WASID Measurement Technique

Rules for Measurement of Percent Stenosis of Intracranial Arteries

  • Diameter measurements of arteries must be done using an electronic cursor provided by the imaging software
  • The image showing the most severe diameter stenosis should be chosen for measuring the stenotic diameter (Ds)
  • To measure the diameter of the reference normal artery (Dn) use the following WASID rules for establishing where to measure Dn  

Location for measuring Dn for the MCA, Intracranial Vertebral and Basilar Arteries

The rules for measuring Dn for these 3 arteries are similar.

  • 1st choice: the non-diseased, proximal part of the artery at its widest, non-tortuous segment that has parallel margins
  • 2nd choice: the non-diseased, distal part of the artery at its widest, parallel, non-tortuous segment. Use 2nd choice if the proximal part of the artery cannot be used e.g., stenosis in the proximal artery
  • 3rd choice: the non-diseased, most distal, parallel, non-tortuous segment of the feeding artery. Use 3rd choice if the entire artery with the stenosis is diseased.  The 3rd choices are: the ipsilateral supraclinoid carotid artery for a MCA stenosis, the ipsilateral extracranial vertebral artery for an intracranial vertebral artery stenosis, and the dominant intracranial vertebral artery for a basilar stenosis

Location for measuring Dn for the Intracranial Carotid Artery

  • 1st choice: the non-diseased, widest, parallel, non-tortuous portion of the petrous carotid artery
  • 2nd choice: the most distal, parallel part of the extracranial internal carotid artery. Use 2nd choice if the entire petrous carotid is diseased

By using the formula (1 – [Ds/Dn]) x 100), the percent diameter stenosis of the target lesion will be calculated