can be used to show blood flow through the valves to visually indicate the direction of blood flow. Abnormal blood flow can reflect stenosis and regurgitation of the valve. Color doppler can also show blood flow in abnormal locations such as with septal defects (ASD or VSD). Color doppler can also be applied to M-mode. Using color doppler in this way gives better visualization of the changes in flow with time due to the higher frame rate with M-mode. Spectral doppler Spectral doppler is presented similarly to M-mode in which the doppler information is plotted as a spectrogram. This can be both "continuous" and "pulse" wave where the former shows the spectrum along a specific line and the latter shows within a small window along that line. Continuous wave is better at showing maximal velocities and pulse wave is better for showing flow through a small volume. Spectral doppler is often used for quantification of flow. For example, the aortic valve area can be estimated using the continuity equation by measuring the velocity time integral (VTI) of the aortic valve & LV outflow tract; the VTI is calculated by tracing the flow on the spectral doppler curve. Spectral doppler is also useful for calculating the maximum flow and mean flow through a valve (used to grade valve stenosis). Tissue doppler Tissue doppler can be used to determine motion of myocardial tissue. This can be used to measure motion of the septal and lateral mitral annulus to suggest diastolic heart failure. Axes The images obtained with echocardiography are in reference to the heart itself. Two key axes of the heart are the long axis and short axis. The long axis is an imaginary line from the apex of the heart through the center of the tricuspid/mitral valve (depending on ventricle of reference). The short axis is perpendicular to the long axis and shows the heart in cross section. Axes are also defined for each valve with long-axis defined as that of blood flow, and short-axis is the plane perpendicular to the flow. Windows Evaluation of the heart with echocardiography requires having "acoustic windows" of the heart. Bone reflects the ultrasound waves and so all structures directly behind bone are not visible with ultrasound. This requires that the heart be viewed between bones and, in particular, between ribs. The most common views are the parasternal, apical, subcostal, and suprasternal windows.. Parasternal: adjacent