High-resolution X-ray Microtomography Research Articles

Quantitative analysis of commercial coating penetration into Fagus crenata wood using X-ray microtomography

Recent advances in wood treatment include the use of eco-friendly coatings to improve the wood’s dimensional stability and appearance. Assessing coating performance during its service life is critical for establishing a knowledge base for product optimization. Numerous approaches, including microimaging, are available for analyzing coating behavior. In addition to conventional microscopic techniques, high-resolution X-ray microtomography is a tool that provides nondestructive imaging of coatings and their substrates. In this study, we performed two-dimensional (2D) and three-dimensional (3D) visualization of tomographic reconstruction images of two coating types, spray and brush, to observe and assess the distribution of several commercial Japanese coating materials in Fagus crenata. X-ray images and plot profiles were used to determine the penetration depths and thicknesses of coatings. Each coated sample was scanned using X-ray microtomography, which allowed successful visualization and quantification of the coating penetration depth. Chemical content and concentration of the coating materials influenced penetration depth and amount.

Steady-state two-phase relative permeability measurements in proppant-packed rough-walled fractures

Understanding multiphase flow in fractures filled with minerals and proppants is vital in various subsurface applications. Limited experimental data have led to reliance on correlations lacking physical basis. We conducted experiments to characterize relative permeability in rough-walled fractures packed with unconsolidated porous media. We tested fractures packed with water-wet 40/70 sand (silica) and surface-coated ceramic proppants. Brine and mineral oil were used as the wetting and non-wetting fluid phases, respectively. Steady-state (SS) drainage (non-wetting-phase displacing wetting-phase) and imbibition (wetting-phase displacing non-wetting-phase) tests were performed under a wide range of saturation histories (full-cycle and scanning-curves) to study relative permeability hysteresis of the propped fractures. Every SS drainage or imbibition test consisted of several discrete points at which fluid saturations and the corresponding relative permeability were measured by varying the fractional flow rates of fluids whilst maintaining a constant total flow rate. We analyzed residual non-wetting phase saturations and relative permeability trends to understand two-phase flow behavior in each proppant pack. High-resolution x-ray microtomography was used to understand the pore-scale topology, wettability, and to provide insights about the pore-scale displacement mechanisms involved in this study. The results showed that commonly used models to estimate relative permeabilities of fractures significantly overestimated the SS brine and oil relative permeabilities (denoted as krw and kro) measured in this study. Further analysis unveiled that the kro values during imbibition exceeded their drainage counterparts in both proppants, the ceramic proppant exhibited a lower initial water saturation and a higher end-point kro permeability at the end of the drainage displacement, as well as higher krw across all flooding processes. Updated fitting parameters for a Brooks-Corey-type relative permeability correlation are introduced. This study presents improved insights, extensive experimentally generated relative permeability data, and an updated relative permeability correlation, which can be collectively utilized to reduce uncertainties associated with continuum-scale forecasts of multiphase flow behavior in fractured subsurface formations.

ТЕРМОМЕХАНИКА ДИСПЕРСНО-НАПОЛНЕННЫХ КОМПОЗИТОВ И КОМПЬЮТЕРНЫЙ ДИЗАЙН МАТЕРИАЛОВ С РЕКОРДНО ВЫСОКОЙ ТЕПЛОПРОВОДНОСТЬЮ

On the example of metal-diamond composites (MDC), a number of issues of thermomechanics of disperse-filled materials with high thermal conductivity used for thermal management are formulated and solved. Due to the importance of the thermal conductivity factor of the interfacial layer, a refined method is proposed for calculating the boundary thermal resistance. This method considers two counter heat flows: from the matrix to the filler and back, and also provides the condition of zero thermal resistance at the same values of the thermomechanical characteristics of these components. Based on the micromechanical model of the disperse-filled composite, an analytical method is developed for determining the effective thermal conductivity coefficient of the metal-diamond composites. The method makes it possible to take into account the boundary thermal resistance, the presence of a thin coating on the diamond particle, the anisometry of diamond particles and the porosity of the metal matrix. The results of the performed parametric analysis are compared with known experimental data and estimates obtained within the framework of existing models. The conclusion on the validity of the developed method is made. A simplified finite-element model is developed for a representative volume of the metal-diamond composites in the form of a cube formed by an aluminum matrix and containing 27 spherical diamond particles of the same radius with a modifying tungsten coating. At a given temperature difference on the opposite faces of the cube, the distribution of heat flux density and the effective heat transfer coefficient of the metal-diamond composites are calculated. Comparison of the results of using the finite element model and the analytical method mentioned above shows their good agreement. Modification of the finite element model is carried out in order to better match the real internal structure of the metal-diamond composites studied by high-resolution X-ray microtomography. Numerical analysis of the temperature field, thermal stress state and fracture kinetics of the aluminum-diamond composite during thermal cycling is performed.

Pore-Scale Characterization of CO2 Trapping and Oil Displacement in Three-Phase Flow in a Heterogeneous Layered Sandstone

Summary Permeability variation in the vertical direction, a typical sandstone reservoir heterogeneity, can trap a large amount of oil in the low-permeability layer. We performed water-alternating-gas (WAG) injection and CO2 foam flooding on a specially constructed millimeter-sized layered sandstone and investigated fluid distribution using high-resolution X-ray microtomography. Based on the segmented images, CO2 capillary-trapping capacity, oil recovery, Euler number, shaper factor, capillary pressure, and fluid flow conductivity were calculated. Our results show that increasing the number of WAG cycles favored CO2 capillary trapping, and oil recovery was enhanced by the WAG strategy. However, there was still a significant amount of oil trapped in the low-permeability layer. After the WAG injection, the connectivity of the residual oil clusters decreased, the capillary pressure of the oil clusters increased, and oil flow conductivity decreased. This was not conducive to further oil recovery. The subsequent injection of CO2 foam effectively recovered the oil in the low-permeability layer. During the no-injection period, we observed a crossflow phenomenon caused by gravity segregation (the high-permeability layer was located below the low-permeability layer), i.e., oil in the low-permeability layer decreased while oil in the high-permeability layer increased, which is beneficial for subsequent oil production. Furthermore, CO2 moved upward driven by gravity, and although capillary barriers could prevent CO2 from escaping, subsequent water injection was essential to improve the stability of CO2 capillary trapping. This work accurately quantifies the distribution of oil and gas in high- and low-permeability layers, thus providing fundamental data for oil recovery and CO2 trapping in reservoirs with vertical heterogeneity. Although the sample used in the experiment was not natural reservoir rock, our results imply that when the permeability ratio between the two layers is greater than 2, sufficient attention must be paid to the fluid distribution differences caused by this layered heterogeneity. Different displacement strategies, such as WAG and CO2 foam flooding, or gravity differences between oil and gas can be used to enhance oil recovery.

Assessment of Thermal Performance of Phase-Change Material-Based Multilayer Protective Clothing Exposed to Contact and Radiant Heat

The research presented in this article concerns the thermal properties of multilayer protective clothing, specifically, the impact of phase-change material (PCM) incorporation on the occurring heat transfer. Multilayer textile assemblies with PCM inserts (macrocapsules containing n-octadecane) and reference assemblies with PP inserts (macrogranules from polypropylene) with very similar geometry and the same textile layers were tested. The spatial geometry of tested assemblies was examined using high-resolution X-ray microtomography (micro-CT). The heating process of the assemblies was examined under the conditions of exposure to contact heat (using thermography) and radiant heat (using a copper plate calorimeter, according to EN ISO 6942). PCM-containing assemblies achieved a temperature rise of 12 °C in a longer period than the reference assemblies; for the contact heat method, the time was longer by 11 and 14 min, and for the radiant heat method by 1.7 and 2.1 min.

Pore-scale characterization of residual gas remobilization in CO2 geological storage

A decrease in reservoir pressure can lead to remobilization of residually trapped CO2. In this study, the pore-scale processes related to trapped CO2 remobilization under pressure depletion were investigated with the use of high-resolution 3D X-ray microtomography. The distribution of CO2 in the pore space of Bentheimer sandstone was measured after waterflooding at a fluid pressure of 10 MPa, and then at pressures of 8, 6 and 5 MPa. At each stage CO2 was produced, implying that swelling of the gas phase and exsolution allowed the gas to reconnect and flow. After production, the gas reached a new position of equilibrium where it may be trapped again. At the end of the experiment, we imaged the sample again after 30 hours. Firstly, the results showed that an increase in saturation beyond the residual value was required to remobilize the gas, which is consistent with earlier field-scale results. Additionally, Ostwald ripening and continuing exsolution lead to a significant change in fluid saturation: transport of dissolved gas in the aqueous phase to equilibriate capillary pressure led to reconnection of the gas and its flow upwards under gravity. The implications for CO2 storage are discussed: an increase in saturation beyond the residual value is required to mobilize the gas, but Ostwald ripening can allow local reconnection of hitherto trapped gas, thus enhancing migration and may reduce the amount of CO2 that can be capillary trapped in storage operations.

3D cellular characterization and finite element analysis of cork compressive behavior based on high-resolution X-ray microtomography

3D cellular characterization and finite element analysis of cork compressive behavior based on high-resolution X-ray microtomography

Characterization of Pharmaceutical Tablets by X-ray Tomography.

Solid dosage forms such as tablets are extensively used in drug administration for their simplicity and large-scale manufacturing capabilities. High-resolution X-ray tomography is one of the most valuable non-destructive techniques to investigate the internal structure of the tablets for drug product development as well as for a cost effective production process. In this work, we review the recent developments in high-resolution X-ray microtomography and its application towards different tablet characterizations. The increased availability of powerful laboratory instrumentation, as well as the advent of high brilliance and coherent 3rd generation synchrotron light sources, combined with advanced data processing techniques, are driving the application of X-ray microtomography forward as an indispensable tool in the pharmaceutical industry.

Micro-scale experimental investigation of the effect of pore space deformation on trapping of supercritical CO2

In this study, we investigate the impact of pore space deformation on various trapping mechanisms of supercritical CO2 (scCO2) relevant to storage of CO2 in deep saline aquifers. A series of unsteady-state two-phase brine/scCO2 drainage, imbibition, and dissolution tests were performed on a miniature sandpack sample under various stress conditions. High-resolution x-ray microtomography techniques were employed to acquire the pore and fluid occupancy maps at each step of the experiment, which were subsequently utilized to characterize the pore space deformation and changes in the frequencies of various pore-scale fluid displacement events. Our results revealed that, during the scCO2 injection stage, additional scCO2 was stored in the sandpack sample after the sandpack was compressed due to an increase in the pressure gradient even though the pore volume had decreased. On the other hand, the capillary trapping was impaired by the pore space contraction because all the imbibition displacement mechanisms at the pore scale, including the piston-like advance and snap-off, were facilitated as a consequence of an increase in their threshold capillary pressures. The increased frequency of snap-off events caused additional trapping, but more importantly, displaced scCO2 from throats by fragmenting large residual scCO2 clusters into smaller globules. During the dissolution process, the trapped scCO2 clusters and globules shrank in both pore bodies and throats, resulting in movement of the Main Terminal Meniscus (MTM) interfaces and snap-off events, respectively. The water relative permeability during the dissolution process decreased, at a fixed saturation, with the increase in the effective stress since the small pores occupied by the water phase deformed more significantly than the large pores.

An efficient 3D extraction and reconstruction method for myelinated axons of mouse cerebral cortex based on mixed intelligence

Accurate reconstruction of the 3D morphology and spatial distribution of myelinated axons in mouse brains is very important for understanding the mechanism and dynamic behavior of long-distance information transmission between brain regions. However, it is difficult to segment and reconstruct myelinated axons automatically due to two reasons: the amount of it is huge and the morphology of it is different between brain regions. Traditional artificial labeling methods usually require a large amount of manpower to label each myelinated axon slice by slice, which greatly hinders the development of the mouse brain connectome. In order to solve this problem and improve the reconstruction efficiency, this paper proposes an annotation generation method that takes the myelinated axon as prior knowledge, which can greatly reduce the manual labeling time while reaching the level of manual labeling. This method consists of three steps. Firstly, the 3D axis equation of myelinated axons is established by sparse axon artificial center point labels on slices, and the region to be segmented is pre-extracted according to the 3D axis. Subsequently, the U-Net network was trained by a small number of artificially labeled myelinated axons and was used for precise segmentation of output by the last step, so as to obtain accurate axon 2D morphology. Finally, based on the segmentation results, the high-precision 3D reconstruction of axons was performed by imaris software, and the spatial distribution of myelinated axons in the mouse brain was reconstructed. In this paper, the effectiveness of this method was verified on the dataset of high-resolution X-ray microtomography of the mouse cortex. Experiments show that this method can achieve an average MIoU 81.57, and the efficiency can be improved by more than 1400x compared with the manual labeling method.

Study on Oil Recovery Mechanism of Polymer-Surfactant Flooding Using X-ray Microtomography and Integral Geometry.

Understanding pore-scale morphology and distribution of remaining oil in pore space are of great importance to carry out in-depth tapping of oil potential. Taking two water-wet cores from a typical clastic reservoir in China as an example, X-ray CT imaging is conducted at different experimental stages of water flooding and polymer-surfactant (P-S) flooding by using a high-resolution X-ray microtomography. Based on X-ray micro-CT image processing, 3D visualization of rock microstructure and fluid distribution at the pore scale is achieved. The integral geometry newly developed is further introduced to characterize pore-scale morphology and distribution of remaining oil in pore space. The underlying mechanism of oil recovery by P-S flooding is further explored. The results show that the average diameter of oil droplets gradually decreases, and the topological connectivity becomes worse after water flooding and P-S flooding. Due to the synergistic effect of “1 + 1 > 2” between the strong sweep efficiency of surfactant and the enlarged swept volume of the polymer, oil droplets with a diameter larger than 124.58 μm can be gradually stripped out by the polymer-surfactant system, causing a more scattered distribution of oil droplets in pore spaces of the cores. The network-like oil clusters are still dominant when water flooding is continued to 98% of water cut, but the dominant pore-scale oil morphology has evolved from network-like to porous-type and isolated-type after P-S flooding, which can provide strong support for further oil recovery in the later stage of chemical flooding.

Dynamic NMR Relaxometry as a Simple Tool for Measuring Liquid Transfers and Characterizing Surface and Structure Evolution in Porous Media.

Porous media containing voids which can be filled with gas and/or liquids are ubiquitous in our everyday life: soils, wood, bricks, concrete, sponges, and textiles. It is of major interest to identify how a liquid, pushing another fluid or transporting particles, ions, or nutriments, can penetrate or be extracted from the porous medium. High-resolution X-ray microtomography, neutron imaging, and magnetic resonance imaging are techniques allowing us to obtain, in a nondestructive way, a view of the internal processes in nontransparent porous media. Here we review the possibilities of a simple though powerful technique which provides various direct quantitative information on the liquid distribution inside the porous structure and its variations over time due to fluid transport and/or phase changes. It relies on the analysis of the details of the NMR (nuclear magnetic resonance) relaxation of the proton spins of the liquid molecules and its evolution during some process such as the imbibition, drying, or phase change of the sample. This rather cheap technique then allows us to distinguish how the liquid is distributed in the different pore sizes or pore types and how this evolves over time; since the NMR relaxation time depends on the fraction of time spent by the molecule along the solid surface, this technique can also be used to determine the specific surface of some pore classes in the material. The principles of the technique and its contribution to the physical understanding of the processes are illustrated through examples: imbibition, drying or fluid transfers in a nanoporous silica glass, large pores dispersed in a fine polymeric porous matrix, a pile of cellulose fibers partially saturated with bound water, a softwood, and a simple porous inclusion in a cement paste. We thus show the efficiency of the technique to quantify the transfers with a good temporal resolution.

Modeling of Heat Transfer through Firefighters Multilayer Protective Clothing Using the Computational Fluid Dynamics Assisted by X-ray Microtomography and Thermography.

This paper explores the modeling of physical phenomena that occur in clothing that affect the safety and biophysical comfort of the user. Three-dimensional models of textile assemblies with complex morphology used in firefighters’ multilayer protective clothing were designed in a CAD environment. The main goal of the research was to design and experimentally verify (by thermography) the models in terms of simulations when the heat transfer occurs through them in selected ambient conditions using the finite volume method. The designed models took into account the subtle differences in the geometry of selected assemblies determined by high-resolution X-ray microtomography. The designed models made it possible to calculate heat transport with a difference of about 2% to 5% in comparison to experiment that depend on the ambient conditions and the complexity of the model geometry. Moreover, the comparison of the simulation results with the experimental outcomes shows that the mapping of subtle differences in the internal structure of the assemblies in the designed models allows us to observe differences in the modeled heat transfer.

4D Synchrotron X-ray Imaging of Grain Scale Deformation Mechanisms in a Seismogenic Gas Reservoir Sandstone During Axial Compaction

Understanding the grain-scale processes leading to reservoir compaction during hydrocarbons production is crucial for enabling physics-based predictions of induced surface subsidence and seismicity hazards. However, typical laboratory experiments only allow for pre- and post-experimental microstructural investigation of deformation mechanisms. Using high-resolution time-lapse X-ray micro-tomography imaging (4D µCT) during triaxial deformation, the controlling grain-scale processes can be visualized through time and space at realistic subsurface conditions. We deformed a sample of Slochteren sandstone, the reservoir rock from the seismogenic Groningen gas field in the Netherlands. The sample was deformed beyond its yield point (axial strain > 15%) in triaxial compression at reservoir P–T-stress conditions (100 °C, 10 MPa pore pressure, 40 MPa effective confining pressure). A total of 50 three-dimensional µCT scans were obtained during deformation, at a spatial resolution of 6.5 µm. Time lapse imaging plus digital volume correlation (DVC) enabled identification of the grain-scale deformation mechanisms operating throughout the experiment, for the first time, both at small, reservoir-relevant strains (< 1%), and in the approach to brittle failure at strains > 10%. During small-strain deformation, the sample showed compaction through grain rearrangement accommodated by inter-granular slip and normal displacements across grain boundaries, in particular, by closure of open grain boundaries or compaction of inter-granular clay films. At intermediate and large strains (> 4%), grain fracturing and pore collapse were observed, leading to sample-scale brittle failure. These observations provide key input for developing microphysical models describing compaction of the Groningen and other producing (gas) reservoirs.

Description of the first cranium and endocranial structures of Stenoplesictis minor (Mammalia, Carnivora), an early aeluroid from the Oligocene of the Quercy Phosphorites (southwestern France)

ABSTRACT We describe a well-preserved cranium of one of the earliest aeluroid carnivorans from the Quercy Phosphorites, southwestern France. The structure of the auditory region (auditory bulla with two chambers separated by a true septum, prominent ventral process of promontorium with facet for the posterior wall of the ectotympanic) reveals that it belongs to a primitive viverrid-like group called ‘stenoplesictoids’, and more precisely to the genus Stenoplesictis. Using high-resolution X-ray micro-tomography, we reconstructed for the first time virtual endocranial structures (brain endocast, stapes, and bony labyrinths) of a ‘stenoplesictoid’. The brain endocast has a well-developed neocortex and simple coronolateral and suprasylvian sulci, more evolved than older Carnivoramorpha and indicates a primitive step towards the extant genera. Based on the characters of the dentition and of the auditory region, we conclude that this cranium belongs to Stenoplesictis minor. While we still cannot suggest phylogenetic relationships between ‘stenoplesictoids’ and other aeluroids, our study constitutes a first attempt to unravel new morphological data to better characterise the enigmatic ‘stenoplesictoids’, a step forward in the understanding of the evolution of early aeluroids.

Quantitative characterization of bamboo cortex structure based on X-ray microtomography

Bamboo is a natural fiber composite with layered structure. Millions of years of evolution have endowed bamboo with the most effective structure in nature. The ingenious microstructure provides bamboo with excellent mechanical properties. Bamboo culm is composed of the cortex, a middle layer, and a pith ring. The cortex refers to the area starting from the periphery of the culm wall to the vascular bundles. The present study obtained the two-dimensional (2D) microstructure of bamboo cortex cells by optical microscopy and characterized the three-dimensional (3D) structure through high-resolution X-ray microtomography (µCT). The 2D anatomical parameters of cortex cells were measured to verify the reliability of cortical cell classification in 3D models. Based on the analysis, the bamboo cortex cells were classified into four layers: epidermis layer, hypodermis layer, transitional layer, and parenchyma layer. The total volume of the reconstructed area of interest in μCT was 7.85 × 106 µm3, in which the total pore volume of bamboo cortex was 2.84 × 106 µm3, the average pore volume of bamboo cortex was about 1.54 × 103 µm3. Thus the porosity was 36.1%, and the relative density was 0.639. Studies on bamboo anatomical structure, especially three-dimensional digital characterization, will enrich the bamboo microstructure database. Besides, the three-dimensional structure of the bamboo cortex revealed in this study can provide a reference for optimizing composite material hierarchy and biomimetic design.

3D Visualization of Bamboo Node’s Vascular Bundle

The vascular bundle is an important structural unit that determines the growth and properties of bamboo. A high-resolution X-ray microtomography (μCT) was used to observe and reconstruct a three-dimensional (3D) morphometry model of the vascular bundle of the Qiongzhuea tumidinoda node due to its advantages of quick, nondestructive, and accurate testing of plant internal structure. The results showed that the morphology of vascular bundles varied significantly in the axial direction. In the cross-section, the number of axial vascular bundles reached a maximum at the lower end of the sheath scar, and the minimum of it was at the middle of the diaphragm. The frequency of axial vascular bundles decreased from the lower end of the node to the nodal ridge, and subsequently increased until the upper end of the bamboo node. The proportion of parenchyma, fibers, and conducting tissue was 65.7%, 30.5%, and 3.8%, respectively. The conducting tissues were intertwined to form a complex 3D network structure, with a connectivity of 94.77%. The conducting tissue with the largest volume accounted for 60.26% of the total volume of the conducting tissue. The 3D-distribution pattern of the conducting tissue of the node and that of the fibers were similar, but their thickness changed in the opposite pattern. This study revealed the 3D morphometry of the conducting tissue and fibers of the bamboo node, the reconstruction of the skeleton made the morphology more intuitive. Quantitative indicators such as the 3D volume, proportion, and connectivity of each type of tissue was obtained, the bamboo node was enlarged mainly caused by the particularly developed fibers. This work laid the foundation for a better understanding of the mechanical properties and water transportation of bamboo and revealed the mystery of bamboo node shedding of Q. tumidinoda.

On the Deviation of Computed Permeability Induced by Unresolved Morphological Features of the Pore Space

This article describes how much the computed absolute permeability is impacted by the slip effect at the fluid/solid interface, in the context of single-phase pore-scale flow. While this effect is well quantified in microchannels or simple geometries, the present study focuses on its average effect in real rock matrix geometries, obtained by means of high-resolution X-ray microtomography. Due to the inherently finite resolution of the technique, an uncertainty exists on the true position of the fluid/solid interface and its morphological features below the image resolution (unseen roughness). We demonstrate that both these uncertainties can be interpreted as a slip condition, and consequently we focus on how a slip length can impact the computed absolute permeability, after having provided an estimation of a meaningful bound on the slip coefficient. To that extent, two strategies are employed: the global deviation of permeability and the theoretically established linear deviation. Three high-definition 3D geometries are used as practical examples of our methodology. Results are discussed in terms of relative deviation versus specific surface area and lead to quantities of interest involving the linear deviation of permeability. Article Highlights Uncertainty on the permeability is quantified by means of a slip length based on micro-CT voxel size. The linear deviation from a permeability value is established asymptotically and involves only a prescribed slip. A ratio involving the relative linear deviation, the specific area and the permeability is a non-dimensional quantity of interest.

Determination of Mineral Liberation of a Bauxite Ore Based on 3D Compositional and Textural Characteristics Using X-ray Microtomography

ABSTRACT Microscope-based automated image analysis systems have been used to obtain data regarding mineral liberation. However, this kind of analysis leads to stereological bias due to the intrinsic two-dimensionality characteristic of the technique. Three-dimensional imaging techniques such as X-ray microtomography comes as an alternative method to measure liberation. We explored the potentiality of high-resolution X-ray microtomography to investigate the characteristics of liberation of a Brazilian bauxite. Grade distributions in 2D and 3D were correspondent when all possible cross-sections were considered in 2D. However, 2D surface exposure did not converge accurately to the 3D method due to the loss of 3D information.

Proleg retractor muscles in Manduca sexta larvae are segmentally different, suggesting anteroposterior specialization.

Manduca sexta larvae are an important model system for studying the neuromechanics of soft body locomotion. They climb on plants using the abdominal prolegs to grip and maneuver in any orientation and on different surfaces. The prolegs grip passively with an array of cuticular hooks, and grip release is actively controlled by retractor muscles inserted into the soft planta membrane at the proleg tip. Until now, the principal planta retractor muscles (PPRMs) in each body segment were thought to be a single fiber bundle originating on the lateral body wall. Here, using high resolution X-ray microtomography of intact animals, we show that the PPRM is a more complex muscle consisting of multiple contractile fibers originating at several distinct sites on the proleg. Furthermore, we show that there are segmental differences in the number and size of some of these fiber groups which suggests that the prolegs may operate differently along the anterior-posterior axis.