Cancer of the colon and rectum is the third most common malignancy and the third leading cause of cancer mortality in the United States, and ovarian cancer remains the deadliest of all the gynecologic malignancies. Most ovarian cancers are diagnosed at stages III and IV, where the survival rate is only 25%–30%. Thus, early diagnosis can help increase the survival rate. Photoacoustic imaging (PAI) and optical coherence tomography (OCT) are emerging imaging modalities that can be implemented endoscopically for colorectal cancer screening and diagnosis and intraoperatively for ovarian cancer diagnosis.
PAI, a hybrid imaging modality using optical absorption contrast and ultrasonic resolution to image biological tissue, has demonstrated its immense potential in many biomedical applications. PAI provides spatial resolution and functional information at depths ranging from several millimeters to several centimeters. Endoscopic PAI has been explored in prostate cancer diagnosis, colorectal cancer diagnosis and treatment response assessment, and cervical and ovarian cancer diagnosis. One problem is delivering the laser illumination within the limited space of the endoscope. The maximum permissible exposure on the tissue surface also limits the applied laser energy, which restricts the imaging depth. OCT endoscopy has been demonstrated to overcome the shortcomings of traditional camera endoscopy in the upper gastrointestinal tract and large intestine, and it offers high optical resolution and an imaging depth of ~1 mm. To implement OCT for ovarian and colorectal cancer imaging, a miniature catheter is required.
Here, I will first present a diffuser-coated, optical-fiber based light delivery design for PAI endoscopy. A diffusive coating on the optical fiber tip creates a large numerical aperture for forward laser energy delivery. The diffusive coating can also be used as optical fiber cladding to achieve homogeneous side illumination. Second, I will demonstrate OCT catheters for ovarian and colorectal cancer imaging. A GRIN lens and DC motor-based miniature OCT catheter has been fabricated and used for colorectal cancer imaging. Additionally, a miniature all-fiber-based OCT catheter for imaging ovarian tissue and fallopian tube is presented and preliminary test results will be discussed.
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