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A clinically acceptable auto-spine detection system, i.e., localization and labeling of vertebrae and inter-vertebral discs, is required to have high robustness, in particular to severe diseases (e.g. scoliosis) and imaging artifacts (e.g. metal artifacts in MR). Our method aims to achieve this goal with two novel components. First, instead of treating vertebrae/discs as either repetitive components or completely independent entities, we emulate a radiologist and use a hierarchial strategy to learn detectors dedicated to anchor (distinctive) vertebrae, bundle (nondistinctive) vertebrae and inter-vertebral discs, respectively. At run-time, anchor vertebrae are detected concurrently to provide redundant and distributed appearance cues robust to local imaging artifacts. Bundle vertebrae detectors provide candidates of vertebrae with subtle appearance differences, whose labels are mutually determined by anchor vertebrae to gain additional robustness. Disc locations are derived from a cloud of responses from disc detectors, which is robust to sporadic voxel-level errors. Second, owing to the non-rigidness of spine anatomies, we employ a local articulated model to effectively model the spatial relations across vertebrae and discs. The local articulated model fuses appearance cues from different detectors in a way that is robust to abnormal spine geometry resulting from severe diseases. Our method is validated by 300 MR spine scout scans and exhibits robust performance, especially to cases with severe diseases and imaging artifacts.

Diagnostic magnetic resonance (MR) image quality is highly dependent on the position and orientation of the slice groups, due to the intrinsic high in-slice and low through-slice resolutions of MR imaging. Hence, the higher speed, accuracy, and reproducibility of automatic slice positioning, make it highly desirable over manual slice positioning. However, imaging artifacts, diseases, joint articulation, variations across ages and demographics as well as the extremely high performance requirements prevent state-of-the-art methods, such as volumetric registration, to be an off-the-shelf solution. In this paper, we address all these issues through an automatic slice positioning framework based on redundant and hierarchical learning. Our method has two hallmarks that are specifically designed to achieve high robustness and accuracy. 1) A redundant set of anatomy detectors are learned to provide local appearance cues. These detections are pruned and assembled according to a distributed anatomy model, which captures group-wise spatial configurations among anatomy primitives. This strategy brings about a high level of robustness and works even if a large portion of the target is distorted, missing, or occluded. 2) The detectors are learned and invoked in a hierarchical fashion, with each local detection scheduled and iterated according to its intrinsic invariance property. This iterative alignment process is shown to dramatically improve alignment accuracy. The proposed system is extensively validated on a large dataset including 744 clinical MR scans. Compared to state-of-the-art methods, our method exhibits superior performance in terms of robustness, accuracy, and reproducibility. The methodology is general and can be applied to other anatomies and other imaging modalities.

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Abstract:The investigation of the internal structure of calcite crystals is a new focus in speleothem science, especially in the range of crystallization temperatures close to 0°C. Recently found calcite spars from Zinnbergschacht Cave of the Franconian Alb (SE Germany) are ideal for multi-method investigation. The elongated calcites (up to 6 cm in length) with three to six lateral faces and basal triangular faces at the ends are observed in collapse-zones in the cave. 230 Th/U-ages of 38.9 ka suggest formation during the periglacial Weichselian, between the Scandinavian and Alpine Glaciations. The δ 18 O and δ 13 C values of the calcite spars vary from -11.18 to -16.11‰ V-PDB and from -4.78 to -6.13‰ V-PDB, respectively. The exceptionally low δ18 O values of these calcites appear to be due to precipitation in pools on ice. The values deviate considerably from those of conventional interglacial speleothems (δ 18 O = -7.21 to -7.55‰, δ 13 C = -9.77 to -10.86‰) and also from true Weichselian cryogenic calcites (composite spherulites and rhombohedral chains with δ 18 O = -15.06 to -18.04‰ and with δ 13 C = -3.52 to -4.13‰). The δ 18 O values of the latter calcites is typical of cryogenesis of calcites with extensive oxygen isotope fractionation (preferred incorporation of 18 O into the co-occurring ice). Thus, the δ 18 O values of the calcites suggest cold conditions up to the beginning of cryogenesis. Cathodoluminescence (CL) and backscattered electrons (BSE) indicate the distribution of impurities within the calcite spars as pigmented triangles surrounded by clear calcite, with a higher density of the triangles in the outer areas. Three hierarchies of triangles can be distinguished by BSE, documenting a filigreed primary structure of the spars. Electron backscatter diffraction (EBSD) reveals a divergent orientation of the triangular subcrystals from the center to the outer corners of the calcites. Thus, their internal structure reflects an example of fascicular optic fibrous calcites (FOFC), frequently discussed in carbonate petrology.Weichselian, cryogenic calcites, fascicular optic fibrous calcite, electron backscatter diffraction, Franconian Alb