Study Of The Endoscopic Spectral-Domain Optical Coherence Tomography

Cancer is one of the most serious diseases to human and the key to cure the canceris early diagnosis and treatment. The biopsy, as the gold standard for diagnosis ofcancer in clinic, suffers from error or missing detection as well as possible pollution,which degrades its accuracy and effectiveness. Therefore, a novel and in vivo imagingmethod for cancer diagnosis will significantly contribute to solving these problems.Optical coherence tomography (OCT) performs non-invasive, micrometer-resolution,high-speed imaging of tissue pathology, showing a greatly significant value for earlydiagnosis of cancer.In this thesis, we studied the spectral domain OCT (SD-OCT) technology and thedevelopment of endoscopic OCT probe as well. The related results of interest aredemonstrated as following.First, the conventional SD-OCT generally requires converting the original detectedspectrum from the wavelength domain to the wavenumber domain by numericalinterpolation, so as to reconstruct a high quality OCT image via the Fourier transform.However, this process is time-consuming and become a bottleneck to enhance imagingspeed. This thesis presents two novel methods for wavenumber linearization. One is theFresnel SD-OCT equipped with a Fresnel spectrometer that utilizes a Fresnel zone plate(FZP) as both dispersion and focusing optics, obtaining a linear-in-wavenumberspectrum directly. It removes the conventional interpolation process and thus isfavorable for enhancing the imaging speed. Another method is compressed sensing withlinear-in-wavenumber sampling (k-linear CS). An array of points that is evenly spacedin wavenumber domain is sampled from an original interferogram by a pre-set k-linearmask. Then the compressed sensing is applied on these points to reconstruct an A-scandata. To get an OCT image, this method uses less than20%of the total data as requiredin the conventional process and gets rid of the spectral calibration with numericalinterpolation in traditional CS-OCT. Therefore k-linear CS is favorable for high speedimaging.In addition, for the endoscopic OCT probe, we proposed new designs to both thecircumferential-imaging and forward-imaging probes, respectively. For thecircumferential-imaging, we presented an endoscopic probe equipped with a miniaturized hollow ultrasonic motor that rotated the objective lens and provided aninternal channel for the fiber to pass through, enabling360deg unobstructedcircumferential scanning. This probe has an ultra-small outer diameter of1.5mm with acustomized aspheric right-angle lens, leading to high transverse resolution. For theforward-imaging, we developed a compact, optical fiber scanning piezoelectrictransducer (PZT) probe with a reverse-mount design which achieved a shorter rigidlength compared with conventional forward-mount fiber designs, while maintaining thescanning performance similar to the forward-mount one. Therefore this new designshows greater potential in clinical applications.Our studies demonstrate the feasibility of endoscopic SD-OCT in breaking thelimitations of conventional imaging method and helping to achieve real-time monitoringand high resolution imaging of early cancer. We believe that endoscopic SD-OCT is apromising technique for the early diagnosis of cancer.