Development of an electromagnetic induction method for non-invasive blood flow measurement

Blood flow is an important measurement in the diagnosis of cardiovascular diseases – the main cause of death globally. Cardiovascular diseases are often associated with atherosclerosis, which is a condition that causes the narrowing of arteries due to a buildup of lipids on the wall of the arterial vessels. Atherosclerosis occurring in the upper or lower limbs (referred to as peripheral arterial diseases) may lead to heart attack, stroke or severe health complications. Early detection of peripheral arterial diseases will enable primary prevention, and thus a reduction in morbidity, mortality and associated resources and financial costs. Limitations and drawbacks in the current methods for peripheral arterial blood flow measurement were primary factors in directing this research, which focuses on developing a reliable, easy-to-use and low-cost, non-invasive blood flow metering method that can replace or be an alternative option to current methods. This thesis describes the design and development of a novel electromagnetic induction method that can be used for peripheral arterial blood flow measurement non-invasively. In general terms, an electromagnetic induction flow metering technique is desirable because it is linear and insensitive to viscosity, temperature, conductivity and pressure loss. Additionally, and unlike previous non-invasive electromagnetic blood flow meters, the proposed method can be calibrated offline and is insensitive to velocity profile. The latter is important in obtaining measurements with high accuracy as blood flow in mammals is asymmetric. A mathematical model was developed for the proposed electromagnetic induction method based on the theory of “weight functions” by Shercliff and the “virtual current” theory by Bevir. This model demonstrated that, for multiple flow channels within a cross-sectional area bounded by a multi-electrode array and across which a uniform magnetic field is applied, flow induced potentials, due to the flow interaction with the magnetic field, can be predicted. From these flow induced potentials, the total volumetric flow rate can be found, irrespective of the number, size and location of the flow channels within the area bounded by the electrode array using a technique based on the Discrete Fourier Transform method. This proposed method allows the venous and arterial blood flow in a limb to be found. Next, a finite element model was developed in COMSOL Multiphysics software to validate the theoretical work. This was achieved by modelling multiple flow channels within a cylindrical region and obtaining flow induced potentials, which were compared with the theoretical values. From these induced potentials, the volumetric flow rate was found, using the DFT method, and confirmed. Finally, a practical model was designed and built which consisted of a physical pipework model (simulating a human limb), an electromagnet and signal conditioning and processing systems. Flow induced potential difference measurements were made using this model and compared with the predicted theoretical values. Overall, a good agreement was found between the theoretical results, computer simulations and practical results. Based on this work and additional work that is suggested in thisresearch, a medical prototype non-invasive electromagnetic blood flow meter device can be developed for clinical trials.