Opencage radio frequency coil for magnetic resonance imaging.
Nikulin, A., J. De Rosny, K. Haliot, B. Larrat, and A. Ourir.
Applied Physics Letters 114, no. 5 (2019).
Résumé: © 2019 Author(s). We present a volume radio frequency coil for Magnetic Resonance Imaging that provides access to the region of interest. While the conventional birdcage coil is composed of a periodic array of similar unit cells making a cylindrical structure, the proposed coil, called “opencage,” is made of an aperiodic array of metamaterial based unit cells presenting different geometries and characteristics. We develop here a dedicated approach based on Bloch impedance matching and phase balance for the design of the opencage coil. We perform full-wave numerical simulations to validate this concept. An experimental demonstration of the opencage coil for small animal imaging at 7 Tesla is presented. The results of the in-vitro, in-vivo imaging and B 1 + map reconstruction achieved with a preclinical MRI scanner are presented. We show that B 1 + field homogeneity and amplitude generated by the opencage coil are comparable to those of a conventional birdcage coil of the same size.
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Characterization of Testicular Masses in Adults: Performance of Combined Quantitative Shear Wave Elastography and Conventional Ultrasound.
Rocher, L., A. Criton, J. L. Gennisson, M. Creze, L. Albiges, S. Ferlicot, M. F. Bellin, V. Izard, and J. M. Correas.
Ultrasound in Medicine and Biology 45, no. 3 (2019): 720–731.
Résumé: © 2018 World Federation for Ultrasound in Medicine & Biology We prospectively evaluated the performance of combined shear wave elastography (SWE) and conventional ultrasound (US) for the characterization of 89 testicular focal masses. Testes were evaluated with B-mode, color Doppler and SWE measurements, locating a region of interest on the normal and pathologic parenchyma. Thirty-seven malignant tumors (MTs), 12 burned out tumors (BOTs), 28 Leydig cell tumors (LCTs), 2 dermoid cysts and other benign lesions were included. MTs + BOTs exhibited more microliths and macrocalcifications compared with benign lesions (p < 10–4). LCTs manifested mostly a dominant peripheral vascularization pattern compared with other lesions. MTs + BOTs were stiffer compared with benign lesions (p < 2 × 10–4) but with a moderate area under the receiver operating characteristic curve (AUROC) of 80%. By focusing on LCTs versus MTs + BOTs, diagnostic performance led to an AUROC of 89% for the best stiffness parameter. For combined conventional US and SWE, the diagnostic performance to differentiate all benign lesions versus MTs + BOTs and LCTs versus MTs + BOTs increased to AUROCs of 93% and 98%, respectively.
Mots-Clés: Burned out germ cell tumor; Color Doppler ultrasound; Leydig cell tumor; Shear wave elastography; Testicular tumor
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Arterial Stiffness Assessment by Shear Wave Elastography and Ultrafast Pulse Wave Imaging: Comparison with Reference Techniques in Normotensives and Hypertensives.
Marais, L., M. Pernot, H. Khettab, M. Tanter, E. Messas, M. Zidi, S. Laurent, and P. Boutouyrie.
Ultrasound in Medicine and Biology 45, no. 3 (2019): 758–772.
Résumé: © 2018 World Federation for Ultrasound in Medicine & Biology Shear wave elastography and ultrafast imaging of the carotid artery pulse wave were performed in 27 normotensive participants and 29 age- and sex-matched patients with essential hypertension, and compared with reference techniques: carotid–femoral pulse wave velocity (cfPWV) determined via arterial tonometry and carotid stiffness (carPWV) determined via echotracking. Shear wave speed in the carotid anterior (a–SWS) and posterior (p-SWS) walls were assessed throughout the cardiac cycle. Ultrafast PWV was measured in early systole (ufPWV–FW) and in end-systole (dicrotic notch, ufPWV-DN). Shear wave speed in the carotid anterior appeared to be the best candidate to evaluate arterial stiffness from ultrafast imaging. In univariate analysis, a-SWS was associated with carPWV (r = 0.56, p = 0.003) and carotid-to-femoral PWV (r = 0.66, p < 0.001). In multivariate analysis, a–SWS was independently associated with age (R² = 0.14, p = 0.02) and blood pressure (R² = 0.21, p = 0.004). Moreover, a–SWS increased with blood pressure throughout the cardiac cycle and did not differ between normotensive participants and patients with essential hypertension when compared at similar blood pressures.
Mots-Clés: Arterial stiffness; Echotracking; Hypertension; Pulse wave velocity; Shear wave elastography; Ultrafast imaging; Vascular ultrasound
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Quantum dipole emitters in structured environments: A scattering approach: Tutorial.
Bouchet, D., and R. Carminati.
Journal of the Optical Society of America A: Optics and Image Science, and Vision 36, no. 2 (2019): 186–195.
Résumé: © 2019 Optical Society of America. We provide a simple semi-classical formalism to describe the coupling between one or several quantum emitters and a structured environment. Describing the emitter by an electric polarizability, and the surrounding medium by a Green function, we show that an intuitive scattering picture allows one to derive a coupling equation from which the eigenfrequencies of the coupled system can be extracted. The model covers a variety of regimes observed in light–matter interaction, including weak and strong coupling, coherent collective interactions, and incoherent energy transfer. It provides a unified description of many processes, showing that different interaction regimes are actually rooted on the same ground. It can also serve as a basis for the development of more refined models in a full quantum electrodynamics framework.
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