WASID Measurement Technique

RULES for Measuring 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 & Basilar Arteries

  • 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

Use the formula (1 – [Ds/Dn]) x 100), to calculate the % diameter stenosis of the target lesion