Reproducibility of measurements of cerebral infarct volume on CT scans

Background and Purpose-Infarct volume is increasingly used as an outcome me asure in clinical trials of therapies for acute ischemic stroke. We tested which of 5 different methods to measure infarct size or volume on CT scans has the highest reproducibility. Methods-Infarct volume and total intracranial volume were measured with Lei ca Q500 MCP image analysis software, or with a caliper, on 38 CT scans of p atients who participated in the Tirilazad Efficacy Stroke Study II (TESS II ). The scans were performed 8 days (+/-2 days) after the onset of symptoms. The 5 methods tested were based on (1) semiautomated pixel thresholding, ( 2) manual tracing of the perimeter, (3) a stereological counting grid, (3) measurement of the 3 largest diameters, and (5) the single largest diameter . The measurements were performed independently by 3, observers; the first observer performed all measurements twice. Results-The single largest diameter did not correlate well with infarct vol ume. Of the other methods, manual tracing of the perimeter of the infarct h ad the lowest intraobserver and interobserver variability: coefficients of variation were 8.6% and 14.1%, respectively. For total intracranial volume, manual tracing also provided the highest reproducibility: intraobserver an d interobserver coefficients of variation were 3.3% and 4.9%, respectively. Conclusions-Manual tracing of the perimeter is the most reproducible method for measuring the volumes of the infarct and the total intracranial space in multicenter trials of therapies for acute ischemic stroke.