The shear stress of blood in arteriès is an important parameter for the diagnosis of hypertension risks, even if its ultimate implications are not yet fully understood. The evaluation of this parameter requires the contemporaneous measurements of viscosity and shear rate, the latter being the gradient of the blood velocity near the vessel wall; remark that the shear stress should be measured during at least one complete heart beat, in order to provide useful diagnostic information. The viscosity can be measured through laboratory analysis, while the shear rate requires the acquisition of the blood velocity over a suitable space and time domain, Our group has recently developed an instrument (Flow Rate ProfUer, FR.P Il) based on ultrasound techniques, capable of measuring the longitudinal component of the blood velocity along the path of the ultrasound; proper space and time periods can be selected by the operator. Unfortunately, the measurements obtained at the periphery of the vessel are substantially affected by echoes reflected by the walls; indeed, even if they originate at distances from the probe different from those at which the blood particles scatter the ultrasound, the two contributions partially overlap because of the limited resolution of the ultrasound apparatus, Furthermore the wall echo is not still, as a consequence of vessel and probe unavoidable displacements. Since the wall motion is slower than the blood velocity, and hence the relevant Doppler frequency is proportionally lower, this interference is reduced by means of a proper high pass filter; however the much higher amplitude of the wall echo prevents its complete rejection, in particular for the most external blood layers, To overcorne this difficulty, our acquisition system has been modified by introducing means for the stabilisation in space of the wall echo; so they can be easily cancelled by the high pass filter. In turn, wall echo stabilisation has been obtained by delaying the ultrasound pulse emitted in such a way to hold in place the first portion of the velocity profile.
A flow rate profiler aimed at shear stress evaluation in arteries
DOTTI, DOMENICO;LOMBARDI, REMO ANGELO;
1996-01-01
Abstract
The shear stress of blood in arteriès is an important parameter for the diagnosis of hypertension risks, even if its ultimate implications are not yet fully understood. The evaluation of this parameter requires the contemporaneous measurements of viscosity and shear rate, the latter being the gradient of the blood velocity near the vessel wall; remark that the shear stress should be measured during at least one complete heart beat, in order to provide useful diagnostic information. The viscosity can be measured through laboratory analysis, while the shear rate requires the acquisition of the blood velocity over a suitable space and time domain, Our group has recently developed an instrument (Flow Rate ProfUer, FR.P Il) based on ultrasound techniques, capable of measuring the longitudinal component of the blood velocity along the path of the ultrasound; proper space and time periods can be selected by the operator. Unfortunately, the measurements obtained at the periphery of the vessel are substantially affected by echoes reflected by the walls; indeed, even if they originate at distances from the probe different from those at which the blood particles scatter the ultrasound, the two contributions partially overlap because of the limited resolution of the ultrasound apparatus, Furthermore the wall echo is not still, as a consequence of vessel and probe unavoidable displacements. Since the wall motion is slower than the blood velocity, and hence the relevant Doppler frequency is proportionally lower, this interference is reduced by means of a proper high pass filter; however the much higher amplitude of the wall echo prevents its complete rejection, in particular for the most external blood layers, To overcorne this difficulty, our acquisition system has been modified by introducing means for the stabilisation in space of the wall echo; so they can be easily cancelled by the high pass filter. In turn, wall echo stabilisation has been obtained by delaying the ultrasound pulse emitted in such a way to hold in place the first portion of the velocity profile.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
