Automatic Lumbar Vertebrae Segmentation in Fluoroscopic Images via Optimised Concurrent Hough Transform

Low back pain is a very common problem in the industrialised countries and its associated cost is enormous. Diagnosis of the underlying causes can be extremely difficult. Many studies have focused on mechanical disorders of the spine. Digital videofluoroscopy (DVF) was widely used to obtain images for motion studies. This can provide motion sequences of the lumbar spine, but the images obtained often suffer due to noise, exacerbated by the very low radiation dosage. Thus determining vertebrae position within the image sequence presents a considerable challenge. In this paper, we show how our new approach can automatically detect the positions and borders of vertebrae concurrently, relieving many of the problems experienced in other approaches. First, we use phase congruency to relieve difficulty associated with threshold selection in edge detection of the illumination variant DVF images. Then, our new Hough transform approach is applied to determine the moving vertebrae, concurrently. We include optimisation via a genetic algorithm as without it the extraction of moving multiple vertebrae is computationally daunting. Our results show that this new approach can indeed provide extractions of position and rotation which appear to be of sufficient quality to aid therapy and diagnosis of spinal disorders

Lumbar Spine Location in Fluoroscopic Images by Evidence Gathering

Low back pain (LBP) is a very common problem and lumbar segmental instability is one of the causes. It is important to investigate lumbar spine movement in order to understand instability better and as an aid to diagnosis. Digital videofluoroscopy provides a method of quantifying the motion of individual vertebrae, but due to the relatively poor image quality, it is difficult and time consuming to locate landmarks manually, from which the kinematics can be calculated. Some semi-automatic approaches have already been developed but these are still time consuming and require some manual interaction. In this paper we apply the Hough transform (HT) to locate the lumbar spinal segments automatically. The HT is a powerful tool in computer vision and it has good performance in noise and partial occlusion. A recent arbitrary shape representation avoids problems inherent with tabular representations in the generalised HT (GHT) by describing shapes using a continuous formulation. The target shape is described by a set of Fourier descriptors, which vote in an accumulator space from which the object parameters of translation (including the x and y direction), rotation and scale can be determined. At present, this algorithm has been applied to the images of lumbar spine, and has been shown to provide satisfactory results. Further work will concentrate on reducing the computational time for real-time application, and on approaches to refine information at the apices, given initialisation by the new HT method

A novel experimental technique and its application to study the effects of particle density and flow submergence on bed particle saltation

This research was sponsored by EPSRC grant EP/G056404/1 which is greatly appreciated.Peer reviewedPublisher PD

The fluctuation energy balance in non-suspended fluid-mediated particle transport

Here we compare two extreme regimes of non-suspended fluid-mediated particle transport, transport in light and heavy fluids ("saltation" and "bedload", respectively), regarding their particle fluctuation energy balance. From direct numerical simulations, we surprisingly find that the ratio between collisional and fluid drag dissipation of fluctuation energy is significantly larger in saltation than in bedload, even though the contribution of interparticle collisions to transport of momentum and energy is much smaller in saltation due to the low concentration of particles in the transport layer. We conclude that the much higher frequency of high-energy particle-bed impacts ("splash") in saltation is the cause for this counter-intuitive behavior. Moreover, from a comparison of these simulations to Particle Tracking Velocimetry measurements which we performed in a wind tunnel under steady transport of fine and coarse sand, we find that turbulent fluctuations of the flow produce particle fluctuation energy at an unexpectedly high rate in saltation even under conditions for which the effects of turbulence are usually believed to be small

Analytical and discrete solutions for the incipient motion of ellipsoidal sediment particles

[EN] This work introduces analytical and numerical approaches to compute the incipient motion of ellipsoidal sediment particles. Initiation of motion of spherical particles is dominated by rolling mode. However, solutions for initiation of motion for non-spherical grains have to incorporate rolling, sliding, and mixed modes. The proposed approaches include a wide variety of shapes and inclinations that represent realistic configurations of sediment bed layers. The numerical procedure is based on the discrete element method, simulating the micro-mechanics of the sediment as an aggregate of rigid ellipsoids interacting by contact. The numerical solution covers a range of incipient movements that cannot be covered by the analytical approach. Hence, some trapped modes observed in analytical calculations are complemented by the numerical computation of threshold stresses. The main results are organized as novel extended Shields diagrams for non-spherical grains, where non-dimensional critical shear stress is represented in terms of friction Reynolds number.This work was supported by the Ministerio de Ciencia e Innovación Grant [#BIA-2012-32918 and #BIA-2015-64994-P (MINECO/FEDER)].Bravo, R.; Ortiz, P.; Pérez-Aparicio, JL. (2018). Analytical and discrete solutions for the incipient motion of ellipsoidal sediment particles. Journal of Hydraulic Research. 56(1):29-43. https://doi.org/10.1080/00221686.2017.1289263S2943561Belytschko, T., & Neal, M. O. (1991). Contact-impact by the pinball algorithm with penalty and Lagrangian methods. International Journal for Numerical Methods in Engineering, 31(3), 547-572. doi:10.1002/nme.1620310309Bravo, R., Ortiz, P., & Pérez-Aparicio, J. L. (2014). Incipient sediment transport for non-cohesive landforms by the discrete element method (DEM). Applied Mathematical Modelling, 38(4), 1326-1337. doi:10.1016/j.apm.2013.08.010Bravo, R., Pérez-Aparicio, J. L., & Gómez-Hernández, J. J. (2015). Numerical sedimentation particle-size analysis using the Discrete Element Method. Advances in Water Resources, 86, 58-72. doi:10.1016/j.advwatres.2015.09.024Bravo, R., Pérez-Aparicio, J. L., & Laursen, T. A. (2012). An energy consistent frictional dissipating algorithm for particle contact problems. International Journal for Numerical Methods in Engineering, 92(9), 753-781. doi:10.1002/nme.4346Buffington, J. M., & Montgomery, D. R. (1997). A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers. Water Resources Research, 33(8), 1993-2029. doi:10.1029/96wr03190Cheng, N.-S., & Chiew, Y.-M. (1999). Incipient sediment motion with upward seepage. Journal of Hydraulic Research, 37(5), 665-681. doi:10.1080/00221689909498522Chiew, Y.-M., & Parker, G. (1994). Incipient sediment motion on non-horizontal slopes. Journal of Hydraulic Research, 32(5), 649-660. doi:10.1080/00221689409498706Derksen, J. J. (2015). Simulations of granular bed erosion due to a mildly turbulent shear flow. Journal of Hydraulic Research, 53(5), 622-632. doi:10.1080/00221686.2015.1077354Dey, S. (1999). Sediment threshold. Applied Mathematical Modelling, 23(5), 399-417. doi:10.1016/s0307-904x(98)10081-1Dey, S. (2003). Threshold of sediment motion on combined transverse and longitudinal sloping beds. Journal of Hydraulic Research, 41(4), 405-415. doi:10.1080/00221680309499985Dey, S., Sarker, H. K. D., & Debnath, K. (1999). Sediment Threshold under Stream Flow on Horizontal and Sloping Beds. Journal of Engineering Mechanics, 125(5), 545-553. doi:10.1061/(asce)0733-9399(1999)125:5(545)Hölzer, A., & Sommerfeld, M. (2008). New simple correlation formula for the drag coefficient of non-spherical particles. Powder Technology, 184(3), 361-365. doi:10.1016/j.powtec.2007.08.021James, C. S. (1990). Prediction of entrainment conditions for nonuniform, noncohesive sediments. Journal of Hydraulic Research, 28(1), 25-41. doi:10.1080/00221689009499145Ji, C., Munjiza, A., Avital, E., Ma, J., & Williams, J. J. R. (2013). Direct numerical simulation of sediment entrainment in turbulent channel flow. Physics of Fluids, 25(5), 056601. doi:10.1063/1.4807075Klamkin, M. S. (1971). Elementary Approximations to the Area of N-Dimensional Ellipsoids. The American Mathematical Monthly, 78(3), 280. doi:10.2307/2317530Mandø, M., & Rosendahl, L. (2010). On the motion of non-spherical particles at high Reynolds number. Powder Technology, 202(1-3), 1-13. doi:10.1016/j.powtec.2010.05.001MILLER, M. C., McCAVE, I. N., & KOMAR, P. D. (1977). Threshold of sediment motion under unidirectional currents. Sedimentology, 24(4), 507-527. doi:10.1111/j.1365-3091.1977.tb00136.xWan Mohtar, W. H. M., & Munro, R. J. (2013). Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence. Physics of Fluids, 25(1), 015103. doi:10.1063/1.4774341Ortiz, P., & Smolarkiewicz, P. K. (2006). Numerical simulation of sand dune evolution in severe winds. International Journal for Numerical Methods in Fluids, 50(10), 1229-1246. doi:10.1002/fld.1138Ortiz, P., & Smolarkiewicz, P. K. (2009). Coupling the dynamics of boundary layers and evolutionary dunes. Physical Review E, 79(4). doi:10.1103/physreve.79.041307Van Rijn, L. C. (1984). Sediment Transport, Part I: Bed Load Transport. Journal of Hydraulic Engineering, 110(10), 1431-1456. doi:10.1061/(asce)0733-9429(1984)110:10(1431)Shi, G.-H., & Goodman, R. E. (1985). Two dimensional discontinuous deformation analysis. International Journal for Numerical and Analytical Methods in Geomechanics, 9(6), 541-556. doi:10.1002/nag.1610090604Shields, A. (1936). Application of similarity principles and turbulence research to bed-load movement (Tech. Rep.). Lab. for Hydraulic Water Resources.Wellmann, C., Lillie, C., & Wriggers, P. (2008). A contact detection algorithm for superellipsoids based on the common‐normal concept. Engineering Computations, 25(5), 432-442. doi:10.1108/02644400810881374Wiberg, P. L., & Smith, J. D. (1985). A theoretical model for saltating grains in water. Journal of Geophysical Research, 90(C4), 7341. doi:10.1029/jc090ic04p0734

Melanoregulin (MREG) Modulates Lysosome Function in Pigment Epithelial Cells

Melanoregulin (MREG), the product of the Mregdsu gene, is a small highly charged protein, hypothesized to play a role in organelle biogenesis due to its effect on pigmentation in dilute, ashen, and leaden mutant mice. Here we provide evidence that MREG is required in lysosome-dependent phagosome degradation. In the Mreg-/- mouse, we show that loss of MREG function results in phagosome accumulation due to delayed degradation of engulfed material. Over time, the Mreg-/- mouse retinal pigment epithelial cells accumulate the lipofuscin component, A2E. MREG-deficient human and mouse retinal pigment epithelial cells exhibit diminished activity of the lysosomal hydrolase, cathepsin D, due to defective processing. Moreover, MREG localizes to small intracellular vesicles and associates with the endosomal phosphoinositide, phosphatidylinositol 3,5-biphosphate. Collectively, these studies suggest that MREG is required for lysosome maturation and support a role for MREG in intracellular trafficking

Effect of Polymer Chemistry on the Linear Viscoelasticity of Complex Coacervates

Complex coacervates can form through the electrostatic complexation of oppositely charged polymers. The material properties of the resulting coacervates can change based on the polymer chemistry and the complex interplay between electrostatic interactions and water structure, controlled by salt. We examined the effect of varying the polymer backbone chemistry using methacryloyl- and acryloyl-based complex coacervates over a range of polymer chain lengths and salt conditions. We simultaneously quantified the coacervate phase behavior and the linear viscoelasticity of the resulting coacervates to understand the interplay between polymer chain length, backbone chemistry, polymer concentration, and salt concentration. Time-salt superposition analysis was used to facilitate a broader characterization and comparison of the stress relaxation behavior between different coacervate samples. Samples with mismatched polymer chain lengths highlighted the ways in which the shortest polymer chain can dominate the resulting coacervate properties. A comparison between coacervates formed from methacryloyl vs acryloyl polymers demonstrated that the presence of a backbone methyl group affects the phase behavior, and thus the rheology in such a way that coacervates formed from methacryloyl polymers have a similar phase behavior to those of acryloyl polymers with ∼10× longer polymer chains