MCA Doppler

What is the appropriate technique for obtaining fetal middle cerebral artery Doppler waveforms? • An axial section of the brain, including the thalami and the sphenoid bone wings, should be obtained and magnified. • Color flow mapping should be used to identify the circle of Willis and the proximal MCA, just caudal to the transthalamic plane • The pulsed-wave Doppler gate should then be placed at the proximal third of the YMCA, close to its origin in the internal carotid artery (the systolic velocity decreases with increasing distance from the point of origin of this vessel). (GRADE OF RECOMMENDATION: C) • The angle between the ultrasound beam and the direction of blood flow should be kept as close as possible to 0◦ . • Care should be taken to avoid any unnecessary pressure on the fetal head, as this may lead to increased PSV, decreased EDV and increased PI16. • At least three and fewer than 10 consecutive waveforms should be recorded. The highest point of the waveform is considered as the PSV (in cm/s). • The PSV can be measured using manual callipers or autotrace. PI is commonly reported using autotrace measurement, but manual tracing is also acceptable. In fact, manual calliper placement was used in the seminal work investigating the value of MCA-PSV for non-invasive detection of fetal anemia15. • Appropriate reference ranges should be used for interpretation and the measurement technique should be the same as that used to construct the reference ranges. • In about 30% of cases, the PI difference between observers was greater than 0.517. Multiple measurements are recommended to assess the true value. • MCA-PSV measurements at the proximal site of the MCA in the near field are comparable to those obtained from the far-field vessel in clinical practice18,19. The far-field vessel may be chosen if obtaining an insonation angle of 0◦ is easier for the far-field than for the near-field MCA (Figure 7). (GRADE OF RECOMMENDATION: C)