Fetal middle cerebral artery pulsatility index

The fetal middle cerebral artery (MCA) pulsatility index (PI) is a key parameter used in fetal middle cerebral arterial Doppler assessment. It is calculated by subtracting the end diastolic velocity (EDV) from the peak systolic velocity (PSV) and then dividing by the time averaged (mean) velocity (TAV):

  • PI = (PSV - EDV) / TAV

Practical points

The fetal MCA PI normally has a high value. The mean value (normal reference range) slowly decreases through gestation from around 28 weeks onwards. A low PI reflects redistribution of cardiac output to the brain due to the fetal head sparing theory.

See also


Ultrasound - obstetric
Share article

Article Information

rID: 33737
Section: Approach
Tags: refs, cases
Synonyms or Alternate Spellings:
  • Fetal MCA PI
  • Fetal MCA pulsatility index (PI)
  • Fetal middle cerebral artery (MCA) pulsality index (PI)

Support Radiopaedia and see fewer ads

Cases and Figures

  • Drag
    Case 1: 3rd trimester normal MCA Doppler
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.