Original Article
A Critical Comparison Between Two Scanning Protocols of High-Resolution Peripheral Quantitative Computed Tomography at the Distal Radius in Adolescents

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Abstract

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a unique technology for assessing bone mineral density and bone microarchitecture. Currently, no universally accepted protocol for selecting the region of interest (ROI) at the distal radius has been established for growing subjects. This study aimed (1) to investigate the differences in HR-pQCT measurements of 2 different ROI protocols applied to the distal radius of healthy adolescents and (2) to identify the least common area of ROI (the least common ROI) between the protocols. Twenty-six boys and 26 girls aged between 13 and 16 yr old were recruited. Nondominant distal radius was scanned by 2 HR-pQCT protocols, namely, the “5-mm protocol,” where the distal end of ROI started at 5 mm proximal to a reference line, and the “4% protocol,” where the ROI started at 4% of the ulnar length proximal to another reference line. The least common ROI between the 2 protocols was identified and the slice numbering within the common ROI was determined. Bland–Altman plots were used to check the agreement of the least common ROIs between the 2 protocols. Paired t-test and Wilcoxon signed-rank test were used for analysis. In boys, significant differences between protocols were found in most parameters with the maximum difference observed in the cortical area (25.0%, p < 0.001). In girls, differences were observed only for total volumetric bone mineral density (3.6%, p = 0.032). The number of slices in the least common ROI was 66 (60.0%) and 57 (51.8%) in boys and girls, respectively. Good agreements on all HR-pQCT parameters from the least common ROI between the 2 protocols were found. Significant differences in bone parameters were noted between the 2 protocols. When comparing the 2 protocols, observed gender differences could reflect the differences in skeletal growth at the peripubertal period between genders. Least common ROI could be useful for cross-center comparisons and when merging datasets from different centers.

Introduction

High-resolution peripheral quantitative computed tomography (HR-pQCT) is an advanced noninvasive 3-dimensional (3D) imaging technique measuring bone morphometry, trabecular bone microarchitecture, and volumetric bone mineral density (vBMD) of the cortical and trabecular compartments at the distal radius and tibia both for bedside clinical assessment and research including therapeutic clinical studies 1, 2, 3, 4.

HR-pQCT is performed by scanning a region of interest (ROI) defined by the manufacturer for adults with the distal border starting at 9.5  and 22.5 mm proximal to the reference line for the distal radius and distal tibia, respectively (5). Official Positions 2013 – Pediatric, published by the International Society for Clinical Densitometry, stated that “QCT, pQCT and HR-pQCT can be used clinically in children where appropriate reference data and expertise are available” (6). Currently, there is no consensus on the scanning protocol for young subjects with open growth plates, which are radiation-sensitive regions and should be avoided during scanning (7). In general, there exist 2 types of scanning protocols, namely, those with ROI starting at a fixed distance (1, 2, 5, or 9.5 mm) or a relative offset (4% or 7%) of the ulnar length proximal to different reference lines 7, 8, 9, 10, 11, 12, 13. Due to the diversity of existing protocols, it is difficult to perform cross-study comparisons and to merge datasets from different centers for analysis.

To the best of our knowledge, there is by far no study investigating how different ROIs affect the measurements obtained from HR-pQCT in young subjects with visible growth plates. In the present study, we compared the “5-mm protocol,” where the distal end of the ROI started at 5 mm proximal to a well-defined reference line, and the “4% protocol,” where the ROI started at 4% of the ulnar length proximal to a different well-defined reference line. The aims of this study were (1) to investigate the differences in HR-pQCT measurements at the distal radius of healthy adolescents between the 2 different protocols and (2) to identify the least common area of ROI (the least common ROI) between the protocols.

Section snippets

Subjects

Twenty-six boys and 26 girls aged between 13 and 16 yr old were recruited from local secondary schools. All subjects had open growth plates at the distal radius. The exclusion criteria were as follows: congenital deformities, neuromuscular diseases, genetic diseases, chromosomal defects, autoimmune disorders, endocrine disturbances, any disorders, or any medication affecting bone metabolism. Written informed consents were obtained from all subjects and guardians. The present study was carried

Basic Characteristics

The basic characteristics of the subjects are shown in Table 1. Boys had higher body height, sitting height, body weight, longer arm span, and ulnar length than girls (all p < 0.05). Boys also had higher sport index in the physical activity level than girls (p = 0.031).

Comparisons on Parameters Based on 110 Slices Between Protocols

Comparisons between the 2 scanning protocols are shown in Table 2 for boys and Table 3 for girls. Discrepancies between the 2 protocols were found in both genders when the complete sets of 110 slices were analyzed, with the

Discussion

The present study compared the 5-mm and 4% protocols at the distal radius of healthy adolescents with visible growth plates. These 2 scanning protocols differ by the placement of the ROI 10, 13. We noted systemic differences in measurements obtained by HR-pQCT with these 2 scanning protocols with ROIs that overlapped, thus allowing a common ROI to be determined for individual cases.

The Bland–Altman plots in Fig. 4 and Supplemental Fig. S1 showed that the mean differences in bone morphometry

Acknowledgments

The authors thank Dr. Ego Seeman of University of Melbourne for his expert advice. This study was supported by the Research Grants Council of Hong Kong S.A.R., China (Project No. 468411).

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