Measuring Scan-Rescan Reliability in Quantitative Brain Imaging Reveals Instability in an Apparently Healthy Imager and Improves Statistical Power in a Clinical Study.

Becky Ilana Haynes¹, Nick G. Dowell¹, Paul S. Tofts¹

Repeatability of MTR and ADC brain histograms of healthy volunteers in our centre showed disturbingly large differences, even though the scanner was producing high quality images. Such instrumental variation could mask small between-group differences in a cross-sectional study, and increase the number of participants needed to see an effect. Repeat scans in phantoms and healthy controls highlighted the variability and showed when the problem had been fixed. Our current normal standard deviations are at the lower end of the published range. Ongoing QA for quantitative studies should include explicit measurement of short- and long-term repeatability in controls.