Current evidence indicates that most plaques classified as vulnerable or ruptured plaques do not lead to
unstable angina or myocardial infarction. Improved methods are needed to risk stratify plaques to identify
those which lead to most acute coronary syndromes. Collagen depletion in the intima overlying lipid
collections appears to be a critical component of unstable plaques. In this study, we use polarization
sensitive optical coherence tomography (PS-OCT) for the assessment of coronary plaque collagen.
Collagen is birefringent, meaning that different polarization states travel through it at different velocities.
Changes in PS-OCT images are a measure of tissue birefringence. Twenty-two coronary artery segments
were imaged with PS-OCT and analyzed by picrosirius staining (a measure of collagen intensity and fiber
size) and trichrome blue. The regression plot between PS-OCT changes and measured collagen yielded a
correlation coefficient value of 0.475 (p<0.002). Good correlation was noted between two blinded
investigators both with respect to PS-OCT measurements as well as luminosity as assessed by picrosirius.
The predictive value of a PS-OCT measurement of negligible birefringence (less than 33% change) for
minimal collagen was 93% while the predictive value of high birefringence (greater than 66% change) for
high collagen concentrations was 89%. The effect of fiber type (chemical composition) was minimal
relative to the effect due to fiber concentration. The capability of PS-OCT to assess plaque collagen
content, in addition to its ability to generate high resolution structural assessments, make it a potentially
powerful technology for identifying high risk plaques.
Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue in situ and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10-15 um for clinical procedures. In this study, in vivo imaging of the gastrointestinal tract is demonstrated at a three-fold higher axial resolution (<5 um), using a portable, broadband, Cr<sup>4+</sup>:Forsterite laser as the optical light source. Images acquired from the esophagus and colon on animal model display tissue microstructures and architectural details at ultrahigh resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using the standard endoscope. OCT images of normal esophagus and Barrett's esophagus are demonstrated with distinct features.
This paper reports preliminary results from the development and application of a two-dimensional MEMS endoscopic scanner for OCT imaging. A 1 mm diameter mirror provides high aperture over large scan angle and can scan at rates of hundreds of Hz in both axes. The mirror is integrated with focusing optics and a fiber-optic collimator into a package of ~5 mm diameter. Using a broadband femtosecond laser light source, ultrahigh axial image resolution of < 5 um in tissue is achieved at 1.06 um center wavelength. Ultrahigh resolution cross-sectional and three-dimensional OCT imaging is demonstrated with the endoscope with ~12 um transverse resolution and < 5 um axial resolution.
Three-dimensional imaging is achieved by optical coherence tomography (OCT) integrated with a two-axis MEMS scanner to enable noninvasive volume imaging of biological tissues. The longitudinal scan is obtained by optical coherence interferometry. The transverse scan is obtained by tilting the two-axis MEMS mirror to scan the optical beam across the target. High-resolution OCT imaging has enabled in vivo observation of tissue architectural layers and differentiation of normal from tumor lesions within the human gastrointestinal tract. MEMS scanner based catheters with distal beam scanning can image with higher speed, precision, and repeatability than conventional linear scanning catheters. In this work, a 1-mm diameter MEMS scanning mirror with collimator and focusing optics is integrated into a compact 5-mm diameter package that is compatible with limited space in the endoscope. A large fill factor mirror provides high aperture over large scan angle and frequencies of hundreds of Hz in both axes. Using a broadband femtosecond laser light source, high axial image resolution of ~5 um is achieved at 1.06 um wavelength. Transverse resolution of ~ 12-um is demonstrated for cross-sectional image with the endoscope.
Early detection of gastrointestinal cancer is essential for the patient treatment and medical care. Endoscopically guided biopsy is currently the gold standard for the diagnosis of early esophageal cancer, but can suffer from high false negative rates due to sampling errors. Optical coherence tomography (OCT) is an emerging medical imaging technology which can generate high resolution, cross-sectional images of tissue <i>in situ</i> and in real time, without the removal of tissue specimen. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10 - 15 m for clinical procedures. In this study, <i>in vivo</i> imaging of the gastrointestinal tract is demonstrated at a three-fold higher resolution (< 5 m), using a portable, broadband, Cr<sup>4+</sup>:Forsterite laser as the optical light source. Images acquired from the esophagus, gastro-esophageal junction and colon on animal model display tissue microstructures and architectural details at high resolution, and the features observed in the OCT images are well-matched with histology. The clinical feasibility study is conducted through delivering OCT imaging catheter using standard endoscope. OCT images of normal esophagus, Barrett's esophagus, and esophageal cancers are demonstrated with distinct features. The ability of high resolution endoscopic OCT to image tissue morphology at an unprecedented resolution <i>in vivo</i> would facilitate the development of OCT as a potential imaging modality for early detection of neoplastic changes.
Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr<sup>4+</sup>:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.
We demonstrate real time, ultrahigh resolution OCT imaging using a portable mode-locked Cr:forsterite laser. OCT imaging at 5.5 um axial resolution was performed of normal and cancerous human prostate tissue and correlated with histology.