Regional Strain Rate Research Articles

Strain rate and flame orientation statistics in the near-wall region for turbulent flame-wall interaction

Flame–wall interaction (FWI) in premixed turbulent combustion has been analysed based on a counter-flow like configuration at the statistically stationary state. For the present configuration, the two FWI sub-zones, i.e the influence zone and the quenching zone, can be identified from the DNS results. Detailed analysis of the important quantities, such as the flame temperature, flame–wall distance, wall heat flux, flame curvature and dilatation (including the flame normal and tangential strain rates), and some orientation relations between the flame normal and the principal strain rate directions, have been reported, together with the physical explanations. All these statistical results are determined by the relative strengths of the wall heat flux, thermal expansion and the flame–turbulence interaction.

Regional myocardial motion in patients with mild cognitive impairment: a pilot study

BackgroundCardiovascular disease (CVD) is a risk factor for cognitive impairment in the elderly. Manifestations of subclinical CVDs can be found in patients with cognitive impairment. The aim of the present study was to test the hypothesis that patients with mild cognitive impairment (MCI) have different magnetic resonance imaging (MRI)-derived regional myocardial motion indices compared with healthy controls.MethodsEleven MCI patients (age, 65.5 years ±5.9; range, 55–81 years old) and 11 sex−/age-matched healthy volunteers were enrolled. All of the participants underwent a head MRI and cardiac MRI. Global cortical atrophy (GCA) was graded on the head MRI. The left ventricular ejection fraction (LVEF) and regional strain, strain rate, displacement and velocity were measured on cine images. The GCA scores, global cardiac function and regional myocardial motion indices were compared between MCI patients and healthy controls using the t-test.ResultsMCI patients had a higher GCA score than healthy controls (p = 0.048). However, there was no significant difference in LVEF between MCI patients and controls. Compared to healthy controls, MCI patients had a lower peak radial strain (29.1% ± 24.1% vs. 46.4% ± 43.4%, p < 0.001), lower peak diastolic radial strain rate (3.2 ± 2.4 s− 1 vs. 6.0 ± 3.0 s− 1, p < 0.001), lower peak diastolic circumferential strain rate (2.5 ± 2.1 s− 1 vs. 3.2 ± 2.1 s− 1, p = 0.002), lower peak systolic radial displacement (4.2 ± 2.2 mm vs. 5.2 ± 3.3 mm, p = 0.002), lower peak diastolic radial velocity (31 ± 18 mm/s vs. 45 ± 33 mm/s, p < 0.001), and lower peak diastolic circumferential velocity (178 ± 124 degree/s vs. 217 ± 131 degree/s, p = 0.005).ConclusionMRI-derived regional myocardial strain, strain rate and velocity were found to be different between MCI patients and healthy controls. Regional myocardial motion indices have the potential to become novel quantitative imaging biomarkers for representing the risk of neurodegenerative disorders, such as Alzheimer’s disease (AD).

Reduction of a detailed chemical mechanism for a kerosene surrogate via RCCE-CSP

Detailed mechanisms for kerosene surrogate fuels contain hundreds of species and thousands of reactions, indicating a necessity for reduced mechanisms. In this work, we employ a framework that combines Rate-Controlled Constrained Equilibrium (RCCE) with Computational Singular Perturbation (CSP) for systematic reduction based on timescale analysis, to reduce a detailed mechanism for a jet fuel surrogate with n-dodecane, methylcyclohexane and m-xylene. Laminar non-premixed flamelets are utilised for the CSP analysis for different strain rates and therefore different scalar dissipation rate, covering the flammable region of strain rates for the surrogate fuel.Two RCCE-reduced mechanisms are developed via an RCCE-CSP methodology, one with 17 and one with 42 species, and their accuracy is assessed in a range of cases that test the performance of the reduced mechanism under both non-premixed and premixed conditions and its dynamic response. These include non-premixed flamelets with varying strain rate, laminar premixed flames for a range of equivalence ratios and pressures, flamelets ignited by an artificial pilot or by hot air, and unsteady flamelets with time-dependent strain rate.The profiles of both major and minor species, as well as important combustion characteristics such as the ignition strain rate and the laminar flame speed, are investigated. The structure of non-premixed flamelets is very well predicted, while the premixed flames are overall well predicted apart from a few deviations in certain species and an underprediction in the laminar flame speed. Apart from the large reduction in dimensionality, the reduction in computational time is also considerable (up to 19 times). As the detailed mechanism comprises 367 species and 1892 reactions, this paper presents the first application of RCCE to a mechanism of this size, as well as a comprehensive validation in a set of cases that include non-premixed and premixed laminar flames, atmospheric and elevated pressures and steady-state and dynamic response.

Fetal regional myocardial strain rate in the membranous ventricular septum: changes with gestational age and the left ventricular mass and predictive value for a complete membranous ventricular septum (without defect).

To describe the fetal regional myocardial strain rate in the membranous ventricular septum across gestation and to determine their predictive value for a complete membranous ventricular septum (without defect) after delivery. In 1150 fetuses, the peak systolic strain rate (SRs), peak early diastolic strain rate (SRe) and peak late diastolic strain rate (SRa) in the membranous ventricular septum were measured at four time points across gestation (18-20, 24-26, 30-32 and 36-38weeks). The integrity of the interventricular septum was examined at 12weeks' postnatal age. The correlations between myocardial strain rates and gestational age as well as fetal left ventricular mass were analyzed, and the performance of myocardial strain rates in predicting a complete membranous ventricular septum was deducted. Strain rate absolute values in the membranous ventricular septum all increased across gestation. They all significantly correlated with gestational age and left ventricular mass. At 24weeks during pregnancy, the areas under the receiver operating characteristics curve (AUC) for SRe and SRa were all > 0.72 (p < 0.05) in predicting a complete membranous ventricular septum, while the AUC for SRs was only 0.55. The sensitivity, specificity and accuracy of the cut off value (> 1.53s-1) for SRe was 62.5, 85.7 and 73.3%, respectively, and the sensitivity, specificity and accuracy of the cut off value (> 1.51s-1) for SRa was 75.2, 71.9 and 73.8%, respectively. The changes of myocardial strain rates in the membranous ventricular septum across gestation maybe can be used to predict a complete membranous ventricular septum after delivery.

Translational and rotational motions of small solid particles in a spatially developing turbulent boundary layer with heat transfer

Direct numerical simulations have been performed to investigate the translational and rotational motions of small solid particles in a spatially developing turbulent boundary layer with heat transfer and two-way coupling, using the Eulerian-Lagrangian point-particle approach. The particles are assumed to be smaller than the Kolmogorov length scale in the dilute gas-solid flow. The simulation results show that the motion of particles is affected by particle inertia, particle preferential concentration and two-way coupling. The mean particle angular velocity is slightly larger than the fluid one in the buffer layer since the small heavy particles preferentially accumulate in regions of high strain rate, whereas the particles rotate slower than the surrounding fluid in the close vicinity of the wall due to their high rotational inertia. In the streamwise direction, the fluid spin intensity exceeds the corresponding particle spin intensity, as a consequence of particle preferential concentration in regions of low streamwise fluid vorticity; while the opposite is true in the wall-normal and spanwise directions. In addition, the differences in the temperature, linear and angular velocities between different inertial particles can be explained in terms of the two-way interactions between dispersed particles and continuous fluid.

Flow Behavior Characteristics and Processing Map of Fe-6.5wt. %Si Alloys during Hot Compression

The flow behavior of Fe-6.5wt. %Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s−1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and work hardening rate increased with the decrease of temperature and the increase of strain rate. The activation energy under all the deformation conditions was calculated to be 410 kJ/mol. The constitutive equation with hyperbolic sine function and Zener–Hollomon parameter was developed. The peak stress, critical stress, and steady-state stress could be represented as σ = A + Bln(Z/A). Dynamic recrystallization occurred under the deformation conditions where the values of Z were lower than 1020. Processing maps were established to optimize the processing parameters. The power dissipation efficiency decreased in the high temperature and low strain rate region, increased in the high temperature and high strain rate region, and remained unchanged in other regions with the increase of true strain. Furthermore, the unstable area expanded. The true strain of 0.7 was the optimum reduction according to the processing map. Based on the analysis of surface quality, microstructures, and ordered structures, the optimized processing parameters for the Fe-6.5wt. %Si alloys were the temperature and strain rate of higher than 900 °C and 0.01–10 s−1, respectively, or 800–900 °C and lower than 0.4 s−1, respectively.

Earthquake Potential in California‐Nevada Implied by Correlation of Strain Rate and Seismicity

AbstractRock mechanics studies and dynamic earthquake simulations show that patterns of seismicity evolve with time through (1) accumulation phase, (2) localization phase, and (3) rupture phase. We observe a similar pattern of changes in seismicity during the past century across California and Nevada. To quantify these changes, we correlate GPS strain rates with seismicity. Earthquakes of M &gt; 6.5 are collocated with regions of highest strain rates. By contrast, smaller magnitude earthquakes of M ≥ 4 show clear spatiotemporal changes. From 1933 to the late 1980s, earthquakes of M ≥ 4 were more diffused and broadly distributed in both high and low strain rate regions (accumulation phase). From the late 1980s to 2016, earthquakes were more concentrated within the high strain rate areas focused on the major fault strands (localization phase). In the same time period, the rate of M &gt; 6.5 events also increased significantly in the high strain rate areas. The strong correlation between current strain rate and the later period of seismicity indicates that seismicity is closely related to the strain rate. The spatial patterns suggest that before the late 1980s, the strain rate field was also broadly distributed because of the stress shadows from previous large earthquakes. As the deformation field evolved out of the shadow in the late 1980s, strain has refocused on the major fault systems and we are entering a period of increased risk for large earthquakes in California.

Processing Map and Hot Deformation Behavior of Mo-Nb Single Crystals

The processing map of Mo-Nb single crystals was established on the base of Prasad instability. The hot deformation behavior of Mo-Nb single crystals has been characterized through stress-strain curves and processing map in the temperature range of 1100∼1300 °C and strain rate range of 0.001∼10 s−1. The results indicate that the flow stress is affected significantly by deformation temperature and strain rate during the hot deformation of Mo-Nb single crystals. Based on the processing map, the optimum condition for hot deformation of Mo-Nb single crystals is in the region of high temperatures (>1190 °C) and high strain rates (>3.16 s−1). Microstructure observation of deformed specimens at different deforming conditions shows that lots of orthogonal cracks, which result from the movement of dislocations along with the glide planes, are observed in specimens deformed at 1100 °C/0.01 s−1 and 1150 °C/10 s−1. Less cracks can be observed in specimens deformed at 1250 °C/0.01 s−1, and few cracks are found in specimens deformed at 1300 °C/10 s−1. The XRD result shows that the specimen deformed at 1300 °C/10 s−1 retains single crystal structure, indicating that the specimen does not undergo instability of flow during hot deformation, which are in good agreement with the results of Mo-Nb single crystals predicted from processing map.

Investigating the creep properties of asphaltic concrete containing nano-silica

This study was aimed at investigating the creep behaviour of a typical asphalt concrete containing different percentages of nano-silica. The penetration grade of 60/70 asphalt cement was modified with different percentages of nano-silica (i.e., 1, 3 and 5%, by the weight) and was used for making the asphalt concrete specimens. The asphalt concrete specimens were subjected to dynamic creep tests. Dynamic creep tests were conducted at different stress levels and temperatures. A three-stage model, developed was fitted to the dynamic creep test results to capture the primary, secondary and the tertiary creep regions, and calculate the flow number and the steady-state strain rate in the secondary creep region. The results showed that, the flow number increased, and the steady-state strain rate decreased with increasing nano-silica content, indicating the increase of resistance against permanent deformation.

Low and high cycle fatigue of heat resistant steels and nickel based alloys in hydrogen for gas, steam turbines and generators applications

It has been established that, at some region of hydrogen pressure and strain rate exists a maximum influence of hydrogen on the plasticity, low cycle fatigue and cyclic crack resistance of Ni-Co alloys and high nitrogen steels. The drop of plasticity of the dispersion-hardening materials within the temperature range of intense phase transformations is caused by the localization of strains on the grain boundaries due to the intense redistribution of alloying elements in the boundary regions. Moreover, the increase in plasticity observed at higher temperatures is caused both by partial coagulation of hardening phases and possible dissolution of small amounts of finely divided precipitations. The effect hydrogen on short-term strength and plasticity, high- and low-cycle durability of 15Cr12Ni2MoNMoWNb martensitic steel, 10Cr15Ni27Ti3W2BMo austenitic dispersion-hardened steel, heat resistant 3,5NiCrMoV rotor steel, 04Kh16Ni56Nb5Mo5TiAl and 05Kh19Ni55Nb2Mo9Al Ni-base superalloys in range of pressures 0–30 MPa and temperatures 293–1073 K was investigated. In the case of 15Cr12Ni2MoNMoWNb steel and 04Kh16Ni56Nb5Mo5TiAl alloy the dependence of low-cycle durability (N) and characteristics of plasticity (δ and φ) on the hydrogen pressure consists of two regions. In the first region (low pressures), the N, δ and φ abruptly drops, and in the second, the negative action of hydrogen becomes stable or decrease negligibility.

Experiment and finite element analysis of U-profile subjected to dynamic loading

The presented study deals with the FEM simulation of dynamic behaviour of U-profile crash under three point bent loading conditions verified by experimental investigations. The material ductile damage behaviour under wide strain rate region covering 0.001 – 1 000 s-1 was experimentally determined with the use of standard and micro tensile tests (M-TT). DIC systems were used for strain field measurements under quasi-static and dynamic loading conditions. Based on these experimental data, material model considering ductile damage was established in Abaqus/Explicit code. Additionally, also metallographic investigations were performed for the fracture behaviour description.

Effects of microstructure on the dynamic strain aging of ferriticpearlitic steels at high strain rates

This paper presents an experimental study of the effects of dynamic strain aging on the mechanical behavior of selected high carbon and chromium-manganese steels in dynamic loading condition. In ferritic-pearlitic steels, the dynamic strain aging is typically caused by carbon, nitrogen, and possibly some other small solute atoms. Therefore, the thermomechanical treatments affect strongly how strong the dynamic strain aging effect is and at what temperature and strain rate regions the maximum effect is observed. In this work, we present results of the high temperature dynamic compression tests carried out for two different ferritic-pearlitic steels, 16MnCr5 and C60, that were heat treated to produce different microstructure variants of these standard alloys. The microstructures were analyzed using electron microscopy, and the materials were tested with the Split Hopkinson Pressure Bar device at three different strain rates at temperatures ranging from room temperature up to 680 °C to study the effect of the heat treatments and the resulting microstructures on the dynamic behavior of the steels and the dynamic strain aging effect. The results indicate that for both steels, a coarse grain structure has the strongest dynamic strain aging sensitivity at small plastic strains. However, at higher strains, all microstructures show similar strain aging sensitivities.

Evaluation of hot deformation characteristics in modified AA5052 using processing map and activation energy map under deformation heating

The hot workability and deformation characteristics of modified AA5052 were evaluated by hot torsion testing in the temperature range 573–773 K and at strain rates of 0.1–10 s−1. Flow curves obtained from the hot torsion test were corrected considering deformation heating during hot deformation. The processing map and activation energy map were developed from this compensated flow data to propose the optimum processing conditions and to reveal the influence of hot processing parameters on microstructure evolution. The validities of the corrected processing map and activation energy map were also analyzed. The processing map showed that this alloy had a wide flow instability region at all working temperatures; in contrast, maximum power dissipation efficiency was shown at the highest and lowest strain rates in the large temperature region (above 723 K). The activation energy for hot working varied from 28 to 497 kJ mol−1 and showed a tendency for relatively small activation energy where higher power dissipation efficiency was observed. Microstructural observations indicated that dynamic recovery considerably contributed to a higher power dissipation efficiency and lower level of activation energy. On the other hand, the main reason for flow instability was attributed to the evolution of deformation bands or liquid phases. Thus, the hot deformation characteristics of the alloy proposed from the processing map and activation energy map were consistent with the deformed microstructure.

Abnormal biventricular performance in asymptomatic adolescents late after repaired Tetralogy of Fallot: Combined two-dimensional speckle tracking and three-dimensional echocardiography study

BackgroundThe aim of this prospective study was to assess biventricular performance in asymptomatic adolescents with repaired tetralogy of Fallot (TOF) using 2D speckle tracking and real time 3D echocardiography simultaneously. MethodsWe studied 31 patients with repaired TOF (M/F: 22/9, age: 16.1 ± 6.1 yrs) who had history of cardiac surgery with mean follow-up duration of 12.8 years, and 32 age- and sex-matched normal individuals (M/F: 23/9, age: 16.6 ± 5.1 yrs). All subjects underwent speckle tracking and 3D echocardiography, electrocardiogram, treadmill, and blood sampling for measurement of brain natriuretic peptide (BNP). ResultsCompared to the control group, the TOF group had higher BNP level (31.8 ± 21.4 vs 14.1 ± 12.4 pg/ml, p < 0.01), lower peak oxygen consumption (8.4 ± 1.7 vs 9.9 ± 1.6 ml/kg/min, p < 0.05), and longer QRS duration (126 ± 30 vs 82 ± 9 ms, p < 0.01). Patients with repaired TOF had significantly impaired right ventricle (RV) global and all six regional longitudinal strain and strain rate than normal controls. Left ventricle (LV) global and mainly apical regional longitudinal strain and strain rate were reduced in patients with repaired TOF. There was a significant correlation of global longitudinal strain (r = 0.456, p = 0.01) and global time to peak longitudinal strain (r = 0.484, p < 0.01) between LV and RV in patients with repaired TOF. In terms of 3D echo cardiographic volume data, patients with repaired TOF had lower LV stroke volume index (p < 0.05), but higher RV end diastolic volume index (p < 0.01), RV end systolic volume index (p < 0.01), RV stroke volume index (p < 0.01), and pulmonary regurgitation fraction (p < 0.01) than normal controls. ConclusionOur results suggest asymptomatic adolescents with repaired TOF had abnormal biventricular myocardial performance, as demonstrated by combined 2D speckle-tracking and 3D echocardiography. The implications of these findings for management of adolescents late after repaired TOF remain to be determined.

Effects of Turbulence on Ignition of Methane–Air and n-Heptane–Air Fully Premixed Mixtures

ABSTRACTWe performed direct numerical simulations (DNS) for the two-dimensional (2D) turbulent ignition of ultra-lean methane–air and n-heptane–air mixtures with a high exhaust gas recirculation (EGR) rate at high pressure to determine the ignition criteria and ignition delay time. We defined an initial high-temperature region as an ignition kernel and conducted one-dimensional preliminary DNS to determine the ignition criteria in terms of the ignition source energy and the thermal conduction from the ignition kernel during the induction period. Additionally, we analyzed the 2D DNS results to clarify the influence of the turbulent strain rate on the ignition delay time and the mechanism by which the turbulence influences the establishment of the ignition kernel. We observed that the distribution of eddies and the strain rate in the high-temperature region influences the success or failure of the ignition process and, therefore, the ignition delay time. The ignition delay time increases proportionally to the square of strain rate averaged in the high concentration region of the intermediate species during the induction period. This suggests that the ignition in a turbulent field is based on the balance between the influence of a locally averaged strain rate in the preheating region and the chemical (flame) time scale. Based on these observations, a simple model for the ignition delay time was constructed based on the mean strain rate in the high concentration region of the intermediate species during the induction period. The strain rate averaged in the high concentration region of the intermediate species was normalized by using the laminar burning velocity and the laminar thermal flame thickness. Additionally, the ignition delay time was normalized by the ignition delay time of the corresponding laminar case, yielding the same ignition model/criterion for both examined fuels, which could be extended to other mixtures.

Forging property, processing map, and mesoscale microstructural evolution modeling of a Ti-17 alloy with a lamellar (α+β) starting microstructure

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10−3 s−1 to 1 s−1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, Tβ (880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above Tβ, continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region.

The impact of streamwise convex curvature on the supersonic turbulent boundary layer

With an inflow Mach number of 2.95, the isolated impacts of the convex curvature and the streamwise favorable pressure gradient on the supersonic turbulent boundary layer are experimentally investigated by employing particle image velocimetry. An experiment on the convex turbulent boundary layer with a zero streamwise pressure gradient is carefully arranged to investigate the impact of the streamline curvature. The results are compared with the favorable-pressure-gradient case (with pressure gradient parameter β = −0.60). For both of the zero-pressure-gradient and the favorable-pressure-gradient convex boundary layers, the log law is found to be well preserved in the streamwise velocity profile with inner scaling. The streamline convex curvature and the streamwise favorable pressure gradient are found to have similar impacts on the distribution of mean streamwise velocity. They both weaken the boundary layer’s wake strength, as well as the principal strain rate in the near wall region. While both of the convex streamline curvature and the favorable pressure gradient are observed to dampen the streamwise turbulent fluctuation, their effects on the normal fluctuation are opposite. The convex curvature reinforces the normal fluctuation, and its strengthening effect is much stronger than the relaxation effect of the favorable pressure gradient. Retrograde vortices are notably weakened by the favorable pressure gradient, which contributes to the relaxation of turbulence. The impacts of the streamline convex curvature and the streamwise favorable pressure gradient are more notable in the outer layer, while in the near wall region their contributions are weakened.

A numerical solution for the axisymmetric flow of a plastic tube on a rigid fibre

In the case of rigid perfectly plastic material the strain rate intensity factor appears in the vicinity of maximum friction surfaces. This factor controls the magnitude of the equivalent strain rate in a narrow region near the surface. On the other hand, the equivalent strain rate controls the evolution of material surfaces. Therefore, the existence of the strain rate intensity factor in theoretical solutions are in qualitative agreement with experimental observations that demonstrate that a narrow layer with drastically modified microstructure is often generated in the vicinity of frictional interfaces in machining and deformation processes. In order to use the strain rate intensity factor for describing such material behaviour, it is necessary to develop an efficient numerical method for calculating the strain rate intensity factor. Since this factor is involved in a singular series expansion, it is evident that commercial finite element packages are not capable of calculating the strain rate intensity factor. In the case of Tresca’s solids the theory of characteristics can be used for the development of the method in question. This paper presents a first step in this direction

9. Role of strain rate imaging in the detection of significant coronary artery stenosis

Clinical Research. Oral Presentation. Nowadays, there are many methods for detection of significant coronary artery stenosis and myocardial ischemia either by imaging the coronaries or detecting myocardial perfusion abnormalities, but the majority of these methods needs either stress imaging or injection of contrast especially in patients with stable coronary artery disease (SCAD) where there is no resting electrocardiogram (ECG) changes or resting echocardiography wall motion abnormalities. With the development of tissue Doppler imaging, new methods like strain and strain rate imaging were developed followed by the development of the speckle tracking imaging. Strain and strain rate imaging can detect myocardial deformation which is the basis of myocardial function, thus with impaired myocardial perfusion the amount and rate of deformation decreases. Thirty patients with SCAD and significant single vessel left anterior descending (LAD) coronary artery stenosis, diagnosed by invasive coronary angiography, undergoing elective percutaneous coronary intervention (PCI) of the LAD lesion with no significant lesions in the other coronary vessels, left circumflex (LCX) and right coronary artery (RCA). Patients with diabetes, regional wall motion and reduced left ventricular systolic function were excluded. Regional systolic strain and strain rate was measured in the ischemic LAD segments which are six, apicoseptal, mid anteroseptal, basal anteroseptal, apicoanterior, mid anterior and basal anterior, and measured in the non-ischemic LCX and RCA segments, before elective PCI of LAD and three months later. By comparing the strain and strain rate of the ischemic segments before and after PCI there was significant improvement of the systolic strain while there were non-significant changes in the non-ischemic segments. Tissue Doppler strain and strain rate imaging during resting echocardiography can be used to detect regional myocardial ischemia in patients with significant coronary artery stenosis.

Correlation of RV Strain Imaging Parameters with Cardiac MRI Parameters in the Assessment of RV Function Among Repaired Tetralogy of Fallot Patients

Background: Strain imaging offers an alternative non-invasive method to quantify right ventricular (RV) function. This study aims to utilize strain imaging in the assessment of RV function among repaired tetralogy of Fallot patients in order to determine clinical RV dysfunction. Methodology: This is a prospective cross-sectional study done at the Philippine Heart Center. Cardiac magnetic resonance imaging (CMR) and echocardiographic strain imaging were done on the same day for each study participant. Statistical comparison was performed. Sensitivity and specificity curves (using CMR-derived RV ejection fraction [RVEF] as the reference test) was used to determine optimal cut off values for global and regional longitudinal systolic strain and strain rate. Intra-observer variability was also determined. Results: Twenty-two participants were included. There was significant inverse moderate correlation between CMR-derived RVEF and RV free wall (RVFW) mid-segment strain (r=–0.42; p=0.05) and global longitudinal strain (r= 0.62; p=0.002). The determined cut-off for RV dysfunction for RV global longitudinal strain was –20.66%, which showed a sensitivity of 88.83%, specificity of 100%, positive predictive value (PPV) of 100% and negative predictive value (NPV) of 88.83%. RVFW mid-segment strain determined cut-off was –16.25, which showed a sensitivity of 83.33%, specificity of 100%, PPV of 100% and NPV of 83.33%. Conclusion: Strain imaging is an easy, feasible and reproducible parameter in two-dimensional echocardiography that can be a good screening tool, with high sensitivity and specificity for detecting RV dysfunction among patients with repaired tetralogy of Fallot. Keywords: tetralogy of Fallot, right ventricular dysfunction, strain imaging.