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Wilko Wilkening

Publications and source records attributed to Wilko Wilkening.

11 recordsLinked to original sources
PubMed2006

Contrast-enhanced ultrasonic parametric perfusion imaging detects dysfunctional tissue at risk in acute MCA stroke.

Ultrasonic perfusion imaging predicts size and localization of acute stroke. It is unclear whether irreversibly damaged tissue can be differentiated from tissue at risk. Thirty-four patients (ischemic stroke <12 h) were included (Phase Inversion Harmonic Perfusion Imaging; bolus kinetic; fitted model function). Three patterns of perfusion were defined in 14 prespecified regions of interest (ROI): 'normal', 'hypoperfusion', and 'no perfusion'. Clinical status was assessed using the National Institutes of Health Stroke Scale (NIHSS) (at baseline and at days 2 to 4). Cranial Computed Tomography (CCT) (days 2 to 4) displayed final infarction. The pattern 'hypoperfusion' (ROIs presumably representing tissue at risk) was tested twofold: (i) Functional impairment by correlating their number with baseline NIHSS. (ii) Viability by correlating their recruitment rate to infarction with clinical course (DeltaNIHSS days 2 to 4). In addition, various predictive values were assessed. Twenty-seven patients were eligible for analysis. The sum of ROIs with 'no perfusion' and 'hypoperfusion' correlated highest with baseline NIHSS (rho=0.78, P<0.001). Recruitment of hypoperfused ROIs to infarction highly correlated with clinical course (rho=0.79, P<0.001). Clinical course dichotomized the patients into subgroups A ('stable', DeltaNIHSS>or=-3) and B ('improved', DeltaNIHSS<or=-4). In A, sensitivity and specificity for hypo- and nonperfused tissue being eventually infarcted were 96% and 88% positive predictive value, PPV 89%, negative predictive value, NPV 96%). In B, sensitivity and specificity for nonperfused tissue eventually being infarcted were 81% and 99% (PPV 99%, NPV 84%). Different perfusion patterns (hypoperfusion, no perfusion) and dysfunctional but viable tissue at risk can be reliably detected by ultrasonic perfusion imaging. This method may give Supplementary information in cases illegible for perfusion-weighted magnetic resonance imaging (PW-MRI).

Aged↗
PubMed2005

Transcranial ultrasound brain perfusion assessment with a contrast agent-specific imaging mode: results of a two-center trial.

BACKGROUND AND PURPOSE: The purpose of this study was to assess brain perfusion with an ultrasound contrast-specific imaging mode and to prove if the results are comparable between 2 centers using a standardized study protocol. METHODS: A total of 32 individuals without known cerebrovascular disease were included in the study. Perfusion studies were performed ipsilaterally in an axial diencephalic plane after intravenous administration of 0.75 mL of Optison. Offline time intensity curves (TIC) were generated in different anatomic regions. Both centers used identical study protocols, ultrasound machines, and contrast agent. RESULTS: In both centers, the comparison of the parameter time to peak intensity (TPI) revealed significantly shorter TPIs in the main vessel structures compared with any parenchymal region of interest (ROI), whereas no significant differences were seen between the parenchymal ROIs. The parameter peak intensity (PI) varied widely interindividually in both centers, whereas the inter-ROI comparison revealed statistical significance (P < 0.05) in most of the cases according to the following pattern: (1) lentiforme nucleus > thalamus and white matter region, (2) thalamus > white matter region, and (3) main vessel > any parenchymal structure. Similar results were achieved in both centers independently. CONCLUSIONS: The study demonstrates that brain perfusion assessment with an ultrasound contrast-specific imaging mode is comparable between different centers using the same study protocol.

Adult↗
PubMed2005

Semiquantitative analysis of ultrasonic cerebral perfusion imaging.

The bolus kinetic in ultrasonic cerebral perfusion imaging is the most favored data acquisition and processing technique. However, there has not yet been convincing evidence for the potential to (semi-) quantitatively describe perfusion. Aim of this study was to determine the intraindividual range of relevant perfusion parameters to describe individual physiological cutoff scores. In 20 healthy volunteers, cerebral perfusion was evaluated using the bilateral approach with phase inversion harmonic imaging and the bolus kinetic. Relevant parameters (time-to-peak intensity, TPI; peak width, PW) were derived in 14 regions-of-interest in both hemispheres. The median and quartile deviation (QD) of these values were individually calculated. Within the 20 individuals, the mean QD of TPI was 0.68 s, and there was no case in which any TPI exceeded the mean more than 2 s. With PW, the mean QD was 1.2 s, and the mean was not exceeded by more than 6 s. Intraindividual perfusion parameters, especially TPI, show a considerable small range. Thus, the bolus kinetic derives reliable semiquantitative information once intraindividual comparison can be accomplished. We therefore propose that bilateral examination with the unaffected hemisphere as referential region should be performed in acute stroke. Future studies have to evaluate the potential of this approach of discriminating ischemia and hypoperfusion in the affected hemisphere.

Adult↗
PubMed2004

Validation of the depletion kinetic in semiquantitative ultrasonographic cerebral perfusion imaging using 2 different techniques of data acquisition.

OBJECTIVE: To validate the potential of ultrasonographic depletion imaging for semiquantitatively visualizing cerebral parenchymal perfusion with contrast burst depletion imaging (CODIM) in comparison with phase inversion harmonic depletion imaging (PIDIM) in healthy volunteers. METHODS: Thirteen healthy adults were examined with both CODIM and PIDIM in accordance with previously described criteria. In addition to the perfusion coefficient, the time to decrease image intensity to 10% above equilibrium intensity from the initial value and the relative error (deviation of measured data from the fitted model) were evaluated to compare the reliability of both techniques in 3 different regions of interest. RESULTS: Perfusion coefficient values did not show significantly differing values in both groups (1.57-1.64 * 10(-2) s(-1) for CODIM and 1.42-1.58 * 10(-2) s(-1) for PIDIM). The relative error was significantly smaller in the PIDIM group (0.38-0.53 for CODIM and 0.18-0.25 for PIDIM; P < .002). CONCLUSIONS: Phase inversion harmonic depletion imaging proved to be more reliable than CODIM because values of the relative error were significantly lower in PIDIM even in this relatively small cohort. This is of interest because the underlying technique, phase inversion harmonic imaging, is more widely available than contrast burst imaging.

Adult↗
PubMed2004

Reliability of semiquantitative ultrasonic perfusion imaging of the brain.

BACKGROUND AND PURPOSE: Contrast burst depletion imaging (CODIM) visualizes cerebral perfusion by destruction of microbubbles and observation of image intensity course. Because of its complexity, artifacts occur. Criteria of reliability to improve diagnostic significance were created and validated. METHODS AND RESULTS: Eighteen healthy volunteers were examined with 2 echo contrast agents (ECAs) and 3 frame rates in 3 regions of interest (ROIs). Perfusion coefficient (PC), Tmin (time to decrease intensity to 10% of its max), and relative error (RE) (deviation of measured data from fitted model) were determined. PC differed significantly neither between CA nor between frame rates (overall mean = 1.60 +/- 0.21 x 10(-2) s-1). Tmin differed significantly between frame rate groups (P < .001, 33.4 +/- 11.2 s/0.5 Hz; 3.6 +/- 2.5 s/5 Hz) since it is related to destruction of microbubbles that occurs with each frame and to the perfusion rate. RE was higher in the Optison group and tended to decrease in ROIs closer to the probe. CONCLUSIONS: PC was independent of frame rate and ECA. Tmin was shorter with higher frame rates. Due to a very rapid decay at 5 Hz, the ideal frame rate should be about 1 Hz, that is, because the number of frames acquired within Tmin and therefore signal-to-noise ratio is higher at 1 Hz. Since the algorithm is complex (high RE) and more artifacts should occur in patients (insufficient bone window, etc), a triggering of the insonations by, for example, heart rate could decrease artifacts and increase diagnostic power of CODIM.

Adult↗
PubMed2003

Parameters of cerebral perfusion in phase-inversion harmonic imaging (PIHI) ultrasound examinations.

The aim was to evaluate phase-inversion harmonic imaging (PIHI) with respect to brain perfusion imaging using a novel "bilateral approach" (depth of examination: 150 mm) and established unilateral approach (100 mm). After bolus injection of two contrast agents (CA, Optison and SonoVue), perfusion-related parameters (time-to-peak intensity, Itpk, peak intensity, Ipk, and peak width, Wpk) were extracted by fitting a model function to time-intensity curves for different regions-of-interest (ROI) in 14 volunteers. In 207 (92%) of 224 ipsilateral ROIs and in 165 (98%) of 168 contralateral ROIs (372 or 95% of 392 altogether), parameters could be derived. Itpk and Wpk of gray matter ROIs did not vary in or between both CA groups (18.1-21.9 s and 7.9-14.2 s). ROIs within arteries showed significantly shorter Itpk (16.1-16.7 s) and longer Wpk (12.8-28.3 s). Level of significance was 0.05 (two-sided). Newer CAs are usable for nonlinear imaging over a wider range of acoustic intensities, so that sensitivity of PIHI is sufficient to image the brain bilaterally. This approach proves to be reliable in patients with adequate bone windows. For acute stroke patients, this implies that both hemispheres can be compared in one instead of two examinations, reducing time of examination by 50%. Furthermore, evaluation of regions close to the probe becomes possible. Thus, the "bilateral approach" should be considered as a new standard approach of acute ultrasonic perfusion imaging.

Adult↗
PubMed2003

Contrast burst depletion imaging (CODIM): a new imaging procedure and analysis method for semiquantitative ultrasonic perfusion imaging.

BACKGROUND AND PURPOSE: Established methods of ultrasonic perfusion imaging using a bolus application of echo contrast agent provide only qualitative data because of various physical phenomena. This study was intended to investigate whether a new ultrasound perfusion imaging method termed contrast burst depletion imaging (CODIM) may provide semiquantitative measures of parenchymal perfusion independent of examination depth and acoustic energy distribution. METHODS: In a system with a constant concentration of contrast agent, analyzing the decrease in image intensity that occurs with microbubble-destructive imaging modes yields parameters that are considered to correlate with tissue perfusion. This method was first evaluated with a perfusion model that showed that the main resulting parameter "perfusion coefficient" (PC) is a monotonic nonlinear function of flow velocity. Seventeen human volunteers were then scanned according to this method with the use of 2 different contrast agents. Results were correlated with those from perfusion-weighted MRI examinations. RESULTS: The PC did not show significant differences in gray matter areas (ranging from 1.466x10(-2) x s(-1) to 1.641x10(-2) x s(-1)) of the brain despite different insonation depths (eg, ipsilateral and contralateral thalamus). In contrast, white matter exhibited significantly lower perfusion values in both imaging modes (PC: 0.604x10(-2) x s(-1) to 0.745x10(-2) x s(-1); P<0.05). CONCLUSIONS: CODIM is a promising new tool of imaging parenchymal (brain) perfusion in healthy persons. The method provides semiquantitative and depth-independent perfusion parameters and in this way overcomes the limitations of the perfusion methods using a bolus kinetic. Further investigations must be done to evaluate the potential of the method in patients with perfusion deficits.

Adult↗
PubMed2003

Brain perfusion imaging of a craniopharyngioma by transcranial duplex sonography.

BACKGROUND AND PURPOSE: The aim of this study was to test a new ultrasound software tool to assess pathological perfusion in a brain tumor patient. METHODS: Tissue harmonic imaging (THI) enables an improved depiction of brain morphology, employing nonlinear parenchyma and ultrasound contrast agent (UCA) backscatter information. With specialized software, morphological information can be separated from perfusion information. Both can be superimposed at a preferred mixing ratio in a single image. RESULTS: Using THI and a perfluoropropane-based UCA, a pathologic perfusion pattern described by abnormal perfused areas in the tumor region could be demonstrated. After superimposing morphologic and perfusion information, subtle structural tumor inhomogeneities were depicted. Craniopharyngioma structure and perfusion defect were confirmed by T2-weighted and perfusion-weighted magnetic resonance imaging. CONCLUSION: Transcranial duplex sonography in combination with contrast specific imaging methods might be helpful to visualize perfusion defects without loss of morphological information.

Adult↗
PubMed2002

Brain perfusion and ultrasonic imaging techniques.

Advances in neurosonology have generated several techniques of ultrasonic perfusion imaging employing ultrasound echo contrast agents (ECAs). Doppler imaging techniques cannot measure the low flow velocities that are associated with parenchymal perfusion. Ultrasonic perfusion imaging, therefore, is a combination of a contrast agent-specific ultrasound imaging technique (CAI) mode and a data acquisition and processing (DAP) technique that is suited to observe and evaluate the perfusion kinetics. The intensity in CAI images is a measure of ECA concentration but also depends on various other parameters, e.g. depth of examination. Moreover, ECAs can be destroyed by ultrasound, which is an artifact but can also be a feature. Thus, many different DAPs have been developed for certain CAI techniques, ECAs and target organs. Although substantial progress in ECA and CAI technology can be foreseen, ultrasound contrast imaging has yet to reliably differentiate between normal and pathological perfusion conditions. Destructive imaging techniques, such as contrast burst imaging (CBI) or time variance imaging (TVI), in combination with new DAP techniques provide sufficient signal-to-noise ratio (SNR) for transcranial applications, and consider contrast agent kinetics and destruction to eliminate depth dependency and to calculate semi-quantitative parameters. Since ultrasound machines are widely accessible and cost-effective, ultrasonic perfusion imaging techniques should become supplementary standard perfusion imaging techniques in acute stroke diagnosis and monitoring. This paper gives an overview on different CAI and DAP techniques with special focus on recent innovations and their clinical potential.

Blood Flow Velocity↗
PubMed2002

Comparison between echo contrast agent-specific imaging modes and perfusion-weighted magnetic resonance imaging for the assessment of brain perfusion.

BACKGROUND AND PURPOSE: Contrast burst imaging (CBI) and time variance imaging (TVI) are new ultrasonic imaging modes enabling the visualization of intravenously injected echo contrast agents in brain parenchyma. The aim of this study was to compare the quantitative ultrasonic data with corresponding perfusion-weighted MRI data (p-MRI) with respect to the assessment of brain perfusion. METHODS: Twelve individuals with no vascular abnormalities were examined by CBI and TVI after an intravenous bolus injection of 4 g galactose-based microbubble suspension (Levovist) in a concentration of 400 mg/mL. Complementary, a dynamic susceptibility contrast MRI, ie, p-MRI, of each individual was obtained. In both ultrasound (US) methods and p-MRI, time-intensity curves were calculated offline, and absolute time to peak intensities (TPI), peak intensities (PI), and peak width (PW) of US investigations and TPI, relative cerebral blood flow (CBF) and relative cerebral blood volume (CBV) of p-MRI examinations were determined in the following regions of interest (ROIs): lentiform nucleus (LN), white matter (WM), posterior (PT), and anterior thalamus (AT). In addition, the M(2) segment of the middle cerebral artery (MCA) was evaluated in the US, and the precentral gyrus (PG) was examined in the p-MRI examinations. In relation to a reference parenchymal ROI (AT), relative TPIs were compared between the US and p-MRI methods and relative PI of US investigations with the ratio of CBF (rCBF) of p-MRI examinations in identical ROIs. RESULTS: Mean TPIs varied from 18.3+/-5.0 (AT) to 20.1+/- 5.8 (WM) to 17.2+/-4.9 (MCA) seconds in CBI examinations and from 19.4+/-5.3 (AT) to 20.4+/-4.3 (WM) to 17.3+/-4.0 (MCA) seconds in TVI examinations. Mean PIs were found to vary from 581.9+/-342.4 (WM) to 1522.9+/-574.2 (LN) to 3400.9+/- 621.7 arbitrary units (MCA) in CBI mode and from 7.5+/-4.6 (WM) to 17.5+/-4.9 (LN) to 46.3+/-7.1 (MCA) arbitrary units in TVI mode. PW ranged from 7.3+/-4.5 (AT) to 9.1+/-4.0 (LN) to 24.3+/-12.8 (MCA) seconds in CBI examinations and from 7.1+/-3.9 (AT) to 8.7+/-3.5 (LN) to 26.7+/-18.2 (MCA) seconds in TVI examinations. Mean TPI was significantly shorter and mean PI and mean PW were significantly higher in the MCA compared with all other ROIs (P<0.05). Mean TPI of the p-MRI examinations ranged from 22.0+/-6.9 (LN) to 23.0+/-6.8 (WM) seconds; mean CBF ranged from 0.0093+/- 0.0041 (LN) to 0.0043+/-0.0021 (WM). There was no significant difference in rTPI in any ROI between US and p-MRI measurements (P>0.2), whereas relative PIs were significantly higher in areas with lower insonation depth such as the LN compared with rCBF. CONCLUSIONS: In contrast to PI, TPI and rTPI in US techniques are robust parameters for the evaluation of cerebral perfusion and may help to differentiate physiological and pathological perfusion in different parenchymal regions of the brain.

Adult↗