Study of catheter designs and drug mixing processes using 2D steady numerical simulations

The effectiveness of substance delivery through catheters is an important issue in interventional radiology, especially for infusion therapies where the pharmacokinetic advantage of local intra-arterial drug administration has been firmly established. In principle, the procedure is used to provide appropriate local concentrations while maintaining low systemic values so as to minimise the global effect and toxicity of the intervention. However, poor drug mixing may produce excessive local concentrations potentially damaging for the surrounding tissues and may lead to unsuccessful therapies. These phenomena have been observed in the infusion therapies of liver cancers through the hepatic artery and with brain tumour therapies through the carotid artery. Many aspects of the drug delivery methodology have been explored in order to determine the infusion conditions that would provide optimal mixing: the catheter tip design is considered one of the most important characteristics to be investigated for this purpose. Interestingly, it turns out that angiographic procedures could also benefit from this, because better mixing properties are associated with designs that provide potentially less harmful flow conditions such as jets, whipping and recoil of the catheter on the vascular wall. A 2D steady numerical model is proposed, to simulate the main physical processes occurring during catheter substance infusion: blood dynamics is taken into account with the Navier-Stokes equations and substance dispersion by the flowing blood with the advection-diffusion equation. The model is used to evaluate mixing properties of certain catheter designs in different flow conditions. In particular, two types of side hole catheter are compared in the context of water bath injection and in the context of vessel injection. The simulations suggest that the improved mixing reported with water bath experiments would not be maintained in the clinical context of arterial circulation.