Advantages of susceptibility-weighted magnetic resonance sequences in the visualization of intravascular thrombi in acute ischemic stroke

Background: In gradient echo magnetic resonance imaging (MRI), intravascular thrombi (IT) can appear as vascular susceptibility artifacts, linked to local presence of intra-arterial deoxyhaemoglobin, and called susceptibility vessel signs (SVS).

Aims: Our objectives were to evaluate the sensitivity of susceptibility-weighted sequences, such as T2* weighted angiography (SWAN) in the visualization of SVS compared with T2*, to consider whether it enabled a better understanding of the importance of SVS, and to compare cerebral circulation regulation profiles according to the localization of the SVS (i.e. proximal or distal).

Methods: We prospectively studied the clinical and imaging data of 78 consecutive patients admitted for acute cerebral ischemia to the stroke unit of Besançon University Hospital between 1 April 2009 and 31 January 2010.

Results: An SVS was visualized in 44/78 (56%) patients using SWAN and in 13/78 (16%) patients using T2*. All the SVS visible using T2* were also visible on the SWAN. The inter-observer kappa score was 0·72 [CI (0·53-0·91)] for T2*, 0·72 [CI (0·57-0·87)] for SWAN, and weighted kappa was 0·77 [CI (0·61-0·92)] for both T2* and SWAN. When an MCA occlusion was visible on MRA imaging (22/78 patients), a SVS was visualized in 7/22 cases (31·8%) using T2* and in 20/22 cases (91%) using SWAN. When the occlusion was visible in the M1 or M2 segments (17/78 patients), an SVS was visualized in 6/17 cases (35·3%) using T2* and in 15/17 cases (88·2%) using SWAN. When the occlusion was visible in the M3 segment (5/78 patients), an SVS was visualized in 1/5 cases (20%) using T2* and in 5/5 cases (100%) using SWAN. Presence of SVS was not associated with cardioembolic etiology of the stroke.

Conclusions: SWAN was more sensitive than T2* in the visualization of SVS in the intracranial arteries during the acute phase of ischemic stroke. Our study shows that the low number of SVS visualized using T2* in previous studies is probably related to a lack of sensitivity of the sequence, rather than to the nature or age of the thrombus. The greater sensitivity of SWAN seems to be linked to the visualization of SVS in cases of small thrombi.