Confirming the Severity of Internal Carotid Stenosis

Dr. David Brazier, M.D.
Head, CT and MRI Imaging
Royal North Shore Hospital
Sydney, Australia

MTT map CBF map CBV map
Fig 1: MTT map
 Fig 1: CBF map Fig 1: CBV map

A 73-year old male was noted to have left sided weakness and decreased power in the left upper and lower limbs. A CT brain scan was performed. The pre-contrast CT scan showed a small area of hypo-attenuation in the region of the left insular cortex. This presumed to represent an area of infarction (not shown).

CT Perfusion study was performed at a higher level and CBF, CBV and MTT maps generated (Fig. 1) showed a much larger area of abnormality.

The mean transit time (MTT) map showed a large area of abnormality involving the distribution of the middle cerebral and post cerebral arteries.

The cerebral blood flow (CBF) map showed a large area of abnormality also involving the middle cerebral artery and posterior cerebral artery distribution.

The cerebral blood volume (CBV) revealed values similar to the left side and therefore showed there was cerebral blood flow and cerebral blood volume mismatch. This is the hallmark of compromised brain, but viable tissue and this indicated that while the patient has had a small area of infarction, a much larger area of brain was at risk.


Fig. 2

The patient went on to have formal angiography. This revealed a very tight stenosis of the right internal carotid artery with a 90% stenosis (Fig. 2).

Slow antegrade flow was also demonstrated up the right internal carotid artery when compared to the right external carotid artery

The patient went on to have a carotid endartarectomy and apart from the abnormalities noted on presentation made a good recovery and proceeded to rehabilitation.



Fig. 3

The Advantages of the Study:

Using CT Perfusion in this patient allowed us to confirm the severity of the internal carotid stenosis and highlight the extensive area of brain which was at risk. It therefore helped confirm the need for surgery. The advantages of CT Perfusion software are:


  • The ease of use of the software which is largely automated with automatic selection of artery and vein and generation of time graphs (Fig. 3)
  • Automated generation of MTT CBF and CBV maps
  • Small contrast dose of only 40 ml
  • Injection rate of only 4 ml/s
  • Ability to combine with CTA at same visit


CT Perfusion Protocol


Technical Parameters:

Scan Type Helical
Rotation Time 0.8 second
Thickness 10 mm
Scan Mode Cine
SFOV 25 cm
kVp 80 kv
mA 240 ma
Prep Delay 5 seconds
Recon Type Standard
Total Acquisition Time 40 seconds
Table Movement 0 mm

Contrast Parameters:

Rate 4.0 ml/second
Total Contrast Amount 40 ml
Type of Contrast Non-Ionic
  (370 mgI/ ml)