Brain Injury Criterion (BrIC)

Overview

The Brain Injury Criterion (BrIC) is a measurement developed by the National Highway Traffic Safety Administration (NHTSA) in 2011 to better assess the risk of brain injuries in automotive impacts [1]. Unlike the Head Injury Criterion (HIC), which only considers linear forces, BrIC accounts for rotational motion of the head which is an important factor in many brain injuries and skull fractures [1]. BrIC works by measuring the peak angular velocity, how quickly the head spins, around the x, y, and z axis during a crash [1]. These values are then normalized and combined into a single BrIC score. This makes it a useful tool for evaluating injuries that HIC might miss [1] [2]. Although BrIC was designed to work alongside HIC, it has limitations in capturing complex head movements and has not yet become an industry standard [1] [2].

BrIC vs HIC

To assess the BrIC outcome, the injury risk curves derived from cumulative strain damage measure (CSDM) are used to understand the likelihood of brain injury[ 3]

Required Signals

• Head angular velocity at Head CG ($w_{x}$, $w_{y}$ and $w_{z}$)

Calculation

1. Each head angular velocity is filtered at CFC = 60

2. Uses critical angular velocities $w_{x,crit} = 66.25$ $rad/sec$, $w_{y,crit} = 56.45$ $rad/sec$, and $w_{z,crit} = 42.87$ $rad/sec$

3. Find maximum of filtered head angular velocity for x, y and z axis

4. Calculates BrIC by taking the square root of normalized maximum angular velocities (relative to the critical angular velocities) in radians/sec

$$BrIC = \sqrt(\frac{w_{x,max}}{w_{x,crit}}^2 + \frac{w_{y,max}}{w_{y,crit}}^2 + \frac{w_{z,max}}{w_{z,crit}}^2) \\$$

Where $w_x$, $w_y$, $w_z$ represent the maximum angular velocities around the x, y, and z axes respectively, and $w_{xc}$, $w_{yc}$, $w_{zc}$ represent the critical angular velocities

5. Compare to the injury risk curves for AIS 1+, 2+, 3+, 4+, and 5+

$$AIS +1 = 1 - e^{(((-\frac{BrIC - 0.523}{0.065}))^{1.8})}$$ $$AIS +2 = 1 - e^{(((-\frac{BrIC - 0.523}{0.324}))^{1.8})}$$ $$AIS +3 = 1 - e^{(((-\frac{BrIC - 0.523}{0.531}))^{1.8})}$$ $$AIS +4 = 1 - e^{(((-\frac{BrIC - 0.523}{0.647}))^{1.8})}$$ $$AIS +5 = 1 - e^{(((-\frac{BrIC - 0.523}{0.673}))^{1.8})}$$

References

[1] Takhounts E, Craig MJ, Moorhouse K, McFadden J, Hasija V. "Development of brain injury criteria (BrIC)." Stapp Car Crash J. 2013 Nov;57:243-66.

[2] Mueller B, MacAlister A, Nolan J, Zuby D. "Comparison of HIC and BrIC Head Injury Risk in IIHS Frontal Crash Tests to Real-World Head Injuries." Insurance Institue for Highway Safety, June 2015. Paper Numner 15-0272.

[3] Takhounts, Erik G et al. “Development of brain injury criteria (BrIC).” Stapp car crash journal vol. 57 (2013): 243-66. doi:10.4271/2013-22-0010