Biomedical subjects

T Schäffter

Publications and source records attributed to T Schäffter.

6 recordsLinked to original sources

PubMed2000

[Radial k-scanning for real-time MR imaging of central and peripheral pulmonary vasculature].

PURPOSE: To depict the central and peripheral pulmonary vessel anatomy with real-time radial MR scanning without respiratory control. METHODS: Three healthy volunteers and one patient with pulmonary embolism proven by spiral CT angiography were studied with a 1.5 T MR imaging system. First, a breath-hold, contrast-enhanced MR angiography was performed for comparison of accuracy. Gradient echo images (TR 16 ms, TE 4 ms, flip angle 18 degrees) were obtained applying a combination of radial scanning and the sliding window reconstruction technique. A dedicated back-projector allowed data reconstruction in real-time with a frame rate of 20 images per second. Scanning was performed during free breathing. RESULTS: The described technique depicted the central and peripheral portions of the normal pulmonary anatomy with comparable image quality as the 3D contrast-enhanced angiography. Visualization of the pulmonary emboli as demonstrated by spiral CT was possible. CONCLUSION: Real-time radial scanning allows promising image acquisition of the pulmonary vasculature without respiratory control. Further technical improvements and clinical trials are required to evaluate its role in the diagnosis of vascular pathologies.

Adult↗

PubMed1999

Motion compensated projection reconstruction.

Over recent years, MRI has shown the capability for real-time applications. Although the acquisition times of fast MRI methods have been reduced significantly, patient motion during a magnetic resonance imaging (MRI) examination still causes artifacts in the image. In this paper, the effects of motion in MRI using a radial acquisition scheme are examined. It is shown that motion can be estimated without the use of additional measurement, based on the acquired projections only. A new reconstruction technique is introduced that integrates a motion compensation algorithm into the MR-reconstruction process, resulting in a significant reduction of blurring artifacts in the reconstructed images. The proposed method is applied to different kinds of motion such as kinetic joint studies.

Algorithms↗

PubMed1999

[MR defecography at 1.5 Tesla with radial real-time imaging and reduced image field].

PURPOSE: To evaluate a new technique for MR defecography with real-time imaging using radial k-space profiles. MATERIALS AND METHODS: A catheter-mounted condom was inserted into the rectum of 16 patients and filled in situ by a mixture of Nestargel and Gadolinium. After multiplanar imaging of the pelvis by high resolution T2-weighted turbo-spin echo sequences, defecation was imaged by a gradient echo sequence with radial k-space filling using a reduced field of view (rFOV) in real-time. The documentation was performed on an S-VHS recorder. RESULTS: At a constant background signal, radial k-space filling yields a real-time impression. An interactive software allowed the operator to modify the slice thickness, slice plane, flip angle and slice angulation during scanning, resulting in an optimum imaging quality of the defecation. CONCLUSIONS: This new imaging technique allows real-time MR defecography in a high-field scanner and provides all anatomical und functional information of the defecation.

Adult↗

PubMed1998

Fast 1H spectroscopic imaging using a multi-element head-coil array.

Fast proton magnetic resonance spectroscopic imaging (MRSI) using a multi-element head-coil array is examined with respect to three aspects: the coil design, the use of an appropriate signal combination method, and the design of the MRSI pulse sequence itself. An eight-element head-coil array has been developed to increase the signal-to-noise ratio (SNR) of MRSI in the human brain. The flexible wraparound design optimally fits different head sizes and thus provides high sensitivity. The signal combination of the individual coil elements is based on the approach proposed by Roemer et al. (Magn. Reson. Med. 16, 192 (1990)). An additional short prescan is performed to provide a good estimate of the complex coil sensitivity profiles, which are used in the signal combination procedure to correct the spectroscopic imaging data for the spatially varying intensity. The use of coil arrays in MRSI has some effect on the requirements for both water and lipid suppression. These techniques and a MRSI pulse sequence that provides a high spectroscopic resolution are described and discussed. Experimental results at 1.5 T show that metabolite maps of N-acetylaspartate (NAA), choline (Cho), phosphocreatine (PCr)/creatine (Cr) can be obtained within a 5-min acquisition time.

Aspartic Acid↗

PubMed1997

Motion-adapted gating based on k-space weighting for reduction of respiratory motion artifacts.

A new modified type of gating is presented that shows the ability to reduce the total scan time with almost conserved image quality compared with conventional gating. This new motion-adapted gating approach is based on a k-space-dependent gating threshold function. MR data acquired are only accepted if the motion-induced displacements measured from a reference position are below the chosen gating threshold function. During the MR measurement the scanner analyses respiratory motion decides in real-time which data in k-space could be measured according to the gating threshold function and performs data acquisition. In the present paper the approach will be described and discussed. Simulations based on in vivo data and initial in vivo experiments are presented to compare different variants of the new approach mutually and to the conventional technique. The analysis given is focused on spin warp type sequences, which are the best candidates for this approach.

Abdomen↗

PubMed1996

Curved slice imaging.

Curved slice imaging based on multidimensional RF pulses is introduced and discussed. This new approach makes it possible to image curved anatomical structures by using MRI. The 2D RF or 3D RF pulses used can be tailored to excite or refocus transverse magnetization of a previously defined arbitrarily curved slice profile in a 3D space. These RF pulses can be integrated into all standard MRI sequences to perform slice selection. The final curved slice image is obtained as a projection of the curved slice magnetization onto a selected imaging plane. The problem of ambiguities arising due to this projection process is addressed. Phantom and in vivo experiments were performed to illustrate the advantages and limitations of this approach.

Brain↗