Magnetic resonance imaging conditional powered microinjector for interventional procedures
Wineland, Adam David
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This thesis describes the development of a magnetic resonance (MR) conditional powered microinjector for use in clinical procedures and experiments taking place inside the magnetic resonance imaging (MRI) scanner. MR Safe devices pose no known hazards resulting from exposure to any MR environment, and they are composed of materials that are electrically nonconductive, nonmetallic, and nonmagnetic. Furthermore, equipment is considered MR Conditional if it poses no known hazards in a specified MRI environment within defined conditions, it does not significantly affect the image quality of the object being scanned, and its operation is not significantly affected by the MR environment. The core advantage of the MR Conditional microinjector is to accurately deliver therapeutics to subjects inside the scanner while reducing waste and inconsistent results which are created by using long transmission tubing between the scanner and an MR Unsafe injector located away from the MRI scanner or outside the MRI scanner room. This is particularly useful for expensive therapeutics such as stem cells. The technical challenges of an MR Conditional microinjector include nonmagnetic actuation as well as high precision for control-release of the therapeutics. This is overcome by a custom-designed stepper motor based on pneumatic principles. The microinjector consists of three units: (1) a syringe actuator that contains a mechanism to precisely deliver therapeutics in a programmable volume or programmable pressure, (2) a pneumatic stepper motor, and (3) a software control panel that consists of a programmable interface for the user to set the volume or pressure of the delivery. The presented microinjector has been validated in a 7 T MRI small bore scanner to ensure its usability in high-field MRI applications with less than 10 percent signal-to-noise ratio reduction in MRI images and with no image artifacts presented. Finally, the presented microinjector has been tested in a clinical proof-of-concept study to investigate the relationship between intraocular pressure and the tension in ocular tissue. The presented injector was utilized to adjust intraocular pressure of sheep eyeballs in vitro while the biomechanical response of the sclera was monitored by MRI and time-lapse photography. The pneumatic-powered microinjector as well as the custom-designed pneumatic stepper motor alone could be utilized in a variety of MRI-guided applications. This project is in collaboration with the NeuroImaging Lab at the University of Pittsburgh.