Bone Exploration Technologies

Bone Densitometry

For many years – and since the World Health Organization (WHO)’s definition of Osteoporosis in 1994, bone mineral density has been the main parameter to evaluate bone health and support medical decision. Bone densitometry (Dual-Energy X-Ray Absorptiometry, or DXA) has become the gold standard examination in clinical practice, to evaluate bone health and risk of fracture. This reliable and low-radiating technique provides accurate assessment of the bone mineral density (areal BMD or aBMD, expressed in g/cm2) at major skeletal sites (spine, hip and forearm) based on a 2D projected image; all International guidelines for osteoporosis management and treatment intervention are based on aBMD results (and the use of Z-scores and T-scores), as measured by DXA.

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Image credit: by Bruce Blaus – Medical gallery of Blausen Medical 2014

Limitations

Some limitations are recognized from DXA, as aBMD helps identify only half of the patients fracturing [7]. In addition, DXA measurements do not  separate cortical from trabecular bone, yet both compartments play an important role in bone strength and fracture resistance[8][9][10]. In secondary osteoporosis and specific pathologies, aBMD may not prove sensitive enough to accurately measure bone changes (in Diabetes, Glucocorticoid-induced osteoporosis etc.)[11] (link). It is also recognized that aBMD measurements may be challenging to interpret, especially at the spine, as the projected image can be affected by the presence of artifacts (most commonly met are osteoarthritis, compression fractures, aortic calcification, scoliosis or metal implants). (International Society for Clinical Densitometry – ISCD – website).

[Recently, the ISCD published a comprehensive Atlas of clinical case to highlight DXA images that shall be excluded from analysis, based on the presence of degenerative changes or other artifacts, leading the DXA examination – and therefore measurements – to be uninterpretable. This valuable work is dedicated to healthcare professionals (DXA clinicians, DXA operators) and can be consulted here. It is also possible to practice by analyzing cases and verifying the experts’ decision in terms of exclusion criteria and image interpretation, so clinicians can confront their decision with the consensual one from ISCD experts.]

Advanced Bone Measurement

Other techniques are used to perform advanced measurements of bone, understand its mechanism and better understand the impact of ageing, pathologies and of course bone treatments.

Histomorphometry analysis via iliac crest biopsy provides direct measurements of the bone composition (structure / microarchitecture) as well as the dynamic of bone remodeling, however it is an invasive technique only performed in case of absolute necessity (for interventional reasons rather than observational studies and definitely not used in clinical practice for diagnosis purposes).

Another technology to perform accurate measurements of the bone is QCT – Quantitative Computed Tomography, or the use of a CT scanner to not only qualify body through visual exploration in-vivo but also quantify bone thanks to the use of a phantom to differentiate X-ray intensities in the bone tissues. The produced high-resolution 3D images allow clinicians to measure volumetric density in the cortical and trabecular bone compartments.

Such accurate bone exploration – being either invasive, expensive and/or radiating – cannot be performed in daily clinical practice. On the other hand, bone examinations are systematically performed using DXA, bringing valuable source of information. Hence the need for advanced imaging applications such as 3D-SHAPER® to exploit existing DXA scans further and extract targeted and high added-value information for clinicians.

 

 

 

 

[7] Siris et al. (2004). Bone mineral density thresholds for pharmacological intervention to prevent fractures. Arch Intern Med 164:1108

[8] V. Bousson et al. “Volumetric quantitative computed tomography of the proximal femur: relationships linking geometric and densitometric variables to bone strength. Role for compact bone” Osteopor. Int 2006

[9] Y. Bala et al. “Role of cortical bone in bone fragility” Curr. Opin. Rheumatol 2015

[10] P.M. Mayhew et al. “ Relation between age, femoral neck cortical stability, and hip fracture risk” Lancet 2005

[11] .Kanis, J.A. et al. A meta-analysis of prior corticosteroid use and fracture risk, J. Bone Miner. Res. 2004; 19: 893-899