SEARCH · PubMed Health

Results for “Doppler Effect”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources

PubMedDate not supplied

[Basic characteristics of duplex sonography in the assessment of lower limb arterial circulation].

INTRODUCTION: Dulpex and color duplex ultrasonography of lower limb arteries are valuable non-invasive diagnostic methods in the pathology of vascular diseases and a major step in diagnostics and in follow-up of hemodynamic and morphologic characteristics. COLOR DUPLEX SONOGRAPHY: The method consists of image analysis and analysis of Doppler information. Real-time-B mode is used to visualize the anatomy of blood vessels and other pathological lesions. Doppler information based on the Doppler effect determine the pulse wave i.e. the shape of flow velocity--hemodynamic characteristics. Spectral analysis is the most important element of Doppler examination of the lower limb peripheral arteries. Based on the spectral analysis, there are four stages of lower limb arterial disease: normal findings--1% - 19% diameter reduction; medium stenosis--artery diameter reduction of 20% - 49%; high level stenosis--artery diameter reduction of 50% - 100%; occlusion--no flow detected within the imaged arterial segment. In the first place, both iliac arteries are examined, which is followed with femoral, popliteal and crural arteries. The examination of iliac arteries is carried out with a 3.5 MHz transducer, and other peripheral arteries of the lower limbs are examined with a 7, 5 or 5 MHz transducer. CONCLUSION: Color Doppler is an extremely valuable diagnostic method in detecting pathology of the lower limb arteries. With high reliability level arterial insufficiency and pathological arterial segments are diagnosed by a duplex-Doppler.

Arteries↗

PubMed1995

Normal uterine arterial blood flow in postmenopausal women assessed by transvaginal color Doppler sonography: the effect of hormone replacement therapy.

We used transvaginal color Doppler sonography to study the effect of hormone replacement on the uterine arterial blood flow for 203 postmenopausal women. The regimens studied involved estrogen replacement alone, continuous combined estrogen and progestogen, and estrogen followed sequentially by combined estrogen-progestogen. The mean pulsatility index fell to 65% +/- 9% and the mean resistive index fell to 87% +/- 4% of baseline during the first month of therapy (P < 0.0001). The addition of a progestogen did not alter the effect of estrogen alone (P > 0.5). Our findings suggest that the increase in vascular flow occurs even in women who begin therapy long after menopause.

Arteries↗

PubMed1994

Ultrasonic colour flow imaging.

Real-time ultrasonic colour flow imaging, which was first demonstrated to be feasible only about a decade ago, has come into widespread clinical use. Ultrasound is scattered by ensembles of red blood cells. The ultrasonic frequency that gives the best signal-to-noise ratio for backscattering from blood depends on the required penetration. The frequency of ultrasound backscattered from flowing blood is shifted by the Doppler effect. The direction of flow can be determined by phase quadrature detection, and range selectivity can be provided by pulse-echo time-delay measurements. The Doppler frequency spectrum can be determined by Fourier analysis. Early two- and three-dimensional flow-imaging systems used slow manual scanning; velocity colour coding was introduced. Real-time colour flow imaging first became feasible when autocorrelation detection was used to extract the Doppler signal. Time-domain processing, which is a broad-band technique, was also soon shown to be practicable, for analysing both radio-frequency pulse-echo wavetrains and two-dimensional image speckle. Frequency- and time-domain processing both require effective cancellation of stationary echoes. The time-domain approach seems to have advantages in relation to both aliasing and the effects of attenuation in overlying tissues. Colour-coding schemes that can be interpreted without the need to refer to keys have been adopted, for both velocity and flow disturbance. Colour coding according to signal power has also been reintroduced. Three-dimensional display has been demonstrated. In interpreting colour flow images, it is important to understand the functions of critical system controls and the origins of artifacts. Various strategies can be adopted to increase the image frame rate. The problems of performance measurement and safety need to be kept under review. There are numerous opportunities for further development of ultrasonic colour flow imaging, including improvements in system design, methods of image display, the use of contrast agents and the solution of previously unexplored clinical problems.

Blood Flow Velocity↗

PubMed1999

Echocardiography in intensive care: the basics. Part I.

OBJECTIVE: To review the current status of echocardiography in critically ill patients with special reference to the advantages and disadvantages of the transthoracic and transoesophageal approaches. DATA SOURCES: A review of articles published in peer reviewed journals from 1976-1999 and identified through a MEDLINE search on echocardiography. SUMMARY OF REVIEW: Echocardiography uses the reflection of high frequency sound waves at tissue boundaries to construct a two-dimensional image of cardiac structures. Two-dimensional echo-cardiography is the cornerstone of cardiac ultrasound, although Doppler techniques (pulsed wave, continuous wave, and colour flow) form an integral part of every modern echocardiographic study. The Doppler effect is based on changes in sound frequency that occur when a sound source moves towards or away from an observer. Blood flow velocities measured by Doppler can be used to estimate pressure, valve area and stroke volume. The standard imaging positions of the probe are either outside the thorax (i.e. transthoraracic echocardiography or TTE) or inside the oesophagus (i.e. transoesophageal echo-cardiography or TOE) both of which provide information that can be helpful in managing critically ill patients. CONCLUSIONS: Echocardiography is a rapidly developing technology. Cardiac structures can be imaged in 'real time'. Image quality continues to improve. The use of transoesophageal probe positioning has also widened the potential of this bedside technique in critically ill patients.

Journal Article↗

PubMed1997

[Doppler color ultrasonography with contrast media in the study of eye and orbit neoplasms].

We investigated the diagnostic efficacy of the i.v. administration of a sonography (US) contrast agent to study eye and orbit tumors at different stages. We administered Levovist (Schering), an air microbubble stabilized by fatty acid, which is specific for angiographic indications. Baseline color Doppler US was performed on 24 selected patients and tumor vascularization patterns were classified into three classes. Color Doppler signal enhancement was assessed after contrast agent administration and the signal-to-noise ratio (SNR) was improved in 70% of cases, which helped identify vascular patterns and improved flowmetric accuracy. The Doppler effect was also improved and vascular signal was always enhanced. The SNR was improved also by the postcontrast detection of small vessels missed on baseline scans. Doppler signal enhancement was proportional to precontrast vascularization and depended on tumor size, with poor results in lesions < 5 mm. In contrast, vascular signal spots with increased postcontrast echogenicity sometimes caused excessive noise affecting the results. No correlation was found between signal enhancement and lesion histotype or between signal and lesion site. Treated lesions exhibited poorer contrast agent enhancement. The examination technique must be accurate and the various parameters set optimally, especially the velocity scale, gain and filtration; the unit must feature adequate recording capabilities (mm/s). To conclude, we believe that the routine use of i.v. US contrast agents will play a major role in improving diagnostic imaging in oculistics also thanks to the lack of untoward reactions and to the ease of contrast agent preparation.

Adult↗

PubMed2003

An analytical image reconstruction algorithm to compensate for scattering angle broadening in Compton cameras.

Compton cameras have been developed for use in gamma-ray astronomy and nuclear medicine. Their defining merit is that they do not need collimators; however, on the demerit side, they need inversion procedures for image reconstruction, since a measured datum is proportional to the integration of incident gamma rays along a cone surface with the same Compton scattering angle. First, an iteration method was adopted for this task. Later, analytical methods were found under restricted conditions. Parra (2000 IEEE Trans. Nucl. Sci. 47 1543-50) deduced a purely analytical reconstruction algorithm for a complete set of scattering-projection data that include data at all the scattering angles. Tomitani and Hirasawa (2002 Phys. Med. Biol. 47 2129-45) found that by making a slight modification, Parra's algorithm could be extended to the scattering-projection data in limited scattering angles. However, their algorithm neglected the effects of practical problems that cause the degradation of spatial resolution. Sources of degradation were identified as noise in the energy signal of their front detector and the Doppler effect in the scattering process. In this paper, we first analyse the effects of these sources on the angular resolution of the scattering-projection data and then present a revised reconstruction algorithm in which these two factors are incorporated. Simulation studies on digital phantoms reveal that the algorithm can reconstruct images even when these two factors are included.

Algorithms↗

PubMed2000

Composite medium with simultaneously negative permeability and permittivity

We demonstrate a composite medium, based on a periodic array of interspaced conducting nonmagnetic split ring resonators and continuous wires, that exhibits a frequency region in the microwave regime with simultaneously negative values of effective permeability &mgr;(eff)(omega) and permittivity varepsilon(eff)(omega). This structure forms a "left-handed" medium, for which it has been predicted that such phenomena as the Doppler effect, Cherenkov radiation, and even Snell's law are inverted. It is now possible through microwave experiments to test for these effects using this new metamaterial.

Journal Article↗

PubMed2005

Antenatal corticosteroid therapy: a comparative study of dexamethasone and betamethasone effects on fetal Doppler flow velocity waveforms.

OBJECTIVE: To compare the effects of antenatal administration of dexamethasone and betamethasone, used in two different regimens, on fetal Doppler flow velocities. STUDY DESIGN: Sixty-seven women at risk for preterm delivery received course of corticosteroids by means of a computer-generated randomization table. The Doppler examination of the pulsatility index (PI) of the umbilical artery (UA), the middle cerebral artery (MCA) and the middle cerebral artery/umbilical artery PI ratio (MCA PI/UA PI) were performed before treatment, 24 and 72 h after the first dose of corticosteroids. The SAS system was used to perform statistical analysis. RESULTS: No significant change was observed in UA PI through dexamethasone therapy. In MCA there was a significant decrease in PI at 72 h (2+/-0.43 before and 1.68+/-0.31 after, p=0.0001). Similarly a significant decrease in MCA PI/UA PI ratio was noted (2.09+/-0.51 before and 1.83+/-0.4 after, p=0.0137). No significant changes were observed in UA PI, MCA PI and MCA PI/UA PI ratio during betamethasone treatment. CONCLUSIONS: Our results indicate significant decrease in fetal middle cerebral artery impedance at 72 h after maternal administration of the first dose of dexamethasone. Effects of dexamethasone on fetal brain warrants further research.

Betamethasone↗

PubMed2004

Doppler application in the delivery timing of the preterm growth-restricted fetus: another step in the right direction.

This article provides an opinion on a study of relationships between umbilical artery (UA) Doppler, ductus venosus (DV) Doppler, fetal heart rate variation, and perinatal outcome in preterm, intrauterine growth-restricted (IUGR) fetuses published in the same issue of this journal by Bilardo and coworkers. Recent evidence on venous Doppler surveillance in preterm IUGR fetuses was also reviewed and discussed in the context of the study with a special emphasis on delivery timing. A search was conducted through MEDLINE and eight articles with similar inclusion criteria and reporting format of outcomes were identified. Numbers for perinatal mortality, intraventricular hemorrhage, respiratory distress syndrome, bronchopulmonary dysplasia and necrotizing enterocolitis (NEC) were extracted for cases where Doppler status was recorded in an identical format. Proportional distribution of outcomes was compared for fetuses with normal DV Doppler velocimetry, absent or reversed UA end-diastolic velocity (UA A/REDV), elevated DV Doppler index (abnormal DV) and absence or reversal of atrial velocity in the DV (DV-RAV). A total of 320 fetuses with normal and 202 with elevated DV Doppler indices were extracted. Of these fetuses, 101 with UA A/REDV only and 34 with DV-RAV were identified. Perinatal mortality was 5.6% (16/282) with normal DV, 11.9% (12/101) with UA A/REDV, 38.8% (64/165) with abnormal DV and 41.2% (7/17) with DV-RAV. With the exception of NEC, all complications were significantly more frequent with abnormal DV. With normal venous Doppler neonatal deaths account for most of the perinatal mortality, while with abnormal DV stillbirths and neonatal mortality are similar contributors to the significantly increased perinatal mortality. In conclusion, UA Doppler is a placental function test that provides important diagnostic and prognostic information in preterm IUGR. DV Doppler effectively identifies those preterm IUGR fetuses that are at high risk for adverse outcome (particularly stillbirth) at least 1 week before delivery, independent of the UA waveform. Relationships between perinatal outcome, arterial and venous Doppler status and gestational age require ongoing observational research effort. Randomized management trials are necessary to verify that delivery timing based on venous Doppler will impact on outcome in preterm IUGR.

Biomedical Research↗

PubMed1981

[Venous Doppler ultrasonography. Methods, indications and limits].

The analysis of velocities by the Doppler effect has limited applications in venous pathology. There are, however, many potential advantages: the introduction of deep venous catheters, early diagnosis of venous thrombosis, studies of venous incompetence, right sided cardiopathies, follow-up of medical and surgical treatment (thrombolytics, venous thrombectomy, bypass surgery, vena cava clips). The results in a series of venous thrombosis are reported: the correlation between Doppler and phlebography was 86,5% in 110 investigations. Doppler sensitivity was 86% and specificity 91%. These results are compared to other reports. A 90% correlation was found with isotope venography in 32 cases in which the permeability of vena cava clips was studied. The sensitivity of doppler in the diagnosis of thrombosis of the clip was 75% and its specificity 100%. The main limitations were the lack of sensitivity in the diagnosis of distal thrombosis and incomplete occlusion (floating thrombi). As a complement to occlusive plethysmography and other non-invasive investigations, Doppler ultrasonography helps determine the indications for phlebography. It is useful in detecting high risk patients and is a sensitive, effective non-invasive method of surveillance in the postoperative period.

Catheterization↗

PubMed2004

The history of echocardiography.

Following a brief review of the development of medical ultrasonics from the mid-1930s to the mid-1950s, the collaboration between Edler and Hertz that began in Lund in 1953 is described. Using an industrial ultrasonic flaw detector, they obtained time-varying echoes transcutaneously from within the heart. The first clinical applications of M-mode echocardiography were concerned with the assessment of the mitral valve from the shapes of the corresponding waveforms. Subsequently, the various M-mode recordings were related to their anatomical origins. The method then became established as a diagnostic tool and was taken up by investigators outside Lund, initially in China, Germany, Japan and the USA and, subsequently, world-wide. The diffusion of echocardiography into clinical practice depended on the timely commercial availability of suitable equipment. The discovery of contrast echocardiography in the late 1960s further validated the technique and extended the range of applications. Two-dimensional echocardiography was first demonstrated in the late 1950s, with real-time mechanical systems and, in the early 1960s, with intracardiac probes. Transesophageal echocardiography followed, in the late 1960s. Stop-action two-dimensional echocardiography enjoyed a brief vogue in the early 1970s. It was, however, the demonstration by Bom in Rotterdam of real-time two-dimensional echocardiography using a linear transducer array that revolutionized and popularized the subject. Then, the phased array sector scanner, which had been demonstrated in the late 1960s by Somer in Utrecht, was applied to cardiac studies from the mid-1970s onwards. Satomura had demonstrated the use of the ultrasonic Doppler effect to detect tissue motion in Osaka in the mid-1950s and the technique was soon afterwards applied in the heart, often in combination with M-mode recording. The development of the pulsed Doppler method in the late 1960s opened up new opportunities for clinical innovation. The review ends with a mention of color Doppler echocardiography. (E-mail:

Echocardiography↗

PubMed1980

Thrombophlebitis of the internal jugular vein secondary to pharyngitis.

A case of septic thrombophlebitis of the internal jugular vein after pharyngitis is reported. Because of the common use and effectiveness of antibiotics against throat infections, this complication is now rarely seen. This condition has characteristic signs and symptoms, and a diagnosis can be obtained when the physician is aware of these characteristics. Radionuclide scan and Doppler effect flow studies of the internal jugular vein are useful diagnostic adjuncts. If recognized early and treated promptly with antibiotics, resolution is the rule. The literature has been reviewed.

Aged↗

PubMed1998

Optical design for laser Doppler angular encoder with sub-nrad sensitivity.

A novel laser angular-encoder system has been developed based on the principles of radar, the Doppler effect, optical heterodyning and self-aligning multiple-reflection optics. Using this novel three-dimensional multiple-reflection optical path, an increase in resolution of 10 to 20 times has been reached compared with commercially available laser Doppler displacement meters or laser interferometer systems. With the new angular encoder, sub-nrad resolution has been attained in the 8 degrees measuring range in a compact set-up [about 60 (H) x 150 (W) x 370 mm (L)] for high-energy-resolution applications at the Advanced Photon Source undulator beamline 3-ID.

Journal Article↗

PubMed2001

[Molecular spectral diagnosis of star forming regions].

Stars are the basic building blocks of our universe, therefore it is one of the most important research topics in astrophysics to understand the origin and the early evolution of these objects. The current picture is that stars are formed during the collapse of a large enough self-gravitating interstellar molecular cloud. The early collapse gives birth to a fetus of a star, which is surrounded by a rotating accretion disk. The proto-star accretes interstellar matter through the disk which in turn transfer the accumulated matter to the central proto-star, then the star gets weight during the process. Observation shows that gorgeous ejection of matter always come along with the accretion process. In the presence of disks, these outflows usually escape from the system along the axis of the disk, forming so called bipolar outflows. Typical tracers of these activities are rich molecules such as CO, SiC2, C3H, C3H2 etc. Observationally, such typical molecular outflows can be detected using Doppler effect by spectroscopic measurements. Using the 13.7 m radio telescope in Delingha station of Purple Mountain Observatory, we performed a survey for 12 low temperature IRAS objects, some of the sources show high velocity properties. Detailed analysis of the Doppler profiles of IRS34 is presented. Star forming activities are clearly seen in this field.

English Abstract↗

PubMed1991

Invariance of the Doppler bandwidth with flow displacement in the illuminating field.

It is known that if single frequency continuously transmitted ultrasound or electromagnetic energy is reflected from "straight line flow," defined here as one or more scatters moving with constant velocity along an infinite straight line, the Doppler effect will shift the echo spectrum center frequency from the transmitted value, and broaden its bandwidth. It is proved that if such straight line flow is shifted laterally or in range anywhere in the field, i.e., without change of orientation, its Doppler bandwidth remains unchanged. (The "Doppler bandwidth" is here defined as the frequency difference between the extrema of the echo power spectrum.) The theorem holds true even though the time domain echo changes dramatically with motion of the flow path, and is believed to be valid for electromagnetic as well as ultrasound waves. Its implications with respect to flow measurement, as well as preliminary experimental and computational confirmation, will be discussed.

Blood Flow Velocity↗

PubMedDate not supplied

[Experience in the use of the Soviet ultrasonic devices "Ritm" and "Ekran" in cardiosurgical practice].

The study is performed to evaluate opportunities of the echotacho-cardiograph Ritm in detecting the velocify of ventricular wall motions by using the Doppler effect and the echocardioscope Ekran++ that provides display and photography of the heart in the B-mode. In combination with a focusing probe, Ritm is a portable, easy in operation model. When operating with a high frequency recorder it indicates the Doppler signals from different myocardium sites at all stages of the surgical intervention. With the model Ekran++ one can display the heart in real time during surgery as well as evaluate anatomic and dynamic interactions between various cardiac structures that is of great importance in making decisions on surgical tactics and methods.

Cardiac Surgical Procedures↗

PubMed1999

Actographic analysis of the effects of an esterase inhibitor on male moth responses to sex pheromone.

The effects of 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP), a trifluoromethyl ketone that inhibits antennal esterases, on male Mamestra brassicae responses to the main pheromone component have been investigated using an actograph. This actograph used a movement detector based on the Doppler effect. The signal from the detector was digitalized and analysed on a PC microcomputer to quantify male activity. When added to the air flowing through the observation chamber, OTFP inhibited the responses of male moths to the pheromone. The number of males responding to the pheromone and the intensity of the response were decreased by OTFP. The latency of the response was increased and its duration decreased. These effects on the kinetics of the behavioural response cannot be directly correlated to the inhibition of pheromone catabolism by OTFP and other targets must be involved. The high level of inhibition of behaviour observed in presence of OTFP demonstrates the interest of trifluoromethyl ketones as mating disruption agents for pest control.

Acetone↗

PubMed1981

[Use of Doppler ultrasonic examination for per-operative checking of non surgical upper dorsal sympathectomy in the treatment of hyperhydrosis (author's transl)].

Doppler ultrasonic examination has been used as an indirect means of per-operative checking of sweat secretion after non surgical upper dorsal sympathectomy performed by percutaneous injection of hot saline into the upper dorsal sympathetic ganglions for the treatment of palmar hyperhydrosis. Their experience with pre, per and post-operative utilisation of Doppler effect in sixty cases has evidenced a full parallelism between the arterial vasodilation and the decrease in sweat secretion following the destruction of the sympathetic ganglions by hot saline. In the last series of thirty-five cases per-operative use of Doppler ultrasonic examination has spared them failures of the procedure. They consider Doppler ultrasonic examination as a precious help in classical open sympathectomy as well in their non surgical method.

Hand↗