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W Wilkening

Publications and source records attributed to W Wilkening.

13 recordsLinked to original sources
PubMed2004

Detection of cerebral perfusion abnormalities in acute stroke using phase inversion harmonic imaging (PIHI): preliminary results.

Phase inversion harmonic imaging (PIHI) with newer contrast agents can display parameters of cerebral perfusion either using the established ipsilateral approach, or the novel bilateral approach in which both hemispheres are assessed in one examination. The aim of this study was to evaluate the potential of PIHI in detecting pathological perfusion in acute stroke, using the bilateral approach. Patients with a hemispheric syndrome presenting within 12 hours after symptom onset were examined with PIHI (SonoVue; bolus kinetics, fitted model function) using the bilateral approach if possible. Semi-quantitative perfusion related parameters (time to peak intensity (TPI) and peak width (PW)) were evaluated, and results correlated to follow up cerebral computed tomography (CCT) scans. In these four preliminary cases (one ipsilateral, three bilateral), PIHI was able to identify the ischaemic region because the function could not be fitted to the data. In one case, there was a difference between a core region where no perfusion was seen, and a surrounding region where hypoperfusion was detected (prolonged TPI and reduced PW). PIHI was able to predict the localisation and size of the eventual infarction even if no early CCT signs were seen. Furthermore, in one case, a surrounding hypoperfused region was identified, where tissue survived after recanalisation of the initially occluded middle cerebral artery. Using the bilateral approach, two advantages in comparison with the ipsilateral approach were obvious: cortical structures could be evaluated, and only one examination was needed to compare unaffected (ipsilateral) with affected (contralateral) tissue. These results should be confirmed by more cases, and should also be correlated to acute perfusion/diffusion weighted MRI data.

Aged↗
PubMed2003

A nonuniform sampling approach for fast ultrasonic flow imaging.

Conventional Pulsed Wave Doppler (PWD) systems acquire an ensemble of N echoes per beam line at a constant pulse repetition frequency fprf, so that the pulse repetition interval equals Tpri = 1/fpn. The total time span determines the velocity resolution, and Tpri the unambiguous velocity range. The ensemble size N is by approximation inversely proportional to the frame rate, assuming that the system performs interleaving. For a given frame rate, a tradeoff can only be made between velocity resolution and velocity range. We propose an approach that allows increasing velocity resolution or range while keeping the frame rate constant. The approach is based on nonuniform sampling, i.e. sampling with varying sampling intervals. Thus, for a given ensemble size N a larger total time span, which would increase velocity resolution, or a shorter minimal Tpn, which would increase the velocity range, may be chosen. The conventional Doppler signal processing techniques are not compatible with nonuniform sampling. We, therefore, developed a velocity estimation algorithm for arbitrary sampling that is based on cross correlation. Furthermore, an adaptive wall filter was implemented that differentiates between tissue motion and blood flow. The new approach was successfully tested with in vitro and in vivo data.

Algorithms↗
PubMed2000

Contrast agent specific imaging modes for the ultrasonic assessment of parenchymal cerebral echo contrast enhancement.

Previous work has demonstrated that cerebral echo contrast enhancement can be assessed by means of transcranial ultrasound using transient response second harmonic imaging (HI). The current study was designed to explore possible advantages of two new contrast agent specific imaging modes, contrast burst imaging (CBI) and time variance imaging (TVI), that are based on the detection of destruction or splitting of microbubbles caused by ultrasound in comparison with contrast harmonic imaging (CHI), which is a broadband phase-inversion-based implementation of HI. Nine healthy individuals with adequate acoustic temporal bone windows were included in the study. Contrast harmonic imaging, CBI, and TVI examinations were performed in an axial diencephalic plane of section after an intravenous bolus injection of 4 g galactose-based microbubble suspension in a concentration of 400 mg/mL. Using time-intensity curves, peak intensities and times-to peak-intensity (TPIs) were calculated off-line in anterior and posterior parts of the thalamus, in the region of the lentiform nucleus, and in the white matter. The potential of the different techniques to visualize cerebral contrast enhancement in different brain areas was compared. All techniques produced accurate cerebral contrast enhancement in the majority of investigated brain areas. Contrast harmonic imaging visualized signal increase in 28 of 36 regions of interest (ROIs). In comparison, TVI and CBI examinations were successful in 32 and 35 investigations, respectively. In CHI examinations, contrast enhancement was most difficult to visualize in posterior parts of the thalamus (6 of 9) and the lentiform nucleus (6 of 9). In TVI examinations, anterior parts of the thalamus showed signal increase in only 6 of 9 examinations. For all investigated imaging modes, PIs and TPIs in different ROIs did not differ significantly, except that TVI demonstrated significantly higher PIs in the lentiform nucleus as compared with the thalamus and the white matter (P < 0.05). The current study demonstrates for the first time that CBI and TVI represent new ultrasonic tools that allow noninvasive assessment of focal cerebral contrast enhancement and that CBI and TVI improve diagnostic sensitivity as compared with CHI.

Adult↗
PubMed1981

Reintegration: the slow march of progress--towards a reality-oriented concept of health education.

The essay sets out to plead for a basic reassessment of many of the implicit or explicit "conceptual props and crutches" upholding traditional health education. Its main thrust is to reconstruct the many disparate bits and pieces of theoretical assumption which have come into being through the various historical phases of health education and, in doing so, to rebuild an image of social reality in which health educators can hope to operate more meaningfully and, possibly, more effectively. The general theory behind the call for an integrated approach to health education is that this art can only thrive when openly confronted with its traditional limitations determined both by limits of social awareness and social structure. These have to be made the subject of discussion on health education "theory" in order to affect change. Examples of an alternate approach applied in the Federal Republic of Germany are quoted to stimulate discussion.

Goals↗