Three-Dimensional Digital Capture of Head Size in Neonates – A Method Evaluation

Introduction: The quality of neonatal care is mainly determined by long-term neurodevelopmental outcome. The neurodevelopment of preterm infants is related to postnatal head growth and depends on medical interventions such as nutritional support. Head circumference (HC) is currently used as a two-dimensional measure of head growth. Since head deformities are frequently found in preterm infants, HC may not always adequately reflect head growth. Laser aided head shape digitizers offer semiautomatic acquisition of HC and cranial volume (CrV) and could thus be useful in describing head size more precisely. Aims: 1) To evaluate reproducibility of a 3D digital capture system in newborns. 2) To compare manual and digital HC measurements in a neonatal cohort. 3) To determine correlation of HC and CrV and predictive value of HC. Methods: Within a twelve-month period data of head scans with a laser shape digitizer were analysed. Repeated measures were used for method evaluation. Manually and digitally acquired HC was compared. Regression analysis of HC and CrV was performed. Results: Interobserver reliability was excellent for HC (bias-0.005%, 95% Limits of Agreement (LoA) −0.39–0.39%) and CrV (bias1.5%, 95%LoA-0.8–3.6%). Method comparison data was acquired from 282 infants. It revealed interchangeability of the methods (bias-0.45%; 95%LoA-4.55–3.65%) and no significant systematic or proportional differences. HC and CrV correlated (r2 = 0.859, p<0.001), performance of HC predicting CrV was poor (RSD ±24 ml). Correlation was worse in infants with lower postmenstrual age (r2 = 0.745) compared to older infants (r2 = 0.843). Discussion: The current practice of measuring HC for describing head growth in preterm infants could be misleading since it does not represent a 3D approach. CrV can vary substantially in infants of equal HC. The 3D laser scanner represents a new and promising method to provide reproducible data of CrV and HC. Since it does not provide data on cerebral structures, additional imaging is required

Correlation and prediction intervals of HC and CrV.

<p>Data points indicate CrV plotted against HC. Grey continuous line is indicating regression line. Dashed lines and light grey filling define the 95% prediction interval.</p

Clinical characteristics.

<p>Clinical characteristics at birth and at the time of head scan. GA = gestational age, HC = head circumference,PMA = postmenstrual age, PNA = postnatal age, HCman. = manually measured HC, HCdig. = digitally measured HC, CrV = cranial volume.</p

Comparison of manual and digital HC measurements.

<p>Bland-Altman-Plot showing the relative differences plotted over the means of both methods. Indicated are Bias (orange dashed line) and 95% Limits of Agreement (blue dashed lines).</p

Distribution of differences between manual and digital HC measurements.

<p>Folded empirical cumulative distribution plot (Mountain-Plot). Percentiles of each ranked difference between the methods are plotted against the relative differences. The orange dashed line indicates bias.</p

Correlation and prediction intervals of HC and CrV at different Postmenstrual Ages (PMA).

<p>CrV plotted against HC for infants A) below 37 weeks PMA and B) greater/equal 37 weeks PMA. Grey continuous line is indicating regression line. Dashed lines and light grey filling define the 95% prediction intervals.</p

Measurement of head circumference and cranial volume.

<p>Measurement software (Cranial Comparison Utility, Vorum Research Corporation, Vancouver, Canada) is used to measure HC and CrV. Cranium is divided into 12 cross-sections parallel to the reference plane. Green lines indicate cross sections 2 and 8, used to measure CrV. Red line indicates cross section 3, used to measure HC.</p

Intraobserver Variability of HC and CrV measurements.

<p>Coefficients of Variation (CV) of different observers (indicated by shape and colour of data points) are shown for HC and CrV of two different examined heads.</p