EVALUATION OF THE VISCOELASTISITY OF THE HUMAN CAROTID
WALL BY ULTRASONOGRAPHY
Keywords:
Yerzley Resilience
1993 Volume 96 Issue 5 Pages 796-809,875
Details
1993 Volume 96 Issue 5 Pages 796-809,875
The purpose of this study is to evaluate non-invasively the viscoelastisity of the human carotid wall by ultrasonographic techniques. After mathematical fundamental experimentation using a rubber tube as a vessel wall model, we observed viscoelastic changes in the carotid wall in normal cases in relation to aging and in treated and non-treated cases with hypertension.
An amplified single rectangular mechanical impulse with a 0.5 msec duration was applied to the carotid wall percutaneously by using Wilcoxon's vibrator.
We converted B-mode images at one point of the carotid wall to ultrasonic variant M-mode images, and damped oscillation waves were thus obtained. The ultrasonic variant M-mode method, which was developed in our department to detect small vibrations of the vocal cord, was used to observe fine impulse excitations of the carotid wall. This ultrasonographic method (variant M-mode) shows the amount of reflected echoes, which are changed to electrical potentials at one point of the carotid wall.
Yerzley Resilience (Y.R.) and resonance frequency (R.F.), as well as the Q-value of resonance, (Q.V.) were measured from these damped oscillation waves. It is widely known that Y.R. shows the degree of viscosity of the carotid wall while R.F. and Q.V. show the stiffness of the carotid wall indirectly. A Y.R. of 100% means complete elasticity with lower viscosity and damping degree.
When Y.R. comes close to 0%, both viscosity and damping degree increase. The carotid wall becomes stiffer in proportion to R.F. and Q.V.
The following results were obtained:
1) Y.R., R.F. and Q.V. increased with aging.
2) In non-treated cases with hypertention, Y.R. was significantly, while R.F. and Q.V. tended to be, higher than in normal cases of the same generation.
3) In treated cases with hypertention, Y.R., R.F. and Q.V. had a tendency to be lower than in non-treated cases.
In conclusion, non-invasive evaluation of carotid wall viscoelastisity appears to be feasible, and further investigation is warranted for applying this ultrasonographic technique to the field of head and neck vessel surgery.
