Biomedical subjects

Michael Szimtenings

Publications and source records attributed to Michael Szimtenings.

5 recordsLinked to original sources

PubMed2004

Rapid extended coverage simultaneous multisection black-blood vessel wall MR imaging.

A two-dimensional rapid extended coverage (REX) rapid acquisition with relaxation enhancement (RARE) pulse sequence for simultaneous multisection double inversion-recovery (DIR) black-blood vessel wall magnetic resonance (MR) imaging was developed. Aortic vessel wall MR imaging was performed in five healthy subjects (mean age, 33 years +/- 4 [SD]) and five patients with atherosclerotic disease (mean age, 67 years +/- 11.7). Shortening of blood inversion time and imaging of multiple sections after single DIR block resulted in simultaneous acquisition of up to 20 aortic wall sections in less than 1 minute (spatial resolution, 0.97 x 0.97 x 3 mm(3)). Higher signal-to-noise ratios per unit time per section (16.0 +/- 2.45 vs 7.5 +/- 1.10, P <.05), no significant changes in contrast-to-noise ratios (15.0 +/- 5.3 vs 20.1 +/- 3.9, P >.05), and 17-fold improvement in acquisition time compared with those at conventional single-section DIR RARE imaging was achieved. Use of the REX method significantly shortened aortic imaging acquisition times without degrading image quality.

Adult↗

PubMed2003

In vivo time-resolved quantitative motion mapping of the murine myocardium with phase contrast MRI.

Myocardial motion of healthy mice and mice with myocardial infarction was assessed in vivo by phase contrast (PC) cine MRI. The imaging module was a segmented fast low angle shot (FLASH) sequence with velocity compensation in all three gradient directions. To accomplish additional motion encoding, the spin phase was prepared using bipolar gradient pulses, which resulted in a linear dependence between the voxel velocity and spin phase. This method provided accurate quantification of the velocity magnitude and direction of the murine myocardium at a spatial resolution of 234 microm and a temporal resolution of about 10 ms. The acquisition was EKG-gated and the mice were anesthetized by inhalation of 1.5-4.0 vol.% isoflurane at 1.5 l/min oxygen flow. To validate the MRI measurements, an experiment with a calibrated rotating phantom was performed. Deviations between MR velocity measurements and optical assessment by a light detector were lower than 1.6%. During our study, myocardial motion velocities between 0.4 cm/s and 1.7 cm/s were determined for the healthy murine myocardium across the heart cycle. Areas with myocardial infarction were clearly segmented and showed a motion velocity which was significantly reduced. In conclusion, the method is an accurate technique for the assessment of murine myocardial motion in vivo.

Animals↗

PubMed2003

High-resolution MRI with cardiac and respiratory gating allows for accurate in vivo atherosclerotic plaque visualization in the murine aortic arch.

Genetically engineered mouse models provide enormous potential for investigation of the underlying mechanisms of atherosclerotic disease, but noninvasive imaging methods for analysis of atherosclerosis in mice are currently limited. This study aimed to demonstrate the feasibility of MRI to noninvasively visualize atherosclerotic plaques in the thoracic aorta in mice deficient in apolipoprotein-E, who develop atherosclerotic lesions similar to those observed in humans. To freeze motion, MR data acquisition was both ECG- and respiratory-gated. T(1)-weighted MR images were acquired with TR/TE approximately 1000/10 ms. Spatial image resolution was 49 x 98 x 300 micro m(3). MRI revealed a detailed view of the lumen and the vessel wall of the entire thoracic aorta. Comparison of MRI with corresponding cross-sectional histopathology showed excellent agreement of aortic vessel wall area (r = 0.97). Hence, noninvasive MRI should allow new insights into the mechanisms involved in progression and regression of atherosclerotic disease.

Animals↗

PubMed2003

Flow encoded NMR spectroscopy for quantification of metabolite flow in intact plants.

An NMR flow quantification technique applicable to metabolite flow in plants is presented. It combines flow sensitive magnetization preparation with slice selective spectroscopy. Flow encoded NMR spectroscopy is described to quantify, for the first time, flow velocities of metabolites in plants non-invasively. Flow sensitivity is introduced by magnetization preparation based on a stimulated echo experiment, prior to slice selective spectroscopy. For flow quantification eight different flow-weighted spectra are collected. With this flow preparation very slow flow velocities down to 0.1mm/s can be detected and small amounts of flowing metabolites can be observed despite the large background signal of stationary and flowing water. Important sequence optimization steps include appropriate choice of experimental parameters used for flow encoding as well as complete balancing of eddy currents from the flow encoding gradients. The method was validated in phantom experiments and applied in vivo. Examples of quantitative flow measurements of water and metabolites in phantoms and plants are provided to demonstrate the reliability and the performance of flow encoded spectroscopy.

Magnetic Resonance Spectroscopy↗

PubMed2002

What are the driving forces for water lifting in the xylem conduit?

After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal- and non-invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high-resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to - 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel- and gas bubble-supported interfacial gradients. The multiforce theory overcomes the problem of the Cohesion Theory that life on earth depends on water being in a highly metastable state.

Journal Article↗