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Biomedical subjects

K D Merboldt

Publications and source records attributed to K D Merboldt.

At least 19 recordsLinked to original sources
PubMed1992

Multiple sclerosis in children: cerebral metabolic alterations monitored by localized proton magnetic resonance spectroscopy in vivo.

In vivo proton magnetic resonance spectroscopy of 8 children (7-16 years) with established multiple sclerosis revealed distinct alterations in regional cerebral metabolism associated with different aspects of the disease: (1) Localized proton spectra (2 to 4-ml volumes of interest) from multiple sclerosis plaques were generally characterized by a decrease in N-acetylaspartate and creatine, and an increase in cholines and myo-inositol relative to age-matched control subjects, (2) neither chronic nor enhancing plaques (by gadolinium-diethylenetriamine pentaacetic acid) during an acute exacerbation showed elevated levels of lactate or lipids, (3) spectra from adjacent white matter that did not appear suspicious in magnetic resonance images were similar to those of normal control subjects, and (4) cortical gray matter related to neighboring multiple sclerosis lesions showed a notable reduction of N-acetylaspartate. The present results show that functional impairment in multiple sclerosis is linked to gross metabolic disturbances of neuronal cell chemistry. We suggest that focal demyelination is accompanied by increased membrane precursors of proliferative turnover and is associated with secondary neuronal shrinkage or loss, perhaps extending into related cortical gray matter.

Adolescent↗
PubMed1992

Diffusion imaging of the human brain in vivo using high-speed STEAM MRI.

This paper describes a new method for diffusion imaging of the human brain in vivo that is based on a combination of diffusion-encoding gradients with high-speed STEAM MR imaging. The single-shot sequence 90 degrees-TE/2-90 degrees-TM-(alpha-TE/2-STE)n generates n = 32-64 differently phase-encoded stimulated echoes STE yielding image acquisition times of 576 ms for a 48 x 128 data matrix. Diffusion encoding is performed during the first TE/2-interval as well as during each readout period. Phantom studies reveal a quantitative agreement of calculated diffusion coefficients with literature values. EKG triggering completely eliminates motion artifacts from diffusion-weighted single-shot STEAM images of human brain in vivo. While signal attenuation of the cerebrospinal fluid (CSF) is predominantly due to flow, that observed for gray and white matter results from diffusion. Evaluated diffusion coefficients yield (1.0 +/- 0.1) x 10(-5) cm2 s-1 for gray matter, (0.5 +/- 0.1) x 10(-5) cm2 s-1 for white matter with the diffusion encoding parallel to the main orientation of the myelin sheath of the neurofibrils, and (0.3 +/- 0.1) x 10(-5) cm2 s-1 for white matter and a perpendicular orientation. All studies were performed at 2.0 T using a conventional 10 mT m-1 gradient system.

Brain↗
PubMed1992

Decrease of glucose in the human visual cortex during photic stimulation.

Localized proton NMR spectroscopy was used to study cerebral metabolism in the visual cortex of healthy adults during rest and photic stimulation. Basal lactate levels showed considerable interindividual differences ranging from below detectability (less than 0.3 mM) to about 1 mM without consistent alteration during photic stimulation. Local brain glucose levels were significantly reduced (approximately 50%) during the entire period of photic stimulation and recovered to resting levels (approximately 0.8 mM) within 10 min after the end of stimulation. This decrease reflects the establishment of a new equilibrium due to enhanced delivery (blood flow) and enhanced consumption. The absence of lactate accumulation supports the hypothesis of a rapid efflux of lactate from brain tissue under activated conditions.

Adult↗
PubMed1991

Localized proton NMR spectroscopy using stimulated echoes: applications to human skeletal muscle in vivo.

Localized proton NMR spectroscopy using stimulated echoes (STEAM) has been used to study metabolites in different proximal skeletal muscles of normal volunteers at rest. Single scan water-suppressed proton NMR spectra obtained at 1.5 and 2.0 T (Siemens Magnetom) from a 64-ml volume-of-interest (VOI) yield resonances due to triglycerides, phosphocreatine plus a minor contribution from creatine, and betaines comprising carnitine and choline-containing compounds. The observation of the pH-dependent resonances of carnosine required multiple acquisitions and echo times as short as 20 ms. T1 and T2 relaxation times of muscle metabolites were obtained by varying the repetition time and echo time of the STEAM sequence, respectively. Although rather long T2 values such as 180 ms for (phospho-) creatine correspond to natural resonance linewidths of only 2 Hz, the observed linewidths of typically 10-12 Hz are entirely determined by the short T2 relaxation times (25-30 ms) of the water protons used for shimming. The spectroscopic results from 24 muscle studies on 17 young male volunteers show remarkable intra- and interindividual differences in the absolute signal intensities of mobile lipids. Further metabolic variations were observed for the relative concentrations of betaines (by a factor of 2) and carnosine (by a factor of 3) when total creatine is assumed to be constant.

Carnitine↗
PubMed1991

Diffusion imaging using stimulated echoes.

The application of stimulated echo acquisition mode (STEAM) sequences for NMR imaging of diffusion is especially suited for spins with T1 much greater than T2 as, e.g., encountered in proton NMR studies of biological systems. Molecular self-diffusion coefficients may be calculated from a set of diffusion-weighted images acquired with different gradient strengths. A variation of the diffusion time allows the determination of restricted and/or anisotropic diffusion in cellular systems ranging from plants to humans. Problems associated with the presence of unavoidable macroscopic motions in vivo are demonstrated in diffusion studies of human brain. Motion ghosting in diffusion-weighted images may be overcome by means of a high-speed STEAM sequence yielding single-shot images within subsecond acquisition times.

Diffusion↗
PubMed1991

Cerebral glucose is detectable by localized proton NMR spectroscopy in normal rat brain in vivo.

This contribution reports the first direct and noninvasive observation of cerebral glucose in normal anesthetized rats (n = 16) using short-echo-time localized proton NMR spectroscopy (2.35 T, STEAM, TR = 6000 ms, TE = 20 ms, 125 microliters). In addition to resonances from N-acetyl aspartate (NAA), glutamate, total creatine, cholines, taurine, and myoinositol, all spectra exhibit strongly coupled resonances from glucose (3.43, 3.80 ppm) that are readily identifiable using model solutions. The observed level of cerebral glucose in fasted rats covered a range of 15-40% of that of NAA giving absolute concentrations of 1.1-2.8 mM when NAA is taken to be 7 mM. The arterial blood glucose concentration was 7.7 +/- 0.8 mM in the same group of animals.

Animals↗
PubMed1991

High-speed STEAM MRI of the human heart.

High-speed STEAM MR images of the normal human heart were obtained from single cardiac cycles using a 2.0-T whole-body system equipped with conventional 10 mT m-1 gradients. The single-shot 90 degrees-TE/2-90 degrees-TM-(alpha-TE/2-Acq)n pulse sequence acquires n differently phase-encoded stimulated echoes. Measuring times of 127-254 ms were achieved using a "repetition time" of 3.96 ms in conjunction with data matrices of 32-64 x 128 pixels covering a field-of-view of 250-350 mm. The sequence provides easy access to anatomical short-axis and long-axis views of the heart by single and double oblique rotation of the image orientation. STEAM images resemble the features of spin-echo images with respect to chemical shifts, susceptibilities, and flow. Thus, no additional techniques are required for the suppression of blood signals. EKG-triggered acquisitions demonstrate that slice-selective STEAM sequences using short TM intervals allow an unambiguous delineation of those parts of the myocardium that remain stationary within the selected plane throughout the entire imaging process. Neither spins leaving nor entering the slice defined by the initial 90 degrees RF pulses give rise to a stimulated echo and therefore do not contribute to the resulting image.

Heart↗
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↗