Does b1000–b0 Mismatch Challenge Diffusion-Weighted Imaging–Fluid Attenuated Inversion Recovery Mismatch in Stroke?

Abstract

Background and Purpose-Our aim was to explore whether the mismatch in lesion visibility between b1000 and b0 images is an alternative to mismatch between diffusion-weighted imaging and fluid-attenuated inversion recovery imaging as a surrogate marker of stroke age. Methods-We analyzed patients from the European multicenter I-KNOW database. Independent readers assessed the visibility of ischemic lesions of the anterior circulation on b0 and fluid-attenuated inversion recovery imaging images. The signal-intensity ratio for b0 and fluid-attenuated inversion recovery imaging images was also measured from the segmented stroke lesion volume on b1000 images. Results-This study included 112 patients (68 men; mean age, 67.4 years) with stroke onset within (n=85) or longer than (n=27) 4.5 hours. b1000-b0 mismatch identified patients within 4.

Synthetic FLAIR as a Substitute for FLAIR Sequence in Acute Ischemic Stroke

“…Rather than aiming at shortening FLAIR acquisition, our approach would allow to effectively omit it. We confirmed that FLAIR signal changes in AIS are embedded in the b0 and b1000 weightings of the DWI sequence (13), allowing generation of synthetic FLAIR images that contain key information for identification of AIS with a time since onset ≤4.5hr, either visually using the DWI-FLAIR mismatch or quantitatively using the rSI. Moreover, synthetic FLAIR mimicked real FLAIR images, with equal labelling time, suggesting the absence of a learning curve.…”

“…Median total duration for 24-slice DWI transfer onto the server, data conversion, synthetic FLAIR generation and transmission to PACS was 22.3 seconds (IQR, 17.9-25.0). Adjudication time for DWI-FLAIR mismatch assessment was similar between real FLAIR and synthetic FLAIR (median time: 13 seconds [IQR, 7-24] and 13 seconds [IQR, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], respectively; P=.55).…”

“…FLAIR sequence acquisition as part of an AIS MR protocol usually requires several minutes, and image quality may be suboptimal in restless patients (12). To overcome these limitations, attempts have been made to use the T2-weighted echo-planar imaging (EPI) sequence before the application of diffusion gradients (b=0 sec/mm 2 [b0]) as substitute for FLAIR (13). The resulting b0-DWI mismatch allowed estimation of AIS onset with a moderate sensitivity (72.9%), in part because analysis of cortical regions was hindered by high signal intensity from cerebrospinal fluid on the b0 images.…”

Acute Ischemic Stroke: A Review of Imaging, Patient Selection, and Management in the Endovascular Era. Part I: Initial Management and Imaging

“…This indicates a stroke onset of < 4.5 hours with a sensitivity and specificity of 86% and 89%, respectively, when compared with DWI-FLAIR mismatch. 46 Fluid-attenuated inversion recovery: The primary utility of FLAIR imaging is to function as an MR "tissue clock" for estimating the time of ictus in unwitnessed or wakeup stroke. At 1.5T, DWI-FLAIR mismatch is the gold standard imaging criterion and reliably indicates < 4.5 hours from ictus.…”