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Biomedical subjects

C Oesterle

Publications and source records attributed to C Oesterle.

7 recordsLinked to original sources
PubMed2001

Separation and quantification of perfusion and BOLD effects by simultaneous acquisition of functional I(0)- and T2(*)-parameter maps.

The nature of the coupling between neuronal activity and the hemodynamic response is the subject of intensive research. As a means to simultaneously measure parametric changes of T2(*), initial intensity (I(0)) and perfusion with high temporal resolution, a multi-image EPI technique with slice-selective inversion recovery (ssIR) for arterial spin labeling was developed and implemented. Comparative measurements with and without the preceding slice-selective inversion pulse were performed. I(0) and R2(*) changes induced by primary visual stimulation were separated. For ssIR-multi-image EPI the average change of I(0) over all 12 subjects was 3.4%, corresponding to a perfusion change of 40 ml/min/100 g, whereas only minor I(0) changes were observed without inversion. On average, the R2(*) of the activated pixels changed by -0.62 sec(-1) without inversion, while a significantly reduced average R2(*) change of -0.46 sec(-1) was calculated for ssIR-multi-image EPI due to a decreased BOLD effect contribution of the intravascular compartment.

Brain↗
PubMed2001

Quiet imaging with interleaved spiral read-out.

The acoustic noise generated during an MRI sequence can be effectively reduced with the help of soft gradient pulses using sinusoidal ramps. The long slope duration, however, leads to long acquisition times. The use of interleaved spiral trajectories, calculated with long gradient slopes, is proposed to reduce the acquisition time while maintaining low acoustic noise levels. The practicality of this approach is demonstrated on phantom and volunteer images.

Acoustics↗
PubMed2000

Benefits and pitfalls of keyhole imaging, especially in first-pass perfusion studies.

A comparison of dynamic results of a multi-echo contrast-enhanced perfusion study obtained from a keyhole imaging experiment and the results from low-resolution updates is presented. If, for each dynamic state, a separate reference image exists, high spatial resolution in the dynamic results can be preserved through keyhole imaging. If only one reference image can be used, the dynamic key-hole results still offer high spatial frequency content due to spatial phase discontinuities in the images. These often exist at the outline of organs and result from the fat in connective tissues. If the basic assumption of keyhole imaging, namely, that the relevant information is centered in k-space, is violated, as in T2*-weighted gradient-echo images, keyhole imaging can lead to erroneous results even though the update images themselves seem to be free of any artifacts.

Animals↗
PubMed1999

Spiral reconstruction by regridding to a large rectilinear matrix: a practical solution for routine systems.

Spiral trajectories offer a number of attractive features for fast imaging. A practical problem for the implementation on routine magnetic resonance scanners is the lack of appropriate and efficient reconstruction algorithms in the available scanner software. In this paper, a simple way to implement a spiral reconstruction algorithm is described that avoids the data interpolation required by gridding approaches commonly used. Using the optimized fast Fourier transform built into each scanner, it offers image reconstruction times of less than 1 second and thus allows the introduction of spiral imaging to routine scanners.

Algorithms↗
PubMed1998

Improvement of spatial resolution of keyhole effect images.

An algorithm is proposed which improves the spatial resolution of difference or effect images acquired with a keyhole sampling strategy. This new reconstruction algorithm uses a priori information about sharp structures in the observed signal changes from a high resolution reference scan. The potential of this algorithm even being able to deal with noisy effect images is illustrated by application to functional MRI data.

Algorithms↗
PubMed1996

Implementation of a fast gradient-echo SVD encoding technique for dynamic imaging.

In the paper, the results of a fast gradient-echo implementation of the singular value decomposition (SVD) encoding technique for dynamic imaging are presented. The method used is an adaptation with several critical modifications of a keyholetype approach previously proposed but not implemented. The method was tested by imaging the events following injection of a contrast agent into a phantom, producing a series of dynamic image updates. It is demonstrated that, for this type of application, the SVD encoding technique adequately follows dynamic changes with even a small number of encodes. The result is compared qualitatively to that obtained by standard Fourier-based keyhole imaging and is shown to provide improved spatial resolution of dynamic events when updating with the same number of encodes.

Algorithms↗