Dual Energy CT Scan
What is a dual energy CT scan? Standard computed tomography (CT) scanners use normal X-rays to make cross-sectional ‘slice-like’ pictures…Read more
The following indicate an increased risk for bone loss (osteoporosis) and might require BMD assessment to confirm osteoporosis.1 Although BMD scanning can be carried out for any of these risk factors, only some satisfy Medicare re batable indications, as specified in the MBS handbook. These indications are generally applicable to patients at increased risk of fracture and include:
The only distinct prerequisites for a BMD scan is that the individual should not have had a previous radiological or nuclear medicine investigation in the last week and that they are known not to be pregnant (see what are the absolute contraindications for a BMD scan).
Pregnancy is the only absolute contraindication. Pregnancy is contraindicated because of the ionising radiation involved in the study. Documentation of the last normal menstrual period or the results of a pregnancy test should be provided.
Bilateral hip replacements or bilateral hip pins or screws would prevent the hip sites from being scanned. Unilateral metallic surgical implants in the hip necessitate the opposite hip being scanned. Similarly, metallic rods or spinal fusion devices in the lumbar spine would preclude scanning at this site. Forearm scans are carried out where either the hip or spine sites are unavailable.
DXA scans are safe for patients with permanent pacemakers and implantable defibrillators.
There are no apparent adverse effects of a BMD scan.
There is no specific post-procedural care required.
Although the currently accepted gold standard for assessing bone density is the DXA scan, an assessment of bone density can also be made by CT scan of the lumbar spine, or by heel ultrasound. There are significant limitations of both of these latter two methods.
CT scan of the lumbar spine is accurate and reproducible; however, it involves significantly higher doses of ionising radiation, and provides information about only one region. The hip and spine are composed of different types of bone, which are variably susceptible to medical or therapeutic insults. Having information about two sites is therefore preferred.
Heel ultrasound is a useful screening method to assess bone structure and density. It does not use ionising radiation, but requires formal DXA assessment for osteoporosis in those patients who have been identified as potential high fracture risk after heel ultrasound measurements.
WHO criteria for BMD results are based on T score values; that is, measurements compared with normal young same sex population:
BMD scanning is also indicated for follow up or monitoring of response to therapy aimed at preventing fracture and bone loss, or monitoring of progress according to medical condition or therapy. The frequency of repeated studies covered by Medicare in Australia varies according to the underlying condition, for example 12-monthly intervals for hypogonadism and glucocorticoid exposure, and 24-month intervals for the remainder.
There are a number of manufacturers of DXA scanners. It is important that follow-up DXA scans be carried out on the same scanner. Scans from different manufacturers, and to some extent those from the same manufacturer at different sites, cannot be directly compared.
Although diffuse bone loss in the elderly is commonly due to osteoporosis, the results of other investigations and clinical presentations need to be taken into account. For example, diffuse metastatic disease or myeloma could also present with vertebral body fractures and reduced BMD. Reduced bone loss in the younger adult warrants further investigation or specialist referral.
Page last modified on 18/8/2017.
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