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P Laugier

Publications and source records attributed to P Laugier.

At least 55 records · Page 3Linked to original sources
PubMed1998

Evaluation of acoustical parameter sensitivity to age-related and osteoarthritic changes in articular cartilage using 50-MHz ultrasound.

The current study reports the sensitivity of acoustical parameters estimated at high frequency to the osteoarthritic morphological and structural changes in patellar cartilage in rat knees. Osteoarthritis (OA) was induced by a single intra-articular injection of mono-iodo-acetic acid in right knees. OA patellas and their contralateral controls were excised at regular intervals after injection and were examined in vitro with a scanning acoustical microscope operating with a poly(vinylidene di-fluoride) (PVDF) 80-MHz focused transducer. Cartilage thickness was estimated using B-scan images. The quantitative analysis of the radiofrequency signal backscattered by the cartilage was performed using integrated reflection coefficient (IRC) and apparent integrated backscatter (AIB), which were estimated in the 20-60-MHz frequency range. One week after injection, a cartilage thickness decrease was detected (-6%, on average) that preceded the significant hypertrophy (20.1%) that occurred 2 weeks after injection and could be due to tissue repair. From 1 week to 3 weeks after injection, the IRC of OA patellas was significantly lower than that of control patellas. The IRC difference increased with time from -3.3 +/- 2.4 dB at 1 week to -8.4 +/- 1.7 dB at 3 weeks. An AIB decrease was observed with time for both OA and control patellas (-2.9 to -4.2 dB per week). An AIB difference between OA and control patellas was detected from 1 week to 3 weeks after injection. This difference decreased with time. IRC variation reflects a change in acoustical impedance of the superficial layer of the cartilage and could be linked to a change in constituent content and/or to a disruption of fibers of the collagen network that led to the fibrillation of the cartilage surface. AIB variation reflects a change in shape, size and/or density of the scatterers and could be related to changes in the constituent content and in the organization of the matrix in the internal layer of the cartilage. IRC and AIB could provide information about the structural modifications of the cartilage due to osteoarthritis or to cartilage maturation.

Aging↗
PubMed1998

In vivo results with a new device for ultrasonic monitoring of pig skin cryosurgery: the echographic cryoprobe.

One of the main difficulties encountered in cryosurgery is the uncertainty in the extent and depth of the tissue effectively treated during the freezing process. The objective of this study was to evaluate in vivo ultrasonic control of skin cryosurgery using a new echographic cryoprobe. An echographic cryoprobe, developed specifically for dermatology applications, combines a high-frequency (20 MHz) miniature ultrasonic transducer and a N2O-driven closed cryoprobe. Knowledge of the ultrasound velocity of frozen skin is a prerequisite for monitoring the iceball formation kinetics. Therefore, in a first study, we estimated the ultrasound velocity of frozen skin specimens. In a second step, the operation of the echographic cryoprobe was assessed, under in vivo conditions similar to those used in human therapeutics, on normal skin of three female "Large-White" pigs under anesthesia. The mean value of ultrasound velocity of frozen skin obtained by pooling the data from all the skin specimens included in this study was 2865 +/- 170 m per s. The average rates of growth (10(-2) mm per s) of the iceballs were found to be 12.2 +/- 1.0 (pig 1), 9.0 +/- 1.0 (pig 2), and 8.4 +/- 0.9 (pig 3). The echographic cryoprobe had a built-in high-frequency ultrasonic transducer that served two functions. It enabled in vivo real-time monitoring of depth penetration of the iceball and it gave important feedback to the operator or to the console relating to the rate of growth of the iceball. Automatic (i.e., operator-independent) detection of the echo signal from the freezing front and calculation of the depth penetration of the iceball was possible.

Animals↗
PubMed1998

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

This paper 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.

Adult↗
PubMed1997

Assessment of the relationship between broadband ultrasound attenuation and bone mineral density at the calcaneus using BUA imaging and DXA.

The purposes of this study was to determine the relationship between broadband ultrasound attenuation (BUA) and bone mineral density (BMD) measured at different regions of the calcaneus with identical site-matched regions of interest (ROIs). Dual-energy X-ray absorptiometry (DXA) measurements of the calcaneus and BUA imaging were performed in 30 women (15 premenopausal and 15 postmenopausal). Four square ROIs were located in the great tuberosity and one square ROI in the foramen calcaneus. A ROI adapted to the shape and size of the whole calcaneus was also considered. All ROIs were analyzed three times with both techniques to minimize intra-observer variability. The correlation coefficient between attenuation and frequency was used as an index of BUA measurement error. Before accepting a measurement of BUA in inhomogeneous material, it could be useful to map the spatial variations of the measurement error. In all ROIs we found the BUA and BMD were strongly related (r = 0.78-0.91, p < 0.001). The correlation between BUA and BMD was slightly higher in the inferior part of the posterior tuberosity than in the superior part and in the foramen calcaneus. The very high correlation between attenuation and frequency found in all ROIs (r = 0.99) suggests that measurement errors of propagation were probably not significant. Ultrasound imaging yields the opportunity for studying the spatial acoustic properties in the calcaneus and their relation to bone mass or structural parameters provided by independent imaging techniques. BUA measured with current transmission techniques reflects mainly bone mass, and microarchitecture to a smaller extent.

Absorptiometry, Photon↗
PubMed1997

Quantitative ultrasound imaging at the calcaneus using an automatic region of interest.

A new approach to measuring bone properties at the calcaneus using ultrasound parametric imaging has recently emerged. However, an additional source of observer-related error is the substantial regional variations in the pattern of ultrasound parameters. The contribution of intra-observer and inter-observer variability to the coefficient of variation can be eliminated using an algorithm which selects the region of interest (ROI) completely automatically. The objective of the present study was the clinical assessment of an automatic ROI for both broadband ultrasonic attenuation (BUA) and speed of sound (SOS) measurement using ultrasound parametric imaging. The automatic ROI was defined as the circular region of lowest attenuation in the posterior tuberosity of the calcaneus. We have tested this algorithm using clinical images of the calcaneus from 265 women. Mean coefficients of variation were 1.6% (95% confidence interval 1.4%-1.9%) and 0.26% (95% confidence interval 0.23%-0.32%) for BUA and SOS respectively (standardized CV was 2.1% for BUA and 2.6% for SOS). Z-scores in an osteoporotic group were -0.61 and -0.52 for BUA and SOS respectively. In healthy women, the age-related decline was -0.50 dB/ MHz per year (0.7%/year) for BUA and -1.2 m/s per year (0.08%/year) for SOS. In the subgroup of healthy postmenopausal women, using stepwise multiple regression, we found that BUA was predicted best by years since menopause (YSM) and weight, with overall model r2 = 0.28; SOS was predicted best by YSM only (r2 = 0.21). Neither the range of biological variation of ultrasound parameters nor the clinical value were affected by the choice of the region of lowest attenuation for measurement. The automatic procedure was totally independent of operator interaction, therefore excluding loss of precision due to intra- or inter-observer variability. The results showed the high precision and robustness of the procedure. These factors make this approach viable for routine clinical use.

Aged↗
PubMed1997

In vitro assessment of the relationship between acoustic properties and bone mass density of the calcaneus by comparison of ultrasound parametric imaging and quantitative computed tomography.

This in vitro study aimed to add new experimental evidence to clarify the relation between acoustic properties of bone and bone mineral density (BMD) of the human calcaneus. Parametric images of normalized broadband ultrasonic attenuation (nBUA) and ultrasound bone velocity (UBV) were compared with quantitative computed tomography (QCT) images of the calcaneus. The experimental protocol was designed to control the different potential sources of error in acoustic measurements, including the shape and thickness of the samples, intervening soft tissues and cortical bone, boundary effects, and variation in location of the regions of interest (ROIs) analyzed by ultrasound and X-ray. The present study was based on bone specimens from calcaneus removed from 15 cadavers (six male and nine female donors ranging from 69 to 89 years of age). Immersion ultrasonic measurements were performed in the through-thickness direction at normal incidence using a pair of focused broad-band 0.5-MHz transducers. QCT of the specimens was performed using standard 10-mm-thick slices with the Cann-Genant calibration standard. Identical, site-matched ROIs were selected for quantitative analysis on the three images. The pattern of acoustic parameters was similar to that of BMD with QCT. The relationships between nBUA and BMD (r2 = 0.75), between UBV and BMD (r2 = 0.88) and between nBUA and UBV (r2 = 0.84) were highly significant (p < 10(-4). From this study, it appears that ultrasound parameters as measured with current transmission techniques reflect mainly bone quantity and only reflect microarchitecture to a small extent and that BUA and UBV reflect the same bone property.

Acoustic Stimulation↗
PubMed1997

Assessment of articular cartilage and subchondral bone: subtle and progressive changes in experimental osteoarthritis using 50 MHz echography in vitro.

The main objectives of this work were to demonstrate the potential of 50 MHz echography for assessing initial and progressive morphological and structural changes of articular cartilage and bone developed in an experimental model of osteoarthritis (OA). Degenerative lesions were induced in rat knees by the unilateral intra-articular injection of a 3 mg dose of mono-iodo-acetic acid. To assess the lesion progression, the animals (n = 30) were sacrificed at different time intervals up to 8 weeks after the injection. Three-dimensional echographic data were acquired in vitro on patellar cartilage and bone at various stages of the remodeling process using a scanning ultrasound microscope. Changes involving the OA cartilage characteristics are discussed relative to those of the contralateral control joint which received a placebo. Images of control cartilage showed a smooth hyperechoic articular surface and an echoic matrix. The cartilage thickness was 266 +/- 44 microns (mean +/- SD) in the central region of the tissue. The precision of ultrasonic thickness measurements was better than 1.3%. First changes in cartilage internal structure and subchondral bone appeared on ultrasound images 3 days after the injection and were even more evident by day 7. They resulted in a slight thinning of the cartilage, a 30% increase of its internal structure echogenicity, and the appearance of echoic zones in subchondral bone. Histologic findings confirmed chondrocyte depletion and degeneration, decrease of matrix proteoglycans, and fibrovascular connective tissue proliferation at the subchondral plate. Progressive and severe lesions at both bone and cartilage surface and internal structure were assessed and correlated to histologic features. These results show that high resolution echography is sensitive to subtle and progressive osteochondral remodeling. This technique has the potential to be used for intra-articular quantitative imaging and assessment of early changes in bone and cartilage structure associated with natural human disease.

Animals↗
PubMed1996

Broadband ultrasound attenuation imaging: a new imaging method in osteoporosis.

The purpose of this study was to evaluate the usefulness in osteoporosis of a new ultrasound imaging device able to create a parametric image of broadband ultrasound attenuation (BUA) at the os calcis. Three regions of interest were located in the great tuberosity of the os calcis. Precision was evaluated in 37 patients. Calcaneal bone mineral density (BMD) and BUA were compared in 33 patients. In 236 patients (including 77 with osteoporotic fractures), BUA and lumbar and femoral BMD measurements were performed. The measurements were compared using correlation coefficients. Their clinical value was estimated by comparisons of the results between patients with fractures and age-matched controls, using comparisons of the means, areas under the ROC curves, and logistic regression. Precision was in a 1.4-3.3% range. Local BUA and BMD were highly correlated (r = 0.88). Significant correlations were found between BUA and lumbar (r = 0.56) and femur (r = 0.66) BMD. In multiple regression, years since menopause and weight were significant predictors of BUA. Patients with fractures had lower BUA and BMD than age-matched controls. BUA showed the largest difference between the two populations (13-16%). Areas under the ROC curves were similar for BUA and BMD. Logistic regression after adjustment for confounding factors showed that BUA discriminated between fracture and nonfracture subjects. Broadband ultrasound attenuation imaging improves the reproducibility of ultrasound measurements. It may be useful in osteoporosis, due to its good discriminating value.

Adult↗
PubMed1996

Ultrasound parametric imaging of the calcaneus: in vivo results with a new device.

An ultrasound transmission scanning system was constructed to make in vivo parametric images of the acoustic properties of the heel. Broadband ultrasonic attenuation (BUA) images were obtained in transmit mode by using a pair of broadband focused transducers (center frequency 0.5 MHz, diameter 29 mm, focus 50 mm) immersed in a water bath at room temperature. With these characteristics, the theoretical beam width at the focus was approximately 5 mm. The total duration of the acquisition period was 3 minutes. Comparison of the BUA image and the radiograph of the calcaneus was possible in one case and showed that all the anatomical details could be identified. The images reported here demonstrate the wide range of BUA found in both the whole bone and within a ROI centered in the posterior part of the bone thus reinforcing the idea of tremendous heterogeneity of the acoustic properties of bone. This suggests that the accurate control of the position of the measurement site is of the utmost importance for between-subject comparison and for repetitive measurements. We proposed a new method, the likelihood image, as an efficient way of highlighting the regions of the image suspected to be subject to waveform distortion. It could be used to guide the selection of the optimal measurement site. Our results suggest that ultrasound parametric imaging has the potential for enhancing the current ultrasound technique by (1) allowing reproducible, repetitive measurements, (2) permitting the selection of similar optimal measurement sites in all subjects, and (3) avoiding accuracy errors due to waveform distortion.

Adult↗
PubMed1994

Broadband ultrasonic attenuation imaging: a new imaging technique of the os calcis.

Ultrasound transmission measurement through the os calcis is an emerging technique and a promising clinical tool for early assessment of osteoporosis. However, several previous studies showed that broadband ultrasonic attenuation (BUA) is sensitive to small variations in bone mass or structure. The os calcis is an inhomogeneous bone and therefore, the attenuation depends on the location in the os calcis. BUA distribution within the os calcis can be measured by rectilinear scanning over the entire bone. We used a mechanical scanning device with both unfocused and focused transducers. The spatial resolution of these was about 25 mm and 4 mm, respectively. There was good agreement (r = 0.97) between the results with unfocused and focused transducers. In addition, imaging the variations of BUA is possible with the focused transducers, and high quality images are obtained. These images permit the selection of optimal regions of interest for ultrasound attenuation measurement.

Aged↗
PubMed1994

Ultrasound attenuation imaging in the os calcis: an improved method.

A complete assessment of the broadband ultrasonic attenuation (BUA) distribution within the os calcis was made using an ultrasonic mechanical scanning device with focused transducers. Measurements were performed on 12 os calces removed from fresh female cadavers. We present the first images of BUA of the os calcis. Reasonably high quality images were obtained compared to computed tomography. The resolution provided by the focused transducers is approximately 4 or 5 mm in the focal zone. Compared to dual energy X-ray absorptiometry (DEXA) or quantitative computed tomography, ultrasound imaging of the os calcis offers the possibility of controlling the placement, size and shape of the region of interest and to use multiple measurement sites. DEXA was used systematically to measure the bone mineral density (BMD) of the os calces. A highly significant correlation between BMD and BUA was found (r = 0.97 p < 0.001).

Absorptiometry, Photon↗
PubMed1994

Bone characterization with ultrasound: state of the art and new proposal.

Ultrasound transmission measurement through the os calcis is an emerging technique and a promising clinical tool for early assessment of osteoporosis. In this paper we first present a short discussion on the physical meaning of ultrasound velocity and attenuation, the methods of measurements and the potential contribution of ultrasound compared to photon absorptiometry. After analysing the various results in vivo published up to now we shall present some new perspectives of ultrasonic bone characterization: broadband ultrasonic attenuation imaging (BUAI) and pulse-echo measurement.

Absorptiometry, Photon↗
PubMed1993

Assessment of echography as a monitoring technique for cryosurgery.

One of the principal difficulties encountered in cryosurgery is to know the extent and depth of the frozen tissue boundary during the freezing process and the extent of the cryonecrosis in the postfreezing period. These problems have to be solved for cryosurgery to be a controlled therapeutic method and to avoid injuries to tissues adjacent to the tumor. The aim of this study was to evaluate echographic possibilities in monitoring the freezing process during cryotherapy in dermatology. In this paper, we describe the first experimental results of ultrasound monitoring of the freezing process with a 15 MHz transducer on pig skin in vitro. We show that it is possible to easily detect the depth boundary of the frozen region. Conventional linear filtering of the echographic signals can be very useful for SNR enhancement in the detection of a target signal drowned in speckle noise. Measurement of the kinetics of the freeze-thaw cycle (thickness of the frozen region versus time) is also measurable, which is of major importance as it allows the exact adjustment of the freezing time as a function the extent of tumor depth. Cryotherapy monitoring by ultrasound, added to the new diagnostic possibilities of high frequency ultrasound transducers, makes it an interesting controlled therapeutic method in such clinical fields as dermatology.

Animals↗
PubMed1990

Global breast attenuation:control group and benign breast diseases.

This paper deals with the estimation of the slope of attenuation in human breast tissue. The measurement is done in the reflection mode with a short time Fourier analysis. All important factors such as diffraction effect, tissue depth and specular reflectors are taken into account. A population of 49 normal women shows large inter-individual variations of the attenuation coefficient. A multiple linear regression allows correlation of this variation with the duration of the woman's genital life and pregnancies. A preliminary study is done on 10 benign diffuse breast diseases and shows a weak correlation with the type of the breast: normal or pathological. The utility of the quantification is discussed for one case of large fibrocystic disease.

Adult↗
PubMed1990

Partially coherent transducers: the random phase transducer approach.

Ultrasound speckle is a consequence of the stochastic nature of the reflectivity of scattering media (e.g., biological tissue) and of the coherent nature of piezoelectric transducers. This speckle noise can be reduced by the use of incoherent processing techniques (e.g., spatial compounding, incoherent summation, random phase and phase insensitive transducers). We present a unified framework that explains the limitations of incoherent processing in terms of the information grain theory. This theory predicts the gains in SNR as well as the losses in directivity. We also present the random phase transducer approach to incoherence to total coherence. We present applications to speckle reduction, detection of specular reflectors, attenuation estimation and ultrasound imaging. We show that totally incoherent transducers completely remove diffraction effects. They might be used in attenuation estimation, in which case, correction for diffraction is no longer required, in order to obtain unbiased estimates. Partially coherent transducers might also be useful in imaging to reduce speckle noise.

Humans↗