Showing papers by "Wilko Wilkening published in 2004"
TL;DR: PIHI was able to predict the localisation and size of the eventual infarction even if no early CCT signs were seen, and a surrounding hypoperfused region was identified, where tissue survived after recanalisation of the initially occluded middle cerebral artery.
Abstract: 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.
37 citations
TL;DR: 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.
Abstract: 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 inversionharmonic 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). Condusions. 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.
18 citations
TL;DR: Criteria of reliability to improve diagnostic significance were created and validated and perfusion coefficient, T min, and relative error (RE) (deviation of measured data from fitted model) were determined, finding PC was independent of frame rate and ECA.
Abstract: 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.
10 citations
23 Aug 2004
TL;DR: To overcome the shortcomings of incoherent superposition, a technique for coherent filtered blending of the echoes is developed that combines echoes representing different transmit foci, and echoes from neighboring beam lines may also be considered.
Abstract: For several practical and technical reasons related to e.g. computational cost, hardware complexity, sensitivity to motion artifacts, frame rate and SNR most medical ultrasound machines use a fixed focus on transmit and dynamic focusing and filtering on receive. To further improve image resolution, multiple focal zones may be used. The resulting A-lines are superimposed (blended) after envelope detection by means of depth dependent weighting. Due to this incoherent superposition, the spatial resolution of the resulting image can only reach the resolution of the images that were superimposed. To overcome the shortcomings of incoherent superposition we have developed a technique for coherent filtered blending of the echoes. In addition to echoes representing different transmit foci, echoes from neighboring beam lines may also be considered.
4 citations
23 Aug 2004
TL;DR: In this article, the authors proposed non-uniform sampling for flow velocity estimation in PWD systems, where the sampling intervals are chosen nonuniformely, and the total time span can be increased, while keeping N and the shortest sampling interval constant.
Abstract: Our group has previously proposed nonuniform sampling for flow velocity estimation. Standard pulsed wave Doppler (PWD) systems acquire an ensemble of N echoes per beam line at a constant pulse repetition frequency f/sub prf/. The total time span determines the velocity resolution, and f/sub prf/ the unambiguous velocity range. The ensemble size N is by approximation inversely proportional to the frame rate, assuming that the system performs interleaving. If sampling intervals are chosen nonuniformely, the total time span can be increased, while keeping N and the shortest sampling interval constant. In this example velocity range and frame rate are unchanged, and measurement accuracy for low flow velocities is gained at the expense of measurement accuracy for high flow velocities. The extended time span makes the flow estimation susceptible to effects of acceleration and decorrelation. Thus, we have refined the flow estimation algorithms by taking into account both effects.
23 Aug 2004
TL;DR: In this paper, the amplitude and phase dependencies of the fundamental and harmonic spectral components in the Doppler processing were incorporated to improve the sensitivity of contrast-specific imaging. But the effect of nonlinear scattering from microbubbles is not contrast specific, yet it contributes more to the echo signal.
Abstract: The measurement of blood flow velocities is a challenging task. The effect of nonlinear scattering from microbubbles is commonly used for contrast specific imaging. Linear scattering from microbubbles is not contrast specific, yet it contributes more to the echo signal. To optimize flow imaging with contrast agents, it is desirable to exploit linear scattering and nonlinear scattering to improve sensitivity without sacrificing specificity. This can be achieved by incorporating the amplitude and phase dependencies of the fundamental and harmonic spectral components in the Doppler processing. The separability of the aforementioned components is achieved by phase-coding (or amplitude-coding) of the transmit pulses.