Hounsfield unit and gray-white matter ratio estimates in pediatric normal controls used in studies evaluating head computed tomography.

Head computed tomography (CT) plays a key diagnostic role in assessing anatomically visible cerebral injury, monitoring the development of edema and ischemia, and, in some diseases, assisting in the prediction of outcome. More specifically, after a cardiac arrest, head CT imaging will reveal the impact of global hypoxic-ischemic injury. In adults, some have shown that the gray-white matter ratio (GWR) calculated with Hounsfield units (HU) may be valuable for prognostication. Few studies have investigated their use in the pediatric population, and even fewer have considered age and maturation in their analyses. The objective of this study was to evaluate pediatric normal controls and report their HU and GWR values for use in future studies. Non-contrast head CT scans of children without neurological diseases were used. HU values were measured using predefined regions of interest and the circular dots method. GWR was estimated with 12 different formulas. Analyses were stratified by age (<2 and ≥ 2 years). We analyzed 42 scans. HU in the caudate nucleus, cortical gray matter, and brain parenchyma were lower in younger (n = 18) compared to older children ≥2 years (n = 24). No HU differences between the age groups were measured in the putamen, thalamus, and white matter. GWR calculated with basal ganglia (caudate nucleus + putamen) and cortical gray matter was lower in the younger group. Head CT measurements of HU and GWR change with age in children under 2 years. This feature was most relevant in gray matter areas. Future studies should evaluate which GWR formulas are most effective in assessing the severity of global hypoxic ischemic encephalopathy after cardiac arrest in the pediatric population.