DK2985_C000 1..28 - AlSharqia Echo Club

32 Transesophageal Echocardiography(A)PVFLAMINAR FLOW(B)PVFIRREGULAR FLOWS 1S 2DSDARAR(C)PVF(D)SDAoLALUPVLVLVFigure 2.10 (A) Laminar flow: in the center of the vessel almost all the blood cells are traveling at the same velocity. The spectraldisplay shows a well-defined narrow envelope. (B) Irregular flow: near the wall of the vessel many different velocities occur; the PWDoppler records a larger spectrum of velocities and the envelope is replaced by a large band of different speeds occurring simultaneouslybecause the sample volume was placed close to the vessel wall. (C–D) Mid-esophageal short axis view with interrogation of left upperpulmonary vein (LUPV). The flow moves from a laminar to irregular pattern as the sampling volume moves from the center to the side ofthe LUPV (Ao, aorta; AR, atrial reversal; LA, left atrium; LV, left ventricle; PVF, pulmonary venous flow).lines is determined by the color sector width and the linedensity.Despite the power of recent microprocessors, this largeamount of information significantly lowers the frame rateof the images displayed on the screen. Therefore, insteadof determining the complete spectrum of frequencies, asin PW spectral display, an autocorrelator analyzes theresultant phase shift between the emitted and receivedwaveforms in order to generate a modal frequency representingthe velocity of the majority of blood cells (13).If the packet size comprises eight pulses, for example,the first pulse travels the scan line and returns to the transducer.It is followed by the second pulse whose recordedfrequency is slightly out of phase with the first pulsebecause the target is moving. The calculation is repeatedfor the eight pulses on the scan line (Fig. 2.12). If pulse(A)(B)Figure 2.11 Pulsed-wave (PW) and continuous-wave (CW) Doppler flow. (A) Pulsed-wave (PW) Doppler examination of the mitralvalve inflow. The flow is interrogated at a specific location by placing the sample volume between the tip of the mitral leaflets. Becausethe flow is laminar at this sampling site, most blood cells are travelling at the same velocity and the envelope is narrow and well-defined.(B) CW Doppler examination of the mitral valve inflow. Since all velocities are recorded along the interrogating beam, there is an envelopewith significant spectral broadening, that is, a curve filled with different velocities. The maximal velocity is assumed to be at thenarrowest area, that is, between the tips of mitral leaflets (TMF, transmitral flow).