Characterization of tissue elasticity (stiffness) and viscosity has important medical applications because these properties are closely related to pathological changes. Quantitative measurement is more suitable than qualitative measurement (i.e., mapping with a relative scale) of tissue viscoelasticity for diagnosis of diffuse diseases where abnormality is not confined to a local region and there is no normal background tissue to provide contrast. Shearwave dispersion ultrasound vibrometry (SDUV) uses shear wave propagation speed measured in tissue at multiple frequencies (typically in the range of hundreds of Hertz) to solve quantitatively for both tissue elasticity and viscosity. A shear wave is stimulated within the tissue by an ultrasound push beam and monitored by a separate ultrasound detect beam. The phase difference of the shear wave between 2 locations along its propagation path is used to calculate shear wave speed within the tissue. In vitro SDUV measurements along and across bovine striated muscle fibers show results of tissue elasticity and viscosity close to literature values. An intermittent pulse sequence is developed to allow one array transducer for both push and detect function. Feasibility of this pulse sequence is demonstrated by in vivo SDUV measurements in swine liver using a dual transducer prototype simulating the operation of a single array transducer.

Our aims were (i) to compare in vivo measurements of myocardial elasticity by shear wave dispersion ultrasound vibrometry (SDUV) with those by the conventional pressure-segment length method, and (ii) to quantify changes in myocardial viscoelasticity during systole and diastole after reperfused acute myocardial infarction. The shear elastic modulus (μ1) and viscous coefficient (μ2) of left ventricular myocardium were measured by SDUV in 10 pigs. Young’s elastic modulus was independently measured by the pressure-segment length method. Measurements made with the SDUV and pressure-segment length methods were strongly correlated. At reperfusion, μ1 and μ2 in end-diastole were increased. Less consistent changes were found during systole. In all animals, μ1 increased linearly with left ventricular pressure developed during systole. Preliminary results suggest that m1 is preload dependent. This is the first study to validate in vivo measurements of myocardial elasticity by a shear wave method. In this animal model, the alterations in myocardial viscoelasticity after a myocardial infarction were most consistently detected during diastole.

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE.

Background-In this study we evaluate the diastolic deformation of ischemic/reperfused myocardium and relate this deformation to tissue elastic properties. Methods and Results-Farm pigs were subjected to left anterior descending coronary artery occlusion followed by reperfusion to create either stunning (nϭ12) or transmural myocardial infarction (nϭ12). Ultrasound-derived radial strain rates (SR) and strain were measured in the ischemic and remote walls. Myocardial stiffness was estimated from diastolic pressure-wall thickness relationship obtained from preload alterations. At reperfusion, end-systolic strain (⑀ sys ) was significantly reduced in both stunned and infarcted walls compared with their remote walls (3Ϯ3% versus 26Ϯ2% and 1Ϯ0% versus 33Ϯ5%, respectively; PϽ0.0001) or baseline values. Diastolic passive deformation (⑀ A ) and rates of deformation during early (E SR ) and late (A SR ) diastole were comparable between stunned and remote walls (⑀ A : 7.3Ϯ1.6% versus 7.9Ϯ1.9%; E SR : Ϫ2.7Ϯ0.4 s Ϫ1 versus Ϫ2.6Ϯ0.5 s

Background: Takotsubo syndrome is an increasingly recognized cause of chest pain and occasionally of cardiogenic shock. Despite rapid improvement of the Left Ventricular Ejection Fraction (LV EF), recent registry data raises concerns about long term prognosis. We hypothesized that restoration of normal EF after acute tako-tsubo is not equivalent to full functional recovery. Methods: We prospectively recruited 52 takotsubo patients [according to the Mayo criteria plus cardiac magnetic resonance imaging (CMR) to exclude myocardial infarction] and 44 healthy controls of the same age, gender and cardiovascular co-morbidity distribution. We focused the investigation on takotsubo patients presenting with ST-elevation type ECG or malignant arrhythmias and with LV apical ballooning variant and examined a 4 months recovery end-point. Patients underwent Echocardiography assessment of LV myocardial deformation (Global longitudinal, radial and circumferential strain, LV twist, torsion, untwist, time to peak twist and untwist) and assessment of LV myocardial structure by pre and post contrast-enhanced CMR by T1 mapping acutely and at 4 months follow-up. Controls had a single time-point investigation. Data were analyzed using paired or unpaired tests, as appropriate for their distribution and corrected for multiple comparisons. Results: The patients' mean age was 66 years (range 28-87) and 92% were women. All abnormal echocardiographic indices observed acutely in takotsubo patients improved (but not necessarily normalized) at followup. Significant mechano-temporal alterations characterizing both systole (global longitudinal strain, apical circumferential strain, both p<0.01; left ventricular twist, twist rate and torsion, all p<0.0001) and diastole (untwist rate and time to peak untwisting, all p<0.001) persisted at 4 months follow-up when compared with controls, despite normalization of LV ejection fraction and volumes. Whilst native T1 (which demonstrates edema) normalized at 4 months follow-up only in segments contracting normally during the acute phase [T1=1180± 40.6ms (normally contracting, p=0.2 vs control values of 1189±16 ms) and 1208± 60.3 ms (dysfunctional segments, p<0.05 vs control)], the extracellular volume fraction (ECV, which demonstrates diffuse fibrosis) remained significantly abnormal in all LV segments (whether normally contracting, 0.328±0.043, p<0.001 or ballooning during acute presentation, 0.320±0.044, p<0.001, both vs control values of 0.273±0.045). Conclusion: In patients with the most clinically severe spectrum of takotsubo cardiomyopathy, regional LV systolic and diastolic deformation abnormalities persist beyond the acute event, despite normalization of global LV EF and size. In addition, although myocardial edema partly subsides, a process of global microscopic fibrosis develops in its place, detected as early as 4 months.Suggested Reviewers:Opposed Reviewers: 1 24 th March, 2017 Dear Dr Pearlman, Thank you once again for your comments and those of the associate editors. I think it i...