Muscle Fiber Orientation Research Articles

Correction:Soleus muscle weakness in cerebral palsy: Muscle architecture revealed with Diffusion Tensor Imaging.

[This corrects the article DOI: 10.1371/journal.pone.0205944.].

Multiparametric MRI characterization of level dependent differences in lumbar muscle size, quality, and microstructure.

Magnetic resonance imaging (MRI) is a diagnostic tool that can be used to noninvasively assess lumbar muscle size and fatty infiltration, important biomarkers of muscle health. Diffusion tensor imaging (DTI) is an MRI technique that is sensitive to muscle microstructural features such as fiber size (an important biomarker of muscle health), which is typically only assessed using invasive biopsy techniques. The goal of this study was to establish normative values of level‐dependent lumbar muscle size, fat signal fraction, and restricted diffusion assessed by MRI in a highly active population. Forty‐two active‐duty Marines were imaged using a (a) high‐resolution anatomical, (b) fat‐water separation, and (c) DT‐MRI scan. The multifidus and erector spinae muscles were compared at each level using two‐way repeated measures ANOVA. Secondary analysis included Three dimensional (3D) reconstructions to qualitatively assess lumbar muscle size, fatty infiltration, and fiber orientation via tractography. The erector spinae was found to be larger than the multifidus above L5, with lower fat signal fraction above L3, and a less restricted diffusion profile than the multifidus above L4, with this pattern reversed in the lower lumbar spine. 3D reconstructions demonstrated accumulations of epimuscular fat in the anterior and posterior regions of the lumbar musculature, with minimal intramuscular fatty infiltration. Tractography images demonstrated different orientations of adjacent lumbar musculature, which cannot be visualized with standard MRI pulse sequences. The level dependent differences found in this study provide a normative baseline, for which to better understand whole muscle and microstructural changes associated with aging, low back pain, and pathology.

Relgulatory Light Chain Orientaiton on Myosin S1 Using a Bifunctional Spin Label

We performed electron paramagnetic resonance (EPR) on the myosin head (S1), labeling the regulatory light chain (RLC) with a bifunctional spin label (BSL). To achieve stereoselective site-directed labeling with BSL, we engineered a pair of cysteines (i, i+4) in RLC. By exchanging BSL-labeled RLC onto S1 and decorating oriented muscle fibers with BSL-RLC-S1, we obtained EPR spectra from which the angular distribution of BSL can be determined with high resolution relative to the muscle fiber axis. In our previous work (Savich et al., JGP, 2019), we exchanged BSL-RLC on intact myosin in skinned muscle fibers and observed substantial angular disorder, which varied with the RLC labeling site. In the present study, papain-digested S1 spin-labeled with BSL and bound to actin in oriented muscle fibers, yields a single oriented population of helix E on RLC, with an angular dispersion of ∼10 degrees. Addition of ATP releases decorated myosin, showing the ATP dependence of actin binding is not perturbed by labeling. Activity of labeled S1 was verified by the actin-activated NADH ATPase assay. We conclude that the lack of uniform orientation in labeled RLC, observed previously in muscle fibers by both EPR and fluorescence, is due to strain between two myosin heads. Sensitivity of the spectral features to the flow rate presents a method to measure a torsion elastic modulus of the light chain domain. This work was supported by NIH R01AR032961 and R37AG26160 to DDT. YS was supported by NIH T32AG29796 and a University of Minnesota Interdisciplinary Doctoral Fellowship.

Influence of Post-Harvest Circulatory Rinse on Tenderness and Objective Color of Cow Striploin Steaks

ObjectivesWhole muscle cuts from cows are often less tender than cuts from young fed beef due to increased collagen cross-linking associated with animal age. The injection of a rinse solution through the carotid artery following exsanguination has been shown to improve tenderness. The objective of this study was to compare the effect of a post-harvest rinse of an isotonic solution through the circulatory system on tenderness of steaks from cows.Materials and MethodsCows (n = 28) were randomly assigned to carcass treatments. The carcass treatments consisted of non-rinsed control (n = 14) and a rinsed (n = 14) treatment, where a chilled isotonic solution (MPSC, Inc., St. Paul, MN) was rinsed through the carotid artery and veins following exsanguination. The isotonic solution consisted of water, glucose, maltose and phosphates. Both control and rinsed treatments were electrically stimulated. At 2 d postmortem, strip loins were removed from one side of each carcass. Strip loins were fabricated into 2.54 cm steaks at 3 d postmortem and objective color measurements (L*, a* and b*) were recorded on a single steak after a 30-min bloom period. Steaks were vacuum packaged and aged at 4°C for 7, 14, and 21 d. Following aging, steaks were frozen (–20°C) for future analysis. Warner-Bratzler Shear Force (WBSF) was used to measure tenderness. Frozen steaks were thawed at 4°C for 24 h before cooking. Internal temperature was monitored on all steaks using a digital thermometer that was placed in the center of each steak. Steaks were cooked on an electric clamshell grill to an internal temperature of 71°C. Peak cook temperature was recorded for each steak. Following cooking, steaks were cooled at 4°C and allowed to equilibrate to room temperature (20°C). Six cores (1.27 cm) were removed from each steak and sheared perpendicular to the muscle fiber orientation. The peak force was recorded for each core and the average calculated for each steak. Data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Shear force data were analyzed as a repeated measure with time and treatment as fixed variables. Color data were analyzed as a completely randomized design using treatment as the fixed variable. Statistical significance was considered at an α of P < 0.05 and trends at 0.05 ≤ P < 0.10.ResultsThere was no interaction (P = 0.6068) between treatment and postmortem aging day. Steaks from the rinsed treatment were more tender (P = 0.0005), than steaks in the control treatment (3.51 ± 0.168 kg vs. 4.41 ± 0.174 kg, respectively). Postmortem aging influenced (P = 0.0310) tenderness. Steaks aged 7 d were less tender (P = 0.0087) than steaks aged for 21 d (4.18 ± 0.155 kg vs. 3.72 ± 0.156 kg, respectively), while 14 d steaks did not differ (P > 0.05) from those aged 7 or 21 d. Objective color was not impacted by rinse treatment (P > 0.05).ConclusionThese data suggest that the application of a post-harvest rinse with an isotonic solution through the circulatory system improves the tenderness of cow steaks but does not influence objective color.

Aging Influences Shear Force of Beef in a Muscle-Specific Manner

ObjectivesTenderness is an important sensory attribute that influences consumers’ overall eating satisfaction and repurchase decisions of beef. However, beef tenderness is a muscle-specific and highly variable trait, with different muscles from the same carcass exhibiting considerable variations. Retailing single-muscle beef cuts, based on quality and palatability traits, can improve value of carcasses. Postmortem wet aging of beef subprimals under vacuum packaging is a widely used industry practice in the U.S. to improve beef tenderness. Although beef muscles differ in their biochemical attributes, different muscles undergo similar aging procedure because wet aging is generally preformed on the subprimals. While beef muscles may respond differentially to wet aging, the effects of aging time on tenderness of three economically important beef hindquarter muscles, i.e., longissimus lumborum (LL), psoas major (PM), and semitendinosus (ST), are yet to be examined. Therefore, the objective of the current study was to examine the effect of aging on tenderness of beef LL, PM, and ST muscles.Materials and MethodsThe LL, PM, and ST muscles were excised (24 h postmortem) from both sides of eight (n = 8) beef carcasses (USDA Choice; A maturity) and was further separated into two equal-length sections, resulting in four muscle sections per carcass. The muscle sections were vacuum packaged and randomly assigned to aging at 2°C for either 0, 7, 14, or 21 d. At the end of each aging period, 2.5-cm steaks were fabricated. The steaks were cooked to an internal temperature of 71°C and chilled to 4°C overnight. Six cylindrical cores (1.27-cm of diameter) parallel to the muscle fiber orientation were obtained from each steak with a hand-held coring device. Shear force was determined by shearing each core with V-shaped blade of Warner-Bratzler shear device, and the values were recorded as the peak force (N). The main effects of muscle source and aging days, and their interactions were analyzed using the Mixed Procedure of SAS. The least square means for protected F-tests (P < 0.05) were separated by using least significant differences and were considered significant at P < 0.05.ResultsMuscle source and aging days influenced (P < 0.05) the tenderness, with an improvement (P < 0.05) in tenderness observed with aging. Moreover, a muscle × aging day interaction (P < 0.05) was observed for tenderness. Shear force of LL decreased (P < 0.05) with aging, although there was no difference (P > 0.05) in tenderness between 7 and 14-d aged LL. However, aging beyond 7 d did not improve (P > 0.05) the tenderness of already tender PM steaks. On the other hand, improvement (P < 0.05) in tenderness was observed in ST until 14 d. After 21 d of aging, LL was the most tender, while ST remained the toughest (P < 0.05).ConclusionThe results indicated that different muscles in beef hindquarters responded differentially to postmortem aging, and the processors could optimize aging time depending on the muscles to improve beef tenderness.

An improved method for studying mouse diaphragm function

Dysfunction in the contractile properties of the diaphragm muscle contributes to the morbidity and mortality in many neuromuscular and respiratory diseases. Methods that can accurately quantify diaphragm function in mouse models are essential for preclinical studies. Diaphragm function is usually measured using the diaphragm strip. Two methods have been used to attach the diaphragm strip to the force transducer. The suture method is easy to adopt but it cannot maintain the physiological orientation of the muscle fibers. Hence, results may not accurately reflect diaphragm contractility. The clamp method can better maintain diaphragm muscle fiber orientation but is used less often because detailed information on clamp fabrication and application has never been published. Importantly, a side-by-side comparison of the two methods is lacking. To address these questions, we engineered diaphragm clamps using mechanically highly durable material. Here, we present a detailed and ready-to-use protocol on the design and manufacture of diaphragm clamps. Also, we present a step by step protocol on how to mount the diaphragm strip to the clamp and then to the muscle force measurement system. We compared the diaphragm force from the same mouse with both suture and clamp methods. We found the clamp method yielded a significantly higher muscle force. Finally, we validated the utility of the clamp method in the mdx model of Duchenne muscular dystrophy. In summary, the clamp method described in this paper yields reliable and consistent diaphragm force data. This method will be useful to any laboratory interested in performing mouse diaphragm function assay.

Influence of Postmortem Aging and Storage Conditions on Tenderness of Grain and Grass Finished Bison Striploin Steaks

ObjectivesThe objectives of this study were to: 1) compare the influence of postmortem aging on tenderness of striploin steaks from grain- and grass-finished bison, and 2) compare the influence of freezing on tenderness of striploin steaks from grain- and grass-finished bison.Materials and MethodsBison heifers were randomly assigned to finishing treatments: Grain-finished (n = 30, backgrounded on pasture and finished for 130 d with ad libitum access to grass hay, alfalfa and a corn and dry distiller’s grain concentrate prior to slaughter) or Grass-finished (n = 30, remained on pasture until slaughter). Heifers were slaughtered at approximately 28 mo of age, and striploins were removed from both sides of the carcass posterior to the 12th rib separation and fabricated into 2.54-cm steaks. One steak was removed from each striploin (n = 60), vacuum packaged and stored fresh for 14 d at 4°C. Four additional steaks were fabricated from each striploin, aged for 4,7,14, or 21 d, vacuum packaged, and frozen for approximately 3 mo. Warner-Bratzler Shear Force (WBSF) was utilized to determine objective tenderness. Frozen steaks were thawed at 4°C for 24 h before cooking. All steaks were weighed prior to cooking to an internal temperature of 71°C. Internal temperature was monitored using a digital thermometer placed near the geometric center of each steak. After cooking, all steaks were reweighed to determine cook loss and cooled to room temperature (20°C). Five to six 1.27-cm cores were removed from each steak and sheared once perpendicular to the muscle fiber orientation and peak force was recorded. A texture analyzer with a Warner-Bratzler attachment was used to assess instrumental tenderness. An average shear force value was then calculated for each steak. For Objective 1, cook loss and shear force data were analyzed as repeated measures using the ante-dependence covariance structure in the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) for effects of finishing treatment, aging, and their interaction; peak temperature was included as a covariate. For Objective 2, shear force data were analyzed for the effects of finishing treatment, storage treatment and their interaction using the GLM procedure of SAS. For both objectives, the interaction was not significant and omitted from the final model. Separation of least-squares main effect means was performed using LSD with a Tukey’s adjustment and assuming a level of 0.05.ResultsSteaks from grain finished bison heifers had tendency to be more tender (P = 0.0552) and had less cook loss (P < 0.0001) than steaks from grass finished heifers. Tenderness of all steaks improved (P < 0.0001) with postmortem aging. Aging time also influenced cook loss (P = 0.0199). Cook loss was greater (P = 0.0133) at Day 4 than Day 7 and tended to be greater (P = 0.0561) at Day 4 than Day 21. Frozen storage improved tenderness (P < 0.0001) and increased cook loss (P < 0.0001) of bison steaks compared to fresh storage.ConclusionCollectively this data indicates postmortem aging, storage conditions, and finishing systems influence meat tenderness of bison striploin steaks. Grain-finishing resulted in reduced cook loss and tended to improved tenderness of bison steaks compared to grass-finishing. Additionally, holding bison steaks in frozen storage improved tenderness, but also increased cook loss.

The effect of fibre orientation, measurement interval and muscle on lamb meat drip loss values

The effect of muscle fibre orientation and measurement interval on lamb meat drip losses was tested using the EZ-DripLoss (EZ) method. Sample cores were removed from 100 semimembranosus (SM) and longissimus lumborum (LL) muscles, sourced from different Merino lamb carcasses. Two cores with either horizontal or vertical fibre orientation, relative to the core diameter, were removed from each SM. One core with vertical fibre orientation was removed from each LL. The drip loss (%) of these cores was then monitored across four 24 h measurement intervals. It was found that fibre orientation did not impact on SM drip losses. Both SM and LL drip losses increased, linear to measurement interval. SM drip loss increased more than LL over the four measurement intervals and consequently, SM drip losses were higher than LL. Longer measurement intervals which are defined in the methods section are recommended when testing lamb meat drip losses using the EZ method.

Anatomically accurate model of EMG during index finger flexion and abduction derived from diffusion tensor imaging.

This study presents a modelling framework in which information on muscle fiber direction and orientation during contraction is derived from diffusion tensor imaging (DTI) and incorporated in a computational model of the surface electromyographic (EMG) signal. The proposed model makes use of the principle of reciprocity to simultaneously calculate the electric potentials produced at the recording electrode by charges distributed along an arbitrary number of muscle fibers within the muscle, allowing for a computationally efficient evaluation of extracellular motor unit action potentials. The approach is applied to the complex architecture of the first dorsal interosseous (FDI) muscle of the hand to simulate EMG during index finger flexion and abduction. Using diffusion tensor imaging methods, the results show how muscle fiber orientation and curvature in this intrinsic hand muscle change during flexion and abduction. Incorporation of anatomically accurate muscle architecture and other hand tissue morphologies enables the model to capture variations in extracellular action potential waveform shape across the motor unit population and to predict experimentally observed differences in EMG signal features when switching from index finger abduction to flexion. The simulation results illustrate how structural and electrical properties of the tissues comprising the volume conductor, in combination with fiber direction and curvature, shape the detected action potentials. Using the model, the relative contribution of motor units of different sizes located throughout the muscle under both conditions is examined, yielding a prediction of the detection profile of the surface EMG electrode array over the muscle cross-section.

Personalized musculoskeletal models based on ultrasound muscle parameters in children with cerebral palsy during walking

The goal of the study was to investigate the quantitative impact of region of interest (ROI), software choice, muscle fiber orientation and preload tension on shear wave velocity (SWV). First, SWV was assessed in an isotropic elasticity phantom and ex vivo porcine muscle using a commercially available clinical ultrasound system. Secondly, SWV was acquired in relaxed and stretched calf muscles of healthy volunteers (dorsal extension of the talocrural joint), for both parallel and transverse probe direction to the fibers, as well as for different ROIs and software versions. The effect of intermediate probe-fiber alignments was also analyzed. Finally, the impact of confounding factors on SWV reproducibility was minimized with a second force-controlled volunteer study, in which the calf was isometrically loaded, and fiber orientation and ROI were well-defined. 2046 in vivoSWE images were acquired to analyze SWV reproducibility with different confounder settings. In healthy volunteers, the main variance-contributing factors were in order of importance muscle tension, fiber orientation, horizontal ROI size and insertion depth. Regression analysis showed significantly reduced SWV with increasing insertion depth for each study material. Parallel probe-fiber orientation, muscle stretch and increasing horizontal ROI size led to significantly higher SWV. Based on the results of the study, we provide recommendations to minimize the impact of confounders in musculoskeletal elastography and discuss the main confounding mechanisms and trade-offs between confounding variables. Coefficients of variation can be significantly reduced with a controlled protocol, if the confounders are clinically taken into account.

Which Confounders Have the Largest Impact in Shear Wave Elastography of Muscle and How Can They be Minimized? An Elasticity Phantom, Ex Vivo Porcine Muscle and Volunteer Study Using a Commercially Available System

The goal of the study was to investigate the quantitative impact of region of interest (ROI), software choice, muscle fiber orientation and preload tension on shear wave velocity (SWV). First, SWV was assessed in an isotropic elasticity phantom and ex vivo porcine muscle using a commercially available clinical ultrasound system. Secondly, SWV was acquired in relaxed and stretched calf muscles of healthy volunteers (dorsal extension of the talocrural joint), for both parallel and transverse probe direction to the fibers, as well as for different ROIs and software versions. The effect of intermediate probe-fiber alignments was also analyzed. Finally, the impact of confounding factors on SWV reproducibility was minimized with a second force-controlled volunteer study, in which the calf was isometrically loaded, and fiber orientation and ROI were well-defined. 2046 in vivoSWE images were acquired to analyze SWV reproducibility with different confounder settings. In healthy volunteers, the main variance-contributing factors were in order of importance muscle tension, fiber orientation, horizontal ROI size and insertion depth. Regression analysis showed significantly reduced SWV with increasing insertion depth for each study material. Parallel probe-fiber orientation, muscle stretch and increasing horizontal ROI size led to significantly higher SWV. Based on the results of the study, we provide recommendations to minimize the impact of confounders in musculoskeletal elastography and discuss the main confounding mechanisms and trade-offs between confounding variables. Coefficients of variation can be significantly reduced with a controlled protocol, if the confounders are clinically taken into account.

Retromastoid-transmuscular identification and harvest of the occipital artery during retrosigmoid craniotomy.

Harvesting the occipital artery (OA) is challenging. The subcutaneous OA is usually found near the superior nuchal line and followed proximally, requiring a large incision and risking damage to the superficially located OA. The authors assessed the anatomical feasibility and safety of exposing the OA through a retromastoid-transmuscular approach. Using 10 cadaveric heads, 20 OAs were harvested though a 5-cm retroauricular incision placed 5 cm posterior to the external auditory meatus. The underlying muscle layers were sequentially cut and recorded before exposing the OA. Changes in the orientation of muscle fibers were used as a roadmap to expose the OA without damaging it. The suboccipital segment of the OA was exposed without damage after incising two consecutive layers of muscles and their investing fasciae. These muscles displayed different fiber directions: the superficially located sternocleidomastoid muscle with vertically oriented fibers, and the underlying splenius capitis with anteroposteriorly (and mediolaterally) oriented fibers. The OA could be harvested along the entire length of the skin incision in all specimens. If needed, the incision can be extended proximally and/or distally to follow the OA and harvest greater lengths. This transmuscular technique for identification of the OA is a reliable method and may facilitate exposure and protection of the OA during a retrosigmoid approach. This technique may obviate the need for larger incisions when planning a bypass to nearby arteries in the posterior circulation via a retrosigmoid craniotomy. Additionally, the small skin incision can be enlarged when a different craniotomy and/or bypass is planned or when a greater length of the OA is needed to be harvested.

Myosin lever arm orientation in muscle determined with high angular resolution using bifunctional spin labels.

Despite advances in x-ray crystallography, cryo-electron microscopy (cryo-EM), and fluorescence polarization, none of these techniques provide high-resolution structural information about the myosin light chain domain (LCD; lever arm) under ambient conditions in vertebrate muscle. Here, we measure the orientation of LCD elements in demembranated muscle fibers by electron paramagnetic resonance (EPR) using a bifunctional spin label (BSL) with an angular resolution of 4°. To achieve stereoselective site-directed labeling with BSL, we engineered a pair of cysteines in the myosin regulatory light chain (RLC), either on helix E or helix B, which are roughly parallel or perpendicular to the myosin lever arm, respectively. By exchanging BSL-labeled RLC onto oriented muscle fibers, we obtain EPR spectra from which the angular distributions of BSL, and thus the lever arm, can be determined with high resolution relative to the muscle fiber axis. In the absence of ATP (rigor), each of the two labeled helices exhibits both ordered (σ ∼9-11°) and disordered (σ > 38°) populations. Using these angles to determine the orientation of the lever arm (LCD combined with converter subdomain), we observe that the oriented population corresponds to a lever arm that is perpendicular to the muscle fiber axis and that the addition of ATP in the absence of Ca2+ (inducing relaxation) shifts the orientation to a much more disordered orientational distribution. Although the detected orientation of the myosin light chain lever arm is ∼33° different than predicted from a standard "lever arm down" model based on cryo-EM of actin decorated with isolated myosin heads, it is compatible with, and thus augments and clarifies, fluorescence polarization, x-ray interference, and EM data obtained from muscle fibers. These results establish feasibility for high-resolution detection of myosin LCD rotation during muscle contraction.

Atomistic Models from Orientation and Distance Constraints Using EPR of a Bifunctional Spin Label

We have used high-resolution orientation and distance measurements derived from electron paramagnetic resonance of a bifunctional spin label (BSL) to build and refine atomistic models of protein structure. We demonstrate this approach by investigating the effects of nucleotide binding on the structure of myosin’s catalytic domain while myosin is in complex with actin. Constraints for orientation of individual helices were obtained in a previous study from continuous-wave electron paramagnetic resonance of myosin labeled at specific sites with BSLs in oriented muscle fibers. In this study, new distance constraints were derived from double electron-electron resonance on myosin constructs labeled with a BSL specifically at two sites. Using these complementary constraints together, we thoroughly characterize the BSL’s rigid, highly stereoselective attachment to protein α-helices, which permits accurate measurements of orientation and distance. We also leverage these measurements to derive a novel, to our knowledge, structural model for myosin-II in complex with actin and MgADP and compare our model to other recent actomyosin structures. The described approach is applicable to any orientable complex (e.g., membranes or filaments) in which site-specific di-Cys mutation is feasible.

Modeling left ventricular dynamics with characteristic deformation modes

A computationally efficient method is described for simulating the dynamics of the left ventricle (LV) in three dimensions. LV motion is represented as a combination of a limited number of deformation modes, chosen to represent observed cardiac motions while conserving volume in the LV wall. The contribution of each mode to wall motion is determined by a corresponding time-dependent deformation variable. The principle of virtual work is applied to these deformation variables, yielding a system of ordinary differential equations for LV dynamics, including effects of muscle fiber orientations, active and passive stresses, and surface tractions. Passive stress is governed by a transversely isotropic elastic model. Active stress acts in the fiber direction and incorporates length–tension and force–velocity properties of cardiac muscle. Preload and afterload are represented by lumped vascular models. The variational equations and their numerical solutions are verified by comparison to analytic solutions of the strong form equations. Deformation modes are constructed using Fourier series with an arbitrary number of terms. Greater numbers of deformation modes increase deformable model resolution but at increased computational cost. Simulations of normal LV motion throughout the cardiac cycle are presented using models with 8, 23, or 46 deformation modes. Aggregate quantities that describe LV function vary little as the number of deformation modes is increased. Spatial distributions of stress and strain change as more deformation modes are included, but overall patterns are conserved. This approach yields three-dimensional simulations of the cardiac cycle on a clinically relevant time-scale.

Soleus muscle weakness in cerebral palsy: Muscle architecture revealed with Diffusion Tensor Imaging.

Cerebral palsy (CP) is associated with movement disorders and reduced muscle size. This latter phenomenon has been observed by computing muscle volumes from conventional MRI, with most studies reporting significantly reduced volumes in leg muscles. This indicates impaired muscle growth, but without knowing muscle fiber orientation, it is not clear whether muscle growth in CP is impaired in the along-fiber direction (indicating shortened muscles and limited range of motion) or the cross-fiber direction (indicating weak muscles and impaired strength). Using Diffusion Tensor Imaging (DTI) we can determine muscle fiber orientation and construct 3D muscle architectures which can be used to examine both along-fiber length and cross-sectional area. Such an approach has not been undertaken in CP. Here, we use advanced DTI sequences with fast imaging times to capture fiber orientations in the soleus muscle of children with CP and age-matched, able-bodied controls. Cross sectional areas perpendicular to the muscle fiber direction were reduced (37 ± 11%) in children with CP compared to controls, indicating impaired muscle strength. Along-fiber muscle lengths were not different between groups. This study is the first to demonstrate along-fiber and cross-fiber muscle architecture in CP using DTI and implicates impaired cross-sectional muscle growth in children with cerebral palsy.

Automatic Muscle Fiber Orientation Tracking in Ultrasound Images Using a New Adaptive Fading Bayesian Kalman Smoother.

This paper proposes a new algorithm for automatic estimation of muscle fiber orientation (MFO) in musculoskeletal ultrasound images, which is commonly used for both diagnosis and rehabilitation assessment of patients. The algorithm is based on a novel adaptive fading Bayesian Kalman filter (AF-BKF) and an automatic region of interest (ROI) extraction method. The ROI is first enhanced by the Gabor filter (GF) and extracted automatically using the revoting constrained Radon transform (RCRT) approach. The dominant MFO in the ROI is then detected by the RT and tracked by the proposed AF-BKF, which employs simplified Gaussian mixtures to approximate the non-Gaussian state densities and a new adaptive fading method to update the mixture parameters. An AF-BK smoother (AF-BKS) is also proposed by extending the AF-BKF using the concept of Rauch-Tung-Striebel smoother for further smoothing the fascicle orientations. The experimental results and comparisons show that: 1) the maximum segmentation error of the proposed RCRT is below nine pixels, which is sufficiently small for MFO tracking; 2) the accuracy of MFO gauged by RT in the ROI enhanced by the GF is comparable to that of using multiscale vessel enhancement filter-based method and better than those of local RT and revoting Hough transform approaches; and 3) the proposed AF-BKS algorithm outperforms the other tested approaches and achieves a performance close to those obtained by experienced operators (the overall covariance obtained by the AF-BKS is 3.19, which is rather close to that of the operators, 2.86). It, thus, serves as a valuable tool for automatic estimation of fascicle orientations and possibly for other applications in musculoskeletal ultrasound images.

Locational and Directional Dependencies of Smooth Muscle Properties in Pig Urinary Bladder.

The urinary bladder is a distensible hollow muscular organ, which allows huge changes in size during absorption, storage and micturition. Pathological alterations of biomechanical properties can lead to bladder dysfunction and loss in quality of life. To understand and treat bladder diseases, the mechanisms of the healthy urinary bladder need to be determined. Thus, a series of studies focused on the detrusor muscle, a layer of urinary bladder made of smooth muscle fibers arranged in longitudinal and circumferential orientation. However, little is known about whether its active muscle properties differ depending on location and direction. This study aimed to investigate the porcine bladder for heterogeneous (six different locations) and anisotropic (longitudinal vs. circumferential) contractile properties including the force-length-(FLR) and force-velocity-relationship (FVR). Therefore, smooth muscle tissue strips with longitudinal and circumferential direction have been prepared from different bladder locations (apex dorsal, apex ventral, body dorsal, body ventral, trigone dorsal, trigone ventral). FLR and FVR have been determined by a series of isometric and isotonic contractions. Additionally, histological analyses were conducted to determine smooth muscle content and fiber orientation. Mechanical and histological examinations were carried out on 94 and 36 samples, respectively. The results showed that maximum active stress (pact) of the bladder strips was higher in the longitudinal compared to the circumferential direction. This is in line with our histological investigation showing a higher smooth muscle content in the bladder strips in the longitudinal direction. However, normalization of maximum strip force by the cross-sectional area (CSA) of smooth muscle fibers yielded similar smooth muscle maximum stresses (165.4 ± 29.6 kPa), independent of strip direction. Active muscle properties (FLR, FVR) showed no locational differences. The trigone exhibited higher passive stress (ppass) than the body. Moreover, the bladder exhibited greater ppass in the longitudinal than circumferential direction which might be attributed to its microstructure (more longitudinal arrangement of muscle fibers). This study provides a valuable dataset for the development of constitutive computational models of the healthy urinary bladder. These models are relevant from a medical standpoint, as they contribute to the basic understanding of the function of the bladder in health and disease.

Myosin Orientation in a Muscle Fiber using Bifunctional Spin Labels with 4 Degrees Angular Resolution

We have measured the orientation of myosin light chain domain in a demembranated muscle fiber bundle using electron paramagnetic resonance (EPR) and a bifunctional spin label (BSL), with the angular resolution of 4 degrees in situ. A pair of (i,i+4) Cys residues was engineered on an alpha-helix of the regulatory light chain (RLC) on the N- and C- lobes. By exchanging endogenous RLC with mutant RLC labeled with BSL on oriented muscle fibers, we were able to resolve angular distributions in several biochemical states due to the stereospecific attachment of BSL's two disulfide bonds. In this setup, the accurate determination of BSL's angular coordinates allowed us to determine the orientation of individual structural elements with respect to the muscle fiber axis. The addition of ATP in the absence of Ca shifted the orientational distribution to a much more disordered one. By decorating demembranated fiber bundle with heavy meromyosin with RLC labeled with BSL, we observed different dynamics in the N- and C- lobe orientation. We compared these results with cardiac myosin. We also developed a new global fitting analysis to narrow the confidence intervals and enhance the sensitivity to azimuthal angle between pi orbital and magnetic field. While we find that the majority of the RLC helices are disordered even in the absence of ATP, we resolved an oriented population of myosin with lever arm being perpendicular to muscle fiber axis previously observed directly in insect flight muscle. This work was supported by NIH R01AR032961 and R37AG26160 to DDT. YS was supported by NIH T32AG29796 and University of Minnesota Interdisciplinary Doctoral Fellowship.

Effects of muscle fiber orientation to main magnetic field on muscle metabolite profiles for magnetic resonance spectroscopy acquisition.

BACKGROUNDProton magnetic resonance spectroscopy (1H MRS) is a technique widely used for investigating metabolites in humans. Lipids are stored outside the muscle cell are called extramyocellular lipids (EMCL), and lipids stored on the inside of muscle cells are called intramyocellular lipids (IMCL). The relationship between metabolic syndrome and IMCL has been extensively studied.AIMTo determine the effects of muscle fiber orientations on muscle metabolites using 1H MRS.METHODSChicken muscles were used as the subject in this study. MRS spectra were performed on a 1.5T Magnetic resonance imaging machine (1.5 Tesla Philips Achieva). A single voxel (8 mm × 8 mm × 20 mm) was placed on the chicken extensor iliotibialis lateralis muscle with the muscle fiber oriented at 0°, 30°, 60°, and 90° to the main magnetic field. 1H MRS spectra were acquired using a point-resolved spectroscopy, TR = 2000 ms, TE = 30 ms, and NSA = 256. Metabolites of interest from each orientation to the main magnetic field were compared using Wilcoxon signed-rank test. Differences less than 0.05 were considered to be statistically significant with 95%CI.RESULTSThe metabolite profiles were different for each orientation of muscle fibers to the main magnetic field. The orientation at 90° was the most different compared to other orientations. The quantity of IMCL and EMCL exhibited statistically significantly changes with impacts at 30°, 60°, and 90° when compared with muscles aligned at 0° to the main magnetic field. Statistical analysis showed statistically significant IMCL (CH3), EMCL (CH3), and IMCL (CH2) at 30°, 60°, and 90° (P = 0.017, 0.018, and 0.018, respectively) and EMCL (CH2) at 30° and 60° (P = 0.017 and 0.042, respectively). EMCL (CH2) at 90° was unable to be measured in this study. The muscle lipids quantified at 30°, 60°, and 90° tended to be lower when compared to 0°.CONCLUSIONCareful positioning is one of the most important factors to consider when studying 1H MRS metabolites in muscles to ensure reproducibility and uniformity of muscle metabolite spectra.