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K D Merboldt

Publications and source records attributed to K D Merboldt.

At least 55 records · Page 3Linked to original sources
PubMed1991

On the identification of cerebral metabolites in localized 1H NMR spectra of human brain in vivo.

Localized 1H NMR spectra of human brain in vivo are affected by signal overlap, strong spin-spin coupling, and complex J modulation, and therefore differ considerably from those obtained at higher magnetic fields. This paper deals with the assignment of 1H NMR resonances of cerebral metabolites under the experimental conditions used for human investigations. Conventional 7.0-T FID spectra and 2.0 T localized, short echo time STEAM spectra (TE = 20 ms) of aqueous metabolite solutions are compared to in vivo brain spectra of human volunteers and patients. In addition to singlet resonances from N-acetyl aspartate (NAA), creatines, and cholines, short echo time STEAM spectra exhibit multiplets due to the NAA aspartyl group, glutamate, taurine, and myo-inositol. Enhanced levels of cerebral glutamine are detected in patients with liver cirrhosis. For the first time elevated levels of brain glucose are observed in patients with diabetes mellitus.

Animals↗
PubMed1991

Non-invasive 1H NMR spectroscopy of the rat brain in vivo using a short echo time STEAM localization sequence.

Fully localized proton NMR spectra were obtained from the brains of normal anaesthetized rats in vivo using stimulated echo (STEAM) spectroscopy sequences. Investigations were carried out at 2.35 T using a 40 cm bore magnet equipped with an actively shielded gradient system. Localized shimming resulted in water proton linewidths of 6.5-7.8 Hz permitting excellent water suppression. Thus, high-quality proton NMR spectra (TE = 20 ms) were acquired within measuring times of 1.5-6.4 min from 64 to 125 microL volumes-of-interest. The spectra show metabolite resonances due to N-acetyl aspartate, glutamate, creatine and phosphocreatine, cholines, taurine and inositols. The assignments of strongly spin-coupled resonances were confirmed by comparison with spectra from model solutions obtained under identical experimental conditions to those used in vivo. T1 relaxation times as well as relative metabolite concentrations were evaluated from spectra obtained for repetition times ranging from 900 to 6000 ms. Sequential acquisitions of 1.5 min spectra before, during and after killing the animals exhibited a rapid accumulation of lactate, but did not reveal significant changes in other metabolite levels for several hours post mortem.

Animals↗
PubMed1991

High-resolution fast low-angle shot magnetic resonance imaging of the normal hand.

Cross-sectional magnetic resonance (MR) images of the normal hand, wrist, and fingers with an inplane resolution of 0.2-0.4 mm and a slice thickness of 1-2 mm were obtained using a 40-cm bore, 2.35-T MRI system equipped with actively shielded 50 mT m-1 gradient coils. A detailed description of the normal anatomy is given. The T1-weighted, multi-slice, fast low-angle shot (FLASH) MR images presented show a substantial improvement in resolution as compared with earlier reports. Typical investigational times of about 15 min offer a fast scan protocol that is suitable for routine clinical applications. The study further demonstrates the potential of dedicated magnets to facilitate and refine diagnostic MR imaging of hand injuries and hand-related diseases.

Adult↗
PubMed1991

[Localized proton MR spectroscopy. A non-invasive insight into brain metabolism].

Recent progress in image-controlled, localized proton MR spectroscopy offers a non-invasive means of gaining unique insights into brain metabolism in man. Combined studies with MR imaging can be performed within about 1 h. Results obtained in healthy subjects provide the basis for reliable identification and quantification of metabolite concentrations in the CNS and allow determination of their regional variability and age dependence. Clinical applications include infarcts, tumors, and neurodegenerative diseases, and also metabolic disturbances resulting from diseases of the internal organs, such as diabetes mellitus or liver cirrhosis.

Adolescent↗
PubMed1990

0.3-second FLASH MRI of the human heart.

Flow-suppressed FLASH MR images of the human heart have been recorded within a measuring time of 0.3 s using a 2.0-T whole-body research system (Siemens Magnetom) equipped with a conventional 10 mT m-1 gradient system. Subsecond imaging times have been achieved by reducing the repetition time to TR = 4.8 ms and by lowering the spatial resolution to 64 X 128 measured data points. The flip angle of the slice-selective radiofrequency (rf) pulses was adjusted to 10 degrees. Cardiac chambers, ventricular walls, and valves are well delineated in images from a single cardiac cycle using a field of 250 mm and a slice thickness of 8 mm. No motion artifacts were observed as a consequence of the short echo time of TE = 2.8 ms. Distinction between flowing blood and solid structures has been achieved by spatial presaturation of adjacent slices using two slice-selective 90 degrees rf pulses preceding the entire imaging sequence.

Heart↗
PubMed1990

Advances in cardiac applications of subsecond flash MRI.

Flow-suppressed, subsecond FLASH MR images of the normal human heart have been obtained from single cardiac cycles using a 2.0-T whole-body MRI/MRS system (Siemens Magnetom) equipped with conventional 10 mT m-1 gradients. The present results demonstrate further technical improvements as compared to a previous report on the same subject (Magn. Reson. Med. 13:150-157; 1990). Measuring times of 139 msec and 209 msec were achieved by reducing the repetition time to TR = 4.36 msec (TE = 2.8 msec) and the spatial resolution to 32 x 128 or 48 x 128 measured data points, respectively. The flip angle was optimized to 12 degrees. Spatial pre-saturation of 60 mm thick sections adjacent to the imaging plane resulted in a suppression of the blood signal and a clear delineation of the myocardium. Oblique rotation of the imaging slice provides convenient access to the anatomical long axis and short axis views of the heart. EKG-triggered images from separate heartbeats but at different cardiac phases demonstrate that the effective time resolution is considerably less than the actual imaging time.

Electrocardiography↗
PubMed1989

Localized high-resolution proton NMR spectroscopy using stimulated echoes: initial applications to human brain in vivo.

Water-suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo. The STEAM spectroscopy sequence allows single-step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical-shift-selective (CHESS) rf pulses. High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5-T whole-body MRI system (Siemens Magnetom). Volumes-of-interest (VOI) of 64 ml (4 x 4 x 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from 1 s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N-acetyl aspartate, gamma-amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N-acetyl aspartate in white matter to be 6 mM.

Adenine Nucleotides↗
PubMed1989

Cerebral metabolism in man after acute stroke: new observations using localized proton NMR spectroscopy.

Localized proton NMR spectroscopy at 1.5 T using stimulated echoes has been applied to study metabolic alterations in the postischemic phase of patients with acute cerebral infarction. A complete depletion of N-acetyl aspartate in the area of infarction has been observed in a patient studied 4 days after stroke. This finding was paralleled by a dramatic increase in the concentration of lactic acid to about 16 mM within the lesion, indicating continued anaerobic glycolysis. The diluting effect of the edema has been estimated to reduce average metabolite concentrations by about a factor of 3.

Adult↗
PubMed1989

MRI of "diffusion" in the human brain: new results using a modified CE-FAST sequence.

"Diffusion-weighted"MRI in the normal human brain and in a patient with a cerebral metastasis is demonstrated. The method employed was a modified CE-FAST sequence with imaging times of only 6-10 s using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). As with previous phantom and animal studies, the use of strong gradients together with macroscopic motions in vivo causes unavoidable artifacts in diffusion-weighted images of the human brain. While these artifacts are shown to be considerably reduced by averaging of 8-16 images, the resulting diffusion contrast is compromised by unknown signal losses due to motion.

Aged↗
PubMed1989

Localized proton NMR spectroscopy in different regions of the human brain in vivo. Relaxation times and concentrations of cerebral metabolites.

High-resolution proton NMR spectra of normal human brain in vivo have been obtained from selected 27- and 64-ml volumes-of-interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, N-acetylaspartate (NAA), gamma-aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. While T1 relaxation times of most of these metabolites were about 1100-1700 ms without significant regional differences, their T2 relaxation times varied between 100 and 500 ms. The longest T2 values of about (500 +/- 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 +/- 30) ms in the other parts of the brain. No significant regional T2 differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mM for total creatine the resulting NAA concentrations of 13-18 mM are by a factor of 2-3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM.

Brain↗
PubMed1989

The influence of flow and motion in MRI of diffusion using a modified CE-FAST sequence.

Severe motion and flow artifacts are a problem in MRI of diffusion in vivo due to the application of strong magnetic field gradients. Here it is shown that image artifacts can be removed by using a modified fast-scan MRI sequence (CE-FAST) in conjunction with averaging of diffusion-weighted images. In phantom studies slow (coherent) flow (less than 1 mm s-1) in the presence of strong diffusion gradients is shown to cause signal losses in diffusion-weighted images that depend on the relative orientations of the flow direction and the diffusion gradient. On the other hand, pulsatile motions of macroscopic dimensions (e.g., 1 mm, 1 Hz, in-plane) lead to smearing and ghosting of signal intensities along the phase-encoding direction of the images. In both phantoms and rabbit brains in vivo motion artifacts were found to be reducible by averaging 8-16 images. Unfortunately, the resulting image contrast no longer represents a "true" diffusion contrast but is affected by additional signal losses due to motion averaging. All experiments were performed on a 40-cm-bore 2.35-T Bruker Medspec system.

Animals↗
PubMed1989

Localized NMR spectroscopy in vivo. Progress and problems.

Metabolites in brain and muscle of normal human volunteers have been studied by localized 1H and 31P NMR spectroscopy in vivo. Localization was achieved by means of stimulated echo (STEAM) sequences for both water-suppressed 1H NMR (TE = 20 ms) and 31P NMR (TE = 3 ms). Volumes-of-interest and measuring times selected for brain spectroscopy were 8 mL and 6.5 min for 1H NMR and 125 mL and 13 min for 31P NMR, respectively. General problems relating to spatial localization, spectral resolution, and quantitation of in vivo NMR data are discussed with respect to the nucleus and organs under investigation. They are correlated to studies of tissue extracts obtained at field strengths of 2.35 T (Bruker Biospec) and 7.0 T (Bruker MSL 300). Human studies were performed at 2.0 T on a whole-body research system (Siemens Magnetom).

Brain↗
PubMed1989

Noninvasive differentiation of tumors with use of localized H-1 MR spectroscopy in vivo: initial experience in patients with cerebral tumors.

A recently developed method for image-selected localized hydrogen-1 magnetic resonance (MR) spectroscopy was assessed in the differential diagnosis of nine primary and secondary cerebral tumors, including four gliomas, two meningiomas, one neurilemoma, one arachnoid cyst, and one metastasis of breast cancer. Well-resolved H-1 MR spectra of these tumors were obtained in vivo with a conventional 1.5-T whole-body MR imaging system. All tumor spectra were remarkably different from spectra from normal brain tissue. Spectra obtained from different tumors exhibited reproducible differences, while histologically similar tumors yielded characteristic spectra with only minor differences. The observed spectral alterations reflect variations in concentrations and relaxation times of the H-1 MR sensitive pool of free (mobile) metabolites within the tissues. In most cases, the concentrations of N-acetyl-aspartate and creatine/phosphocreatine are reduced below detectability, whereas choline-containing compounds are generally enhanced. The spectral differences between the tumors are mainly due to the differing concentrations of lipids, lactic acid, and carbohydrates. Localized H-1 MR spectroscopy may become an important clinical tool for the differentiation of tumors as well as for therapeutic control.

Adult↗
PubMed1988

Direct FLASH MR imaging of magnetic field inhomogeneities by gradient compensation.

MR images based on gradient echoes are sensitive to artifacts caused by inhomogeneities of the static magnetic field. This paper describes the effects of local gradients in rapid FLASH MR images and presents a way of directly imaging affected areas. The idea is to compensate for signal losses due to mutual cancellation of dephased magnetizations by deliberate "misadjustments" of the refocusing part of the slice selection gradient. In contrast to conventional field imaging techniques no three-dimensional data acquisition or subsequent Fourier analysis is required to obtain images at a particular gradient strength. Conventional as well as inhomogeneity compensated FLASH images have been obtained on phantoms and human heads using a 2.35-T 40-cm magnet and a 1.5-T whole-body system, respectively.

Head↗
PubMed1988

Rapid line scan NMR angiography.

This paper describes a new technique for NMR angiography based on rapid line scan projection imaging and presaturation of stationary spins. The resulting line scan angiograms are free from both misregistration artifacts common to subtraction methods and motion artifacts encountered in Fourier imaging. Moreover, line scan angiograms may be recorded within seconds and offer arbitrary fields of view as well as gradient zooming without problems due to aliasing. Three-dimensional information is obtained by rotation of the read gradient axis generating multiple view angles. Experimental line scan angiograms of the forearms of healthy volunteers have been recorded using a Bruker 2.35-T 40-cm magnet.

Angiography↗
PubMed1987

Flow suppression in rapid FLASH NMR images.

Rapid FLASH (fast low angle shot) NMR images are very sensitive to flow phenomena. In particular, a steady reflow of unsaturated spins from outside the imaging plane results in high image intensities which depend on the flip angle, the repetition time, and the flow velocity. Here we describe a technique that suppresses these signals by saturating remote spins prior to entering the imaging plane, e.g., by intercalating the FLASH sequence with slice-selective 1-2-1 pulse packages. Experiments have been carried out on phantoms and human extremities. Flow artifacts in the phase-encoding direction of the images are strongly reduced. Vascular structures may be easily delineated using difference images obtained with and without flow suppression.

Arm↗
PubMed1987

ECG-triggered arterial FLASH-MR flow measurement using an external standard.

In ECG-triggered FLASH-MR images, the inflow of unsaturated spins into the imaging plane results in the reproducible delineation of time variant flow in the arterial system. With the additional acquisition of an external reference image upstream the arterial vessel under investigation, the quantification of flow is possible with the FLASH-MR sequence in one measurement. The method allows the rapid measurement of arterial flow at least in great vessels.

Aorta, Abdominal↗