A Novel Application of Musculoskeletal Ultrasound Imaging

The overall goal of this procedure is to estimate contraction, velocities, strain and strain rate of the rectus femoral muscle with sub millisecond temporal resolution during a drop landing task using vector tissue doppler imaging. This is accomplished by first preparing the subject by placing reflective markers on the subject's lower limbs and the transducer on the subject's thigh. Next, the subject is asked to stand with arms across the chest on the middle of the motion capture volume, and a static trial is captured.

Then while standing on a platform, the subject performs the drop landing task by dropping from the platform and landing with both legs simultaneously. Ultimately, results can be obtained that show the rectus femoral muscle kinematic during a drop landing task through vector tissue doppler imaging, as well as quantifying joint kinematic and kinetics using the motion capture system. The main advantage of this technique or other existing methods like 3D, motion capture and electromyography is ultrasound imaging can provide direct estimates of individual muscle motion.

Additionally, vector tissue Doppler imaging has several advantages over currently existing ultrasound imaging techniques since it can provide both the magnitude and the direction of muscle motion at very high frame rates, especially in activities like drop landing. This method can answer key questions in the fields of biomechanics and rehabilitation signs by providing quantitative measures of musculoskeletal kinematic during dynamic tasks. This method can be applied to understand the pathophysiological process of degenerative disease, such as early onset of osteoarthritis, post anterior curate ligament injuries.

This is because we can concurrently quantify joint mechanics and musculoskeletal function during dynamic activities. To understand the underlying processes of these early development For this procedure, ask the subject to wear a sports bra or short t-shirt, shorts and running shoes. To begin instruct the subjects to perform a 10 minute self-directed warmup and stretching prior to the data collection.

This is to avoid any abnormal muscular contractions and reduce the scope of any muscle cramps. After the warmup session, use adhesive tape to place reflective calibration markers on the greater chanters, the bilateral, medial and lateral knee, and the lateral meli. Then place tracking markers on the posterior and anterior superior iliac crests.

Place clusters on the thighs and shanks, and finally, adhere five markers to each foot. Next, place the ultrasound transducer securely in a custom designed transducer holder, and to ensure good contact between it and the skin, apply a generous amount of ultrasound transmission gel. Then place the ultrasound transducer with holder on the subject's thigh halfway between the anterior iliac spine and the lateral epicondyle.

Before securing the ultrasound transducer and holder to the leg, obtain an axial or cross-sectional view of the quadriceps muscle group. Using this as a guide, rotate the transducer to a longitudinal view and to make sure the ultrasound transducer is now imaging the rectus fems and does not move lateral or medial. To avoid imaging the vast eye muscle groups without blocking any of the reflective markers, use a self-adhesive bandage to comfortably secure the holder to the subject's thigh.

Then to obtain a static 3D motion capture trial, direct the subject to stand on the force plates in the center of the focus area of the 3D cameras with their arms across their shoulders. To complete the setup, place the high speed camera at least two meters away from the subject in the sagittal plane and focus the camera lens to ensure that the entire drop landing sequence of the subject can be captured. Ask the subject to stand on a platform 30 centimeters high and 50 centimeters from the force plates and clear of any objects, instruct the subject to place their hands on their hips prior to starting the drop landing task and during the entire drop landing sequence prior to the start of the drop landing task, start the data collection for ultrasound 3D.

Motion capture the force plates and the high speed camera. Next, direct the subject to perform the drop landing task by dropping rather than jumping from the platform and landing with both legs simultaneously. Once the subject has fully stabilized and completed the drop landing sequence, stop the data collection.

To analyze the raw radio frequency ultrasound data, use MATLAB to import the ultrasound data file and perform quadrature demodulation on the data to remove the carrier frequency. Generate en mode images from both the receive beams to visualize the motion of the muscle, use the conventional auto correlation velocity estimator to estimate the velocities along both receive beams. Combine the individual velocity waveforms to obtain lateral and axial velocity waveforms throughout the drop landing sequence.

Using the following equation, obtain the magnitude of the resultant velocity vector from the individual velocity components where beta is the beam steering angle. F1 and F two are the two received frequency components, and FT is the transmit frequency. Calculate the lateral and axial strain rate de epsilon over DT using the spatial gradients in the lateral and axial velocities.

Were V two and V one are instantaneous velocities estimated at two spatial locations separated by a distance L.Then calculate the axial and lateral strain epsilon by integrating the axial and lateral strain rate respectively. After exporting the 3D motion capture data, use 3D motion capture software with at least squares optimization to create a kinematic model of the pelvis, thigh shank and foot. Using the model, quantify the motion at the hip, knee, and ankle joints.

To filter the reflective marker trajectories and ground reaction forces. Use a fourth order low-pass Butterworth filter with a cutoff frequency of seven hertz and 25 hertz respectively. Using a standard inverse dynamics analysis and segment inertial characteristics estimated for the subject.

As per the methods of dempster, calculate 3D joint forces and moments from the kinematic and ground force data to analyze the high speed camera data. After exporting the video, play it at 15 frames per second and observe the drop landing dynamics. Then using the data, 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 as seen here, analysis of the temporal characteristics of the axial and lateral rectus femoral muscle velocities throughout the drop landing sequence illustrate that positive lateral velocities correspond to eccentric contraction of the rectus femoral muscle during knee flexion while negative lateral velocities correspond to concentric contraction of the muscle during knee extension. The entire drop landing sequence for all subjects lasted approximately 1.45 plus or minus 0.27 seconds for each subject as demonstrated in this plot, the axial and lateral muscle velocities showed a strong repeatability between trials with the slope of 0.99 and r squared equaling 0.75. Velocity values for six out of eight subjects were in a similar range of 48 to 62 centimeters per second.

While two male subjects had higher velocities, males presented significantly higher muscle velocity than females when adjusting for each subject's individual weight and muscle thickness. The position of the ultrasound transducer was tracked through the drop landing sequence using the high speed camera. The angle between the line segment made between the trant and the cuff and the line segment between the mid thigh and the cuff was calculated.

This figure represents a total of 16 trials with two trials per subject. Minimal angular variation of the transducer holder relative to the anatomical markers during landing was observed over all 16 trials. The ultrasound transducer, angular variation produced a high repeatability as well.

This shows that the transducer movement during the landing trial was minimal and the velocity measurements were not affected by any transducer movement focusing on knee and hip flexion angles, knee valgus angle, and knee valgus moment, the following kinematic patterns were found through initial contact with the ground hip flexion, 41 plus or minus 13 degrees knee flexion 23 plus or minus nine degrees and knee valgus 0.03 plus or minus six degrees as they progressed during the landing phase. The maximum angles attained were hip flexion 58 plus or minus 19 degrees, knee flexion 54 plus or minus 24 degrees, and knee valgus minus four plus or minus eight degrees. In addition, knee valgus moment decreased from 0.03 plus or minus 0.03 to 0.1, plus or minus 0.1 newton meters per kilogram from initial ground contact to its maximum during the landing phase.

Once proficient with the entire methodology, this process can take approximately one hour to do the entire data collection. While performing this procedure, it's important to ensure that there is adequate contact between the ultrasound transducer and the skin throughout the task, and to ensure that the none of the 3D markers gets dislodged. If there is excessive transducer motion.

The procedure will need to be repeated. After watching this video, you should have had a good understanding of how to estimate velocities strain and strain rate of the rectus femoral muscle with high temporal resolution during a drop landing task using vector tissue Doppler imaging.