1.    Ultrasound Assessment for Articular Cartilage

We have developed a number of ultrasound systems for the investigation of dynamic depth-dependent mechanical properties of articular cartilage. 1D and 2D ultrasound elastomicroscopy has been used to map the Young's modulus of articular cartilage. High-frequency ultrasound has also been used to monitor the transient swelling behavior induced by changing the bathing saline concentration. In addition, the transient penetration of the trypsin has been successfully monitored using ultrasound method. Meanwhile, we have been conducting a systematic study for the variation of the ultrasound speed in articular cartilage caused by the variation of temperature, bathing concentration, tissue depth, testing site, applied stress, and degeneration conditions.

2.   Soft Tissue Elasticity Measurement

In clinics, the thickness and stiffness of soft tissues are traditionally determined by the impression of hand palpations, which suffers from the qualitative and subjective features of this feel-telling method. We have developed a Tissue Ultrasound Palpation System (TUPS) using the indentation test for the quantitative and objective measurement of tissue thickness and stiffness. The operation principle of this system is quite similar to that of a conventional palpation but the most important improvement is that the outcome has become quantitative and more reliable for inter-laboratory comparisons or longitudinal follow-ups. It has been successfully used for the assessment of various human tissues in vivo, including residual limb tissues, fibrotic tissues induced by radiotherapy, burn and surgical scars, plantar foot tissues of subjects with diabetes and rheumatoid arthritis, etc. Efforts were also made to minimize the TUPS and make it be accessible through PDA or smart phone -based platforms utilizing the fast-developing wireless transmission techniques such as Wi-Fi and bluetooth. Recent work in this direction includes the study of breast elasticity change within a menstrual period and with breast cancer patients, non-contact indentation by water jet or air jet and the further development of a probe for endoscopic use.

3.   Ultrasound Elasticity Imaging

The elastography, i.e. elasticity imaging,  is the technique for imaging the elastic properties of compliant tissues. Since the stress-strain relationship for most tissues is nonlinear, to generate local strain, usually a slight compression (<1% strain in vivo) is loaded and then the pre- post-compression of local tissue displacements are estimated using various methods, such as the classical 1D normalized cross-correlation, the 2D block-matching or 2D gradient-based methods. As the most popular modality used to generate elastograms, ultrasound today has been, more and more widely, applied to for the diagnosis of various tumors, such breast cancer. A number of ultrasound systems now have elastogrpahy function embedded.

Figure : Up-left, up-right panels:  Two images before and after compression, respectively, down-left: displacement field, down-right: strain estimation.

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4.  Ultrasound Elastomicroscopy (UEM) for Tissue Characterization

Research in elasticity imaging typically relies on 1 to 10 MHz ultrasound which is the frequency range used for most medical imaging applications. Elasticity at these frequencies can provide strain maps with a resolution on the order of millimeters, but this is not sufficient for applications to skin, articular cartilage, or other fine structures. We have developed a high resolution elastomicroscopy system consisting of a 50 MHz ultrasound backscatter microsccope system and a calibrated compression device using a load cell to measure compression in the specimen between a rigidly fixed face-plate and the specimen platform. We expect that this system can also be potentially used for the assessment of biological tissues, bioengineered tissues or biomaterials with fine structures. 

5.   3D Ultrasound Imaging for Musculoskeletal Tissues

3D ultrasound is a promising imaging modality particularly for its easy accessibility for clinical diagnosis and treatment monitoring. In this study, we developed an easy-to-use, portable freehand 3D ultrasound imaging system for the assessment of musculoskeletal body parts. In the system, a portable ultrasound scanner was used to obtain B-mode ultrasound images of musculoskeletal tissues. An electromagnetic spatial sensor was fixed on the ultrasound probe to acquire the position and orientation of the images. Real-time ultrasound images were digitized with a video digitization device and displayed with its orientation and position synchronized in real-time with the data obtained by the spatial sensor. A program was developed for volume reconstruction, visualization, segmentation and measurement . An improved distance-weighted grid-mapping algorithm was proposed for volume reconstruction. Temporal calibrations were conducted to correct the delay between the collections of images and spatial data. Spatial calibrations were performed using a cross-wire phantom. The system has been successfully used to obtain the volume images of a fetus phantom, the fingers and forearms of human subjects. It is believed that such a portable volume imaging system will have many applications in the assessment of musculoskeletal tissues because of its easy accessibility.

6. Sonomyography (SMG) of Muscles and Tendons for Control and Monitoring  

Ultrasound is used to monitor the architectural changes of muscles, such as muscle thickness, pennation angle, cross-sectional area, tissue elasticity. We named the signals representing these changes as sonomyography (SMG). Similar to electromyography (EMG), SMG can be used to assess muscle functions and to serve as interfacing signals between human and device, such as prosthesis and robots. We have successfully demonstrated its application for powered prosthesis control and assessment of muscle fatigue. The SMG signals can come from dynamic 2D B-mode ultrasound images or 1D A-mode ultrasound signals. Our software for Ultrasound Measurement of Motion and Elasticity (UMME) can simultaneously collect ultrasound, EMG, joint angle and other related signals for a comprehensive analysis of functions and biomechanical properties of muscles and tendons.

7.   Ultrasound Measurement of Blood Vessel, Flow and Pressure

Blood pressure is one of the most important hemodynamic characters for cardiovascular system. Our study is to design a new device for continuous non-invasive blood pressure (NIBP) measurement using volume-clamp and echo-tracking technologies in order to improve the accuracy of blood pressure measurement compared with existing similar devices. In addition, the elasticity of blood vessels can also be estimated using the obtained information. Together with the blood flow measured using Transcranial Doppler, the blood pressure inside the brain can be more accurately estimated.

The webpage for this solution is under construction.

8.   Software for Ultrasound Measurement of Motion and Elasticity (UMME)

We have developed a program for the ultrasound measurement of motion and elasticity. It includes functions to collect dynamic RF ultrasound signals via high-speed A/D cards, to collect dynamic ultrasound images outputted from ultrasound scanners via video capture cards. During the data collection, the ultrasound signals and images can be synchronized with other parameters collected simultaneously, such as force, angle, temperature, displacement, etc. It also provides functions to track the motion of the ultrasound echoes using pattern recognition techniques in 1D and 2D configurations. The strain and displacement images can also be extracted using this program. In addition, it can be used to control 3D translating devices for the configurations of scanning acoustic microscopes (ultrasound biomicroscope).  

The webpage for this solution is under construction.