Biomedical subjects

Ute Goerke

Publications and source records attributed to Ute Goerke.

3 recordsLinked to original sources

PubMed2006

Application of parallel imaging to fMRI at 7 Tesla utilizing a high 1D reduction factor.

Gradient-echo EPI, blood oxygenation level-dependent (BOLD) functional MRI (fMRI) using parallel imaging (PI) is demonstrated at 7 Tesla with 16 channels, a fourfold 1D reduction factor (R), and fourfold maximal aliasing. The resultant activation detection in finger-tapping fMRI studies was robust, in full agreement with expected activation patterns based on prior knowledge, and with functional maps generated from full field of view (FOV) coverage of k-space using segmented acquisition. In all aspects the functional maps acquired with PI outperformed segmented coverage of full k-space. With a 1D R of 4, fMRI activation based on PI had higher statistical significance, up to 1.6-fold in an individual case and 1.25+/-.25 (SD) fold when averaged over six studies, compared to four-segment/full-FOV data in which the square root R reduction in the image signal-to-noise ratio (SNR) due to k-space undersampling was compensated for by acquiring additional repetitions of the undersampled k-space. When this compensation for loss in SNR was not performed, the effect of PI was determined by the ratio of physiologically induced vs. intrinsic (thermal) noise in the fMRI time series and the extent to which physiological "noise" was amplified by the use of segmentation in the full-FOV data. The results demonstrate that PI is particularly beneficial at this ultrahigh field strength, where both the intrinsic image SNR and temporal signal fluctuations due to physiological processes are large.

Brain↗

PubMed2005

A comparison of signal instability in 2D and 3D EPI resting-state fMRI.

Spatiotemporally structured noise, such as physiological noise, is a potential source of artifacts in functional magnetic resonance imaging (fMRI) and is the main limiting factor for the detection of small blood oxygen level-dependent (BOLD) signal variations. fMRI was employed to detect low-frequency BOLD signal fluctuations, which are thought to be related to spontaneous neuronal activity in the resting human brain. The sensitivity to noise, that is, signal variations of non-BOLD origin, was investigated for two- (2D) and three-dimensional (3D) imaging techniques. Incomplete relaxation between subsequent scans increases the level of temporally and spatially correlated signal variations originating from physiological and/or systemic noise. Although inflow effects are suspected to be reduced in 3D echo-planar imaging (EPI) compared with multi-slice 2D EPI, the noise level was higher in the 3D technique. The noise level in 3D fMRI experiments was significantly increased by instabilities of the transverse steady-state magnetization as the repetition time was of the order of T(2). By implementing radiofrequency spoiling, temporal signal fluctuations and erroneous inter-regional correlation in connectivity maps were diminished to a level present in data sets acquired with 2D EPI.

Adult↗

PubMed2002

Continuous arterial spin labeling using a local magnetic field gradient coil.

Continuous arterial spin labeling (ASL) using a locally induced magnetic field gradient for adiabatic inversion of spins in the common carotid artery of human volunteers is demonstrated. The experimental setup consisted of a helmet resonator for imaging, a circular RF surface coil for labeling, and gradient loops to produce a magnetic field gradient. A spin-echo (SE) echo-planar imaging (EPI) sequence was used for imaging. The approach is independent of the gradients of the MR scanner. This technology may be used if the imaging gradient system does not produce an appropriate magnetic field gradient at the location of the carotid artery-for example, in a head-only scanner-and is a prerequisite for the development of a system that allows continuous labeling during the imaging experiment.

Adult↗