Convergence for the /3-CI model conformer was obtained by constructing, at each cycle, not an extrapolated density matrix, but one representing 0.7 of the previous density matrix and 0.3 of the current density matrix. This is equivalent to applying a damping factor to the change in each array element of 0.3. ( 21) This anomeric energy may be an overestimate for the glycosyl chlorides, since it assumes that the CH3-0-CH2-CI torsion angle is unrestricted and 825 can have the optimum value of 74°. In a pyranose ring, this angle is constrained by the ring closure to be closer to 60°; In the two a glycosyl chlorides for which experimental data are available (see Table III), the C(5)-0(5)-C(1)-CI torsion angles are 68 and 72°.(22) These values represent energy differences between the actual minima and are a refinement of those reported previously (ref 14 and 15), where the standard torsion angles of 60 and 180°g ave energy differences of 3.0 and 2.4 kcal/mol for CH3-0-CH2-0H and CH3-0~CH2-0CH3, respectively.
MRI can be used to noninvasively detect, monitor, and quantify the chronic synovitis and progressive destruction of soft tissue and bone in live AIA rats, thereby improving the ability to evaluate disease progression in this preclinical animal model of rheumatoid arthritis.
Purpose:To evaluate the feasibility of using dynamic contrast-enhanced magnetic resonance imaging (MRI) for assessment of muscle perfusion in a rat model of hind-limb ischemia.
Materials and Methods:The acute alteration and chronic recovery in muscle perfusion and perfusion reserve after femoral artery ligation were quantified using the maximum Gd-DTPA uptake rate obtained by a T 1 -weighted gradient-recalled echo sequence. Radionuclide-labeled microsphere blood flow measurements were performed for comparison with the MR perfusion measurement on a separate set of animals.Results: After femoral artery ligation, a significant reduction in resting muscle perfusion was only observed at 1 hour post-ligation during the 28-day follow-up period. Muscle perfusion reserve was severely diminished following the ligation. Despite significant recovery over time, perfusion reserve to the ligated limb reached only 63% of the perfusion capacity in the unaffected limb by 42 days post ligation. A strong correlation (r ϭ 0.86) between MR perfusion and microsphere blood flow measurements was observed for evaluation of relative changes in muscle perfusion.
Conclusion:Dynamic contrast-enhanced MRI with Gd-DTPA is useful to assess time-dependent changes in muscle perfusion and perfusion reserve in this hind-limb ischemia model.
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