Developments towards in vivo particle image velocimetry

This thesis provides a brief introduction into the field of haemodynamics, a review a biological velocimetry, and presents four publications in the field of biological particle image velocimetry (PIV), divided into two main chapters; in vitro and ex vivo X-ray velocimetry measurements, and in vivo velocity measurements of the developing heart. The in vitro and ex vivo X-ray velocimetry measurements develop the X-ray velocimetry technique to enable measurement of physiological flow rates in vitro, and enable measurement of ex vivo flows, respectively. The in vitro investigation quantified flow rates that were two orders of magnitude greater than had previously been measured using the X-ray velocimetry technique. The ex vivo investigation added the complexity of living tissue, further demonstrating the capability of X-ray velocimetry to acquire measurements in flows that replicate true in vivo flow. This was the first use of X-ray velocimetry to study the haemodynamics of blood flow under physiologically relevant conditions. The in vivo velocity measurements of the heart develop two new methods that have led to more accurate calculation of shear stress in vivo. The methods relate to removing heart wall artefacts that are introduced during bright field imaging, which interfere with accurate velocity measurement, and identifying the internal wall of the heart, which enables calculation of wall shear stress and is shown to correct a severe (3-fold) under-estimation in the PIV measurements. The identification of the internal wall of the heart, from the images that are also used for PIV, is shown to provide convenient and accurate calculation of the wall shear stress, without the need to breed transgenic fluorescent strains.