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Biomedical subjects

L Pourcelot

Publications and source records attributed to L Pourcelot.

At least 37 records · Page 2Linked to original sources
PubMed1999

Clinical use of ultrasound tissue harmonic imaging.

The recent introduction of tissue harmonic imaging could resolve the problems related to ultrasound in technically difficult patients by providing a marked improvement in image quality. Tissue harmonics are generated during the transmit phase of the pulse-echo cycle, that is, while the transmitted pulse propagates through tissue. Tissue harmonic images are formed by utilizing the harmonic signals that are generated by tissue and by filtering out the fundamental echo signals that are generated by the transmitted acoustic energy. To achieve this, two processes could be used; one by using filters for fundamental and harmonic imaging and the second using two simultaneous pulses with a 180 degrees difference in phase. The introduction of harmonics allows increased penetration without a loss of detail, by obtaining a clearer image at depth with significantly less compromise to the image quality caused by the use of lower frequencies. This imaging mode could be used in different organs with a heightening of low-contrast lesions through artefact reduction, as well as by the induced greater intrinsic contrast sensitivity of the harmonic imaging mode.

Acoustics↗
PubMed1999

MR assessment of the brain maturation during the perinatal period: quantitative T2 MR study in premature newborns.

The purpose of our study is to trace in vivo and during the perinatal period, the brain maturation process with exhaustive measures of the T2 relaxation time values. We also compared regional myelination progress with variations of the relaxation time values and of brain signal. T2 relaxation times were measured in 7 healthy premature newborns at the post-conceptional age of 37 weeks, using a Carr-Purcell-Meiboom-Gill sequence (echo time 60 to 150 ms), on a 2.35 Tesla Spectro-Imaging MR system. A total of 62 measures were defined for each subject within the brain stem, the basal ganglia and the hemispheric gray and white matter. The mean and standard deviation of the T2 values were calculated for each location. Regional T2 values changes and brain signal variations were studied. In comparison to the adult ones, the T2 relaxation time values of both gray and white matter were highly prolonged and a reversed ratio between gray and white matter was found. The maturational phenomena might be regionally correlated with a T2 value shortening. Significant T2 variations in the brainstem (p < 0.02), the mesencephalon (p < 0.05), the thalami (p < 0.01), the lentiform nuclei (p < 0.01) and the caudate nuclei (p < 0.02) were observed at an earlier time than they were visible on T2-weighted images. In the cerebral hemispheres, T2 values increased from the occipital white matter to parietal, temporal and frontal white matter (p < 0.05) and in the frontal and occipital areas from periventricular to subcortical white matter (p < 0.01). Maturational progress was earlier and better displayed with T2 measurements and T2 mapping. During the perinatal period, the measurements and analysis of T2 values revealed brain regional differences not discernible with T2-weighted images. It might be a more sensitive indicator for assessment of brain maturation.

Adult↗
PubMed1999

High frequency (20 MHz) ultrasonic devices: advantages and applications.

OBJECTIVE: This paper investigates the problems, advantages and potential applications of 20 MHz ultrasonic devices. METHOD: Aqueous gel and a thin appropriate membrane to enclose the front tip were used with 20 MHz probes without obvious decrease in resolution and sensitivity compared to the results obtained without a membrane and this considerably facilitates their routine use. RESULTS: Many applications with linear scanning were evaluated in dermatology, ophthalmology (investigations of the anterior chamber of the eye, checking of corneal grafts), stomatology (detection and evaluation of periodontal disease) and in the field of measurement of very low velocities in small vessels by means of a duplex probe comprising two 20 MHz transducers: an imaging transducer and an inclined blood flow measurement transducer. Velocity profiles (velocities less than 0.50 mm/s) were measured in 100-300 microm diameter vessels using a cross-correlation method. CONCLUSION: The use of 20 MHz frequency limits resolution but we have shown that this frequency allows the development of easy to handle probes.

Blood Flow Velocity↗
PubMed1999

New blind mobility aid devices based on the ultrasonic Doppler effect.

An original approach to electronic blind mobility aid combined with ultrasonic wave processing and spatial hearing has allowed the design of new blind mobility aid devices. These devices convert inaudible ultrasound echoes into audible sound via the Doppler effect, preserving even slight modification of the high frequency wave, so as to provide the user with higher acuity information regarding his movement, as well as object movement and their spatial location.

Activities of Daily Living↗
PubMed1999

Effects of the method of drawing regions of interest on the differential diagnosis of extrapyramidal syndromes using 123I-iodolisuride SPET.

Various parameters are currently used for the semi-quantitative assessment of dopamine D2 receptors and differ according to the delineation of the striatal region of interest (ROI) and the choice of the reference ROI. The aim of this study was to assess the value of different ROI approaches in differentiating patients with normal or increased numbers of D2 dopamine receptors (group 1 = Parkinson's disease, n = 8) from patients with decreased dopamine D2 receptors (group 2 = other extrapyramidal syndromes, n = 9) using 123I-iodolisuride SPET (ILIS-SPET). 123I-iodolisuride (190 +/- 31 MBq) and 99Tcm-ethyl cysteinate dimer (99Tcm-ECD) perfusion SPET were performed in the same position, with a dual-headed gamera camera equipped with fan beam collimators. Both a geometric approach (ellipse, circle or rectangle) and an anatomical approach using the CT scan and perfusion SPET as anatomical guides were used to draw striatal and reference ROIs. A total of 33 different parameters were calculated for each patient, indicating the ratio of counts between the striatal and reference ROIs (frontal, occipital cortex or cerebellum) and the asymmetry between the right and left striatum. More significant differences between group 1 and group 2 were found by using geometric ROIs than by using anatomical ROIs. The most discriminant ratios were the caudate/occipital, caudate/frontal and striatum/occipital ratios (P = 0.001, P = 0.002, P = 0.003 respectively). A close correlation was found between the striatum/caudate and striatum/occipital ratios, but not between the striatum/frontal and striatum/occipital ratios or between the striatum/frontal and striatum/caudate ratios. We conclude that the occipital cortex is the best reference for the semi-quantitative evaluation of dopamine D2 receptors as the frontal cortex could include some dopamine D2 receptor-bound radioligand, and that the caudate/occipital ratio is an appropriate parameter for differentiating Parkinson's disease from non-Parkinson extrapyramidal syndrome by 123I-iodolisuride SPET.

Adult↗
PubMed1998

Effects of neonatal focal cerebral hypoxia-ischemia on sleep-waking pattern, ECoG power spectra and locomotor activity in the adult rat.

The aim of this study was to determine the influence of neonatal focal cerebral hypoxia-ischemia (HI) on sleep-waking pattern, electrocorticogram (ECoG) power spectra and locomotor activity (LA) in adult Wistar rats. Seven-day old pups were subjected to permanent unilateral ligation of the common carotid artery and transient hypoxia (8% O2). At 10 weeks of age, the extent of brain damages was evaluated by magnetic resonance imaging (MRI) and homogenous injured animals were selected before chronic implantation of radiotelemetry device. Using a single ECoG recording channel method, waking (W), paradoxical sleep (PS) and slow wave sleep (SWS) were continuously recorded for 72 h and they were semi-automatically analyzed off-line. We observed that neonatal HI triggers a cascade of events leading, in adult rats, to brain dysfunction characterized by an increase in SWS (55.0 vs. 40.2% in sham-operated rats, p<0.05) and a marked decrease in W phases duration (43.4 vs. 51.5%, p<0.05) while PS was almost suppressed in HI rats (1.6 vs. 8.3%, p<0.05). In addition, power spectral analysis of ECoG revealed significant (p<0.05) alteration in PS power density with a shift of the dominant frequency peak (5.0 to 7.5 Hz for HI and sham-operated rats, respectively). During the light period, we found that HI induced a pronounced reduction of LA (-30%, p<0.05). These results indicate that Wistar rats exposed to a neonatal unilateral cerebral HI present significant ECoG activity, sleep-waking pattern and behavioral disturbances when adults. However, it remains to establish whether such alterations can be prevented by neuroprotective agents.

Animals↗
PubMed1998

Influence of neonatal focal cerebral hypoxia-ischemia on cardiovascular and neurobehavioral functions in adult Wistar rats.

No experimental studies looked at the disturbances appearing after a neonatal focal cerebral hypoxia-ischemia (HI) when animals become adults. Using radiotelemetry, we examined the effects of neonatal focal cerebral HI on blood pressure (BP), heart rate (HR), locomotor activity (LA), body temperature (BT) levels and circadian rhythm parameters of unrestrained adult Wistar rats. At 15 weeks of age, we continuously recorded the cardiovascular and neurobehavioral parameters of HI (n = 6) and sham-operated (n = 6) rats. In adult rats, HI induced persistent hypertensive effects associated with alteration in BP circadian rhythms and pronounced decreases in mesor and percent rhythm of LA. HR and BT parameters were not significantly modified. Therefore, our results suggest that the rat cardiovascular and behavioural circadian control systems may involve several structures which present selective vulnerability to early cerebral HI.

Animals↗
PubMed1998

Feto-maternal circulation: mathematical model and comparison with Doppler measurements.

OBJECTIVES: Clinicians are more and more frequently studying fetal blood flow velocity curves recorded by Doppler ultrasound in vital organs such as the placenta and fetal brain to evaluate fetal well-being. We have therefore developed a mathematical model of the utero-placental and fetal circulations which could be used for teaching and for a better understanding of regulatory mechanisms. METHODS: The model is based on two basic elements-an arterial segment and a bifurcation-and we have reproduced the major arteries of the feto-maternal circulation combining these basic elements. The mathematical model of the system is based on the Navier-Stokes equations. The peripheral areas such as the brain, kidneys and placenta are modeled by a simple Windkessel model and the model computes instantaneous flow and pressure at any point in the fetal arterial tree and the uterine arteries. RESULTS: We have compared the computed instantaneous flow curves and pressure with in vivo data and our results agree with the findings in physiological situations and in gravidic hypertension. CONCLUSIONS: Our model provides new interesting insights into fetal hemodynamics such as a better understanding of the mismatch impedance phenomena and is a promising model for the study of blood redistribution mechanisms in hypoxic situations.

Blood Vessels↗
PubMed1998

Exploration of the dopamine transporter: in vitro and in vivo characterization of a high-affinity and high-specificity iodinated tropane derivative (E)-N-(3-iodoprop-2-enyl)-2beta-carbomethoxy-3beta-(4'-m ethylph enyl)nortropane (PE2I).

For the diagnosis and follow-up of neurodegenerative diseases, many cocaine derivatives have been proposed as radioligands to explore the dopamine transporter. As none of them have all the criteria of specificity and kinetics for human use, we have developed a new derivative, (E)-N-(3-iodoprop-2-enyl)-2beta-carbomethoxy-3beta-(4'-methy lphenyl)nortropane (PE2I), which displays promising properties. We report the characterization of PE2I in vitro on rat striatal membranes and in vivo in rats and in monkeys. PE2I had a high affinity (Kd = 0.09 +/- 0.01 nM) and high specificity for the dopamine transporter. In rats we observed a high accumulation in the striatum; by contrast, a very low fixation was measured in the cortex. Moreover, a preinjection of a saturating dose of GBR 12909 prevented the striatal accumulation of PE2I by 74%. These results confirmed the specificity of PE2I for the dopamine transporter. In vivo in monkeys, SPECT studies showed a high accumulation in striatum. Moreover, an equilibrium state was obtained 1 h after injection. PE2I seemed to be the most promising ligand for the dopamine transporter exploration by SPECT using a single-day protocol.

Animals↗
PubMed1998

Distance of foetal movement measured using the analytical signal derived from non-directional Doppler sound.

Foetal heart rate (FHR) monitoring using the Doppler shift resulting from the movements of the foetal heart is a standard examination in most obstetrical wards. Other movements also give rise to a low frequency Doppler shift. These signals are incompletely understood. Their characteristics may offer a way for diagnostic exploitation through complementing or replacing time consuming ultrasound observation of foetal movements. It is shown that a wealth of information is contained in these signals which can easily be extracted on line by a standard PC computer using straightforward methods of signal processing. In its amplitude an ultrasonic Doppler signal contains information concerning the size of the reflector in movement and speed as frequency. The displacement of the reflector can also be derived from the phase evolution of a complex Doppler signal. Examples of signals generated by various types of foetal activity are shown and analyzed.

Female↗
PubMed1998

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.

Computer Simulation↗
PubMed1998

[Esophageal morphology with ultrasound imaging after laryngectomy: effect on quality of esophageal speech].

PURPOSE: In patients with aerodigestive cancer, laryngectomy places the esophagus in a superficial position, allowing easy ultrasound examination of this organ. The purpose of the present study was to assess oesophagus morphology after laryngectomy using echotomography and to compare this morphology with voice quality. MATERIAL AND METHODS: In the present study, ultrasonography was performed in 28 patients (delay from surgery: 3 +/- 3 years): 15 were operated using laryngectomy technique (LT) and 13 with pharyngolaryngectomy technique (PLT). On transversal echography, antero-posterior and latero-lateral diameters, esophagus area and dilatation during phonation were systematically measured. These data were compared to the voice quality assessed by two independent observers. RESULTS: A smaller latero-lateral diameter and area were found in the PLT group than in the LT group (p < 0.05) with a flat aspect in group LT. This was associated with faster and better voice acquisition in the PLT group. CONCLUSION: Morphologic study of the esophagus after laryngectomy using ultrasound is in favor of pharyngolaryngectomy technique which allows better conditions for acquiring esophageal voice in better conditions. This could be due to the small area, circle shape and tonicity of the esophagus after this type of surgery.

Esophagus↗
PubMed1997

Fetal heart modelling based on a pressure-volume relationship.

Study of the cardiovascular system of the human fetus is based on non-invasive measurement methods such as Doppler echography systems. The circulation conditions in fetal vessels are usually evaluated by resistance indices, giving limited physiological information on distal territories such as the placenta or the brain. To enhance the understanding of human fetal haemodynamics, a numerical model of the fetal heart has been developed, using the hydraulic-electric analogy. The model is based on a mechanical hypothesis of parallel functioning of the right and left ventricles, considered to have analogue elastance properties. Their behaviour is equivalent to that of a single ventricle ejecting an equivalent blood volume of 7 ml in the aorta. The characterisation of the equivalent ventricle is based on the determination of a set of four parameters (Emax, Vo, kv and Po) representing the maximum ventricle contractility, a reference volume, and volume and pressure constants, respectively. The model proposed is validated by studying the effects of preload and afterload variations on the fetal heart work, and by comparing the numerical results with literature and measured data. The model constitutes the first step towards a global model of the cardiovascular system of the human fetus.

Blood Pressure↗
PubMed1997

Non-invasive quantification of diaphragm kinetics using m-mode sonography.

PURPOSE: The standard conditions of spirometry (i.e., wearing a noseclip and breathing through a mouthpiece and a pneumotachograph) are likely to alter the ventilatory pattern. We used "time motion" mode (M-mode) sonography to assess the changes in diaphragm kinetics induced by spirometry during quiet breathing. METHODS: An M-mode sonographic study of the right diaphragm was performed before and during standard spirometry in eight patients without respiratory disease (age 34 to 68 yr). RESULTS: During spirometry, the diaphragm inspiratory amplitude (DIA) increased from 1.34 +/- 0.18 cm to 1.80 +/- 0.18 cm (P = 0.007), whereas the diaphragmatic inspiratory (T1 diaph) increased from 1.27 +/- 0.15 to 1.53 +/- 0.23 sec, (P = 0.015, without change in diaphragmatic total time interval (Ttot diaph). Therefore, the diaphragm duty cycle (T1 diaph/Ttot diaph) increased from 38% +/- 1% to 44% +/- 4% (P = 0.023). The diaphragm inspiratory (DIV) and expiratory (DEV) motion velocity (P = 0.007). CONCLUSION: M-mode sonography enabled us to demonstrate that the wearing of a nose clip and breathing through a mouthpiece and a pneumotachograph induce measurable changes in diaphragm kinetics.

Adult↗
PubMed1997

[Cerebral HITS: diagnosis, clinical relevance, outlook].

After 6 years of experience, Spencer and colleagues described the detection of embolus signals as height intensity transient signals (HITS) within Doppler flow spectrum from intracranial vessels. These signals (gaseous or materials) are recorded in many situations such as cardiac prosthetic valves, atrial fibrillation, carotid stenosis, carotid surgery or angioplasty. The clinical value is not well known: neurological impairment associated with brain lesions is described in case of cardiac prosthetic valves. The observation of HITS in carotid stenosis is associated with an increased risk of stroke. The detection of HITS offers a new orientation in studying stroke but some technical and/or clinical difficulties have to be solved.

Carotid Stenosis↗
PubMed1997

Ultrasound contrast agents. Examples of blood pool agents.

PURPOSE: The concept of contrast agents has been extended to ultrasonography (US) almost 30 years ago. Due to technical limitations, the development of US contrast agents (USCA) was slow until the last decade. The ideal USCA should be nontoxic, i.v. injectable, capable to cross the pulmonary capillary bed after a peripheral injection, and be stable enough to achieve enhancement for the total duration of the examination. It should provide not only Doppler but also B-mode enhancement, at a reasonable cost. The efficacy of the most advanced USCA has been reviewed. RESULTS AND CONCLUSION: Doppler examinations improved in cases of deep or small vessels, vessels with low or slow flow, or vessels studied with a bad insonation angle. USCA also enhanced detection of flow within normal and abnormal vessels, including tumor and stenotic vessels. Ischemic areas were better delineated. Specific settings and software developed by US equipment manufacturers and US sequences (such as second harmonic imaging or transient imaging) prefigured the necessary adaptation of US units to the new potentials of USCA. Second harmonic properties will improve detection of smaller vessels including neovascularization associated with tumors. Targeting possibilities will increase the efficacy of USCA, and allow specific delivery of active drugs such as anticoagulants or cytotoxic compounds. New generations of USCA appear very promising, and are becoming part of the US future.

Contrast Media↗
PubMed1997

[Circulation and cerebral metabolism in neonatal hypoxia-ischemia].

The basic physiological variable in hypoxic-ischaemic brain injury is cerebral oxygen delivery. When oxygen delivery becomes insufficient to meet the cellular demands for oxygen, a sequence of biochemical events will be triggered leading to cell death. High levels of CBF following severe birth asphyxia is now well documented by Doppler ultrasound which has been shown to be a useful prognostic indicator following birth asphyxia. Near infrared spectroscopy (NIRS) is of great potential value since it may be used at the bed-sid and allows to measure the cerebral blood volume and the concentrations of cytochrome aa3. Magnetic resonance spectroscopy (MRS) allows noninvasive assessment of cerebral metabolism in asphyxiated neonates. 31P MRS has demonstrated that birth asphyxia leads to delayed impairment of cerebral energy metabolism and is predictive of later neurodevelopmental outcome. 1H MRS has shown lactate accumulation and a later decline in N-acetyl aspartate concentration.

Asphyxia Neonatorum↗