T2* “Susceptibility Vessel Sign” Demonstrates Clot Location and Length in Acute Ischemic Stroke

Abstract

ObjectivesThe aim of our study was to evaluate, in acute ischemic stroke patients, the diagnostic accuracy of the MRI susceptibility vessel sign (SVS) against catheter angiography (DSA) for the detection of the clot and its value in predicting clot location and length.Materials and MethodsWe identified consecutive patients (2006–2012) admitted to our center, where 1.5 T MRI is systematically implemented as first-line diagnostic work-up, with: (1) pre-treatment 6-mm-thick multislice 2D T2* sequence; (2) delay from MRI-to-DSA <3 hrs; (3) no fibrinolysis between MRI and DSA. The location and length of SVS on T2* was independently assessed by three readers, and compared per patient, per artery and per segment, to DSA findings, obtained by two different readers. Clot length measured on T2* and DSA were compared using intra-class correlation coefficient (ICC), Bland & Altman test and Passing & Bablok regression analysis.ResultsOn DSA, a clot was present in 85 patients, in 126 of 1190 (10.6%) arteries and 175 of 1870 (9.4%) segments. Sensitivity of the SVS, as sensed by the used protocol at 1.5 T, was 81.1% (69 of 85 patients) and was higher in anterior (55 of 63, 87.3%), than in posterior circulation stroke (14 of 22, 63.6%, p=0.02). Sensitivity/specificity was 69.8/99.6% (per artery) and 76.6/99.7% (per segment). Positive (PPV) and negative predictive value (NPV) and accuracy were all >94%. Inter- and intra-observer ICC was excellent for clot length as measured on T2* (ĸ ≥0.97) and as measured on DSA (ĸ ≥0.94). Correlation between T2* and DSA for clot length was excellent (ICC: 0.88, 95%CI: 0.81–0.92; Bland & Altman: mean bias of 1.6% [95%CI: -4.7 to 7.8%], Passing & Bablok: 0.91).ConclusionsSVS is a specific marker of clot location in the anterior and posterior circulation. Clot length greater than 6 mm can be reliably measured on T2*.

Susceptibility Vessel Sign on MRI Predicts Favorable Clinical Outcome in Patients with Anterior Circulation Acute Stroke Treated with Mechanical Thrombectomy

“…11 Identification of SVS on these GRE T2* sequences is considered reliable and reproducible because studies have shown excellent inter-and intraobserver agreement. 12 Similarly, our study, excellent intra-and interreader variabilities were observed confirming these results.…”

Negative Susceptibility Vessel Sign and Underlying Intracranial Atherosclerotic Stenosis in Acute Middle Cerebral Artery Occlusion

“…4,6,12 Paramagnetic intracellular deoxyhemoglobin is present at high concentrations in acute clots, leading to a nonuniform magnetic field that causes marked signal loss on the GRE sequence because of dephasing of spins. 13 Recently, several investigators reported the results of histologic studies analyzing the composition of the clots retrieved by mechanical thrombectomy in patients with acute ischemic stroke.…”

Optimal MRI Sequence for Identifying Occlusion Location in Acute Stroke: Which Value of Time-Resolved Contrast-Enhanced MRA?

“…Similarly, GRE T2 achieved only 56% agreement with DSA ( ϭ 0.31), despite its expected high sensitivity for thrombus detection (81.2%). [15][16][17] In contrast, TR-CE MRA proved a reliable non-time-consuming tool for occlusion location, with 88% agreement with DSA ( ϭ 0.81). The superior diagnostic performance of TR-CE MRA compared with 3D-TOF was not hampered by the lower image quality, probably due to the poorer spatial resolution, and may be the result of several factors: First, the T1 effect of gadolinium compensates for the signal loss caused by spin-dephasing that occurs in 3D-TOF when the flows are slow, turbulent, or oriented parallel to the section plane, in this case essentially upstream of the real occlusion site diagnosed on the DSA (standard of reference) image and especially within the IICA segment.…”

“…13,14 The gradient-echo T2 (GRE T2) sequence provides additional data at 77%-83% sensitivity for intracranial thrombus identification. [15][16][17] Nevertheless, it may also misidentify the occlusion location because the associated susceptibility vessel sign depends on thrombus composition. Finally, none of these sequences provides supra-aortic artery (SAA) as-sessment, though some of the recent grade A recommendations highlighted its utility in steno-occlusive disease screening for etiologic evaluation and subsequent appropriate endovascular therapy.…”