Reference Values Found for Osteoporosis Screening With CTs

Veronica Hackethal, MD

April 18, 2019

A new study has identified normal reference values that could be used to opportunistically screen for osteoporosis using CT scans done for other reasons.

Results were published online on March 26 in Radiology.

"Our study provides normative values of L1 vertebra trabecular attenuation, which can serve as a quick reference for opportunistic osteoporosis screening at routine CT to identify adults with low bone mineral density who are at risk for osteoporosis and who could potentially benefit from further evaluation and possible intervention," Samuel Jang, MD, of the University of Wisconsin School of Medicine and Public Health, Madison, and colleagues write.

Current screening for osteoporosis consists of assessment for clinical risk factors combined with dual-energy X-ray absorptiometry (DXA), a radiological technique that measures bone mineral density.

One problem is that not everyone can afford or has access to DXA screening.  Screening for osteoporosis could be improved by looking for it on CTs done for other reasons.

Past work by this group evaluated CTs of trabecular bone (which is porous and found inside bones). These studies showed that Hounsfield units (HUs), a measure of radiodensity, correlated with DXA T-scores, particularly for the first lumbar vertebra. HUs were lower in vertebral compression fractures, which commonly occur in osteoporosis. Moreover, elderly women and men with low HUs were at significantly increased risk for osteoporotic fractures.

The next step was to determine reference ranges for HUs in trabecular bone of the first lumbar vertebra that could be used for CT screening of osteoporosis across all ages. So the researchers conducted a retrospective study in which they analyzed results from abdominal and/or thoracic CTs performed with and without intravenous contrast for a range of indications other than osteoporosis. The analysis included data from 20,374 adults (mean age 60 years, 56.1% women, 90% white).

Results were adjusted for age, sex, contrast agent, and manual versus automated technique of assessing HUs.

Age-related trabecular bone density loss turned out to be the primary determinant of decrease in HUs. Bone density loss appeared to be "fairly constant and predictable," according to the authors, and decreased linearly at a rate of 2.5 HU per year.

Because bone mineral density in women decreases more rapidly after menopause, researchers also analyzed the data for sex differences. Women had significantly higher HU values compared with men until age 54 years (P < .01). After menopause, women and men had similar HU values (P = .02-.99).

Researchers used these results to calculate references values for HUs in 5-year age increments, starting at age < 30 years (mean reference value, 226 HU) and increasing up to age ≥ 90 years (mean reference value, 89 HU).

"With this study, Jang et al advanced the science of opportunistic bone density screening," Andrew Smith, MD, PhD, of the University of Alabama at Birmingham, writes in an editorial published in Radiology.

Opportunistic CT scanning may have several advantages over DXA scanning, he added. CT scans can avoid confounders like large body size, atherosclerotic calcifications, and degenerative spine changes that complicate interpretation of DXA scans. Also, opportunistic CT scans could be done without adding to patient time, costs, or radiation exposure.

The study has several potential limitations. As a single center study, results may not apply to other settings or more diverse patient groups. The study used a CT scanner with a peak voltage of 120 kV made by a single company (GE Healthcare), so the results may not apply to other scanners.

The authors have reported financial relationships with Ethicon, HistoSonics, iCAD, ScanMed, Philips, Imbio, Zebra Medical, Ping An, Ping An Nvidia, Bracco, Elsevier, Shine, Elucent, Cellectar, and VirtuoCTC. Smith has reported receiving an institutional grant from GE and having a patent for color enhanced detection for CT screening of bone density.

Radiology. Published online on March 26, 2019. Abstract, Editorial

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