Kerker Effect in Ultrahigh-Field Magnetic Resonance Imaging.
Dubois, M., L. Leroi, Z. Raolison, R. Abdeddaim, T. Antonakakis, J. De Rosny, A. Vignaud, P. Sabouroux, E. Georget, B. Larrat et al.
Physical Review X 8, no. 3 (2018).
Résumé: © 2018 authors. Published by the American Physical Society. Ultrahigh-field (UHF) magnetic resonance imaging (MRI) systems are getting a lot of attention as they ensure high intrinsic signal-to-noise ratio resulting in higher spatial and temporal resolutions as well as better contrast. This promises improved clinical results with regard to morphological as well as functional and metabolic capabilities. Traditionally, MRI relies on volume coils (birdcage) able to deliver a homogeneous radio frequency field exciting the nuclei magnetic spin. However, this strategy is hindered at UHF because of the rf field inhomogeneities yielded by the increased Larmor frequency. A standard approach consists of inserting passive dielectric elements within the volume coil in order to locally enhance the rf field and mitigate these inhomogeneities. However, the lack of control over their electromagnetic properties prevents the development of optimal solutions. Here, a single meta-atom is used to achieve efficient and tunable rf field control in UHF MRI. We demonstrate theoretically and experimentally a full overlap between the electric dipolar and magnetic dipolar resonances of the meta-atom. This interaction is precisely tuned to reach the so-called Kerker scattering conditions when illuminated in the near field by a birdcage coil. At these conditions, a strong enhancement or suppression of the rf field is achieved in the vicinity of the meta-atom within the MRI volume coil.
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The Reissner Fiber in the Cerebrospinal Fluid Controls Morphogenesis of the Body Axis.
Cantaut-Belarif, Y., J. R. Sternberg, O. Thouvenin, C. Wyart, and P. L. Bardet.
Current Biology 28, no. 15 (2018): 2479–2486.e4.
Résumé: © 2018 The Authors Organ development depends on the integration of coordinated long-range communication between cells. The cerebrospinal fluid composition and flow properties regulate several aspects of central nervous system development, including progenitor proliferation, neurogenesis, and migration [1–3]. One understudied component of the cerebrospinal fluid, described over a century ago in vertebrates, is the Reissner fiber. This extracellular thread forming early in development results from the assembly of the SCO-spondin protein in the third and fourth brain ventricles and central canal of the spinal cord [4]. Up to now, the function of the Reissner fiber has remained elusive, partly due to the lack of genetic invalidation models [4]. Here, by mutating the scospondin gene, we demonstrate that the Reissner fiber is critical for the morphogenesis of a straight posterior body axis. In zebrafish mutants where the Reissner fiber is lost, ciliogenesis and cerebrospinal fluid flow are intact but body axis morphogenesis is impaired. Our results also explain the frequently observed phenotype that mutant embryos with defective cilia exhibit defects in body axis curvature. Here, we reveal that these mutants systematically fail to assemble the Reissner fiber. We show that cilia promote the formation of the Reissner fiber and that the fiber is necessary for proper body axis morphogenesis. Our study sets the stage for future investigations of the mechanisms linking the Reissner fiber to the control of body axis curvature during vertebrate development. Cantaut-Belarif et al. unravel a developmental role for the Reissner fiber, a long-known structure found in the cerebrospinal fluid. Zebrafish embryos lacking this extracellular thread develop a curled-down axis reminiscent of cilia-defective mutants. This fiber needs cilia to form and is required for straight axis morphogenesis.
Mots-Clés: body axis morphogenesis; central canal; cerebrospinal fluid; cilia; development; extracellular protein; fluid dynamics; fluid dynamics; Reissner fiber; zebrafish
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Ultrasound-modulated optical tomography in scattering media: Flux filtering based on persistent spectral hole burning in the optical diagnosis window.
Venet, C., M. Bocoum, J. B. Laudereau, T. Chaneliere, F. Ramaz, and A. Louchet-Chauvet.
Optics Letters 43, no. 16 (2018): 3993–3996.
Résumé: © 2018 Optical Society of America. Ultrasound-modulated optical tomography (UOT) is a powerful imaging technique to discriminate healthy from unhealthy biological tissues based on their optical signature. Among the numerous detection techniques developed for acousto-optic imaging, only those based on spectral filtering are intrinsically immune to speckle decorrelation. This Letter reports on UOT imaging based on spectral hole burning in Tm:YAG crystal under a moderate magnetic field (200G) with a well-defined orientation. The deep and long-lasting holes translate into a more efficient UOT imaging with a higher contrast and faster imaging frame rate. We demonstrate the potential of this method by imaging calibrated phantom scattering gels.
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Pkd2l1 is required for mechanoception in cerebrospinal fluid-contacting neurons and maintenance of spine curvature.
Sternberg, J. R., A. E. Prendergast, L. Brosse, Y. Cantaut-Belarif, O. Thouvenin, A. Orts-Del’Immagine, L. Castillo, L. Djenoune, S. Kurisu, J. R. McDearmid et al.
Nature Communications 9, no. 1 (2018).
Résumé: © 2018, The Author(s). Defects in cerebrospinal fluid (CSF) flow may contribute to idiopathic scoliosis. However, the mechanisms underlying detection of CSF flow in the central canal of the spinal cord are unknown. Here we demonstrate that CSF flows bidirectionally along the antero-posterior axis in the central canal of zebrafish embryos. In the cfap298tm304mutant, reduction of cilia motility slows transport posteriorly down the central canal and abolishes spontaneous activity of CSF-contacting neurons (CSF-cNs). Loss of the sensory Pkd2l1 channel nearly abolishes CSF-cN calcium activity and single channel opening. Recording from isolated CSF-cNs in vitro, we show that CSF-cNs are mechanosensory and require Pkd2l1 to respond to pressure. Additionally, adult pkd2l1 mutant zebrafish develop an exaggerated spine curvature, reminiscent of kyphosis in humans. These results indicate that CSF-cNs are mechanosensory cells whose Pkd2l1-driven spontaneous activity reflects CSF flow in vivo. Furthermore, Pkd2l1 in CSF-cNs contributes to maintenance of natural curvature of the spine.
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