# A Review of Validation Methods for the Intracranial Response of FEHM to Blunt Impacts
## 2 Experimental Procedures Used in FEHM Validation
### Cadaver Experimentation  
#### 2.1.1 Intracranial Pressure Response  
The Intracranial Pressure (ICP) response is the most frequently considered FEHM validation metric. Practically every FEHM in the public domain has replicated impact conditions from [PERSON] et al. [34] and many supplement this with a scenario from [PERSON] et al. [38]. Both [PERSON] et al. [34] and [PERSON] et al. [38] place transducers at various locations in the sub-dural region of re-pressurised, un-embalmed cadaver samples. The cadavers are then secured and impacted by a piston travelling at a constant velocity. [PERSON] et al. [34] conducted 15 impacts in total, across two investigations. In the first investigation they impacted eight cadaver samples once, changing the mass, surface material and impact velocity of the piston to study the effect of impact characteristics on the ICP response. These are listed by [PERSON] et al. [34] as experiments 36 to 38, 41 to 44, and 54. In the second experiment they impacted a single cadaver seven times with the same piston at five different velocities to consider the relationship between head acceleration and ICP peaks. These are experiments 46 to 52. All the cadavers had transducers fitted in the frontal, parietal and occipital sub-dural regions, and in the posterior fossa. In two cases (tests 36 and 37) transducers were located bilaterally in the occipital region to monitor the symmetry of the pressure response. The second occipital transducer in experiment 36 was also placed in the epidural layer (all other transducers were sub-dural). In further experiments, transducers were placed adjacent to each other in the posterior fossa (tests 46 to 52) and occipital region (36) to monitor experimental procedure. The pressure in the carotid siphon was also monitored for experiments 41 to 54. The location of each transducer is described in relation to skull sutures with the exception of the frontal transducer, which is placed adjacent to the impact site. Exact distances from a datum are however, not detailed. The cadaver head was secured in a forward tilted position to allow the horizontally travelling piston to impact the front of the head, in line with the mid-sagittal plane and 45\({}^{\circ}\) above the Frankfurt plane, targeting the crown of the forehead. For each impact, [PERSON] et al. [34] measure and report the mass and velocity of the piston prior to impact and the peak values for impact force and linear acceleration, alongside severity measures for each impact (e.g., GSI [42], HIC [43] and injury damage codes). The peak pressures recorded by each transducer are also given for the first investigation, as summarised in Table 1. Case 37 is reported in more detail, where each response metric is plotted throughout the duration of the impact, as illustrated in Figure 1. Consequently, this is the most commonly replicated scenario in FEHM validation. Prior to the study discussed above, [PERSON] and [PERSON] [37] conducted a series of experiments following a similar protocol, with a static cadaver head impacted in the frontal region. Ten cadavers were impacted once each by a piston of mass between 5.31 and 5.39 kg at velocities between 3.96 and 9.70 m/s with a variety of padding materials on the impactor. During the tests, the impact force, accelerations of the impactor and cadaver arterial and CSF pressures were monitored and the impact force and kinematic response of each impact reported. Pressure responses, however, were not, as readings were distorted by cannulas in the assembly. After impact, the brain tissue of each cadaver was inspected for contusion and any observed damage was described in detail. Five of the 10 cases resulted in no physical injury. The remaining five presented evidence of haemorrhage and/or vascular rupture in various locations. The five no-injury cases and one injury example (presenting coup contusion) was used from [PERSON] and [PERSON] [37] during the validation of the GHMBC (Global Human Body Models Consortium) FEHM [44].