# A Review of Validation Methods for the Intracranial Response of FEHM to Blunt Impacts
## 5 Conclusions  
Current FEHM produce different responses within the brain to similar impacts, despite being considered validated and, as yet, there is no widely accepted set of validation criteria. This paper reviews and discusses experimental data and methods that could be applied during the validation of the intracranial response of FEHM, and how it has been implemented in previous validation efforts. Surveying the experimental data available showed there was no single source providing sufficient data to completely validate the intracranial response FEHM. However, there are multiple options available to validate the intracranial pressure [34; 36; 38; 39], relative brain displacement [35; 36; 39; 40; 54] and brain strain responses [46; 52; 53; 54; 55; 60]. Across each of these there are combinations of cadaver and in vivo experimentation, blunt impacts and controlled impulses providing a range of kinematic profiles and subsequently brain response characteristics. The range of methods used to record impact responses also adds depth to the measures FEHM can be validated against. For example, analysis of tagged MRI data allows the area fractions of the brain experiencing strains above a given threshold to be introduced. There is unarguably scope and value in an experimental procedure being developed to specifically provide a comprehensive and more efficient FEHM validation tool. Adapting data from studies with a research focus beyond this application has limitations. [PERSON] and [PERSON] [111] highlighted these to include a lack of external and internal dimensions of the empirical subjects, limited cohort sizes and a lack of in vivo injury data and understanding. Whilst [PERSON] et al. [60] have gathered response data from larger volunteer groups and [PERSON] et al. [39] have attempted to introduce procedures that allow for dimension changes, these have not yet been widely implemented and only provide a single, rotational impulse each. Combinations of the experimental data currently available have the ability to reasonably assess the behaviour of FEHM. Researchers should be aware of the limitations and potential errors of each data source; for example the sensitivity the relative brain displacement response has to the monitored location [28]. This is how validation has been approached to date. However, as summarised in Table 4, the selection of cases between research groups has been inconsistent and [PERSON] et al. [31] included differences in validation tests conducted on FEHM in the limitations of comparing their validity and accuracy. [PERSON] and [PERSON] [105] addressed these issues by proposing a standardised impact case selection protocol. This has been acknowledged as promising in principle. Further research is, however, required to reach a consensus on the selection criteria and weighting factors suggested [91; 111], or if such selection should occur at all [111]. Should a protocol become approved and adopted, it would need to be applied to a wider selection of empirical data than the limited range previously \begin{table}
\begin{tabular}{l r r r} \hline \hline  & \multicolumn{3}{c}{**Validation Criteria**} \\ \hline  & **Intracranial** & **Relative Brain** & **Brain** \\
**CORA Parameter** & **Pressure** & **Displacement** & **Deformation** \\ \hline A\_THRES & 0.030 & 0.030 & 0.030 \\ B\_THRES & 0.075 & 0.075 & 0.075 \\ A\_VAL & 0.010 & 0.010 & 0.010 \\ B\_DELTA\_END & 0.200 & 0.200 & 0.200 \\ T\_MIN/MAX & 0.000/0.030 & 0.000/0.040 (min) & 0.000/0.040 (min) \\ D\_MIN/MAX & 0.01/0.12 & 0.01/0.40 & 0.01/0.25 \\ INT\_MIN & 0.70 & 0.80 & 0.7 \\ K\_V/P/G & 3/1/1 & 3/1/1 & 3/1/1 \\ G\_V/P/G & 0.33/0.33/0.33 & 0.33/0.33/0.33 & 0.33/0.33/0.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Optimised parameters for CORA (ver. 3.6.1) [48] analysis of FEHM performance against cadaver data from [PERSON] et al. [35; 36], as determined by [PERSON] and [PERSON] [105]. considered [34; 35; 36; 38]. Furthermore, there should be evidence that all test examples within a given research effort were assessed.