1Faculty of Engineering, Osaka University, 2Osaka National Hospital
We developed a system that can visualize rate of expansion and contraction of the carotid artery in the
short-axis view, using time-series echograms that were recorded by high-frame-rate echography (maximum rate, 303 frames/s). Subjects ranged from infants to the elderly. The principles of this method are (1)
extension of spread of scatter in echograms using convolution in a Gaussian distribution function and (2)
subtraction of two sequential time-series echograms. Static parts produce a zero value, while dynamic parts
produce a non-zero value on subtraction. The next steps are (3) calculation of brightness gradient from the
center point of the original echogram and (4) division of the image resulting from subtraction by the brightness gradient. This normalization by the brightness gradient gives expansion and contraction desplacement
lengths on the image plane. (5) Velocity of expansion and contraction of scatter is obtained to normalize displacement by dividing by the time interval between the two images. Last, (6) the velocities are superimposed
on the original echogram according to a color classification scheme. Expanding velocities appear as shades
of red; contracting velocities, as shades of green. We applied this method to some carotid arteries. In the
elastic arteries of youg subjects, uniform arterial expansion was observed when blood pressure increased.
On reaching maximum expansion, the arteries slowly contracted. Contrast between motion and rest was
clearly indicated. Uniform transition was not observed in the rigid arteries of elderly subjects, however, because of increase in the pulsatile surge of arteries themselves. As blood pressure in an artery changes, the
arterial cross section being observed also changes as a result of arterial surge. This method can be used to
analyze precise arterial motion noninvasively and has the potential to be applied to any organ. Because of the
simplicity of the algorithm, hardware integration will make real time visualizaion of velocity practically.