Apparent diffusion coefficient thresholds and diffusion lesion volume in acute stroke

Apparent diffusion coefficient (ADC) thresholds are used to determine acute stroke lesion volume, but the reliability of this approach and comparability to the volume of the magnetic resonance diffusion-weighted imaging (MR-DWI) hyperintense lesion is unclear. Methods: We prospectively recruited and clinically assessed patients who had experienced acute ischemic stroke and performed DWI less than 24 hours and at 3 to 7 days after stroke. We compared the volume of the manually outlined DW hyperintense lesion (reference standard) with lesion volumes derived from 3 commonly used ADC thresholds: .55 x 10(-3)/mm(2)/second(-1), .65 x 10(-3)/mm(2)/second(-1), and .75 x 10(-3)/mm(2)/second(-1), with and without "editing" of erroneous tissue. We compared the volumes obtained by reference standard, "raw," and "edited" thresholds. Results: Among 33 representative patients, the acute DWI lesion volume was 15,284 mm(3); the median unedited/edited ADC volumes were 52,972/2786 mm(3), 92,707/6,987 mm(3), and 227,681/unmeasureable mm(3) (.55 x 10(-3)/mm(2)/second(-1), .65 x 10(-3)/mm(2)/second(-1), and .75 x 10(-3)/mm(2)/second(-1) thresholds, respectively). Subacute lesions gave similar differences. These differences between edited and unedited diffusion-weighted imaging and ADC volumes were statistically significant. Conclusions: Threshold-derived ADC volumes require substantial manual editing to avoid over-or underestimating the visible DWI lesion and should be used with caution