Statistical error mapping for reliable quantitative T1 imaging.

We developed a statistically based error image for rapid appreciation of unreliable regions in quantitative water proton T1 images. The chi-squared error and co-efficient of variation of the fitted parameter were used to estimate uncertainties in the goodness-of-fit to mono-exponential T1 relaxation and the reliability of the calculated T1, respectively, for each pixel. Errors exceeding a statistical threshold based on a .1 acceptance criterion were displayed as a color-coded overlay on the T1 image. Error maps of quantitative T1 images from 31 healthy volunteers showed a characteristic error structure; few pixels within the parenchyma had excessive errors. Clinical cases with stroke and sickle cell disease showed deviations from the normal pattern in the spatial distribution and magnitude of chi-squared errors. Disease states may deviate from mono-exponential T1 relaxation more than normal brain does. The color-coded error map is a valuable tool for investigators using quantitative MR imaging to determine tissue relaxation parameters.