Effect of b value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic stroke
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Updated: Oct 1, 2026
A Magnetic Resonance Imaging Protocol for Stroke Onset Time Estimation in Permanent Cerebral Ischemia
Published on: September 16, 2017
Raoul S Pereira1, Ashley D Harris, Robert J Sevick
1Department of Radiology, University of Calgary, Calgary, Alberta, Canada.
Purpose:
To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, Delta S) between damaged and normal tissue during diffusion-weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke.
Materials And Methods:
Phantoms with diffusion values approximating those expected in acutely infarcted and normal tissue were constructed from a mixture of agar and formaldehyde and imaged at varying b values (0-3000 mm(-2) second). Ten patients were imaged with multiple b values (500-2500 mm(-2) second) within 12 hours of stroke onset.
Results:
Theoretical calculations showed that for any combination of diffusion coefficients there existed an optimal b value that was higher than the standard setting of 1000 mm(-2) second, and this was confirmed by the phantom studies. In the patients, increasing b from 1000 to 1500 mm(-2) second increased Delta S (average, 22.4%; P = 0.001), but no consistent benefit was seen at b = 2000 mm(-2) second (P = 0.408). This compared favorably with the average optimal b value of 1662 mm(- 2) second calculated from the patients.
Conclusion:
These results suggest that increasing the b value from 1000 to 1500 mm(-2) second would increase contrast between infarcted and normal tissue in the setting of acute ischemic stroke.
