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. Author manuscript; available in PMC: 2019 Oct 1.
Published in final edited form as: Magn Reson Med. 2018 Feb 6;80(4):1666–1675. doi: 10.1002/mrm.27115

Figure 5.

Figure 5

Performance of SIMEX and bootstrap across a range of SNR. (a) The root mean squared error (RMSE) of the SIMEX GFA estimation (log-scale) after bias-correction shows improvement over the RMSE without bias-correction. Within the meaningful SNR range (shown in the gray box), the bias-corrected estimates show a 5–7% improvement over the uncorrected estimates in white matter and a 5–8% improvement over the uncorrected estimates in gray matter. Within the range, lower SNR shows greater improvements. (b) The ratios of mean estimated standard deviation of GFA and mean true standard deviation of GFA within white matter and gray matter are shown across a range of SNR values. We find that the wild bootstrap procedure slightly underestimates the standard deviation in white matter, where the estimates are about 97% of the true values in our specified meaningful SNR range. In gray matter, the underestimation is larger, though the bootstrap procedure still captures 86% of the true variation. Within the typical clinical SNR range, the methods estimate the standard deviation well. Below this range, we see lower performance and above this range, we see small improvements.