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REPRODUCIBILITY OF SKIN CHARACTERIZATION WITH BACKSCATTERED SPECTRA (12-25 MHz) IN HEALTHY SUBJECTS

Ultrasonic techniques were developed for quantitative in vivo analysis of skin composition based on measurements of apparent integrated backscatter (IBS) and its frequency dependence (n) between 12.5 and 25 MHz. Parameters were measured at five depths in healthy dermis of the midforearm of 29 volunteers (13 women, 16 men, 20 to 76 years old) on three different days. Reproducibility of measurements was evaluated (standardized coefficients of variation: 7% to 11% for IBS and 9% to 20% for n). Parameter values were significantly influenced by pressure of the ultrasonic probe on the skin, and both room and skin-surface temperatures were correlated to IBS measured in a single subject on 28 days. More precise control of these factors could further improve measurement reproducibility and sensitivity to skin composition. Significant (p < 0.05) differences of parameter values with respect to region of interest depth, age and gender of subjects were discussed in comparison with dermal composition and offer promise that these parameters could be used to characterize skin modifications.

Ultrasonic Backscatter and Attenuation (11–27 MHz) Variation with Collagen Fiber Distribution in Ex Vivo Human Dermis

This ex vivo study explores the relationship of ultrasonic attenuation and backscatter to dermal microarchitecture by comparing ultrasonic measurements of these parameters (11–27 MHz) to a microscopic analysis of three parameters describing the collagen distribution (mean thickness and spacing of collagen bundles along the insonification direction and the percent area occupied by collagen). Skin samples (N = 31) were obtained from patients undergoing breast or abdominal reduction surgery. Radio-frequency (rf) signals were acquired in a B-scan format using an ultrasound system developed for skin imaging (Ultrasons Technologies, Tours, France). Ultrasonic data were analyzed to calculate average integrated backscatter (IBS in dB) and frequency dependence of backscatter (n, dimensionless) of each specimen at depths centered approximately 370, 620 and 880 μm beneath the skin surface. Average integrated attenuation coefficient (IA in dB.cm−1) and frequency dependence of attenuation coefficient (β in dB.cm−1.MHz−1) were estimated across the depth between 240 and 1,000 μm. The three collagen distribution parameters were estimated using digitized microcopic fields from matched regions of histological sections stained with hematoxylin-eosin-saffron. No significant correlation was identified between collagen distribution parameters and IA or β. For the most superficial depth studied in abdominal skin, n was inversely correlated to collagen bundle thickness (r = −0.67, p = 0.002) and percent area (r = −0.65, p = 0.003). At the same depth, IBS was inversely correlated to percent area of collagen (r = −0.51, p = 0.03). The rather high collagen packing (48 to 82% area) measured in histological sections and the inverse relationship observed between IBS and percent area of collagen suggest that a packing factor should be included in models relating skin collagen distribution to ultrasound spectral parameters. A better understanding of the relationship between ultrasound parameters and the microarchitecture of the dermis should help to interpret changes in ultrasonic parameters observed during in vivo ultrasonic skin examinations.

Optimization of attenuation estimation in reflection for in vivo human dermis characterization at 20 MHz

In vivo skin attenuation estimators must be applicable to backscattered radio frequency signals obtained in a pulse-echo configuration. This work compares three such estimators: short-time Fourier multinarrowband (MNB), short-time Fourier centroid shift (FC), and autoregressive centroid shift (ARC). All provide estimations of the attenuation slope (/spl beta/, dB.cm/sup -1/.MHz/sup -1/); MNB also provides an independent estimation of the mean attenuation level (IA, dB.cm/sup -1/). Practical approaches are proposed for data windowing, spectral variance characterization, and bandwidth selection. Then, based on simulated data, FC and ARC were selected as the best (compromise between bias and variance) attenuation slope estimators. The FC, ARC, and MNB were applied to in vivo human skin data acquired at 20 MHz to estimate /spl beta//sub FC/, /spl beta//sub ARC/, and IA/sub MNB/, respectively (without diffraction correction, between 11 and 27 MHz). Lateral heterogeneity had less effect and day-today reproducibility was smaller for IA than for /spl beta/. The IA and /spl beta//sub ARC/ were dependent on pressure applied to skin during acquisition and IA on room and skin-surface temperatures. Negative values of IA imply that IA and /spl beta/ may be influenced not only by skins attenuation but also by structural heterogeneity across dermal depth. Even so, IA was correlated to subject age and IA, /spl beta//sub FC/, and /spl beta//sub ARC/ were dependent on subject gender. Thus, in vivo attenuation measurements reveal interesting variations with subject age and gender and thus appeared promising to detect skin structure modifications.

P1C-2 Liver Stiffness Measurement Using Transient Elastography in Patients with Non-Alcoholic Fatty Liver (NAFLD) and Non-Alcoholic Steatohepatitis (NASH)

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of injury in many countries around the world. NAFLD covers a wide spectrum, ranging from simple steatosis, which is generally non progressive, to nonalcoholic steatohepatitis. There are no established noninvasive methods of evaluation for patients with NASH and until recently, liver biopsy was the unique method to quantify liver fibrosis. Liver stiffness measurement (LSM) has been proposed as non invasive tool to assess liver fibrosis in patients with hepatic chronic disease. This poster presents 3 clinical studies which demonstrate the usefulness of LSM to assess liver fibrosis in patients with histological features of NAFLD and which compared the efficiency of LSM and of two blood markers.

Transient elastography: changing clinical practice in hepatology

Transient elastography is one of several new approaches that have recently been proposed to manage liver diseases. This quantitative method is used in clinical practice to assess liver fibrosis noninvasively and rapidly. The technique consists in generating low‐frequency elastic shear waves through the liver and measuring their velocity using ultrafast pulse‐echo ultrasound acquisition. Liver stiffness is directly related to shear waves velocity. Nowadays more than 400 devices (Fibroscan®, Echosens, Paris, France) are being used worldwide in clinical practice. Studies reported a strong correlation between liver stiffness and the fibrosis stage obtained by liver biopsy in patients with chronic liver diseases: hepatitis B and/or C, HCV co‐infection, HIV, alcoholism, etc. Stiffness measurements obtained using transient elastography are in good agreement with measurements performed using other elastography techniques (magnetic resonance elastography and radiation force). Main limitations of transient elastogr...

Fibroscan® in hepatology: a clinically-validated tool using vibration-controlled transient elastography

Vibration-Controlled Transient Elastography (VCTE¿) based Fibroscan® (Echosens, Paris, France) is more and more used in clinical practice for the staging of liver fibrosis. Fibroscan® offers a rapid, simple, non-invasive and reliable means to quantify liver stiffness (LS). The most complete meta-analysis reported a strong correlation between liver fibrosis stage obtained by liver biopsy and LS. Area under the receiver operating curve (AUROC) for the diagnosis of significant fibrosis and cirrhosis are close to 0.84 and 0.94, respectively. However other factors may affect LS. We report here the effect of intravenous pressure that was studied in landrace pigs. Pig LS measurements were performed with increasing intravenous hydrostatic pressure up to 50 cm water. LS increases from 4.9 kPa before clamping to the maximum measurement value 75 kPa for hydrostatic pressure superior to 36 cm water. LS is directly influenced by intravenous pressure. Other studies reported that LS is also correlated to necrosis and inflammatory activity in patients suffering from chronic liver diseases. As a conclusion many disease related factors affect LS which emphasizes the role of LS measured by Fibroscan® as a key parameter for the diagnosis of liver health status.

P5D-4 Advances in Liver Stiffness Measurements Using Transient Elastography

Transient elastography has been extensively validated for in vivo liver stiffness measurement (LSM) using Fibroscanreg (Echosens, Paris, France). This non invasive and rapid procedure is used to assess liver fibrosis in adult patients. We present the recent advances in transient elastography for liver stiffness measurements in children and obese patients. Liver stiffness measurements were performed on children using a dedicated probe. Obese patients were measured with the standard probe. Patient position was changed and an ultrasound scanner was used to locate the measurement window in obese and morbid obese patients. Results show that liver stiffness measurements with Fibroscanreg is feasible on children using the dedicated probe. Measurement success rate in obese patients is signifcantly improved using the left lateral decubitus position under ultrasound guidance. More patients would therefore benefit from this non invasive method to assess liver fibrosis and cirrhosis.

20-MHZ US BACKSCATTER MEASUREMENTS AND REPRODUCIBILITY : NORMAL HUMAN DERMIS IN VIVO

In conclusion, this study demonstrates that, in certain regions of the dermis, measurements of IBS and n can be made with a CVglobal less than 7%. Furthermore, several tendencies in parameter value variation were identified and hypothesis were proposed linking these changes to temperature, pressure and skin anatomy. This work provides the basis from which to explore these relationships further in order to establish techniques for the detection of pathologies and for monitoring of changes in the skin produced by medical and cosmetic therapies.

Application of Short-Time Fourier Multi-Narrowband Analysis to In Vivo Human Skin Between 12 and 25 MHz

Development of high frequency (≥ 20 MHz) ultrasonic imaging systems allows in vivo, real-time visualization of the cutaneous tissues and structures. Ultrasound imaging is currently used in dermatology for morphological assessments of tumor extent 1 or skin layer (epidermis, dermis) thickness.2 However, ultrasonic imaging lacks specificity, leaving biopsy and histological analysis the only recourse for tissue identification.

In vivo normal human dermis characterization by 20-MHz ultrasound backscatter

Backscattered 20-MHz radio frequency (RF) signals were acquired from 10 sites of normal anterior mid-forearm of 29 subjects on three days and from one subject on 28 days. Using spectral analysis (12-25 MHz), apparent integrated backscatter (IBS) and frequency dependence of backscatter (n) were estimated at 5 successive dermal depths. Values of both parameters increased when greater pressure was placed on the skin during acquisition. IBS increased with depth while n decreased. In the most superficial depth studied, IBS was significantly correlated with age and was significantly higher in men. Parameter variations are discussed in terms of skin composition. Standardized coefficient of variation ranged from 7.7 to 10.3% for IBS and from 9 to 20% for n. Precise control of factors such as contact pressure and temperature could further improve reproducibility thus optimizing the technique for detection of pathologies or changes due to cosmetic or medical therapy.