Imaging of In-Vivo Pressure using Ultrasound

The main purpose of this PhD project was to develop an ultrasonic method capable of determining intravascular pressure changes non-invasively. Measuring pressure variations is used clinically as a diagnostic marker for the physiological state of a cardiovascular region. Current clinical procedures for assessing pressure changes are by means of invasive devices such as pressure sensing catheters. Such devices suffer severe limitations as they are invasive and require the use of ionizing radiation for guidance and positioning. To overcome the concerns related to the use of invasive pressure catheters this project introduces a method that derives pressure changes from 2-D vector velocity flow data acquired non-invasively. The method is based on the Navier-Stokes equations and is tested on fabricated flow models. Results from the flow models are compared with simulations from finite element modeling. The developed technique showed a standard deviation and bias across constricted flow domains of 9 % and 8 %, respectively. Finally, the first in-vivo examples of deriving pressure changes from 2-D vector velocity ultrasound data is presented. Based on the presented results it is concluded that non-invasive determination of pressure changes from 2-D flow data is feasible. However, when transferring the method into clinical practice, where blood vessels follow more complex flow geometries, the influence of out-of-plane flow movement becomes increasingly more important. Therefore, for scans using a 1-D transducer it is crucial that the out-of-plane flow component is negligible.