Noninvasive estimation of 2-D pressure gradients in steady flow using ultrasound

Abstract

A noninvasive method for estimating 2-D pressure gradients from ultrasound vector velocity data is presented. It relies on vector velocity fields acquired using the transverse oscillation method during steady flow conditions. The pressure gradients are calculated from the velocity fields using the Navier-Stokes equations. Scans of a carotid bifurcation phantom with a 70% constriction are performed using a linear transducer connected to a scanner. The performance of the estimator is evaluated by comparing its results to those of a computational fluid dynamics model of the carotid bifurcation phantom. The geometry of the model is determined from magnetic resonance imaging. The presented study is conducted assuming steady flow using velocity data acquired at 18 frames per second. The proposed method shows pressure gradients at the constricted region from -8 kPa/m to 9 kPa/m, with a maximum bias of -7% for the axial component and -8% for the lateral component. The relative standard deviation of the estimator is 5% (axial component) and 30% (lateral component) when studying the pressure gradient across the constriction using 3 velocity frames per pressure estimate. The study shows that 2-D pressure gradients can be achieved noninvasively using ultrasound data in a constant flow environment.

Assessing the blood pressure waveform of the carotid artery using an ultrasound image processing method

“…Olesen et al [35] applied an ultrasonic method for estimating 2D hemodynamic pressure gradients in a flow model, which mimicked the carotid bifurcation having 70% occlusion at the beginning of the internal carotid artery. Pressure gradients were calculated using Navier-Stokes equations in which the vector velocity fields were obtained by processing ultrasound radiofrequency data.…”

“…The results were compared to the pressure resultant from 3D finite element modeling of a phantom. In the mentioned study, steady flow conditions were set up and the gravitational force and the out-of-plane velocity component were neglected [35]. …”

“…In the present study, invasively measured BPs were not available and this may pose errors. Further, the error of the acquired pressures in our study may be associated partly with the incorrect estimation of the centerline velocity profile caused by the insonation angle error [24] and the weakness of the 33% rule as compared to the precise method of measuring MBP via an intra-arterial catheter [35]. …”

Ultrasound Vector Flow Imaging: I: Sequential Systems

“…Comparisons with micromanometers were performed in an animal model. Recently, Olesen et al determined longitudinal pressure gradients in a steady flow carotid model using the transverse oscillation method [174]. They then tested their technique with pulsatile flows [175].…”

Non-invasive estimation of pressure gradients in pulsatile flow using ultrasound

“…A second-order polynomial is fitted to a subset of adjacent data points by the linear least-squared method, which results in a smoothed data set. From this data set the first and second-order derivatives are found using the convolution coefficients [8], [9].…”