Detecting Early Choroidal Changes Using Piecewise Rigid Image Registration and Eye-Shape Adherent Regularization

Choroidal and retinal thickness changes can occur in patients with refractive errors (e.g. myopia) or ocular diseases (e.g. central serous chorioretinopathy, glaucoma, etc.) and must therefore be detected as early as possible and monitored. Image acquisition is usually done with the help of optical coherence tomography (OCT), which allows 2- and 3-dimensional images with micrometer resolution. Segmentation-based image analysis methods are used to detect and quantify thickness changes. However, segmenting the choroid is often a challenging task because of low contrast, loss of signal and the presence of artifacts in the acquired images. In particular, in vivo imaging of the choroid-sclera interface (CSI), the border separating the choroid from the sclera, is prone to these image degradations. In this thesis, we present CRAR, a novel method for the early detection of choroidal changes based on piecewise rigid image registration. CRAR allows elastic modeling of the relatively soft choroid without affecting the more rigid properties of the surrounding sclera and retina. Rather than insisting on finding the exact position of the CSI, we focus on the changes of the entire choroid-sclera border. This enables us to circumvent the aforementioned difficulties because, using this approach, an exact recognition of the choroid-sclera boundary is not required. In this approach, we focus on juvenile myopia (also called “school myopia”), which in Asian regions, and especially in China, has reached almost epidemic dimensions by now. Since juvenile myopia correlates with changes in the thickness of the choroid, but not with its structure as such, we restrict the transformation model to the anterior-posterior (z-) direction. The proposed regularization allows respecting the eye's natural shape. In this context, the local homogeneity of the transformations in nasal-temporal (x-) and superior-inferior (y-) direction are boosted by penalizing their radial differences. However, a comprehensive evaluation of the performance in detecting such changes is challenging, as a ground truth for comparison with the in vivo situation does not exist. In order to overcome this limitation, we present a statistical validation framework for automated choroidal thickness changes detection, in which a method purely based on the common agreement between the algorithm and all experts is combined with an exhaustive power analysis approach. We show the strengths of the framework with the example of CRAR: the framework demonstrates if an algorithm functions at an expert level, while the integrated power analysis allows concluding whether the algorithm performs even better than the experts. We further applied CRAR to macular telangiectasia type 2 (MacTel2). The analysis of follow-up images of this disease suggests that there might be a correlation between changes in the choroidal thickness and the further development of MacTel2. The further refinement of the presented method CRAR can provide an objective and sensitive tool to analyze and monitor the progress of myopia, and beyond

Objective measurement of motion in the orbit

The research described in the thesis had two major aims: to find methods for objective measurement of motion in the orbit, and to determine the clinical use of these methods in patients with orbital disorders. This implied that a number of research questions had to be answered in the fields of both image science and of ophthalmology and orbitology. The results have established that measurement of the two- and three-dimensional motion of tissues in the orbit is feasible in humans. It can be imaged in 2-D and 3-D with Magnetic Resonance Imaging (MRI) sequences. It can be calculated objectively from these sequences using optical flow methods. First order techniques were found to be superior for this purpose as they are less sensitive to noise, partial volume effects and aliasing. A new first-order 3-D optical flow algorithm was developed for robust and computationally efficient three-dimensional optical flow estimation. A number of techniques were developed to visualize 2- and 3-D motion combined with the anatomy in 3-D space, using color-coding. The results of two clinical studies have established the clinical use of objective measurement of motion in the orbit in a number of orbital and motion disorders. The studies have resulted in an explanation for the persistent pain that may occur after enucleation of the globe, based on motion measurements in patients after enucleation. They have also shown that orbital tumors can be differentiated using motion studies. The results have also shown that the position of the rectus muscle pulleys is the same in patients with Graves disease and in normals. After surgical decompression of the orbit, the muscles and their pulleys are usually not displaced, except in cases where specific muscle paths and pulleys are displaced in specific patterns, resulting in specific motility disturbances. Thus, a new explanation has been found for the motility disturbances that may occur in some patients after decompression surgery for Graves orbitopathy. These last findings have led to the notion central to this thesis, namely that the orbital tissues are an organ in their own right, the organ of gaze, and do not need their bony orbit to function normally

Detecting Early Choroidal Changes using Piecewise Rigid Image Registration and Eye-Shape Adherent Regularization

Recognizing significant temporal changes in the thickness of the choroid and retina at an early stage is a crucial factor in the prevention and treatment of ocular diseases such as myopia or glaucoma. Such changes are expected to be among the first indicators of pathological manifestations and are commonly dealt using segmentation-based approaches. However, segmenting the choroid is challenging due to low contrast, loss of signal and presence of artifacts in optical coherence tomography (OCT) images. In this paper, we present a novel method for early detection of choroidal changes based on piecewise rigid image registration. In order to adhere to the eye’s natural shape, the regularization enforces the local homogeneity of the transformations in nasal-temporal (x-) and superior-inferior (y-) direction by penalizing their radial differences. We restrict our transformation model to anterior-posterior (z-) direction, as we focus on juvenile myopia, which correlates to thickness changes in the choroid rather than to structural alterations. First, the precision of the method was tested on an OCT scan-rescan data set of 62 healthy Asian children, ages 7 to 13, from a population with a high prevalence of myopia. Furthermore, the accuracy of the method in recognizing synthetically induced changes in the data set was evaluated. Finally, the results were compared to those of manually annotated scans

Advances in Bioengineering

The technological approach and the high level of innovation make bioengineering extremely dynamic and this forces researchers to continuous updating. It involves the publication of the results of the latest scientific research. This book covers a wide range of aspects and issues related to advances in bioengineering research with a particular focus on innovative technologies and applications. The book consists of 13 scientific contributions divided in four sections: Materials Science; Biosensors. Electronics and Telemetry; Light Therapy; Computing and Analysis Techniques