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M Hájek

Publications and source records attributed to M Hájek.

At least 19 recordsLinked to original sources
PubMed2001

Application of two-dimensional CSI for absolute quantification of phosphorus metabolites in the human liver.

There have recently been a number of studies dealing with the absolute quantification of concentrations of MR-visible phosphorus compounds in different tissues. The use of absolute values rather than intensity ratios may furnish additional information about metabolic changes associated with different diseases. The purpose of this study was to develop a general procedure for measuring molar metabolite concentrations and to apply it with respect to the evaluation of human liver 31P-MRS data measured using a standard slice-selective two-dimensional CSI sequence and commercial 1H/31P surface coil. The experimental determination of all surface coil-related factors influencing signal intensity was undertaken using a gradient echo imaging technique that can be adapted to commercial systems. The resulting values for healthy volunteers (N = 9) showed concentrations of PME = 2.8 +/- 1.3 mM, PDE = 9.9 +/- 2.7 mM, P(i) = 1.7+/-0.7 mM, and ATP = 3.6 +/- 0.9 mM in the human liver. The data are quite consistent with published findings.

Adenosine Triphosphate↗
PubMed2001

Chronic liver disease: relaxometry in the brain after liver transplantation.

Relaxometry revealed changes in the basal ganglia in T(1) and T(2) relaxation times due to liver disease. Manganese is probably responsible for T(1) and T(2) shortening (as the concentration is known to be higher in both the liver and blood due to hepatic cirrhosis). The aim of this study was to follow possible recovery after liver transplantation by MR relaxometry. Together with a group of 20 healthy volunteers we scanned 53 patients before and after liver transplantation (some of them repeatedly). Both T(1) and T(2) values were evaluated in the basal ganglia, thalamus, and frontal white matter. T(1) relaxation time was shortened by approx. 20-25% compared to the control group, probably the result of manganese deposition in the brain caused by hepatic cirrhosis. After liver transplantation the relaxation time recovered gradually with almost normal values reached approx. 2 years after surgery. T(1) recovery was observed in all evaluated structures. Similar results were observed with T(2) relaxation in the basal ganglia and thalamus. In the white matter T(2) remained low even 2 years after surgery.

Adolescent↗
PubMed2000

Application of LCModel for quality control and quantitative in vivo 1H MR spectroscopy by short echo time STEAM sequence.

The linear combination of model spectra (LCModel) calculation of a parameter for long-term quality control, kT, was introduced, representing the ratio of the temporal and nominal intensities of CH3 groups of lactate and acetate in a quality control phantom. This procedure is a part of the quality assurance of the scanner using fully automatic measurement and calculation of kT parameters, and utilizing Shewhart regulation control charts for continuous evaluation of the magnetic resonance (MR) scanner setting. The application of the kT parameter for the correction of in vivo data increases the precision of molar concentration determination by about 4%. This was tested by the quantitative in vivo MR determination of the molar concentrations of 13 prominent metabolites (N-acetylaspartate (NAA), N-acetylaspartylglutamate, creatine and phosphocreatine (Cr), choline-containing compounds (Cho), myo-inositol, scyllo-inositol, gamma-aminobutyric acid, glutamine, glutamate, glucose, lactate, alanine, taurine) in the white matter and hippocampus of the brain in groups of volunteers, using a short echo time stimulated echo acquisition mode sequence (echo time = 10 ms) and the LCModel technique. The repeatability of the measurement of prominent metabolites such as NAA, Cr and Cho was found to be around 10% (relative standard deviation, n = 6); precision in a group of volunteers (n = 20 and 28, respectively) was in the range of approximately 13-20%. For other metabolites, which are measured with a lower signal-to-noise ratio, the precision can be much lower.

Acetates↗
PubMed1999

Comparison of MR spectroscopy and MR imaging with contrast agent in children with cerebral astrocytomas.

We studied 33 patients with astrocytomas of different grades (68 examinations) by magnetic resonance imaging (MRI) and proton MR spectroscopy ((1)H-MRS). We found that in 80% of the spectra, the presence of signals in the area of 0.8-1.5 ppm, assigned to lipids/lactate in (1)H-MR spectra, correlated with signal enhancement after Gd-DTPA administration. We suggest that visibility of lipid/lactate signals could be due to blood-brain barrier damage, which is characterized by contrast agent enhancement.

Adolescent↗
PubMed1999

MR relaxometry on a whole-body imager: quality control.

Long-term monitoring of the average proton relaxation time T2 of phantoms measured on a Siemens MR whole-body imager showed very good repeatability and reproducibility. The repeatability (short-term precision) and reproducibility (long-term precision) of the average values of a relaxation time T2 approximately/= 81 ms, obtained by a standard 16-echo CPMG pulse sequence, were 2.6% and 9.7%, respectively. The Siemens Vision imager proved to be a suitable tool for T2 evaluation in vivo. Quality control was performed using the techniques of control diagrams developed by Shewhart, which proved to be an appropriate method for continuous quality control of relaxation time determination.

Magnetic Resonance Spectroscopy↗
PubMed1998

1H MR spectroscopy in patients with mesial temporal epilepsy.

The study provides a review of the basic examination procedures and results of proton magnetic resonance spectroscopy (1H MRS) in patients suffering from mesial temporal lobe epilepsy (MTLE). The source of seizures in MTLE is most often an epileptogenic focus secondary to hippocampal sclerosis. 1H MRS currently plays an important role in the non-invasive diagnosis of this type of epileptogenic lesion. The decisive 1H MRS parameter characterizing an epileptogenic lesion is a statistically significantly decreased value of N-acetylaspartate levels compared with control values, most often associated with a decrease in the ratios of the intensities of NAA/Cr, NAA/Cho and NAA/(Cr + Cho) signals. Moreover, MRS makes it possible to distinguish bilateral involvement of mesial temporal structures typically associated with a bilateral decrease in the levels of metabolites and/or their ratios. As regards other metabolic compounds which play an important role in the pathobiochemistry of epilepsy, MRS is employed to study the action of gamma-aminobutyric acid (GABA), inositol, lactate, glutamine, and glutamate, the clinical function of which has not been fully clarified as yet. It is in this context that one should consider the application of 1H MRS in evaluating the action of some new anti-epileptic agents affecting excitatory and inhibitory amino acids. There is no doubt that in vivo 1H MRS, along with other imaging methods, has made a significant contribution to the clinical and biochemical description of epileptic seizures and has assumed a prominent position among the techniques of pre-operative examination in epileptic surgery.

Aspartic Acid↗
PubMed1998

[A rare case of bronchial mucoepidermoid tumor].

The authors describe a rare case of a mucoepidermoid bronchial tumour in a young patient. The main clinical manifestation was relapsing bronchopneumonia behind the stenosis. The authors analyze in detail the histological characteristics of the tumour and its behaviour and present a review of the literature.

Adult↗
PubMed1995

T2 relaxation time study of the pig renal allografts.

A previous study showed the possibility of the dependence of the T2 maps measured by Siemens Magnetom MR imager 1.5 T on the viability of the cadaveric kidney. For the T2 relaxometry study the pig model was used. Ten pig renal allografts were examined during 68 h after removal. Significant differences were found in the change of the initial Tini2 values in the histogram within the first 20 h [delta 1 = Tini2 (2) - Tini2 (20)] or 8 h [delta 2 = Tini2 (2) - Tini2 (8)] after removal between the groups of the damaged kidneys (delta 1 = 20.2 +/- 6.8 ms, delta 2 = 19.4 +/- 3.0) and the kidneys without apparent damage (delta 1 = 9.4 +/- 8.5 ms, delta 2 = 5.4 +/- 5.8).

Animals↗
PubMed1995

[Modern dressings. Hydrogels].

Hydrogels are occlusive types of dressings. They are three-dimensional nets made up of hydrophil polymers. They can be produced from synthetic or semisynthetic materials or a combination of the two. Hydrogels retain different percentages of water but are themselves insoluble in water. This is why they maintain on the wound surface their structure and do not dissolve. They are suited for the dressing of wounds with low secretion such as grade I and II burns, grade I and II bedsores and above all epithelial defects, major skin abrasions and areas after collection of epithelial grafts. Their use is contraindicated in infected wounds, in wounds with a massive secretion and ulcers of arterial origin. Although the domain of their clinical use are clean granulating or already epithelizing wounds, they are very well suited also for rehydration of dry and black skin necroses. Their advantages include minimal pain in the wound as well as the fact that they can be left on the wound without redressing till complete healing. This is made possible also by the fact that they are translucent.

Bandages↗