Background
—Myocardial perfusion reserve can be noninvasively assessed with cardiovascular MR. In this study, the diagnostic accuracy of this technique for the detection of significant coronary artery stenosis was evaluated.
Methods and Results
—In 15 patients with single-vessel coronary artery disease and 5 patients without significant coronary artery disease, the signal intensity–time curves of the first pass of a gadolinium-DTPA bolus injected through a central vein catheter were evaluated before and after dipyridamole infusion to validate the technique. A linear fit was used to determine the upslope, and a cutoff value for the differentiation between the myocardium supplied by stenotic and nonstenotic coronary arteries was defined. The diagnostic accuracy was then examined prospectively in 34 patients with coronary artery disease and was compared with coronary angiography. A significant difference in myocardial perfusion reserve between ischemic and normal myocardial segments (1.08±0.23 and 2.33±0.41;
P
<0.001) was found that resulted in a cutoff value of 1.5 (mean minus 2 SD of normal segments). In the prospective analysis, sensitivity, specificity, and diagnostic accuracy for the detection of coronary artery stenosis (≥75%) were 90%, 83%, and 87%, respectively. Interobserver and intraobserver variabilities for the linear fit were low (
r
=0.96 and 0.99).
Conclusions
—MR first-pass perfusion measurements yielded a high diagnostic accuracy for the detection of coronary artery disease. Myocardial perfusion reserve can be easily and reproducibly determined by a linear fit of the upslope of the signal intensity–time curves.
Zinc hydroxide nitrate, Zns(OH)s(NO3)2.2HzO, is monoclinic with a= 19.480 (5), b=6.238 (1), c= 5.517 (1) A, fl= 93-28 o (2), space group C2/m, two formula units per cell. The structure has been determined from Patterson and Fourier syntheses. The refinement was done by the method of least squares. The final R value for 491 observed Weissenberg reflexions was 6"4%. The structure is characterized by zinc atoms occuring in both octahedral and tetrahedral coordination in the ratio 3:2. The octahedral zinc atoms, surrounded by six OH groups, belong to a CdI~-type sheet with ¼ of the metal atoms missing. The tetrahedrally coordinated zinc atoms are located above and below the empty octahedra. The tetrahedra are formed by three OH groups and one water molecule. The nitrate group is not directly involved in the coordination of the metal atoms. The average tetrahedral Zn-O distance of 1.95 A is significantly shorter than the mean octahedral Zn-O distance of 2.13 A.
Zinc hydroxide nitrate is obtained as a microcrystalline powder by reaction of ZnO or Zn(OH)z with aqueous
Zn(NO3)2 solutions (Feitknecht, 1933). Single crystals can be grown by precipitation from homogeneous solution of zinc nitrate with urea at 60 °C (both concentrations e.g. 1 molar).
ExperimentalThe chemical formula Zns(OH)s(NO3)z. 2H20 was established by chemical and thermogravimetric analysis. X-ray powder diagrams for the determination of ac-curate unit-cell dimensions were taken with a focusing camera of the Guinier-de Wolff type with Fe Ke and Cu Kcc radiation. High purity potassium chloride was used as an internal standard. Multiple-film integrated Weissenberg photographs of the layers hOl, hll to h41 were taken on a Nonius camera with Cu Kcc radiation (Ni filter). Intensities of the layers hkO and Okl were collected by the multiple exposure technique with Zrfiltered Mo radiation on a Buerger precession camera. The blackening of the films was measured with a Joyce-Loebl mark III CS double-beam microdensitometer. The data from the layers hk0 and Okl were used to
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