Study Of The High-resolutionand Zooming Endoscopic Optical Coherence Tomography

Optical coherence tomography(OCT)is an emerging medical imaging method that is based on low coherence interferometry.Due to its various advantages such as non-invasive,low optical damage,depth resolving and high-resolution imaging,OCT has achieved applications in various biomedical fields.With the combination of endoscopy technology,the endoscopic optical coherence tomography(E-OCT)may deliver light to various part of human body for imaging and is therefore of high potential for clinical application,especially for high-resolution OCT because of its function of optical biopsy for early diagnosis of cancer.In this thesis,E-OCT technology is investigated.The endoscopic OCT probes are designed by combining microelectromechanical system(MEMS)together with optical design and simulation.The main results are as follows:Firstly,the conventional design of distal scanning E-OCT cannot provide the advantages of high-speed rotation,high resolution(<10?m),small size(<2mm)and no power wire artifacts in a single OCT probe.This problem has limited E-OCT technology for further clinical applications.Focused on this problem,we present a new stationary-fiber ultra-small probe,which is equipped with a novel miniaturized hollow ultrasonic motor(USM)and a custom-designed objective lens.The hollow USM can enable the fiber to pass its inside,and permits the fiber,the objective lens and the motor on the same side.Thus,our probe provides an unobstructed 360 deg view for circumferential imaging with a spatial resolution of 7.5?m(axial)× 6.6?m(lateral).Ex-vivo images of chicken trachea and a phantom are shown to demonstrate the performance.The prototype probe is packaged within 1.4mm and 1.5mm catheter,which is ultra-small for shadow-free motorized probe in distal scanning E-OCT.These experimental results prove the feasibility of this novel type of OCT probes based on hollow USM,which is of high potential in clinical application.Secondly,we have studied the trade-off between lateral resolution and depth of focus(DOF),which is a common problem in high-resolution E-OCT.With optical design and simulations,we present novel design of a zooming probe based on self-heat shape-memory alloy(SMA)string and hollow USM,which can dynamically change the fiber-lens spacing for zooming.The schematics and optical simulations on this design are discussed and demonstrated as well.This is the first time that E-OCT is equipped with a zooming probe.The performance of prototype probes is experimentally investigated.Imaging of phantom is also implemented to demostrated the zoom effect.In addition,considering the precision and complexity of the endoscopic technology,design detail and assembling process of the probe are included in this thesis as appendix for further reference when needed.To conclude,high resolution and zoom endoscopic OCT probes are successfully developed.Combined with the OCT imaging system,they can provide high resolution,noninvasive,three-dimensional tomographic image for clinical diagnosis.Therefore,this technology will promote the real time monitoring of lesions in situ and play an important role in the early diagnosis of serious diseases.