Wilko Wilkening

Bio: Wilko Wilkening is an academic researcher from Ruhr University Bochum. The author has contributed to research in topics: Perfusion scanning & Ultrasound. The author has an hindex of 19, co-authored 57 publications receiving 906 citations. Previous affiliations of Wilko Wilkening include Siemens.

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

Abstract: 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 posterio...

Contrast Burst Depletion Imaging (CODIM). A New Imaging Procedure and Analysis Method for Semiquantitative Ultrasonic Perfusion Imaging

Abstract: 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 1.466×10−2 s−1 to 1.641×10−2 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: 0.604×10−2 s−1 to 0.745×10−2 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.

Feasibility of contrast-enhanced sonography during resection of cerebral tumours: initial results of a prospective study.

Abstract: The aim of this study was to adapt the ultrasonographical techniques developed for brain perfusion imaging to an intraoperative setting for topographic diagnosis of cerebral tumours During surgery, the patients underwent contrast-enhanced ultrasonography (phase inversion harmonic imaging, bolus kinetic, fitted model function) Endocavity curved array (65EC10, 65 MHz) was used intraoperatively The ultrasound contrast agent SonoVue (Bracco) was administered IV as a bolus injection Off-line, time-intensity curves as well as perfusion maps were calculated and parameters such as peak intensity were locally extracted to characterise perfusion Seven patients with brain tumours of different histologic types were subjected to contrast-enhanced ultrasonography during surgery Tissue differentiation with contrast agent was superior to conventional B-mode ultrasound imaging Intraoperative contrast-enhanced ultrasonography enabled visualisation of cerebral tumours in high spatial resolution

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

Abstract: 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.

Comparison Between Echo Contrast Agent-Specific Imaging Modes and Perfusion-Weighted Magnetic Resonance Imaging for the Assessment of Brain Perfusion

Abstract: 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 M2 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 18.35.0 (AT) to 20.15.8 (WM) to 17.24.9 (MCA) seconds in CBI examinations and from 19.45.3 (AT) to 20.44.3 (WM) to 17.34.0 (MCA) seconds in TVI examinations. Mean PIs were found to vary from 581.9342.4 (WM) to 1522.9574.2 (LN) to 3400.9621.7 arbitrary units (MCA) in CBI mode and from 7.54.6 (WM) to 17.54.9 (LN) to 46.37.1 (MCA) arbitrary units in TVI mode. PW ranged from 7.34.5 (AT) to 9.14.0 (LN) to 24.312.8 (MCA) seconds in CBI examinations and from 7.13.9 (AT) to 8.73.5 (LN) to 26.718.2 (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 (P0.05). Mean TPI of the p-MRI examinations ranged from 22.06.9 (LN) to 23.06.8 (WM) seconds; mean CBF ranged from 0.00930.0041 (LN) to 0.00430.0021 (WM). There was no significant difference in rTPI in any ROI between US and p-MRI measurements (P0.2), 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. (Stroke. 2002;33:2433-2437.)

The EFSUMB Guidelines and Recommendations on the Clinical Practice of Contrast Enhanced Ultrasound (CEUS): Update 2011 on non-hepatic applications

Abstract: Authors F. Piscaglia1, C. Nolsøe2, C. F. Dietrich3, D. O. Cosgrove4, O. H. Gilja5, M. Bachmann Nielsen6, T. Albrecht7, L. Barozzi8, M. Bertolotto9, O. Catalano10, M. Claudon11, D. A. Clevert12, J. M. Correas13, M. D’Onofrio14, F. M. Drudi15, J. Eyding16, M. Giovannini17, M. Hocke18, A. Ignee19, E. M. Jung20, A. S. Klauser21, N. Lassau22, E. Leen23, G. Mathis24, A. Saftoiu25, G. Seidel26, P. S. Sidhu27, G. ter. Haar28, D. Timmerman29, H. P. Weskott30

Pulse inversion Doppler: a new method for detecting nonlinear echoes from microbubble contrast agents

Abstract: A novel technique for the selective detection of ultrasound contrast agents, called pulse inversion Doppler, has been developed. In this technique, a conventional Doppler or color Doppler pulse sequence is modified by inverting every second transmit pulse. Either conventional or harmonic Doppler processing is then performed on the received echoes. In the resulting Doppler spectra, Doppler shifts from linear and nonlinear scattering are separated into two distinct regions that can be analyzed separately or combined to estimate the ratio of nonlinear to linear scattering from a region of tissue. The maximum Doppler shift that can be detected is 1/2 the normal Nyquist limit. This has the advantage over conventional harmonic Doppler that it can function over the entire bandwidth of the echo signal, thus achieving superior spatial resolution in the Doppler image. In vitro measurements comparing flowing agent and cellulose particles suggest that pulse inversion Doppler can provide 3 to 10 dB more agent to tissue contrast than harmonic imaging with similar pulses. Similar measurements suggest that broadband pulse inversion Doppler can provide up to 16 dB more contrast than broadband conventional Doppler. Nonlinear propagation effects limit the maximum contrast obtainable with both harmonic and pulse inversion Doppler techniques.

The EFSUMB guidelines and recommendations for the clinical practice of contrast-enhanced ultrasound (CEUS) in Non-Hepatic Applications: Update 2017 (Long Version)

Abstract: The updated version of the EFSUMB guidelines on the application of non-hepatic contrast-enhanced ultrasound (CEUS) deals with the use of microbubble ultrasound contrast outside the liver in the many established and emerging applications.

Microbubble Ultrasound Contrast Agents: An Update

Abstract: Microbubble contrast agents for ultrasound (US) have gained increasing interest in recent years, and contrast-enhanced US (CEUS) is a rapidly evolving field with applications now extending far beyond the initial improvements achieved in Doppler US. This has been achieved as a result of the safe profile and the increased stability of microbubbles persisting in the bloodstream for several minutes, and also by the availability of specialized contrast-specific US techniques, which allow a definite improvement in the contrast resolution and suppression of signal from stationary tissues. CEUS with low transmit power allows real-time scanning with the possibility of prolonged organ insonation. Several reports have described the effectiveness of microbubble contrast agents in many clinical applications and particularly in the liver, spleen, and kidneys. CEUS allows the assessment of the macrovasculature and microvasculature in different parenchymas, the identification and characterization of hepatic and splenic lesions, the depiction of septal enhancement in cystic renal masses, and the quantification of organ perfusion by the quantitative analysis of the echo-signal intensity. Other fields of application include the assessment of abdominal organs after traumas and the assessment of vesico-ureteral reflux in children. Finally, tumor-targeted microbubbles make possible the depiction of specific biologic processes.

Pulse inversion Doppler: a new method for detecting nonlinear echoes from microbubble contrast agents

Abstract: A novel technique for the selective detection of ultrasound contrast agents, called pulse inversion Doppler, has been developed. In this technique, a conventional Doppler pulse sequence is modified by inverting every second transmit pulse. Either conventional or harmonic Doppler processing is then performed on the received echoes. In the resulting Doppler spectra, Doppler shifts from linear and nonlinear scattering are separated into two distinct regions which can be analyzed separately or combined to estimate the ratio of nonlinear to linear scattering from a region of tissue. The maximum Doppler shift which can be detected is 1/2 the normal Nyquist limit. In vitro measurements comparing flowing agent and cellulose particles suggest that pulse inversion Doppler can provide 3 to 10 dB more agent to tissue contrast than harmonic imaging with similar pulses. Similar measurements suggest that broadband pulse inversion Doppler can provide up to 16 dB more contrast than broadband conventional Doppler.