Biomedical subjects

Alexander Rauscher

Publications and source records attributed to Alexander Rauscher.

7 recordsLinked to original sources

PubMed2006

Contrast-enhanced, high-resolution, susceptibility-weighted magnetic resonance imaging of the brain: dose-dependent optimization at 3 tesla and 1.5 tesla in healthy volunteers.

OBJECTIVES: We sought to determine the optimal dose of a contrast agent with known high relaxivity on 1.5 and 3 Tesla scanners that would achieve the best compromise between image quality and scan time for the clinical application of contrast-enhanced susceptibility-weighted imaging (CE-SWI). METHODS: Pre- and postcontrast SWI was performed with different contrast agent doses (0.05, 0.1, and 0.2 mmol/kg gadobenate dimeglumine) at both 1.5 and 3 T in 6 healthy volunteers, resulting in 72 examinations. Venograms were created from minimum intensity projection reconstructions over specified deep white matter volumes to enhance the visual appearance of connected venous structures. Three independent radiologists blindly rated the visibility of the veins on a continuous scale of 1 to 10. A general linear model was used for statistical evaluation, with fixed effects of the contrast agent dose, the field strength, the rater and the patients as a random effect. RESULTS: With CE-SWI, we found significant differences in the visibility of the deep veins dependent on the contrast media dose (P=0.02). At 3 T, the visibility of deep venous vessels, with regard to susceptibility effect, image quality, and scan time reduction after a standard contrast agent dose 0.1 mmol/kg was significantly better than that achieved with 0.05 mmol/kg. The visibility was considered equal with 0.1 mmol/kg of the contrast agent to the precontrast images and a dose of 0.2 mmol/kg. At 1.5 T, no significant difference was found between the 4 contrast agent doses. We found no difference in the visibility of the veins with the shorter sequences at 3 T compared with the sequences at 1.5 T. CONCLUSIONS: Only a standard dose (0.1 mmol/kg) of gadobenate dimeglumine is required to achieve the optimum susceptibility effect and image quality at 3 T, together with a reduced scan time. This result can be attributed to the higher relaxivity of gadobenate dimeglumine, compared with conventional gadolinium chelates.

Adult↗

PubMed2005

Subtraction of in-phase and opposed-phase images in dynamic MR mammography.

PURPOSE: To develop and to evaluate an advanced image acquisition and analysis method for collecting T(1)-weighted dynamic 3D MR mammography data sets by using a combined in-phase (IP) and opposed-phase (OP) imaging procedure. MATERIALS AND METHODS: 3D MR mammography data sets were acquired by applying an interleaved gradient-echo OP and IP imaging sequence during administration of contrast agent. A phantom data set, two volunteer breast data sets, and six patient breast data sets were recorded. Subtraction of dynamic in-phase magnitude images was performed for clinical assessment. In addition, the magnitude subtraction (SIPOP) as well as the complex subtraction (cSIPOP) of the IP and OP magnitude and phase images were considered. RESULTS: The detection of small lesions, lesion boundaries, and tumor offshoots in fatty tissue was improved by the subtraction of IP and OP images without the risk of signal cancellation due to partial volume effects. CONCLUSION: Dynamic MR mammography acquisition of IP and OP images in combination with appropriate data processing yields important supplementary information that can support routinely applied diagnostics of breast lesions that are fully embedded in fatty tissue by only marginally increasing acquisition time.

Aged↗

PubMed2005

Nonnvasive assessment of vascular architecture and function during modulated blood oxygenation using susceptibility weighted magnetic resonance imaging.

Susceptibility weighted imaging (SWI) is a BOLD-sensitive method for visualizing anatomical features such as small cerebral veins in high detail. The purpose of this study was to evaluate high-resolution SWI in combination with a modulation of blood oxygenation by breathing of air, carbogen, and oxygen and to directly visualize the effects of changing blood oxygenation on the magnetic field inside and around venous blood vessels. Signal changes associated with the response to carbogen and oxygen breathing were evaluated in different anatomic regions in healthy volunteers and in two patients with brain tumors. In the magnitude images inhalation of carbogen led to significant signal intensity changes ranging from +4.4 +/- 1.9% to +9.5 +/- 1.4% in gray matter and no significant changes in thalamus, putamen, and white matter. During oxygen breathing mean signal changes were smaller than during carbogen breathing. The method is capable of producing high-resolution functional maps of BOLD response to carbogen and oxygen breathing as well as high-resolution images of venous vasculature. Its sensitivity to changes in blood oxygenation was demonstrated by in vivo visualization of the BOLD effect via phase imaging.

Administration, Inhalation↗

PubMed2005

Magnetic susceptibility-weighted MR phase imaging of the human brain.

BACKGROUND AND PURPOSE: MR gradient echo imaging is sensitive to the magnetic susceptibility of different tissue types. The purpose of this study was to investigate the diagnostic potential of MR phase imaging of the human brain. METHODS: High-spatial-resolution, T2*-weighted, single-echo images were acquired in five volunteers and one patient with a brain tumor on a 1.5T system by applying a 3D, first-order, velocity-compensated gradient echo sequence by using a quadrature transmit-receive head coil. Phase images were reconstructed from the raw data and unwrapped by using a region-growing phase-unwrapping algorithm. Low-spatial-frequency components originating from static background susceptibility effects were removed by high-pass filtering. RESULTS: Phase images showed excellent image contrast and revealed anatomic structures that were not visible on the corresponding magnitude images. CONCLUSION: Improved processing of susceptibility-weighted MR phase images offers a new means of contrast for neuroimaging applications.

Adult↗

PubMed2004

Application of an exogenous hyperoxic contrast agent in MR mammography: initial results.

There is interest in applying novel methods to dynamic MR mammography (MRM). One such possibility is to administer an exogenous hyperoxic contrast agent, such as carbogen (95-98% O2 and 2-5% CO2) or pure oxygen (100% O2). We report our first experiences with these agents in a patient with an invasive lobular carcinoma. Fourteen dynamic series were acquired with an rf-spoiled 2D multislice gradient echo sequence, including three measurements while breathing air, four measurements with 100% oxygen, three measurements with air and four measurements with carbogen. Afterwards, 0.1 mmol/kg bw of Gd-DTPA was administered to obtain dynamic T1-weighted double-echo 3D axial gradient echo images (TR/TE1/TE2/alpha=7.8 ms/2 ms/4.76 ms/15 degrees) every 90 s up to 4.5 min after injection. The lesion was well delineated on the contrast-enhanced images, contrary to magnitude images reconstructed from the raw data sets acquired during air/oxygen/carbogen breathing. A ROI-based median-filtered signal-time course revealed a tumor signal increase of roughly 15% between scans acquired during air and oxygen breathing. Though preliminary, these first results are encouraging concerning the exploration of these alternative contrast agents in MRM in greater detail.

Breast Neoplasms↗

PubMed2004

Robust field map generation using a triple-echo acquisition.

PURPOSE: To establish a fast and robust technique for generating magnetic field maps for the correction of geometric distortions in echo-planar magnetic resonance (MR) images. MATERIALS AND METHODS: Multislice gradient-echo (GE) images were acquired at echo times of 6, 6.5, and 7.5 msec in order to cover a field shift range of +/-666 Hz in the resulting B0 maps. To account for possible phase wrap scenarios, seven phase triples were calculated for each pixel. Linear regression of the phase vs. echo time was performed for each set. The slope of the set with the minimum fitting error was taken as the true magnetic field in the respective pixel. RESULTS: Based on the fitting error distribution, the technique is shown to be feasible and effective for assessing the field distribution in the brain at 3 T, especially in inferior brain areas (amygdalae, hippocampus). Examples of echo-planar images distortion corrected using the calculated field maps are shown. CONCLUSION: The approach presented yields robust estimation of magnetic field maps and requires under a minute of additional acquisition time and only seconds of computational time. As such, it is easily possible to apply image distortion correction in routine functional MR imaging (fMRI) studies, enabling improved coregistration of brain activation maps with structures on anatomical images.

Algorithms↗

PubMed2003

Automated unwrapping of MR phase images applied to BOLD MR-venography at 3 Tesla.

PURPOSE: To improve the diagnostic value of BOLD MR-Venography by removing artifacts related to phase wrapping, particularly in regions of large background susceptibilities at high magnetic field strengths. MATERIALS AND METHODS: High resolution, T(2)(*)-weighted, single echo images were acquired on a 3 T system (Medspec 30/80 Avance, Bruker Medical, Ettlingen, Germany) with a three-dimensional, first order velocity compensated gradient echo sequence using a quadrature transmit/receive birdcage head coil. Data of nine healthy subjects and 19 patients were evaluated (age range: 27 to 76 years). To achieve improved MR-venograms, a fully automated region-growing phase unwrapping algorithm and subsequent high pass filtering were applied to phase images prior to the computation of minimum intensity projections. RESULTS: Considerably improved visualization of venous structures in regions of large background susceptibility-induced field inhomogeneities is demonstrated in healthy subjects and patients with brain tumors. CONCLUSION: BOLD MR venograms are improved compared to previous post-processing algorithms. It is now feasible to obtain high-resolution images also in inhomogeneous regions, which increases the clinical potential of BOLD MR-Venography.

Adult↗