Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By means of harmonic imaging, it is possible to display brain perfusion qualitatively using ultrasound (US) contrast agent (UCA) bolus injection. With UCA continuous infusion reaching a steady state, mean microbubble velocity can be measured, analyzing the reappearance rate after microbubble destruction by US (refill kinetics). We performed an animal pilot study to investigate this new method for the assessment of brain perfusion. Using harmonic grey-scale imaging, five sedated male beagle dogs were investigated through the intact skull with increasing pulsing intervals (250 to 8000 ms) and three UCA infusion rates (0.5, 1.0 and 1.5 mL/min of Optison). Cerebral blood flow was increased by acetazolamide (30 mg/kg BW). Intensity vs. pulsing interval curves were analyzed using an exponential curve fit [I(t) = A(1-e(-beta t))] and parameters of the curve were compared. We found that increasing the pulsing interval above 4000 ms led to no further increase of echo enhancement for infusion rates. Mean beta values were not influenced by infusion rate (p = 0.25 and p = 0.55). Mean F values increased nonsignificantly with rising infusion rate (p = 0.25 and p = 0.86). Acetazolamide led to an increase of mean beta and F values (p = 0.18 and p = 0.025, respectively). It is possible to evaluate changes in brain perfusion through the intact skull by analyzing the UCA refill kinetics after US-induced microbubble destruction.
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PMID:Evaluation of blood flow in the cerebral microcirculation: analysis of the refill kinetics during ultrasound contrast agent infusion. 1152 92

With ultrasound (US) contrast agent (UCA) continuous infusion providing a steady state, mean tissue microbubble velocity can be assessed by analyzing the reappearance rate after microbubble destruction with US energy (refill kinetics). In this study, we investigated this new approach for the assessment of human cerebral perfusion. A total of 12 healthy volunteers were investigated transtemporally with increasing pulsing intervals (250, 500, 750, 1000, 1250, 1500, 2000, 3000 and 4000 ms) and two UCA infusion rates (0.5 and 1.0 mL/min of Optison). Intensity vs. pulsing interval curves were analyzed using an exponential curve fit and parameters of the curve (plateau echo enhancement, A, representing the microbubble concentration within the interrogated tissue; rate constant, beta, which is related to blood flow and their product, F = Abeta) were compared. For 20/20 investigations being available for further analysis, it was possible to generate a typical exponential intensity vs. pulsing interval curve from the ipsilateral thalamus. The plateau echo enhancement A showed a significant (p = 0.02), and the beta as well as the F values displayed a nonsignificant (p = 0.06, both), increase with infusion rate. The qualitative analysis of beta and F parameter images displayed the most homogeneous visualisation of perfusion in the ipsilateral thalamus and main territory of the middle cerebral artery. In conclusion, it is possible to display the UCA refill kinetics in human cerebral microcirculation after microbubble destruction by transcranial US. Grey-scale harmonic imaging allows a quantitative approach to cerebral perfusion with a large interindividual variation of the parameters.
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PMID:Human cerebral perfusion analysis with ultrasound contrast agent constant infusion: a pilot study on healthy volunteers. 1193 80

Analysis of contrast diminution kinetics after bubble destruction is a new aspect in harmonic imaging. The purpose of this study was to investigate this approach to human cerebral perfusion. A total of 12 healthy volunteers were investigated transtemporally (Philips SONOS 5500, S4-probe, 1.8 to 3.6 MHz, 10 cm) at two ultrasound (US) contrast agent (UCA) infusion rates (0.5 and 1.0 mL/min of Optison). After achieving a steady-state, a set of 12 US pulses (6.67 Hz, MI 1.6) was applied. Time-intensity plots of three regions-of-interest (ROIs) (thalamus, white matter and cortex) were analyzed, using an exponential curve fit (I((t)) = I(0)e(-betat) + B). A total of 20 of 20 successful investigations showed a signal decrease after pulsed US application. In all cases, it was possible to generate exponential time-intensity curves. Half-life (T(1/2) = ln2/beta) and baseline intensity (B) showed a significant dependence on infusion rate (p = 0.01). At 1.0 mL/min, T(1/2) also depended on investigation depth (p = 0.01). It is possible to assess contrast diminution kinetics in human cerebral microcirculation. This new approach may provide additional information on cerebral perfusion within a short investigation time.
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PMID:Transcranial contrast diminution imaging of the human brain: a pilot study in healthy volunteers. 1249 38

Noninvasive measurement of pressure within the heart cavities and other internal organs (e.g., kidney, liver) has significant clinical value, but currently is not feasible. Noninvasive pressure estimation using encapsulated ultrasound (US) contrast agents (UCA) as sensors is a challenge because they supposedly respond to their ambient pressure, but they are more rigid and less sensitive to pressure than gas microbubbles. Here, Optison sensitivity was studied (f(resonance) = approximately 2 MHz) to varying pressures, when excited at 2 times and also at 0.5 times f(resonance). Cyclic momentary increases in ambient pressure of 0 to 5, 0 to 10, 0 to 15 or 0 to 20 kPa at 1.0 Hz, mimicking left ventricular (LV) pressure changes, caused amplitude decrease of echoes at 0.5, 1 and 2 times the transmitted frequency and decrease of attenuation. Changes at 0.5 times the transmitted frequency correlated best, but only after 70 to 150 s. The correlations (mean +/- SD) during 150 to 300 s were 0.706 +/- 0.072 for 0 to 10 kPa, 0.844 +/- 0.042 for 0 to 15 kPa and 0.859 +/- 0.031 for 0 to 20 kPa. Attenuation presented less correlation. For 1.0 Hz, 10 to 15 kPa or 15 to 20 kPa pressures, mimicking systemic pressures, the attenuation decayed fast and even faster for slow (0.05 Hz) cyclic varying pressures, or elevated steady-state pressures (of 10 kPa and 20 kPa). Thus, cyclic pressure effects on UCA are demonstrated to be reversible, but elevated static pressures cause UCA destruction. This allows cyclic pressure variations to be detected, using the subharmonics of the transmitted frequency, down to 10 kPa.
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PMID:On the relationship between encapsulated ultrasound contrast agent and pressure. 1586 17

The small thermal lesions induced when using high-intensity focused ultrasound (HIFU) to ablate tumors results in long treatment duration. In this study, the effect of using ultrasound contrast agent (UCA, Definity) to enhance the ultrasound (US) thermal effects and, thus to enlarge the lesion size, was studied in transparent tissue phantoms insonified by 1.85-MHz US with acoustical powers of 28.9 and 40.4 W. The experimental results show that the lesion size depended strongly on the electrical power and the concentration of UCA. UCA also reduced the power required to form a lesion of a certain size by about 30%. However, UCA moved the greatest heating position from the transducer focus, by 2.16 cm for 0.015% UCA at 40.4 W, and with lesions forming at the surface for UCA concentrations higher than 0.1%. An optimal result was obtained when using 0.001% UCA and 28.9-W US, which produced a lesion 12 times larger and an acceptable shift (less than half of the lesion length). UCA can effectively increase the size of the HIFU lesions, but lesion shift should be carefully considered while performing HIFU ablations.
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PMID:Contrast-agent-enhanced ultrasound thermal ablation. 1682 24