Search

Transcranial Doppler has been used previously to determine hemodynamic response to sensorial stimulation in adults but not in the neonatal period. Cerebral blood flow velocity (CBFV) was recorded in both middle cerebral arteries (MCA) and posterior cerebral arteries (PCA) in 100 premature neonates (male 56; female 44; 26 to 36 weeks gestation) from birth to 12 months. Brain development was evaluated on clinical examination. No difference in velocities was noted on prestimulation recordings from birth to 12 months. During light stimulation before six months, the CBFV was reduced (-11 +/- 6% in MCA and -13 +/- 5% in PCA compared with baseline values). After stimulation, the CBFV was increased (+6.7 +/- 3% in MCA and + 10.5 +/- 4% in PCA compared with baseline values). This study is in favor of cortex maturation in normal premature neonates at only six months. Consequently, functional transcranial Doppler technique will be helpful for the diagnosis of abnormal maturation timing in neonates with possible developmental retardation.

Fetal heart rate (FHR) monitoring is a crucial part of monitoring at-risk pregnancies and labor. Its aim is to detect any abnormalities that might indicate acute fetal distress and a need for rapid treatment to avoid death or serious sequelae, including cerebral handicap. The use of fetal biophysical profiles in high-risk pregnancies (gravidic hypertension, in utero infection, etc.) helps to distinguish healthy fetuses from those with chronic conditions. Fetal biophysical profile scores have been developed that integrate five biophysical parameters, one of which is derived from the FHR. The major parameters detected are the rate of fetal movements, fetal tone, fetal breathing movement and amniotic fluid volume. All of those parameters except FHR are obtained by prolonged echographic observation and cannot be used routinely. We developed in this study a new multigate multitransducer pulsed Doppler system for survey of fetal behavior. Fast Fourier transform and autocorrelation function have been used for processing and analyzing ultrasonic Doppler signals generated by fetal movements. Several parameters are analyzed in each of the 12 x 5 = 60 Doppler gates: amplitude of signals reflected by moving fetal structures, velocity, direction and amplitude of displacement of fetal structure (heart, chest, limbs). From these parameters it is possible to calculate FHR and characterize fetal activity. Preliminary in vivo results obtained in 15 pregnant women (30 to 36 wk) are very encouraging but they have yet to be confirmed in future studies. These results also demonstrate the advantages of transducers designed for improved fetal movement detection. The algorithms needs to be precise enough to allow the Actifetus system to function in real time. We now have at our disposal some algorithms that succeed in quantifying FHR and fetal movements with a signal from a given sensor at a given depth. This study confirms the feasibility of monitoring fetal movements by the Actifetus system and demonstrates the importance of the characterization of fetal rhythms (and fetal behavior). The Actifetus system will serve as a new mean for studying fetal response to environment and detecting anomalies related to fetal suffering.

Autoregressive (AR) modelling has already been proposed as an alternative to fast Fourier transform to process ultrasound (US) Doppler signals. Previous works introduced long AR models, set up under a regularization framework. The latter may be in 1-D (frequency) or 2-D (frequency and space or time). This study generalizes the spectrum regularization in the three dimensions frequency, space and time. The problem of the penalization function is addressed, and a new convex solution is proposed, taking into account possible nonstationarity of the Doppler signal. The parameter tuning is based on simulations using a standard Doppler signal model. The first results show that this processing improves the spectral estimation, and is well suited to flow interpretation.

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.

To enable the investigation of fetal movement in a manner similar to fetal heart rate (FHR) monitoring we have developed an apparatus (the DopFet system) that consists of a pair of miniature sensors, a 2-MHz continuous-wave directional Doppler electronic module and a laptop personal computer. One of the sensors is aimed at the fetal limbs and the other at the thorax to detect heart and upper body movements. The signals are analyzed, presented in real-time and postprocessed by software developed by us. The postprocessing software computes a number of parameters (the DopFet parameters) describing fetal movement. These parameters can be divided into two categories: parameters that describe the quantity of fetal movement (i.e., number of movements) and parameters that describe qualitative aspects of fetal movement (i.e., average movement duration). Future studies using the DopFet system will be aimed at discovering which of these parameters or combination of parameters is the best indicator of fetal well-being. We present an example of a 0.5 h recording and the results of testing on 23 volunteer mothers. These results show good sensitivity of the system compared to real-time ultrasound (US). The system detects 96% of rolling movements, 100% of flexion movements and 97% of leg movements.

To study the recovery periods of blood flow parameters in muscles after anaerobic exercise, instantaneous and mean blood flow velocity curves were recorded in the femoral artery in 22 sportsmen at rest and during the first 4 min of recovery after exercise (Ruffier-Dickson test). A flat ultrasonic probe connected to a Doppler system (Flow-Tester) was fixed on the skin at the level of the common femoral artery. From Doppler recordings, we calculated periods of recovery (return to baseline) of femoral blood flow velocity (FBFV RP), heart rate (HR RP) and femoral stroke distance (FSD RP). Also, Ruffier-Dickson index (RDI), VO(2)max in mL/kg(-1)/min(-1) and number of training hours were determined. We observed a high correlation between FBFV RP and VO(2)max (p = 0. 0002), and significant correlation between FSD RP and VO(2)max (p = 0.0238) and RDI (p = 0.0451). In conclusion, there is a excellent correlation between blood flow velocity recovery period in femoral artery after moderate exercise and VO(2)max in high-level sportsmen. The method of testing is simple and based on conventional Doppler technique. It can be used for the follow-up of training levels in sportsmen.

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.

In vivo ultrasonic characterization of the skin was performed at 40 MHz by estimating the slope of the attenuation coefficient in the human dermis. The centroid algorithm was first tested on simulated backscattered RF lines with a second-order autoregressive model to carry out the spectral analysis. A relative error of less than 8.5% and a relative precision of less than 6% were predicted for a 2-mm tissue thickness and for temporal window sizes ranging from 0.25 to 0.45 micros. In vivo measurements performed on 138 healthy volunteers yielded values of the attenuation coefficient slope ranging from 0.8 to 3.6 dB/cm MHz. A decrease was observed with advancing age, but no significant difference appeared between men and women. The results from this study suggest that this acoustic parameter shows the effect of the ageing process on normal skin tissue in vivo.

High spatial resolution is required for echographic exploration of the skin, microvessels or small laboratory animals. With the scanner described here, high resolution is obtained by means of a strongly focused, wide-band 17 MHz center frequency transducer (-6 dB bandwidth: 22 MHz). The movement of this transducer above the skin provides a 6 mm wide and 5 mm deep echographic cross-section with an image rate of 15 images/s. The resolution is about 0.08 mm in axial and 0.2 to 0.3 mm in lateral directions. The device was tested on phantoms in water and in vivo on normal and pathological skin in the Department of Dermatology. With the easy-to-handle probe, explorations were made on psoriasis, basocellular carcinoma, malignant melanoma and sarcoidosis.

Cardiovascular assessment by ultrasound methods was performed during two long duration (1 month) Head Down Tilt (HDT) on 6 healthy volunteers. On a first 1 month HDT session, 3 of the 6 subjects (A, B, C) had daily several lower body negative pressure tests (LBNP), whereas the 3 subjects remaining (D, E, F) rested without LBNP. On a second 1 month HDT session subjects D, E, and F had daily LBNP tests and the A, B and C subjects did not. The cardiac function was assessed by Echocardiography, (B mode, TM mode). On all the "6 non LBNP" subjects the left ventricule diastolic volume (LVDV), the stroke volume (SV) and the cardiac output (CO) increase (+10%, -15%) after HDT then decrease and remain inferior (-5%, -5%) or equal to the basal value during the HDT. Immediately after the end of the HDT the heart rate (HR) increase (+10%, +30%) whereas the cardiac parameters decrease weakly (-5%, -10%) and normalize after 3 days of recovery. On the "6 LBNP" subjects the LVDV, SV and CO increase (+10%, 15%) after 1 h HDT as in the previous group then decrease but remain superior (+5%, +15%) or equal to the basal value. After the HDT session, the HR is markedly increased (+20%, +40%) the LVDV and SV decrease (-15%, -20%) whereas the CO increases or decreases depending on the amplitude of the HR variations. These parameters do not completely normalize after 3 day's recovery. Repeated LBNP sessions have a significant effect on the cardiovascular function as it maintains all cardiac parameters above the basal value. The LBNP manoeuvre can be considered as an efficient countermeasure to prevent cardiac disadaptation induced by HDT position and probably microgravity.

A transcranial Doppler sonographic system with a special 2-MHz probe for prolonged experimentation has been developed for Doppler waveform recordings from the basilar artery on rabbits. Measurements were made from the maximum velocity wave form, and Pourcelot's resistance index was used to express the results. The diastolic flow, similar to that observed in humans in physiological conditions, decreases with increased intracranial pressure during chronic intracranial hypertension. This Doppler model may be valuable for assessing rapid changes of cerebral blood flow in conscious animals during prolonged or acute experimental procedures.

Radioiodinated m-iodobenzylguanidine [( 125I]MIBG) and tritiated norepinephrine [( 3H]NE]) uptake and release were compared, in different regions of the brain of the rat. The classification of the regions according to uptake was the same for both tracers:striatum greater than hypothalamus greater than hippocampus greater than cortex greater than brainstem. Tetrabenazine (TBZ), a granular monoamine uptake inhibitor reduced the uptake in the different regions. The inhibition rate was higher for [3H]NE uptake than for [125I]MIBG. The spontaneous release was the same for [125I]MIBG and [3H]NE and was the lowest in the striatum. The K+ stimulated release of [3H]NE was more complete than the release of [125I]MIBG and was the most important in the striatum. From these results, it is inferred that MIBG enters the brain tissue via NE uptake mechanisms. It appears that MIBG is stored in the chromaffin granules, as NE, but also in the cytoplasm. A modified molecule derived from MIBG which would cross the blood-brain barrier, would then appear as a potential scintigraphic marker of monoamine uptake, storage and release.

A study of a method for exploration of microvessels is presented. Theoretical considerations taking into account the backscattering of ultrasound wave from a red cell and the attenuation versus frequency (up to 180 MHz) show that a frequency in the range of 80 to 120 MHz is most favorable for small depths of exploration (300 microns). The characteristics of the 113 MHz Doppler system which was built are described. The minimum detectable signal is 3 microV, the lateral resolution around 20 microns and the minimum length of the Doppler sample volume about 80 microns. The Doppler data are displayed in the form of a frequency spectrum. The first encouraging tests carried out using 20 microns rectangular glass capillary tubes and 50 to 150 microns microvessels of the mesentery of rat have demonstrated the resolution and the sensitivity of the system. A discussion illustrates the difficult problem of motion artefacts and the improvements which have to be made. From a technical point of view the authors think that it is possible to work with such a high frequency but there are two main difficulties: the processing of a very low frequency Doppler spectrum and the optimization of the probe (dimensions and shape).

The uptake and release of mIBG, a tracer of the monoamine uptake and storage function, were studied on superfused rat cerebral cortex sections. mIBG was taken up and released by a mechanism comparable to that of norepinephrine (NE), but this storage appeared to be less specific for mIBG than for NE. This implies that when mIBG is used as a scintigraphic tracer of monoaminergic synaptic vesicles, imaging should be delayed long enough to ensure release of the molecule from its nonspecific binding sites.

Main results of cardiovascular investigation, performed with ultrasound methods during the common French/Soviet flight aboard Salyut VII in June 1982, are compared to variations of the same parameters studied during ground-based simulations on the same subject or observed by other investigators during various ground-based experiences. The antiorthostatic bed rest simulation partly reproduces microgravity conditions and seems to be better adaptated to cardiac hemodynamics, despite some differences, and to the cerebral circulation, than to the inferior limb circulation.

A system for the exploration of deep vessels is proposed. This device is based on a single 300 element linear array in which a "Doppler area" is selected to electronically steer a Doppler beam. Characteristics of the equipment are excellent and it is as easy to handle as a simple linear array scanner. A real-time spectrum analyser is used to process the Doppler signals. The probe and the associated electronics are described and some results are given to illustrate the capabilities of the device such as blood flow estimation and deep vessel studies.

The umbilical circulation can be investigated by Doppler ultrasound techniques very easily. The Doppler frequency spectrum from the umbilical arteries provides information on the placental circulation. The diastolic flow amplitude is directly related to the vascular resistances of the placenta (Rp). In cases of pathological pregnancies with hypertension the decrease of the diastolic flow and the increase of the resistance index Rp have been correlated with intrauterine fetal growth retardation. Fetal cerebral arteries have also been explored during normal pregnancies (n = 40). The index of cerebral resistance (Rc) as defined by Pourcelot is Rc = S-D/S (with S systolic amplitude and D diastolic amplitude) and shows variations similar to the placental index. During normal pregnancy, the cerebral index is higher than the placental index and the cerebro-placental ratio (Rc/Rp) is greater than 1. This preliminary study of both umbilical and cerebral circulation seems to demonstrate that during pathological pregnancies with hypertension (n = 21), with fetal growth retardation one of the indices, Rc or Rp may be out of the normal range but the cerebro-placental ratio (CPR) is always less than 1. However a larger number of patients should be explored in order to evaluate the clinical usefulness of such an observation.