High-resolution cardiac imaging and fiber analysis methods are desired for deeper understanding cardiac anatomy. Although refraction-contrast X-ray CT (RCT) has high contrast for soft tissues, its scanning cost is very high. On the other hand, micro-focus X-ray CT (μCT) is a modality that is commercially available with lower cost, but its contrast for soft tissue is not as high as RCT. To investigate the efficacy of μCT for fiber analysis, we scanned a common rabbit heart with both modalities with our original protocol of preparing materials, and compared their image-based analysis results. Their results were very similar, with correlation coefficient of 0.95. We confirmed that µCT volumes prepared by our protocol are useful for fiber analysis as well as RCT.
A surgical simulator with elaborate artificial eyeball models has been developed for ophthalmic surgeries, in which sophisticated skills are required. To create the elaborate eyeball models with microstructures included in an eyeball, a database of eyeball models should be compiled by segmenting eye structures based on high-resolution medical images. Therefore, this paper presents an automated segmentation of eye structures from micro-CT images by using Fully Convolutional Networks (FCNs). In particular, we aim to construct a method for accurately segmenting eye structures from sparse annotation data. This method performs end-to-end segmentation of eye structures, including a workflow from training the FCN based on sparse annotation to obtaining the segmentation of the entire eyeball. We use the FCN trained on the slices sparsely annotated in a micro-CT volume to segment the remaining slices in the same volume. To achieve accurate segmentation from less annotated images, the multi-class segmentation is performed by using the network trained on the preprocessed and augmented micro-CT images; in the preprocessing, we apply filters for removing ring artifacts and random noises to the images, while in the data augmentation process, rotation and elastic deformation operations are performed on the sparsely-annotated training data. From the results of experiments for evaluating segmentation performances based on sparse annotation, we found that the FCN trained with data augmentation could achieve high segmentation accuracy of more than 90% even from a sparse training subset of only 2.5% of all slices.