Steady-state Resonance Research Articles

Influence of Aortic Dilation on the Regional Aortic Stiffness of Bicuspid Aortic Valve Assessed by 4-Dimensional Flow Cardiac Magnetic Resonance: Comparison With Marfan Syndrome and Degenerative Aortic Aneurysm

ObjectivesThis study sought to ascertain whether patients with a bicuspid aortic valve (BAV) have an intrinsic alteration in regional aortic stiffness compared with patients with tricuspid aortic valve (TAV) and Marfan syndrome (MFS) patients with similar aortic sizes, as well as to assess the influence of ascending aorta (AAo) dilation on regional stiffness parameters in BAV patients. BackgroundImaging biomarkers as predictors of BAV, MFS, and degenerative AAo aneurysms in TAV patients (DA-TAV) are lacking. Biomechanical characterization has been proposed as a possible tool for further aneurysm stratification. MethodsA total 234 subjects (136 BAV, 44 MFS, and 18 DA-TAV patients and 36 healthy control subjects) were included. The cardiac magnetic resonance protocol comprised 4-dimensional flow to assess AAo and descending aorta (DAo) pulse wave velocities (PWVs) and double-oblique, 2-dimensional, steady-state free-precession cine cardiac magnetic resonance to compute aortic distensibility (AD). ResultsOn adjusted analysis, nondilated BAV patients had similar PWV and AD as healthy control subjects in both AAo and DAo, whereas dilated BAV did not differ from DA-TAV. In contrast, AAo and DAo stiffness in MFS patients was markedly greater than in BAV patients, increasing slightly with dilation severity. AAo PWV showed a biphasic pattern in BAV patients: it first decreased and then increased throughout AAo dilation, with a clear turning point at 50 mm, whereas distensibility did not discern mildly dilated aorta. In multivariate analysis adjusted for clinical and demographic characteristics, only PWV was related to AAo dilation in BAV patients. ConclusionsThe mechanical properties of AAo aneurysms are similar in BAV and TAV patients, whereas MFS patients have a stiffer aorta. Aortic stiffness strongly depends on dilation severity. AAo PWV resulted in a potentially clinically useful biphasic trend with respect to aneurysm diameter, whereas distensibility did not discern mildly dilated aorta. Beyond clinical risk factors, PWV but not AD was independently related to AAo dilation in BAV patients.

Cardiovascular cine imaging and flow evaluation using Fast Interrupted Steady-State (FISS) magnetic resonance

BackgroundExisting cine imaging techniques rely on balanced steady-state free precession (bSSFP) or spoiled gradient-echo readouts, each of which has limitations. For instance, with bSSFP, artifacts occur from rapid through-plane flow and off-resonance effects. We hypothesized that a prototype cine technique, radial fast interrupted steady-state (FISS), could overcome these limitations. The technique was compared with standard cine bSSFP for cardiac function, coronary artery conspicuity, and aortic valve morphology. Given its advantageous properties, we further hypothesized that the cine FISS technique, in combination with arterial spin labeling (ASL), could provide an alternative to phase contrast for visualizing in-plane flow patterns within the aorta and branch vessels.Main bodyThe study was IRB-approved and subjects provided consent. Breath-hold cine FISS and bSSFP were acquired using similar imaging parameters. There was no significant difference in biplane left ventricular ejection fraction or cardiac image quality between the two techniques. Compared with cine bSSFP, cine FISS demonstrated a marked decrease in fat signal which improved conspicuity of the coronary arteries, while suppression of through-plane flow artifact on thin-slice cine FISS images improved visualization of the aortic valve. Banding artifacts in the subcutaneous tissues were reduced. In healthy subjects, dynamic flow patterns were well visualized in the aorta, coronary and renal arteries using cine FISS ASL, even when the slice was substantially thicker than the vessel diameter.ConclusionCine FISS demonstrates several benefits for cardiovascular imaging compared with cine bSSFP, including better suppression of fat signal and reduced artifacts from through-plane flow and off-resonance effects. The main drawback is a slight (~ 20%) decrease in temporal resolution. In addition, preliminary results suggest that cine FISS ASL provides a potential alternative to phase contrast techniques for in-plane flow quantification, while enabling an efficient, visually-appealing, semi-projective display of blood flow patterns throughout the course of an artery and its branches.

Diagnosis of demyelinating brain lesion simulating brain tumors on fast imaging employing steady-state acquisition magnetic resonance imaging.

Background:A single inflammatory demyelinating brain lesion sometimes mimics a brain tumor on conventional magnetic resonance imaging (MRI), and thus poses a considerable diagnostic challenge. We assessed the usefulness of a new MRI technique, fast imaging employing steady-state acquisition (FIESTA), for the diagnosis of inflammatory demyelinating disease (IDD).Methods:Three patients (2 males, 1 female) with a histopathologically proven inflammatory demyelinating brain lesion which mimicked a brain tumor on MRI were evaluated with a post-contrast three-dimensional FIESTA sequence before biopsy and treatment. Those images were compared with the images of intra-axial brain tumors (n = 147).Results:Preoperative FIESTA showed an iso- or slightly hyperintense distinct intralesional structure that appeared reticulate or broad-line in patients with IDD. These structures traversed a hyperintense demyelinating lesion in the deep grey matter (DGM) and were connected to the surrounding extralesional area, which appeared to be dense fibers between DGM. Such distinct intralesional structures were not observed in most brain tumors.Conclusion:Reticulate or broad-line-like intralesional structures on FIESTA may, therefore, be suggestive of IDD rather than indicate a brain tumor.

Magnetic resonance imaging characteristics of lesions relate to the difficulty of peripheral arterial endovascular procedures

ObjectiveLimitations with current peripheral arterial imaging modalities make selection of patients for percutaneous vascular interventions difficult. The purpose of this study was to determine whether a novel preprocedural magnetic resonance imaging (MRI) method can identify lesions that would be more challenging to cross during percutaneous vascular intervention. MethodsFourteen patients with peripheral arterial disease underwent MRI before their intervention. A novel steady-state free precession flow-independent magnetic resonance (MR) angiogram was used to locate lesions, and an ultrashort echo time image was used to characterize hard lesion components including calcium and dense collagen. Lesions were characterized as hard if ≥50% of the lumen was occluded with calcium or collagen (as determined by MR image characteristics) in the hardest cross section within the lesion. The primary outcome was the time it took to cross a guidewire through the target lesion. The secondary outcome was the need for stenting. ResultsOf 14 lesions, 8 (57%) were defined as hard and 6 (43%) were soft on the basis of MR image characteristics. Hard lesions took significantly longer to cross than soft lesions (average, 14 minutes 49 seconds vs 2 minutes 17 seconds; P = .003). Hard lesions also required stenting more often than soft lesions (Fisher exact test, P = .008). Of 14 lesions, 2 (14%) could not be crossed with a guidewire, and both lesions were hard. MR images also detected occult patencies and noncalcified hard lesions that could not be seen on X-ray angiography. ConclusionsMRI can be used to determine which peripheral arterial lesions are more difficult to cross with a guidewire. Future work will determine whether MRI lesion characterization can predict long-term endovascular outcomes to aid in procedure planning.

Mass, momentum, and energy flux conservation between linear and nonlinear steady-state wave groups

This paper provides a mass, momentum, and energy flux conservation analysis between the linear and nonlinear steady-state wave groups. Convergent high-order solutions for nonlinear wave groups with multiple steady-state near resonances in deep water have been obtained by means of the homotopy analysis method. The small divisors associated with nearly resonant components are transformed to singularities that are originally caused by exact resonances by a piecewise auxiliary linear operator. Both two primary components and other nearly resonant ones are considered in the initial guess to search for finite amplitude wave groups. It is found that as nonlinearity of wave groups increases, more wave components appear in the spectrum due to the nearly resonant interactions. The nonlinear wave fields change from the initial bi-chromatic waves that contain only two nontrivial primary components into the steady-state resonant waves that contain both two primary components and other nearly resonant ones. The conservation of mean rates of mass, momentum, and energy fluxes is established between the nonlinear wave groups and linear waves that are combined by two primary components with the same frequencies as in nonlinear wave groups. Comparison of the linear and nonlinear wave fields shows that the nearly resonant components influence the wave field distribution significantly: the nonlinear free surfaces have more peaked crests, steeper troughs, and more flatten wave nodes, and the related velocities at the crests and troughs increase more rapidly with the nonlinearity. All of these findings are helpful to enrich and deepen our understanding about nonlinear wave groups.

Ultrawide thermal free-carrier tuning of dielectric antennas coupled to epsilon-near-zero substrates

The principal challenge for achieving reconfigurable optical antennas and metasurfaces is the need to generate continuous and large tunability of subwavelength, low-Q resonators. We demonstrate continuous and steady-state refractive index tuning at mid-infrared wavelengths using temperature-dependent control over the low-loss plasma frequency in III–V semiconductors. In doped InSb we demonstrate nearly two-fold increase in the electron effective mass leading to a positive refractive index shift (Δn > 1.5) that is an order of magnitude greater than conventional thermo-optic effects. In undoped films we demonstrate more than 10-fold change in the thermal free-carrier concentration producing a near-unity negative refractive index shift. Exploiting both effects within a single resonator system—intrinsic InSb wires on a heavily doped (epsilon-near-zero) InSb substrate—we demonstrate dynamically steady-state tunable Mie resonances. The observed line-width resonance shifts (Δλ > 1.7 μm) suggest new avenues for highly tunable and steady-state mid-infrared semiconductor antennas.

Radial fast interrupted steady-state (FISS) magnetic resonance imaging.

To report a highly interrupted radial variant of balanced steady-state free precession (bSSFP) imaging, termed fast interrupted steady-state (FISS), for decreasing flow artifact as well as fat signal conspicuity with respect to bSSFP, and saturation effects vis-à-vis fast low-angle shot (FLASH) imaging. Numerical simulations, phantom studies, and human studies were conducted to examine the imaging contrast, off-resonance behavior, and flow properties of FISS. Human studies applied FISS for cine cardiac imaging and ungated nonenhanced MR angiography (MRA) of the legs, neck, and brain. Comparisons were made with bSSFP and FLASH imaging. Simulations revealed that FISS retains the high signal levels of bSSFP for stationary on-resonant spins, while reducing undesirable signal heterogeneity from flowing spins. Phantom studies agreed with the simulations, and showed that FISS reduces fat signal and flow artifact with respect to bSSFP imaging. FISS imaging in human subjects agreed with the simulations and phantom studies, and showed reduced saturation artifact compared with FLASH imaging. FISS imaging reduces flow artifact and fat signal conspicuity with respect to bSSFP imaging, and ameliorates arterial signal saturation observed with FLASH imaging. Potential clinical applications include fat-suppressed cine imaging and ungated nonenhanced MRA. Magn Reson Med 79:2077-2086, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The third ventricle roof: an anatomical study using constructive interference in steady-state magnetic resonance imaging.

The third ventricle roof in vivo has been infrequently explored. The aim of the present study was to delineate the neurovascular structures relevant to the third ventricle roof using magnetic resonance (MR) imaging. A total of 78 patients were enrolled in the study. Following initial examinations with conventional MR sequences, the constructive interference in steady-state (CISS) sequence was performed in coronal sections on 67 patients and in sagittal sections on 11 patients. In the coronal sections, the fornices and internal cerebral veins were delineated in all 67 patients. The cross-sectional appearance and size of the fornices were variable, and the relationship between fornices presented as five different types. In 82% of patients, dominance of one relationship type was not found. The diameter of the internal cerebral veins (ICVs) was also variable, and the relationship between ICVs presented as four different types. In 70% of patients, dominance of one relationship type was not found. In 52% of patients, the lower layer of the third ventricle roof was identified as an inhomogeneous membranous structure. In the sagittal sections, the lower layer of the third ventricle roof was delineated as an inhomogeneous linear structure with variable slopes. The third ventricle roof appears highly variable in morphology. Visualization of the third ventricle roof using the CISS sequence may be useful for planning safe and effective surgical maneuvers around the region.

Vascular Compression of the Anterior Optic Pathway: A Rare Occurrence?

BackgroundVascular compression of the anterior optic pathway has been documented as an infrequent cause of visual impairments. Here we characterize such vascular compression using magnetic resonance imaging. MethodsA total of 183 patients without pathologies affecting the optic pathways underwent T2-weighted or constructive interference steady-state sequence magnetic resonance imaging. Imaging data from coronal sections were analyzed. ResultsA vascular compression of the anterior optic pathway was identified in 20 patients (11%). They comprised 13 men and 7 women with a mean age of 60.8 years. The vascular compressions were observed at 22 sites, 15 on the optic nerve (ON) and 7 on the optic chiasm (OC). Twelve of them were on the right and 10 were on the left side. The offending vessels were the supraclinoid portion of the internal carotid artery in 86.4% and the A1 segment of the anterior cerebral artery in 13.6%. Compression sites at the ON and OC were variable, with the inferolateral surface being the most frequent (77.3% occurrences). In 2 patients (9.1%), the ON was compressed in a sandwich manner. ConclusionsVascular compression of the ON and OC may not be an infrequent occurrence in the cranial cavity. Progressive and unexplainable visual impairment might possibly be caused by vascular-compressive neuropathy.

Alkyne-Bridged Multi[Copper(II) Porphyrin] Structures: Nuances of Orbital Symmetry in Long-Range, Through-Bond Mediated, Isotropic Spin Exchange Interactions.

Spin and conformational dynamics in symmetric alkyne-bridged multi[copper(II) porphyrin] structures have been studied in toluene solution at variable temperature using steady-state electron paramagnetic resonance (EPR) spectroscopy. Comparison of the dimer EPR spectra to those of Cu porphyrin monomers shows evidence of an isotropic exchange interaction (Javg) in these biradicaloid structures, manifested by a significant line broadening in the dimer spectra. The extent line broadening depends on molecular structure and temperature, suggesting Javg is modulated by conformational dynamics that impact the torsional angle distribution between the porphyrin-porphyrin least-squares planes. Computational simulation of the experimental EPR spectra, using a developed algorithm for J modulation in flexible organic biradicals, supports this hypothesis. Comparison of ethyne and butadiyne alkyne bridges reveals remarkable sensitivity to orbital interactions between the spacer and the metal, reflected in measurements of Javg as a function of temperature. The results suggest orbital symmetry relationships may be more important than recognized in design of optimized molecular spintronic devices.

Radical-Enhanced Intersystem Crossing in New Bodipy Derivatives and Application for Efficient Triplet-Triplet Annihilation Upconversion.

A long-lived triplet excited state of the well-known fluorophore boron dipyrromethene (Bodipy) was observed for the first time via efficient radical-enhanced intersystem crossing (EISC). The triplet state has been obtained in two dyads in which the Bodipy unit is linked to a nitroxide radical, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), with two different length spacers. The photophysical properties were studied with steady-state and time-resolved transient optical spectroscopies and electron spin resonance (cw-ESR and TR-ESR). The fluorescence of Bodipy units is significantly quenched in the dyads, and the spin-polarized TEMPO signals were observed with TR-ESR, generated by a radical triplet pair mechanism. Efficient EISC (ΦT = 80%) was observed for the dyad with a shorter linker, and the triplet state lifetime of the Bodipy chromophore is exceptionally long (62 μs). The EISC takes 250 ps. Poor ISC was observed for the dyad with a longer linker. The efficient ISC and long-lived triplet excited state in this flexible system are in stark contrast to the previously studied rigid EISC systems. The EISC effect was employed for the first time to perform triplet-triplet annihilation (TTA) upconversion (quantum yield ΦUC = 6.7%).

Dynamics of a super-critically axially moving beam with parametric and forced resonance

In the super-critical regime, steady-state responses of an axially moving beam are analyzed subjected to parametric combined with forced excitations. By employing the method of multiple scales, the primary resonance is investigated. Steady-state resonances exist unless the parametric frequency and the external frequency are commensurable. Natural modes are triggered when the parametric frequency is close to two times of or just the natural frequency. For the case of the first one, the combined excitation deduces a response curve with twin resonance peaks. Distance of them is determined by the parametric excitation, and the widths are depended on the external force. Double jumping is found in the response curve. For the case of the second one, the combined excitation produces a simple resonance in the form of a typical forced vibration. The response curve is superimposed by each of the excitations. With the numerical method, the incommensurability of excitation frequencies is found to produce beats and quasi-periodicity vibrations.

On Steady-State Multiple Resonances for a Modified Bretherton Equation

Abstract In this article, a modified Bretherton equation is considered to further check if steady-state multiple resonances exist not only for water waves but also for other dispersive medium. The linear resonance condition analysis shows that different components may interact with each other so multiple resonances may happen. Convergent steady-state solutions are obtained by solution procedure based on the homotopy analysis method (HAM) and the collocation method. Amplitude spectrum analysis confirms that more components indeed join the resonance as the nonlinearity increases. This article suggests that steady-state multiple resonance may exist in other dispersive system.

On the generation of nonlinear damage resonance intermodulation for elastic wave spectroscopy.

Recent nonlinear elastic wave spectroscopy experiments have shown that the nonlinear ultrasonic response of damaged composite materials can be enhanced by higher vibrations at the local damage resonance. In this paper, the mathematical formulation for the generation of nonlinear wave effects associated with continuous periodic excitation and the concept of local defect resonance is provided. Under the assumption of both quadratic and cubic approximation, the existence of higher harmonics of the excitation frequency, superharmonics of the damage resonance frequency and nonlinear wave effects, here named as nonlinear damage resonance intermodulation, which correspond to the nonlinear intermodulation between the driving and the damage resonance frequencies, is proved. All these nonlinear elastic effects are caused by the interaction of propagating ultrasonic waves with the local damage resonance and can be measured at locations different from the material defect one. The proposed analytical model is confirmed and validated through experimental transducer-based measurements of the steady-state nonlinear resonance response on a damaged composite sample. These results will provide opportunities for early detection and imaging of material flaws.

Reaction intermediates in the heme degradation reaction by HutZ from Vibrio cholerae.

HutZ is a heme-degrading enzyme in Vibrio cholerae. It converts heme to biliverdin via verdoheme, suggesting that it follows the same reaction mechanism as that of mammalian heme oxygenase. However, none of the key intermediates have been identified. In this study, we applied steady-state and time-resolved UV-vis absorption and resonance Raman spectroscopy to study the reaction of the heme-HutZ complex with H2O2 or ascorbic acid. We characterized three intermediates: oxyferrous heme, meso-hydroxyheme, and verdoheme complexes. Our data support the view that HutZ degrades heme in a manner similar to mammalian heme oxygenase, despite their low sequence and structural homology.

Quantification of myocardium at risk in ST- elevation myocardial infarction: a comparison of contrast-enhanced steady-state free precession cine cardiovascular magnetic resonance with coronary angiographic jeopardy scores

BackgroundClinical outcome following acute myocardial infarction is predicted by final infarct size evaluated in relation to left ventricular myocardium at risk (MaR). Contrast-enhanced steady-state free precession (CE-SSFP) cardiovascular magnetic resonance imaging (CMR) is not widely used for assessing MaR. Evidence of its utility compared to traditional assessment methods and as a surrogate for clinical outcome is needed.MethodsRetrospective analysis within a study evaluating post-conditioning during ST elevation myocardial infarction (STEMI) treated with coronary intervention (n = 78). CE-SSFP post-infarction was compared with angiographic jeopardy methods. Differences and variability between CMR and angiographic methods using Bland-Altman analyses were evaluated. Clinical outcomes were compared to MaR and extent of infarction.ResultsMaR showed correlation between CE-SSFP, and both BARI and APPROACH scores of 0.83 (p < 0.0001) and 0.84 (p < 0.0001) respectively. Bias between CE-SSFP and BARI was 1.1% (agreement limits -11.4 to +9.1). Bias between CE-SSFP and APPROACH was 1.2% (agreement limits -13 to +10.5). Inter-observer variability for the BARI score was 0.56 ± 2.9; 0.42 ± 2.1 for the APPROACH score; -1.4 ± 3.1% for CE-SSFP. Intra-observer variability was 0.15 ± 1.85 for the BARI score; for the APPROACH score 0.19 ± 1.6; and for CE-SSFP -0.58 ± 2.9%.ConclusionQuantification of MaR with CE-SSFP imaging following STEMI shows high correlation and low bias compared with angiographic scoring and supports its use as a reliable and practical method to determine myocardial salvage in this patient population.Trial registrationClinical trial registration information for the parent clinical trial:Karolinska Clinical Trial Registration (2008)Unique identifier: CT20080014. Registered 04th January 2008

SUPRATHERMAL SOLAR WIND ELECTRONS AND LANGMUIR TURBULENCE

ABSTRACT The steady-state model recently put forth for the solar wind electron velocity distribution function during quiet time conditions, was originally composed of three population electrons (core, halo, and superhalo) with the core remaining nonresonant with any plasma waves while the halo and superhalo separately maintained steady-state resonance with whistler- and Langmuir-frequency range fluctuations, respectively. However, a recent paper demonstrates that whistler-range fluctuations in fact have no significant contribution. The present paper represents a consummation of the model in that a self-consistent model of the suprathermal electron population, which encompasses both the halo and the superhalo, is constructed solely on the basis of the Langmuir fluctuation spectrum. Numerical solutions to steady-state particle and wave kinetic equations are obtained on the basis of an initial trial electron distribution and Langmuir wave spectrum. Such a finding offers a self-consistent explanation for the observed steady-state electron distribution in the solar wind.

Dynamics of Cubic and Vibro-Impact Nonlinear Energy Sink: Analytical, Numerical, and Experimental Analysis

This paper is devoted to study and compare dynamics of primary linear oscillator (LO) coupled to cubic and vibro-impact (VI) nonlinear energy sink (NES) under transient and periodic forcing. The classic analytical procedure combining the approach of invariant manifold and multiple scales is extended from the analysis of steady-state resonance to other regimes, especially strongly modulated response (SMR). A general equation governing the variation of motion along the slow invariant manifold (SIM) is obtained. Numerical results show its convenience to explain the transition from steady-state response to SMR and the characteristics of SMR for periodic forcing. Targeted energy transfer (TET) under transient forcing can also be well understood. Experimental results from LO coupled to VI NES under periodic forcing confirm the existence of SMR and its properties (e.g., chaotic). They also verify the feasibility of the general equation to explain complicated case like SMR in experiments.

Effect of atomic diffusion on the Raman–Ramsey coherent population trapping resonances

We experimentally investigated the characteristics of two-photon transmission resonances in Rb vapor cells with different amount of buffer gas under the conditions of steady-state coherent population trapping (CPT) and pulsed Raman-Ramsey (RR-) CPT interrogation scheme. We particularly focused on the influence of the Rb atoms diffusing in and out of the laser beam. We showed that this effect modifies the shape of both CPT and Raman-Ramsey resonances, as well as their projected performance for CPT clock applications. In particular we found that at moderate buffer gas pressures RR-CPT did not improved the projected atomic clock stability compare to the regular steady-state CPT resonance.

Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid.

Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.