Yong-Ping Zheng

An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues

A novel noncontact indentation system with the combination of an air jet and optical coherence tomography (OCT) was presented in this paper for the quantitative measurement of the mechanical properties of soft tissues. The key idea of this method is to use a pressure-controlled air jet as an indenter to compress the soft tissue in a noncontact way and utilize the OCT signals to extract the deformation induced. This indentation system provides measurement and mapping of tissue elasticity for small specimens with high scanning speed. Experiments were performed on 27 silicone tissue-mimicking phantoms with different Youngs moduli, which were also measured by uniaxial compression tests. The regression coefficient of the indentation force to the indentation depth (N mm(-1)) was used as an indicator of the stiffness of tissue under air jet indentation. Results showed that the stiffness coefficients measured by the current system correlated well with the corresponding Youngs moduli obtained by conventional mechanical testing (r = 0.89, p < 0.001). Preliminary in vivo tests also showed that the change of soft tissue stiffness with and without the contraction of the underlying muscles in the hand could be differentiated by the current measurement. This system may have broad applications in tissue assessment and characterization where alterations of mechanical properties are involved, in particular with the potential of noncontact micro-indentation for tissues.

Estimating the effective Young's modulus of soft tissues from indentation tests—nonlinear finite element analysis of effects of friction and large deformation

A nonlinear finite element model was developed to investigate the biomechanics of indentation, particularly the influence of friction and large deformation on the calculation of the effective Youngs modulus from the cylindrical, flat-ended indentation test of soft tissues. A new kappa table was given for calculation of the effective Youngs modulus to account for the effects of layered geometry with consideration of the larger deformation. The results indicate that the effect of friction on the calculation of Youngs modulus becomes significant with a large aspect ratio and with a large Poissons ratio. It is found that the factor kappa increases almost proportionally to the increase of the indentation depth, especially obvious with a larger Poissons ratio v and a larger aspect ratio a/h.

An ultrasound indentation system for biomechanical properties assessment of soft tissues in-vivo

An ultrasound indentation system for biomechanical assessment of soft tissues in vivo was developed. The pen-size, hand-held probe was composed of an ultrasound transducer and a load cell. The ultrasound transducer was at the tip of the probe serving also as the indentor. The thickness and deformation of the soft tissue layer were determined from the ultrasound echo. A compressive load cell was connected in series with the ultrasound transducer to record the force response. A validation experiment was performed on porcine tissues. Force and deformation acquired with the present system was in good comparison with those obtained from a Housfield material testing machine. Material constants were obtained via a curve-fitting procedure by predicting the force transient response from the deformation-time data using a quasilinear viscoelastic model. In addition, deformation in the fat and in the muscle could be differentiated. The potential applications of this type of indentation probes are many. The specific application of this current development is for stump tissue assessment in the design of prosthetics.

BIOMECHANICAL ASSESSMENT OF PLANTAR FOOT TISSUE IN DIABETIC PATIENTS USING AN ULTRASOUND INDENTATION SYSTEM

The biomechanical properties of plantar tissues were investigated for four older neuropathic diabetic patients and four healthy younger subjects. Indentation tests were performed at four high-pressure areas with three postures in each subject. The tissue thickness and effective Youngs modulus were measured by an ultrasound (US) indentation system. The system comprised a pen-size probe having a US transducer at the tip and a load cell connected in series with it. Results showed that the plantar soft tissues of the elderly diabetic patients were significantly stiffer and thinner when compared with the healthy young subjects. For the diabetic subjects tested, the Youngs modulus at the 1st metatarsal head was significantly larger than those at the other three sites. This site-dependence was not observed in the healthy young subjects. The plantar tissue became significantly stiffer in the healthy young subjects as a result of posture changes. This posture-dependence of the Youngs modulus was not established for the elderly diabetic group.

Effective elastic properties for lower limb soft tissues from manual indentation experiment

Quantitative assessment of the biomechanical properties of limb soft tissues has become more important during the last decade because of the introduction of computer-aided design and computer-aided manufacturing (CAD/CAM) and finite element analysis to the prosthetic socket design. Because of the lack of a clinically easy-to-use apparatus, the site and posture dependences of the material properties of lower limb soft tissues have not been fully reported in the literature. In this study, an ultrasound indentation system with a pen-size hand-held probe developed earlier by the authors was used to obtain the indentation responses of lower limb soft tissues. Indentation tests were conducted on normal young subjects with four females and four males at four sites with three body postures. A linear elastic indentation solution was used to extract the effective Youngs modulus from the indentation responses. The determined modulus ranged from 10.4 to 89.2 kPa for the soft tissues tested. These results were in a similar range as those reported in the literature. The thickness of the lower limb soft tissues varied slightly with body posture changes. The Youngs modulus determined was demonstrated to be significantly dependent on site, posture, subject and gender. The overall mean modulus of male subjects was 40% larger than that of female subjects. No significant correlation was established between the effective Youngs modulus and the thickness of entire soft tissue layers.

Classification of the mechanomyogram signal using a wavelet packet transform and singular value decomposition for multifunction prosthesis control.

Previous works have resulted in some practical achievements for mechanomyogram (MMG) to control powered prostheses. This work presents the investigation of classifying the hand motion using MMG signals for multifunctional prosthetic control. MMG is thought to reflect the intrinsic mechanical activity of muscle from the lateral oscillations of fibers during contraction. However, external mechanical noise sources such as a movement artifact are known to cause considerable interference to MMG, compromising the classification accuracy. To solve this noise problem, we proposed a new scheme to extract robust MMG features by the integration of the wavelet packet transform (WPT), singular value decomposition (SVD) and a feature selection technique based on distance evaluation criteria for the classification of hand motions. The WPT was first adopted to provide an effective time-frequency representation of non-stationary MMG signals. Then, the SVD and the distance evaluation technique were utilized to extract and select the optimal feature representing the hand motion patterns from the MMG time-frequency representation matrix. Experimental results of 12 subjects showed that four different motions of the forearm and hand could be reliably differentiated using the proposed method when two channels of MMG signals were used. Compared with three previously reported time-frequency decomposition methods, i.e. short-time Fourier transform, stationary wavelet transform and S-transform, the proposed classification system gave the highest average classification accuracy up to 89.7%. The results indicated that MMG could potentially serve as an alternative source of electromyogram for multifunctional prosthetic control using the proposed classification method.

Estimation of Young's modulus and Poisson's ratio of soft tissue from indentation using two different-sized indentors: finite element analysis of the finite deformation effect.

Youngs modulus and Poissons ratio of a tissue can be simultaneously obtained using two indentation tests with two different sized indentors in two indentations. Owing to the assumption of infinitesimal deformation of the indentation, the finite deformation effect of indentation on the calculated material parameters was not fully understood in the double indentation approach. However, indentation tests with infinitesimal deformation are not practical for the measurement of real tissues. Accordingly, finite element models were developed to simulate the indentation with different indentor diameters and different deformation ratios to investigate the finite deformation effect of indentation. The results indicated that Youngs modulus E increased with the increase in the indentation deformation w, if the finite deformation effect of indentation was not considered. This phenomenon became obvious when Poissons ratio v approached 0.5 and/or the ratio of indentor radius and tissue thickness a/h increased. The calculated Youngs modulus could be different by 23% at 10% deformation in comparison with its real value. The results also demonstrated that the finite deformation effect to indentation on the calculation of Poissons ratio v was much smaller. After the finite deformation effect of indentation was considered, the error of the calculated Youngs modulus could be controlled within 5% (a/h=1) and 2% (a/h=2) for deformation up to 10%.

Estimation of muscle fiber orientation in ultrasound images using revoting hough transform (RVHT).

Ultrasound imaging has been used frequently for the study of muscle contraction, including measurements of pennation angles and fascicle orientations. However, these measurements were traditionally conducted by manually drawing lines on the ultrasound images. In this study, we proposed a modified Hough transform (HT), aiming at automatically estimating orientations of straight line-shaped patterns, such as muscle fibers and muscle-bone interface in ultrasound images. The new method first located the global maximum in the HT accumulator matrix, which corresponded to the most dominant collinear feature points globally, using the standard HT; then the pixels close to the detected line were removed from the edge map, the HT accumulator matrix was calculated again, i.e., revoting, and a new line was detected. The iteration was repeated until the predefined termination conditions were satisfied. The performance of the algorithm was tested using computer-generated images with different levels of noises, as well as clinical ultrasound images, and compared with that of the conventional method. It was found that the orientation estimation results obtained by the new algorithm were well correlated (R2 = 0.965), with those obtained using the traditional method, i.e., drawing lines manually and reading the angles with the assistance of software. Further mean-difference plots revealed a difference of 0.18 +/- 2.41 degrees between the two methods at the 95% confidence level. Compared with the traditional method, the new algorithm was more capable of handling with highly noisy data and could avoid the aliasing problem, i.e., reporting multiple lines instead of single expected line. The results of this study suggested that the proposed revoting HT can be potentially used for the reliable and nonsubjective automatic estimation of the orientations of muscle fibers in musculoskeletal ultrasound images.

A randomized clinical trial to study the effect of silicone gel dressing and pressure therapy on posttraumatic hypertrophic scars.

To investigate the effect of pressure therapy (PG), silicone gel sheeting (SGS), and combined therapy on the management of posttraumatic hypertrophic scar (HS) using a randomized controlled clinical trial. A total of 104 subjects with HS mostly resulting from burns and scald injuries (63 men and 41 women; average age: 21.8 ± 18.7 years) were recruited from Jiangsu Peoples First Affiliated Hospital in Nanjing, China. The mean scar formation period was 14.9 ± 30.8 months. All subjects were randomly allocated into four groups, namely the PG, SGS, combined PG and SGS groups, and single-blinded control group for the treatment of 6 months. Standardized scar assessments (pigmentation, vascularity, thickness, pain, and itchiness) were conducted before the intervention, 2, 4, and 6 months of the intervention, and 1 month after completion of the program, respectively, to observe the progress of the treatments. The results showed that the combined therapy seemed to be more effective in improving the thickness of scar after 2 months of intervention (P < .001). After 6 months of intervention, both the combined therapy group and the PG group showed significant improvement in scar thickness. The improvement in scar thickness was most significant in the combined therapy group. SGS was found to be more effective in alleviating the pain and pruritus rather than the scar thickness. This randomized clinical trial has demonstrated the evidence of the effect of combined PG and gel intervention on posttraumatic HS. The PG group showed an improvement in scar thickness too. Further studies are needed to investigate the biomechanical and physiological effect that PG and gel sheeting would exert on the scar tissues.

Fuzzy approximate entropy analysis of chaotic and natural complex systems : detecting muscle fatigue using electromyography signals

In the present contribution, a complexity measure is proposed to assess surface electromyography (EMG) in the study of muscle fatigue during sustained, isometric muscle contractions. Approximate entropy (ApEn) is believed to provide quantitative information about the complexity of experimental data that is often corrupted with noise, short data length, and in many cases, has inherent dynamics that exhibit both deterministic and stochastic behaviors. We developed an improved ApEn measure, i.e., fuzzy approximate entropy (fApEn), which utilizes the fuzzy membership function to define the vectors’ similarity. Tests were conducted on independent, identically distributed (i.i.d.) Gaussian and uniform noises, a chirp signal, MIX processes, Rossler equation, and Henon map. Compared with the standard ApEn, the fApEn showed better monotonicity, relative consistency, and more robustness to noise when characterizing signals with different complexities. Performance analysis on experimental EMG signals demonstrated that the fApEn significantly decreased during the development of muscle fatigue, which is a similar trend to that of the mean frequency (MNF) of the EMG signal, while the standard ApEn failed to detect this change. Moreover, fApEn of EMG demonstrated a better robustness to the length of the analysis window in comparison with the MNF of EMG. The results suggest that the fApEn of an EMG signal may potentially become a new reliable method for muscle fatigue assessment and be applicable to other short noisy physiological signal analysis.