Biomedical subjects

J Vymazal

Publications and source records attributed to J Vymazal.

At least 19 recordsLinked to original sources

PubMed2005

[Time perception in functional brain imaging].

BACKGROUND: Knowledge of physiological mechanisms underlying time perception is still rather limited. The aim of our study was to search for a 'time accumulator', i.e. the part of the brain where information on the duration of time is stored. METHODS AND RESULTS: Nine healthy volunteers were given a time reproduction task during event-related fMRI. Subjects were instructed to retain the duration of the stimulus presented (presentation phase) and then to reproduce it by pressing a button (reproduction phase). Two different analyses were made: event-related (P < 0.05, FWR corrected) and parametric (BOLD signal increase/decrease during the presentation/reproduction phases correlated with the time intervals; P < 0.01, FDR corrected). When the event-related approach was employed, activation was noted bilaterally in the inferior prefrontal cortex (IPFC), supplementary motor area (SMA), precuneus and secondary visual cortex. On the right, there was activation in the dorsolateral prefrontal cortex (DLPFC), gyrus cinguli and inferior parietal lobule. On the left, the primary sensory-motor cortex was activated. While during the presentation phase the left DLPFC activity inversely correlated with the presented duration, a nearly identical area showed positive correlation in the reproduction phase. CONCLUSIONS: The event-related analysis did not allow distinguishing the process of time perception from many cognitive processes running simultaneously. In turn, the parametric analysis was based on visualizing regions, in which the signal correlated with the varying duration of the time interval provided the level of attention, decision-making and the processes of behavioral response planning and execution were constant. Moreover, the right and left DLPFC seem to play different roles in time perception. While the left one is functioning as a "time accumulator", the right one is rather involved in the recognition of previously perceived intervals.

Adult↗

PubMed2003

Horizontal sub-surface flow constructed wetland with pulsing water level.

A constructed wetland with horizontal sub-surface flow at Dolni Mesto (Czech Republic) was put into operation in 1999 and treats municipal wastewater from 522 PE. The total area of vegetated beds of 2,646 m2 is divided into two parallel sections of equal size, each with two beds in series. Between two periods of water discharge there is no outflow from the bed. During the period of September 1999-September 2000 one bed was operated with a pulsing water level while the other one was not pulsing, i.e., was operated as regular sub-surface flow in order to evaluate the effect of pulsing on treatment efficiency, especially on removal of NH4-N. Between September 1999 and February 2000 the pulse was 8 cm, for the rest of the experimental period the pulse was 15 cm. The results indicate a positive effect of pulsing on removal of BOD5 (annual average of 53%), COD (30%) and NH4-N (27%) as compared to non-pulsing beds. For SS, a decrease in removal effect by 30% was observed. This is probably due to the higher outflow velocity of discharged water from pulsing beds which can flush out settled particles. The results also indicate that a pulsing level of 15 cm was more efficient than 8 cm.

Ammonia↗

PubMed2003

Distribution of Mn, Al, Cu and Zn in a constructed wetland receiving municipal sewage.

A constructed wetland at Nucice near Prague, Czech Republic, has been in operation since 1996 and the system is designed to treat sewage from 650 PE together with stormwater. The total area of the beds planted with Phalaris arundinacea and Phragmites australia is 3,224 m2 (two beds 62 x 26 m each). Pea gravel (8/16 mm) is used as a filtration material. During the period 1998-1999, removal of Mn, Al, Cu and Zn from wastewater and distribution of the metals in sediments and plants were studied. Metals were measured in three vertical profiles of the filtration bed (0-15, 15-30 and 30-60 cm) and at four locations along the longitudinal profile of the bed (5, 16, 32, 48 m from the inlet). Metal concentrations in plant tissues (roots, stems, leaves) of Phalaris arundinacea were measured along the longitudinal profile of the bed at the same locations as for sediments. The results showed that the retention of metals is high (up to 98%) with the major decrease in metal concentrations within the first 5 metres of the bed. The major decrease in metal concentration in the filtration material was observed in the inlet zone between 5 and 16 metres. In Phalaris tissue, metal concentrations decreased in the order roots > stems > leaves but statistically significant differences varied among the studied metals.

Biodegradation, Environmental↗

PubMed2003

[Initial experience with magnetic resonance cholangiopancreatography].

BACKGROUND: Magnetic resonance cholangiopancreaticography (MRCP) is based on heavily weighted T2 sequences (ETSE--echo-train spin echo) with suppression of fat, giving visualisation of slowly flowing or stagnating fluid. MRCP are short sequences in coronary plane with thickness of 8 cm or 4 mm. Retrospective analysis of all MRCP examinations performed during last 12 months is presented. METHODS AND RESULTS: Eighty-eight examinations were done, of which 67 ones with both adequate technical quality and clinical indication were included into the study (20 males aged 25-83 years, 47 women aged 19-82 years). Patients were divided into 4 groups regarding to the indications (group I.--temporary cholestasis, normal abdominal ultrasound, II.--definite cholestasis, III.--pathologic findings on pancreas, IV.--other). Vast majority of patients were included into group I (35 subjects). In 7 (20%) of them choledocholithiasis and/or stenoses (including multiple stenoses in primary sclerotizing cholangoitis) were found. MRCP brought diagnostic information in subjects with cholestasis (group II.) and answered questions given by clinicians. However, in 1 of 4 subjects with primary sclerotizing cholangoitis, MRCP did not reveal intra-hepatic stenoses, which were later visualised by classical ERCP. Only the extrahepatic stenoses were diagnosed by MRCP in the latter subject. CONCLUSIONS: MRCP should become a standard examination in the diagnostic algorithm in patients with cholangiopathies. MRCP has its value not only in subjects with unsuccessful or contraindicated ERCP, but also in subjects with temporary cholestasis with negative ultrasound finding.

Adult↗

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↗

PubMed2001

Temperature dependence of polymer-gel dosimeter nuclear magnetic resonance response.

The purpose of this study was to find a physical-mathematical description capable to correct a polymer-gel dosimeter relaxation rate R2-dose response for different temperatures. Four different modifications of polymer-gel dosimeters were used in this study. Samples with polymer-gel dosimeter in glass test vessels were homogeneously irradiated by 60Co gamma photons. A multi-echo sequence with 16 equidistant echoes was used for evaluation of irradiated polymer-gel dosimeters. The sequence parameters were as follows: TR 2000 ms, TE 22.5-360.0 ms, slice thickness 5 mm, FOV 255 mm, one acquisition. The proposed description recommends to subtract R2 response of the nonirradiated dosimeter from the total R2-dose response. The relaxation rate for the irradiated dosimeter can be expressed as a function of temperature and dose. The temperature dependence has an exponential behavior in the measured range. The proposed description allows to correct the measured NMR R2-dose responses for different temperatures.

Dose-Response Relationship, Radiation↗

PubMed2001

Bacterial dynamics in the sub-surface constructed wetland.

Constructed wetlands have been shown to be capable of removing a wide variety of contaminants, including bacterial pollution. However, only limited information exists on the distribution of bacteria on roots of macrophytes growing in constructed wetlands. Constructed wetland with sub-surface horizontal flow at Nucice near Prague, Czech Republic, was put in operation in 1996. The system treats municipal sewage from 650 PE and the total area of the beds, planted with Phalaris arundinacea and Phragmites australis in alternate stripes perpendicular to the flow direction, is 3,224 m2 (2 beds 62 x 26 m each). Pea gravel (8/16 mm) was used as a filtration material. During the period 1998-1999, distribution of total aerobic and anaerobic bacteria, coliform bacteria and fecal streptococci was monitored in wastewater as well as on roots of both macrophyte species. Counts of bacteria on root surface in the system at Nucice indicate that there is a steep decrease in bacterial numbers within the first few metres of the bed and that there is significantly more bacteria on roots of Phragmites as compared to Phalaris. There was no statistically significant influence of the season on the bacterial counts on roots of macrophytes.

Bacteria, Aerobic↗

PubMed2001

Biota participating in wastewater treatment in a horizontal flow constructed wetland.

During the period 1996-1997, three constructed wetlands with sub-surface horizontal flow were investigated. All systems are designed to treat municipal sewage from small villages (150, 200 and 300 PE). The survey included microscopical identification of organisms in both wastewater and filtration substrate. The organisms were used as an indication of oxygen conditions (aerobic, anoxic and anaerobic) in the particular microenvironment. Saprobiological terms characterizing different levels of saprobity were employed to characterize inflowing wastewater, filtration bed and outflowing water. The occurrence of organisms was correlated with BOD5 values in particular profiles. It has been found that the biocenosis in the inflowing wastewater differs from those found in the filtration bed and water outflowing from the vegetated beds. The organisms were grouped into those living under anaerobic and anoxic conditions and those living under aerobic conditions. More than 70 species of bacteria, amoebae, ciliates, rotifers, colorless flagellates, cyanobacteria and algae were found and the most important 45 species were figured in a plate together with saprobiological information for each species. Biota of the inflowing water is usually restricted to bacteria, ciliata and colorless flagellata while the organisms found in outflowing water as well as in periphyton growing on outflow structures indicate 2-3 levels better quality.

Animals↗

PubMed2001

Constructed wetlands for wastewater treatment in the Czech Republic.

The first constructed wetland (CW) for wastewater treatment was built in the Czech Republic in 1989. This recent survey shows that at the end of 1999 101 systems are in operation and several more are under construction. 95 CWs are designed with sub-surface horizontal flow, 6 systems are hybrid with a combination of vertical and horizontal flow beds. Most systems (56) were designed for the treatment of municipal and domestic sewage while 38 CWs were designed for the treatment of wastewater from combined sewer systems. The most commonly used size of vegetated beds is 1,001-2,500 m2 (31 systems) followed by the area between 51-250 m2 (19%). The area of vegetated bed of the largest system is 4,493 m2. Size distribution is quite evenly spread from very small systems (PE = 3 or 4) up to 1,000 PE. However, most systems (44) were sized to treat wastewater from sources between 101 and 500 PE. The most commonly used macrophyte is Common reed (Phragmites australis) which is used in 34 systems as a monotypic stand and in 44 systems in combination with other macrophytes, most frequently with Reed canarygrass (Phalaris arundinacea) (31 systems) and cattails (Typha spp.) (8 systems).

Biodegradation, Environmental↗

PubMed2000

[Radiosurgical treatment of hypophyseal adenomas with the gamma knife: results in a group of 163 patients during a 5-year period].

BACKGROUND: Gamma knife radiosurgery of pituitary adenomas is considered to be very perspective. It can be a very useful complement of traditional microsurgery, pharmacotherapy or fractionated radiotherapy which are seldom a sufficient treatment on their own. The modern radiosurgery does not offer the experience representative enough in this indication. We can offer results of medium long follow-up for tumor growth and hormonal hypersecretion of pituitary adenomas in a relatively large series of patients. METHODS AND RESULTS: We have analyzed a group of 163 patients with pituitary adenoma treated with gamma knife during 5 years and followed 12-60 months, median 24 months after irradiation. An antiproliferative effect has been achieved in 1-2 years using the minimal dose to the margin 16-35 Gy, median 20 Gy in all our patients who were controlled by MRI (n = 126 patients). One half of these adenomas evidently decreased their size. Our effective antiproliferative dose was safe for the surrounding structures. The hormonal normalization has been achieved at 50.4% from 133 hypersecreting adenomas (39/91 = 43% of acromegalics, 11/13 = 85% of patients with Cushing's disease, 2/9 = 22% of patients with Nelson's syndrome, 11/18 = 61% of prolactinomas). The median latency was 12 months. The minimal dose to the margin was 10-45 Gy, median 35 Gy. Rare side effects were provoked only by increasing the dose to influence the hypersecretion-the development of partial hypopituitarism in 3.1% of patients, the panhypopituitarism in 0.6% of patient and there was 1 hemianopic visual field defect (0.6%). CONCLUSIONS: Radiosurgery by gamma knife has a similar value for pituitary adenomas as microsurgery has with different distribution of advantages and drawbacks. This makes it suitable for the combined treatment where pharmacotherapy has its place under special conditions. Fractionated radiotherapy has now a marginal importance.

Adenoma↗

PubMed2000

Gamma knife radiosurgery of the brain stem cavernomas.

Over 6 years (1992-1998) 26 patients with brain stem cavernomas were treated using the Leksell gamma knife in Prague. 25 patients had a follow up of 6-66, median 24 months. Annual risk of bleeding before radiosurgery was 4%. After gamma knife treatment sudden impairment of neurodeficit reported as rebleeding was observed in 4 patients at 6-51 months, median 16.5 months, after radiosurgery. This represented a 6.8% risk of rebleeding after radiosurgery, which is not significantly different from the risk before radiosurgery. MRI or CT was performed in 24 patients 6-48, median 24, months after radiosurgery. There were no signs of rebleeding in any of the patients, nor any increase of the cavernoma. A decrease of cavernoma size was observed in 8 (33%) of patients. Temporary collateral edema after radiosurgery was detected in 5 (21%) of patients 3-12, median 11, months after radiosurgery. Neurodeficit was observed in 21 of 26 patients before radiosurgery. Improvement of the neurodeficit was detected in 9 (43%) of them 6-36, median 8, months after radiosurgery. Temporary morbidity caused by collateral edema or rebleeding occurred in 7 patients (28%) and permanent morbidity remained in 2 patients (8%). 2 patients died because of rebleeding 6 and 51 months after radiosurgery and the third patient for unrelated reason. Radiosurgery of the brain stem cavernomas was indicated when there was bleeding in the history or progressive neurodeficit and microsurgery was considered too risky. Leksell gamma knife radiosurgery of cavernomas has proved its low morbidity and zero mortality. In case of an insufficient effect of radiosurgery, or if the protective effect from rebleeding comes too late, morbidity and mortality can correspond to the natural course of the disease, as it was left without any treatment.

Adolescent↗

PubMed2000

Gamma knife radiosurgery as a primary treatment for prolactinomas.

OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.

Humans↗

PubMed2000

Differentiation between hemosiderin- and ferritin-bound brain iron using nuclear magnetic resonance and magnetic resonance imaging.

MRI is an optimal clinical (research) tool to provide information on brain morphology and pathology and to detect metal ions that possess intrinsic magnetic properties. Non-heme iron is abundantly present in the brain in three different forms: "low molecular weight" complexes, iron bound to "medium molecular weight complexes" metalloproteins such as transferrin, and "high molecular weight" complexes as ferritin and hemosiderin. The total amount and form of iron may differ in health and disease, and MRI can possibly quantify and monitor such changes. Ferritin-bound iron is the main storage form of iron and is present predominantly in the extrapyramidal nuclei where its amounts normally increase as a function of age. Ferritin is water soluble and shortens both, T1 and T2 relaxation, with as result a signal change on the MR images. Hemosiderin, a degradation product of ferritin, is water-insoluble with a stronger T2 shortening effect than ferritin. The larger cluster size of hemosiderin and its water-insolubility also explain a lack of significant T1-shortening effect on T1-weighted images. Using both in vitro specimens and intact brain tissue in vivo we demonstrate here that MRI may be able to distinguish between ferritin- and hemosiderin-bound iron.

Aged↗

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

Gamma knife radiosurgery of meningiomas in the cavernous sinus region.

For 6 years (1992-1998) we have treated 67 patients with cavernous sinus meningioma using the Leksell gamma knife in the Hospital Na Homolce, Prague. The age of the patients ranged between 19-82 years, median 57 years. Radiosurgery was the primary treatment in 64.2% of the patients, in the rest a microsurgical resection preceded. The volume of the tumour ranged from 0.9-31.4 cm3, median 7.8 cm3. The meningioma was distant from the optic tract in 58% of the cases, in 12% of the cases there was a contact with the tumour and the optic tract without its compression and in 30% of the cases there was a compression of the optic tract caused by the meningioma. The dose to the tumour margin ranged from 10-14 Gy, median 12 Gy. The follow up was available in 53 patients, in intervals of 2-60 months, median 19 months. There was no change in the tumour volume in 48% of the cases, in 52% of the cases a decrease of the tumour volume occurred. No increase of the tumour volume was observed. Clinical symptoms and signs improved in 35.8% of the patients, temporary morbidity was 3.8%. The mortality of the treatment was zero. Hitherto, the results of gamma knife radiosurgery of cavernous sinus meningioma have proved its safety and efficiency, although long term experience with a large group of patients is missing. Advances in neuroradiology and radiosurgical technique have allowed us to treat tumours with a closer contact to the optic tract and nerves compared with the past.

Adult↗

PubMed1999

T1 and T2 in the brain of healthy subjects, patients with Parkinson disease, and patients with multiple system atrophy: relation to iron content.

PURPOSE: To investigate the potential of magnetic resonance imaging for identification and quantification of brain iron in healthy subjects, patients with Parkinson disease, and patients with multiple system atrophy. MATERIALS AND METHODS: Forty-nine subjects were studied at 1.5 T. Regional T1 and T2 values were compared among groups and also with histopathologic estimates of iron concentration. RESULTS: In healthy subjects, interregional T1 and T2 differences in the cortex and basal ganglia showed a good correlation with reported values for iron concentration, and intraregional variations were generally consistent with reported variability of iron concentration. Patients with multiple system atrophy had T1 and T2 shortening in the globus pallidus consistent with reported increases in ferritin-bound iron and changes in the putamen consistent with accumulation of hemosiderin (posterior portion) and neuromelanin (remainder). Both groups of patients had changes in the cortex that are consistent with decreased ferritin concentration and T2 changes in white matter consistent with demyelination. Patients with Parkinson disease also had a (nonsignificant) T2 shortening in the substantia nigra that was suggestive of iron accumulation. CONCLUSION: Most of the T1 and T2 findings appear to be related to changes in iron content and form and may possibly be used as indicators of such changes.

Aged↗

PubMed1999

The role of Gamma Knife radiosurgery in arteriovenous malformation with aneurysms.

A review of 217 patients treated with Gamma knife radiosurgery (GKRS), at Hospital Na Homolce, Prague, between October 1992 and January 1998 for arteriovenous malformation (AVM) is presented. Forty-one patients (18.9%) with an AVM and associated aneurysm are the subjects of special interest for this study. The nidus volume in the presence of an aneurysm lying close to the nidus or within it was significantly larger than the nidus volume in cases where the AVMs had no associated aneurysm, suggesting that an increased flow in a larger AVM may be an important factor for aneurysm formation. The association of an arterial aneurysm with an AVM significantly increased the chance of hemorrhage when compared to the group with AVM and no aneurysm. Ten patients out of 14, who had an aneurysm close to or within the nidus, showed a complete obliteration of their AVM and aneurysm, although the latter was not always included within the irradiated volume. Thus, this study indicates that radiosurgery alone could be the method of choice for the treatment of a combination of AVM and aneurysm, if the aneurysm is close to or within the nidus.

Adolescent↗

PubMed1998

Relaxometry and magnetometry of ferritin.

By combining nuclear magnetic relaxometry on 39 ferritin samples with different iron loading with magnetometry, results were obtained that suggest a new interpretation of the core structure and magnetic properties of ferritin. These studies provide evidence that, contrary to most earlier reports, the ferritin core is antiferromagnetic (AFM) even at body temperature and possesses a superparamagnetic (SPM) moment due to incomplete cancellation of antiparallel sublattices, as predicted by Néel's theory. This moment also provides a likely explanation for the anomalous T2 shortening in ferritin solution. However, the number of SPM moments derived from this model is less than the number of ferritin molecules determined chemically, and a similar discrepancy was found by retrospectively fitting previously published magnetometry data. In other words, only a fraction of the ferritin molecules seem to be SPM. The studies also provide evidence for paramagnetic (PM) Curie-Weiss iron ions at the core surface, where the local Néel temperature is lower; these ions are apparently responsible for the weaker T1 shortening. In fact, the conversion of uncompensated AFM lattice ions to PM ions could explain the small number of SPM particles. The apparent Curie Law behavior of ferritin thus appears to be a coincidental result of different temperature dependences of the PM and SPM components.

Ferritins↗