A multitechnique evaluation of topical corticosteroid treatment.

BACKGROUND/PURPOSE: Corticosteroids are widely prescribed for systemic or local treatment of inflammatory autoimmune disorders. Long-term therapy is associated with side effects and causes cutaneous atrophy of the epidermis and the dermis. The present study aims to evaluate with several noninvasive techniques, the skin modifications observed during corticosteroids treatment. The potential of skin mechanical measurement and ultrasound radio frequency (RF) signal analysis are proposed as new measures more closely related to the functional impairments. METHODS: Thirteen young healthy women volunteers had two applications per day on one arm of topical Clobetasol propionate 0.05% for 28 days, and they were followed for 28 days more. Skin modifications were studied by high-frequency ultrasound imaging, ultrasound RF signal analysis, optical coherence tomography and by the suction test. RESULTS: For all the techniques, a statistically significant change is observed with treatment. Large variations, around 30%, are observed for all techniques, but less for ultrasound imaging (10%). Dermis and epidermis thickness presented stable measurements on the nontreated zone. At the end of the study, measures returned to normal. The dynamic is mainly observed within the first 14 days of treatment and within the first 14 days after its cessation. CONCLUSION: Similar dynamics of skin modification during corticosteroid treatment was observed with very different techniques. Moreover, the potential of RF ultrasound analysis and mechanical skin measurement for characterizing skin structural and functional impairments has been evaluated.

[High-resolution ultrasonography: utility in diagnosis, treatment, and monitoring dermatologic diseases]. / L'échographie cutanée haute résolution: utilité pour le diagnostic, le traitement et la surveillance des maladies dermatologiques.

Although less precise than histological examination, high-resolution skin imaging is a noninvasive technique that provides complementary information to the clinical examination: the lesion's US structure as well as its lateral and depth extension. Ultrasonography helps in diagnosis and initial management by measuring melanoma thickness (so as to remove this lesion with safety margins) before destructive treatment (cryosurgery or radiotherapy), by showing tumor limits, or by detecting subclinical recurrence during the follow-up. In this paper, ultrasound images will be correlated with clinical and histological data in various clinical situations such as tumors, edema, cutaneous infiltration, sclerous tissues, hyperlaxity, and cutaneous aging.

[Techniques and applications of noninvasive high-resolution ultrasound imaging]. / Techniques et applications de l'échographie haute résolution non invasive.

Today manufacturers propose echographic systems with a resolution ranging from 100 microm down to 30 microm. This requires ultrasonic frequencies ranging from 20 to 60 MHz. However, when associated with an increase in the attenuation of the wave in the media this limits the applications to superficial exploration. High frequencies also bring special technological limitations mainly in the fields of transducers, electronics, and acoustic coupling. Although high-resolution echography has long remained marginal and been used for the exploration of the skin or the anterior chamber of the eye, new powerful and easy-to-use devices have recently appeared on the market. With these new products, new applications have also appeared such as the exploration of the oral cavity or small laboratory animals (mice).

Ultrasonic characterization of maturation of fetal lung microstructure: an animal study.

Scattering parameters and histological properties of the ewe fetal lung microstructure were examined in vitro. Four groups of lamb fetuses were chosen at 80, 100, 130 and 145 days of gestation (10 lambs in all). The acoustic parameters of the lung (backscatter coefficient, integrated backscatter coefficient and effective scatterer size), texture parameter of the lung (effective density of scatterers) and a relative lung/liver maturation parameter (the integrated spectral ratio) were measured at 19 degrees +/- 2 degrees C within the frequency range 3-11 MHz. Values of integrated backscatter coefficient significantly decreased between 80 and 130 days gestation (from -73.0 +/- 5.7 dB to -84.0 +/- 0.9 dB between 3 to 7 MHz and from -70.0 +/- 0.8 dB to -81.3 +/- 0.5 dB between 5 to 11 MHz). Values of the integrated spectral ratio indicate that the echogenicity of the lung is greater than that of the liver. These values also decreased between 80 and 130 days gestation (from 10.5 +/- 1.1 dB to 5.1 +/- 0.9 dB between 3 to 7 MHz and from 10.0 +/- 0.8 dB to -6.4 +/- 0.6 dB between 5 to 11 MHz). Texture analysis showed that the K distribution is a good model to describe the envelope of the backscattered signals from the lung and the values of the effective density of scatterers that decrease between 80 and 130 days. These trends seem to be linked to the maturation of the microstructure of the lung and, particularly, to the development of respiratory terminal structures.

High-frequency estimation of the ultrasonic attenuation coefficient slope obtained in human skin: simulation and in vivo results.

In vivo ultrasonic characterization of the skin was performed at 40 MHz by estimating the slope of the attenuation coefficient in the human dermis. The centroid algorithm was first tested on simulated backscattered RF lines with a second-order autoregressive model to carry out the spectral analysis. A relative error of less than 8.5% and a relative precision of less than 6% were predicted for a 2-mm tissue thickness and for temporal window sizes ranging from 0.25 to 0.45 micros. In vivo measurements performed on 138 healthy volunteers yielded values of the attenuation coefficient slope ranging from 0.8 to 3.6 dB/cm MHz. A decrease was observed with advancing age, but no significant difference appeared between men and women. The results from this study suggest that this acoustic parameter shows the effect of the ageing process on normal skin tissue in vivo.

In vivo high-frequency ultrasonic characterization of human dermis.

The aim of this study is in vivo skin tissue characterization of young and old human cutaneous tissues by estimating the slope of the attenuation coefficient. The method used is the centroid algorithm with a second-order autoregressive model to perform the spectral analysis. Backscattered signals are acquired with a 40-MHz transducer fixed on a three-dimensional robot. Diffraction phenomena are eliminated via an axial translation of the transducer that allows the acquisition of the signal in the focal zone. The slope of the attenuation coefficient is estimated on phantoms of known attenuation, in order to validate the method. Preliminary measurements of the slope of the attenuation coefficient are subsequently performed in the echographic mode on abdominal human skin samples in vitro at 40 MHz. After assessing the reproducibility of the measurement of the attenuation coefficient slope in human dermis at 40-MHz in vivo, this is carried out on the volar face of the forearm of 150 healthy subjects aged 14-85 yr. The values measured range from 0.7 to 3.6 dB/cm.MHz. The main result of this study is the decrease with advancing age of the attenuation coefficient slope, which may reflect structural modifications of human dermis with age.

Time-varying autoregressive spectral estimation for ultrasound attenuation in tissue characterization.

In the field of biological tissue characterization, fundamental acoustic attenuation properties have been demonstrated to have diagnostic importance. Attenuation caused by scattering and absorption shifts the instantaneous spectrum to the lower frequencies. Due to the time-dependence of the spectrum, the attenuation phenomenon is a time-variant process. This downward shift may be evaluated either by the maximum energy frequency of the spectrum or by the center frequency. In order to improve, in strongly attenuating media, the results given by the short-time Fourier analysis and the short-time parametric analysis, we propose two approaches adapted to this time-variant process: an adaptive method and a time-varying method. Signals backscattered by an homogeneous medium of scatterers are modeled by a computer algorithm with attenuation values ranging from 1 to 5 dB/cm MHz and a 45 MHz transducer center frequency. Under these conditions, the preliminary results obtained with the proposed time-variant methods, compared with the classical short-time Fourier analysis and the short-time auto-regressive (AR) analysis, are superior in terms of standard deviation (SD) of the attenuation coefficient estimate. This study, based on nonstationary AR spectral estimation, promises encouraging perspectives for in vitro and in vivo applications both in weakly and highly attenuating media.

[In vivo assessment of corneal epithelial toxicity of timolol with benzalkonium chloride using very-high-frequency ultrasound imaging]. / Evaluation in vivo par échographie à très haute fréquence des modifications épithéliales cornéennes induites par un bêta-bloquant avec 0,01% de chlorure de benzalkonium.

PURPOSE: To assess in vivo the corneal epithelial damage caused by a topical toxic medication using a 60-MHz ultrasound device. MATERIAL: and methods: A solution of timolol with 0.01% benzalkonium chloride (BAC) was applied twice a day in the test eyes of ten rabbits, and a BAC-free solution of timolol in the control eyes, for 56 days. We used a 60-MHz ultrasound device to evaluate the epithelial damage in BAC-exposed eyes, compared to control eyes. The clinical and ultrasound examinations were performed every week, and the histological analysis at the end of the experiment. RESULTS: The clinical findings were conjunctival redness, corneal staining and instability of the tear film. In vivo VHF ultrasound revealed a thinning of the epithelium of test eyes (from 40.9+/-1,6 microm at D0 to 31.8+/-3.4 microm at D56; p=0.0006 for D0 vs D56), while the epithelium of control eyes remained unchanged. Ultrasound epithelial thickness was correlated with corneal staining (at D34 and D56; p=0.0025 and 0.0377, respectively) and histological epithelial pachymetry (p=0.0176 for control and 0.0505 for tested epithelium). Moreover, we report qualitative VHF ultrasound imaging of early epithelial damage. CONCLUSION: This new device could be very useful in ocular toxicity evaluation as a reproducible and reliable tool for multicentric clinical research.

Effective density estimators based on the K distribution: interest of low and fractional order moments.

The K distribution is an efficient model to the nonRayleigh statistics of the envelope of backscattered signals in random media. This modeling leads to estimate a parameter of effective density by means of the calculation of statistical moments of the envelope signal. In this study, we propose a mathematical analysis of an effective density estimator previously used and based on superior order moments. In order to improve the effective density estimate, we propose several estimators based on low and fractional order moments. The performances of these estimators are evaluated both with simulated signals and in an experimental context with synthetic foams. Estimators based on low and fractional moments appear to be more robust than superior moment-based estimator and an improvement of the spatial resolution of the estimate can be obtained. Results also confirm the capability of the effective density parameter to characterize the spatial distribution of scattering structures.