Biomedical subjects

J P Guglielmi

Publications and source records attributed to J P Guglielmi.

10 recordsLinked to original sources

PubMed2000

Fluid mechanics of regurgitant jets and calculation of the effective regurgitant orifice in free or complex configurations.

The velocity fields of turbulent jets can be described using a single formula which includes two empirical constants: k(core) determining the length of the central core and k(turb) the jet widening. Flow models simulating jet adhesion, confinement and noncircular orifices were studied using laser Doppler anemometer and the modifications of the constants were derived from series of velocity profiles. In circular free jets, k(core) was found equal to 4.1 with a variability of 1.4%. In complex configurations, its variability was equal to 15.2%. For k(turb), the value for free circular jets was of 45.2 with a variability of 6.0% and this variability in complex configurations was significantly higher (30. 1%, p=0.025). The correlation between the actual orifice size and the jet extension was poor (r=0.52). However, the almost constant value of k(core) allowed to define a new algorithm calculating the regurgitant orifice diameter with the use of outlines of the jet image (r=0.89). In conclusion, the fluid mechanics of regurgitant jets is modified in complex configurations but, due to the relative independency of the central core, velocity fields could be used to evaluate the dimensions of the effective regurgitant orifice.

Algorithms↗

PubMed1996

In vitro flow mapping of regurgitant jets. Systematic description of free jet with laser Doppler velocimetry.

BACKGROUND: Color Doppler and magnetic resonance imaging give pictures of abnormal jets within which the respective contribution of fluid mechanics and image artifacts are difficult to establish because of current technical limitations of these modalities. We conducted the present study to provide numerical descriptions of the velocity fields within regurgitant free jets. METHODS AND RESULTS: Laser Doppler measurements were collected in rigid models with pulsatile flow conditions, giving several series of two-dimensional flow images. The data were studied with the use of two-dimensional or M-mode flow images as well as regular plots. Numerical descriptions validated in steady flow conditions were tested at the various times of the cycle. In these free jets, the momentum was conserved throughout the cycle. The transverse velocity profiles were approximately similar. A central laminar core was found at peak ejection and during the deceleration. Its length (l = 4.08 d-0.036 mm, r = .99) and its diameter (d) were proportional to the orifice diameter. At peak ejection, the velocity decay was hyperbolic, and the transverse velocity profiles were clearly gaussian. The different relations that were tested could be combined in a single formula describing the velocity field: V(x,y,t peak) = V(O,O,t peak).4.(d/x).10(-45(y/x)2) (r = .92). CONCLUSIONS: These in vitro measurements demonstrated the presence of a central laminar core and similar transverse velocity profiles in free turbulent jets. This allowed us to validate a series of numerical relations that can be combined to describe the velocity fields at peak ejection. On the other hand, further studies are needed to describe the various singularities often encountered in pathology.

Heart Valve Diseases↗

PubMed1991

Adaptive estimation of the mean frequency of a Doppler signal from short data windows.

The color Doppler estimator (CE1), which is calculated from the phase of the first correlation lag of the Doppler signal, is compared to the general mean frequency estimator (CEn), which is based on a weighted summation of all the available correlation lags, for long and short Doppler data sets (typically 48 and 8 Doppler samples). A new estimator of the Doppler signal mean frequency is derived from the results of this study. It optimizes the compromise between the range of analyzable frequencies and the estimation variance for the characteristics of the Doppler signal. Demonstration is provided that the behavior of this estimator shifts from that of CE1 to that of CEn, according to the setting of a single parameter. An adaptive version of this estimator is implemented and applied to Doppler recordings. Applications can be contemplated for color Doppler imaging.

Algorithms↗

PubMed1990

In vitro analysis of a model of intracardiac jet: analysis of the central core of axisymmetric jets.

In order to provide physical information supporting the clinical use of flow mapping, an in vitro model was designed to measure the velocity fields in a pulsatile hydraulic turbulent jet. We used a peak velocity ranging from 2.5 to 5.5 m.s-1, an orifice diameter ranging from 5.8 to 11.3 mm and confined the jet in a receiving tube whose diameter ranged from 16 to 30 mm, thus simulating a large variety of valvular leaks. In steady flow conditions, our results agreed with previously reported descriptions. Under pulsatile conditions, the same structure was found at peak velocity and during the beginning of the deceleration. Below a threshold velocity, the length of the central core was independent of the peak velocity and proportional to about six times the orifice diameter. Above the threshold velocity, this relationship was no longer true, the threshold value being related to the ratio of the orifice diameter to the diameter of the receiving tube.

Blood Flow Velocity↗

PubMed1989

High-resolution, reflection mode tomographic imaging. Part I: Principles and methods.

A general method for improving image resolution is derived and applied to ultrasound signals; it combines the principles of both reflection mode tomography and deconvolution. The different possibilities of applying these principles allow two types of approaches to be defined, depending upon whether image reconstruction is achieved on radiofrequency or detected signals. A thorough description of three methods that are of particular interest due to their lower computation costs is presented, and their results quantified. They permit a gain in resolution of the order of ten with respect to two-dimensional deconvolution of images, as well as an improvement of the S/N ratio, which is related to the square root of the number of projections used in the reconstruction process, and a decrease of about four in computation time.

Humans↗

PubMed1989

High-resolution, reflection mode tomographic imaging. Part II: Application to echography.

Principles of high-resolution, ultrasonic imaging using data acquisition by a compound scanning with a sector echograph are presented. The signal processing is based on both deconvolution and reflection mode tomography. Three of the methods that can be derived from these principles are selected due to their lower computation costs. Applications of these methods to synthetic data and test targets demonstrate that, with respect to 2D deconvolution, they offer: a gain in computation time of more than 8, an improvement in resolution of the order of 10 and an increase of S/N ratio of the order of 4. Finally, both the effects of limited acquisition angular window and of a variable propagation speed are illustrated.

Humans↗

PubMed1987

Quantification of aortic regurgitation using Doppler imaging.

Aortic insufficiency induces the development of a jet within the left ventricular outflow tract. The cross sectional area of this jet at its origin is the major determinant of the severity of the regurgitation. M mode Doppler imaging reportedly allows the measurement of jet diameter. This study was designed to evaluate the quantification of aortic regurgitation using a measurement of the jet diameter by M mode Doppler imaging. The left ventricular outflow tract of 32 patients was imaged using either a multigate pulsed Doppler velocimeter of color flow mapping system (Hewlett Packard). The jet diameter was compared to a 4 grade semiquantification derived from supravalvular aortography. Adequate imaging was obtained in the 32 patients. Four of them had no regurgitation: no diastolic flow image could be found during their Doppler investigation. A clear jet image was obtained in the 28 remaining patients. We found a close relationship between the jet diameter (jd in mm) and the angiographic grade (ag): jd = 2.4 + 6.1 ag, r = 0.88, the most significant differences being found between grade 0 and grade 1, and grade 1 and grade 2. In conclusion, direct M mode measurement of the regurgitant jet of aortic insufficiency at its origin offers an additional approach of the severity of the leak.

Adult↗

PubMed1987

Limitations of ultrasound imaging and image restoration.

The definition of medical ultrasound images is strongly limited by the need for low examination frequencies which is imposed by the high attenuation of acoustic waves in tissues. The filtering effect of imaging systems is described and quantified for echography, transmission tomography and reflection tomography. Improvement of image definition is demonstrated to be the result of a numerical restoration of the received echoes implemented, in the present case, by a simplified Kalman filter. The improvement in definition obtained is emphasized on simulated data and tissue images. The comparison between the results obtained from the three techniques shows that: if only echography provides a real-time acquisition of signals, tomographic methods lead to faster processing associated with a better signal-to-noise ratio on the reconstructed images, and reflection tomography offers the best definition.

Animals↗

PubMed1987

Doppler imaging of regurgitant jet in aortic insufficiency: experimental validation and preliminary clinical evaluation.

Aortic insufficiency induces the development of a jet within the left ventricular outflow tract. The diameter of a laminar jet is a well-defined hydraulic parameter. This study was designed to evaluate, both experimentally and in patients, the accuracy of its measurement using a Doppler imaging performed with a multigate pulsed Doppler velocimeter. The experimental validation was conducted on a water tank pulsatile model including calibrated orifices. Jet images appeared clearly delineated and were not modified when changing imaging angulation (from 85 degrees to 65 degrees), pump frequency (from 60 to 100 c min-1), pump output (from 0.5 to 3.8 l min-1), wall filtering, orifice shape, or signal-to-noise ratio. The measured jet diameter (jd) correlated closely with the orifice diameter (od): jd (mm) = 1.22 + (0.79 X od), r = 0.98. A preliminary clinical evaluation was performed on jets of aortic insufficiency on a series of 26 patients. Jet cross-section was studied within the left ventricular outflow tract using a parasternal approach. A high setting of wall filters allowed good quality imaging in 24 patients. In the absence of a diastolic jet, jd was taken equal to 0. Measured jet diameters were compared to the angiographic grade (ag): jd (mm) = 2.7 + (3.9 X ag), r = 0.86. In conclusion, jet diameter measurement using M-mode Doppler imaging is experimentally accurate and potentially valuable in patients with aortic insufficiency.

Aortic Valve Insufficiency↗

PubMed1983

Estimation of blood-flow quality by statistical analysis or an ultrasonic Doppler signal: application to the study of perturbations caused by a vascular stenosis.

The noninvasive detection of pathological stenoses by Doppler ultrasound velocimetry is based on the appearance of modifications in velocity waveform or of a local increase in velocity. Nevertheless, these methods suffer from a lack of sensitivity. An extension of ultrasonic velocimetry including a statistical treatment of the Doppler signals affords a quantitative approach to the flow quality and seems to be able to improve the diagnosis of vascular obliterans. Accordingly a perturbation index can be computed on a microprocessor as the relative standard deviation of the zero-crossings histogram of the Doppler signal. A theoretical and experimental approach has been attempted to validate this method. Moreover, this index has been tested in vitro on calibrated flows. The in vivo experiments, performed on the abdominal aorta of the dog with artificial stenoses (0 to 50% in diameter) show a significant increase in the index value downstream from the stenosis. The relative increase of the index is greater than that of velocities for the same degree of obstruction. At the moment, it is possible to detect stenoses of 20% and above. It should be noted that changes in the perturbation index can be observed on a large part of the arterial segment, in relation with the severity of teh stenosis. Taking into account the increase in the index value and the length of the disturbed zone downstream of the stenosis, an estimation of the severity itself can be attempted. Clinical applications are in progress pointing out the diagnostic and prognostic abilities of the index method. The index perturbation method adds to velocity measurement the possibility of blood flow stability estimation. It appears useful for the localisation of stenoses, offers the possibility of quantifying their severity and could help the prognosis of their development.

Animals↗