Pierce et al., (2014)
A threshold of 0.9 x10-3 mm2/s was proposed by Rumboldt et al., (2006) \cite{Rumboldt2006} to identify MB (N=8) with a sensitivity of 87.5% and a specificity of 100% from both EP (N=5) and PA (N=17).
Assis et al., (2015) \cite{Assis2015} agress with this threshold, suggesting that an average ADC of lower than this suggests a diagnosis of MB (N=8).
A lower threshold of 0.8x10-3mm2/s reported by Jaremko et al., (2010) \cite{Jaremko2010} allowed MB (N=7) to be distinguished from PA (N=12) with a sensitivity of 83% and specificity of 92%.
\cite{Pierce2014a}
These cutoffs are in good agreement and yield good sensitivity and specificity for MB with both EP and PA.
A meta-analysis of the reported values (taking into account the sample sizes and including each study only once) shows that MB typically have an ADC of 0.70±0.16 x10-3mm2/s, whereas PA and EP have ADCs of 1.62±0.36 and 1.07±0.23 x10-3mm2/s. A total of 261 MB, 78 EP and 196 PA were included in the meta-analysis. Using these means and standard deviations to produce a normal distribution, mean ADC values were simulated for each tumour type, where the number of samples for each tumour match the proportions of tumours types from the meta-analysis. Using ROC analysis (Figure \ref{436425}), optimal thresholds can be found which minimises the sum of square differences between 100% sensitivity and specificity between different tumour types. When considering upper threshold for distinguishing MB from EP, it can be found that <0.872x10-3 mm2/s provides a sensitivity/specificity of 85/82%. Likewise, the upper threshold for distinguishing MB from PA can be found to be <1.00x10-3 mm2/s, providing a sensitivity/specificity of 97/95%. Finally, MB can be distinguished from non-MB (PA and EP) using a threshold of <0.946x10-3 mm2/s with a sensitivity/specificity of 93/90%.
These results suggest that average ADC is a useful measure in distinguishing MB from PA, however the mean ADC lacks the necessary sensitivity and specificity when attempting to distinguish