Factor analysis with a priori knowledge--application in dynamic cardiac SPECT

Two factor analysis of dynamic structures (FADS) methods for the extraction of time-activity curves (TACs) from cardiac dynamic SPECT data sequences were investigated. One method was based on a least squares (LS) approach which was subject to positivity constraints. The other method was the well known apex-seeking (AS) method. A post-processing step utilizing a priori information was employed to correct for the non-uniqueness of the FADS solution. These methods were used to extract 99mTc-teboroxime TACs from computer simulations and from experimental canine and patient studies. In computer simulations, the LS and AS methods, which are completely different algorithms, yielded very similar and accurate results after application of the correction for non-uniqueness. FADS-obtained blood curves correlated well with curves derived from region of interest (ROI) measurements in the experimental studies. The results indicate that the factor analysis techniques can be used for semi-automatic estimation of activity curves derived from cardiac dynamic SPECT images, and that they can be used for separation of physiologically different regions in dynamic cardiac SPECT studies.

Multiple line source array for SPECT transmission scans: simulation, phantom and patient studies

Accurate attenuation and scatter corrections in quantitative SPECT studies require attenuation maps of the density distribution in the scanned object. These can be obtained from simultaneous emission/transmission scans.

METHODS

A new method has been developed using a multiple line source array (MLA) for transmission scans, and its performance has been investigated using computer simulations and experimental data. The activity in the central lines of the MLA was higher than at the edges of the system, so that more transmission photons would be directed toward the thicker parts of the human body. A series of transmission-only and simultaneous emission/transmission studies were performed for different phantom configurations and human subjects. Attenuation maps were generated and used in reconstruction of attenuation-corrected emission images.

RESULTS

The mu coefficients for attenuation maps obtained using the MLA system and simulated and experimental data display no artifacts and are qualitatively and quantitatively correct. For phantoms, the agreement between the measured and the true value of mu for water was found to be better than 4%. The attenuation-corrected emission images for the phantom studies demonstrate that the activity in the heart can be accurately reconstructed. A significant qualitative improvement was also obtained when the attenuation correction was used on patient data.

CONCLUSION

Our results indicate that the MLA transmission source can be used in simultaneous transmission/emission imaging to generate accurate attenuation maps. These maps allow for performing an object-specific, attenuation correction of the emission images.

1H-NMR studies on association of mRNA cap-analogues with tryptophan-containing peptides

1H-NMR spectroscopy was applied to a study of the mode of interaction, in aqueous medium in the pH range 5.2-8.5 and at low and high temperatures, between several mono- and dinucleotide analogues of the mRNA cap m7GpppG and a selected tripeptide Trp-Leu-Glu, and a tetrapeptide Trp-Glu-Asp-Glu, the sequence of which corresponds to one of the suspected binding sites in the mRNA cap-binding protein (CBP). A program, GEOSHIFT, was developed, based on ring-current anisotropy theory, for analysis of experimentally observed changes in chemical shifts accompanying interactions between aromatic heterocyclic rings. This permitted quantitative evaluation of stacking interactions between the m7G cap and the tryptophan indole ring, and the relative orientations of the planes of the two rings, spaced about 3.2 angstroms apart. The structures of the stacked complexes were determined. In particular, stacking between m(2,2,7)3G (which has no free amino group for hydrogen bonding) and the indole ring is weaker and quite different from that between m7G and m(2,7)2G and indole. With the dinucleotide cap-analogues, only the m7G component stacks with the indole ring, without disruption of intramolecular stacking. In contrast to numerous earlier reports, the calculated stacking interactions are quantitatively in accord with the values derived from fluorescence measurements. It also has been shown that the positively charged (cationic) form of m7G stacks much more efficiently with the indole ring than the zwitterionic form resulting from dissociation of the guanine ring N1H (pKa approximately 7.3).