Assessment of Regional Myocardial Function in Patients with Hypertrophic Cardiomyopathy by Tissue Strain Imaging

The value of tissue strain imaging （SI） in regional myocardial systolic and diastolic func tion assessment was studied. In 18 patients with nonobstructive hypertrophic cardiomyopathy （HCM） and 20 age-matched healthy subjects, regional myocardial longitudinal peak systolic strain in eject time （represented by εet） was measured at basal, mid and apical segments of septal, lateral and posterior walls of the left ventricle （LV） and compared between groups, εet had no significant difference between segments in control group （P〉0.05）, which displayed a decreasing trend from basal segments to apical ones. εet in the HCM group was significantly decreased （P（0. 05） as compared with that in the healthy group. In the HCM group, εet in the midseptum was significantly less than at the basal and apical septum, and was also less than at the rest LV walls in the same group （P〉0.01）. The systolic reversed εet was noticed in 35% of the hypertrophic segments in HCM group. Significantly negative correlation existed between the absolute value of εet and wall thickness in the midseptum （r= -0.83）. The post-systolic strain（PSS） segment number the and amplitudes in healthy group were significantly less than those in HCM group （P〈0.05）. Both regional myocardial systolic and diastolic functions were impaired in hypertrophic or non-hypertrophic segments in patients with the HCM, especially in hypertrophic segments. Strain imaging technique is a sensitive and accura tool in myocardial dysfunction assessment.

Assessment of Left Ventricular Longitudinal Regional Myocardial Systolic Function by Strain Imaging Echocardiography in Patients with Hypertrophic Cardiomyopathy

To assess the left ventricular longitudinal regional myocardial systolic function by strain imaging （SI） echocardiography and to study the relationship between regional myocardial systolic function and left ventricular structure in patients with hypertrophic cardiomyopathy （HCM）. S1 echocardiography were performed in 18 patients with HCM and 17 healthy subjects. For each wall, regional myocardial systolic strain was analyzed at the basal, mid, and apical level respectively. And the peak systolic strain was measured. Our results showed that the patients with HCM had reduced peak systolic strain at almost each segment of different walls when compared with healthy subjects. There was significant correlation between the mid-septum peak systolic strain and the thickness of IVS, so was the correlation between the mid-septum peak systolic strain and the IVS to LVPW thickness ratio. This study demonstrated that the left ventricular longitudinal regional myocardial systolic function was abnormal in HCM, and this kind of abnormalities existed extensively in hypertrophic and non-hypertrophic cardiac segments. The degrees of left ventricle hypertrophy and asymmetry are related to the myocardial regional systolic function in HCM.

Magnetic resonance imaging characterization of circumferential and longitudinal strain under various coronary interventions in swine

AIM:To compare the acute changes in circumferential and longitudinal strain after exposing a coronary artery to various interventions in swine.METHODS:Percutaneous balloon angioplasty catheter was guided to location aid device(LAD)under X-ray fluoroscopy to create different patterns of ischemic insults.Pigs(n=32)were equally divided into 4 groups:controls,90 min LAD occlusion/reperfusion,LAD microembolization,and combined LAD occlusion/microembolization/reperfusion.Three days after interventions,cine,tagged and viability magnetic resonance imaging(MRI)were acquired to measure and compare left and right circumferential strain,longitudinal strain and myocardial viability,respectively.Measurements were obtained using HARP and semi-automated threshold method and statistically analyzed using unpaired t-test.Myocardial and vascular damage was characterized microscopically.RESULTS:Coronary microemboli caused greater impairment in l left ventricular(LV)circumferential strain and dyssynchrony than LAD occlusion/reperfusion despite the significant difference in the extent of myocardial damage.Microemboli also caused significant decrease in peak systolic strain rate of remote myocardium and LV dyssynchrony.Cine MRI demonstrated the interaction between LV and right ventricular(RV)at 3 d after interventions.Compensatory increase in RV free wall longitudinal strain was seen in response to all interventions.Viability MRI,histochemical staining and microscopy revealed different patterns of myocardial damage and microvascular obstruction.CONCLUSION:Cine MRI revealed subtle changes in LV strain caused by various ischemic insults.It also demonstrated the interaction between the right and left ventricles after coronary interventions.Coronary microemboli with and without acute myocardial infarction(AMI)cause complex myocardial injury and ventricular dysfunction that is not replicated in solely AMI.

Fano Resonance Enabled Infrared Nano-Imaging of Local Strain in Bilayer Graphene

Detection of local strain at the nanometer scale with high sensitivity remains challenging.Here we report near-field infrared nano-imaging of local strains in bilayer graphene by probing strain-induced shifts of phonon frequency.As a non-polar crystal,intrinsic bilayer graphene possesses little infrared response at its transverse optical phonon frequency.The reported optical detection of local strain is enabled by applying a vertical electrical field that breaks the symmetry of the two graphene layers and introduces finite electrical dipole moment to graphene phonon.The activated phonon further interacts with continuum electronic transitions,and generates a strong Fano resonance.The resulted Fano resonance features a very sharp near-field infrared scattering peak,which leads to an extraordinary sensitivity of-0.002%for the strain detection.Our results demonstrate the first nano-scale near-field Fano resonance,provide a new way to probe local strains with high sensitivity in non-polar crystals,and open exciting possibilities for studying strain-induced rich phenomena.

Non-invasive assessment of hepatic fibrosis by tissue strain imaging in chronic hepatitis C patients

The development of fibrosis in hepatitis C patients is associated with increased rates of liver cancer. Assessing hepatic fibrosis during interferon treatment for chronic hepatitis C is thus an important factor in treatment planning. Complications such as bleeding may occur in association with liver biopsy and there are also some reports of sampling error [1,2]. In recent years, however, a number of studies looking at noninvasive means of assessing hepatic fibrosis have appeared in the literature [3-5]. The present study was conducted to determine whether it would be possible to apply an easily performed technique of myocardial examination to hepatic fibrosis. We have already documented our findings for strain rate imaging used to differentiate the normal condition, chronic hepatitis and cirrhosis of the liver identified by diagnostic imaging and haematology data [6]. In this study, patients identified by liver biopsy were investigated, and a comparative investigation with several fibrosis markers was carried out.

Diagnostic Accuracy of Strain Imaging of the Left Ventricle in Detection of Obstructive Coronary Artery Disease

Background: Speckle tracking echocardiography using average global strain and strain rate (SR) parameters for early detection of high risk patients with coronary artery disease (CAD) has gained a substantial clinical interest. Objective: Assessment of the diagnostic accuracy of strain imaging of the left ventricle in detection of obstructive coronary artery disease. Methods: One hundred patients were enrolled. They were divided into 3 groups: Group I (n = 40 patients) presented with ST segment elevation myocardial infarction (STEMI), Group II (n = 40 patients) presented with non-ST segment elevation myocardial infarction (NSTEMI) or unstable angina (UA) and Group III (n = 20 patients) with normal coronary angiography served as a control group. All patients were subjected to 2D speckle tracking echocardiography (2D STE) to assess LV longitudinal strain and strain rate (SR). Sensitivity, specificity and diagnostic accuracy of 2D STE in prediction of CAD and its severity using Gensini score were assessed. Results: The mean age for Group I, II and III was 52.20 ± 11.83, 51.97 ± 14.53 and 52.75 ± 10.75 respectively. LV average global systolic strain (AGS) was significantly lower in group I and II when compared to group III. AGS and average global systolic SR showed significant direct correlation with Gensini score. The diagnostic accuracy of 2D STE in prediction of significant LAD stenosis was 92.5%, and it was 89.5% in prediction of 3 vessels CAD. Conclusion: Strain imaging using 2D STE can predict the territory and severity of CAD with high diagnostic accuracy and can be used as a simple noninvasive diagnostic tool to identify high risk CAD patients.

Quantification of Regional Left Ventricular Systolic Dysfunction in Patients With Coronary Artery Disease by Strain Rate Imaging

Objectives To detect and compare the systolic strain rate (SR) and strain in the infarct and ischemic myocardium by strain rate imaging (SRI), in order to explore the clinical value of SRI in evaluating regional left ventricular systolic dysfunction. Methods Patients with coronary artery disease were divided into angina pectoris (11 cases) and myocardial infarction (21 cases) groups. Twenty age-matched normal subjects served as the control group. Septal, lateral, anterior, inferior, anteroseptal and posterior walls of the left ventricle were respectively scanned using color tissue Doppler imaging (TDI). Then SR and strain curves were derived from TDI for basal, middle and apical segments of each wall. SRI parameters were: Systolic SR (SRsys), systolic strain (εsys) and maximum strain (εmax). Results Compared with normal segments, SRsys, εsys and εmax decreased significantly in the infarct and ischemic segments (P<0.01). Compared with ischemic segments, SRsys, εsys and εmax decreased significantly in the infarct segments (P<0.05). Conclusions SRsys, εsys and εmax measured by SRI can be used to quantitatively analyze regional left ventricular systolic dysfunction in patients with coronary artery disease, and aid in differentiating infarct from ischemic myocardium.

QUANTIFICATION OF RIGHT VENTRICULAR FUNCTION IN ATRIAL SEPTAL DEFECT USING ULTRASOUND- BASED STRAIN RATE IMAGING

Objective To study the validation of ultrasound-based strain rate imaging in the quantitative assessment of right ventricular （RV） function in atrial septal defect （ASD）. Methods Tissue Doppler images （TDI） of RV longitudinal and short axes were recorded from the apical 4-chamber view and the subcostal short-axis view in 18 normal controls, 28 children with ASD and 14 children after Amplazter closure of ASD respectively. Peak systolic velocities （ V）, peak systolic strain rates （SR）, peak systolic strains （S） at the basal segment, middle segment of RV lateral wall and the basal septum from the longitudinal axis, the middle segment of RV free waU from the short axis were quantitatively measured using QLAB^TM tissue velocity quantification software system respectively. Peak dp/ dt from the RV isovolumic contraction determined during the right cardiac catheterization in 28 ASD patients was used as the gold standard of RV contractility. Peak systolic indices were compared against max dp/dt by linear correlation, Results Peak systolic indices at the basal and middle segments of RV lateral wall from the longitudiual axis increased significantly in 28 ASD patients. Peak systolic indices at the basal septum also increased in patient group, but not significantly. Significant decreases in peak systolic indices at the basal and middle segments of RV lateral wall were observed after the Amplatzer closure in 14 ASD patients. There was no significant difference at the middle segment of RV free wall from the short axis between patient group and normal control. A strong correlation was found between max dp/dt and peak systolic indices at the basal and middle segments of RV lateral wal l （ P 〈 0. 05 ）. Conclusion Ultrasound-based strain rate imaging can assess quantitatively RVfunction in CHD. Peak systolic strains determined at the basal and middle segments of RV lateral wall are strong noninvasive indices of RV contractility.

Specimen aspect ratio and progressive field strain development of sandstone under uniaxial compression by three-dimensional digital image correlation

The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in specimens with different aspect ratios was also examined.Peak stress,post-peak portion of stress-strain,brittleness,characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio.Strain patterns of the rocks were obtained by applying three-dimensional(3D) digital image correlation(DIC) technique.Unlike conventional strain measurement using strain gauges attached to specimen,3D DIC allowed not only measuring large strains,but more importantly,mapping the development of field strain throughout the compression test,i.e.in pre-and post-peak regimes.Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime.However,in post-peak regime,strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone.The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation.Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.

Assessment of Right Ventricular Free Wall Longitudinal Myocardial Deformation Using Speckle Tracking Imaging in Normal Subjects

To assess fight ventficular free wall longitudinal myocardium deformation and examine the changes with normal age by speckle tracking imaging （STI）, myocardial systolic peak strain （ε）, systolic peak strain rate （SRs）, early diastolic peak strain rate （SRe）, late diastolic peak strain rate （SRa）, the ratio of SRe/SRa were measured in the basal, middle and apical segments of right ventficular free wall in 75 healthy volunteers （age range： 21-71 y） by STI from the apical 4-chamber view. RV longitudinal strain and strain rate were highest in the basal segment of the free wall. Older subjects had lower early diastolic strain rate （SRe） than younger subjects, but they had higher late diastolic strain rate （SRa）. A negative correlation between age and the ratio of SRe/SRa was found in all RV free wall segments （r=-4）.466 - -0.614, P〈0.01）. It is concluded that RV diastolic strain rate changes with age and STI can be used for the study of RV myocardial deformation.

Assessment of Left Ventricular Radial Deformation by Speckle Tracking Imaging

The left ventricular radial strain in the inner and outer layers was evaluated by using two-dimensional speckle tracking imaging （2DS）. Twenty-five piglets were studied. The short axis views were acquired. Peak systolic radial strain was measured from 6 circumferential points related to 6 standard segments in the inner and outer layers respectively using 2DS methods. The peak positive first derivative （dp/dt） of left ventricular pressure was compared to the radial strain from 2DS. The inner band showed higher peak radial strain values as compared to the outer band at all of the segments （P〈0.0001）, but the differences had significance just in anteroseptal, posterior, inferior and septal segments （P〈0.05）. Good correlation could be found between radial strain of inner and outer layers and peak dp/dt （P〈0.001）. These preliminary results showed that the degree of local deformation or wall thickening of the ventricular wall in its inner layer was more obvious than its outer layer. It is suggested that the 2DS technique is useful and sensitive for better understanding the regional and global myocar- dial motion and its relationship to the complex architecture of myocardium.

Assessment of digital image correlation method in determining large scale cemented rockfill strains

A conventional contact method(using linear transducers)and a non-contact method are deployed to measure the axial and lateral deformations of large scale cylindrical cemented rockfill specimens.Experimental works incorporating two pinhole cameras to create one stereovision by digital image correlation shows that the non-contact method is as reliable for testing large cylindrical specimens as measurements done by using linear variable displacement transformer and string potentiometer.Considering this particular large specimen,the experiment resulted in the acceptable mean difference between lateral strain using both methods is 5.1 percent,and 14.5 percent for the axial strain.This occurrence is inevitable due to the heterogeneity of the concrete system and the placement of the monitoring point in digital image correlation method,although the comparison of stress-strain relationship in both methods still indicates a conformity.Based on the results of the present experiments,the authors recommend the noncontact method for a detailed investigation of the material behavior during the uniaxial compressive strength tests.Full field strain measurement enables this digital method to examine local strains near cracks at any point,a very useful tool for studying material deformation behavior.

Strain field investigation of limestone specimen under uniaxial compression loads using particle image velocimetry

The particle image velocimetry (PIV) method was used to investigate the full-field displacements and strains of the limestone specimen under external loads from the video images captured during the laboratory tests.The original colorful video images and experimental data were obtained from the uniaxial compression test of a limestone.To eliminate perspective errors and lens distortion,the camera was placed normal to the rock specimen exposure.After converted into a readable format of frame images,these videos were transformed into the responding grayscale images,and the frame images were then extracted.The full-field displacement field was obtained by using the PIV technique,and interpolated in the sub-pixel locations.The displacement was measured in the plane of the image and inferred from two consecutive images.The local displacement vectors were calculated for small sub-windows of the images by means of cross-correlation.The video images were interrogated in a multi-pass way,starting off with 64×64 images,ending with 16×16 images after 6 iterations,and using 75% overlap of the sub-windows.In order to remove spurious vectors,the displacements were filtered using four filters:signal-to-noise ratio filter,peak height filter,global filter and local filter.The cubic interpolation was utilized if the displacements without a number were encountered.The full-field strain was then obtained using the local least square method from the discrete displacements.The strain change with time at different locations was also investigated.It is found that the normal strains are dependant on the locations and the crack distributions.Between 1.0 and 5.0 s prior to the specimen failure,normal strains increase rapidly at many locations,while a stable status appears at some locations.When the specimen is in a failure status,a large rotation occurs and it increases in the inverse direction.The strain concentration bands do not completely develop into the large cracks,and meso-cracks are not visible in some bands.The techniques presented here may improve the traditional measurement of the strain field,and may provide a lot of valuable information in investigating the deformation/failure mechanism of rock materials.

Cardiac functional magnetic resonance imaging at 7T:Image quality optimization and ultra-high field capabilities

BACKGROUND 7T cardiac magnetic resonance imaging(MRI)introduces several advantages,as well as some limitations,compared to lower-field imaging.The capabilities of ultra-high field(UHF)MRI have not been fully exploited in cardiac functional imaging.AIM To optimize 7T cardiac MRI functional imaging without the need for conducting B1 shimming or subject-specific tuning,which improves scan efficiency.In this study,we provide results from phantom and in vivo scans using a multi-channel transceiver modular coil.METHODS We investigated the effects of adding a dielectric pad at different locations next to the imaged region of interest on improving image quality in subjects with different body habitus.We also investigated the effects of adjusting the imaging flip angle in cine and tagging sequences on improving image quality,B1 field homogeneity,signal-to-noise ratio(SNR),blood-myocardium contrast-to-noise ratio(CNR),and tagging persistence throughout the cardiac cycle.RESULTS The results showed the capability of achieving improved image quality with high spatial resolution(0.75 mm×0.75 mm×2 mm),high temporal resolution(20 ms),and increased tagging persistence(for up to 1200 ms cardiac cycle duration)at 7T cardiac MRI after adjusting scan set-up and imaging parameters.Adjusting the imaging flip angle was essential for achieving optimal SNR and myocardium-toblood CNR.Placing a dielectric pad at the anterior left position of the chest resulted in improved B1 homogeneity compared to other positions,especially in subjects with small chest size.CONCLUSION Improved regional and global cardiac functional imaging can be achieved at 7T MRI through simple scan set-up adjustment and imaging parameter optimization,which would allow for more streamlined and efficient UHF cardiac MRI.

In-situ strain measurement and error analysis of arc welding with 2D digital image correlation

The deformation and residual stress generated by the welding process can seriously affect the use of components.As a result,it is very important to understand the evolution of stress and strain during the welding process.The strain measurement method based on digital image correlation(DIC)is an excellent method to detect welding strain and residual stress.The out-of-plane translation and out-of-plane rotation introduce errors to the two-dimensional DIC.In this paper,the causes of errors are analyzed theoretically,and the formulas of errors caused by the out-of-plane displacement and the out-of-plane rotation are derived.The out-of-plane translation experiment and the out-of-plane rotation experiment were carried out to verify the theory,and the experimental results are consistent with the theoretical analysis results.The error caused by the out-of-plane translation can be reduced by increasing the object distance;the error caused by the out-of-plane rotation is greatly affected by the rotation angle.

Measurement and evaluation of strain fields in T23 steel based on digital image correlation method

Surface strain fields of the designed compact tension(CT)specimens were investigated by digital image correlation(DIC)method.An integrative computer program was developed based on DIC algorithms to characterize the strain fields accurately and graphically.Strain distribution of the CT specimen was predicted by finite element method(FEM).Good agreement is observed between the surface strain fields measured by DIC and predicted by FEM,which reveals that the proposed method is practical and effective to determine the strain fields of CT specimens.Moreover,strain fields of the CT specimens with various compressive loads and notch diameters were studied by DIC.The experimental results can provide effective reference to usage of CT specimens in triaxial creep test by appropriately selecting specimen and experiment parameters.

Revealing the role of local shear strain partition of transformable particles in a TRIP-reinforced bulk metallic glass composite via digital image correlation

The coupling effects of the metastable austenitic phase and the amorphous matrix in a transformation-induced plasticity(TRIP)-reinforced bulk metallic glass(BMG)composite under compressive loading were investigated by employing the digital image correlation(DIC)technique.The evolution of local strain field in the crystalline phase and the amorphous matrix was directly monitored,and the contribution from the phase transformation of the metastable austenitic phase was revealed.Local shear strain was found to be effectively consumed by the displacive phase transformation of the metastable austenitic phase,which relaxed the local strain/stress concentration at the interface and thus greatly enhanced the plasticity of the TRIP-reinforced BMG composites.Our current study sheds light on in-depth understanding of the underlying deformation mechanism and the interplay between the amorphous matrix and the metastable crystalline phase during deformation,which is helpful for design of advanced BMG composites with further improved properties.

Walking with Gianluca Di Bella during the development of clinical cardiac imaging

Cardiac magnetic resonance imaging(MRI) for the diagnosis and management of many cardiac diseases has been established in clinical practice.It provides anatomic and functional information and is the most precise technique for quantification of ventricular volume,function and mass.Among cardiac MRI sequences used in clinical practice,delayed contrast enhancement is an accurate and reliable method used in the diagnosis of ischemic and nonischemic cardiomyopathies.In addition,new technology applied in echocardiographic imaging has permitted quantification of myocardial deformations with 2-dimensional strain imaging(longitudinal,circumferential and radial strain).Cardiac MRI and echocardiography therefore both play a crucial role in the diagnosis and management of cardiovascular disease.Dr.Di Bella and colleagues have defined the roles of cardiac MRI and echocardiography in many clinical and experimental settings.

Assessment of Left Ventricular Mechanical Function in Cardiac Syndrome X: Speckle Tracking Imaging Study

Objective: Early detection of LV mechanical abnormalities in patients with cardiac syndrome X (CSX) by speckle tracking echocardiography (STE). Background: Cardiac syndrome X is a triad of angina pectoris, positive stress test for myocardial ischemia and angiographically free coronary arteries. Two dimensional speckle tracking?echocardiography (2D-STE) provides a more sensitive method for evaluation of global and segmental LV function than conventional two dimensional echocardiographic parameters. Subjects and Methods: Seventy patients proved to have CSX and 20 healthy control volunteers were included with a mean age of 49.43 ± 5.92 vs. 49.40 ±6.27 years respectively with no difference regarding sex for both patients and controls. Patients with hypertension, diabetes mellitus, valvular heart disease, cardiomyopathies, inflammatory diseases, myocarditis and arrhythmias were excluded. All included individuals were subjected to complete conventional echocardiographic assessment and left ventricular global and segmental mechanical function was assessed using 2D based strain and strain rate (longitudinal, radial and circumferential) imaging. Results: There was no statistically significant difference in LV conventional echo parameters between patients and controls. However, global mean longitudinal strain was significantly lower in patients than controls (-15.05 ± 3.28 vs. -20.22 ± 2.49;p 0.001). For radial and circumferential strain stain, there was no significant changes between patients vs. controls (29.75 ± 18.26 vs. 28.09 ± 15.48;p = 0.74) and (-19.88 ± 8.63 vs. -21.93 ± 5.69;p 0.05) respectively. Conclusion: In spite of normal conventional echo parameters among patients and controls, LV longitudinal strain and strain rate by 2D speckle tracking imaging were lower in the patients denoting subclinical left ventricular mechanical dysfunction in patients with CSX.