Biomedical subjects

H Bruhn

Publications and source records attributed to H Bruhn.

63 records · Page 4Linked to original sources

PubMedDate not supplied

Dynamic MR imaging of human brain oxygenation during rest and photic stimulation.

Dynamic FLASH (fast low-angle shot) magnetic resonance (MR) imaging was used to monitor changes in brain oxygenation in the human visual cortex during photic stimulation. The approach exploits the sensitivity of the gradient-echo signal to susceptibility changes induced by varying concentrations of paramagnetic deoxyhemoglobin in the cerebral blood pool. After the onset of binocular photic stimulation (10 Hz, red light, checker-board), there was a distinct increase in the MR signal in the calcarine cortex within 6-9 seconds, indicating a decrease in the total deoxyhemoglobin concentration. After the stimulation was switched off, the MR signal returned to a basal value within a similar period of time. Assuming enhanced blood flow and only a minor increase in oxygen consumption (production of deoxyhemoglobin) during physiologic activation, the results reflect an enhanced supply of diamagnetic oxyhemoglobin and an increase in the partial oxygen pressure in the capillary and venous blood pools. In addition, a decrease in the basal MR signal in the calcarine cortex was observed during the first 60-90 seconds of persistent activation, which may be understood as an autoregulatory adaptation to increased overall brain activity associated with information processing due to continuous perception of visual stimuli.

Adult↗

PubMedDate not supplied

On the interpretation of proton NMR spectra from brain tumours in vivo and in vitro.

Localized proton NMR spectroscopy in vivo allows focal studies of cerebral metabolites in both man and laboratory animals from image-defined regions as small as 1 mL or 64 microL, respectively. Although brain tumours lead to remarkable spectral alterations relative to normal brain, a number of problems may compromise the interpretation of the results. Potential complications arise from the chosen experimental conditions (method, TE, size and location of volume of interest), from regional metabolic heterogeneity in and around tumours, from differences between human tumours and animal models, and from discrepancies between in vivo and in vitro findings. Strategies and pitfalls are illustrated with use of selected examples from primary brain tumours, a rat tumour model and perchloric acid extracts of resected specimens.

Adult↗

PubMedDate not supplied

Identification of Scyllo-inositol in proton NMR spectra of human brain in vivo.

Scyllo-inositol has been identified in proton NMR spectra of mammalian brain in vitro and in vivo. In contrast to myo-inositol this isomer comprises six equivalent CH protons that yield a singlet resonance at a chemical shift of 3.35 ppm. 1-D and 2-D J-resolved proton NMR studies (7.0 T) of perchloric acid extracts of brain tissues revealed different amounts of scyllo-inositol in man, sheep, cow and rat. Absolute quantification of localized short-echo time proton NMR spectra (2.0 T) of human brain in vivo resulted in scyllo-inositol concentrations of 0.35 +/- 0.06 mM for white matter (n = 25), 0.43 +/- 0.11 mM for grey matter (n = 23) and 0.57 +/- 0.14 mM for cerebellum (n = 10). Evidence for a tight metabolic link to myo-inositol was supported by a simultaneous variation of myo- and scyllo-inositol in patients with various brain diseases.

Animals↗

PubMedDate not supplied

Alzheimer disease: absolute quantification of cerebral metabolites in vivo using localized proton magnetic resonance spectroscopy.

In vivo magnetic resonance spectroscopy of brain metabolites such as N-acetylaspartate and myo-inositol has been proposed for the diagnosis of Alzheimer disease. Thirty patients with probable Alzheimer disease as well as 22 elderly controls underwent quantitative proton magnetic resonance spectroscopy of parietal gray and white matter with use of a short-echo time localization technique (echo time, 20 ms; repetition times, 6,000 and 3,000 ms, 2.0 Tesla) providing access to the regional concentrations of N-acetylaspartate, creatine, choline-containing compounds, myoinositol, glutamate, glutamine, and lactate. No statistically significant alterations of the metabolites were found in patients relative to controls. There were also no differences between patients with early and late onset of the disease and with respect to the presence of APOE-epsilon4 phenotype. A general trend for slightly decreased levels of N-acetylaspartate and creatine was not observed for their respective concentration ratios. In summary, the spectroscopic findings were in accord with known Alzheimer disease neuropathology, i.e., mild gliosis in white matter as well as mildly enhanced cortical atrophy in comparison to elderly controls. However, cortical atrophy with little or no N-acetylaspartate changes provided no evidence for a major decrease of neuronal density or loss of viable neurons. The data do not support the utility of proton magnetic resonance spectroscopy as an early diagnostic tool for Alzheimer disease.

Age of Onset↗

PubMedDate not supplied

Localized proton NMR spectroscopy of brain tumors using short-echo time STEAM sequences.

Recent progress in localized proton NMR spectroscopy has been utilized to improve the spatial resolution and the metabolic specificity in a study of 19 patients with intracranial tumors. Selected examples demonstrate that short echo time stimulated echo acquisition mode sequences are able (a) to account for macroscopic tissue heterogeneity by reducing the volume of interest to 2-8 ml and (b) to facilitate a reasonable characterization of tumor metabolism by increasing the number of accessible metabolites. Proton NMR spectra were acquired within measuring times of 6.5 min on a 2.0 T whole-body system using the imaging headcoil.

Adult↗

PubMedDate not supplied

Proton NMR spectroscopy of cerebral metabolic alterations in infantile peroxisomal disorders.

Noninvasive studies of cerebral metabolism were performed with use of localized proton MR spectroscopy (MRS) in both healthy controls (n = 4, age 6 weeks to 2 years) and infants (n = 4, age 3-15 months) who had impaired peroxisomal functions classified as variants of Zellweger syndrome. All patients revealed a marked decrease of N-acetylaspartate in white and gray matter, thalamus, and cerebellum, indicating impairment of normal neuronal development as well as neuronal loss. In two cases an increase of cerebral glutamine and a decrease of the cytosolic polyol myo-inositol in gray matter and striatum reflected the impact of a concomitant effect on hepatic function. Two cases 3 and 6 months of age exhibited a notable elevation of mobile lipids and/or cholesterol in white matter. These patients with severe disease died within 4 weeks after the MRS examination. While an increase of free fatty acids generally associated with a lysosomal storage disease was not consistently observed by proton MRS of brain, this technique provides a convenient and safe tool for the direct assessment of neuropathologic aspects of Zellweger syndrome such as neuronal degeneration, demyelination, and consequences of compromised liver function.

Adrenoleukodystrophy↗

PubMedDate not supplied

MR-guided localization of suspected breast lesions detected exclusively by postcontrast MRI.

OBJECTIVE: We describe and evaluate a preoperative MRI localization procedure for suspected breast lesions. MATERIALS AND METHODS: Fourteen consecutive patients underwent MR localization of suspected breast lesions discovered with contrast-enhanced MRI but not detected by conventional mammography or ultrasound. In each case diagnostic MRI was repeated after the application of special skin markers. A non-magnetic wire was subsequently inserted into the breast and a second MRI performed to document the position of the wire tip relative to the lesion. RESULTS: The procedure was successful in all 14 patients, enabling excision of the lesion and allowing histological diagnoses. CONCLUSION: We found the described procedure to be quite useful.

Adult↗

PubMedDate not supplied

Signal strength in subsecond FLASH magnetic resonance imaging: the dynamic approach to steady state.

Subsecond fast low-angle shot (FLASH) magnetic resonance imaging (MRI) allows single shot studies of the human heart within measuring times of about 100-300 ms depending on the data matrix. In contrast to conventional FLASH MRI subsecond applications acquire data during the approach to steady state. A detailed analysis of the saturation behavior of the signal is given for the ideal case of a rectangular slice profile. In a second step, realistic slice profiles assuming Gaussian-shaped excitation pulses were taken into account by means of a numerical solution of the Bloch equations. It turns out that the signal strength and the resulting image intensity is considerably higher than may be expected from steady-state considerations. Correspondingly optimized flip angles depend on the number of phase-encoding steps. Assuming long T1 relaxation times as, for example, encountered in muscle and brain tissue and repetition times of 5 ms or less, optimum flip angles are 12 degrees-16 degrees. The use of even higher flip angles (greater than or equal to 20 degrees) causes heavily distorted slice profiles and a dynamic increase of the effective slice thickness. Flip angles of the order of the Ernst angle (6 degrees) correspond to steady-state conditions and lead to considerable signal losses. The theoretical results are confirmed by subsecond FLASH MRI studies of the human heart using a 2.0 T whole-body system (Siemens Magnetom).

Biophysical Phenomena↗

PubMedDate not supplied

Comparative modeling of amoebapores and granulysin based on the NK-lysin structure-structural and functional implications.

Amoebapores, the pore-forming polypeptides of the protozoan parasite Entamoeba histolytica, and effector proteins of porcine and human lymphocytes, namely NK-lysin and granulysin, reveal a substantial sequence similarity despite their enormous evolutionary distance. Moreover, all these polypeptides display antibacterial activity and are in higher concentrations cytolytic to eukaryotic cells. The recently solved NMR structure of NK-lysin enabled us to build the three dimensional structures of amoebapores and granulysin by comparative modeling. The generated models revealed the expected similarities, but also fundamental differences with respect to charge distribution, hydrophobicity and core packing. The combination of these structural properties and known biochemical data provides insight in the different membrane-interacting mechanisms of the proteins. For amoebapores, exposed hydrophobic grooves and a locally loosely packed protein core may allow a rearrangement of the protein and therefore may account for its ability to penetrate the target membrane and to form defined ion channels in planar lipid bilayers. In contrast, the structural features of NK-lysin and granulysin appear to be suitable for a membrane-perturbing mode of action rather than for channel formation.

Amino Acid Sequence↗