Patients
We retrospectively reviewed MR images of 1627 patients admitted in our institution for suspicion of acute ischemic stroke between July 2011 and December 2012.
We considered patients to be eligible for inclusion in our study if they met the following criteria:
1.
Patients had clear symptom onset maximum 4,5 hours before being admitted to our stroke center.
2.
The MRI exams were performed on our 3T GE MRI machine.
3.
Patients underwent a complete MRI exam following our stroke protocol which consistently includes DWI,
FLAIR,
TOF,
T2* and Susceptibility Weighted Imaging (SWI).
4.
MRI images were of diagnostic quality.
5.
Patient had a MCA territory ischemic stroke secondary to proximal MCA occlusion in the M1-M3 segment.
A total of 73 patients met the inclusion criteria.
Technique
The examinations were performed on a 3T MR (Signa HDX,
GE Medical System).
The protocol included echo-planar sequences with diffusion weighted Imaging,
T2 gradient echo (GRE),
T2 FLAIR,
3D time of flight (TOF) MRA and 3D SWAN (GE susceptibility weighted imaging sequence) for a total acquisition time of 17 minutes.
The sequences parameters were:
DWI: 4mm slice thickness,
slice interval 1.5mm, TR=10.000ms,
TE=94ms,
260x260mm FOV,
192x192 matrix and 3 nex.
The acquisition time is 2:10min.
GRE: 4mm slice thickness,
TR=820ms,
TE=20ms,
1.5mm slice interval and a flip angle of 15°.
A 220x165 mm FOV was used with a matrix of 320x256 and 0.75 nex.
The scan time is 2 :01min.
TOF: 3 slabs of 46 slices,
1mm slice thickness,
TR=19ms,
TE=2.7ms,
a flip angle of 20°,
220x165mm FOV ,
416X288 matrix.
Acquisition time 4:59min.
T2: 4mm slice thickness,
TR=10.000ms,
TE=132ms,
inversion time(IT)=2250ms, 220x220mm FOV,
320X256 matrix.
Acquisition time 3:21min.
3D SWAN: 2 slabs of 32 slices each,
2mm slice thickness,
TR=37.7ms,
TE=22.8ms,
230x173mm FOV,
426x324 matrix,
a flip angle 15° and 0.69 Nex.
Acquisition time 4:00min
Image analysis
The images of all selected patients were retrospectively analyzed by an investigator (D.S.) who was blinded to clinical data and had access only to FLAIR and T2* and/or SWI images when the latter were available.
The reviewer was asked to look for the following signs:
(1) hyperintense arteries (HA) on FLAIR,
defined as high arterial signal intensity on Fluid Attenuated Inversion Recovery sequences within the subarachnoid space(3).
(2) hypointense superficial and deep veins (HSV and HDV) on T2* and Susceptibility Weighted Imaging (SWI) defined as hypointense vascular signal within vascular cisterns on T2* and SWI which exceeds the contralateral vessel diameter(1,2).
(3) hypointense thrombus (HT) on T2* and Susceptibility Weighted Imaging defined as focal vascular hypointense signal which depasses the diameter of the corresponding vessel,
frequently associating a multilayered appearance.
Our investigator's findings were subsequently noted along with patient's sex, age and site of MCA occlusion (M1-M3) and compared to the definitive diagnostic based on clinical assessment,
full MRI stroke protocol exploration and/or digital subtraction angiography when it was performed.