The Effect of Bone Strontium on BMD for Different Manufacturers' DXA Systems

Osteoporotic patients treated with strontium ranelate show relatively large increases in bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) due to the replacement of some of the calcium atoms in bone by strontium. A study published by Pors Nielsen and colleagues reported that replacement of 1% of calcium atoms by strontium causes a 10% increase in BMD. 

We refer to the ratio of the percentage increase in BMD to the molar percentage of strontium in bone as the strontium ratio. Theoretically it is expected that the strontium ratio should vary between different manufacturers' DXA equipment depending on the effective photon energy of the device, an effect that arises because of the proximity of the X-ray energies produced by lower energy devices to the strontium K-edge at 16 keV. 

In this study we report theoretical estimates of the strontium ratio for two axial DXA systems and two peripheral DXA devices based on their broad spectrum X-ray emission. The theoretical figures were verified in an experimental study in which the strontium ratio for each device was measured using phantoms containing mixtures of hydroxyapatite and strontium hydrogen-phosphate. 

The theoretical values/experimental results of the strontium ratio were: 

11.0/11.2 for the Hologic Discovery,

9.9/9.9 for the GE-Lunar Prodigy, 

9.1/8.6 for the Demetech Calscan, and 

8.5/6.3 for the Osteometer Dexacare G4. 

The results confirm both theoretically and experimentally that the effect of bone strontium on BMD measurements is different for different DXA systems. In the future it might be possible to exploit this effect to make a non-invasive estimate of average bone strontium content in groups of patients receiving strontium medication for osteoporosis.

https://pubmed.ncbi.nlm.nih.gov/20699129/

BMD Increases by Varying Amounts with Strontium Citrate and Decreases by Varying Amounts after Discontinuation

A study published September 13, 2016, presents three case studies of patients who took strontium citrate (680 mg strontium per day) for six years, five years, and four years (Cases 1, 2, and 3, respectively) and then stopped taking it for two years, one year, and one year (Cases 1, 2, and 3, respectively). The study gives the increases in BMD with SrC and the decreases when the supplement was discontinued.  Of note is the fact that both the increases and decreases vary with the site (lumbar spine or total hip), the individual, and the number of years of use or discontinuation of SrC. Also, keep in mind that stopping any of the osteoporosis drugs will also result in loss of some of the BMD gains because there is no cure for osteoporosis.

Case 1

A 76-year-old female with osteoporosis (OP) took alendronate weekly for 10 years till 2006, then every other week for another year and was initiated on a drug holiday. She started self-administrating SrC (680mg/day) in 2006 and continued to take daily calcium (600mg bid) and vitamin D (2000units). Serum calcium and Vitamin D (32-66ng/ml) remained normal. She continued SrC on her own till 2012, when she agreed to stop taking it due to concerns about accumulation and toxicity.

On dual-energy X-ray absorptiometry (DXA) scan, total hip mean BMD increased 2.7% in the first 2 years on SrC after stopping alendronate, and continued to increase to a maximum of 9.2% after 6 years of treatment with SrC (1.53%/year). Lumbar Spine (LS) BMD was non-diagnostic due to degenerative changes in the spine.

In the first 2 years off of SrC, total hip mean BMD decreased by 5.7%.

Case 2

A 64-year-old female with history of OP, which was diagnosed in 2001, took Actonel 35mg weekly for 5 years, stopped for more than a year and resumed Actonel intermittently for another 2 years before starting drug holiday. She was taking Calcium 500 mg in the multivitamin and 2500 mg of vitamin D. Serum calcium and vitamin D were within normal range. She started strontium citrate (680mg strontium) daily in 2009 and took it for 5 years, stopping it in 2014.

Yearly assessment of her BMD via DEXA scan showed an increase of 4.3% at LS spine (L1-L4 vertebrae), and 7.6 % at total hip within 1 year of SrC treatment. At 5 years, BMD increase was 6.5 % at LS and 12% for mean total hip. She agreed to stop SrC at this time.

One year after stopping SrC, LS BMD decreased by 9.1 % and total hip BMD decreased by 4.2%.

Case 3

A 59-year-old female with OP was treated with weekly alendronate for 4 years till 2007, when she stopped it due to concerns for osteonecrosis of jaw. She was advised to resume alendronate in 2008 due to declining BMD, but opted not to take it.

She started self-administration of 680mg of SrC daily in February 2009 and continued it for four years till January 2013, when she stopped it due to myalgias and concern about risk for toxicity. Due to her history of ulcerative colitis, she was limited in dairy intake, although she averaged half a cup of almond milk daily and took calcium supplements. Serum calcium and vitamin D were within normal range.

BMD via DEXA scan showed an increase of 10.7 % at LS (L1-L4) at 2 years after starting SrC, and 4.3 % at total hip.

BMD decreased by 14% at LS and by 6.4% at total hip a year after stopping SrC.

Mirza FS, Azim S, Bhargava A (2016) Change in Bone Mineral Density with Strontium Citrate: An Illusion or Reality. J Nutrition Health Food Sci 4(3): 1-3. DOI: http://dx.doi.org/10.15226/jnhfs.2016.00167

https://pdfs.semanticscholar.org/bdce/ac5e3fae890f6dd1902cb45734b96433b165.pdf

TBS iNsight® – a Novel Osteoporotic Fracture Assessment Diagnostic Tool

Medimaps Group announced that a novel method for improving osteoporotic fracture risk assessment, TBS iNsight^®, is now globally available to clinicians through a distribution partnership with General Electric Healthcare (NYSE: GE). GE Healthcare provides transformational medical technologies and services to meet the demand for increased access, enhanced quality and more affordable healthcare around the world and is the market leader in the development and manufacture of Dual Energy X-Ray Absorptiometry (DXA) bone densitometry systems.

On June 10, 2014, Medimaps Group – developers of the TBS iNsight^® diagnostic tool – and General Electric Healthcare signed a distribution agreement to distribute TBS iNsight^® on a global basis leveraging GE Healthcare’s extensive direct sales and distribution organization.

TBS iNsight^® is a unique, easy-to-use software application that assesses bone texture - an index of bone microarchitecture – which in turn is expressed as the Trabecular Bone Score (TBS). The measurement is performed seamlessly using DXA images acquired from a bone mineral densitometry (BMD) scan. No additional patient scan time or radiation exposure is required and results are easily interpreted by physicians to enable them to better manage patients with high risk of fractures. TBS iNsight® has been cleared for marketing by the U.S. Food and Drug Administration.

Prof. Didier Hans, Chairman and Chief Executive Officer of Medimaps Group states; “It is well documented that 40-50% of osteoporotic fracture occurs in patients who are not determined to be osteoporotic by BMD alone, yet BMD remains the only diagnostic method available to most clinicians. A significant body of literature, including a recent study of over 29,000 women, has demonstrated that TBS, when combined with hip and/or spine BMD and FRAX^® clinical factors, can help improve the prediction of future osteoporotic fracture risk in a clinically meaningful way. We’re very pleased to partner with General Electric Healthcare to bring this valuable new predictive tool for better management of osteoporotic patients across the globe.”

For more information on Medimaps and TBS iNsight^®, please visit www.medimapsgroup.com and www.tbsinsight.com

About Medimaps Group

Medimaps group – a Swiss company founded by a group of clinical practitioners and researchers - is a developer of innovative imaging software used in clinical practice for improved patient management with minimum impact on the workflow of the practitioner. The company has raised several rounds of venture capital to further commercialize TBS iNsight^® in the osteoporosis treatment market and for product development of the TBS iNsight^® tool for optimizing implant surgery in the dental and orthopedic markets.

Contacts

Medimaps Group
Oscar Lazaro, +1 781-492-2012
Chief Commercial Officer
olazaro@medimapsgroup.com

http://www.businesswire.com/news/home/20140909005180/en/Medimaps-Group-appoints-General-Electric-Healthcare-Global#.VVC46fCgseM

Trabecular Bone Score

"The trabecular bone score (TBS) is a gray-level textural metric that can be extracted from the two-dimensional lumbar spine dual-energy X-ray absorptiometry (DXA) image. TBS is related to bone microarchitecture and provides skeletal information that is not captured from the standard bone mineral density (BMD) measurement. Based on experimental variograms of the projected DXA image, TBS has the potential to discern differences between DXA scans that show similar BMD measurements. An elevated TBS value correlates with better skeletal microstructure; a low TBS value correlates with weaker skeletal microstructure. Lumbar spine TBS has been evaluated in cross-sectional and longitudinal studies."

"The following conclusions are based upon publications reviewed in this article:
1) TBS gives lower values in postmenopausal women and in men with previous fragility fractures than their nonfractured counterparts;
2) TBS is complementary to data available by lumbar spine DXA measurements;
3) TBS results are lower in women who have sustained a fragility fracture but in whom DXA does not indicate osteoporosis or even osteopenia;
4) TBS predicts fracture risk as well as lumbar spine BMD measurements in postmenopausal women;
5) efficacious therapies for osteoporosis differ in the extent to which they influence the TBS;
6) TBS is associated with fracture risk in individuals with conditions related to reduced bone mass or bone quality."

"Based on these data, lumbar spine TBS holds promise as an emerging technology that could well become a valuable clinical tool in the diagnosis of osteoporosis and in fracture risk assessment."
http://www.ncbi.nlm.nih.gov/pubmed/24443324

Study Demonstrates DXA Scan Is Obviously Flawed

Most clinically important vertebral body compression fractures found on abdominal multidetector computed tomography (CT) scans would go unreported if sagittal reconstructions were not routinely evaluated, according to a new study.

"At this point, it is routine to evaluate sagittal reconstructions at abdominal multidetector CT (MDCT), and whenever vertebral fractures are detected, they are reported." However, this has not always been the case, said Travis Lauder, BS, a fourth-year medical student at the University of Wisconsin School of Medicine and Public Health in Madison.

"The studies we reviewed were done before 2007, when sagittal reconstructions were not automatically provided. We showed that without them, we missed a lot of vertebral compression fractures in patients who underwent abdominal multidetector CT," he explained.

Lauder presented the study results at the American Roentgen Ray Society 2013 Annual Meeting in Washington, DC. First results were published online February 28 in Radiology.

Lauder and his team retrospectively analyzed 2041 consecutive patients (mean age, 70.8 years) who had undergone abdominal multidetector CT and dual-energy x-ray absorptiometry (DXA) within 6 months of each other. The images were taken from 2000 to 2007, before sagittal CT reconstructions were routinely obtained.

The researchers used the Genant visual semiquantitative method to review transverse (axial) and retrospective sagittal multidetector CT reconstructions for the presence of moderate to severe fractures of the lower thoracic and lumbar spine. They also reviewed the electronic medical records of these patients to determine whether the fracture was reported at prospective CT interpretation, was known previously, or was subsequently diagnosed.

"At least 1 moderate or severe vertebral body compression fracture was retrospectively identified on CT in 97 patients," the researchers report. The fractures involved 1 level in 67 patients and 2 or more levels in 30 patients. In total, 141 fractures were identified.

In patients with an unreported fracture, vertebral body compression fracture was not recognized clinically in 64% and there was no evidence of osteoporosis on DXA in 48%.

"DXA is still the gold standard," Lauder noted, "but this analysis demonstrated that a lot of these patients have false negatives on DXA, and that the DXA test is obviously flawed."

Incidental findings are a well-known "double-edged sword" in cross-sectional imaging, said Abraham Dachman, MD, professor of radiology and director of the fellowship programs at the University of Chicago in Illinois, who was asked by Medscape Medical News to comment on the study.

"Many findings — some previously known by the referring physician and some not — can be found on CT. It is often difficult for the radiologist to know what findings to report, what findings to ignore, and what incidental findings are sufficiently important to require personal communication with the referring physician," Dr. Dachman said.

However, this study highlights the potential of abdominal CT to detect vertebral body compression fractures, he noted. Coronal and sagittal reconstructions are often done by the technologist who performs the exam using software on the CT scanner console; they do not require dedicated workstations.

"This study did not address how often the observation of vertebral body compression fractures changed patient management because it was retrospective in nature," Dr. Dachman said. "Still, it highlights the potential of CT to reveal information and provides a rationale to radiologists who wish to routinely report this observation."

This article appeared on Medscape under the title, “Vertebral Fractures Go Undetected without Sagittal Views.”

http://www.medscape.com/viewarticle/782730

The abstract and full text with CT images for “Unreported Vertebral Body Compression Fractures at Abdominal Multidector CT,” which was published in Radiology  in July 2013, can be read here:

http://pubs.rsna.org/doi/full/10.1148/radiol.13121632

For an excellent description of computed tomography (CT) and multidetector computed tomography (MDCT), see:

http://www.amic-chicago.com/Multidetector%20CT.pdf

For a description of an abdominal CT scan, see:

http://www.nlm.nih.gov/medlineplus/ency/article/003789.htm

For information on computed tomography angiography (CTA), see:

http://www.vascularweb.org/vascularhealth/Pages/ct-angiography.aspx