Confocal laser endomicroscopy (CLE) has found an increasing number of applications in clinical and pre-clinical studies, for it allows intraoperative in-situ tissue morphology at cellular resolution. CLE is considered as one of the most promising systems for in-vivo pathological diagnostics. Miniaturized imaging probes are designed for intraoperative applications. Due to less sophisticated optical design, CLE systems are more prone to image aberrations and distortions. While diagnostics with CLE takes reference from the corresponding histological images, the determination of the resolution and aberrations of the CLE systems becomes essential. Thereby on-site quality check of system performance is required. Additionally, these compact systems enable a field of view of less than half square millimeter without zooming function, which makes it difficult to correlate human vision to the microscopic scenes. Therefore, it is necessary to have defined microstructures working as a test target for CLE systems. We have extended the 2D bar pattern in 1951 USAF test chart to 3D structures for both lateral and axial resolution assessment, since axial resolution represents the optical sectioning ability of CLE systems and is one of the key parameters to be assessed. The test target was produced by direct laser writing. Yellow-green fluorescence emission can be excited at 488 nm. It can also be used for other fluorescence microscopic imaging modalities in the corresponding wavelength range.
Y. Su. Simulation model for resolution and contrast analysis of microscopic images based on optical coherence contrast method. In BMTMedPhys 2017, vol. 62(s1) , pp. S87, 2017
Optical methods of imaging biological tissues are non-contact and low-risk techniques, which are of great advantage over conventional medical imaging modalities such as X-ray computed tomography (CT) and ultrasound imaging. On the microscopic level, scattering property of biological tissues is associated with tissue inhomogeneity. By detecting the backscattered light signal, structures of different reflectance can be distinguished. Coherent-gating gets rid of unwanted light resulting in further improvements of signal-to-noise ratio (SNR) and image contrast. Recent years optical imaging methods based on coherent-gating, optical coherence tomography (OCT) in particular, have been applied to medical diagnosis for its ability to localize pathological changes in tissues. Even cellular-resolution images have been demonstrated, where enlarged nuclei of neoplastic cells are visualized. However, a realistic modeling of microscopic image resolution and contrast using such methods are rarely reported. In this work, simulation of en face images from low-coherence interferometry (LCI) and spectral domain OCT (SD-OCT) is performed by our self-developed Matlab tool-kit. The image resolution and contrast are then examined with different system configurations, i.e. objectives with different numerical apertures (NAs), low-coherent light source of various central wavelength, bandwidth and optical power. Unlike the standard applications in ophthalmology, the tissue model in our tool-kit is designed to be less transparent than the eye. Thus the microscopic image contrast of such methods on turbid tissues is studied. This tool-kit can be further used to evaluate the performance of LCI or OCT systems for en face imaging, as well as to improve system design.