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Medicine

A Novel Application of Musculoskeletal Ultrasound Imaging

Published: September 17, 2013 doi: 10.3791/50595

Summary

We describe a new ultrasound-based vector tissue Doppler imaging technique to measure muscle contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities. This approach provides complementary measurements of dynamic muscle function and could lead to a better understanding of mechanisms underlying musculoskeletal disorders.

Abstract

Ultrasound is an attractive modality for imaging muscle and tendon motion during dynamic tasks and can provide a complementary methodological approach for biomechanical studies in a clinical or laboratory setting. Towards this goal, methods for quantification of muscle kinematics from ultrasound imagery are being developed based on image processing. The temporal resolution of these methods is typically not sufficient for highly dynamic tasks, such as drop-landing. We propose a new approach that utilizes a Doppler method for quantifying muscle kinematics. We have developed a novel vector tissue Doppler imaging (vTDI) technique that can be used to measure musculoskeletal contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities using ultrasound. The goal of this preliminary study was to investigate the repeatability and potential applicability of the vTDI technique in measuring musculoskeletal velocities during a drop-landing task, in healthy subjects. The vTDI measurements can be performed concurrently with other biomechanical techniques, such as 3D motion capture for joint kinematics and kinetics, electromyography for timing of muscle activation and force plates for ground reaction force. Integration of these complementary techniques could lead to a better understanding of dynamic muscle function and dysfunction underlying the pathogenesis and pathophysiology of musculoskeletal disorders.

Introduction

Musculoskeletal disorders are widely prevalent in adulthood 1. They are a leading chronic condition in the United States 2 and are reported to affect 25% of people worldwide 3. Musculoskeletal disorders are associated with decreased function in activities of daily living (ADL), functional limitations and lower quality of life 4. Their economic burden is significant because of lost productivity and high healthcare costs 4. The pathophysiology of several of these disorders remains inadequately understood. For example, the pathogenesis of osteoarthritis (OA) 4 following reconstruction of anterior cruciate ligament (ACL) injuries has been linked to alterations in quadriceps muscle strength and function 5, but the underlying mechanisms are unclear. To elucidate the underlying mechanisms, there is a need to better understand dynamic muscle function.

The functional assessment of individual muscles, during the performance of a partial or an entire task related to ADL and active lifestyles (i.e. sports) can provide further insight about muscle function and its potential role in the pathogenesis and pathophysiology of these disorders. Further the quantification of muscle function improvement during rehabilitation can be used as an outcome measure. Conventional techniques of measuring muscle and joint function in the clinic involve physical examination such as range of motion, muscle strength and/or muscle group endurance. Currently in the clinic, electromyography (EMG) is used to assess muscle activation/co-activation, frequency, and amplitude of muscle activity. However, EMG is a measure of electrical activation in the muscle and does not necessarily provide information about the muscle strength, contraction ability and other functional factors of the muscle. Other sophisticated biomechanical assessments, such as 3D motion capture system for joint kinetics and kinematics and force plates for ground reaction force can be performed in a gait lab 6-9. The measurements made by these techniques are at the joint level and do not necessarily provide a direct understanding of individual muscle function during a dynamic or functional activity. The ability to perform imaging of the muscle simultaneously while performing a dynamic activity could potentially lead to a better and more realistic functional assessment at the muscle level.

The majority of studies have focused on muscle function in static prone positions, and this method can open new avenues to further enhance our understanding of muscle behavior during real-time situations.

Diagnostic ultrasound can enable direct imaging of muscle and tendons in real time, and therefore is an attractive alternative for measuring musculoskeletal dynamics and function during ADL. Ultrasound-based quantitative measures of muscle morphology and architecture, such as muscle thickness, length, width, cross sectional area (CSA), fiber pennation angle and fascicle length have been widely used 10-12. In recent years, image-processing methods have been employed to assess and quantify these quantitative measures during dynamic tasks 13-14. These advances have enabled a new methodological approach to understanding in vivo muscle function. However, these methods have primarily relied on using conventional grayscale (or B-mode) ultrasound imaging, and therefore have not fully exploited the possibilities of ultrasound to measure tissue velocities, strain and strain rate using Doppler principles, that have been shown to be valuable in evaluating cardiac muscle function 15-16.

We have developed a vector tissue Doppler imaging (vTDI) technique that can measure contraction velocity, strain and strain rate with high temporal resolution (sub millisecond) during dynamic activities 17-18. Specifically, the vTDI technique can make measurements of muscles and tendons during highly dynamic tasks (e.g. drop-landing, gait, etc.) at high frame rates. The vTDI technique is an improvement over conventional Doppler ultrasound, which estimates only the component of the velocity along the ultrasound beam, and is therefore dependent on the insonation angle. vTDI estimates the velocity of the muscle and tendon using two different ultrasound beams steered at different angles, and is therefore independent of the insonation angle in the imaging plane. However, since muscle contraction happens in 3D, the angulation of the imaging plane is still important. We have implemented this method on a commercially available ultrasound system with a research interface, enabling these measurements to be made in a clinical setting.

To investigate the repeatability and potential applicability of the vTDI system in measuring the rectus femoris muscle velocities during a dynamic task, we performed a preliminary study on healthy adult volunteers. This paper demonstrates the methodology and experimental setup for estimating contraction velocities, strain and strain rate of the rectus femoris muscle with sub-millisecond temporal resolution during a drop-landing task.

Protocol

1. Instrumentation

Vector TDI is based on estimating the resultant velocity vector from Doppler velocity measurements taken from two or more independent directions. An ultrasound system with a research interface was used for developing vTDI. The research interface allowed low level beamforming and pulse sequence control using a software development kit (SDK). A 5-14 MHz linear array transducer, consisting of 128 transducer elements and with a 38 mm field of view was used. The research interface was employed to split the array transducer into two transmit and receive apertures and steer the receive beams by 15° with respect to the normal. The transmit beam was focused in the region of interest (e.g. muscle belly). Transmit and receive apertures were set to 32 elements.

Eight subjects, 4 men and 4 women (29.7±6.5 years) were recruited in this study. Kinematic measures from the subjects of the right lower extremities were captured using an eight-camera motion capture system with high speed capability and a sampling rate of 200 Hz. Ground reaction force data during the experiment were obtained through two force plates sampling at 2,000 Hz.

A high-speed camera mounted on a tripod and placed at 2 m from the subject, was used to capture the drop landing at 500 frames/sec.

2. Subject Preparation

  1. Ask the subjects to wear a pair of shorts, sports bra or a short t-shirt and running shoes.
  2. Instruct the subjects to perform a 10 min self-directed warm-up and stretching prior to the data collection. This is to avoid any abnormal muscular contractions and reduce the scope of any muscle cramps.
  3. After the warm-up session, place reflective markers on specific landmarks on the body. Specifically, place calibration markers on the greater trochanters, bilateral medial and lateral knee and medial and lateral malleoli. Place tracking markers on the posterior and anterior superior iliac crests, and place clusters on the thighs and shanks, and five markers on each foot 19-20.
  4. Direct the subjects to the stand in the center of the focus area of the 3D cameras to obtain a static trial. The participants must stand on the force plates with their arms across their shoulders, to obtain static 3D motion capture data.
  5. Then, place the ultrasound transducer in a transducer holder and ensure good contraption, to avoid dislodging of the ultrasound transducer from the transducer holder. The transducer holder was made using Lexen polycarbonate and moldable plastic.
  6. To ensure good contact with the skin and ultrasound transducer, apply generous amount of ultrasound transmission gel on the transducer.
  7. Place the ultrasound transducer along with the transducer holder on the thigh of the subject to image the rectus femoris muscle in the longitudinal axis. The transducer must be placed halfway between the anterior iliac spine and the lateral epicondoyle to image the belly of the rectus femoris muscle. Before securing the ultrasound transducer and the transducer holder to the leg, obtain an axial slice of the quadriceps muscle group. Using this as a guidance, make sure the ultrasound transducer is now imaging the rectus femoris and does not move more lateral or medial, to avoid imaging the vastii muscle group.
  8. Now, use a cohesive self-adhesive bandage to secure the transducer holder onto the subject’s thigh. Make this procedural step does not block or cover the reflective markers. The self-adhesive bandage must not be lax or excessively tight. Lax bandaging will risk the ultrasound transducer to fall during the drop-landing task and an excessively tight bandaging will cause discomfort, disrupt superficial blood flow and possibly alter drop landing dynamics.
  9. Place the high speed camera at least 2 m away from the subject in the sagittal plane to collect videos at a 500 frames/sec. Focus the camera lens to ensure that the entire drop landing sequence of the subject can been captured.

3. Experiment Protocol

  1. Once all the markers and the ultrasound transducer are secure, ask the subjects to stand on a platform of height 30 cm place at 50 cm from the force plates. Ensure that the area around the platform (about 2.5 m) is clear of any objects that could hinder the drop landing task or injure the subject. This includes the ultrasound transducer cord.
  2. Instruct the subjects to place their hands on their hips prior starting the drop landing task and during the entire drop landing sequence.
  3. Start the data collection for ultrasound, 3D motion capture, force plates and the high speed camera prior to start of the drop landing task. Synchronization between the different instruments can be achieved by using a single key press to start all the data acquisition. A pressure sensor attached to the keyboard can be used to generate a synchronizing trigger signal when a specific key is pressed.
  4. Direct the subject to perform the drop-landing task from the platform and land with both legs, simultaneously. Ensure that the subjects drop from box instead of jumping from it. No specific instructions are provided regarding landing technique.
  5. Stop the data collection once the subject has fully stabilized and completed the drop landing sequence.
  6. Repeat this protocol five times per subject.

4. Ultrasound Data Analysis

  1. Export and store the raw data from the ultrasound system to a computer.
  2. The raw radiofrequency (rf) ultrasound data from each receive beam is digitized at 40 MHz. Process the data using MATLAB.
  3. Perform quadrature demodulation on the RF data to remove the carrier frequency. Remove stationary and low-frequency clutter by filtering the quadrature data from each the receive beams and for each depth using a 20 Hz high pass filter.
  4. Estimate the velocities along both receive beams using the conventional autocorrelation velocity estimator 21.
  5. Combine the individual velocity waveforms to obtain lateral (along the transducer) and axial (perpendicular to the transducer) velocity waveforms throughout the drop landing sequence, as seen in Figure 1.
  6. Obtain the magnitude of the resultant velocity vector from the individual velocity components using equation 1 as described previously 22:
    Equation 1
    where β is the beam steering angle, f1 and f2 are the two received frequency components and ft is the transmit frequency.
  7. Calculate the lateral and axial strain rate de/dt using the spatial gradients in the lateral and axial velocities.
    Equation 2
    where V2 and V1 are instantaneous velocities estimated at two spatial locations separated by a distance L.
  8. Calculate the axial and lateral strain, e, by integrating the axial and lateral strain rate respectively.
    Equation 3

5. 3D Motion Capture Data Analysis

  1. Export the 3D motion capture data to a computer for further analysis.
  2. Using the static standing trial, create a kinematic model (pelvis, thigh, shank, and foot) using 3D motion capture software with a least-squares optimization 23.
  3. Use this kinematic model to quantify the motion at the hip, knee, and ankle joints.
  4. Filter the reflective marker trajectories and ground reaction forces using a 4th order low-pass Butterworth filter with a cutoff frequency of 7 Hz and 25 Hz, respectively using 3D motion capture software.
  5. Calculate 3-D joint forces and moments from the kinematic and ground force data using a standard inverse dynamics analysis, using segment inertial characteristics estimated for each participant as per the methods of Dempster. Inter-segmental joint moments are defined as internal moments (e.g. a knee internal extension moment will resist a flexion load applied to the knee).

6. High Speed Camera Data Analysis

  1. Export the videos from the high speed camera data to a computer for analysis and comparison with ultrasound and 3D motion capture kinematic data.
  2. Play the movie at 15 frames/sec and observe the drop landing dynamics.
  3. Then, quantify the movement of the transducer holder and the displacement of the ultrasound transducer during the entire drop landing trial by tracking the visible markers on the anatomical landmarks using the high speed video data. Assessing the drop landing dynamics can also be done simultaneously to better understand the different launch and landing styles.

Representative Results

Representative results from our previous work demonstrating the methods are presented below. While the methods utilized in our current research integrate imaging and motion capture, the representative results presented below are from studies where these measurements were performed separately.

I. Ultrasound (vTDI)

Using the data from the 3D motion capture and the high speed camera, the pattern of subject’s jump, landing and stabilization phases were studied for each trial. The axial and lateral rectus femoris muscle velocities from vTDI were compared to data collected from 3D motion capture and high speed camera. Using this data, the temporal characteristics of the axial and lateral rectus femoris muscle velocities throughout the drop landing sequence were studied. Positive lateral velocities correspond to eccentric contraction of the rectus femoris muscle during knee flexion, while negative lateral velocities correspond to concentric contraction of the muscle during knee extension. This is illustrated in Figure 2. The entire drop-landing sequence for all subjects lasted approximately 1.45±0.27 seconds.

For each subject, the axial and lateral muscle velocities showed a strong repeatability between trials with a slope of 0.99 and R2 = 0.75 (Figure 3). Velocity values for six out of eight subjects were in a similar range of 48-62 cm/sec, while two subjects (both men) had higher velocities. Males (72.96 cm/sec) presented significantly higher muscle velocity than females (48.71 cm/sec), p=0.029, when adjusting for each subject's individual weight and muscle thickness.

The position of the ultrasound transducer was tracked thought the drop-landing sequence using the high-speed camera. The angle between the line segment made between the trochanter and the cuff (green dashed line segment) and the line segment between the mid-thigh and the cuff (purple dashed line segment) was calculated. A total of 16 trials, with 2 trials per subject (trial 1 & 2 relate to subject 1 and so on) are observed in Figure 4. Minimal angular variation (0.91°±0.54 degrees) of the transducer holder relative to the anatomical markers during landing was observed over all 16 trials. The ultrasound transducer angular variation presented a high repeatability as well (ICC2,1 = 0.90, p<0.05).This shows that the transducer movement during the landing trial was minimal and the velocity measurements were not affected due to any transducer movement.

II. 3D Motion Camera & Force Plates

We primarily focused on knee and hip flexion angles, knee valgus angle, and knee valgus moment. We found that during the initial contact with the ground, subjects had the following kinematic patterns: hip flexion 41°±13 degrees, knee flexion 23°±9 degrees, and knee valgus 0.03°±6 degrees. As they progress during the landing phase, the maximum angles attained were: hip flexion 58°±19 degrees, knee flexion 54°±24 degrees, and knee valgus -4°±8 degrees (Figure 5). Knee valgus moment presented a decrease from 0.03±0.03 to 0.1±0.1 Nm/km from initial ground contact to its maximum during the landing phase (Figure 6).

Figure 1
Figure 1. Representation of the vTDI velocity measurement of the rectus femoris muscle. The grey beam represent the two individual transmit and receive beams and the red line represents the lateral velocity component (along proximal-distal direction of the knee) and the blue line represents the axial velocity component (along the thickness of the muscle).

Figure 2
Figure 2. Axial and Lateral velocities during drop landing are compared to the sequence of video frames (upper panel). The lower panel is the axial and lateral velocities, where A corresponds to the initial knee flexion, B corresponds to the knee extension, C corresponds to the toe striking the ground, D corresponds to the heel striking the ground, E corresponds to knee flexion post landing and F corresponds to the knee extension and stabilization.

Figure 3
Figure 3. Repeatability of the magnitude of the resultant velocity vector for all 8 subjects (2 trials per subject). Men are denoted in red diamonds and women in blue circles.

Figure 4
Figure 4. Panel A. The error in the angle between the line segment made by ultrasound transducer holder and the marker on the mid-thigh (purple dashed line segment) and the line segment made by the ultrasound transducer and the marker on the trochanter (green dashed line segment). Panel B. The absolute error in the angle between the line segment made by ultrasound transducer holder and the marker on the mid-thigh and the line segment made by the ultrasound transducer and the marker on the trochanter.

Figure 5
Figure 5. Figure shows the 3D motion capture during the drop landing task. A corresponds to the initial knee flexion for launch from platform, B corresponds to the toe striking the ground, C corresponds to the heel striking the ground, D corresponds to knee flexion post landing and E corresponds to the knee extension and stabilization. Click here to view larger figure.

Figure 6
Figure 6. Figure shows representative knee valgus moment changes during the stance phase of drop-jump. Knee valgus moment presented an increase from 0.03±0.03 to 0.1±0.1 Nm/km from initial ground contact to its maximum during the landing phase. Click here to view larger figure.

Discussion

Ultrasound imaging has the ability to provide direct assessment of muscle kinematics in dynamic studies that can complement conventional measures, such as 3D motion capture, dynamometry, electromyography, and ground reaction force measurements. This approach can be broadly applicable for fundamental biomechanics research and clinical evaluation. There are three main approaches to estimating tissue motion using ultrasound: (1) speckle tracking methods that use cross-correlation on raw radiofrequency (RF) ultrasound data or envelope-detected gray scale (or B-mode) image data. These techniques have been widely used in both skeletal 24-25 and cardiac 26 muscle motion tracking and estimation; (2) image processing methods that track the muscle fascicles or features 27-28 and (3) tissue Doppler imaging techniques used in both cardiac 29-30 and skeletal 31 motion estimation. Speckle tracking based on spatial cross-correlation has been used widely to track motion of tissue and can track motion with sub-pixel resolution. However, speckle patterns decorrelate quickly during larger motions. Motion out of the image plane also poses a challenge for speckle tracking. Methods for tracking muscle fascicle length have better applicability where the entire fascicle is visualized in the image during the dynamic task. Methods that rely on processing image data have low temporal resolution limited by the imaging frame rate and hence cannot track motion at high velocities. In addition, these fascicle tracking methods are very sensitive to out of plane motion. Thus probe movement relative to the muscle could cause the tracking to fail. Velocity estimates from conventional tissue Doppler imaging (TDI) can have higher temporal resolution, as well are more robust to small probe movements. Doppler methods can estimate velocities components only along the ultrasound beam, thus Doppler estimates could be inaccurate due to the varying angle of insonation with the motion of the muscle. Our proposed vTDI method overcomes this problem by utilizing two different ultrasound beams steered at different angles; therefore the velocity estimate is independent of the insonation angle in the imaging plane. Also, the effective temporal resolution of vTDI can be approximately 0.1 ms and therefore this method can track motion of skeletal muscle during dynamic activities (e.g. drop-landing, gait and jogging).

Other advantages of our approach include the use of a linear array imaging transducer based on a clinical ultrasound system for performing vector tissue Doppler imaging. We electronically controlled the transmit/receive beam steering, aperture size and focus locations, for scanning a large field of view. Furthermore, this approach can be extended to perform duplex vTDI with simultaneous real time imaging. Our system also allows us to perform conventional B-mode imaging to locate the region of interest for quantification of tissue strain and kinematics. Since this method was implemented on a clinical scanner, we have been able to deploy this vTDI method in a gait lab for biomechanics research.

Limitations of this technique must be acknowledged. Various factors affect the accuracy of Doppler measurements. vTDI based velocity estimates in two dimension (along and across muscle fibers) requires the linear array transducer to be split into two transmit/receive sub-apertures (32 elements wide) and steer the beams by 15°. Steering the ultrasound transmit and receive beams to higher angles could affect velocity measures due to grating lobes. Also, the area of the beam overlap region in vTDI changes with varying beam focus depths 32, potentially affecting the velocity estimates. The variance of the Doppler estimates depend upon (1) acceleration and deceleration of tissue within the analysis time window (2) variance of tissue velocity within the Doppler range gate (3) the varying Doppler angle within the aperture used for Wideband spectral the transmitted and received ultrasound beams, also known as geometric broadening 33 and (4) the bandwidth of the transmitted ultrasound pulse, since the Doppler shift is proportional to the carrier frequency 34. Several methods can be used to limit the variance. Phase based velocity estimators, such as the autocorrelation, typically utilize smaller analysis time windows compared to spectral estimators, but they estimate mean Doppler shift rather than the peak shift. Wideband spectral estimators like the 2D Fourier transform 35 can reduce the variance due to the pulse bandwidth. In the case of vTDI, which utilizes two steered Doppler beams, the variance of tissue velocities in the beam-overlap region relative to the muscle is another factor to consider. The rectus femoris muscle contraction is in 3D and the contraction velocity varies spatially along the muscle. Therefore, it is important to carefully select the region of interest.

In this study, we investigated the repeatability of the rectus femoris muscle kinematics during a drop-landing task in eight healthy volunteers using vTDI. Even though the trials were independent, we observed highly correlated and repeatable peak muscle contraction velocities for individuals between trials. We are currently recruiting more subjects in our study to further examine this pattern. This study has provided non-invasive and real time measurement of the contraction velocities of the rectus femoris muscle during drop-landing. The following patterns of contraction velocities were observed during the various phases of the drop landing task (Figure 2): 1. Muscle contraction velocities dominate in the lateral direction compared to axial direction during the knee flexion (launch phase) and extension (in-the-air phase). This is expected, since the rectus femoris muscle is undergoing eccentric contraction during the launch phase and concentric contraction during in-the-air phase. 2. Low lateral muscle velocities during the third phase (toe touching the ground), with negligibly low axial muscle velocities. This corresponds to lower rectus femoris muscle contraction during this phase 3. Substantial increase in axial and lateral muscle velocities just after the heel touches the ground. This is probably due to the muscle undergoing both eccentric contraction and change in shape due to compression, causing increase in velocities along the muscle fibers and normal to the muscle fibers, respectively. Despite the fact that the drop landing task is a high impact task, vTDI demonstrated repeatable rectus femoris muscle velocities. This ultrasound technique could have clinical impact since this muscle is primarily responsible for protecting the knee joint from excessive loading. Therefore, further assessment of the rectus femoris muscle in patients with ACL reconstruction is warranted to understand the mechanisms leading to the early and accelerated onset of OA.

Although the participants in this study were all asked to perform a natural drop-landing task from a 30 cm tall platform, we found differences in the height of the jump or launch. Also, using the high speed camera data, it was observed that all the subjects had a different drop landing style. This could explain the slight differences between subjects in the peak resultant velocity values of the rectus femoris muscle as a consequence of possible differences in activation patterns during the task. Another possible factor is the differences in cross-sectional area of the rectus femoris muscle, which could potentially lead to different levels of muscle contraction and force production.

Disclosures

None of the authors have any financial disclosures or conflicts of interest and the study was approved by our institution's IRB.

Acknowledgments

This work was supported in part by Grant Number 0953652 from the National Science Foundation and in part by the George Mason University libraries open access publishing fund. We would like to thank Dr. John Robert Cressman Jr. for providing access to the high-speed camera.

Materials

Name Company Catalog Number Comments
Ultrasound System Ultrasonix Sonix RP
3D Motion Capture System Vicon Motion Systems Vicon T-20
Force Plates Bertec Corporation Bertec 4060-10
High Speed Camera Photron Photron 512 PCI 32K

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Tags

Musculoskeletal Ultrasound Vector Tissue Doppler Imaging VTDI Muscle Kinematics Muscle Contraction Velocity Strain Strain Rate Drop-landing Biomechanics Motion Capture EMG Force Plates
A Novel Application of Musculoskeletal Ultrasound Imaging
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Cite this Article

Eranki, A., Cortes, N.,More

Eranki, A., Cortes, N., Ferenček, Z. G., Sikdar, S. A Novel Application of Musculoskeletal Ultrasound Imaging. J. Vis. Exp. (79), e50595, doi:10.3791/50595 (2013).

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  • Research • Medicine
    Simultaneous Laryngopharyngeal and Conventional Esophageal pH Monitoring
  • Research • Medicine
    Real-Time Monitoring of Neurocritical Patients with Diffuse Optical Spectroscopies
  • Research • Neuroscience
    Evaluating Postural Control and Lower-extremity Muscle Activation in Individuals with Chronic Ankle Instability
  • Research • Medicine
    Assessment of Dependence in Activities of Daily Living Among Older Patients in an Acute Care Unit
  • Research • Medicine
    Validated LC-MS/MS Panel for Quantifying 11 Drug-Resistant TB Medications in Small Hair Samples
  • Research • Medicine
    International Expert Consensus and Recommendations for Neonatal Pneumothorax Ultrasound Diagnosis and Ultrasound-guided Thoracentesis Procedure
  • Research • Biology
    A Finite Element Approach for Locating the Center of Resistance of Maxillary Teeth
  • Research • Medicine
    Lower Limb Biomechanical Analysis of Healthy Participants
  • Research • Neuroscience
    Assessing Early Stage Open-Angle Glaucoma in Patients by Isolated-Check Visual Evoked Potential
  • Research • Medicine
    Oral Health Assessment by Lay Personnel for Older Adults
  • Research • Medicine
    Determining and Controlling External Power Output During Regular Handrim Wheelchair Propulsion
  • Research • Medicine
    A Whole Body Dosimetry Protocol for Peptide-Receptor Radionuclide Therapy (PRRT): 2D Planar Image and Hybrid 2D+3D SPECT/CT Image Methods
  • Research • Medicine
    Measurement of Carotenoids in Perifovea using the Macular Pigment Reflectometer
  • Research • Medicine
    Assessment of Static Graviceptive Perception in the Roll-Plane using the Subjective Visual Vertical Paradigm
  • Research • Medicine
    Learning Modern Laryngeal Surgery in a Dissection Laboratory
  • Research • Medicine
    DIPLOMA Approach for Standardized Pathology Assessment of Distal Pancreatectomy Specimens
  • Research • Medicine
    A Computerized Functional Skills Assessment and Training Program Targeting Technology Based Everyday Functional Skills
  • Research • Medicine
    Imaging Features of Systemic Sclerosis-Associated Interstitial Lung Disease
  • Research • Medicine
    Integrating Augmented Reality Tools in Breast Cancer Related Lymphedema Prognostication and Diagnosis
  • Research • Medicine
    Ultrasonographic Assessment During Cardiopulmonary Resuscitation
  • Research • Medicine
    Measurement of the Hepatic Venous Pressure Gradient and Transjugular Liver Biopsy
  • Research • Medicine
    Patient Directed Recording of a Bipolar Three-Lead Electrocardiogram using a Smartwatch with ECG Function
  • Research • Medicine
    Traditional Trail Making Test Modified into Brand-new Assessment Tools: Digital and Walking Trail Making Test
  • Research • Medicine
    Use of Magnetic Resonance Imaging and Biopsy Data to Guide Sampling Procedures for Prostate Cancer Biobanking
  • Research • Medicine
    A Fluorescence-based Assay for Characterization and Quantification of Lipid Droplet Formation in Human Intestinal Organoids
  • Research • Medicine
    A Novel Non-invasive Method for the Detection of Elevated Intra-compartmental Pressures of the Leg
  • Research • Medicine
    Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent
  • Research • Neuroscience
    Portable Thermographic Screening for Detection of Acute Wallenberg's Syndrome
  • Research • Medicine
    Use of MRI-ultrasound Fusion to Achieve Targeted Prostate Biopsy
  • Research • Medicine
    Testing of all Six Semicircular Canals with Video Head Impulse Test Systems
  • Research • Medicine
    Protocol and Guidelines for Point-of-Care Lung Ultrasound in Diagnosing Neonatal Pulmonary Diseases Based on International Expert Consensus
  • Research • Neuroscience
    Bilateral Assessment of the Corticospinal Pathways of the Ankle Muscles Using Navigated Transcranial Magnetic Stimulation
  • Research • Medicine
    Targeting Gray Rami Communicantes in Selective Chemical Lumbar Sympathectomy
  • Research • Medicine
    Multi-Modal Home Sleep Monitoring in Older Adults
  • Research • Medicine
    Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques
  • Research • Medicine
    Observational Study Protocol for Repeated Clinical Examination and Critical Care Ultrasonography Within the Simple Intensive Care Studies
  • Research • Medicine
    Measurements of Motor Function and Other Clinical Outcome Parameters in Ambulant Children with Duchenne Muscular Dystrophy
  • Research • Medicine
    Assessment of the Efficacy of An Osteopathic Treatment in Infants with Biomechanical Impairments to Suckling
  • Research • Medicine
    Quantification of Levator Ani Hiatus Enlargement by Magnetic Resonance Imaging in Males and Females with Pelvic Organ Prolapse
  • Research • Medicine
    Quantitative [18F]-Naf-PET-MRI Analysis for the Evaluation of Dynamic Bone Turnover in a Patient with Facetogenic Low Back Pain
  • Research • Medicine
    Generation of Human 3D Lung Tissue Cultures (3D-LTCs) for Disease Modeling
  • Research • Medicine
    Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
  • Research • Medicine
    Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship
  • Research • Medicine
    Two-Dimensional X-Ray Angiography to Examine Fine Vascular Structure Using a Silicone Rubber Injection Compound
  • Research • Medicine
    Preparation, Procedures and Evaluation of Platelet-Rich Plasma Injection in the Treatment of Knee Osteoarthritis
  • Research • Medicine
    Cardiac Magnetic Resonance Imaging at 7 Tesla
  • Research • Medicine
    Semi-quantitative Assessment Using [18F]FDG Tracer in Patients with Severe Brain Injury
  • Research • Medicine
    Handheld Metal Detector Screening for Metallic Foreign Body Ingestion in Children
  • Research • Medicine
    Conducting Maximal and Submaximal Endurance Exercise Testing to Measure Physiological and Biological Responses to Acute Exercise in Humans
  • Research • Medicine
    A Metadata Extraction Approach for Clinical Case Reports to Enable Advanced Understanding of Biomedical Concepts
  • Research • Medicine
    Autonomic Function Following Concussion in Youth Athletes: An Exploration of Heart Rate Variability Using 24-hour Recording Methodology
  • Research • Medicine
    Hydra, a Computer-Based Platform for Aiding Clinicians in Cardiovascular Analysis and Diagnosis
  • Research • Medicine
    Objective Nociceptive Assessment in Ventilated ICU Patients: A Feasibility Study Using Pupillometry and the Nociceptive Flexion Reflex
  • Research • Medicine
    'Boden Food Plate': Novel Interactive Web-based Method for the Assessment of Dietary Intake
  • Research • Medicine
    Anogenital Distance and Perineal Measurements of the Pelvic Organ Prolapse (POP) Quantification System
  • Research • Medicine
    Bedside Ultrasound for Guiding Fluid Removal in Patients with Pulmonary Edema: The Reverse-FALLS Protocol
  • Research • Medicine
    Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
  • Research • Medicine
    Isolation of Primary Human Decidual Cells from the Fetal Membranes of Term Placentae
  • Research • Medicine
    Skeletal Muscle Neurovascular Coupling, Oxidative Capacity, and Microvascular Function with 'One Stop Shop' Near-infrared Spectroscopy
  • Research • Medicine
    Collecting Hair Samples for Hair Cortisol Analysis in African Americans
  • Research • Medicine
    In Vivo Morphometric Analysis of Human Cranial Nerves Using Magnetic Resonance Imaging in Menière's Disease Ears and Normal Hearing Ears
  • Research • Medicine
    Measuring the Carotid to Femoral Pulse Wave Velocity (Cf-PWV) to Evaluate Arterial Stiffness
  • Research • Medicine
    Standardized Measurement of Nasal Membrane Transepithelial Potential Difference (NPD)
  • Research • Medicine
    Taste Exam: A Brief and Validated Test
  • Research • Medicine
    Absorption of Nasal and Bronchial Fluids: Precision Sampling of the Human Respiratory Mucosa and Laboratory Processing of Samples
  • Research • Medicine
    Methodology for Sputum Induction and Laboratory Processing
  • Research • Medicine
    Electrophysiological Measurement of Noxious-evoked Brain Activity in Neonates Using a Flat-tip Probe Coupled to Electroencephalography
  • Research • Medicine
    A Detailed Protocol for Physiological Parameters Acquisition and Analysis in Neurosurgical Critical Patients
  • Research • Medicine
    Oral Biofilm Sampling for Microbiome Analysis in Healthy Children
  • Research • Medicine
    Using Retinal Imaging to Study Dementia
  • Research • Medicine
    Application of an Amplitude-integrated EEG Monitor (Cerebral Function Monitor) to Neonates
  • Research • Medicine
    3D Ultrasound Imaging: Fast and Cost-effective Morphometry of Musculoskeletal Tissue
  • Research • Medicine
    The 4-vessel Sampling Approach to Integrative Studies of Human Placental Physiology In Vivo
  • Research • Medicine
    A Component-resolved Diagnostic Approach for a Study on Grass Pollen Allergens in Chinese Southerners with Allergic Rhinitis and/or Asthma
  • Research • Medicine
    A Novel Method: Super-selective Adrenal Venous Sampling
  • Research • Medicine
    A Method for Quantifying Upper Limb Performance in Daily Life Using Accelerometers
  • Research • Medicine
    Non-invasive Assessments of Subjective and Objective Recovery Characteristics Following an Exhaustive Jump Protocol
  • Research • Medicine
    Experimental Protocol of a Three-minute, All-out Arm Crank Exercise Test in Spinal-cord Injured and Able-bodied Individuals
  • Research • Medicine
    Phosphorus-31 Magnetic Resonance Spectroscopy: A Tool for Measuring In Vivo Mitochondrial Oxidative Phosphorylation Capacity in Human Skeletal Muscle
  • Research • Medicine
    Assessment of Pulmonary Capillary Blood Volume, Membrane Diffusing Capacity, and Intrapulmonary Arteriovenous Anastomoses During Exercise
  • Research • Medicine
    Assessment of Child Anthropometry in a Large Epidemiologic Study
  • Research • Medicine
    Video Movement Analysis Using Smartphones (ViMAS): A Pilot Study
  • Research • Medicine
    Network Analysis of Foramen Ovale Electrode Recordings in Drug-resistant Temporal Lobe Epilepsy Patients
  • Research • Medicine
    A Model to Simulate Clinically Relevant Hypoxia in Humans
  • Research • Medicine
    Interictal High Frequency Oscillations Detected with Simultaneous Magnetoencephalography and Electroencephalography as Biomarker of Pediatric Epilepsy
  • Research • Medicine
    Induction and Assessment of Exertional Skeletal Muscle Damage in Humans
  • Research • Medicine
    A Detailed Protocol for Perspiration Monitoring Using a Novel, Small, Wireless Device
  • Research • Medicine
    Drug-Induced Sleep Endoscopy (DISE) with Target Controlled Infusion (TCI) and Bispectral Analysis in Obstructive Sleep Apnea
  • Research • Medicine
    Integrated Compensatory Responses in a Human Model of Hemorrhage
  • Research • Medicine
    Transthoracic Speckle Tracking Echocardiography for the Quantitative Assessment of Left Ventricular Myocardial Deformation
  • Research • Medicine
    Impression Cytology of the Lid Wiper Area
  • Research • Behavior
    A Protocol of Manual Tests to Measure Sensation and Pain in Humans
  • Research • Medicine
    Unbiased Deep Sequencing of RNA Viruses from Clinical Samples
  • Research • Medicine
    A Choroid Plexus Epithelial Cell-based Model of the Human Blood-Cerebrospinal Fluid Barrier to Study Bacterial Infection from the Basolateral Side
  • Research • Medicine
    Isolation and Profiling of MicroRNA-containing Exosomes from Human Bile
  • Research • Medicine
    Generation of Microtumors Using 3D Human Biogel Culture System and Patient-derived Glioblastoma Cells for Kinomic Profiling and Drug Response Testing
  • Research • Medicine
    Ultrasound Assessment of Endothelial Function: A Technical Guideline of the Flow-mediated Dilation Test
  • Research • Medicine
    Using a Laminating Technique to Perform Confocal Microscopy of the Human Sclera
  • Research • Medicine
    Intravenous Endotoxin Challenge in Healthy Humans: An Experimental Platform to Investigate and Modulate Systemic Inflammation
  • Research • Medicine
    Modeling and Simulations of Olfactory Drug Delivery with Passive and Active Controls of Nasally Inhaled Pharmaceutical Aerosols
  • Research • Medicine
    Exosomal miRNA Analysis in Non-small Cell Lung Cancer (NSCLC) Patients' Plasma Through qPCR: A Feasible Liquid Biopsy Tool
  • Research • Medicine
    A Multimodal Imaging- and Stimulation-based Method of Evaluating Connectivity-related Brain Excitability in Patients with Epilepsy
  • Research • Medicine
    Measuring Cardiac Autonomic Nervous System (ANS) Activity in Toddlers - Resting and Developmental Challenges
  • Research • Medicine
    Using Saccadometry with Deep Brain Stimulation to Study Normal and Pathological Brain Function
  • Research • Medicine
    Quantitative Fundus Autofluorescence for the Evaluation of Retinal Diseases
  • Research • Medicine
    Diagnosis of Musculus Gastrocnemius Tightness - Key Factors for the Clinical Examination
  • Research • Medicine
    Stereo-Electro-Encephalo-Graphy (SEEG) With Robotic Assistance in the Presurgical Evaluation of Medical Refractory Epilepsy: A Technical Note
  • Research • Medicine
    Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
  • Research • Medicine
    Transcutaneous Microcirculatory Imaging in Preterm Neonates
  • Research • Medicine
    Using an Ingestible Telemetric Temperature Pill to Assess Gastrointestinal Temperature During Exercise
  • Research • Medicine
    Design, Fabrication, and Administration of the Hand Active Sensation Test (HASTe)
  • Research • Medicine
    MRI-guided dmPFC-rTMS as a Treatment for Treatment-resistant Major Depressive Disorder
  • Research • Medicine
    Functional Human Liver Preservation and Recovery by Means of Subnormothermic Machine Perfusion
  • Research • Medicine
    A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis
  • Research • Medicine
    Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test
  • Research • Medicine
    Use of Electromagnetic Navigational Transthoracic Needle Aspiration (E-TTNA) for Sampling of Lung Nodules
  • Research • Medicine
    Trabecular Meshwork Response to Pressure Elevation in the Living Human Eye
  • Research • Medicine
    In Vivo, Percutaneous, Needle Based, Optical Coherence Tomography of Renal Masses
  • Research • Medicine
    Establishment of Human Epithelial Enteroids and Colonoids from Whole Tissue and Biopsy
  • Research • Medicine
    Human Brown Adipose Tissue Depots Automatically Segmented by Positron Emission Tomography/Computed Tomography and Registered Magnetic Resonance Images
  • Research • Medicine
    Preparation and Respirometric Assessment of Mitochondria Isolated from Skeletal Muscle Tissue Obtained by Percutaneous Needle Biopsy
  • Research • Medicine
    A Methodological Approach to Non-invasive Assessments of Vascular Function and Morphology
  • Research • Medicine
    Isolation and Immortalization of Patient-derived Cell Lines from Muscle Biopsy for Disease Modeling
  • Research • Medicine
    State of the Art Cranial Ultrasound Imaging in Neonates
  • Research • Medicine
    Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact
  • Research • Medicine
    The Supraclavicular Fossa Ultrasound View for Central Venous Catheter Placement and Catheter Change Over Guidewire
  • Research • Medicine
    Ultrasound Assessment of Endothelial-Dependent Flow-Mediated Vasodilation of the Brachial Artery in Clinical Research
  • Research • Medicine
    Tracking the Mammary Architectural Features and Detecting Breast Cancer with Magnetic Resonance Diffusion Tensor Imaging
  • Research • Medicine
    A Neuroscientific Approach to the Examination of Concussions in Student-Athletes
  • Research • Medicine
    DTI of the Visual Pathway - White Matter Tracts and Cerebral Lesions
  • Research • Medicine
    Collection, Isolation, and Flow Cytometric Analysis of Human Endocervical Samples
  • Research • Medicine
    Fundus Photography as a Convenient Tool to Study Microvascular Responses to Cardiovascular Disease Risk Factors in Epidemiological Studies
  • Research • Medicine
    A Multi-Modal Approach to Assessing Recovery in Youth Athletes Following Concussion
  • Research • Medicine
    Clinical Assessment of Spatiotemporal Gait Parameters in Patients and Older Adults
  • Research • Medicine
    Multi-electrode Array Recordings of Human Epileptic Postoperative Cortical Tissue
  • Research • Medicine
    Collection and Extraction of Saliva DNA for Next Generation Sequencing
  • Research • Medicine
    Fast and Accurate Exhaled Breath Ammonia Measurement
  • Research • Medicine
    Developing Neuroimaging Phenotypes of the Default Mode Network in PTSD: Integrating the Resting State, Working Memory, and Structural Connectivity
  • Research • Medicine
    Two Methods for Establishing Primary Human Endometrial Stromal Cells from Hysterectomy Specimens
  • Research • Medicine
    Assessment of Vascular Function in Patients With Chronic Kidney Disease
  • Research • Medicine
    Coordinate Mapping of Hyolaryngeal Mechanics in Swallowing
  • Research • Medicine
    Network Analysis of the Default Mode Network Using Functional Connectivity MRI in Temporal Lobe Epilepsy
  • Research • Medicine
    EEG Mu Rhythm in Typical and Atypical Development
  • Research • Medicine
    The Multiple Sclerosis Performance Test (MSPT): An iPad-Based Disability Assessment Tool
  • Research • Medicine
    Isolation and Functional Characterization of Human Ventricular Cardiomyocytes from Fresh Surgical Samples
  • Research • Medicine
    Dynamic Visual Tests to Identify and Quantify Visual Damage and Repair Following Demyelination in Optic Neuritis Patients
  • Research • Medicine
    Primary Culture of Human Vestibular Schwannomas
  • Research • Medicine
    Utility of Dissociated Intrinsic Hand Muscle Atrophy in the Diagnosis of Amyotrophic Lateral Sclerosis
  • Research • Medicine
    Lesion Explorer: A Video-guided, Standardized Protocol for Accurate and Reliable MRI-derived Volumetrics in Alzheimer's Disease and Normal Elderly
  • Research • Medicine
    Pulse Wave Velocity Testing in the Baltimore Longitudinal Study of Aging
  • Research • Medicine
    Isolation, Culture, and Imaging of Human Fetal Pancreatic Cell Clusters
  • Research • Medicine
    3D-Neuronavigation In Vivo Through a Patient's Brain During a Spontaneous Migraine Headache
  • Research • Medicine
    A Novel Application of Musculoskeletal Ultrasound Imaging
  • Research • Medicine
    Computerized Dynamic Posturography for Postural Control Assessment in Patients with Intermittent Claudication
  • Research • Medicine
    Collecting Saliva and Measuring Salivary Cortisol and Alpha-amylase in Frail Community Residing Older Adults via Family Caregivers
  • Research • Medicine
    Diffusion Tensor Magnetic Resonance Imaging in the Analysis of Neurodegenerative Diseases
  • Research • Medicine
    Transcriptomic Analysis of Human Retinal Surgical Specimens Using jouRNAl
  • Research • Medicine
    Improved Protocol For Laser Microdissection Of Human Pancreatic Islets From Surgical Specimens
  • Research • Medicine
    Evaluation of Respiratory Muscle Activation Using Respiratory Motor Control Assessment (RMCA) in Individuals with Chronic Spinal Cord Injury
  • Research • Medicine
    Minimal Erythema Dose (MED) Testing
  • Research • Medicine
    Measuring Cardiac Autonomic Nervous System (ANS) Activity in Children
  • Research • Medicine
    Collecting And Measuring Wound Exudate Biochemical Mediators In Surgical Wounds
  • Research • Medicine
    A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis
  • Research • Medicine
    Using a Chemical Biopsy for Graft Quality Assessment
  • Research • Medicine
    Characterizing Exon Skipping Efficiency in DMD Patient Samples in Clinical Trials of Antisense Oligonucleotides
  • Research • Medicine
    In Vitro Assessment of Cardiac Function Using Skinned Cardiomyocytes
  • Research • Medicine
    Normothermic Ex Situ Heart Perfusion in Working Mode: Assessment of Cardiac Function and Metabolism
  • Research • Medicine
    Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats
  • Research • Medicine
    Bronchoalveolar Lavage (BAL) for Research; Obtaining Adequate Sample Yield
  • Research • Medicine
    Non-invasive Optical Measurement of Cerebral Metabolism and Hemodynamics in Infants
  • Research • Medicine
    Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
  • Research • Medicine
    Driving Simulation in the Clinic: Testing Visual Exploratory Behavior in Daily Life Activities in Patients with Visual Field Defects
  • Research • Medicine
    Isolation, Characterization and Comparative Differentiation of Human Dental Pulp Stem Cells Derived from Permanent Teeth by Using Two Different Methods
  • Research • Medicine
    Portable Intermodal Preferential Looking (IPL): Investigating Language Comprehension in Typically Developing Toddlers and Young Children with Autism
  • Research • Medicine
    Intraoperative Detection of Subtle Endometriosis: A Novel Paradigm for Detection and Treatment of Pelvic Pain Associated with the Loss of Peritoneal Integrity
  • Research • Medicine
    The Use of Primary Human Fibroblasts for Monitoring Mitochondrial Phenotypes in the Field of Parkinson's Disease
  • Research • Medicine
    Collection Protocol for Human Pancreas
  • Research • Medicine
    The α-test: Rapid Cell-free CD4 Enumeration Using Whole Saliva
  • Research • Medicine
    The Measurement and Treatment of Suppression in Amblyopia
  • Research • Medicine
    Corneal Donor Tissue Preparation for Endothelial Keratoplasty
  • Research • Medicine
    Quantification of Atherosclerotic Plaque Activity and Vascular Inflammation using [18-F] Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG-PET/CT)
  • Research • Medicine
    Eye Tracking Young Children with Autism
  • Research • Medicine
    Doppler Optical Coherence Tomography of Retinal Circulation
  • Research • Medicine
    Utilizing Transcranial Magnetic Stimulation to Study the Human Neuromuscular System
  • Research • Medicine
    Detection and Genogrouping of Noroviruses from Children's Stools By Taqman One-step RT-PCR
  • Research • Medicine
    Method to Measure Tone of Axial and Proximal Muscle
  • Research • Medicine
    The Trier Social Stress Test Protocol for Inducing Psychological Stress
  • Research • Medicine
    Probing the Brain in Autism Using fMRI and Diffusion Tensor Imaging
  • Research • Medicine
    Multifocal Electroretinograms
  • Research • Medicine
    Isolation of Human Islets from Partially Pancreatectomized Patients
  • Research • Medicine
    Examining the Characteristics of Episodic Memory using Event-related Potentials in Patients with Alzheimer's Disease
  • Research • Medicine
    Magnetic Resonance Imaging Quantification of Pulmonary Perfusion using Calibrated Arterial Spin Labeling
  • Research • Medicine
    Manual Muscle Testing: A Method of Measuring Extremity Muscle Strength Applied to Critically Ill Patients
  • Research • Medicine
    Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
  • Research • Medicine
    A Protocol for Comprehensive Assessment of Bulbar Dysfunction in Amyotrophic Lateral Sclerosis (ALS)
  • Research • Medicine
    An Investigation of the Effects of Sports-related Concussion in Youth Using Functional Magnetic Resonance Imaging and the Head Impact Telemetry System
  • Research • Medicine
    Corneal Confocal Microscopy: A Novel Non-invasive Technique to Quantify Small Fibre Pathology in Peripheral Neuropathies
  • Research • Medicine
    Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI
  • Research • Medicine
    Multispectral Real-time Fluorescence Imaging for Intraoperative Detection of the Sentinel Lymph Node in Gynecologic Oncology
  • Research • Medicine
    Technique to Collect Fungiform (Taste) Papillae from Human Tongue
  • Research • Medicine
    Assessing Endothelial Vasodilator Function with the Endo-PAT 2000
  • Research • Medicine
    Making Sense of Listening: The IMAP Test Battery
  • Research • Medicine
    An Experimental Paradigm for the Prediction of Post-Operative Pain (PPOP)
  • Research • Biology
    Bioelectric Analyses of an Osseointegrated Intelligent Implant Design System for Amputees
  • Research • Biology
    Demonstration of Cutaneous Allodynia in Association with Chronic Pelvic Pain
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