MEMS sensor platform for vital monitoring under mri and intraocular pressure measurement

Abstract

In part of this study, we aim to develop optical-based Microelectromechanical System (MEMS) sensors for minimally invasive and non-invasive medical devices used for Magnetic Resonance Imaging (MRI) interventions.The use of MEMS in medical and biological applications has been rising steadily because it allows multifunctional devices to be integrated on the same substrate with the help of miniaturization. These sensors will be used to track the location of medical devices in real-time as well as measure pressure and ambient temperature. The operator can see environmental factors like temperature and pressure as well as the locations of surgical tools like catheters with the aid of this cutting-edge technology. This improves the success of the procedure by enabling tracking and information gathering from the interventional device without degrading the quality of the collected images. This work aims to integrate MEMS and fiber optical components to be compatible with the imaging modality. It also develops a microfabrication sequence for MEMS sensor implementation. In the first approach, microsystems sensors are integrated on a fiber optics-based platform for use in therapies supported by magnetic resonance imaging. MEMS sensors are implemented on a platform, and single-mode fiber cables are integrated with this platform. During imaging-assisted surgical operations, the described platform provides real-time and in-situ pressure, temperature, and location feedback. A medical interventional device with an inner diameter of 1.8 mm may accommodate the platform. The platform has a three-dimensional printed polymer cap with perforation utilized for the circulation of blood in the vessel to allow correct monitoring of the temperature and pressure in real-time. At the fiber cable ends, Graded Index (GRIN) lenses were used to increase the effectiveness of optical signal collecting. Three laser beams illuminate the MEMS platform that contains temperature (T), pressure (P), and localisation (∆X) sensors. Each sensor used a separate light source with a different wavelength: a 637 nm laser for pressure, a 780 nm laser for localization, and an 875 nm LED (with 50 nm bandwidth) for temperature. A released metal-polymer-metal hybrid membrane changes the environment's pressure relative to the membrane's chamber pressure using an interferometer readout method based on diffraction gratings. To research and develop the best membrane for the intended blood pressure range (from 5 mmHg to 240 mmHg), we designed and made the membrane of the optical pressure sensor (over the platform) in multiple sizes between 200 and 400 um. Based on fluctuations in the energy bandgap with ambient temperature, temperature sensing is performed in semiconductors (such as GaAs) by changing the absorption and transmission. The incident light on the semiconductor (such as GaAs) at a certain wavelength are reflected with the temperature change signature. As an optical thermometer integrated on the platform and lighted by light-coupled fiber optic, we used a Gallium Arsenide die, where one surface of GaAs is coated with metal to operate as a mirror. The magneto-optical Kerr effect (MOKE), which describes the change in polarization on the reflected light beam caused by variable magnetization in a magnetic substance like Iron(III) Oxide, is used to determine the location of the medical device. Prisms are incorporated under the platform in a retro-reflector shape and covered with magnetic material to reflect lit polarized light in the direction of the fiber optic. The sensor chip's measurements of temperature precision (0.22 ◦C), pressure resolution (1 mmHg), and localization resolution (3 mm), all of which are pertinent to medical practice, were made. In a second study; the integrated MEMS pressure, temperature, and magneto-optical sensors are developed enabling the operator to get real-time data from all MRI-compatible fiber-based devices on a single platform. As a result, the operator will be able to undertake interventions with a solid collection of real-time information about the patient's condition during the procedure. By incorporating the sensors developed in this work, medical equipment like catheters and stents can open up new possibilities for interventional surgery. We developed our first proposed multi-sensor platform as a second approach, using one fiber optic and one light source. In order to do this, we describe a stacked temperature, pressure, and localization platform designed for magnetic resonance imaging-based minimally invasive surgical and diagnostic procedures. The platform includes a magnetized material on a double prism retro-reflector that uses the MOKE as a magnetic field sensor to provide localization feedback during magnetic resonance imaging, a Gallium Arsenide band-gap temperature sensor, and a titanium, parylene, and titanium three-layer membrane pressure sensor. In order to determine where the sensor and the interventional device, such as a catheter, ablation probe, etc. to which our platform is attached are located, we used the MOKE technique to assess the spatially changing magnetic field density. A single fiber optic connection may connect all sensors, and the gathered light is sent to a spectrometer and a polarimeter. To employ interferometry to measure the pressure, a microfabricated three-layer sealed membrane with embedded diffraction gratings is used. An analytical formulation that connects the pressure to optical intensity is developed for the three-layer microfabricated membrane sensor. The analytical conclusions are also supported by finite-element simulation results. The use of wavelength division multiplexing allows for simultaneous sensor addressing. A magnetic field sensor, a pressure sensor, and a temperature sensor each had proof-of-concept operations that revealed sensitivities of 25 mdeg/mG rotation of polarization, 1.5 nm/mmHg displacement in agreement with simulation results and analytical findings, and 0.36 nm/◦C bandgap wavelength shift, respectively. The suggested gadget can be modified for usage in clinical settings for magnetic resonance-assisted surgical operations with future development. Overall, new application areas, including those for RF ablation catheters, highly focused ultrasonic catheters, and laser ablation catheters, will be made possible by the successful demonstration of sensor functioning in the MRI modality. The results of this study could inspire the development of novel interventional medical systems and technologies. In a third study, we presented a novel implanted MEMS sensor-readout glasses pair for the real-time monitoring of intraocular pressure based on the design and manufacturing of several optical pressure sensors in varied membrane widths that are acceptable for human physiological pressure. The entire system consists of two components: (i) a diffraction grating interferometric MEMS sensor that can be implemented into the cornea or intraocular lens, and (ii) readout glasses embedded with a laser diode, miniaturized aspheric lenses, and a CMOS camera. The suggested intraocular pressure measuring device allows for an eye tilt tolerance of around ±8 degrees while being monitored by a camera because to the number of diffracted orders. Additionally, the sensor is protected from the effects of changing optical power (caused by eye movement or laser noise) by the use of one or more reference gratings nearby. The ray-tracing simulations of the readout glasses, the analytical modeling of the diffracted orders from the pressure sensor, and the FEM results showcasing the deflection versus pressure behavior of the MEMS sensor are all included in the detailed design of the proposed device. We demonstrated pressure measurement in the range of ∆ p = 40 mmHg using in-vitro tests, with an average deflection sensitivity of 4.06 nm/mmHg and a resolution of 2.5 mmHg. Overall, in this part of the study, we present the design, manufacturing, and characterization of the optical sensor-glasses pair for real-time monitoring of intraocular pressure. To track the diffracted order intensity as a function of IOP, the readout glasses are equipped with a light source, a telescope aspheric lens pair unit, a scattering plate, and an endoscopic camera. A reference grating is placed next to the sealed membrane-based pressure sensor in order to distinguish the recorded pressure from variations in optical laser power. With a Polydimethylsiloxane(PDMS)-based inflated eye phantom, the combined sensor-glasses platform was put to the test. We took measurements of the diffracted order intensities for eyeball rotations up to ±8 degrees with a potential increment of ±15 degrees. The glasses were 3D printed in a modular form using the Selective Laser Sintering (SLS) technique. According to ANSI laser safety guidelines, a 1 mW laser was used in the application. The last section of the thesis study includes the latest results on a non-contact, non-invasive device for measuring intraocular pressure. The pressure-monitoring device is a pair of wearing 3D printed glasses that includes a laser source, several miniature lenses and mirrors, a mask for structured corneal illumination, and a miniature camera. By measuring the radius of curvature of the grid-like pattern on the cornea, the pressure level may be determined. We use tests on an elastic eye phantom at various tilt angles, analytical modeling, ray tracing, finite element simulations, and experiments to support our concept. In addition, we have shown the innovative non-contact smart glass in proof-of-concept functioning. The findings show that a pressure measurement resolution of 2.4 mmHg between the 0-55 mmHg pressure range may be achieved. This is based on the change in the radius of curvature of the projected grid pattern on the eyeball with altering internal pressure. The laser diode (with a wavelength of 650 nm), the lenses, and the miniature camera all had their own cylindrical grooves. A PDMS-based eye phantom was utilized in the studies due to the elasticity property of a PDMS with a Young's modulus of roughly 1.5 MPa. The suggested device may be employed for individualized real-time intraocular pressure monitoring throughout the daylight with additional in-vivo testing and development.