Recommendations for High-resolution Peripheral Quantitative Computed Tomography Assessment of Bone Density, Microarchitecture, and Strength in Pediatric Populations

Abstract

Purpose of review: The purpose of this review is to summarize current approaches and provide recommendations for imaging bone in pediatric populations using high-resolution peripheral quantitative computed tomography (HR-pQCT).

Recent findings: Imaging the growing skeleton is challenging and HR-pQCT protocols are not standardized across centers. Adopting a single-imaging protocol for all studies is unrealistic; thus, we present three established protocols for HR-pQCT imaging in children and adolescents and share advantages and disadvantages of each. Limiting protocol variation will enhance the uniformity of results and increase our ability to compare study results between different research groups. We outline special cases along with tips and tricks for acquiring and processing scans to minimize motion artifacts and account for growing bone. The recommendations in this review are intended to help researchers perform HR-pQCT imaging in pediatric populations and extend our collective knowledge of bone structure, architecture, and strength during the growing years.

Keywords: Bone; HR-pQCT; Imaging; Pediatric.

Fig. 1

Longitudinal growth of the distal radius. The growth plate is adding cartilage tissue at a rate of about 1 cm per year. At the border between the growth plate and the metaphysis, this cartilage is replaced by bone tissue (labeled as new bone). With increasing distance from the growth plate, the bone is increasingly older (as indicated by darker color in this schematic), cortical thickness is increasing, and the outer size of the metaphysis is decreasing. The region of interest (ROI) for HR-pQCT includes metaphyseal bone that typically has been formed 1 to 2 years before, depending on how the measurement site is selected by the investigator. Modified with permission from [18]

Fig. 2

a Limb length measurements prior to scanning; b positioning of the limb in the HR-pQCT scanner. Pillows can be used to provide support and fill the extra space on the seat to prevent movement; c other tips for scanning children to reduce motion include using a smaller pediatric arm cast and playing videos to distract the child

Fig. 3

Reference line placement for current pediatric HR-pQCT protocols at the radius (top row) and tibia (bottom row). UBC, University of British Columbia; XCTI, first-generation HR-pQCT; XCTII, second-generation HR-pQCT; GP, growth plate; SS, single stack; DS, double stack

Fig. 4

Examples of 3D image registration at the distal radius with and without landmarks. In the example with landmark, a 13.5-year-old boy with type I osteogenesis imperfecta (OI) is scanned at two time points, 12 months apart. Due to bisphosphonate treatment, the remnants of the growth plate are visible on the scans as distinct lines. These lines provided enough features between the scans for correct image registration, when accompanied by proper initial translation enforced by the user. The line could also be used for visual verification of the registration. For the case without landmark, a 13.3-year-old healthy boy was scanned at two time points, 13 months apart. In this case, 3D registration failed to properly align the scans. Due to the lack of any distinct landmark, proper registration could not be visually verified