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Doppler echocardiography is a procedure that uses ultrasound technology to examine the heart or blood vessels. An echocardiogram uses high frequency sound waves to create an image of the heart while the use of Doppler technology allows determination of the speed and direction of blood flow by utilizing the Doppler effect. An echocardiogram can, within certain limits, produce accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using the Doppler effect. One of the limitations is that the ultrasound beam should be as parallel to the blood flow as possible. Velocity measurements allow assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), calculation of the cardiac output and calculation of E/A ratio〔() Abdul Latif Mohamed, Jun Yong, Jamil Masiyati, Lee Lim, Sze Chec Tee. ''The Prevalence Of Diastolic Dysfunction In Patients With Hypertension Referred For Echocardiographic Assessment of Left Ventricular Function.'' Malaysian Journal of Medical Sciences, Vol. 11, No. 1, January 2004, pp. 66-74〕 (a measure of diastolic dysfunction). Contrast-enhanced ultrasound using gas-filled microbubble contrast media can be used to improve velocity or other flow-related medical measurements. An advantage of Doppler echocardiography is that it can be used to measure blood flow within the heart without invasive procedures such as cardiac catheterization. In addition, with slightly different filter/gain settings, the method can measure tissue velocities by Tissue Doppler echocardiography. The combination of flow and tissue velocities can be used for estimating left ventricular filling pressure, although only under certain conditions. Although "Doppler" has become synonymous with "velocity measurement" in medical imaging, in many cases it is not the frequency shift (Doppler shift) of the received signal that is measured, but the phase shift (when the received signal arrives). However, the calculation result will end up identical. This procedure is frequently used to examine children's hearts for heart disease because there is no age or size requirement. == 2D Doppler Imaging == Unlike 1D Doppler imaging, which can only provide one-dimensional velocity and has dependency on the beam to flow angle,〔J. A. Jensen, Estimation of Blood Velocities Using Ultrasound, A Signal Processing Approach, New York: Cambridge University Press, 1996.〕 2D velocity estimation using Doppler ultrasound is able to generate velocity vectors with axial and lateral velocity components. 2D velocity is useful even if complex flow conditions such as stenosis and bifurcation exist. There are two major methods of 2D velocity estimation using ultrasound: Speckle tracking and crossed beam Vector Doppler, which are based on measuring the time shifts and phase shifts respectively.〔P. S. a. L. L. Abigail Swillens, "Two-Dimensional Blood Velocity Estimation With Ultrasound: Speckle Tracking Versus Crossed-Beam Vector Doppler Based on Flow Simulations in a Carotid Bifurcation Model," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, pp. 327-338, 2010.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Doppler echocardiography」の詳細全文を読む スポンサード リンク
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