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Bone health in children is a rapidly growing area of clinical concern. The recent interest in this field is a response to the rising incidence of childhood fractures as well as the concept that early bone development could be a major determinant of adult osteoporosis and fragility fractures. In the past few years, there has been a marked increase in the use of bone densitometry in children and adolescents, primarily using dual-energy x-ray absorptiometry (DXA). Although a valuable tool, the use of DXA to evaluate children has highlighted its limitations. By recognizing the shortcomings, yet exploiting the strengths of DXA, this noninvasive, low-risk, readily available tool could aid in identifying children at risk for inadequate bone development and monitoring treatment.

This chapter provides an overview of the current densitometry techniques that are used in children. The strengths and limitations of each of the techniques are discussed. Dualenergy x-ray absorptiometry (DXA) is discussed only briefly, as the remainder of this book concentrates on this technique in detail. Table 1 provides a technical overview of costs, uses, precision, and radiation exposure associated with densitometry methods. Radiation doses associated with other imaging modalities and with natural background sources are provided for comparison in Table 2.

Early attempts at bone densitometry used conventional x-rays with a step wedge made from an aluminum or ivory phantom included in the field of view as a means of calibration. The bone density was calculated by a visual comparison of the density of the bone and the known densities of the each of the steps on the phantom.

The demand for bone mineral assessments in pediatrics has grown in the past decade. This trend likely reflects greater awareness of the importance of early bone health for osteoporosis prevention (),(). An estimated 60% of the variable risk of osteoporosis has been attributed to the magnitude of peak bone mass reached by early adulthood; the remaining 40% is explained by subsequent bone loss. Genetic factors, undernutrition, hormone disorders, medications, immobilization, and chronic illness during childhood and adolescence may compromise the rate at which bone size, mineral content, and quality are accrued (–(). If not reversed, this results in reduced peak bone, increasing the lifetime risk of osteoporotic fracture. In severely affected children, low-impact or fragility fractures can begin in childhood.

The aim of this chapter is to provide the operator with the basic information required to achieve a good-quality dual-energy x-ray absorptiometry () scan. Topics such as patient preparation, standard scan acquisition, and typical acquisition problems are discussed. This information is intended to supplement instructions provided in operator manuals and individual department protocols.

Analysis is a key step between image acquisition and the interpretation required for clinical decision making. The technologist performing this step is responsible for making informed decisions to provide accurate baseline and serial measurements. Originally, software programs were designed to analyze the adult skeleton, that is, a skeleton that is fully mineralized with well-developed skeletal landmarks and regions of interest (s) that do not change markedly in size or shape over time.

As with scan acquisition and analysis, interpretation of pediatric dual-energy x-ray absorptiometry (DXA) scans presents a myriad of challenges. Historically, DXA was developed predominantly for the diagnosis and management of postmenopausal osteoporosis. For older adults, the amount of bone mineral mass is a reasonable surrogate of bone strength because adult bone does not change much in size or shape, and low bone mineral density (BMD) measured by DXA is predictive of fragility fractures.

Acquisition and accurate interpretation of bone densitometry scans in the pediatric patient are necessary first steps toward any clinical assessment process. The dual-energy x-ray absorptiometry report fulfills the role of transmitting data clearly to the clinician. A timely, concise, and informative report is essential to relay the findings and to avoid costly and potentially dangerous misinterpretations by physicians unfamiliar with pediatric densitometry data.

A number of physical disabilities and medical conditions may adversely affect the growth and development of the immature skeleton, including cerebral palsy, muscular dystrophy, juvenile rheumatoid arthritis, acute lymphoblastic leukemia, cystic fibrosis, Prader-Willi syndrome, and various hematological disorders (–). In these pediatric patients at risk for osteoporosis, bone mineral density (BMD) findings at one skeletal site cannot be reliably generalized to other areas of the skeleton (). Although BMD of the lumbar spine and hip regions are strongly related in healthy children, considerable anatomic differences between the two sites may become apparent as BMD decreases ().

The preceding chapters of this text are primarily dedicated to the optimal acquisition and interpretation of dual-energy x-ray absorptiometry (DXA) scans in children in clinical practice. In addition to these techniques, many investigators have proposed novel methods for scan acquisition and analysis in order to overcome the limitations of DXA and to improve estimates of bone strength. Although these techniques are not yet available for clinical use, consideration of research strategies highlights the potential limitations of conventional DXA techniques and may aid in the interpretation of clinical scan results. This chapter summarizes these methods, cites examples of research applications in healthy children and children with chronic disease, and considers the potential strengths and weaknesses of these techniques.