Backward Volume Research Articles

Four-dimensional flow MRI quantification of pulmonary regurgitation in patients with repaired tetralogy of Fallot: a study on reproducibility and consistency

Objective To investigate the feasibility and consistency of four-dimensional flow (4D flow) quantification of pulmonary regurgitation in patients with repaired Tetralogy of Fallot (ToF) by comparing with conventional two-dimensional flow (2D flow) and echocardiography. Methods Both the 4D flow and 2D flow imaging were acquired with repaired ToF (a total of 21 patients) consecutively on 3.0 T MR scanner from May 2018 to August 2018. Pulmonary flow and regurgitant fraction were measured by a commercial post processing software Circle CVI42. All patients underwent echocardiography within one week after or before MR examination. The inter/intra-observer variability by 2D/4D f1ow and agreement between the two methods were investigated by interclass correlation coefficients (ICC) and Bland-Altman analyses. The agreement between MR and echocardiography were analyzed by weighted Kappa coefficient. The correlation between pulmonary regurgitation and cardiac function was also investigated by Pearson analysis. Results All patients were included and completed the examinations successfully. Both inter-observer and intra-observer agreement by 4D flow for total forward volume (ICC=0.993, 0.996, respectively, P<0.001), total backward volume (ICC=0.994, 0.997, respectively, P<0.001) and regurgitant fraction (ICC=0.968, 0.985, respectively, P<0.001) were good. The total forward volume, total backward volume and regurgitant fraction measured by 2D flow and 4D flow reached a good agreement (ICC=0.954, 0.913,0.721,respectively,P<0.001). The consistency was good for severity of regurgitation measured by 2D flow (weighted Kappa=0.897, P<0.001) and 4D flow (weighted Kappa=0.710, P=0.001) compared with echocardiography. Significant correlation was found among right ventricular cardiac index(r=0.600, P<0.05), right ventricular end-diastolic volume index(r=0.788, P<0.05), right ventricular end-systolic volume index(r=0.683, P<0.05) and left ventricular end-diastolic volume index(r=0.578, P<0.05), left ventricular end-systolic volume index(r=0.687, P<0.05) with regurgitant fraction measured by 2D flow. Regurgitant fraction measured by 4D flow had a significant correlation with right ventricular cardiac index(r=0.606, P<0.05), right ventricular end-diastolic volume index(r=0.685,P<0.05), right ventricular end-systolic volume index(r=0.534, P<0.05) and left ventricular end-diastolic volume index(r=0.459, P<0.05), left ventricular mass index(r=0.633, P<0.05). Conclusion 4D flow MRI provides highly reproducible measurements of pulmonary flow on morphology and haemodynamics in patients with repaired ToF compared with 2D flow MRI and echocardiography. Key words: Magnetic resonance imaging; Pulmonary regurgitation; Tetralogy of Fallot

Do DWI and quantitative DCE perfusion MR have a prognostic value in high-grade serous ovarian cancer?

To evaluate whether perfusion and diffusion parameters from staging MR in ovarian cancer (OC) patients may predict the presence of residual tumor at surgery and the progression-free survival (PFS) in 12months. Patients who are from a single institution, candidate for OC to cytoreductive surgery and undergoing MR for staging purposes were included in this study. Inclusion criteria were: preoperative MR including diffusion-weighted imaging (DWI) and perfusion dynamic contrast-enhanced (DCE) sequence; cytoreductive surgery performed within a month from MR; and minimum follow-up of 12months. Patients' characteristics including the presence of residual tumor at surgery (R0 or R1) and relapse within 12months from surgery were recorded. DWI parameters included apparent diffusion coefficient (ADC) of the largest ovarian mass (O-ADC) and normalized ovarian ADC as a ratio between ovarian ADC and muscle ADC (M-ADC). DCE quantitative parameters included were descriptors of tumor vascular properties such as forward and backward transfer constants, plasma volume and volume of extracellular space. Statistical analysis was performed, and p values < 0.05 were considered significant. Forty-nine patients were included. M-ADC showed a slightly significant association with the presence of residual tumor at surgery. None of the other functional parameters showed either difference between R0 and R1 patients or association with PFS in the first 12months. This preliminary study demonstrated a slightly significant association between normalized ovarian ADC and the presence of residual tumor at surgery. The other perfusion and diffusion parameters were not significant for the endpoints of this study.

Sex and Age Dependencies of Aqueductal Cerebrospinal Fluid Dynamics Parameters in Healthy Subjects.

ObjectivesTo assess the influence of age and sex on 10 cerebrospinal fluid (CSF) flow dynamics parameters measured with an MR phase contrast (PC) sequence within the cerebral aqueduct at the level of the intercollicular sulcus.Materials and Methods128 healthy subjects (66 female subjects with a mean age of 52.9 years and 62 male subjects with a mean age of 51.8 years) with a normal Evans index, normal medial temporal atrophy (MTA) score, and without known disorders of the CSF circulation were included in the study. A PC MR sequence on a 3T MR scanner was used. Ten different flow parameters were analyzed using postprocessing software. Ordinal and linear regression models were calculated.ResultsThe parameters stroke volume (sex: p < 0.001, age: p = 0.003), forward flow volume (sex: p < 0.001, age: p = 0.002), backward flow volume (sex: p < 0.001, age: p = 0.018), absolute stroke volume (sex: p < 0.001, age: p = 0.005), mean flux (sex: p < 0.001, age: p = 0.001), peak velocity (sex: p = 0.009, age: p = 0.0016), and peak pressure gradient (sex: p = 0.029, age: p = 0.028) are significantly influenced by sex and age. The parameters regurgitant fraction, stroke distance, and mean velocity are not significantly influenced by sex and age.ConclusionCSF flow dynamics parameters measured in the cerebral aqueduct are partly age and sex dependent. For establishment of reliable reference values for clinical use in future studies, the impact of sex and age should be considered and incorporated.

Spin wave propagation in ferrimagnetic GdxCo1−x

Recent advances in antiferromagnetic spin dynamics using rare-earth (RE) and transition-metal (TM) ferrimagnets have attracted much interest for spintronic devices with a high speed and density. In this study, the spin wave properties in the magnetostatic backward volume mode and surface mode in RE-TM ferrimagnetic GdxCo1−x films with various composition x are investigated using spin wave spectroscopy. The obtained group velocity and attenuation length are well explained by the ferromagnet-based spin wave theory when the composition of GdxCo1−x is far from the compensation point.

Ferromagnet/Superconductor Hybrid Magnonic Metamaterials.

In this work, a class of metamaterials is proposed on the basis of ferromagnet/superconductor hybridization for applications in magnonics. These metamaterials comprise of a ferromagnetic magnon medium that is coupled inductively to a superconducting periodic microstructure. Spectroscopy of magnetization dynamics in such hybrid evidences formation of areas in the medium with alternating dispersions for spin wave propagation, which is the basic requirement for the development of metamaterials known as magnonic crystals. The spectrum allows for derivation of the impact of the superconducting structure on the dispersion: it takes place due to a diamagnetic response of superconductors on the external and stray magnetic fields. In addition, the spectrum displays a dependence on the superconducting critical state of the structure: the Meissner and the mixed states of a type II superconductor are distinguished. This dependence hints toward nonlinear response of hybrid metamaterials on the magnetic field. Investigation of the spin wave dispersion in hybrid metamaterials shows formation of allowed and forbidden bands for spin wave propagation. The band structures are governed by the geometry of spin wave propagation: in the backward volume geometry the band structure is conventional, while in the surface geometry the band structure is nonreciprocal and is formed by indirect band gaps.

The Ineffectiveness of Water Splash on Paddlewheel Aerator

The successful of intensive aquaculture is strongly influenced by the ability of the farmers to overcome the deterioration of water quality. The problem is low dissolved oxygen through aeration process. The aerator device which widely used in pond farming is paddle wheel aerator because it is the best aerator in aeration mechanism and usable driven power. However, the paddlewheel has a slow aeration rate resulting in low aeration efficiency. The problem is caused by the backward water splash ineffectively. The backward water of the paddlewheel that is already aerated, but it is splashed again so it wastes the power. However, only the forward splash is effectively. The aim of this study was to determine the ineffectiveness of paddlewheel aerator based on the backward water splash. The paddlewheel used an 1 phase motor, 1 hp power, 1400 rpm motor speed, and 2 pieces of wheels. The treatment was carried out by varying the blade of 65, 85, and 105 mm submerged. The test was done by collecting the forward and backward water splash and calculating its volume. The normal position of the float on the blade submerged by 85 mm was obtained that the forward and backward splash volume of water was 17.99 and 13.74 m3/hour. Only 56.70% the effectiveness of the water splash compared to 43.30% the backward water splash. In fact, the forward splash coverage volume of water was 47.83% compared to the forward was 52.17%. This result shown that the water splash of paddlewheel aerator was not effective, so the backward water splash need to optimize to the effectiveness of water splash.

Direct detection of multiple backward volume modes in yttrium iron garnet at micron scale wavelengths

Using a set of wave-vector-specific multielement antennas, we have characterized the dispersion of spin waves in an yttrium iron garnet film at submicron lengths and resolved the dispersion relations of multiple backward volume modes, particularly in the region of their minima. The techniques developed now facilitate the characterization of spin waves at length scales limited only by available lithography and at a spectral resolution that generally exceeds that of Brillouin scattering. The data obtained are in excellent agreement with theoretical predictions based on a model Hamiltonian.

Volume Magnetostatic Spin Waves in 3D Ferromagnetic Structures

Propagation of volume spin magnetostatic waves in meander-shaped ferromagnetic films with vertically and horizontally coupled segments is studied. Conditions under which forward and backward volume magnetostatic waves simultaneously exist in the films are determined. Micromagnetic simulation and expansion in terms of plane waves are used to calculate internal effective magnetic fields and dispersion characteristics of the waves in such structures. Spectra of coupled waves in meander-shaped vertically coupled ferromagnetic films are studied. Prospects for application of the above structures in the development of magnonic elements are analyzed.

Nonreciprocity of backward volume spin wave beams excited by the curved focusing transducer

The focusing effect for spin waves excited by a curved micrometer-sized coplanar waveguide transducer on top of a 5-μm-thick epitaxial yttrium iron garnet film is studied by means of the micro-focused Mandelstam-Brillouin light scattering technique and micromagnetic simulations. The curvilinear transducer is designed to focus the backward volume spin waves on the in-plane bias magnetic field applied along the symmetry axis of the transducer. We show that two-dimensional maps of spin wave intensity exhibit nonreciprocal properties without mirror symmetry with respect to the magnetic field direction and the focusing effect. The observed effects are the consequence of nonreciprocity of the backward volume spin waves travelling at an angle toward the bias field direction.

Spin-wave propagation through a magnonic crystal in a thermal gradient

The properties of a magnonic crystal are expected to be strongly influenced by the presence of a thermal gradient. We investigated the propagation of backward volume and surface magnetostatic spin-waves in a 1D magnonic crystal (MC) exposed to a continuous spatial temperature gradient. It is shown that the thermal gradient applied along the propagation direction leads to a frequency shift and a modification of the transmission characteristics of the spin-waves. The frequency shift is caused by a variation in saturation magnetization due to the change in absolute temperature. The altered transmission manifests itself in a broadening of MC band gaps and the corresponding narrowing of the MC passbands and is understood to be a result of a spatial transformation of the spin-waves wavelengths in a thermal gradient. Furthermore, the transmission characteristics of spin-waves in a thermal gradient have been verified by numerical calculations based on the approach of the transmission matrix. The results of the calculations demonstrate a good agreement with the experimentally measured data.

Control of Spin-Wave Propagation using Magnetisation Gradients

We report that in an in-plane magnetised magnetic film the in-plane direction of a propagating spin wave can be changed by up to 90 degrees using an externally induced magnetic gradient field. We have achieved this result using a reconfigurable, laser-induced magnetisation gradient created in a conversion area, in which the backward volume and surface spin-wave modes coexist at the same frequency. Shape and orientation of the gradient control the conversion efficiency. Experimental data and numerical calculations agree very well. Our findings open the way to magnonic circuits with in-plane steering of the spin-wave modes.

Time-domain propagating spin-wave spectroscopy for forward spin waves in a ferromagnetic metal

We performed time-domain propagating spin-wave spectroscopy for forward spin waves in a ferromagnetic metallic waveguide in the presence of electric current. The forward spin waves exhibit a large propagation delay and a 35% amplitude change with a smaller current injection of 6 × 1010 A/m2, showing a 2 times larger modulation than backward volume spin waves. By measuring electric-current effects in 4 distinct experimental configurations, we found that a current-induced Doppler shift coincided with an Oersted field frequency shift under our experimental conditions. By separating the two phenomena, we evaluated each contribution on the propagating forward spin-wave packet.

Dipolar interaction induced band gaps and flat modes in surface-modulated magnonic crystals

Theoretical results for the magnetization dynamics of a magnonic crystal formed by grooves on the surface of a ferromagnetic film, called a surface-modulated magnonic crystal, are presented. For such a system, the role of the periodic dipolar field induced by the geometrical modulation is addressed by using the plane-wave method. The results reveal that, under the increasing of the depth of the grooves, zones with magnetizing and demagnetizing fields act on the system in such a way that magnonic band gaps are observed in both Damon-Eshbach and backward volume geometries. Particularly, in the backward volume configuration, high-frequency band gaps and low-frequency flat modes are obtained. By taking into account the properties of the internal field induced by the grooves, the flattening of the modes and their shift towards low frequencies are discussed and explained. To test the validity of the model, the theoretical results of this work are confirmed by micromagnetic simulations, and good agreement between both methods is achieved. The theoretical model allows for a detailed understanding of the physics underlying these kinds of systems, thereby providing an outlook for potential applications on magnonic devices.

Measurements of long-wavelength spin waves for the magnetic field in the Damon-Eshbach, backward-volume and forward-volume geometries of an yttrium iron garnet film

We report systematic measurements of the dispersion of long wavelength spin waves for a wide range of wave vectors for the magnetic field along the three principal directions defining the forward volume, backward volume and Damon-Eshbach modes of a 9.72 μm thick film of an yttrium iron garnet obtained using lithographically patterned, multi-element, spatially resonant, antennas. Overall good agreement is found between the experimental data for the backward volume and Damon-Eshbach modes and the magnetostatic theory of Damon and Eshbach. Also, good agreement is found between the experimental data for the forward volume mode and the theory of Damon and van de Vaart.

Propagation of magnetostatic spin waves in an yttrium iron garnet film for out-of-plane magnetic fields

We have observed the propagation of spin waves across a thin yttrium iron garnet film on (1 1 1) gadolinium gallium garnet for magnetic fields inclined with respect to the film plane. Two principle planes were studied: that for H in the plane defined by the wave vector k and the plane normal, n, with limiting forms corresponding to the Backward Volume and Forward Volume modes, and that for H in the plane perpendicular to k, with limiting forms corresponding to the Damon-Eshbach and Forward Volume modes. By exciting the wave at one edge of the film and observing the field dependence of the phase of the received signal at the opposing edge we determined the frequency vs. wavevector relation, ω = ω (k), of various propagating modes in the film. Avoided crossings are observed in the Damon-Eshbach and Forward Volume regimes when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. The experimental results are compared with theoretical simulations.

Strong excitation of surface and bulk spin waves in yttrium iron garnet placed in a split ring resonator

This paper presents an experimental study of the inverse spin Hall effect (ISHE) in a bilayer consisting of a yttrium iron garnet (YIG) and platinum (Pt) loaded on a metamaterial split ring resonator (SRR). The system is excited by a microstrip feed line which generates both surface and bulk spin waves in the YIG. The spin waves subsequently undergo spin pumping from the YIG film to an adjacent Pt layer, and is converted into a charge current via the ISHE. It is found that the presence of the SRR causes a significant enhancement of the mangetic field near the resonance frequency of the SRR, resulting in a significant increase in the ISHE signal. Furthermore, the type of spin wave generated in the system can be controlled by changing the external applied magnetic field angle (). When the external applied magnetic field is near parallel to the microstrip line (), magnetostatic surface spin waves are predominantly excited. On the other hand, when the external applied magnetic field is perpendicular to the microstrip line (), backward volume magnetostatic spin waves are predominantly excited. Hence, it can be seen that the SRR structure is a promising method of achieving spin-charge conversion, which has many advantages over a coaxial probe.

Dispersion of the magnetostatic volume waves in a medium with damping

In magnetostatic approximation of electrodynamics the dispersion relation for magnetostatic back-ward volume waves (MSBVW) in a ferrite film, placed in a constant longitudinal and transverse alternating magnetic field is obtained. The magnetic field, damping and temperature influence on the spectrum and dispersion characteristics of the MSBVW is regarded.

Superdirected beam of the backward volume spin wave

Visualized patterns of the backward volume spin wave (BVSW) excited by arbitrarily oriented linear transducer in tangentially magnetized ferrite film are investigated experimentally in the plane of ferrite film for the case where the transducer length D is much larger than the wavelength λ0. Superdirected BVSW beam having zero angular width and minimal smearing of the beam energy along the film surface is observed experimentally. Thus, it is proved that such phenomenon as “superdirected propagation of the wave” exists in the nature.

Excitation of the three principal spin waves in yttrium iron garnet using a wavelength-specific multi-element antenna

We report systematic measurements of the dispersion of long wavelength spin waves for the magnetic field along the three principal directions (supporting the forward volume, backward volume and Damon-Eshbach modes) of a 3.05 μm thick yttrium iron garnet film on a lattice-matched (111) gadolinium gallium garnet substrate obtained using a lithographically patterned, multi-element, 50 μm spatially-resonant, antenna.

Characterization of complex flow patterns in the ascending aorta in patients with aortic regurgitation using conventional phase-contrast velocity MRI

Ascending aorta (AA) flow displacement (FD) is a surrogate for increased wall shear stress. We prospectively studied the flow profile in the AA in patients with aortic regurgitation (AR), to identify predictors of FD and investigate whether magnetic resonance imaging (MRI) phase-contrast flow rate curves (PC-FRC) contain quantitative information related to FD. Forty patients with chronic moderate (n = 14) or severe (n = 26) AR (21 (53%) with bicuspid aortic valve) and 22 controls were investigated. FD was determined from phase-contrast velocity profiles and defined as the distance between the center of the lumen and the “center of velocity” of the peak systolic forward flow or the peak diastolic negative flow, normalized to the lumen radius. Forward and backward volume flow was determined separately for systole and diastole. Seventy percent had systolic backward flow and 45% had diastolic forward flow in large areas of the vessel. AA dimension was an independent predictor of systolic FD while AA dimension and regurgitant volume were independent predictors of diastolic FD. Valve phenotype was not an independent predictor of systolic or diastolic FD. The linear relationships between systolic backward flow and systolic FD and diastolic forward flow and diastolic FD were strong (R = 0.77 and R = 0.76 respectively). Systolic backward flow and diastolic forward flow identified marked systolic and diastolic FD (≥0.35) with a positive likelihood ratio of 6.0 and 10.8, respectively. In conclusion, conventional PC-FRC data can detect and quantify FD in patients with AR suggesting the curves as a research and screening tool in larger patient populations.