Sturdivan's formula revisited: MRI assessment of anterior chest wall thickness for injury risk prediction of blunt ballistic impact trauma.

Background: The thickness and composition of the chest wall are important quantities in multiparametric trauma models for the assessment of injury severity due to blunt ballistic chest impact. While ballistic parameters of non-penetrating projectiles can routinely be measured with high accuracy, data on the thickness of the anterior chest wall is unreliable. Therefore, it is the aim of this work to provide data on the thickness and composition of the anterior chest wall based on MRI examinations of healthy volunteers and to compare these measurements with different empirical estimation rules for the chest wall thickness.

Methods: The study encompassed consecutive male patients from an ongoing population-based cohort study. Each subject underwent standardized whole-body MRI (1.5Tesla). Thickness of total chest wall (CWT) and of adipose tissue (AT) were measured by two independent readers at ten anatomic locations on two cross-sectional planes over the centre of the left ventricle and over the tracheal bifurcation. For each subject, chest wall thickness was estimated based on ten different empirical estimation rules and percent errors were calculated.

Results: The study encompassed 250 male volunteers (average age 55.5 years, range 21-84 years, SD 13.6 years). Mean intraclass correlation coefficient of the two readers was 0.90 (range 0.59-1.0, SD 0.08). Average CWT was 31.2mm (range 17.3-51.6mm, SD 5.8mm) while average thickness of AT was 13.1mm (range 3.6-26.7mm, SD 4.6mm). Relative adiposity was 0.41 on average (range 0.19-0.61, SD 0.09). There was significant correlation between CWT and body weight and between CWT and body mass index. Sturdivan's approximation formula showed strong correlation with the measured values (percent error 3.58%, SD 16.26%).

Conclusion: In this population, Sturdivan's equation formula which is based on the individual's body weight provides valid approximation values for the chest wall thickness and may be used for the optimal design of protective devices and personal body armor as well as for the development of anthropomorphic based test methodologies.