A. Naber, D. Berwanger, G. K. Steinberg, and W. Nahm. Spatial gradient based segmentation of vessels and quantitative measurement of the inner diameter and wall thickness from ICG fluorescence angiographies. In SPIE Photonics West, vol. 11229 1122916-2, 2020
During neurovascular surgery the vascular function can be checked intraoperatively and qualitatively by observing the blood dynamics inside the vessel via Indocyanine Green (ICG) Fluorescence Angiography. This state-of-the- art method provides the surgeon with valuable semi-quantitative information but needs to be improved towards a quantitative assessment of vascular volume flow. The precise measurement of volume flow rely on the assumption that both the inner geometry of the blood vessel and the blood flow velocity can be precisely obtained from Fluorescence Angiography. The correct reconstruction of the inner diameter of the vessel is essential in order to minimize the propagated error in the flow calculation. Although ICG binds specifically on blood plasma proteins the fluorescence light radiates also from outside the inner vessel volume due to multiple scattering in the vessel wall, causing a fading edge intensity contrast. A spatial gradient based segmentation method is proposed to reliably estimate the inner diameter of cerebral vessels from intraoperative Fluorescence Angiography images. As result the minimum of the second deviation of the intensity values perpendicular to the vessels edge was identified as the best feature to assess the inner diameter of artificial vessel phantoms. This method has been applied to cerebrovascular vessel images and the results, since no ground truth is available, comply with literature values.
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.