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At least 181 records · Page 10Linked to original sources
PubMed2002

Planar near-field acoustical holography in a moving medium.

Near-field acoustical holography (NAH) is a well-established method to study acoustic radiation near a stationary sound source in a homogeneous, stationary medium. However, the current theory of NAH is not applicable to moving sound sources, such as automobiles and trains. In this paper, the inclusion of a moving medium (i.e., moving source and receiver) is introduced in the wave equation and a new set of equations for plannar NAH is developed. Equations are developed for the acoustic pressure, particle velocity, and intensity when mean flow is either parallel or perpendicular to the hologram plane. If the source and the measurement plane are moving at the same speed, the frequency Doppler effect is absent, but a wave number Doppler effect exists. This leads to errors when reconstructing the acoustic field both towards and away from the source using static NAH. To investigate these errors, a point source is studied analytically using planar NAH with flow in one direction. The effect of the medium moving parallel to the hologram plane is noted by a shift of the radiation circle in wave number space (k-space). A k-space Green's function and a k-space filter are developed that include the effects of the moving medium.

Journal Article↗
PubMed1991

Static versus dynamic exercise: effects on Doppler echocardiographic indices of left ventricular performance.

In order to compare the effects of static exercise with those of dynamic exercise on the Doppler echocardiographic measurements of ascending aortic blood flow velocity and acceleration, Doppler echocardiography was performed with sustained handgrip exercise and with supine bicycle exercise in 12 normal subjects, 12 patients with coronary artery disease, and 7 patients with heart failure. In normal subjects: peak velocity decreased by 16 +/- 11% with handgrip from the resting value and increased by 49 +/- 19% with bicycle exercise (p less than 0.01); mean acceleration decreased by 6 +/- 30% with handgrip and increased by 162 +/- 83% with bicycle exercise (p less than 0.01). In patients with coronary artery disease: peak velocity declined by 9 +/- 14% with handgrip and increased by 19 +/- 18% with bicycle exercise (p less than 0.01); mean acceleration increased by 13 +/- 27% with handgrip and by 41 +/- 33% with bicycle exercise (NS). In patients with congestive heart failure: peak velocity decreased by 19 +/- 13% with handgrip and increased by 5 +/- 17% with bicycle exercise (p less than 0.01); mean acceleration decreased by 12 +/- 23% with handgrip and by 4 +/- 37% with bicycle exercise. A marked increase in afterload stress induced by static exercise presumably offsets the moderately increased contractility and accounts for the decline of peak velocity and mean acceleration with static exercise both in normals and cardiac patients. In contrast, marked increase in contractile state along with little change in afterload with dynamic exercise results in markedly increased peak velocity and mean acceleration in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMedDate not supplied

Preoperative selective portal vein embolization (PSPVE) before major hepatic resection. Effectiveness of Doppler estimation of hepatic blood flow to predict the hypertrophy rate of non-embolized liver segments.

Hepatocellular carcinoma may be unresectable for volumetric reasons. The future remaining liver after hepatectomy might be too small to ensure survival. Preoperative selective portal vein embolization of the tumorous lobe can induce hypertrophy of the future remaining liver and enable safer surgery. A 76-year-old patient with hepatocellular carcinoma needed right lobectomy however, the future remaining liver was judged insufficient to ensure an uneventful postoperative course. The left lobe to whole liver volumetric ratio was to small (29.7%) and a preoperative selective portal vein embolization of the right portal branch via a percutaneous, transhepatic, contralateral approach was performed without side effects. A Doppler estimation of left branch portal blood flow and velocity was carried out before and after preoperative selective portal vein embolization. After 21 days the left lobe volume increased by about 44.2% with a safe left lobe/whole liver ratio of 40.8%. The portal blood flow and portal blood flow velocity showed an increase of 253% and 122%, respectively. A right lobectomy was performed without complications. Three months later, computed tomography scan showed no hepatocellular carcinoma recurrence. Preoperative selective portal vein embolization is a safe technique which can enable major hepatectomy to be performed in situations otherwise judged unresectable for a life-threatening volumetric insufficiency. The portal blood flow and portal blood flow velocity evaluations can easily predict the hypertrophy rate of non-embolized liver segments.

Aged↗
PubMed1999

Correlational analysis of acoustic cues for the discrimination of auditory motion.

The sound of a source moving in a straight path and passing directly in front of the listener on the azimuthal plane was synthesized over headphones to include three dynamic cues for motion: Doppler effect, overall intensity, and interaural time difference. Discriminability of a change in displacement, velocity, and acceleration of this source was measured using a standard two-interval, forced-choice procedure. In each case, the relative reliance or weight given to the three acoustic cues was estimated from correlations of the listener's response with small independent pertubations imposed on cues from trial to trial. Group estimates of threshold agreed well with results from past studies, while the obtained pattern of weights depended on the individual, starting velocity, and discrimination task. For the discrimination of displacement at moderate velocity (10 m/s), responses were most highly correlated with intensity or interaural time difference. For the discrimination of velocity and, to a lesser extent, acceleration, responses were most highly correlated with Doppler effect. At higher velocity (50 m/s) responses in all discrimination tasks were most strongly correlated with Doppler effect with few exceptions. Randomizing source spectrum or roving distance of the source from trial to trial did not significantly affect the pattern of results. The results suggest that motion perception is mutable, and not in all cases based on a single invariant acoustic cue.

Auditory Perception↗
PubMed2000

[The outline of diagnostic procedures in the cases of focal lesions in liver].

The majority of focal lesions in liver is typified by none or scant clinical symptoms and the first diagnosis is usually made during the ultrasonographic examination (USG). The first examinations usually performed in these cases are: the assignment of neoplastic markers in the serum (alpha-fetoprotein--AFP, carcinoembryonal antigen--CEA), imaging methods (USG, USG using Doppler effect, computer tomography--CT) and isotopic methods. The goal of the study is to present the proposal of outline of diagnostic procedures in the cases of focal lesions in liver based on the data from references. As the first step of diagnostic procedures non-invasive screening examinations are recommended (AFP, CEA, USG, USG using Doppler effect, CT of the abdominal cavity). The increase of the concentration of CEA in serum can suggest the metastatic tumour from the large bowel. The increase of the concentration of AFP makes possible to distinguish hepatocellular carcinoma from other malignant lesions. USG is useful to detect focal lesions which diameter is over 1.5 cm. USG has limited value to qualify the nature of the tumour. On the base of echogenicity of examined lesion we are able to make an initial selection to distinguish single from multiple and cystiform from solid lesions. USG using Doppler effect to detect vessel-signal helps to distinguish sound parenchyma from pathologically changed tissues. CT qualifies focus or dissemination of the disease. After screening examinations we use specialistic or invasive methods which are usually performed in the clinical circumstances. CT connected with angiography has a high sensitivity in detecting hepatocellular carcinoma. Isotopic methods help to confirm the depletion of sound parenchyma of the liver (colloidal scintigraphy) as well as sensitive and specific diagnostics of some types of neoplasms (scintigraphy using labelled erythrocytes to detect angioma). Guided fine-needle biopsy under the USG control makes possible to evaluate the nature of the tumour by means of cytological examination. Diagnosis made by means of sonolaparoscopy and nuclear magnetic resonance (NMR) is described in references, but these examinations have not been used in Poland by this time. Methods which were presented make possible to assign the outline of diagnostic procedures. The outline will help to differentiate precisely and quickly the nature and size of focal lesions in liver.

Carcinoma, Hepatocellular↗
PubMed1989

Semiquantitative evaluation of aortic regurgitation by Doppler echocardiography: effects of associated mitral stenosis.

The accuracy of pulsed and continuous wave (CW) Doppler methods for evaluating aortic regurgitation (AR) was compared in patients with and without mitral stenosis (MS), with aortic root angiography as a gold standard. AR was diagnosed with pulsed Doppler echocardiography, by the detection of broad frequency spectral patterns in the isovolumic relaxation time. If these indications were present, AR was graded by examining the extent of diastolic turbulence in the left ventricular cavity (flow mapping method). With CW Doppler echocardiography, AR was diagnosed by the detection of a peak velocity of greater than 2 m/s; if this velocity was attained, AR was graded by measuring the time from the peak velocity to half the peak velocity (half-time method). The angiographic grade corresponded to that determined by the pulsed and CW Doppler methods in 37 and 37 of 46 patients without MS, respectively. Angiographic grade corresponded to the grade determined by the pulsed and CW Doppler methods in 13 and 17 of the 23 patients with MS, respectively. Eight of 10 discrepancies between pulsed Doppler and angiographic grades were due to overestimation of AR by the flow mapping method, apparently because the transmitral jet produces diastolic turbulence in the left ventricular cavity independent of AR. On the other hand, three of six discrepancies between CW Doppler and angiographic grades were due to the incapability of detecting signals of AR by CW Doppler echocardiography. Thus both the pulsed and the CW Doppler methods are useful to evaluate AR in patients without MS. In patients with MS, however, AR is most accurately diagnosed by the detection of AR signals in the isovolumic relaxation time by pulsed Doppler echocardiography, and the degree of AR is more accurately assessed by the CW Doppler half-time method.

Adult↗
PubMed1988

[Doppler diagnosis in peripheral arterial occlusive disease].

PHYSICAL AND TECHNICAL FUNDAMENTALS OF DOPPLER ULTRASONOGRAPHIC METHODS: In addition to units recording both velocity and direction of blood flow, mostly using two ultrasonic frequencies and phase-out technique, there are small non-directional units available which provide useful diagnostic information from the acoustic Doppler signal derived. Doppler ultrasonic techniques utilize two physical phenomena: a) High-frequency ultrasonic energy penetrates biologic tissue and is partially reflected at borders between tissues of differing density. b) If the border area is in motion, due to the Doppler effect, there is a change in the reflected ultrasonic frequency with respect to the frequency emitted. In blood vessels the ultrasonic beam is primarily reflected from the flowing red blood cells where the change in frequency is a function of the velocity of flow (Doppler effect). From the Doppler transducer, the continuously-emitted ultrasonic beam is also received after being reflected. The frequency of the reflected beam is directly proportional to the velocity of the flowing blood. If flow is directed toward the transducer, the frequency of the reflected beam increases and if the flow is away from the transducer, the converse is true. The best Doppler signals can be received when the angle beta of the transducer to the studied vessel is about 45 degrees. The unprocessed Doppler signal represents a frequency spectrum corresponding to the various velocities of the individual lamina of the blood stream from which the prevailing velocity is integrated and registered. The penetration depth is dependent on the frequency emitted. Doppler units are preferred with working frequencies of 8 to 10 MHz and 3 to 5 MHz. With 8 MHz, the maximal depth of penetration is 3.5 cm, with 4 MHz, 8 cm. The lowest detectable velocity is also dependent on the frequency emitted: with 8 MHz, minimum is 3 cm/s. Since flow toward the transducer results in a positive Doppler shift and flow away in a negative shift, with the Doppler signal, the direction of flow can also be determined. The recorded Doppler curves enable a qualitative and, to some degree, quantitative assessment. Phase-out and frequency analysis systems enable differentiation of forward and backward flow components. From separate forward and backward flow curves, the instantaneous summation curve (integrated instantaneous hemotachygram) as well as a trend curve over 5 to 7 seconds can be constructed and the mean flow velocity displayed.

Arterial Occlusive Diseases↗
PubMed2005

Christian Andreas Doppler--the man and his legacy.

AIMS: Reminding the life and legacy of the Austrian Scientist who discovered the famous 'Doppler Effect'. METHODS AND RESULTS: C.A. Doppler was born the 29th of November 1803 in Salzburg. After studies in Linz and Vienna, he graduated in mathematics, became assistant at the University and later worked as a professor in Prague. Back to Vienna, he was appointed as professor at the Polytechnic School and --in 1850--as first director of the new Institute of Physics. C.A. Doppler did publish on magnetism, electricity, optics, and astronomy. He remains in the history of science due to the discovery presented (May 25, 1842) at the Royal Bohemian Society of Science entitled "On the colored light of the double stars and certain other stars of the heavens"; the paper described (applied to light) the shift of frequency which bears nowadays his name. The theory was later experimentally proven and--extended for any electromagnetic and acoustic waves--got myriads if applications in astronomy, physics, aviation, meteorology, and health science. Satomura in Japan (1955) published it's first ultrasound vascular application--with successive achievements in the next decades. CONCLUSION: Doppler ultrasonagraphy became the main noninvasive instrument for functional assesment of heart and vessels.

Austria↗
PubMed1996

Effect of Doppler echocardiography on utilization of hemodynamic cardiac catheterization in the preoperative evaluation of aortic stenosis.

OBJECTIVE: To examine the use of Doppler echocardiography in preoperative assessment of aortic stenosis and to determine its effect on subsequent use of hemodynamic cardiac catheterization. MATERIAL AND METHODS: We retrospectively reviewed a consecutive series of 574 adult patients who underwent aortic valve replacement for aortic stenosis between 1990 and 1992 at our institution. The use of Doppler echocardiography and cardiac catheterization and the predictive factors for use of hemodynamic catheterization were analyzed. RESULTS: After Doppler echocardiography in 423 patients, invasive hemodynamic assessment of the severity of aortic stenosis was performed in only 42% (179 patients). The use of cardiac catheterization declined over time (54% in 1990, 40% in 1991, and 35% in 1992) (P = 0.003), whereas no significant change in the baseline clinical characteristics of the population or in severity of stenosis as determined by Doppler echocardiography occurred during that time. Multivariate analysis identified the following variables as independent predictors of use of cardiac catheterization after Doppler echocardiography: clinically not severe aortic stenosis, mean gradient of less than 50 mm Hg determined by Doppler echocardiography, Doppler-determined aortic valve area of more than 0.8 cm2 or not calculated, attending cardiologist not specialized in echocardiography, and earlier year of assessment. CONCLUSION: After Doppler echocardiography, less than 50% of our patients undergoing aortic valve replacement for aortic stenosis have cardiac catheterization preoperatively. The use of cardiac catheterization after Doppler echocardiography--thus, duplication of hemodynamic assessment--declined significantly over time during the study period. Decline in the use of catheterization is related to the degree of diagnostic certainty provided by Doppler echocardiography and to the level of familiarity of the attending cardiologist with the technique.

Adult↗
PubMed2005

Computer-assisted quantitative assessment of power Doppler US: effects of microbubble contrast agent in the differentiation of breast tumors.

RATIONALE AND OBJECTIVES: To objectively quantify the effects of a microbubble contrast agent to differentiate breast tumors with power doppler ultrasound and to compare these results with color doppler ultrasound (CD US). METHODS: In 47 patients a microbubble contrast agent was injected intravenously. Computer-assisted quantitative assessment of the color pixel density was performed to evaluate the increase in Doppler signals. Results were compared to previously published results of a color Doppler ultrasound study. RESULTS: Peak color pixel density at contrast-enhanced power Doppler ultrasound was higher for carcinomas than for benign tumors (P < 0.03). Time to peak enhancement was shorter in carcinomas than in benign tumors (P < 0.01). For both parameters, diagnostic accuracy of power Doppler ultrasound was 69 and 78%, and for color Doppler ultrasound 62 and 76%, respectively. CONCLUSIONS: Quantitative assessment of contrast-enhanced power Doppler ultrasound showed significant differences in malignant and benign breast tumors. Diagnostic accuracy of contrast-enhanced power Doppler ultrasound was higher compared to color Doppler ultrasound.

Adult↗
PubMed1989

Technical introduction to echocardiography.

Pulse-echo ultrasound can be used to measure distance along a narrow beam with resolution limited by the wavelength and, ultimately, by attenuation. Time-position (M-mode) recording can be used to study structure motion. Real-time two-dimensional imaging can be achieved with mechanical scanning or electronically controlled phase array transducers, the frame rate being limited by the depth of penetration and the image line density. Blood flow can be detected by the Doppler effect. Continuous wave Doppler systems lack depth discrimination, but this can be provided by pulsed Doppler although range-velocity ambiguities may occur. Blood flow volume rate can be estimated from measurements of velocity and area; the simultaneous use of wide and narrow beams reduces the errors. Duplex scanning uses two-dimensional real-time imaging for Doppler sample volume localization. Two-dimensional colour-coded images of blood flow can be produced in real time. Endoscopic scanning avoids problems due to bone and gas. Contrast agents can be used to enhance the echogenicity of blood.

Echocardiography↗
PubMed1988

Endoscopic measurement of gastric mucosal blood flow by laser Doppler velocimetry: effect of chronic esophageal variceal sclerosis.

A technique of endoscopic measurement of gastric mucosal blood flow using laser Doppler velocimetry was described. The technique was validated in the laboratory by performing endoscopic measurement of gastric mucosal blood flow in the dog simultaneously with application of a second probe at open operation, utilizing the same laser Doppler flowmeter. Probe pressure causing minor dimpling (less than 20 gm/cm2) was found to cause insignificant alteration of mucosal blood flow. Criteria were developed to aid separation of artifacts introduced by probe motion. A conversion factor was established for converting the readout of the instrument (Hertz x 10(2] into ml/100g/min by synchronously measuring mucosal blood flow by hydrogen gas clearance technique and laser Doppler velocimetry in the gastric and duodenal mucosa. In patients with portal hypertension gastric mucosal blood flow was determined before and after sclerotherapy, and compared to the gastric mucosal blood flow in subjects without portal hypertension. Gastric mucosal blood flow was elevated in portal hypertensives, but sclerotherapy did not appear to cause changes in blood flow. Endoscopic mucosal blood flow measurement is non-invasive, practical and of potential value in clinical investigation of gastrointestinal pathophysiology.

Animals↗
PubMed1994

Comparison of hemodynamic and Doppler echocardiographic effects of a new low osmolar nonionic and a standard ionic contrast agent after left ventriculography.

The hemodynamic effects of a new nonionic low osmolar contrast agent (iomeprol) during left ventriculography (LC) was compared with a standard ionic contrast agent (meglumine diatrizoate) in a randomized double blind study in 30 patients with suspected coronary artery disease and normal systolic ventricular function. LV diastolic function was assessed by Doppler echocardiographic recording of the transmittal filling curve and by intraventricular tip-manometry before and within 30 sec of the LC. In the group receiving the ionic contrast agent the systolic pressure fell from 126 +/- 23 to 111 +/- 18 mmHg (P < 0.05), and heart rate increased from 64 +/- 9 to 71 +/- 11 min-1 (P < 0.05), while no such effects were observed with the nonionic contrast agent, indicating differences in the vasodilator properties. The latter caused an increase of the peak early Doppler velocity (52 +/- 11 to 62 +/- 14 cm/sec; P < 0.05). After the ionic contrast agent, the effect on the peak early Doppler velocity was less pronounced, probably due to an interaction with the known depressant effect of the increase in heart rate on the early Doppler velocity. In both groups the left ventricular end diastolic pressure was increased from 7 +/- 3 to 10 +/- 4 mmHg. No significant effects on peak-dp/dt and dp/dt were observed in either group. The nonionic contrast agent iomeprol had no significant effect on systolic arterial pressure and heart rate in contrast to the ionic contrast agent, probably due to a less pronounced vasodilator effect. Despite these differences of the global hemodynamic response, there were similar effects of both contrast agents on LV diastolic filling.

Adolescent↗
PubMedDate not supplied

[Renal eco Doppler in pediatrics].

During the last few years, technological improvements in Doppler sonography have transformed a primitive imaging technique in a sophisticated diagnostic tool. The complexity of the physical concept which is at the basis of technique, the different ways to use it and the results depending on either the equipment quality or the operator's skill, have produced confusion and doubts about the real value of Doppler sonography for assessing diseases of the kidney and urinary tract in infants and children. The purpose of this article is to review the basic concepts concerning the physics of Doppler effect, to describe the principal Doppler sonography instrumentation (continuous-wave, pulsed-wave, color Doppler and power Doppler equipment) and to discuss the diagnostic applications of renal Doppler in paediatric imaging.

Acute Disease↗
PubMed1993

Superior mesenteric artery blood flow in man measured with intra-arterial Doppler catheters: effect of octreotide.

Changes in splanchnic blood flow are important in the pathogenesis of portal hypertension, but research in this area is hampered by the difficulty in measuring splanchnic arterial blood flow in man. We therefore investigated the use of intra-arterial Doppler catheters in measuring superior mesenteric artery blood flow in man and assessed the effect of intravenous octreotide on superior mesenteric artery blood flow in a placebo-controlled double-blind study. Nine experiments were performed in a flow model using vessels with internal diameters of 6.5, 4.5 and 3.0 mm, with flow rates ranging from 50 to 700 ml/min. In this model the catheters gave instantaneous, reproducible measurements of blood flow in vessels of 6.5 mm internal diameter with a mean error ranging from +5.3% to +36.4%, compared to electromagnetic flowmetry, but were less accurate in smaller vessels. When used in patients, the catheters provided stable, reproducible measurements of superior mesenteric blood flow, in 16 out of 20 patients studied. In a double-blind placebo-controlled study, including 12 subjects, superior mesenteric artery blood flow was significantly reduced in patients receiving octreotide. We suggest that measurement of splanchnic arterial blood flow using intra-arterial Doppler catheters may be a useful additional investigation in the assessment of splanchnic vascular pathophysiology and pharmacology in man.

Adenoma↗
PubMed1996

Microbubble contrast agent for color Doppler US: effect on breast masses. Work in progress.

PURPOSE: To evaluate the effects of a new microbubble contrast agent for ultrasound (US) on breast masses. MATERIALS AND METHODS: Thirty-four patients underwent color Doppler US before and after intravenous injection of a "contrast agent" containing microbubbles. The authors subjectively evaluated the increase in intensity of the Doppler signals, the changes in the vascular patterns, and the timing of the transit of the microbubble bolus. The diagnostic confidence was assessed before and after administration of contrast material. RESULTS: After contrast material injection, there was greater and longer signal enhancement in the cancers than in the benign lesions. The cancers displayed characteristic vascular morphologic features, with more additional vessels visualized in relation to the lesion and a greater increase in vascular tortuousity. Shunts between vessels were demonstrated in all cancers but were not seen in any benign lesion. The diagnostic confidence increased with use of the contrast agent. The appearance at contrast-enhanced US led to a change in the US diagnosis in four patients. This increased both sensitivity and specificity to 100%. CONCLUSION: Injection of a microbubble agent enabled accurate differentiation of benign masses from carcinomas.

Adult↗
PubMed1990

[The value of obstetrical continuous-wave Doppler sonography: effect of various study modifications on the diagnosis of fetal growth retardation].

In a comparative study on 484 pregnant women the influence of different modifications of the examination by continuous wave (cw)--Doppler was tested. The aim was to improve the detection rate of foetal growth retardation (IUGR): 1. Among different definitions of normal ranges the mathematical "smoothing" of normal values by regression analysis improves the results. 2. Of the most commonly used flow indices the A/B ratio is more reliable than the resistance and the pulsatility index. 3. Comparing the results of one to three examinations of the same patient in the course of pregnancy the relation of sensitivity to specificity is best after two examinations. 4. On evaluating the examinations of the umbilical arteries and the arcuate arteries, an intolerably false positive rate was found in the evaluation of arcuate arteries by cw Doppler.

False Positive Reactions↗
PubMed1990

Reactive hyperaemia in skin of the human foot measured by laser Doppler flowmetry: effects of duration of ischaemia and local heating.

The effect of duration of ischaemia and of local heating on reactive hyperaemia in dorsal foot skin was determined in normal subjects using laser Doppler flowmetry. In the nine subjects studied, peak post-ischaemic blood flow continued to increase significantly with up to 10 min ischaemia and mean peak response was positively correlated with duration of ischaemia (r = 0.997, p less than 0.0002). This is in contrast to whole limb plethysmographic studies which have reported maximal peak flow responses after 3-5 min arterial occlusion. Resting blood flow was found to increase rapidly at skin temperatures above 33 degrees C. In ten subjects, local conductive heating from a median (range) skin temperature of 29.8(26.5-31.0) to 32.5(32.2-33.1) degrees C increased peak flow response after 4 min ischaemia from a mean (95% confidence interval) of 0.778(0.630-0.926) to 0.965(0.788-1.142) arbitrary units, p less than 0.001. The time course of the hyperaemic response was not altered. Local skin warming reduced the within subject coefficient of variation for peak response, calculated from 10 paired recordings, in two out of three subjects. These results show that the duration of ischaemia required to produce a maximal post-ischaemic peak flow response is longer for foot skin than for the whole limb and are consistent with temperature differences being the cause of this. A standard skin temperature (32-33 degrees C) may be useful for studying cutaneous blood flow responses.

Adult↗