Biomedical subjects

V Herynek

Publications and source records attributed to V Herynek.

7 recordsLinked to original sources

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

Dynamic relaxometry: application to iron uptake by ferritin.

We introduce dynamic relaxometry as a novel technique for studying biochemical reactions, such as those leading to mineral formation (biomineralization). This technique was applied to follow the time course of iron oxidation and hydrolysis by the protein ferritin. Horse spleen apoferritin was loaded with single additions of 4, 10, 20, 40, and 100 ferrous ions per protein, and with multiple additions of 4, 10, 20, and 100 ferrous ions. The NMR T2 relaxation time was then measured sequentially and continuously for up to 24 h. At low loading factors of 4-10 Fe atoms/molecule, the iron is rapidly bound and oxidized by the protein on a time scale of approximately 15 s to several minutes. At intermediate loading factors (10-40), rapid initial oxidation was observed, followed by the formation of antiferromagnetic clusters. This process occurred at a much slower rate and continued for up to several hours, but was inhibited at lower pH values. At higher loading factors (40-1000), iron oxidation may occur directly on the core, and this process may continue for up to 24 h following the initial loading. Dynamic relaxometry appears to be a potentially powerful technique that may well have applications beyond the study of iron uptake by the ferritin protein.

Animals↗

PubMed1999

Neurotransplantation of magnetically labeled oligodendrocyte progenitors: magnetic resonance tracking of cell migration and myelination.

Demyelination is a common pathological finding in human neurological diseases and frequently persists as a result of failure of endogenous repair. Transplanted oligodendrocytes and their precursor cells can (re)myelinate axons, raising the possibility of therapeutic intervention. The migratory capacity of transplanted cells is of key importance in determining the extent of (re)myelination and can, at present, be evaluated only by using invasive and irreversible procedures. We have exploited the transferrin receptor as an efficient intracellular delivery device for magnetic nanoparticles, and transplanted tagged oligodendrocyte progenitor cells into the spinal cord of myelin-deficient rats. Cell migration could be easily detected by using three-dimensional magnetic resonance microscopy, with a close correlation between the areas of contrast enhancement and the achieved extent of myelination. The present results demonstrate that magnetic resonance tracking of transplanted oligodendrocyte progenitors is feasible; this technique has the potential to be easily extended to other neurotransplantation studies involving different precursor cell types.

Animals↗

PubMed1999

Synthesis and relaxometry of high-generation (G = 5, 7, 9, and 10) PAMAM dendrimer-DOTA-gadolinium chelates.

A series of high-generation (G) ethylenediamine-core polyamidoamine (PAMAM) dendrimers corresponding to G = 5, 7, 9, and 10 were conjugated with the bifunctional chelate 2-(4-isothiocyanatobenzyl)- 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetate (p-SCN-Bz-DOTA). Gadolinium (III) ion was added to the macromolecules, and the 1/T1 and 1/T2 NMRD profiles were measured at 3 degrees, 23 degrees, and 37 degrees C. The synthesis resulted in preparations that ranged from an average of 127 chelates and 96 Gd3+ ions per G = 5 dendrimer to an average of 3727 chelates and 1860 Gd3+ ions per G = 10 dendrimer. At 20 MHz and 23 degrees C, the 1/T1 ion relaxivity increased from 30 mM(-1) s(-1) for the G = 5 to 35 mM(-1) s(-1) for the G = 7 PAMAM dendrimer-DOTA-Gd, reaching a plateau at 36 mM(-1) s(-1) for the G = 9 and G = 10 dendrimers. A similar plateau was observed for 1/T2 with values of 36 mM(-1) s(-1) for G = 5, 42 mM(-1) s(-1) for G = 7, and 45 mM(-1) s(-1) for the G = 9 and G = 10 dendrimers. This "saturation" of ion relaxivity for high-generation dendrimers occurred over the entire frequency range studied. The 1/T1 and 1/T2 relaxivities decreased as the temperature decreased for each generation of dendrimer studied, implying that slow water exchange of bound water molecules with the bulk solvent limits the relaxivity. In such circumstances, increases in the rotational correlation time of the macromolecules associated with higher generations of dendrimer does not result in significant increases in the ion relaxivity. Although the ion relaxivity does not increase, the total molecular relaxivities increased from 2880 mM(-1) s(-1) to 66960 mM(-1) s(-1) for the G = 5 to the G = 10 dendrimer. The current findings are relevant for the design of high-generation dendrimer-based receptor agents.

Contrast Media↗

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↗

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

Potential of 31P magnetic resonance spectroscopy in monitoring the viability of human renal grafts stored in Euro-Collins perfusion solution.

The relative concentrations of inorganic phosphate and phosphomonoesters (PME) of 18 human cadaveric kidneys stored in Euro-Collins perfusion solution were measured by 31P MR spectroscopy. The signals of intracellular inorganic phosphate (Pii) and inorganic phosphate contained in the perfusion solution (Pie) were separated by the deconvolution technique. The ratio of the signal intensities of phosphomonoesters and intracellular inorganic phosphate (PME/Pii) was used as a marker of kidney viability and correlated with kidney function after transplantation. Separation of the Pii and Pie signals in the measured spectra was successful in 72% of kidneys. The results of MR analysis satisfactorily agree in 78% with the post-transplant function of kidneys.

Humans↗