On the coupling and detection of motion between an artery with a localized lesion and its surrounding tissue

Non-contact cardiac monitoring from carotid artery using optical vibrocardiography

The aim of the present work is to establish a protocol for monitoring the cardiac activity measuring the skin surface vibrations of the main neck vessels, caused by vascular wall motion in carotid artery. The method is based on the optical recording of the movements of the neck by means of laser Doppler interferometry. The ECG signal and the velocity of vibration of the skin in correspondence of the carotid artery (named optical vibrocardiography: VCG) have been simultaneously recorded on five healthy subjects. Standard heart rate variability tests have been carried out. The capability of VCG signals to be used as a surrogate of the ECG in assessing both cardiac rate and heart rate variability (HRV) has been tested using time and spectral descriptors, and specific statistical analysis. Mean differences have been found lower than 3.13%. Optical vibrocardiography might be a simple approach to the clinical practice of cardiovascular screening, in particular in harsh environment, such as MR clinical practice, where ECG recordings are corrupted by artefacts and ECG cables might represent an hazard for the patients.

Radiation impedance of a finite circular piston on a viscoelastic half-space with application to medical diagnosis

In a recent study a new analytical solution was developed and validated experimentally for the problem of surface wave generation on a linear viscoelastic half-space by a rigid circular disk located on the surface and oscillating normal to it. The results of that study suggested that, for the low audible frequency range, some previously reported values of shear viscosity for soft biological tissues may be inaccurate. Those values were determined by matching radiation impedance measurements with theoretical calculations reported previously. In the current study, the sensitivity to shear viscoelastic material constants of theoretical solutions for radiation impedance and surface wave motion are compared. Theoretical solutions are also compared to experimental measurements and numerical results from finite-element analysis. It is found that, while prior theoretical solutions for radiation impedance are accurate, use of such measurements to estimate shear viscoelastic constants is not as precise as the use of surface wave measurements.

Excitation and propagation of surface waves on a viscoelastic half-space with application to medical diagnosis

An analytical solution is developed for the problem of surface wave generation on a linear viscoelastic half-space by a finite rigid circular disk located on the surface and oscillating normal to it. The solution is an incremental advancement of theoretical work reported in articles focused on seismology. Since the application of interest here is medical diagnostics, the solution is verified experimentally using a viscoelastic phantom with material properties comparable to biological soft tissue. Findings suggest that prior estimates in the literature of the shear viscosity in human soft tissue may not be accurate in the low audible frequency range. Measurement of wave motion on the skin surface caused by internal biological functions or external stimuli has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in tissue shear elasticity or variations in density due to gaseous inclusions.

Suspension model for blood flow through stenotic arteries with a cell-free plasma layer

The effects of the red cell concentration, the shape of the stenosis and a peripheral layer on blood flow characteristics due to the presence of a mild stenosis, are investigated. To account for the red cell concentration and the peripheral layer, blood is represented by a two-fluid model of particle-fluid suspension, and to estimate the effect of the stenosis shape, a suitable geometry has been considered such that the axial shape of the stenosis can be changed easily just by varying a parameter (referred to as the shape parameter). It is shown that the flow resistance increases with the cell concentration but decreases with increasing shape parameter. The existence of the peripheral layer causes significant reduction in the flow resistance. The wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis (i.e., at stenosis throat) possess the variations similar to the resistance to flow with respect to any parameter except the shape parameter. The latter is independent of the shape whereas the former decreases in the converging zone as the shape parameter increases while it increases in the diverging zone in a similar situation. To discuss the physiological relevance, the analytical results are used to estimate the blood flow characteristics for different diseases using the experimental data and the present theoretical approach.

No touch pulse measurement by optical interferometry

Arterial pulsatility was measured using an optical interferometer. As opposed to laser Doppler flow meters, the prototype system we evaluated can detect pulsation profiles of major arteries with potentially useful information including pulse wave velocity, profile of pulse pressure, etc.