Category: Bone Densitometry or Body Composition

34 - Hologic Horizon spine, forearm and lateral distal femur precision in young children

Precision characterization is vital to determine when significant changes in bone mineral density (BMD) and bone mineral content (BMC) have occurred as an individual is monitored over time. Precision can vary due to bone density, body size, system make and model, and technologist skill. We have previously presented that DXA precision estimates for infants and children ages 6 years to 16 years old. The purpose of this study was to evaluate the DXA precision error from multiple measurement sites of young children, from 1 to 3 years old.

Bone Mineral Accretion in Young Children is a longitudinal study to create DXA reference data for children from 1 to 5 years. Duplicate scans with repositioning were acquired of the spine, lateral distal femur (LDF) and distal forearm (FA) using Hologic Horizon scanners (Hologic, Inc., Bedford, MA). One trained research assistant analyzed all scans using Hologic Apex software version 5.5. Standard analysis procedures were used for analyzing spine and FA scans. LDF was analyzed using a modified Harcke method. Regions of Interests (ROIs) were defined in the anterior distal metaphysis (R1), metadiaphysis (R2), and diaphysis (R3), an additional region (R4) was defined in the metaphysis similar to R1 and located just posterior of R1. All precision scans were analyzed using the compare mode to match the ROIs and analysis algorithm. Precision of the spine, FA and LDF measures were expressed as percent coefficients of variation (%CV) and root mean square errors (RMSE). Age, weight, and standardized height were explored as possible covariates.

A total of 51 healthy children age ranged from 13 to 44 months were enrolled in the precision study. The mean and standard deviation of weight and standardized height were 12.3 ± 1.7 kg, 86.8 ± 6.2 cm respectively. The %CV of all the variables investigated are summarized in Table 1. For all skeletal sites, BMD had better precision than corresponding BMC estimates. Spine BMD had the best precision of (%CV=1.66%), while lateral distal femur R1 BMC had the poorest precision of (%CV= 4.11%). Precision estimates for LDF R2 and R3,which are mainly cortical bone, were better (%CV < 2%) than ROIs R1 and R4,which were mainly trabecular bone (%CV>2%). Least significant change estimates ranged from 4.6% to 11.4%. Precision estimates were not associated with age, weight or height as well as mean BMD or BMC results.

Discussion &
The precision for DXA scans in young children were reasonable for monitoring bone density changes over time. In addition, when compared to the previously reported precision values for similar scan types and make of DXA system, young children had more precise measures than infants but not quite as good as children 6 years and older. We attribute these findings to lower bone mass and poorer bone mapping the younger a child. As children grow, their bone mass increases and the precision improves.

Natasha Din

Clinical Research Coordinator, Radiology, UCSF
University Of California, San Francisco (UCSF)
Ssf, California

Heidi Kalkwarf

UC Department of Pediatrics
Cincinnati, Ohio

Leila Kazemi

Program Manager
San Francisco, California

John Shepherd

Adjunct Professor
San Francisco, California

Professor John Shepherd is a Professor in the Department of Radiology and the Director of the Body Composition, Exercise Physiology, and Energy Metabolism Lab at the University of California, San Francisco. He is a Fulbright fellow to the Karolinska Institute in Stockholm, and the current President of the International Society for Clinical Densitometry. He is an expert in quantitative breast imaging as well as musculoskeletal imaging using X-ray absorptiometry techniques. Dr. Shepherd received his BS in Engineering Physics from Texas Tech University and his PhD in Engineering Physics from the University of Virginia followed by a postdoctoral fellowship in Biophysics at Princeton University. He is also a Certified Clinical Densitometrist.

Dr. Shepherd’s research interests involve quantitative imaging methods for tissue composition using X-rays. He is the PI for the Shape Up! Study to examine 3D optical whole body scans in 1500 indivuduals from 5 to 85 years, and the PI of the 3CB study to extend mammography to measure the composition of invasive lesions. He has been the DXA CORE director for NHANES study since 1999. His current research interests include shape and appearance modeling and deep learning methods to big imaging datasets including DXA bone denisty scans. He has published over 150 peer reviewed articles in these fields.

Babette Zemel

Division of GI, Hepatology and Nutrition The Children's Hospital of Philadelphia
Philadelphia, Pennsylvania

Bo Fan

San Francisco, California