Bwamm Bart Beulen

Toward Noninvasive Blood Pressure Assessment in Arteries by Using Ultrasound

A new method has been developed to measure local pressure waveforms in large arteries by using ultrasound. The method is based on a simultaneous estimation of distension waveforms and velocity profiles from a single noninvasive perpendicular ultrasound B-mode measurement. Velocity vectors were measured by applying a cross-correlation based technique to ultrasound radio-frequency (RF) data. From the ratio between changes in flow and changes in cross-sectional area of the vessel, the local pulse wave velocity (PWV) was estimated. This PWV value was used to convert the distension waveforms into pressure waveforms. The method was validated in a phantom set-up. Physiologically relevant pulsating flows were considered, employing a fluid which mimics both the acoustic and rheologic properties of blood. A linear array probe attached to a commercially available ultrasound scanner was positioned parallel to the vessel wall. Since no steering was used, the beam was perpendicular to the flow. The noninvasively estimated pressure waveforms showed a good agreement with the reference pressure waveforms. Pressure values were predicted with a precision of 0.2 kPa (1.5 mm Hg). An accurate beat to beat pressure estimation could be obtained, indicating that a noninvasive pressure assessment in large arteries by means of ultrasound is feasible.

Estimation of volume flow in curved tubes based on analytical and computational analysis of axial velocity profiles

To monitor biomechanical parameters related to cardiovascular disease, it is necessary to perform correct volume flow estimations of blood flow in arteries based on local blood velocity measurements. In clinical practice, estimates of flow are currently made using a straight-tube assumption, which may lead to inaccuracies since most arteries are curved. Therefore, this study will focus on the effect of curvature on the axial velocity profile for flow in a curved tube in order to find a new volume flow estimation method. The study is restricted to steady flow, enabling the use of analytical methods. First, analytical approximation methods for steady flow in curved tubes at low Dean numbers (Dn) and low curvature ratios (δ) are investigated. From the results a novel volume flow estimation method, the cos θ-method, is derived. Simulations for curved tube flow in the physiological range (1≤Dn≤1000 and 0.01≤δ≤0.16) are performed with a computational fluid dynamics (CFD) model. The asymmetric axial velocity pro...

Ultrasound flow assessment in curved vessels: an in-vitro study

In clinical practice, ultrasound is frequently used as a non-invasive method to assess blood velocity and vessel wall position. For the velocity assessment, often Doppler ultrasound is applied. To perform Doppler velocity measurements, the ultrasound probe needs to be positioned at a certain insonification angle (non perpendicular) with respect to the blood velocity vector (figure 1). For volume flow estimation, both an accurate assessment of vessel wall position and axial velocity distribution is necessary. However, in order to achieve an accurate wall position assessment, a perpendicular insonification is necessary. As a result, a simultaneous assessment of velocity by Doppler ultrasound and wall position is impossible, which hampers an accurate flow assessment.Copyright