Bernard Querleux

Super-helices for predicting the dynamics of natural hair

Simulating human hair is recognized as one of the most difficult tasks in computer animation. In this paper, we show that the Kirchhoff equations for dynamic, inextensible elastic rods can be used for accurately predicting hair motion. These equations fully account for the nonlinear behavior of hair strands with respect to bending and twisting. We introduce a novel deformable model for solving them: each strand is represented by a Super-Helix, i.e., a piecewise helical rod which is animated using the principles of Lagrangian mechanics. This results in a realistic and stable simulation, allowing large time steps. Our second contribution is an in-depth validation of the Super-Helix model, carried out through a series of experiments based on the comparison of real and simulated hair motions. We show that our model efficiently handles a wide range of hair types with a high level of realism.

A computational skin model: fold and wrinkle formation

This paper presents a computational model for studying the mechanical properties of skin with aging. In particular, attention is given to the folding capacity of skin, which may be manifested as wrinkles. The simulation provides visual results demonstrating the form and density of folds under the various conditions. This can help in the consideration of proper measures for a cosmetic product for the skin.

Assessment of elastic parameters of human skin using dynamic elastography

Sonoelastography and transient elastography are two ultrasound-based techniques that facilitate noninvasive characterization of the viscoelastic properties of soft tissues by investigating their response to shear mechanical excitation. Youngs modulus is the principle assessment parameter. Because it defines local tissue stiffness, it is of major interest for the medical imaging and cosmetic industries as it could replace subjective palpation by yielding local, quantitative information. In this paper, we describe a new high-resolution device capable of measuring local Youngs modulus in very thin layers (1-5 mm) and devoted to the in vivo evaluation of the elastic properties of human skin. It uses an ultrasonic probe (50 MHz) for tracking the displacements induced by a 300 Hz shear wave generated by a ring surrounding the transducer. The displacements are measured using a conventional cross-correlation technique between successive ultrasonic back-scattered echoes. First, this noninvasive technique has been experimentally proven to be accurate for investigating elasticity in different skin-mimicking phantoms. Second, data were acquired in vivo on human forearms. As expected, Youngs modulus was found to be higher in the dermis than in the hypodermis and other soft tissues.

SkinChip®, a new tool for investigating the skin surface in vivo

Background/aims: Non‐invasive methods used for characterizing skin micro‐relief and skin surface hydration were developed in the 1980s. Although they allowed some progress in the knowledge of skin properties, they are not completely satisfactory in many aspects. Today, new technologies are emerging that may address such issues.

Comparative study of the hydration of the stratum corneum between four ethnic groups: influence of age

Background  Several recent overviews have reported that significant work remains to be performed to understand and quantify the ethnic differences in skin properties.

In vivo hydration profile in skin layers by high-resolution magnetic resonance imaging.

In recent years magnetic resonance imaging has become a very efficient tool for in vivo quantification of water content and water behavior in living tissues. We have applied this technique to the study of the in vivo hydration profile in heel skin layers by quantification of the mobile water proton density versus depth. Effects of a bath, a moisturizer and repeated soaping are present. Hydration profiles by magnetic resonance imaging delineate two different structures in stratum corneum: an outer layer where hydration can be modified by external mechanisms and an inner layer where hydration is not altered. The main interest of this method lies in the fact that the physical signal is exactly located, as spatial encoding is the basis of in vivo imaging. This method differs from other noninvasive methods which acquire an averaged signal from a nondelimited volume of interest.

In vivo Cross-Sectional Ultrasonic Imaging of Human Skin

This paper describes a new experimental set-up allowing routine cross-sectional ultrasonic images of human skin to be obtained in vivo and presents the first high-resolution images it gives. This system is characterized by the utilization of damped, high-frequency ultrasonic transducers. This type of transducer is longitudinally driven along the skin by a stepping motor under the control of a computer, which at the same time stores the digitized reflected signals. After the acquisition sequence, the image of the skin is displayed on a video monitor after data processing of the ultrasonic signals. On the images thus obtained, fascia, hypodermis, reticular dermis, pilosebaceous units, and adventitial dermis can be visualized. Due to a lack of resolution (about 80 microns) epidermis can only be viewed on certain zones like the hand.

Skin from various ethnic origins and aging: an in vivo cross-sectional multimodality imaging study

Background: Ethnic differences in skin structural features have not been thoroughly investigated, and the few reported studies are contradictory. Thus, we have carried out a set of in vivo measurements on the skin of about 400 volunteers from various ethnic origins living in the same environment.

The effect of age on skin color and color heterogeneity in four ethnic groups

Background: Few comparative data are available on age‐related changes in skin color among different ethnic groups. The aim of the study was to measure and analyze the skin color and color heterogeneity in four different ethnic groups living in the same local environment and to determine the effects of age on these skin color characteristics.

Predicting Natural Hair Shapes by Solving the Statics of Flexible Rods

This paper presents a new physically-based method for predicting natural hairstyles in the presence of gravity and collisions. The method is based upon a mechanically accurate model for static elastic rods (Kirchhoff model), which accounts for the natural curliness of hair, as well as for hair ellipticity. The equilibrium shape is computed in a stable and easy way by energy minimization. This yields various typical hair configurations that can be observed in the real world, such as ringlets. As our results show, the method can generate different hair types with a very few input parameters, and perform virtual hairdressing operations such as wetting, cutting and drying hair.