Fig. 5.

Reliability assessment of differential tractography using the length threshold. (a) Differential tractography is applied to a multiple sclerosis patient at different length thresholds. Only the tracks with decreased anisotropy in the patient may contain true positive findings. A longer length threshold (e.g. > 40mm) can reduce false findings at the expense of sensitivity, whereas a shorter threshold may introduce more false results. (b) Differential tractography is applied to a healthy subject, and any findings in the normal subject are false positives for neuronal injury. (c) The numbers of findings at different length thresholds and change thresholds are listed in tables. The patient has substantially large numbers of tracks with decreased anisotropy, suggesting a possible neurological injury. In comparison, the healthy subject has similar numbers of tracks with increased and decreased anisotropy. (d) False discovery rate (FDR) of the findings in a patient can be calculated by using the patient’s numbers of tracks with increased anisotropy as an estimation of the number of false findings. It allows for adjusting the sensitivity and specificity of differential tractography and quantifying the reliability at different length and percentage change thresholds.