Biomedical subjects

F Patat

Publications and source records attributed to F Patat.

At least 19 recordsLinked to original sources

PubMed2006

An optical supernova associated with the X-ray flash XRF 060218.

Long-duration gamma-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not hitherto known to be associated with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether X-ray flashes--analogues of GRBs, but with lower luminosities and fewer gamma-rays--can also be associated with supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst, is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but more luminous than many supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output and the supernova radio flux. Our data, combined with radio and X-ray observations, suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB-supernovae.

Journal Article↗

PubMed2006

[In vivo assessment of corneal epithelial toxicity of timolol with benzalkonium chloride using very-high-frequency ultrasound imaging].

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.

Animals↗

PubMed2006

[Techniques and applications of noninvasive high-resolution ultrasound imaging].

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).

Adult↗

PubMed2005

[Assessment of a matrix-based quantitative ultrasound imaging device (Beam scanner): reproducibility].

PURPOSE: A new matrix-based quantitative ultrasound (QUS) device was developed for the assessment of two parameters: BUA (Broadband Ultrasound Attenuation) and SOS (Speed Of Sound). This device, called Beam scanner, is a contact imaging device designed to evaluate the calcaneus. The aim of this preliminary study was to evaluate the reproducibility of results in a sample of patient with heterogeneous age distribution. MATERIALS AND METHODS: Seventy-six subjects were included: 18 healthy young males, 18 healthy young women and 40 women aged over 50 years old, including 19 osteoporotic patients according to WHO criteria. Five measurements were made for each patient after foot repositioning. Short-term precision was estimated using the coefficient of variation (CV), standardized CV (SCV) and intra-class correlation coefficient (ICC). RESULTS: SCV varied with the group of subjects between 2.0 and 4.3% for BUA, and between 3.1 and 4.5% for SOS. Mean values of BUA and SOS were statistically lower for osteoporotic women compared with healthy young women or healthy young males (p<0.001). For BUA, only SCV and ICC were better for women aged over 50 years old but without statistical difference. CONCLUSION: This study shows that the heterogeneity of the studied sample population is not a significant factor when assessing precision. This new device has a precision similar to others QUS devices.

Absorptiometry, Photon↗

PubMed2004

2D arrays device for calcaneus bone transmission: an alternative technological solution using crossed beam forming.

In the context of manned space flight with the European Space Agency, a quantitative ultrasound device for transmission imaging through the calcaneus bone has been developed. It includes two matrix transducers of 576 elements each in order to electronically perform the scanning and the focusing of the 500 kHz ultrasonic beam. This device called the BEAM scanner, provides two parametric images of attenuation (BUA, broadband ultrasonic attenuation) and velocity (SOS, speed of sound) of the investigated skeletal site. The cost and complexity of such a device has motivated the study of an alternative solution, less demanding in terms of technology, based on a crossed beam former [H. Ermert et al., A new concept for a real-time ultrasound transmission camera, in: IEEE Ultrasonics Symposium Proceedings, 2000, pp. 1611-1614]. It consists in forming two perpendicular cylindrically focused planes, one in emission, one in reception, instead of two spherically focused apertures. The crossing line of the two planes replaces the focused beam. The 2D beam forming technological challenge is moved to a 1D simpler and cheaper architecture. In this work the two solutions have been compared for in vivo measurements. Data sets have been acquired using all spatial combinations of emission and reception single elements of the matrix. Then signals have been processed using either the cylindrical or the spherical focussing mode. For cylindrical focussing, the increased level of the side lobes caused severe artefacts. Several apodization techniques have been implemented to reduce these artefacts, resulting in encouraging results. After a brief description of this new ultrasonic method for bone quantitative assessment, several reconstructed images using both processing schemes are presented. Corresponding statistical results obtained in 29 subjects are also provided.

Algorithms↗

PubMed2004

Influence of acousto-optic interactions on the determination of the diffracted field by an array obtained from displacement measurements.

This paper deals with the influence of acousto-optic interactions on the displacement measurements performed over transducer array and their effects on the predicted diffraction field. Changes on the temporal/spatial responses and the plane wave decomposition of the displacement are discussed. Modifications made on the directivity pattern are shown. A theoretical analysis of acousto-optic phenomenon, based on the plane wave decomposition of radiated field by the array is developed. Theoretical and experimental results are compared, showing first that waves with phase velocity near the one of the fluid are greatly amplified. Second, the interaction of laser beam with edge wave produced by the vertical size of elements induces a parasitic temporal pulse on the x-t diagram and so an interference pattern in the omega-k diagram. Corrections are proposed to eliminate errors induced by acousto-optic interactions and validated by comparing predicted diffraction field with measurements.

Journal Article↗

PubMed2003

[Medical, cognitive and affective status of four-year-old very premature babies without severe disability. A case-control study].

AIM: To determine cognitive performances and affective development of a cohort of very premature babies at the age of 4 years. POPULATION AND METHODS: Longitudinal case-control study. Newborns less than 33 weeks gestation were included from 1992 to 1994 and were matched with two full-term newborns. At 4 years of age, they have been evaluated for medical status, cognitive functions with the K-ABC test and affective condition with the PSA and Conners' tests. RESULTS: The preterm group was significantly different from the controls for: a smaller height, (P < 0.01), a lower socioeconomic level (P = 0.027), a lower nursery school level (44% versus 27,6%, P = 0.05), the incapacity to draw "a bonhomme" (55,3% versus 93%, P < 0.001), lower performances for the K-ABC and PSA tests, a pathologic Conners score (20.4% versus 2.4%, P < 0.001). Multivariate analysis by logistic regression showed a similar neuropsychological results: a lower score of K-ABC (< 80, P = 0.0006, odds-ratio = 33.2), and a lower social competence score of PSA (< 45, P = 0.004, odds-ratio = 35.9). CONCLUSION: Follow-up of premature babies is required, and measures to prevent or minimize cognitive and social disabilities are mandatory.

Affect↗

PubMed2002

Presence of nonlinear interference effects as a source of low frequency excitation force in vibro-acoustography.

The vibro-acoustography imaging method consists of forming an image of the deformability of a tissue submitted to a low frequency fLF stress field. This sound field can be created locally by means of a focused annular array emitting two primary beams driven at two close frequencies fa and fb = fa + fLF. In the existing literature, the origin of this stress field has been identified as the low frequency radiation pressure of the two primary beams. However, this work intends to show that another contribution to this internal stress is the low frequency field distributed in the object volume and created by the nonlinear interferences of the two primary beams. This nonlinear field was calculated in the case of multiple ring annular arrays and compared with the qLF beam experimentally measured in a water tank. The agreement between the theoretical and experimental curves provides information on the possibility that this nonlinear effect takes place in vibro-acoustography.

Journal Article↗

PubMed2002

In vivo performance of a matrix-based quantitative ultrasound imaging device dedicated to calcaneus investigation.

We developed a prototype of an ultrasound (US) bone matrix densitometer, the BEAM scanner, in the context of a European Space Agency research program. This device, which is a contact imaging device, was designed to overcome the limitations of immersion devices in space. Broadband US attenuation (BUA) and speed of sound (SOS) parameters were calculated from the radiofrequency (RF) signal. The principle aim of this study was to evaluate in vivo performance in direct comparison with a currently available device (UBIS 3000, DMS, France). The short-term precision of the BEAM scanner for BUA was estimated at 2.8%, whereas it was 2.3% with UBIS 3000. The short-term precision for SOS was 0.3%, and this was the same as the coefficient of variation (CV) of the UBIS 3000. CVs of 3.4% and 0.6% for midterm precision were found for BUA and SOS, respectively, and UBIS 3000 scores were 3% and 0.4%, respectively. This preliminary study demonstrates the high performance of the BEAM scanner and its new concept offers a wide range of improvements and new applications.

Adult↗

PubMed2001

In vitro study of low-frequency ultrasound-enhanced transdermal transport of fentanyl and caffeine across human and hairless rat skin.

The effect of low-frequency sonophoresis on fentanyl and caffeine permeation through human and hairless rat skin was studied in vitro. Experiments were performed using 20 kHz ultrasound applied at either continuous or discontinuous mode and with an average intensity of 2.5 W/cm(2). The results showed that low-frequency ultrasound enhanced the transdermal transport of both fentanyl and caffeine across human and hairless rat skin. This was explained by both increasing flux during sonication and shortening the lag time. Discontinuous mode was found to be more effective in increasing transdermal penetration of fentanyl while transdermal transport of caffeine was enhanced by both continuous and pulsed mode. Histological and electron microscopy studies showed that human and hairless rat skin was unaffected by ultrasound exposure. Further studies will be necessary to determine the relative contribution of ultrasound parameters in low-frequency ultrasound-induced percutaneous enhancement of drug transport.

Administration, Cutaneous↗

PubMed2001

Clinical, histologic, and electron microscopy study of skin exposed to low-frequency ultrasound.

The use of low-frequency ultrasound has been proposed to enhance the transdermal transport of various drugs, a technique referred to as sonophoresis. The aim of the present study was to determine the safety of low-frequency sonophoresis on human and rat skin by evaluating their structural modifications after ultrasound exposure. Human skin samples and hairless rats were exposed to 20 kHz ultrasound in vitro and in vivo, respectively. Ultrasound was used with average intensities ranging from 0.25 to 7 W/cm(2) in pulsed or continuous mode. Hairless rats were also exposed to a heat source mimicking the temperature versus time profile during sonication. Skin samples were observed under optical and electron microscopy to detect any structural changes. Human skin samples exposed to intensities lower than 2.5 W/cm(2) showed no modification. For hairless rats, slight and transient erythema was observed after 2.5 W/cm(2) exposure, whereas deep lesions (dermal and muscle necrosis) were observed 24 hr later. These lesions were also observed when a plastic film was placed between the coupling medium and the animals' skin during sonication. In contrast, no histologic lesion could be seen when a heat source was applied to animal skin. Low-frequency ultrasound induces delayed and deep lesions in hairless rat skin at 2.5 W/cm(2) which are not only attributable to the increase in temperature at the skin surface during ultrasound exposure. By using the same ultrasound conditions, human skin seems to be less sensitive in vitro.

Animals↗

PubMed2001

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.

Animals↗

PubMed2001

Investigation of cross-coupling in 1-3 piezocomposite arrays.

Plate waves inside the piezoelectric layer are much involved in the elements cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S0 mode is responsible for the inter-element coupling, whereas the S3 mode widens the effective width of the excited element.

Journal Article↗

PubMed2000

The Properties of Supernova 1997cy Associated with GRB 970514.

The extraordinary SN 1997cy associated with GRB 970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery, SN 1997cy was the brightest supernova (SN) ever observed (MV</=-20.1, vhel=19,140 km s-1, H0=65 km s-1 Mpc-1). Up to the last available observations (600 days after the gamma-ray burst), the total time-integrated flux was equal to or larger than that expected from the complete thermalization of the gamma-rays produced by 2.3 M middle dot in circle of 56Co. However, starting already on day 60 the luminosity decline is slower than the 56Co decay rate, indicating that the SN ejecta was interacting with circumstellar material (CSM). The interaction appeared to weaken around day 550. The spectra of SN 1997cy are dominated at all epochs by Halpha emission, which shows at least three components of different widths, as in SN 1988Z. Several other lines with different widths are also visible, especially at early epochs. The entire light curve of SN 1997cy is reproduced by a model of the interaction of the very energetic (E=3x1052 ergs) ejecta of a massive star (25 M middle dot in circle) with the CSM, with some contribution from radioactive decays. The CSM could have been ejected with a mass-loss rate of M&d2; approximately 4x10-4 M middle dot in circle yr-1 as the progenitor star evolved from a blue to a red supergiant about 104 yr before the explosion. The lack of oxygen and magnesium lines in the spectra at nebular phases poses a problem for models requiring high-mass progenitors. The possibility that most of the core material of the progenitor has fallen onto a massive black hole so that the reverse shock dies at the inner edge of the H/He envelope is discussed.

Journal Article↗

PubMed2000

Characterization of airborne transducers by optical tomography

This paper describes the application of an acousto-optic method to the measurement of airborne ultrasound. The method consists of a heterodyne interferometric probing of the pressure emitted by the transducer combined with a tomographic algorithm. The heterodyne interferometer measures the optical phase shift of the probe laser beam, proportional to the acoustic pressure integrated along the light path. A number of projections of the sound field, e.g. a set of ray integrals obtained along parallel paths, are made in moving the transducer to be tested. The main advantage of the method is its very high sensitivity in air (2 x 10(-4) Pa Hz-1/2), combined with a large bandwidth. Using the same principle as X-ray tomography the ultrasonic pressure in a plane perpendicular to the transducer axis can be reconstructed. Several ultrasonic fields emitted by wide-band home made electrostatic transducers, with operating frequencies between 200 and 700 kHz, have been measured. The sensitivities compared favorably with those of commercial airborne transducers.

Journal Article↗

PubMed2000

Time-domain modeling of nonlinear distortion of pulsed finite amplitude sound beams.

This work aims to validate a time domain numerical model for the nonlinear propagation of a short pulse of finite amplitude sound beam propagation in a tissue-mimicking liquid. The complete evolution equation is simply derived by a superposition of elementary operators corresponding to the 'one effect equation'. Diffraction LD, absorption and dispersion LAD, and nonlinear distortion LNL effects are treated independently using a first order operator-splitting algorithm. Using the method of fractional steps, the normal particle velocity and the acoustical pressure are calculated plane by plane, at each point of a two-dimensional spatial grid, from the surface of the plane circular transducer to a specified distance. The LA operator is a time convolution between the particle velocity and the causal attenuation filter built after the Kramers-Kroning relations. The LNL operator is a time-based transformation obtained by following an implicit Poisson analytic solution. The LD operator is the usual Rayleigh integral. We present a comparison between theoretical and experimental temporal pressure waveform and axial pressure curves for fundamental (2.25 MHz), second, third and fourth harmonics, obtained after spectral analysis.

Absorption↗

PubMed2000

Harmonic propagation of finite amplitude sound beams: experimental determination of the nonlinearity parameter B/A

We propose a method to determine the nonlinearity parameter B/A of a liquid from the spatial evolution of harmonic components. We describe an analytical model, in the parabolic and quasi-linear approximations, that predicts the continuous finite amplitude sound beam propagation radiated by a plane piston source. This model takes into consideration attenuation, diffraction and nonlinear effects. The fundamental and second harmonic ultrasonic fields are expressed as the superposition of Gaussian beams. Axial propagation curves are then compared with those obtained by direct numerical solution of the transformed beam equation using the finite difference method, and with experimental results. Accurate measurements of pressure levels for the nonlinearly generated harmonics in water are performed along and across the propagation axis for different pressure values delivered at the piston surface. Experimental results, for water and ethanol, are in agreement with those of our model, which allows us to obtain the expected value of the nonlinearity parameter B/A.

Journal Article↗

PubMed2000

Estimation of the blood Doppler frequency shift by a time-varying parametric approach.

Doppler ultrasound is widely used in medical applications to extract the blood Doppler flow velocity in the arteries via spectral analysis. The spectral analysis of non-stationary signals and particularly Doppler signals requires adequate tools that should present both good time and frequency resolutions. It is well-known that the most commonly used time-windowed Fourier transform, which provides a time-frequency representation, is limited by the intrinsic trade-off between time and frequency resolutions. Parametric methods have then been introduced as an alternative to overcome this resolution problem. However, the performance of those methods deteriorates when high non-stationarities are present in the Doppler signal. For the purpose of accurately estimating the Doppler frequency shift, even when the temporal flow velocity is rapid (high non-stationarity), we propose to combine the use of the time-varying autoregressive (AR) method and the (dominant) pole frequency. This proposed method performs well in the context where non-stationarities are very high. A comparative evaluation has been made between classical (FFT based) and AR (both block and recursive) algorithms. Among recursive algorithms we test an adaptive recursive method as well as a time-varying recursive method. Finally, the superiority of the time-varying parametric approach in terms of frequency tracking and delay in the frequency estimate is illustrated for both simulated and in vivo Doppler signals.

Algorithms↗