Resistance of human hair cuticle after a shaking process in wet conditions: comparison between Chinese and Caucasian hair.

Hair cuticle is the first protection shield of hair against external aggressions such as daily combing or brushing that induce friction, mechanical stress leading to ageing process. The identification of alterations of the hair surface induced by shaking process of various hair fibres, such as virgin and chemically treated Chinese and Caucasian hair, sheds some light on some specific features, e.g. Chinese cuticle is torn out in smaller particles than Caucasian, which seems to be related to geometrical rather than ethnic reasons. The present work also shows that two geometrical parameters of human hair, the inter-scale distance and the scale angle are directly linked to fibre dimensions, regardless of ethnic origin. Representative of hair with an average larger cross-sectional area, Chinese hair shows a slightly smaller inter-scale distance as well as a higher scale angle. On the other hand, Chinese hair cuticle seems to be more sensitive to chemical treatment than Caucasian hair, at least for straightening treatment taken here as an example. Such an approach can be of interest in designing cosmetic products more suited to specific needs of human hair.

In vivo proton relaxation times analysis of the skin layers by magnetic resonance imaging.

If in vivo magnetic resonance imaging is nowadays a powerful non-invasive method in medical diagnosis, its application in order to study the skin in vivo is not yet in common use because skin imaging requires a high resolution, at least in the direction perpendicular to the skin surface. We have therefore designed a specific imaging module, which, connected to a standard whole-body imager at 1.5 Tesla, allows us to obtain in vivo magnetic resonance images of skin on most parts of the body. With a depth resolution of about 70 microns, we are able to differentiate the skin layers: epidermis, dermis, subcutaneous fat, and even a thickened stratum corneum on palm as well as on heel. This paper reports the T1 and T2 water proton relaxation times of the different skin layers, in vivo, which are magnetic resonance parameters extracted from the images. Results show that skin layers are characterized by shorter T2 relaxation times than other biologic soft tissues. On the contrary, the measured T1 values are in the same range as in other tissues. These short T2 values may be assigned to the fibrous protein content of the skin and particularly of the dermis. This study on normal skin is the precursor of further works such as the influence of aging. As regards skin pathologies, it will be a powerful tool to follow the evolution of skin diseases under treatment.

Assessment of aging of the human skin by in vivo ultrasonic imaging.

The ultrasonic imaging technique that we have developed provides cross-sectional images of human skin in vivo with a resolution of about 80 microns axially (i.e., deep into the skin) and 250 microns lateral (parallel to the surface). In order to study aging skin, we obtained ultrasonic images from the mid-forearm (volar and dorsal sides) of 142 women. Ultrasonically, on the images, the dermis appears composed of two bands: a dark superficial one where the ultrasonic waves are propagated in a relatively homogeneous or non-echogenic medium, and a deeper one, which is lighter in color, suggesting a heterogeneous medium. Our results show that skin is thicker on the dorsal than on the volar forearm. In contrast to previously published results, skin thickness remains constant until the seventh decade of life, diminishing thereafter. The relative thickness of the two bands show marked variations with age: a progressive thickening of the dark band, from zero in infants to approximately 75% of total skin thickness in aged subjects, while the light band shows the inverse trend. Comparing the amplitude of the bands on the volar and dorsal forearm, the relative thickness of the dark band is larger on the dorsal (exposed) side and increases with age. These findings and the analysis of variously stained biopsies taken in some of our patients lead us to assign this dark band to a zone in the upper dermis where the collagen network is delicate, dense, and well organized. This is supported by some data in the literature. The thickness of this subepidermal non-echo-genic band appears to be a far more sensitive marker of skin aging at the dermal level than is the measurement of skin thickness.

Characterization of the skin in vivo by high resolution magnetic resonance imaging: water behavior and age-related effects.

The age-related modifications of magnetic resonance imaging parameters in the skin have been studied in vivo. Modification of these parameters should provide important information about alterations in water structure and content in aged skin. Relaxation times, T1 and T2, and relative proton density, which corresponds to the mobile water proton fraction of tissues, have been measured on people under age 40 and over 70 on a sun-protected area. Results have confirmed in vivo skin layer differentiation through relaxation times performed in a previous study. Moreover, relative proton density quantification has shown that epidermal mobile water is at least twice as abundant as dermal mobile water. No significant age-related T1 and T2 modification could be established, basically because of a large dispersion of values. The main result concerns the upper part of dermis (about 200 microns in thickness) which contains significantly more mobile water protons in chronologic aged skin than in young adult skin. This increase has been related both to an increase of total water content in dermis with age and to an apparent decrease of collagen and proteoglycan content. Associated with alterations of their structure, this decrease reduces macromolecular-water interaction sites. This finding has to be compared with ultrasound evaluation of aged skin, which is characterized by modifications of the echogenicity, related to collagen bundles size and density, in the outer part of dermis, too. Both of the imaging techniques tend to consider the outer part of dermis as one of the privileged sites of skin aging.

Lymphedematous skin and subcutis: in vivo high resolution magnetic resonance imaging evaluation.

Physico-chemical and morphologic parameters of skin layers and subcutaneous tissue in lymphedematous limb were studied in vivo using magnetic resonance imaging. High resolution images were obtained with a depth resolution of about 70 microm, using a specific surface gradient coil specially designed for skin imaging and connected to a standard whole-body imager at 1.5 T. Twenty-one patients with unilateral lower extremity lymphedema (11 primary and 10 secondary) were examined. Skin thickness, relaxation times, and relative proton density were calculated in lymphedematous limbs and in contralateral extremities. In diseased limbs, the average skin thickness (2.17 mm) was significantly larger (p = 1.5 x 10(-4)) than that of contralateral limb (1.14 mm). Major cutaneous alterations due to lymphedema took place in dermis. In lymphedematous dermis, the significant increase of relaxation time values could be due to a shift in the equilibrium of water inside this tissue in relation to the interactions between macromolecules and water molecules. In lymphedematous epidermis our results showed an increase in the number of free water protons. Information about water and fat distribution in lymphedema was also obtained using chemical shift weighted images. Our results demonstrated a water retention diffusely spread over the entire dermis, and an important fluid retention located in the interlobular spacing and beside the superficial fascia. Inside the subcutis, the mean thickness of the superficial fat lobules was increased more than that of the deep fat lobules. From all the various measurements we could not distinguish primary from secondary lymphedema.

Investigation of dyed human hair fibres using apertureless near-field scanning optical microscopy.

We present the first studies of dyed human hair fibres performed with an apertureless scanning near-field optical microscope. Samples consisted of 5-microm-thick cross-sections, the hair fibres being bleached and then dyed before being cut. Hair dyed with two molecular probes diffusing deep inside the fibre or mainly spreading at its periphery were investigated at a wavelength of 655 nm. An optical resolution of about 50 nm was achieved, well below the diffraction limit; the images exhibited different optical contrasts in the cuticle region, depending on the nature of the dye. Our results suggest that the dye that remains confined at the hair periphery is mainly located at its surface and in the endocuticle.

Anatomy and physiology of subcutaneous adipose tissue by in vivo magnetic resonance imaging and spectroscopy: relationships with sex and presence of cellulite.

BACKGROUND: Little is still known concerning subcutaneous adipose tissue and cellulite, and controversial questions are still under discussion. AIMS: Magnetic resonance imaging and spectroscopy were used to address two unresolved questions relating to the anatomy and physiology of subcutaneous adipose tissue. METHODS: Using high spatial resolution magnetic resonance imaging we characterized the topography of the dermo- hypodermal junction, and the three-dimensional architecture of the subcutaneous fibrous septae. Using proton spectroscopy, we measured water and lipid fractions within a fat lobule, and T1 and T2 values of the detected compounds. All these data were analysed according to sex and presence of cellulite. RESULTS: MR imaging quantified deeper indentations of adipose tissue into the dermis, and evidenced for the first time a great increase in the thickness of the inner fat layer in women with cellulite. Moreover, 3D reconstruction of the fibrous septae network showed a higher percentage of septae in a direction perpendicular to the skin surface in women with cellulite; but our study also depicted the tortuous aspect of this network. MR proton spectroscopy could not show any differences related to sex or presence of cellulite concerning T1 and T2 relaxation times of the detected compounds within a fat lobule, neither the unsaturated lipid fraction, the saturated lipid fraction, nor the water fraction. CONCLUSIONS: Magnetic resonance imaging showed that the 3D architecture of fibrous septae couldn't be modelled simply as perpendicular planes for women and tilted planes at 45 degrees for men. MR spectroscopy did not confirm the hypothesis of increased water content in the adipose tissue of women with cellulite as suggested by others, except if such water would be located in the connective septae.

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.

Imaging the hamster flank organ by an ultrasonic technique: a new approach to animal tests.

Images of the hamster flank organ were obtained in vivo by high resolution ultrasound (B-scan). The planimetric measurements of the ultrasonic image that determined the size of the flank organ, with a reproducibility of about 10%, highly correlated with the measurements of histological sections. This new method provides a simple and non-invasive method for determining the size of the hamster flank organ after various treatments which does not involve the killing of the animal under investigation.

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 high-resolution MR imaging of the skin in a whole-body system at 1.5 T.

High-resolution magnetic resonance (MR) images of the skin were acquired with a whole-body MR system at 1.5 T by adding a specific imaging module: A saddle-shaped surface gradient coil was connected in place of one of the gradient coils of the system, and a surface radio-frequency coil with a 1.5-cm radius was placed at the center of the gradient coil. The images, acquired in 3 minutes 25 seconds, represent a field of view of 18 x 50 mm2, which corresponds to a pixel size of 70 x 390 micro2; the section thickness was 1.2 mm. With this spatial resolution, the different layers of the skin are clearly delineated: Epidermis appears as a high-signal-intensity layer, while dermis appears hypointense due to its very short T2. Pilosebaceous units appear as inclusions of epidermis inside dermis. The high quality of the images obtained enables in vivo MR characterization of skin.

Echographic assessment of corticosteroid-induced skin-thinning, including echogenicity measurement.

BACKGROUND/AIMS: Skin atrophy is one of the main side effects of long-term topical corticosteroid therapy. It has already been studied through ultrasound skin-thickness measurement. In this study, the quantification of dermal echogenicity was introduced to provide new information on this phenomenon. METHODS: Skin thinning induced by topical application (without occlusion) of the superpotent corticosteroid clobetasol propionate (0.05% lotion), was assessed by means of ultrasonography in terms of thickness and echogenicity. 15 healthy volunteers were treated for 6 weeks, 1 daily, 5 days a week on the forearms. RESULTS: The thinning showed a biphasic pattern, with a 1st period of rapid change (about 15% of thinning in a week) followed by a period of slower but significant change. Skin thickness returned to baseline values 3 weeks after the end of treatment. Dermal echogenicity, which represents the mean intensity of the ultrasound signals reflected by the dermis, was found to follow the same variations, increasing strongly during the 1st week, then more slowly. The 2 parameters are correlated and probably reflect the same physiological modifications responsible for skin thinning, i.e., a reduction in glycosaminoglycan synthesis (leading to a drastic fall in dermal water content) and vasoconstriction. CONCLUSION: This sensitive and non invasive method enables us to identify the effects of clobetasol propionate on the healthy dermis in the absence of any clinical signs of thinning.

Brain activation in response to a tactile stimulation: functional magnetic resonance imaging (FMRI) versus cognitive analysis.

Objective. The aim of this study was to compare fMRI analysis of somatosensory areas activated by passive touch, to cognitive analysis of the psychological profile of human subjects. Methods. The study was carried out on 21 females, after informed consent. Two artificial textures (smooth and rough), and two natural textures (the skin of an operator modified or not by a cosmetic product), were applied on the fingers of the subjects. A period of imagination to be touched was also included in the study. MR images of the somatosensory cortex were acquired on a 1.5T MRI system during the different behavioral conditions. Series of images were first processed to compensate for the inter-frame motions and then activation was assessed with a statistical method based on conditional analysis. After the MRI protocol, each subject was interviewed following a questionnaire from which psychological descriptors were extracted. Results. 1) Activations were quite similar for all textures in the contralateral sensory areas 2) In the ipsilateral sensory areas, activations were more important in response to a stimulation with the skin of an operator than with artificial textures. The activation was even more important after application of a cosmetic product on the skin. 3) Imagination of the tactile stimulation resulted in an activation mostly localized in the ipsilateral cortex. 4) A PLS analysis assessed that 2 psychological descriptors, rationality and sensorial reactivity, were related to an activation in the contralateral cortex, while 2 others, imagination and sensitivity, were related to ipsilateral areas activation. Conclusion. fMRI and cognitive analysis allowed us to map the physical component of the tactile perception in the contralateral cortex. This study also gave rise to a better understanding of the activation in ipsilateral areas, which was found to be mainly related to the subjective component of the stimulation.