Search PubMed⌕ Search

Biomedical subjects

H Bruhn

Publications and source records attributed to H Bruhn.

At least 37 records · Page 2Linked to original sources
PubMed1995

[Patchy changes in white matter in cranial computerized and magnetic resonance tomography--significance for (differential) diagnosis of dementia of the Alzheimer type and vascular dementia].

With the advancement of technical progress, especially with respect to magnetic resonance imaging, patchy cerebral white matter lesions (WML) are being found with increasing frequency. The (differential) diagnosis between the two main dementias of old age, (senile) dementia of the Alzheimer type ([S]DAT) and vascular dementia (VD) is made more frequently in favour of the latter, since the detection of WML leads to support a vascular origin for dementia. The present article reviews the literature concerning X-ray computed tomography (CT) and magnetic resonance imaging (MRI) in these disorders. For comparison purposes some methodological problems must be taken into account including different scoring systems for WML severity, differences in imaging techniques and in the criteria for the selection of patients and controls. A great number of studies demonstrates a strong association of frequency and severity of WML with increasing age and presence of cerebrovascular risk factors such arterial hypertension. Some studies revealed an association with neuropsychiatric deficits including gait disorders, urinary incontinence, affective lability and reduced attention and information processing speed. In CT studies, about 30% of patients with (S)DAT had WML but 36-88% in MR studies. However, only few studies controlled for the presence of cerebrovascular risk factors. More recent studies - with improved techniques - revealed a higher frequency of (slight or moderate) WML in the (S)DAT group compared to controls. The prevalence of WML in VD patients was 75-97% in CT studies and about 100% in MR studies. Therefore, without the presence of WML, the diagnosis of VD is currently in doubt. A number of in vivo investigations proved consistently - and with different methods - that cerebral blood flow was reduced in WML regions. As shown in some studies the neuropathologic correlates of WML have in common that the relative tissue water content is increased: This includes inflammation, gliosis, complete and incomplete infarctions, dilation of the perivascular (Virchow-Robin) spaces with myelin atrophy. Thus the finding of WML in watershed areas can be understood. Three case reports serve to illustrate the problems pointed out. In conclusion, the occurrence of WML is an unspecific finding which is observed in up to 50% of the elderly. Diagnostic classification as "vascular lesions" or signs of "vascular encephalopathy" or VD based on CT or MRI alone, should not be made.

Aged↗
PubMed1994

The effect of acetazolamide on regional cerebral blood oxygenation at rest and under stimulation as assessed by MRI.

The sensitivity of gradient echo magnetic resonance imaging (MRI) to changes in cerebral blood oxygenation (CBO) has been introduced for mapping functional brain activation. Here, we report that this approach allows monitoring autoregulation in the human brain under vasodilatory stress. Following the administration of acetazolamide, signal intensities of deoxyhemoglobin-sensitive images increased in cortical and subcortical gray matter and to a lesser extent in white matter. This result reflects a venous hyperoxygenation stemming from an increase in cerebral perfusion with oxygen consumption remaining constant. In addition, pharmacologic induction of vasodilation attenuated activity-related MRI signal changes in the visual cortex under photic stimulation. Although intersubject variability was high, this finding indicates individually persisting autoregulatory responsiveness to functional challenge despite an "exhausted" reserve capacity. It is suggested that recording CBO by MRI will foster our understanding of modulation of vasomotor tone and cerebral perfusion. Furthermore, this technique may prove valuable for assessing the cerebrovascular reserve capacity in patients with carotid artery occlusive disease.

Acetazolamide↗
PubMed1994

[The determination of the T2* relaxation time for characterizing trabecular bone].

Spongy bone produces local magnetic field inhomogeneities and leads to shortening of the transverse relaxation time from bone marrow. This increased signal decay affects the T2 relaxation time. Measurements of the T2* time from the 4th lumbar vertebra were carried out in 48 normals and 20 patients with osteoporosis. A special multigradient echo technique was used, the echo times selected in relation to phase coherence of the water and fat signals. T2* times showed slight increase in relation to age. Patients with osteoporosis showed significantly increased T2* times (19.9 +/- 3.8 ms) compared to the normal control group (13.4 +/- 1.9 ms). From these findings it is possible to judge the quality of the trabecular structure.

Adult↗
PubMed1994

MR-guided biopsy of suspect breast lesions with a simple stereotaxic add-on-device for surface coils.

A guiding attachment is described that transforms a conventional magnetic resonance (MR) imaging surface coil into a stereotaxic biopsy unit. Eight patients, aged 38-66 years (mean, 54 years), with suspect breast lesions detected exclusively at contrast material-enhanced MR imaging underwent MR-guided needle biopsy with this unit. Diagnostic material was successfully aspirated in all patients (four carcinomas, three fibroadenomas, and one intraductal hyperplasia), and the diagnosis was subsequently confirmed at surgical biopsy. This technique promises to increase the diagnostic specificity for lesions seen solely at MR imaging.

Adult↗
PubMed1994

In vivo proton magnetic resonance spectroscopy of the brain in a patient with L-2-hydroxyglutaric acidemia.

Morphologic appearance and metabolic disturbances of the brain of a patient with L-2-hydroxyglutaric acidemia were investigated with use of magnetic resonance imaging and localized proton magnetic resonance spectroscopy in vivo. Whereas magnetic resonance imaging revealed increased internal and external cerebrospinal fluid spaces as well as patchy white matter lesions, metabolic deviations included a 50% decrease of N-acetylaspartate (neuronal marker), a 75% increase of myo-inositol (glial marker), and a 40% decrease of choline-containing compounds in white matter relative to age-matched controls. A clinical deterioration of the patient was clearly reflected in a follow-up examination 22 mo later, resulting in a further reduction of N-acetylaspartate and a more pronounced enhancement of myo-inositol. No elevation of lactate was observed. The magnetic resonance spectroscopy findings are in line with a generalized neurodegenerative process in L-2-hydroxyglutaric acidemia but also suggest a defect in phosphatidyl inositol metabolism of glial cells.

Adolescent↗
PubMed1993

Molecular self-diffusion of intracellular metabolites in rat brain in vivo investigated by localized proton NMR diffusion spectroscopy.

Molecular self-diffusion coefficients of water (0.75 +/- 0.05), N-acetylaspartate (0.27 +/- 0.04), creatines (0.27 +/- 0.04), and cholines (0.28 +/- 0.08) x 10(-5) cm2 s-1 were obtained from localized proton NMR spectra of rat brain in vivo using diffusion-weighted stimulated-echo (STEAM) sequences with a diffusion time of (delta--delta/3) = 17 ms.

Animals↗
PubMed1993

Alterations of brain metabolites in metachromatic leukodystrophy as detected by localized proton magnetic resonance spectroscopy in vivo.

The brain morphology and chemistry of seven children with late infantile (4/7) and juvenile (3/7) forms of metachromatic leukodystrophy (MLD) were investigated by magnetic resonance imaging (MRI) and localized proton magnetic resonance spectroscopy (MRS). Patients who were examined at least 6 months after the onset of symptoms (6/7) had severe leukodystrophic changes on MRI. Proton MRS revealed a marked reduction of the neuronal marker N-acetylaspartate in white and grey matter and elevated lactate in demyelinated areas. In contrast to other leukodystrophies MLD patients showed a generalized increase of brain myo-inositol (2- to 3-fold in white matter), indicating a specific role in the pathophysiology of demyelination in MLD.

Adolescent↗
PubMed1993

Absolute concentrations of metabolites in the adult human brain in vivo: quantification of localized proton MR spectra.

In vivo concentrations of cerebral metabolites were obtained by means of 52 single-voxel, localized proton magnetic resonance (MR) spectroscopic examinations of different regions of the brain performed in 26 healthy adults aged 21-32 years. The study was performed at 2.0 T with use of a circularly polarized head coil to ensure homogeneous radio-frequency excitation and signal reception. Proton MR spectra were obtained in the stimulated-echo acquisition mode under fully relaxed conditions (repetition time > or = 6,000 msec) and at short echo times (20 msec) to minimize corrections due to T1 and T2 attenuation and depict the spectra of metabolites with strongly coupled resonances. Absolute concentrations were obtained by means of calibration of resonance signal areas with those of pertinent metabolite solutions from separate studies and correction for coil loading and partial volume effects (eg, with perfused capillary networks and cerebrospinal fluid). The results provide a quantitative basis for studies of both normal human neurochemistry in vivo and metabolic alterations in diseases of the brain.

Adult↗
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↗
PubMed1992

Acute demyelinating disease. Classification and non-invasive diagnosis.

Five young patients are described with biopsy-proven acute demyelinating disease. Two cases are classified as Schilder's disease, a particular childhood form of multiple sclerosis (MS) with atypical clinical manifestation, normal or atypical CSF-findings and large bilateral lesions in magnetic resonance imaging (MRI). Two further cases presented with a fulminant bout of MS with typical clinical picture and CSF-findings; they are classified as Marburg's disease. The last case was an acute second bout of classical MS. The biopsy seemed to be justified in 4 cases, but unnecessary in the last case. Localized proton magnetic resonance spectroscopy (MRS) performed in one case allowed us to examine the focal cerebral abnormalities directly and non-invasively. The spectra revealed a pattern typical of acute demyelination suggesting potential for a replacement of biopsy in the future.

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

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↗