Osteoporosis is the most common form of metabolic bone disorder and is a significant disorder in Western populations, particularly among women. The condition leads to increased bone fragility, which in turn may lead to a significant increase in the risk of fractures. As the current population is increasing in age this makes effective diagnosis and treatment of the condition increasingly important (Papadakis et al. , 2009). The disease may often go undiagnosed in the population which then results in high levels of debilitating fractures in the affected population (Barnes, 2009).
This then has important consequences for the individual, health care providers and insurers, all of which can also impact on the general population. It is therefore becoming increasingly important to develop effective screening techniques to increase the number of detected cases of osteoporosis (Barnes, 2009). There have been several researchers who have begun to investigate new techniques for diagnosis of osteoporosis using already available technologies, among them multi-detector computed tomography (MDCT) (Masako, 2004). The Importance of Advancement
Bone mineral density (BMD) is the accepted measure of osteoporosis, with low quantitative measures of BMD indicating osteoporosis and increased risk of fracture (Link et al. , 2005). At the present time, both dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) are accepted as clinically relevant methods of diagnosing BMD. DXA is generally the accepted gold standard in diagnosis according to the World Health Organization (WHO) although QCT may offer a more sensitive test including in those without current fractures (Lang et al. , 2002).
One of the main benefits of QCT over DXA are that a true volumetric quantification of BMD may be obtained as each image slice represents a particular tissue volume. This is clearly beneficial when compared to the estimation achieved with DXA. In addition, trabecular and cortical BMD may be assessed separately in QCT, something which cannot be done with DXA (Papadakis et al. , 2009). Neither method is however routinely used in screening in the general population; this may largely be related to some problems identified with both methods, where BMD itself has been suggested to be an insufficiently accurate measure of osteoporosis risk.
Therefore the search for new techniques has focused so far on finding other methods which may produce measures which more accurately correlate with osteoporosis risk. Correlation with QCT measures has so far been used as the starting point for this, as this is the best known measure of osteoporotic risk so far. It has been shown that single-slice CT may not correlate accurately with QCT values, which makes it difficult to differentiate between those with osteoporosis and healthy adults (Hopper, Wang & Kunselman, 2000).
Masako (2004) investigated the use of MDCT in examination of trabecular bone structure and found that the three-dimensional images generated were sufficiently sensitive to detect age-related changes to bone mineral density, indicating that MDCT would be suitable for detection of osteoporosis. Papadakis and colleagues (2009) showed that this QCT could be generated based on MDCT examinations of the abdomen and successfully differentiate females with spinal osteoporosis from healthy females. This therefore indicates that MDCT should be better suited to osteoporotic assessment than single-slice CT.
MDCT Technology The promise of MDCT as an alternative to BMD lies in it offering a detailed interpretation of trabecular structure (Figure 1), which should then offer an insight into the likelihood of age-related bone deterioration having occurred, or being in the process of occurring (Barnes, 2009). Therefore research has focused on developing the technique to a clinically applicable format. Different scanner types and protocols have since been studied in the application of MDCT to osteoporosis assessment.
Researchers from the Charite Medical University in Berlin and the University of California, San Francisco showed that there was little difference in performance between 320-detector-row CT and 64-detector-row CT. Both have been shown to perform well in imaging trabecular bone at the distal radius. These researchers suggest that the research currently available does not sufficiently support the use of MDCT in assessment of spinal osteoporosis (Barnes, 2009), although the findings of Papadakis and colleagues (2009) support the possibility of this technique being useful in that particular context.
Figure 1: Image of the trabecular structure of a human radius bone produced by MDCT (Barnes, 2009) Future Development The main area with MDCT which requires further development is in setting standards for the use of the technique. This will involve setting normal ranges of values for the parameters of trabecular structure which it measures, based on studies which show the levels predicting osteoporosis (Barnes, 2009).
At the present time, it would appear that the lack of accurate standards would indicate that reading of images may be more of an art-form than a science, which is unlikely to be acceptable in the clinical environment. There also would appear to be a requirement for further investigation in its use in other areas of the body, possibly with further studies on its use in prediction of osteoporosis in the spine, one of the most important areas affected by the condition. Conclusions
It would appear that MDCT offers a promising alternative to methods of diagnosing osteoporosis which rely on BMD measurements. There is yet required more research to ensure that the method is the best available for wider population screening, and further work would be required to standardize the procedure before it may be applied clinically.
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