T Aach | PubMed Health

PubMed2002

Human cerebral perfusion analysis with ultrasound contrast agent constant infusion: a pilot study on healthy volunteers.

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.

Adult↗

PubMed2000

Digital radiography enhancement by nonlinear multiscale processing.

Today's digital radiography systems mostly use unsharp maskinglike enhancement algorithms based on splitting input images into two or three frequency channels. This method allows fine detail enhancement as well as processing of global contrast (harmonization). However, structures of medium size are not accessible. In extension of a standard algorithm of such type, we develop and test a new enhancement algorithm based on hierarchically repeated unsharp masking, resulting in a multiscale architecture allowing consistent access to structures of all sizes. Our algorithm decomposes a radiograph by a pyramid-architecture, dividing it into eight or more channels representing structures of different sizes, known as "scales." At each scale, weakly contrasting structures are then enhanced by suitable nonlinear processing. We emphasize two points: first, backward compatibility to the standard algorithm which is used routinely in clinical practice. This allows reuse of current parametrization know-how as well as a smooth transition from current to new processing. Second, our enhancement is noise-resistant in the sense that it prevents unacceptable noise amplification. A prototype implementation of the algorithm is undergoing trials in the clinical routine of radiology departments of major German hospitals. Results strongly indicate the superior performance and high acceptance of the new processing.

Algorithms↗