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M von Kienlin

Publications and source records attributed to M von Kienlin.

18 recordsLinked to original sources
PubMed1998

Three-dimensional 31P magnetic resonance spectroscopic imaging of regional high-energy phosphate metabolism in injured rat heart.

The purpose of this study was to measure the spatially varying 31P MR signals in global and regional ischemic injury in the isolated, perfused rat heart. Chronic myocardial infarcts were induced by occluding the left anterior descending coronary artery eight weeks before the MR examination. The effects of acute global low-flow ischemia were observed by reducing the perfusate flow. Chemical shift imaging (CSI) with three spatial dimensions was used to obtain 31P spectra in 54-microl voxels. Multislice 1H imaging with magnetization transfer contrast enhancement provided anatomical information. In normal hearts (n = 8), a homogeneous distribution of high-energy phosphate metabolites (HEP) was found. In chronic myocardial infarction (n = 6), scar tissue contained negligible amounts of HEP, but their distribution in residual myocardium was uniform. The size of the infarcted area could be measured from the metabolic images; the correlation of infarct sizes determined by histology and 31P MR CSI was excellent (P < 0.006). In global low-flow ischemia (n = 8), changes of HEP showed substantial regional heterogeneity. Three-dimensional 31P MR CSI should yield new insights into the regionally distinct metabolic consequences of various forms of myocardial injury.

Adenosine Triphosphate↗
PubMed1998

Magnetic resonance microimaging for noninvasive quantification of myocardial function and mass in the mouse.

The purpose of this work was to develop high-resolution cardiac magnetic resonance imaging techniques for the in vivo mouse model for quantification of myocardial function and mass. Eight male mice were investigated on a 7-Tesla MRI scanner. High-quality images in multiple short axis slices (in-plane resolution 117 microm2, slice thickness 1 mm) were acquired with an ECG-gated cine sequence. Left ventricular end-diastolic and end-systolic volumes and mass were calculated from segmented slice volumes. There was precise agreement of left ventricular mass determined ex vivo and by MRI. Intraobserver (5%) and interobserver (5%) variability of in vivo MR measurements were low.

Animals↗
PubMed1998

Localized spectroscopy from anatomically matched compartments: improved sensitivity and localization for cardiac 31P MRS in humans.

Several pioneering studies have demonstrated that localized 31P NMR spectroscopy of the human heart might become an important diagnostic tool in cardiology. The main limitation is due to the low sensitivity of these experiments, allowing only crude spatial resolution. We have implemented a three-dimensional version of SLOOP ("spectral localization with optimal pointspread function") on a clinical instrument. SLOOP takes advantage of all available a priori information to match the size and the shape of the sensitive volumes to the anatomical structures in the examined subject. Thus, SLOOP reduces the contamination from adjacent organs and improves the sensitivity compared to conventional techniques such as ISIS or chemical shift imaging (CSI). Initial studies were performed on six healthy volunteers at 1.5 T. The good localization properties are demonstrated by the absence of resonances from blood in the heart spectra, and by PCr-free spectra from the liver. Compared to conventional CSI, the signal-to-noise ratio of the SLOOP heart spectra was improved by approximately 30%. Taking into account the varying excitation angle in the inhomogeneous B1 field of the surface coil, the SLOOP model computes the local spin saturation at every point in space. Therefore, no global saturation correction is required in the quantitative evaluation of local spectra. In this study, we found a PCr/gamma-ATP ratio in the left ventricular wall of 1.90 +/- 0.33 (mean +/- standard deviation).

Adenosine Triphosphate↗
PubMed1997

Theoretical evaluation and comparison of fast chemical shift imaging methods.

Magnetic resonance chemical shift imaging (CSI) is becoming the method of choice for localized NMR spectroscopic examinations, allowing simultaneous detection of NMR spectra from a large number of voxels. The main limitation of these methods is their long experimental duration. A number of fast CSI experiments have been presented, promising to reduce that duration. In this contribution the criteria for evaluating and optimizing the sensitivity of fast CSI experiments are elaborated. For a typical experiment in the human brain, the performance of various methods is compared. While conventional CSI provides optimal sensitivity per unit time, it is shown in which circumstances fast sequences allow a shorter experimental duration. Using these results, the best method for any experimental requirements can be selected.

Brain Chemistry↗
PubMed1997

Double-tuned four-ring birdcage resonators for in vivo 31P-nuclear magnetic resonance spectroscopy at 11.75 T.

A high signal-to-noise ratio (SNR) in 31P-nuclear magnetic resonance (31P-NMR) spectroscopy can be obtained only with good B0-field homogeneity and optimal coil sensitivity. This demands double-tuned coils with a highly sensitive 31P channel and an additional 1H channel for 1H-magnetic resonance imaging, shimming, 1H decoupling, and nuclear Overhauser enhancement (NOE). For studies on an 11.75 T magnet, we built coils derived from the four-ring birdcage design originally described by Murphy-Boesch. A comparison with conventional, single-tuned coils shows that, in spite of double tuning, there is no significant loss in 31P sensitivity while the 1H channel provides the requested performance. The coil design offers the advantage of circular polarization on both channels.

Animals↗
PubMed1996

Correlation-peak imaging.

Identification and quantitation in conventional 1H spectroscopic imaging in vivo is often hampered by the small chemical-shift range. To improve the spectral resolution of spectroscopic imaging, homonuclear two-dimensional correlation spectroscopy has been combined with phase encoding of the spatial dimensions. From the theoretical description of the coherence-transfer signal in the Fourier-transform domain, a comprehensive acquisition and processing strategy is presented that includes optimization of the width and the position of the acquisition windows, matched filtering of the signal envelope, and graphical presentation of the cross peak of interest. The procedure has been applied to image the spatial distribution of the correlation peaks from specific spin systems in the hypocotyl of castor bean (Ricinus communis) seedlings. Despite the overlap of many resonances, correlation-peak imaging made it possible to observe a number of proton resonances, such as those of sucrose, beta-glucose, glutamine/glutamate, lysine, and arginine.

Ricinus communis↗
PubMed1994

Investigation of the 1H NMR visibility of lactate in different rat and human brain cells.

In recent years, 1H MRS has been used in a number of studies to measure the lactate content of brain, and it is generally assumed that the methyl resonance at 1.3 ppm reflects the total amount of lactate present in the tissue. However, reduced NMR visibility of lactate has recently been reported for blood, heart and skeletal muscle as well as for bacteria. We have assessed the NMR visibility of lactate in cultures of human and rat brain cells, comparing the concentrations measured by NMR and by biochemical methods. Contributions of fatty acids have been eliminated using their different relaxation behavior. We found approximately 30% of the lactate to be undetectable by NMR in the studied cell cultures. While the mechanism partially masking lactate in 1H spectra is not yet understood, the potential invisibility of some pools of lactate to NMR may greatly affect the interpretation of brain spectra.

Animals↗
PubMed1991

Biotransformation of 2-fluoroaniline in rats studied by in vivo 19F NMR.

The present study describes results from an in vivo 19F NMR study on rats exposed to the xenobiotic compound 2-fluoroaniline. Qualitative pharmacokinetics and the biotransformation of 2-fluoroaniline were studied after exposure to 50 mg/kg body wt 2-fluoroaniline. Accumulation and elimination of the parent compound in and from the liver of exposed animals were readily observed. Metabolites formed in the liver were shown to be efficiently excreted from the liver, as the amount of metabolites in this organ was always less than 10% of the maximum amount of the parent compound observed. In the bladder, rapid accumulation of 2-fluoroaniline-derived metabolites was detected. The metabolite pattern was shown to change in time, with the parent compound being dominantly present during the first hours of exposure. N-acetylated products (4-acetamido-3-fluorophenyl sulphate and 4-acetamido-3-fluorophenyl glucuronide) were observed to accumulate more slowly in the bladder than the non-acetylated products (4-amino-3-fluorophenyl sulphate and 4-amino-3-fluorophenyl glucuronide). Urine metabolite patterns obtained from the bladder in vivo were compared to those obtained during metabolic cage experiments.

Administration, Oral↗
PubMed1990

Echo-planar imaging with asymmetric gradient modulation and inner-volume excitation.

Single-shot echo-planar imaging is notoriously vulnerable to image artifacts, arising from the necessity of alternate echo time reversal during image reconstruction and from static field inhomogeneity. A technique for overcoming these problems, which further permits imaging on systems with relatively poor gradient waveforms, when data are collected always with the same gradient polarity, is presented. Subsectional and 3D volume imaging are presented as well as a novel phase-correction method for Hermitian symmetry in "half-Fourier" echo-planar imaging.

Humans↗
PubMed1990

Single-shot localized echo-planar imaging (STEAM-EPI) at 4.7 tesla.

The resolution and homogeneity limitations of echo-planar imaging (EPI) are overcome by zoom imaging of an easily shimmed localized volume. Use of the stimulated echo enables single-shot localization. In vivo 0.5-mm resolution EPI images of selected regions of a cat brain at 4.7 T are presented.

Animals↗
PubMed1989

Correlation between intracellular pH and lactate levels in the rat brain during potassium cyanide induced metabolism blockade: a combined 31P-1H in vivo nuclear magnetic spectroscopy study.

Female Sprague-Dawley rats were chronically implanted with nuclear magnetic resonance (NMR) surface coils tuned to both 31P and 1H NMR frequencies. Alternated 31P and 1H NMR spectra were recorded at 2.5 min intervals in waking rats or rats under pentobarbital or chloral hydrate anesthesia. After a reference period, the metabolic changes were observed following intraperitoneal injection of potassium cyanide (KCN, 5 mg/kg). Among previously observed changes typical of cellular anoxia, attention was specifically paid to the relationship between the intracellular pH values and the lactate levels. The results show a strong lactate-pH correlation in waking rats, a partial decoupling under nembutal anesthesia and a complete decoupling under chloral hydrate anesthesia.

Animals↗
PubMed1989

Comparison of single-shot localization methods (STEAM and PRESS) for in vivo proton NMR spectroscopy.

Two single-shot localization techniques, STEAM and PRESS, are analyzed with regard to specifications for in vivo localized proton NMR. In particular, attention is paid to optimum signal intensity per unit volume, sensitivity to motion and diffusion, shortest attainable echo time, water suppression and editing possibilities. Experimental results are shown for cat brain at 4.7 T and human brain at 1.5 T. Both STEAM and PRESS are highly effective localization methods. For long echo times, PRESS is the method of choice, because it offers a factor of two gain in signal intensity. In addition, the method is less sensitive to motion and diffusion, and not susceptible to multiple-quantum effects. STEAM offers advantages for observation of (coupled) metabolites with short T2, because (a) shorter TEs can be attained and (b) effective water suppression sequences can be implemented without penalty in echo time. Differences relating to editing possibilities and B1 dependence, possibly important in choosing a method, are discussed.

Animals↗
PubMedDate not supplied

Three-dimensional coronary angiography of the perfused rat heart.

The purpose of this work was to visualize the whole three-dimensional coronary artery tree of the perfused beating rat heart using three-dimensional MRI. The spatial resolution amounts to 140 microns. Also, vessels having smaller diameters could be detected. Different strategies for the visualization of the three-dimensional coronary angiograms including maximum intensity projection, data thresholding, and segmentation, were shown. The coronary artery tree was best visualized by hysteresis threshold segmentation and subsequent surface reconstruction.

Animals↗