A study of tablet dissolution by magnetic resonance electric current density imaging.

The electric current density imaging technique (CDI) was used to monitor the dissolution of ion releasing tablets (made of various carboxylic acids and of sodium chloride) by following conductivity changes in an agar-agar gel surrounding the tablet. Conductivity changes in the sample were used to calculate spatial and temporal changes of ionic concentrations in the sample. The experimental data for ion migration were compared to a mathematical model based on a solution of the diffusion equation with moving boundary conditions for the tablet geometry. Diffusion constants for different acids were determined by fitting the model to the experimental data. The experiments with dissolving tablets were used to demonstrate the potential of the CDI technique for measurement of ion concentration in the vicinity of ion releasing samples.

Dynamic contrast enhanced MRI of mouse fibrosarcoma using small-molecular and novel macromolecular contrast agents.

The aim of the study was a comparison of 2 novel macromolecular contrast agents, Gadomer-17 and Polylysine-Gd-DTPA, with commercially available Gd-DTPA in determining the quality of tumor microvasculature by dynamic contrast enhanced MRI. Three groups of 5 mice with SA-1 tumors were studied. To each group of animals one contrast agent was administered; i.e. the first group got Gd-DTPA, the second group Gadomer-17 and the third group Polylysine-Gd-DTPA. To perform dynamic contrast enhanced MRI a standard keyhole approach was used by which consecutive signal intensity change due to contrast agent accumulation in the tumor was measured. From the obtained data, tissue permeability surface area product PS and fractional blood volume BV were calculated on a pixel-by-pixel basis. PS and BV values were calculated for each contrast agent. Based on the values, contrast agents were classified according to their performance in characterizing tumor microvasculature. Results of our study suggest that Gadomer-17 and Polylysine-Gd-DTPA are significantly superior to Gd-DTPA in characterizing tumor microvasculature.

Fast frequency selective MR imaging.

With the proposed fast frequency selective MR imaging (FFSMRI) method, we focused on the elimination of all off-resonance components from the image of the observed object. To maintain imaging speed and simultaneously achieve good frequency selectivity, MRI was divided into two steps: signal acquisition and postprocessing. After the preliminary phase in which we determine imaging parameters, MRI takes place; the signal from the same object is successively acquired M times. As a result, we obtain M partial signals in k-space, from which we calculate the image of the observed object in postprocessing phase, after signal acquisition has been completed. With proper selection of parameters, it is possible to exclude from the image a majority of off-resonance components present in the observed object. However, we can decide to keep only a chosen off-resonance component in the image and eliminate all other components, including the on-resonance component and thus producing a different image from the same acquisition. The experiments with Fe(OH)(3) and oil showed that signal-to-noise ratio (SNR) can be improved by about a factor of four. The proposed FFSMRI method is suitable for frequency selective MR imaging and quantitative measurements in dynamic MRI where exclusion of off-resonance components can improve the reliability of measurement.

Assessment of kainate toxicity using contrast enhanced magnetic resonance imaging.

The purpose of this study was to test the capability of contrast enhanced magnetic resonance imaging (MRI) in assessing lesion formation in rat brain after systemic (i.v.) administration of kainate. MRI was performed with T1 -weighted spin echo sequence before and after the administration of kainate and contrast media. Contrast media used were based on paramagnetic gadolinium (III) ion: Gd-DTPA (gadoliniumdiethylene-triaminepentaacetic acid) and prototype agents for blood-pool enhancement Gadomer-17 and polylysine-Gd-DTPA. Enhancement of lesion rims and other brain tissue abnormalities due to kainate with Gd-DTPA, Gadomer-17 and polylysine-Gd-DTPA were observed mainly in the region of hippocampus and in the areas not protected by the blood-brain-barrier (BBB).

Subchronic liver injuries caused by microcystins.

The subchronic effects of cyanobacterial lyophilizate (CL) containing microcystins on liver were investigated in female New Zealand rabbits. Sterilised CL containing microcystins was injected i.p. Liver toxicity was assessed by histological examination of liver samples. Non-invasive magnetic resonance imaging (MRI) of liver was also performed in order to assess changes in the homogeneity of liver tissue. Subchronical intoxication with microcystins caused morphological changes of liver tissue that were also detected by use of MRI. Histological analysis showed that changes seen on MRI represent liver injury characterised with fatty infiltration and periportal fibrosis. This demonstrates that subchronic exposure to microcystins can lead to liver degeneration, which can easily be detected in vivo by use of MRI.

Electric current density imaging of tablet dissolution.

The Electric current density imaging technique (CDI) was used to monitor the dissolution of and ion migration from tablets of different acids in agar-agar gel. Conventional MRI cannot monitor these processes, since it can only show changes in the size of the tablet during the dissolving process. CDI traces the dissolved ions thanks to changes in conductivity.