Pislaru, Cristina

Ultrasound (US) enhancement of plasmid-based gene transfer is an emerging technique. Our hypothesis was that two contrast agents (Optison and PESDA), and two US exposure modalities (dedicated continuous wave system and diagnostic scanner) may have different effects. Luciferase plasmid with or without contrast agent was added to vascular smooth muscle cells and endothelial cells, followed by US exposure. Luciferase activity was measured 24 h later. US exposure consistently induced higher transfection rates than all controls. PESDA was superior to Optison in both cell lines. In vitro, continuous wave and diagnostic US were not significantly different. In vivo, Lux and PESDA were injected into skeletal muscles of rats (IM or intra-arterial) followed or not by US exposure. In separate animals, adenovirus encoding for luciferase was injected IM and was not followed by US exposure. Gene transfer efficacy was 8–10 fold higher with US and PESDA than with plasmid alone, but 2 fold lower than with adenovirus. However, as opposed to adenovirus, US-enhanced plasmid gene transfer was highly localized to the injected muscle, with no expression at distal sites. Our results support the hypothesis that contrast agents and exposure modalities are not equivalent with regard to gene transfer efficacy.

The cardiovascular diseases such as atherosclerosis, coronary artery disease, hypertension and diastolic dysfunction have been associated with arterial stiffening and decreased ventricular compliance. Noninvasive techniques capable of quantifying elasticity and viscosity of cardiovascular tissues could facilitate early diagnosis and improve treatment. Here, we present a technique that uses focused ultrasound radiation force to excite mechanical waves in the tissue of interest and pulse echo to track the tissue deformation. Analysis of tissue deformation as a function of time using Fourier transforms allows calculation of the phase wave velocity dispersion (change of velocity as a function of frequency) of various modes of deformation. Continuum mechanics equations governing the motion of a viscoelastic plate and a tube are used to model the myocardial wall and arteries, respectively. Dispersion equations are derived for the two geometries and fit to the measured velocity dispersion to estimate tissue elasticity and viscosity. ECG-gated in vivo measurements of porcine myocardial and arterial elasticity and viscosity through a heart cycle are reported. The results show that both elasticity and viscosity increase during systole and decrease during diastole in the myocardium and arteries, consistent with underlying physiology.

Diastolic dysfunction is characterized by the stiffening of the left-ventricular myocardium. An imaging technique capable of quantifying viscoelasticity of the left-ventricle would aid clinicians in evaluating diastolic function. Lamb wave dispersion ultrasound vibrometry (LDUV) is an ultrasound-based method for measuring viscoelasticity of plate-like materials by exciting Lamb waves and measuring change of wave velocity as a function of frequency (dispersion). Lamb wave dispersion equation is fit to the dispersion data to estimate mechanical properties. We report in vivo transthoracic studies aimed at quantifying elasticity and viscosity of a beating porcine left-ventricle using LDUV. A single ultrasound probe operating at 5 MHz was used for impulse excitation in the myocardium and to track the wave motion. A Fourier space-time analysis of the motion was used to obtain Lamb wave velocity dispersion. ECG-gated transthoracic in vivo measurements of group velocity, elasticity, and viscosity throughout a single heart cycle were obtained. Group velocity, elasticity, and viscosity in the frequency range from 50 to 500 Hz increased by at least two-fold from diastole to systole, consistent with contraction and relaxation of the myocardium.

Pulse wave velocity (PWV) is widely used for estimating the stiffness of an artery. PWV is measured by the time of travel of the “foot” of the pressure wave over a known distance. This technique has a low time resolution and is an average measurement of artery stiffness between the two measuring positions. In this paper an arterial wave is generated non-invasively in the vessel wall by the radiation force of ultrasound. The wave velocity in the vessel is measured non-invasively by ultrasound with high time resolution over a short distance of a few millimeters.

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 (n=12) or transmural myocardial infarction (n=12). 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 (ε sys ) was significantly reduced in both stunned and infarcted walls compared with their remote walls (3±3% versus 26±2% and 1±0% versus 33±5%, respectively; P <0.0001) or baseline values. Diastolic passive deformation (ε A ) and rates of deformation during early (E SR ) and late (A SR ) diastole were comparable between stunned and remote walls (ε A : 7.3±1.6% versus 7.9±1.9%; E SR : −2.7±0.4 s −1 versus −2.6±0.5 s −1 ; A SR : −1.8±0.2 s −1 versus −1.9±0.3 s −1 ; P =NS for all) but were of significantly lower magnitude in infarcted walls versus remote walls (ε A : 1.1±0.2% versus 11.4±1.9%; E SR : −0.3±0.1 s −1 versus −2.4±0.4 s −1 ; A SR : −0.3±0.1 s −1 versus −2.5±0.4 s −1 ; P <0.0001 for all). Stiffness coefficient of exponential diastolic pressure–wall thickness relation was higher for infarcted ( P <0.05) but not for stunned walls ( P =NS) compared with their remote walls. Conclusions— Early after postischemic reperfusion and in the presence of severely reduced systolic deformation, diastolic passive deformation (and rates of deformation) can distinguish stiff, noncompliant, transmurally infarcted myocardial walls from those more compliant walls containing viable but stunned myocardium.