero‐TE (ZTE) pulse sequences offer promising solutions as they overcome the issue of short T2∗. Nevertheless, as they rely on continuous readout gradients, the trajectories they follow in k‐space are not adapted to retrospective gating and inferred motion correction. Theory and methods We propose AZTEK (adaptive ZTE k‐space trajectories), a set of 3D radial trajectories featuring three tuning parameters, to adapt the acquisition to any moving organ while keeping seamless transitions between consecutive spokes. Standard ZTE and AZTEK trajectories were compared for static and moving phantom acquisitions as well as for human thoracic imaging performed on 3 volunteers (1 healthy and 2 patients with lung cancer). Results For the static phantom, we observe comparable image qualities with standard and AZTEK trajectories. For the moving phantom, spatially coherent undersampling artifacts observed on gated images with the standard trajectory are alleviated with AZTEK. The same improvement in image quality is obtained in human, so details are more delineated in the lung with the use of the adaptive trajectory. Conclusion The AZTEK technique opens the possibility for 3D dynamic ZTE lung imaging with retrospective gating. It enables us to uniformly sample the k‐space for any arbitrary respiratory motion gate, while preserving static image quality, improving dynamic image quality and guaranteeing continuous readout gradient transitions between spokes, which makes it appropriate to ZTE.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.