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Ba phương thức: xung sóng TDI (PW-TDI) 2 chiều-TDI (2-D-TDI) M chế độ TDI (MM-TDI) mẫu khối lượng được đặt lên cơ tim hoặc A-V van-vòng tần số cao, tín hiệu biên độ thấp từ máu lọc ra các biện pháp vận tốc cao điểm của một khu vực được lựa chọn có nghĩa là vận tốc tính toán để cung cấp cho các bản đồ tốc độ màu | 34 Transoesophageal Echocardiography Velocity resolution depth line density frame rate Many pulses down each line averaged to give mean velocity n X PRP X N X F 1 n pulses line PRP 1 PRF N lines frame F frame rate Therefore increase in one parameter leads to decrease in others Tissue Doppler imaging TDI Three modalities Pulse wave-TDI PW-TDI 2-dimensional-TDI 2-D-TDI M mode-TDI MM-TDI Sample volume placed on myocardium or A-V valve annulus High frequency low amplitude signals from blood filtered out Measures peak velocities of a selected region Mean velocities calculated to give colour velocity maps PW-TDI Good temporal resolution Wave pattern S wave ventricular systole IVRT E wave rapid diastolic filling Diastasis A wave atrial contraction Tissue Doppler velocities 5-15 cm s Physics of ultrasound 35 2-D-TDI Poor temporal resolution good spatial resolution Uses colour flow imaging Low velocity myocardium coded with dark colours High velocity myocardium coded with lighter colours MM-TDI Excellent temporal resolution Uses colour flow imaging with M mode Artefacts Reverberations Secondary reflection along the path of the U S pulse due to the U S bouncing between the structure and another strong reflector or the transducer Creates parallel irregular lines at successively greater depths from the primary target Two types Fig. 1.32 i linear reverberation ii ring down solid line directed away from TX due to merging of reverberations Ghosting Type of reverberation artefact when using colour flow Doppler Fig. 1.33 Amplitude of ghost A of initial reflector if target is moving Mirror images Occurs with Doppler CW and PW dd A of fD spectrum signal in opposite direction normally below threshold therefore filtered out exceeds threshold Fig. 1.34 38 Transoesophageal Echocardiography False image .U S beam refracted Fig. 1.36 Near field clutter In the near field strong signals are received from reflectors which dominate the image Amplitude of near field echoes reduced by near field
