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Acute Ischemic Stroke: Accuracy of Diffusion-weighted MR Imaging—Effects of b Value and Cerebrospinal Fluid Suppression¹

¹ From the Seaman Family MR Research Centre (P.E.C., J.E.S., M.D.H., C.H.S., R.J.S., R.F.) and Calgary Stroke Program (J.E.S., M.D.H.), Foothills Medical Centre, Calgary Health Region, 1403 29th St NW, Calgary, AB, Canada T2N 2T9; and Departments of Clinical Neuroscience (J.E.S., M.D.H., R.J.S., R.F.), Radiology (C.H.S., P.D., W.F.M., R.J.S., R.F.), Medicine (M.D.H.), and Community Health Sciences (M.D.H.), University of Calgary, Calgary, Alberta, Canada. Received June 24, 2004; revision requested August 25; revision received February 1, 2005; accepted February 28. Supported by the Alberta Foundation for Health Research, Canadian Institutes for Health Research (CIHR), and the Heart and Stroke Foundation of Canada (HSFC). J.E.S. is an Alberta Heritage Foundation for Medical Research (AHFMR) Fellow; M.D.H. is an HSFC and CIHR Research Scholar; and R.F. is an AHFMR Medical Scholar, an HSFC Research Scholar, and a Canada Research Chair. Address correspondence to R.F. (e-mail: rfrayne{at}ucalgary.ca).

Purpose: To prospectively determine which diffusion-weighted magnetic resonance (MR) imaging technique (ie, conventional diffusion-weighted MR imaging [b = 1000 or 1500 sec/mm²] or fluid-inversion prepared diffusion [FLIPD] MR imaging [b = 1500 sec/mm²]) is most accurate in depicting acute ischemic stroke at 3 T.

Materials and Methods: The Health Research Ethics Board approved this study; written informed consent was provided by all participants or their surrogate. Diffusion-weighted MR imaging was performed in 75 consecutive patients (43 men, 32 women; mean age, 64.0 years) with acute ischemic stroke. Two experienced neuroradiologists determined the presence of hyperacute stroke lesions at diffusion-weighted MR imaging by locating areas of hyperintensity that corresponded to regions with a decreased diffusion coefficient. These findings were used as the reference standard. Four raters who were blinded to patient history assessed all images and apparent diffusion coefficient maps for the presence of changes that were consistent with acute ischemic stroke. Accuracy, sensitivity, specificity, negative predictive value, positive predictive value, and inter- and intrarater reliability scores were calculated for each technique.

Results: Specificity, positive predictive value, and accuracy were not significantly different among the techniques. FLIPD MR images obtained with a b value of 1500 sec/mm² had decreased sensitivity for acute ischemic stroke (mean, 61.8%; 95% confidence interval [CI]: 55.4%, 67.9%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm² (mean, 82.5%; 95% CI: 77.1%, 87.0%) or 1500 sec/mm² (mean, 84.5%; 95% CI: 79.3%, 88.9%). FLIPD MR images also had decreased negative predictive value (mean, 96.5%; 95% CI: 95.7%, 97.2%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm² (mean, 98.4%; 95% CI: 97.8%, 98.8%) or 1500 sec/mm² (mean, 98.6%; 95% CI: 98.1%, 99.0%). Intra- and interrater reliability scores were generally excellent for all three techniques.

Conclusion: FLIPD MR images obtained with a b value of 1500 sec/mm² are less suitable for the detection of acute ischemic stroke owing to a decreased sensitivity and negative predictive value. The performance of the two conventional diffusion-weighted MR imaging techniques (b = 1000 and 1500 sec/mm²) was equivalent.

© RSNA, 2006

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