Date Published: January 27, 2017
Publisher: Public Library of Science
Author(s): Christian Enders, Eva-Maria Braig, Kai Scherer, Jens U. Werner, Gerhard K. Lang, Gabriele E. Lang, Franz Pfeiffer, Peter Noël, Ernst Rummeny, Julia Herzen, Alfred S Lewin.
Due to limited X-ray contrast, the use of micro-CT in histology is so far not as widespread as predicted. While specific staining procedures—mostly using iodine—address this shortcoming, long diffusion times restrict its use in the often time-constrained daily routine. Recently, a novel staining protocol has been proposed using a biochemical preconditioning step, which increases the permeability of the cells for the staining agent. This could enable the imaging of entire organs of small mammals at a yet unmatched image quality with reasonable preparation and scan times. We here propose an adaptation of this technique for virtual ophthalmology and histology by volumetrically assessing both human and porcine eyes. Hereby, we demonstrate that (contrast-enhanced) micro-CT can outperform conventional histology in the assessment of tumor entities, as well as functioning as a supplementary tool for surgeons in the positioning of intraocular implants in-vitro and as a general assessment tool for ophthalmologic specimens.
Histopathological work-up using light microscopy is the current gold-standard in the assessment and evaluation of pathological changes at a microanatomical level. The preparation protocol includes embedding of the tissue into paraffin and subsequent micro-scale slicing of the specimen. However, it is well known that the underlying slicing process carries the risk of material loss and sample distortion, among others folding, detachment and dislocation of anatomical structures [1–3]. Furthermore, the specimen itself as well as the information carried by its geometric/volumetric properties are irreversibly lost during the slicing procedure. Especially in the field of biological basic research, three-dimensional reconstruction methods have been proposed to circumvent the aforementioned shortcomings [4–8]: volumetric data are reconstructed by step-wise assembling of serial image slices. Although reconstruction and alignment procedures have been optimized over the years, the underlying methods are not applicable to a clinical setting, as preparation is extremely time consuming [9, 10]. Further, the repeated slicing process is especially vulnerable to the accumulation of geometrical distortions and, not least the resulting image quality is low.
The study was conducted in accordance with the declaration of Helsinki and was approved by the institutional review board (Institutional review board of the University of Ulm, application number 100/15, approval received 29/07/2015). Written informed consent was obtained from the included patient. Fresh, non-processed porcine eyes were acquired from the local slaughter house (Fleischmarkt Donautal, Steinbeisstraße 17, 89079 Ulm, Germany).
Within this study, we demonstrated the potential of micro-CT in an ophthalmology setting for visualizing normal anatomy, intraocular implants and pathological findings. First, we evaluated micro-CT as a helpful tool in the ex-vivo position control of a novel surgical implant, e.g. a measure to evaluate the results of operation in surgeon training. Within the histological slicing process the stent must be removed or will artificially be broken. The former position of the stent is then roughly approximated by assessing remaining cavities as well as stent-fragments in the surrounding tissue. Here, X-ray micro-CT provides an easy and much more precise method to image the surgical implant in situ without prior modification of the actual physiological conditions, which may alter the results. In addition, geometrical configuration data of the whole region of interest can be provided digitally, increasing accessibility and reproducibility of the findings. In addition, this method could substantially improve the assessment of procedures performed as part of ophthalmological surgical training, as the volumetric high-resolution visualization enhances the precision of evaluating the degree of success of ocular stent implantation in an animal model.