Miniature forward-viewing common-path OCT probe for imaging the renal pelvis

Imaging of Atrioventricular Nodal Conduction Tissue in Porcine Hearts Using Optical Coherence Tomography

Optical coherence tomography (OCT) employs near-infrared light to image the microstructure of different tissues. Clinically, it has been used to image the walls of coronary arteries. In research settings, one of the applications for OCT is visualizing endocardial and subendocardial structures. The present experiment sought to determine whether OCT can identify native conduction tissues in adult porcine hearts. During the study, the right atrial endocardial surfaces of excised adult porcine hearts were exposed. The triangle of Koch was imaged with the OCT system and the conduction tissue was identified. The area was then prepared for histologic examination with Masson's trichrome stain. The results of histologic preparations and OCT images were then compared. Ultimately, nine porcine hearts were examined using this methodology. OCT imaging successfully identified subendocardial structures presumed to be the compact atrioventricular node. Histologic images of the preparations delineated the different tissue types and conduction tissue was easily identified. The location of distinctive hyporeflective areas in the OCT images correlated with the location of conduction tissue in the histology images. In light of the findings of this study, it is suggested that atrioventricular nodal tissue can be identified by OCT in freshly dissected unfixed porcine hearts. OCT images distinguished the differentiated conduction tissue in close proximity with the endocardium, myofibers, and fibrous tissue, and the success of this was verified with histology. This technology may be useful for the direct visualization of the native conduction system during procedures in the operating room and electrophysiology laboratory. Further studies with perfused tissue samples and live animal experiments are needed to better assess the efficacy of this novel application.

Full-field swept-source optical coherence tomography and neural tissue classification for deep brain imaging

Optical coherence tomography can differentiate brain regions with intrinsic contrast and at a micron scale resolution. Such a device can be particularly useful as a real-time neurosurgical guidance tool. We present, to our knowledge, the first full-field swept-source optical coherence tomography system operating near a wavelength of 1310 nm. The proof-of-concept system was integrated with an endoscopic probe tip, which is compatible with deep brain stimulation keyhole neurosurgery. Neuroimaging experiments were performed on ex vivo brain tissues and in vivo in rat brains. Using classification algorithms involving texture features and optical attenuation, images were successfully classified into three brain tissue types.

Long-range common-path spectral domain optical coherence tomography

Fiber-based common-path spectral domain optical coherence tomography (SD-OCT) is compact and polarization insensitive, which is usually used in endoscopic biomedical imaging. In this study, we investigate a method to extend the working distance of a common-path SD-OCT system. Common-path OCT light, which consisting of sample and reference light signal, is directed into a free space optical interferometer. The OCT light is split spatially into two beam segments by a wavefront-splitting mirror, and the two parallel beams interfere noncollinearly in the interferometer. Distance between the end of the probing fiber, which serves as the reference plane of our OCT system, and the OCT sample is about 140 mm. The OCT performance is demonstrated by imaging biological samples. The proposed method can be used to develop polarization insensitive OCT probe for biomedical imaging applications.

Depolarization characteristics of spatial modes in imaging probe using short multimode fiber

Optical coherence tomography is one of the standard imaging modalities at present, widely used in the medical and biological fields to obtain three-dimensional (3D) images with high spatial resolution. However, the depth up to which the 3D images can be directly obtained is limited to within 3 mm. Therefore, the suitability of many kinds of catheters and needles has been considered for minimally invasive imaging. We have examined the utility of a short multimode fiber (SMMF) using graded index optical fibers for minimal invasive imaging of deeper areas, up to 6-8 mm. The diameter and length of the SMMF are 125 μm and 6-8 mm, respectively. In the core of the SMMF, scattering and multirefraction occur due to small variations in the refractive index to generate deformations and depolarization of images. In order to investigate the depolarization characteristics, the images reflected at the facet of the SMMF were measured by changing the angle of the polarizer, using an LED as the light source. The reflection image almost corresponds to that obtained with combined linearly polarized modes with the ratio of LP₀₁∶LP₁₁∶LP₂₁ equal to 1∶0.2∶0.7. Comparing the measured results with simulations in the simple model, the depolarization ratio was estimated at 0.7 in the core. The degrees of polarization were measured to be 0.15 around the center and increased to 0.90 at the periphery.

Imaging characteristics of an 8.8 mm long and 125 μm thick graded-index short multimode fiber probe

We demonstrated the feasibility of an ultrathin imaging probe with a 50-μm core diameter, a 125 μm total diameter, and an 8.8 mm length, which is a typical graded-index multimode fiber for optical communications. We used an ABCD matrix to analyze the imaging conditions and magnification, which corresponded closely to the measured results. The lateral resolution was calculated at 1.2 μm with a wavelength of 730 nm, which reflects the image test pattern where a period of 4.38 μm was measured with a wavelength of 730 nm. In the numerical aperture of the objective lens, we experimentally evaluated the tradeoff between the magnification and the coupling efficiency. At four wavelengths of 540 nm, 632 nm, 730 nm, and 852 nm, the contrast and signal intensity versus the wavelength were investigated to show that the contrast at 632 and 730 nm is relatively high. By using a thin random phase screen model, we explained that as the wavelength decreases the greater the decrease in the optical transfer function at higher spatial frequencies. Using a 635 nm LED light source, we imaged the surfaces of chicken tendons in contact and the surface roughness was visible.