Applications of MRI in Fluidics: Single Echo Acquisition MRI Toward Microfluidics
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Microscale devices capable of manipulating fluids have potential to give rise to a paradigm shift in the fields of biology and medicine. The purpose of this research is to assess the feasibility of applying single echo acquisition (SEA) magnetic resonance imaging (MRI) to microscale fluid flow quantification. This is important because development and improvement of microfluidic devices requires the ability to accurately and non-invasively measure microscale flow. Lab-on-a-chip aims to integrate an array of chemical laboratory tools onto a single chip, utilizing microfluidic flow for mass transport. Use of microfluidics results in improved speed and efficiency and allows operations that harness physical properties unique to the microscale. Current microscale flow visualization methods rely on fluorescence, requiring optically non-opaque fluids and device boundaries. Furthermore, these methods require insertion of labeled chemicals or seed particles into the flow, which may interfere with processes under observation. MRI has an established history of non-invasively quantifying flow through opaque boundaries but is limited by its slow image acquisition rate. SEA employs a 64-channel array coil to acquire a full image with each echo, significantly improving temporal resolution. Methods involve assessing the performance of SEA flow velocimetry on a scale of several millimeters by utilizing time-of-flight techniques. By taking a series of 5 ms snapshots, quantitative velocity information is obtained for laminar, transitional, and turbulent flow with Reynolds numbers ranging from 100 to 1200. Findings show that the turbulent eddies are visible and velocity information can be extracted from images, which means that SEA can accurately asses flow at the millimeter scale. In addition, SEA allows visualization of turbulent flow not accessible to standard MRI velocimetry techniques. It is concluded that SEA could be adapted as new tool for non-invasive quantification of optically inaccessible flow. Implications of this are that through integrated radio frequency microcoils, SEA MRI could be adapted as a new tool to study microfluidic flow resulting in improved microfluidic devices.
Bosshard, John (2006). Applications of MRI in Fluidics: Single Echo Acquisition MRI Toward Microfluidics. Available electronically from