Evaluation of skin viscoelasticity and anisotropy by measurement of speed of shear wave propagation with viscoelasticity skin analyzer

Radiation therapy in cancer patients with psoriasis. The fractionated daily dose and the Koebner phenomenon

Skin side effects following XRT take place more often in patients with skin disorders. In this study six patients with psoriatic lesions were evaluated. The total/daily XRT dose to the tumor site was 50-70/1.8-2.0 Gy. No debilitating effect of XRT was observed in both the psoriatic lesions and in the surrounding normal skin.

Sonoelastographic imaging of interference patterns for estimation of the shear velocity of homogeneous biomaterials

The shear wave velocity is one of a few important parameters that characterize the mechanical properties of bio-materials. In this paper, two noninvasive methods are proposed to measure the shear velocity by inspecting the shear wave interference patterns. In one method, two shear wave sources are placed on the opposite two sides of a sample, driven by the identical sinusoidal signals. The shear waves from the two sources interact to create interference patterns, which are visualized by the vibration sonoelastography technique. The spacing between the pattern bands equals half of the shear wavelength. The shear velocity can be obtained by taking the product of the wavelength and the frequency. An alternative method is to drive the two vibration sources at slightly different frequencies. In this case, the interference patterns no longer remain stationary. It is proved that the apparent velocity of the moving patterns is proportional to the shear velocity in the medium. Since the apparent velocity of the patterns can be measured by analysing the video sequence, the shear velocity can be obtained thereafter. These approaches are validated by a conventional shear wave time-of-flight approach, and they are accurate within 4% on various homogeneous tissue-mimicking phantoms.

Accuracy and reliability of a dynamic biomechanical skin measurement probe for the analysis of stiffness and viscoelasticity

A novel instrument has been devised for the in vivo examination of the dynamic biomechanical properties of skin. These properties include stiffness and viscoelasticity. The advantage of the device is its ability to examine the skin dynamically, thereby eliminating preconditioning effects. Furthermore, it is portable, hand-held and easy to operate in the clinical environment. The objective of this study was to determine the accuracy and reliability of the dynamic biomechanical skin measurement (DBSM) probe. The accuracy was determined by examining a series of silicone elastomer specimens. A comparison of the shear modulus (G*), obtained from a static indentation system, with stiffness, obtained from the DBSM probe, was performed. The reliability was determined by examining both silicone elastomers and forearm volar skin in vivo. In both cases assessment was by six different operators (inter-reliability) and also by an individual operator (intra-reliability). Statistical analysis was performed using Levene's test of homogeneity and analysis of variance to ascertain if there were significant differences between operators (inter-reliability) and with one individual operator (intra-reliability). It can be concluded, from this study, that the DBSM probe is accurate (R2 = 0.96, p = 0.01). It is also inter- and intra-reliable when assessing elastomer stiffness and skin stiffness. However, phase lag was not found to be a useful indicator of device reliability. It is anticipated that this device will be used to examine dermatological conditions and the benefits, or otherwise, of treatment. The DBSM probe promises to contribute to the objective measurement of physical properties of the skin in future investigative studies.

Skin tensile properties revisited during ageing. Where now, where next?

Skin and its subcutaneous layer represent a complex composite of tissues, whose mechanical characteristics depend upon the mutual interdependence of their constituent parts. The molecular and microanatomical structures of skin allow it to meet normal mechanical demands. They also determine the orientation both of Langer's lines and of relaxed skin tension lines. Ageing, photodamage, hormones, drugs, cosmetic products and dermatological interventions may modify the skin's overall tensile properties. In turn, any variation in mechanical stresses and strains imposed upon the skin's connective tissue influences the metabolic activity and phenotypic expression of fibroblasts and dermal dendrocytes. The viscoelastic functions of ageing skin can be tested by altering the orientation and magnitude of imposed stresses and strains over time. Assessment can be made of various biomechanical properties of skin: tensile, torsional, acoustic shear wave, indentation, impact and elevation. Such objective biomechanical assessments may be applied to dermocosmetic interventions, so providing opportunity for progress in cosmetic dermatological science.

Measurement of skin stretch via light reflection

A noninvasive technique for measuring the stretch of skin is described. The technique utilizes changes in the reflectivity of polarized light intensity as a monitor of skin stretch. Measurements of in vitro pigskin and in vivo human skin show that the reflectivity of polarized light intensity increases linearly with stretch. The changes in diffusive reflectivity properties of skin result from the alterations that take place in the roughness across the thickness of the skin layers due to stretch. Conceptually, as the roughness of a layer decreases with stretch, a smoother reflecting media is produced, resulting in a proportional increase in the specular reflection. Results can be easily extended to a real-time stretch analysis of large tissue areas that would be applicable for mapping the stretch of skin.

Factor XIII a-positive dermal dendrocytes and shear wave propagation in human skin

BACKGROUND

The in vivo interdependence between the phenotypic characteristics of dermal cells and the strain imposed on the tissue has not been studied thoroughly in humans. In particular the mechanical force modulation of Factor XIII a expression in dermal dendrocytes (DD) remains unknown.

MATERIALS AND METHODS

The present study compares the numerical density of Factor XIII a-positive DD and the in vivo shear wave velocity in the skin. The investigation was performed in 20 men of normal weight and 20 obese men before and after entering a slimming process.

RESULTS

Excess cutaneous fat places the skin under increased intrinsic tension. The resonance running time measurement (RRTM) and the DD density were significantly reduced in overweight individuals. After a short-term but intense slimming process, the same individuals showed a trend to normalization of these two parameters without, however, reaching significance. Pooling all data yielded a significant logarithmic correlation between RRTM values and densities in Factor XIII a-positive DD.

CONCLUSION

Factor XIII a expression in human DD may be partially regulated by the intrinsic resting tensions in the skin.

Split face study on the cutaneous tensile effect of 2-dimethylaminoethanol (deanol) gel

BACKGROUND/AIMS

Beyond subjective assessments, the effect of skin tensors is difficult to assess. The present 2-phase randomized double-blind split face study was designed to compare the effect of a gel containing 3% 2-dimethylaminoethanol (deanol, DMAE) with the same formulation without DMAE.

METHODS

In a first pilot study, sensorial assessments and measures of the skin distension under suction were performed in eight volunteers. In a second study conducted in 30 volunteers, shear wave propagation was measured.

RESULTS

Large interindividual variations precluded any significant finding in the first study. The DMAE formulation showed, however, a significant effect characterized by increased shear wave velocity in the direction where the mechanical anisotropy of skin showed looseness.

CONCLUSION

The DMAE formulation under investigation increased skin firmness.

Scar assessment tools: implications for current research

Scarring is considered a major medical problem that leads to cosmetic and functional sequelae. Scar tissue is clinically distinguished from normal skin by an aberrant color, rough surface texture, increased thickness (hypertrophy), occurrence of contraction, and firmness. Marked histologic differences are the change in dermal architecture and the presence of cells such as the myofibroblast. Many assessment tools are available for analysis of pathologic conditions of the skin; however, there is no general agreement as to the most appropriate tools for evaluation of scar tissue. This review critically discusses currently available objective measurement tools, subjective assessment tools, and potential devices that may be available in the future for scar assessment.

Age- and body mass index-related changes in cutaneous shear wave velocity

BACKGROUND

The in vivo visco-elastic characteristics of skin depend on a series of physiopathological parameters. Among them, the age-related intrinsic tensile properties and the preconditioning of the tissues set under tension by the hypodermal volume might be of importance.

AIMS

To revisit the influence of age and body mass on the firmness and mechanical anisotropy of the skin as determined by the velocity of the shear wave propagation.

METHOD

Resonance running time measurements (RRTM) were performed on the mid volar forearm in 110 adults of both sexes. In each subject 16 RRTM were collected at four different precise angles with regard to the limb axis. We recorded the lowest, the highest and the mean multidirectional RRTM as well as the coefficient of variation (CV) of the latter value. In addition, the body mass index (BMI) was calculated.

RESULTS

Age and BMI did not influence the minimum RRTM. In contrast, the maximum RRTM as well as the mean and CV of the multidirectional RRTM, significantly rose in a progressively increasing proportion of the subjects older than 60 years. These changes were only encountered in subjects with a normal BMI ranging from 18 to 25. Sex-related differences were not disclosed.

CONCLUSIONS

The intrinsic skin tension lines identified by the minimum RRTM are not significantly altered with age and BMI variations. In contrast, skin laxity identified by larger maximum and mean multidirectional RRTM may increase after 60 years of age in subjects with a normal BMI. This is accompanied by increased skin mechanical anisotropy identified by CV values of the multidirectional RRTM over 40%.