Sensing using optical fibers is quite an established technology and is increasingly used in the field of bio-medical sensing applications owing to its small size, light weight, immunity towards electromagnetic interference, biocompatibility, sensitivity, and the ease with which it can be integrated with standard catheters leading to a designated point of inspection. Fiber Bragg gratings (FBGs), due to their ease of multiplexing, inherent sensitivity towards strain, and thereby pressure, can be suitably designed to make a novel pressure sensor for diagnosing and monitoring angiogenesis in brain tumors and for assessing vascular lesions inside coronary arteries. However, standard FBGs have a poor pressure sensitivity of 4pm/MPa (0.5fm/mmHg), which is insufficient to detect a few mmHg blood pressure changes. By utilizing the mechanical properties of modified FBGs with an elastomeric material coating, it is possible to improve the transduction mechanism of effectively translating pressure to strain and increase the resolution and sensitivity by two orders of magnitude (53.4 times) compared to standard FBGs. These modified FBGs could then be used to monitor respective pressure indices, i.e., Intracranial Pressure (ICP) and Instantaneous wave-free Ratio (iFR), by integrating them with catheters or endoscopes and using appropriate signal-processing algorithms. Moreover, a simulation of the modification of the blood vessel flow with respect to the secondary vessel formation is done to study the impact of different blood vessel formations during angiogenesis on pressure, thereby co-relating flow patterns to angiogenesis.
State-of-the-art optical fiber pressure sensors use displacement diaphragms and mechanical transducers to enhance pressure sensitivity, however, due to their bulkiness and large size they can’t be easily integrated inside pressure guide wire for intravital monitoring. Fiber Bragg Gratings (FBGs) due to their inherent advantages can be designed in a way that is suitable for monitoring Intracranial Pressure (ICP) and Instantaneous Wave-Free Ratio (iFR) pressure indices. The main disadvantage of FBG is that it has a low-pressure sensitivity of 3.04pm/MPa, which is insufficient for these applications and is made worse by the cross-sensitivity caused by temperature. We hereby present a two-pronged strategy to tackle this issue. The first step in improving sensitivity is to modify FBGs, and the second is to use signal processing methods to recover minor wavelength shifts. A frequency-selective detection technique can be used to measure sub-pm wavelength shifts for small modulated pressure signals. This technique was used to establish a test bench for measuring the pressure sensitivity of standard acrylate and polyimide coated FBGs as well as to confirm a linear relationship between the pressure range of interest and Bragg wavelength shift.
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