Ultrasonic Methods for 2D Arterial Wall Movement Measurements

Abstract: Cardiovascular diseases constitute the major cause of morbidity and mortality in the Western World. To increase our knowledge of cardiovascular diseases, it is important to find methods, preferably non-invasive ones, to study very early manifestations of vascular disease. Changes in the mechanical properties of the arteries can be an early manifestation of vascular disease. Further, changes in the mechanical properties of arteries can have important haemodynamic consequences, and are being increasingly recognised as important factors in cardiovascular morbidity and mortality. To obtain a measure of the mechanical properties in the arteries, arterial characterisation is performed. This thesis consists of seven papers concerning arterial characterisation and new ultrasonic methods for arterial characterisation. The first paper is an introduction and an overview of the area around vessel characterisation. Papers II and III describe and evaluate a new method for local non-invasive pulse-wave velocity (PWV) estimation. The PWV estimation was based on arterial-wall movement, which was detected by Tissue Doppler Imaging (TDI). The method was evaluated and optimised on an in vitro set-up and validated in vivo with respect to repeatability and reproducibility in a clinical study. In the evaluation, it was shown that system parameters have a significant effect on the PWV variance, whereas the PWV mean remains unchanged. Furthermore, it was established that high temporal resolution is the most vital parameter for minimising the PWV variance. The longitudinal movement of blood-vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. The fourth paper presents results from the first in vivo study with a new unique ultrasonic method for measurement of both the radial and the longitudinal movement of the arterial wall, and it is shown that the magnitude of the longitudinal movement is not negligible, that movement due to breathing affects the recording of arterial longitudinal movement in common carotid artery, and that there was a shear stress present within the arterial wall in one volunteer. The new unique ultrasonic method is evaluated in vitro in paper V, and accuracy, reproducibility, and resolution were all considerably better than the resolution of the applied ultrasound scanner. The sixth paper describes a new method for arterial luminal diameter measurement with ultrasound. Features of the new method are its robustness, fastness, and resolution. The method was calibrated on a vessel phantom and was evaluated in vivo with respect to accuracy and reproducibility, which both were considerably better than the resolution of the applied ultrasound scanner. The seventh paper presents results from an in vivo study where a new digitised ultrasonic method called Elastart, which measures arterial lumen diameter at diastole and arterial distension with tissue Doppler, is compared with a golden standard method. The evaluation of the method in vivo against a golden standard showed that no difference in reproducibility between the two systems could be found. However, measurements of the arterial lumen diameter showed a slight underestimation of the Elastart system compared with the golden standard.