Biomedical subjects

M Hajek

Publications and source records attributed to M Hajek.

39 records · Page 3Linked to original sources

PubMedDate not supplied

The quantitative relation between T1-weighted and T2-weighted MRI of normal gray matter and iron concentration.

A retrospective analysis of 158 T1-weighted and T2-weighted MRI scans of normal brains at 0.5 and 1.5 Tesla was performed. Signal intensities in the frontal cortex, caudate nucleus, putamen, and globus pallidus were divided by those of frontal white matter; and these gray/white ratios were correlated with iron concentration, estimated from the anatomical region and age of the patient. Intraregional plots were also made of gray/white ratio versus age for the 1.5 Tesla scans. The changes in both T1-weighted and T2-weighted ratios were consistent with the hypothesis that 1/T1 and 1/T2 vary linearly with iron concentration, and the corresponding coefficients, determined separately from the interregional and intraregional plots, were generally in agreement. Furthermore, the variability of the MRI ratios at 1.5 Tesla was consistent with expected iron variability except for the cortex, in which partial volume errors due to sulci and white matter caused increased variations. The MRI results agreed well with in vitro data on T1 and T2 in tissue specimens and with other MRI studies. When compared with T1 and T2 in ferritin solution, a significant "tissue relaxation enhancement" was found, attributable to slower diffusion and clustering of ferritin in tissue.

Adult↗

PubMedDate not supplied

Epilepsia partialis continua studied by PET.

We report an [18F]fluordeoxyglucose (FDG)-PET study performed in an 11-year-old girl with a 5-month history of epilepsia partialis continua (epc). Visual inspection of PET images showed a hypermetabolic focus in the right central cortex and in the ipsilateral thalamus, which was confirmed by the absolute values of regional cerebral glucose metabolism (rCMRGlu). The thalamic hypermetabolism provides evidence for an involvement of thalamic nuclei in this ictally epileptic process. The scalp EEG revealed a theta-delta and sharp wave focus in the right Rolandic cortex at the same location as the hypermetabolic zone seen in PET. Simultaneously recorded EMG of the left tibialis anterior muscle showed regular jerks, time-locked to the sharp waves at the right central region, and myoclonic 'storms' during focal motor seizures. The results of the brain biopsy and the child's clinical course led us to a diagnosis of 'chronic encephalitis' of Rasmussen.

Brain↗

PubMedDate not supplied

Studies on the hydrogenation of the progestagen dienogest in vivo and in vitro in the female rabbit.

The biotransformation of the progestagen dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-4,9-estradien-3-one) was studied in vivo in female rabbits and in vitro by liver homogenates from female rabbits and rats. In vivo, in the female rabbit, 3H-dienogest was the subject of an extensive biotransformation. A significant difference between the composition of the urinary and biliary metabolite patterns of dienogest was found. While in the urinary metabolite pattern more polar metabolites dominated, in bile of animals with a bile fistula, a dienogest metabolite of medium polarity was prevalent. This main metabolite of dienogest was identified by MS, 1H- and 13C-NMR spectroscopy and CD measurement of an enzymatic dehydrogenation product as the tetrahydro metabolite 17 alpha-cyanomethyl-5 alpha-estr-9-en-3 beta,17 beta-diol. Thus, in vivo, the 4,9-dien-3-oxo-19-norsteroid dienogest is hydrogenated to a 5 alpha H-9-en metabolite. In vitro, however, 3H-dienogest was only poorly transformed by liver homogenates from both species, whereas 3H-levonorgestrel and 3H-3-keto-desogestrel were converted partially by liver homogenates from female rabbits and completely by liver homogenates from female rats. The principal biotransformation reactions of levonorgestrel and 3-ketodesogestrel were the reduction of the 3-oxo group to 3-OH and the 5 beta- and 5 alpha-hydrogenation of the 4-double bond by homogenates of female rabbit liver and female rat liver, respectively. A dihydro metabolite of dienogest, in which the 3-oxo group had been reduced to 3-OH, was isolated in small amounts from the incubation with rabbit liver homogenate. The data indicate that the enzymatic hydrogenation of the 4-double bond of the 4,9-dien-3-oxo steroid dienogest is inhibited in vitro. The hindered hydrogenation reaction in vitro has to be seen in association with the 9-double bond in the steroid molecule.

Animals↗