Abstract
In this paper, we aim to provide optimal parameters for micro-computed tomography scans of fish otoliths. We tested fifteen different combinations to sagittae. The images were scaled to Hounsfield units, and segmented in two distinct volumes-of-interest (external and internal). The strategy we applied, for identifying optimum scan settings for otoliths, included analyses of the sinogram, the distribution of the Hounsfield units and the signal-to-noise ratio. Based on these tests, the optimum sets of parameters for the acquisition of tomographic images of sagittal otoilths were 80 kV, 220 microA and 0.5 mm aluminum filter.The method allowed 3D shape analysis, internal and external density distribution, layer-by-layer density segmentation, and a potential objective method to count growth rings in otoliths. It was possible to compare mean densities between species, and we observed a significant difference among them. In addition, there are ontogenic changes, which could be increasing or decreasing the density. In this study, we applied tomography for several otolith analysis, that could be of great interest for future studies in diverse areas that use otoliths as the basic structure of analysis, or represents a new research line called eco-densitometry of otoliths, where tomography could be applied to explore the density within an ecological perspective.
Highlights
Over recent years, x-ray computed tomography (CT) has evolved from an exclusive tool of medicine into a widely accepted technique for analyzing the internal structure of objects in a non-destructive way (Schoepf and Costello, 2004; Budoff and Shinbane, 2016; Jalaguier-Coudray et al, 2016)
A micro-computed tomography scan involves digitally reconstructing a set of projections formed by the transmitted x-ray beam through the sample (Kak and Slaney, 2001)
We evaluated the possible correlation between the mean radiodensity of each otolith and the respective fish length, using simple linear correlation analysis, in order to detect ontogenetic trends for each species
Summary
X-ray computed tomography (CT) has evolved from an exclusive tool of medicine into a widely accepted technique for analyzing the internal structure of objects in a non-destructive way (Schoepf and Costello, 2004; Budoff and Shinbane, 2016; Jalaguier-Coudray et al, 2016). A micro-computed tomography (micro-CT) scan involves digitally reconstructing a set of projections formed by the transmitted x-ray beam through the sample (Kak and Slaney, 2001). These projections are two-dimensional images with micrometric pixel resolution, and the gray-scale of the pixels reflects the mean of the attenuation coefficient of the material, caused by the scattering and/or absorption of photons due to interactions with the object (Grodstein, 1957). In conventional tomography, during the photons production, the X-ray beam contains different energy values. Finding an optimal combination of these parameters is a process required for each type of structure (Kak and Slaney, 2001; Hsieh, 2009)
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