Bone Abstracts

Considerable progress has been made over the past half century in the development of imaging methods for assessing the skeleton noninvasively or nondestructively, so that osteoporosis can be detected early, its progression and response to therapy monitored, and the risk of fracture determined. Clinicians and researchers can now evaluate the peripheral, central, or entire skeleton as well as the trabecular, cortical, and endosteal envelopes with a high degree of accuracy and precision, and they can reliably estimate bone strength and the propensity to fracture. The purposes of this presentation are to review the historical evolution of the methods for bone imaging and bone densitometry, and to assess their current capabilities.

The numerous methods for noninvasive assessment of the skeleton began their evolution in the 1960s and 1970s, with simple X-ray-based radiogrammetry, high-resolution fine-detail radiography, radiographic absorptiometry, and single-photon absorptiometry (SPA), all emerging as research tools, with only the latter becoming a clinical tool available in Europe and North America. Supporting and driving these methodological advances were the growing interests in postmenopausal osteoporosis and in bone loss during space flight, as evidenced by the first NIH, NASA and University sponsored bone density workshops, and the initiation of the biennial series of International Bone Density Workshops (IBDW). During this early period the nascent foundations were laid for what has evolved as our most eminent bone mineral societies, namely, the ECTS, IBMS, ASBMR, and IOF.

During the 1980s and 1990s, the medical imaging technologies exploded with the advent of computed tomography (CT) and then a decade later, with magnetic resonance imaging (MRI), each opening new perspectives with in vivo three-dimensional sectioning of the body. Quantitative computed tomography (QCT) was extensively investigated both for central and peripheral (pQCT) skeletal imaging. The early isotope-based pQCT systems were converted to X-ray based systems in the late 1980s. Similarly, during this period, the SPA technique was advanced to dual photon absorptiometry (DPA), permitting quantitative imaging of the central skeleton, mainly the spine and hip. At the same time pharmaceutical interest expanded in the area of osteoporosis therapeutics with exploration of a variety of estrogen and HRT regimens and the development of first and later generation bisphosphonates. Dual-X-ray absorptiometry (DXA) represented a major technological advance, replacing isotope-based DPA, and improving the speed, precision and spatial resolution, thus thrusting it into routine clinical practice.

During the most recent 20 years, the DXA technology has further advanced from pencil-beam, single-detector to fan-beam multi-detector array, further improving performance. Similarly, CT has evolved dramatically, to a high-resolution, fan-beam, multi-detector, spiral-scanning mode, greatly enhancing speed, coverage and efficiency. Special purpose advanced Micro-CT systems have also been developed, these for imaging small animals and bone specimens, or for in vivo imaging of the quasi-micro structure of the distal radius and tibia. Simultaneously over this time, MRI technology has continued its remarkable evolution, through many configurations, becoming today the most diverse and powerful medical imaging system. For both MRI and CT, the equipment and hardware advances have been accompanied by impressive developments in computer sciences and image processing, which have facilitated applications for analysis of skeletal macro and microscopic structure, extending well beyond simple BMD measures.

In summary, the past 50 years has witnessed tremendous progress in the development and application of bone imaging and bone densitometry techniques, currently providing a vast array of exquisite research and clinical tools to examine and explore the depths and boundaries of the skeleton in health and disease.