Velocity-encoded cine-magnetic resonance imaging (VEC-MRI) is a new method for quantitation of blood flow with the potential to measure high-velocity jets across stenotic valves. The objective of this study was to evaluate the ability of VEC-MRI to measure transmitral velocity in patients with mitral stenosis. Sixteen patients with known mitral stenosis were studied. A 1.5 Tesla superconducting magnet was used to obtain velocity-encoded images in the left ventricular short-axis plane. Images were obtained throughout the cardiac cycle at 3 consecutive slices beginning proximal to the mitral coaptation point. To determine the optimal slice thickness for MRI imaging, both 10 mm and 5 mm thicknesses were used. Echocardiography including continuous-wave Doppler was performed on every patient within 2 hours of MRI imaging. Peak velocity was determined for both VEC-MRI and Doppler-echo images. Two observers independently measured the VEC-MRI mitral inflow velocities. Of the 16 patients, imaged data were incomplete in only 1 study, and all images were adequate for analysis. Strong correlations were found for measurements of mitral valve gradient for both 10 mm (peak r = 0.89, mean r = 0.84) and 5 mm (peak r = 0.82, mean r = 0.95) slice thicknesses. Measurements of peak velocity with VEC-MRI (10 mm) agreed well with Doppler: mean 1.46 m/s, mean of differences (Doppler MRI) 0.38 m/s, standard deviation of differences 0.2 m/s. These findings suggest that VEC-MRI can noninvasively determine the severity of mitral stenosis.

Japanese and American economists assess the present economic status of the elderly in the United States and Japan, and consider the impact of an aging population on the economies of the two countries.

With essays on labor force participation and retirement, housing equity and the economic status of the elderly, budget implications of an aging population, and financing social security and health care in the 1990s, this volume covers a broad spectrum of issues related to the economics of aging. Among the book's findings are that workers are retiring at an increasingly earlier age in both countries and that, as the populations age, baby boomers in the United States will face diminishing financial resources as the ratio of retirees to workers sharply increases.