Fabrice Lefebvre

Automatic detection of the boundary of the calcaneus from ultrasound parametric images using an active contour model; clinical assessment

Presents a computerized method for automated detection of the boundary of the os calcis on in vivo ultrasound parametric images, using an active dynamic contour model. The initial contour, defined without user interaction, is an iso-contour extracted from the textural feature space. The contour is deformed through the action of internal and external forces, until stability is reached. The external forces, which characterize image features, are a combination of gray-level information and second-order textural features arising from local cooccurrence matrices. The broadband ultrasound attenuation (BUA) value is then averaged within the contour obtained. The method was applied to 381 clinical images. The contour was correctly detected in the great majority of the cases. For the short-term reproducibility study, the mean coefficient of variation was equal to 1.81% for BUA values and 4.95% for areas in the detected region. Women with osteoporosis had a lower BUA than age-matched controls (p=0.0005). In healthy women, the age-related decline was -0.45 dB/MHz/yr. In the group of healthy post-menopausal women, years since menopause, weight and age were significant predictors of BUA. These results are comparable to those obtained when averaging BUA values in a small region of interest.

SIMS determination of the distribution of the main mineral cations in the depth of the cuticle and the pecto-cellulosic wall of epidermal cells of flax stems: problems encountered with SIMS depth profiling

Depth profiles of C, Na, Mg, Al, K and Ca were performed in the cuticle and wall of epidermal cells of flax hypocotyls, with current densities ranging from 0.2 to 1 pA μm−2. The crater bottoms were never flat, but exhibited fairly complex, filiform or alveolar structures. The profiles of K, Ca and Mg were reasonably parallel to one another. The Ca/Mg signal ratio was in the magnitude of 3.5 in the cuticle. The Na profile, except perhaps in the cuticle, did not parallel the K, Ca and Mg profiles, but rather paralleled the C profile. At the outset of the depth profiles, ie in the cuticle, the intensity of the Na signal, although fairly variable, was usually above that of K; then there was an abrupt decrease of the Na signal, possibly at the border of the cuticle and of the wall. The Al signal usually began to increase, thus revealing the occurrence of perforations through the epidermis sample, after 80 min sputtering at a current density of 1 pA μm−2; the mean sputtering rate was thus estimated to be in the order of 1 μm h−1.

New Cixiidae and Achilidae fossils from Middle Eocene Baltic amber (Hemiptera: Fulgoromorpha)

Abstract Three fossil planthoppers (Hemiptera: Fulgoromorpha) are described from Middle Eocene Baltic amber, viz. Balticixius n. gen. (Cixiidae) for a species already described as Cixius insignis Germar & Berendt for which a new specimen has been discovered; and two new Achilidae species: Cixidia christinae n. sp. and Angustachilus longirostris n. gen., n. sp. Some taxonomic data about the genus Cixidia are also provided.

Chemical Microscopy of Biological Samples by Dynamic Mode Secondary Ion Mass Spectrometry (SIMS)

3D chemical microscopy is one of the emerging applications of secondary ion mass spectrometry (SIMS) in biology. Tissues, cells, extracellular matrices, and polymer films can be imaged at present with a lateral resolution of 50 nm and depth resolution of 1 nm using the latest generation of CAMECA magnetic sector NanoSIMS 50 or with a lower lateral resolution (above 100 nm) using IMS 4f Cameca SIMS equipped with cold stage. Dynamic mode SIMS analysis is performed in ultrahigh vacuum and thus requires specific and careful preparation of biological samples aimed at preserving and minimizing destruction of the original structural and chemical properties of the samples. Here we describe a methodology based on the ultrafast plunge-freezing of biological tissues, preparation of the sample for SIMS analyses and transfer to the SIMS cold stage without interruption of the cold chain during the mounting procedure and subsequent SIMS analyses. Using this strategy, SIMS chemical microscopy can be performed on biological tissue in which unwanted molecular and/or structural reorganization, loss of constituents and chemical modifications are minimized and in which structures are therefore optimally preserved.

The determination of the viscoelastic properties of liquid materials at ultrasonic frequencies by CW mode impedance measurements

A method is described for measuring shear mechanical properties of liquids at ultrasonic frequencies. The method is based on the process of the electrical impedance of a sensor in contact with the liquid. The sensor is composed of a piezoelectric transducer bonded to a delay line. The process determines the complex reflection coefficient of shear waves reflecting from the delay line-liquid interface, and the mechanical impedance is deduced. Experimental determination of dynamic shear properties of a series of saccharose solutions is presented as an example of the method.

Low frequency composite acoustic sensor for highly absorbing media characterization

Ultrasonic techniques are widely used in nondestructive testing and evaluation of media. But when media are highly absorbing, it becomes often impossible to operate at classical ultrasonic frequencies. In this work, we propose a low frequency acoustic device to characterize such highly absorbing media. This device is composed of a piezoelectric disc embedded in a metallic ring. The technique consists in bringing into resonance the entire structure. Firstly, we will study analytically and numerically the main resonance modes of the sensor, which are the flexion modes and the radial modes. The results of the modelization are compared to measurements obtained through an impedance analyzer. In a second part, we will use this model of sensor to characterize two different media. The first type consists of a series of polymer disks with different viscoelastic properties. Using radial modes of vibration, we will characterize these polymer disks through measurement of the acoustic velocity. After that, we will cha...

Ultrasonic and acoustic method for viscoelastic complex media characterization

In this paper, the potentialities of a low frequency ultrasonic/acoustic technique devoted to the study and characterization of the viscoelastic complex media is investigated. This work shows the limit of the use of ultrasound in a viscoelastic media with a complex matrix. In this context the cheese was indicated as a model of propagation medium, such a product having a very complex matrix in term of texture, openings, crystallization, moisture,... . Theoretical basis of sound attenuation in cheese is recalled, especially the effects of the matrix viscoelasticity and the scattering of ultrasonic energy by holes and cracks. Depending on the degree of openness, ultrasonic velocity or attenuation is chosen to represent the evolution of the cheese. For very high degree of openness, ultrasounds are no longer usable and a tap‐test acoustic technique is employed and allows a quality indicator to be constructed. Experimental validations were done with optical images of cut cheeses and rheological measurements. Th...

Study and development of a low‐frequency acoustic sensor dedicated to the vibratory analysis and the mechanical characterization of the plates

A low‐frequency acoustic method was implemented for the purpose of nondestructive control and evaluation of metal plates coating. In this method, a mechanical pulse (acoustic impact) is used to generate acoustic vibrations on a frequency band between 100 Hz to 20 kHz, and a compact acoustic sensor, constructed with by composite materials with an embedded ferroelectric disk, is used to receive the acoustic vibrations. The technique consists in setting in resonance the integrality of a reduced size mechanical structure. The modal frequencies of plates are calculated by two methods: analytically and by finite element method. Then, a numerical modeling of the acoustic behaviour of the sensor is presented. Finally, experimental trials are described and results showing the sensitivity of the method to evaluate coating of metal plates are analyzed.

Sims imaging of the seasonal changes of the Na, Mg and Ca distributions in the cambial area of beech branches

The Fast Fourier Transform (FFT) is a powerful tool used m image analysis to assess the quality of images and to extract structural informations from noisy pictures We have used these properties of the FFT to evaluate the quality of digitizing devices usually found in laboratorres, from the scanning microdensitometer to desktop publishing scanners. Such devices have to f%ll several criterions efficiency of information transfer in terms of detection, dynamic and resolution, and also capacity to digitize large size images. Images of negative stained Catalase crystals have been recorded using a CM12 Philips Electron Microscope operated at 80 KV and with a nominal magnification of 35000 Micrographs were evaluated for focus, astigmatism, and drift by optical diffraction. To standardize measurements, a picture having a limited astigmatism and a first Ton ring defocus at 116 A” was selected and digitized. For comparison, we used a video camera linked to the electron microscope permitting to record an electron image into a video image, subsequently converted into a digital format Informations concerning induced anisotropy, loss of structural information are easily retrieved from a visual inspection of the power spectrum calculated from the image FFT, In addition, the averaged profile of the power spectrum gives a global information concerning the dynamic of the information transfer and the induced noise level Finally, the relative modulation transfer fimction (rh4TF), which is the amplitude ratio of a given diffraction spot to a reference diffraction spot of high amplitude, will quantify the loss of information in terms of frequency and in both axes of the reciprocaf space.