The aim of this study was to visualize the complicated blood flow of the cerebral
arteries in patients with post extracranial-intracranial (EC-IC) bypass using time-resolved
three dimensional phase-contrast (4D-Flow) MRI.
EC-IC bypass surgery is performed in the patients with internal carotid artery occlusion
(ICO) or who undergo ligature of the internal carotid artery (ICA) for the treatment
of aneurysm. The flow directions are varied according to the relative pressure of
some intracranial arteries following post EC-IC bypass. Abnormal retrograde flow is
often observed at the ipsilateral M1 segment of the middle cerebral artery (MCA),
circles of Willis and ophthalmic artery (OphA) to compensate the decrease of flow
from ICA. 4D-Flow can be a valuable tool for visualizing these complicated flows with
unrestricted view, non-invasiveness, and high reproducibility.
19 patients (12 men; mean age, 64 years), including 10 with ICO and 9 with post ligation
of ICA, were investigated. The EC-IC bypass was successfully achieved and clinical
status was improved in all patients. MR studies were performed on a 3T unit (Philips).
The imaging parameters of 4D-Flow MRI were as follows; TR/TE=8.4/5.4, FA=13, FOV=210X210mm,
VENC=70cm/sec, voxel size=0.82X0.82X1.4mm, heart phase= 15. 4D Flow -streamline images
of the cerebral arteries were generated using the GTFlow software (GyroTools). The
patency of donor artery was assessed. The direction of flow at M1 segment of middle
cerebral artery, A1 segment of anterior cerebral artery, posterior communicating artery
(PCoA) and OphA were assessed in the ipsilateral side. The direction of each flow
was categorized into retrograde, anterograde and unclear (very slow or no flow).
In all 19 patients, 4D-Flow MRI successfully visualized the whole cerebral arteries.
The patency of donor artery was proved in all cases. Abnormally retrograde flow was
observed at M1 (n = 9: 47.4%), A1 (n=5: 26.3%), PCoA (n=13: 68.4%), and OphA (n=6:
31.6%). The retrograde flow was observed more frequently at M1 in the patients with
post ligation of ICA than in those with ICO (77.8%: n=7/9pts vs. 20.0%: n=2/10pts,
p < 0.05). No patients with retrograde flow of M1 showed the retrograde flow at A1
or OphA (p < 0.05).
4D-Flow is valuable for depicting the complicated flow at M1, A1, PCoA and OphA. Abnormally
retrograde flow at M1 was related to the pathological condition before surgery and
the flow direction at A1 and OphA. 4D-Flow can visualize the complementary flow from
circles of Willis, OphA and donor artery.
The case with IC aneurysm post ligation of ICA and EC-IC bypass. Left: Whole cerebral
arteries image. Right: a: retrograde A1 flow; b: anterograde PCoA flow; c: retrograde
The case with ICO post EC-IC bypass. Left: Whole cerebral arteries image. Right: a:
anterograde A1 flow; b: retrograde PCoA flow; c: anterograde M1 flow; d,e: flow via