摘要 :
Ultrasound contrast agents (UCAs) are widely used in Doppler studies, either for simple echo enhancement purposes, or to increase the low signal-to-clutter ratio typical of microcirculation investigations. Common to all Doppler te...
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Ultrasound contrast agents (UCAs) are widely used in Doppler studies, either for simple echo enhancement purposes, or to increase the low signal-to-clutter ratio typical of microcirculation investigations. Common to all Doppler techniques, which are briefly reviewed in this paper, is the basic assumption that possible phase and amplitude changes in received echoes are only associated with UCA microbubble movements due to the drag force of blood. Actually, when UCAs are insonified, phenomena such as rupture, displacement due to radiation force, and acoustically driven deflation might influence the results of Doppler investigations. In this paper, we investigate the possible Doppler effects of such phenomena by means of a numerical simulation model and a special acousto-optical set-up which allows analysis of the behavior of individual microbubbles over relatively long time intervals. It is thus found that all phenomena produce evident Doppler effects in vitro, but that bubble displacement and deflation in particular, are not expected to significantly interfere with clinical measurements in standard conditions.
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摘要 :
Ultrasound contrast agents (UCAs) are widely used in Doppler studies, either for simple echo enhancement purposes, or to increase the low signal-to-clutter ratio typical of microcirculation investigations. Common to all Doppler te...
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Ultrasound contrast agents (UCAs) are widely used in Doppler studies, either for simple echo enhancement purposes, or to increase the low signal-to-clutter ratio typical of microcirculation investigations. Common to all Doppler techniques, which are briefly reviewed in this paper, is the basic assumption that possible phase and amplitude changes in received echoes are only associated with UCA microbubble movements due to the drag force of blood. Actually, when UCAs are insonified, phenomena such as rupture, displacement due to radiation force, and acoustically driven deflation might influence the results of Doppler investigations. In this paper, we investigate the possible Doppler effects of such phenomena by means of a numerical simulation model and a special acousto-optical set-up which allows analysis of the behavior of individual microbubbles over relatively long time intervals. It is thus found that all phenomena produce evident Doppler effects in vitro, but that bubble displacement and deflation in particular, are not expected to significantly interfere with clinical measurements in standard conditions.
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Color doppler imaging (GDI) is a diagnostic tool that allows non-invasive evaluation of the orbital and intra-cranial structures. It operates by the doppler principle, which is detecting changes in the frequency of sound that is r...
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Color doppler imaging (GDI) is a diagnostic tool that allows non-invasive evaluation of the orbital and intra-cranial structures. It operates by the doppler principle, which is detecting changes in the frequency of sound that is reflected from flowing blood, allowing estimation of flow velocity. GDI has been used in the diagnosis and follow up of ophthalmic conditions such as central retinal artery occlusion, central retinal vein occlusion, arteritic and non-arteritic ischemic optic neuropathy and the ocular ischemic syndrome. In addition, orbital conditions like varices can be evaluated. Transcranial doppler has been used to assess strokes and arteriovascular malformations of the brain. The main limitation of GDI is that it provides information about velocity and not flow. Despite this, it remains a valuable tool to diagnose ocular and intracranial conditions characterized by ischemia or abnormal blood flow.
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Objective:The goal of this work was to develop a clinically applicable method for non-invasive acoustic determination of hematocrit in vivo.Methods:The value of hematocrit (HCT) was determined initially in vitro from the pulse-ech...
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Objective:The goal of this work was to develop a clinically applicable method for non-invasive acoustic determination of hematocrit in vivo.Methods:The value of hematocrit (HCT) was determined initially in vitro from the pulse-echo measurements of acoustic attenuation.The testing was carried out using a laboratory setup with ultrasound transducer operating at 20 MHz and employing human blood samples at the temperature of 37 deg C.The attenuation coefficient measurements in blood in vitro and in vivo were implemented using multi-gated (128-gates),20 MHz pulse Doppler flow meter.The Doppler signal was recorded in the brachial artery.Both in vitro and in vivo HCT data were compared with those obtained using widely accepted,conventional centrifuge method.Results:The attenuation coefficient in vitro was determined from the measurements of 168 samples with hematocrit varying between 23.9 and 51.6%.Those experiments indicated that the coefficient increased linearly with hematocrit.The HCT value was obtained from the 20 MHz data using regression analysis.The attenuation (() was determined as a 42.14+1.02 centre dot HCT (Np/m).The corresponding standard deviation (SD),and the correlation coefficient were calculated as SD=2.4 Np/m,and R=0.9,(p < 0.001 ),respectively The absolute accuracy of in vivo measurements in the brachial artery was determined to be within +-5% HCT.Conclusions:The method proposed appears to be promising for in vivo determination of hematocrit as 5% error is adequate to monitor changes in patients in shock or during dialysis.It was found that the multigate system largely simplified the placement of an ultrasonic probing beam in the center of the blood vessel.Current work focuses on enhancing the method's applicability to arbitrary selected vessels and reducing the HCT measurement error to well below 5%.
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This review pays tribute to those pioneers in Doppler flow during an early and exciting period ranging from the end of the 1960s to the 1990s. Three major 'approaches' contributed to what is nowadays built into every patient's inv...
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This review pays tribute to those pioneers in Doppler flow during an early and exciting period ranging from the end of the 1960s to the 1990s. Three major 'approaches' contributed to what is nowadays built into every patient's investigation. The source was Daniel Kalmanson, who developed flow directionality, assigning a physiological meaning to the recordings. This was the first time Doppler flow was used on the heart, providing new insights in cardiac pathophysiology. The second approach relied on the Norwegian group who applied the laws of physics to fluid dynamics. Simplification of the formula provided a new non-invasive approach enabling quantification of valvular lesions and haemodynamic measurements. This new tool pushed back previous routine catheterisation. To crown it all, the introduction of colour Doppler flow, mainly relying on the Japanese groups, overcame the long-lasting scepticism of the scientific community: cardiologists started to 'believe' in the Doppler technique. Other innovative pioneers around the world joined the three groups to develop this new field of cardiology. At the turning of the new millennium, the Doppler technique is mature, through a strong methodology. Convergence of the three original approaches for mutual benefit, constant update of examination modalities according to improved technology, and new insights into cardiac dynamics, are the three cornerstones supporting this methodology. They should contribute to keep it alive and efficient, independently of the imaging modality of the future.
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Power Doppler (PD) is used widely in musculoskeletal ultrasound, especially in the assessment of structures for evidence of
inflammation and in evaluating soft tissue neoplasms. We reinforce and delineate the three cardinal princ...
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Power Doppler (PD) is used widely in musculoskeletal ultrasound, especially in the assessment of structures for evidence of
inflammation and in evaluating soft tissue neoplasms. We reinforce and delineate the three cardinal principles of optimising
PD assessment in order to avoid false positive or false negative results; namely (1) Optimal gain settings (2) Adequate
transducer pressure, and (3) Proper patient/anatomical structure-of-interest positioning with complete tissue relaxation.
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The special theory of relativity takes particular pride in the transverse Doppler effect (TDE). Apart from Voigt's (1887) work which has an incomplete explanation, the equation from which the TDE is derived is first seen in Einste...
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The special theory of relativity takes particular pride in the transverse Doppler effect (TDE). Apart from Voigt's (1887) work which has an incomplete explanation, the equation from which the TDE is derived is first seen in Einstein's (1905) work. However, in this equation, the cosine of the angle and Lorentz factor are inserted arbitrarily. This paper will, through calculation and with precision (without postulates, without additional assumptions, and without approximation), derive a general formula for the Doppler effect at an arbitrary angle between the direction of motion of the source and the direction in which the observer receives the signal. Finally, the longitudinal Doppler effect and TDE can be obtained quite naturally from this formula.
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In this letter, we use the summation-by-parts formula as a simple tool to extend the estimation range of a certain class of the already existing correlation-based Doppler centroid estimators. The resulting estimators are as robust...
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In this letter, we use the summation-by-parts formula as a simple tool to extend the estimation range of a certain class of the already existing correlation-based Doppler centroid estimators. The resulting estimators are as robust as the original ones but cover a much larger estimation range of about $ pm$50% of the pulse-repetition frequency. Two examples with simulations are provided to demonstrate the benefits of the proposal.
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Estimated foetal weight less than the 10th percentile at that gestational age is known as intra st st uterine growth restriction (IUGR). Over the period of 1 July 2021 till 31 June 2022, a descriptive longitudinal study was conduc...
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Estimated foetal weight less than the 10th percentile at that gestational age is known as intra st st uterine growth restriction (IUGR). Over the period of 1 July 2021 till 31 June 2022, a descriptive longitudinal study was conducted in department of OBGY DVVPF’s medical college and hospital Ahmednagar. 90 women visiting OBGY OPD at DVVPF’s medical college and hospital Ahmednagar carrying single fetus with 32 completed weeks of gestation, having IUGR were included in the study. There are considerable differences between categories and within categories when umbilical artery Doppler indices were used to analyse newborn outcome in terms of birth weight. P value exceeded 0.0005. A better outcome in terms of birth weight of more than 2 kg occurs when the umbilical artery Doppler diastolic flow revealed strong forward diastolic flow. Planning the antenatal fetal surveillance requires the identification of IUGR fetuses caused by uteroplacental insufficiency. Doppler imaging of the umbilical artery reveals changes, which in turn forecasts the resistance present at the placenta. Increased prenatal mortality and morbidity are related to the absence or reversal of umbilical artery diastolic flow. Hence One of the most useful tools for performing prenatal fetal surveillance on IUGR fetuses is the umbilical artery Doppler.
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