Effect of calcium tablets on interpretation of lumbar spine DXA scans

Clinical Use of Trabecular Bone Score: The 2023 ISCD Official Positions

Osteoporosis can currently be diagnosed by applying the WHO classification to bone mineral density (BMD) assessed by dual-energy x-ray absorptiometry (DXA). However, skeletal factors other than BMD contribute to bone strength and fracture risk. Lumbar spine TBS, a grey-level texture measure which is derived from DXA images has been extensively studied, enhances fracture prediction independent of BMD and can be used to adjust fracture probability from FRAX® to improve risk stratification. The purpose of this International Society for Clinical Densitometry task force was to review the existing evidence and develop recommendations to assist clinicians regarding when and how to perform, report and utilize TBS. Our review concluded that TBS is most likely to alter clinical management in patients aged ≥ 40 years who are close to the pharmacologic intervention threshold by FRAX. The TBS value from L1-L4 vertebral levels, without vertebral exclusions, should be used to calculate adjusted FRAX probabilities. L1-L4 vertebral levels can be used in the presence of degenerative changes and lumbar compression fractures. It is recommended not to report TBS if extreme structural or pathological artifacts are present. Monitoring and reporting TBS change is unlikely to be helpful with the current version of the TBS algorithm. The next version of TBS software will include an adjustment based upon directly measured tissue thickness. This is expected to improve performance and address some of the technical factors that affect the current algorithm which may require modifications to these Official Positions as experience is acquired with this new algorithm.

A Newly Recognized DXA Confounder: The Potassium-Binding Medication Sodium Zirconium Cyclosilicate

OBJECTIVE

Radio-dense artifacts, including contrast material, alter dual-energy X-ray absorptiometry (DXA) results. An apparent diffuse artifact was identified during spine DXA acquisition in a patient without recent radiographic procedures. The patient reported taking sodium zirconium cyclosilicate (SZC; Lokelma®) 10 g 1 h before scanning. SZC is a potassium-binding agent recently marketed to treat hyperkalemia. Given the chemical composition, we hypothesized that SZC may alter DXA results. This study evaluated if SZC affects DXA results using an encapsulated spine and a total body phantom.

METHODOLOGY

An encapsulated spine and total body phantom were scanned using a Lunar iDXA. Each phantom was scanned 5 times serially without repositioning in 5 configurations: (1) Bare, (2) 45 mL tap water, (3) 90 mL water, (4) 10 g SZC in 45 mL of water, and (5) 30 g SZC in 90 mL of water. Water and SZC was contained in plastic quart bags, folded, and placed over L2-3 on the spine phantom and flat over the pelvis/torso of the total body phantom.

RESULTS

Tap water did not change spine phantom measurements, but did increase (p < 0.05) total body phantom lean mass 46 g and 89 g with 45 mL and 90 mL, respectively. SZC 10 g or 30 g increased (p < 0.001) L2 and L3 bone mineral density (BMD) 18%-110%, mean 0.295 and 0.924 g/cm², respectively, while L1 and L4 BMD was statistically, but not clinically, altered by <0.010 g/cm². A dose-dependent change (p < 0.001) in total body phantom trunk measurements was demonstrated. The 10 g dose increased lean mass 16.8% and BMC 1%; fat mass was reduced 16.6%, while 30 g increased lean 41.9%, BMC 3.2%, and decreased fat 42.9%.

CONCLUSION

SZC confounds BMD and body composition phantom measurements. It is likely that SZC alters DXA results in humans. DXA technologists and interpreters should be aware of this confounder.

DXA in Children and Adolescents

DXA plays a critical role in assessing skeletal health and disease, as well as, fat and muscle status in children and adolescents. Quality DXA requires training, expertise and attention to details, as in adults, but there are key differences in performing and interpretations in children. These include choice of measurement site, skills required, reference data and software, and considerations for indications and underlying disorders to facilitate correct interpretation. The International Society for Clinical Densitometry (ISCD) has been pivotal in establishing official positions and training for people who are interested in performing or interpreting such examinations, and guiding clinicians who may request such studies. However training in the performance and interpretation of scans of individuals with more complex needs falls outside the scope of this review, and consideration should be given to refer such examinations to a specialist pediatric DXA unit. Others may be scanned and reported by those with expertise in densitometry, as long as due diligence is paid to standard quality procedures, as well as knowledge of the special circumstances and training required for this field. In this invited review we outline some of these considerations, highlight key messages, and provide some appropriate references to help guide clinicians, technologists and scientists involved or interested in DXA use in children and adolescents.

"Effect of very dense artifacts on Hologic and general electric bone densitometry results"

Very dense artifacts confound bone density measurement. Hologic and GE densitometers exclude artifact density and GE also excludes associated area. Consequently, BMD is decreased with Hologic software. Despite different manufacturers' approaches, when dense artifacts overlay the spine, the affected vertebral body should be excluded from the reported BMD.

PURPOSE

Very dense objects, such as lead bullets are described as "black hole" artifacts on Hologic densitometers. Whether similar results occur on GE scanners is not reported. We hypothesized that dense artifacts confound both brands of densitometers.

METHODS

Three lead bullets of varying size were placed overlying or adjacent to L3 on anthropomorphic and encapsulated aluminum spine phantoms. Three scans were acquired with and without projectiles on a Hologic Discovery W, GE iDXA, and Prodigy densitometer.

RESULTS

Lead bullets are measured as having high bone mineral content (BMC); they appear black in dual-energy mode on Hologic scanners and are colored blue on GE scanners. On Hologic scanners, BMC of a dense artifact over bone is excluded, but the bone area is not altered. Consequently, bone mineral density (BMD) of the affected vertebra, and of L1-4, is decreased. For example, a .45 caliber bullet over L3 decreased BMD (p < 0.05) by 48.3% and L1-4 by 9.1%. GE scanners excluded associated BMC and area covered by the artifact, thereby minimizing impact on BMD. Dense artifacts over soft tissue on a phantom do not substantially affect BMD on either manufacturer's densitometer when scanned.

CONCLUSION

Densitometer manufacturers handle very dense artifacts differently. GE software removes artifact BMC and area with resultant minimal impact on BMD, Hologic removes only BMC, not area, thereby decreasing BMD. Regardless of this difference, when dense artifacts overlay the spine, it is best to exclude the affected vertebral body. Finally, the BMD stability observed with artifacts over soft tissue may not be replicated in humans.

ARTIFACTS AFFECTING DUAL-ENERGY X-RAY ABSORPTIOMETRY MEASUREMENTS

OBJECTIVE

To present 3 cases in which the presence of artifacts altered the dual-energy X-ray absorptiometry (DXA) measurements of bone mineral density (BMD) in the lumbar field.

METHODS

Clinical presentation and literature review.

RESULTS

The first patient was a 49-year-old premenopausal woman with a spinal cord stimulator implanted in her lumbar spine. The implant increased the measured BMD in the lumbar region from osteopenia to normal range. The second patient was a 56-year-old man who had a DXA scan after he was administered oral and intravenous iodine-based contrast earlier the same day. The oral contrast in the patient's colon created a dense artifact, which overlapped the lumbar spine and adjacent soft tissue. The effect almost changed his DXA diagnosis from osteoporosis to osteopenia. The third patient was a 64-year-old woman who had undergone laparoscopic adjustable gastric banding (LAGB). A part of the LAGB system adjacent to lumbar vertebra 3 was mistakenly included as part of the vertebrae by the DXA scanner, causing an increase in the measured BMD.

CONCLUSION

There are numerous artifacts that can alter DXA BMD measurement. It is important for providers who interpret DXA scans to be familiar with the potential effects of artifacts and how to adjust for their presence, since erroneous measurements can lead to incorrect decisions regarding treatment and follow-up.

Sodium loading, treadmill walking, and the acute redistribution of bone mineral content on dual energy X-ray absorptiometry scans

The purpose of this study was to assess relationships between plasma sodium concentration ([Na⁺]) and bone mineral content (BMC) after an acute sodium load plus treadmill walking and then quantify the amount of sodium the dual energy X-ray absorptiometry (DXA) scan could detect. The primary study was a single-blind randomized control crossover trial under two conditions: ingestion of six flour tablets (placebo trial) or six 1-g NaCl tablets (salt intervention trial). The tablets were ingested after baseline blood and urine collection followed immediately by the DXA scan. After 60 min of rest, a 45-min treadmill walk was conducted. Immediately postexercise, blood and urine were collected and the DXA scan was repeated. Main outcomes included changes (∆: post minus pre) in plasma [Na⁺] and BMC. Additionally, six 1-g NaCl tablets were superimposed over a DXA spine phantom for separate quantification of sodium as BMC. Fourteen subjects completed the primary study. Two-way repeated measures ANOVA tests revealed significant interaction ( F = 13.06; P = 0.0007), condition ( F = 21.88; P < 0.001), and time ( F = 6.51; P = 0.014) effects in plasma [Na⁺]. A significant condition ( F = 6.46; P = 0.014) effect was also noted in urine [Na⁺]. Total body BMC∆ was negatively correlated with plasma [Na⁺]∆ ( r = -0.43; P = 0.02) and urine [Na⁺]∆ ( r = -0.47; P = 0.01). Total body BMC∆ in the salt intervention trial [-5.5 (27) g] closely approximated the amount of NaCl ingested and subsequently absorbed into the bloodstream. The DXA scan quantified 67% of NaCl tablets as BMC in spine phantom analyses. Total body BMC∆ was negatively related to plasma and urine [Na⁺]∆ after treadmill walking. Reductions in total body BMC closely approximated the amount of NaCl ingested (~6 g). The DXA scan quantified NaCl as BMC.

Quality in dual-energy X-ray absorptiometry scans

Dual-energy X-ray absorptiometry (DXA) is the gold standard for measuring bone mineral density (BMD), making the diagnosis of osteoporosis, and for monitoring changes in BMD over time. DXA data are also used in the determination of fracture risk. Procedural steps in DXA scanning can be broken down into scan acquisition, analysis, interpretation, and reporting. Careful attention to quality control pertaining to these procedural steps should theoretically be beneficial in patient management. Inattention to procedural steps and errors that may occur at each step has the possibility of providing information that would inform inappropriate clinical decisions, generating unnecessary healthcare expenses and ultimately causing avoidable harm to patients. This article reviews errors in DXA scanning that affect trueness and precision related to the machine, the patient, and the technologist and reviews articles which document problems with DXA quality in clinical and research settings. An understanding of DXA errors is critical for DXA quality; programs such as certification of DXA technologists and interpreters help in assuring quality bone densitometry. As DXA errors are common, pay for performance requiring DXA technologists and interpreters to be certified and follow quality indicators is indicated.

Common Mistakes in the Dual-Energy X-ray Absorptiometry (DXA) in Turkey. A Retrospective Descriptive Multicenter Study

BACKGROUND

Osteoporosis is a widespread metabolic bone disease representing a global public health problem currently affecting more than two hundred million people worldwide. The World Health Organization states that dual-energy X-ray absorptiometry (DXA) is the best densitometric technique for assessing bone mineral density (BMD). DXA provides an accurate diagnosis of osteoporosis, a good estimation of fracture risk, and is a useful tool for monitoring patients undergoing treatment. Common mistakes in BMD testing can be divided into four principal categories: 1) indication errors, 2) lack of quality control and calibration, 3) analysis and interpretation errors, and 4) inappropriate acquisition techniques. The aim of this retrospective multicenter descriptive study is to identify the common errors in the application of the DXA technique in Turkey.

METHODS

All DXA scans performed during the observation period were included in the study if the measurements of both, the lumbar spine and proximal femur were recorded. Forearm measurement, total body measurements, and measurements performed on children were excluded. Each examination was surveyed by 30 consultants from 20 different centers each informed and trained in the principles of and the standards for DXA scanning before the study.

RESULTS

A total of 3,212 DXA scan results from 20 different centers in 15 different Turkish cities were collected. The percentage of the discovered erroneous measurements varied from 10.5% to 65.5% in the lumbar spine and from 21.3% to 74.2% in the proximal femur. The overall error rate was found to be 31.8% (n = 1021) for the lumbar spine and 49.0% (n = 1576) for the proximal femur.

CONCLUSION

In Turkey, DXA measurements of BMD have been in use for over 20 years, and examination processes continue to improve. There is no educational standard for operator training, and a lack of knowledge can lead to significant errors in the acquisition, analysis, and interpretation.

Vitamin D and bone disease

Vitamin D is important for normal development and maintenance of the skeleton. Hypovitaminosis D adversely affects calcium metabolism, osteoblastic activity, matrix ossification, bone remodeling and bone density. It is well known that Vit. D deficiency in the developing skeleton is related to rickets, while in adults is related to osteomalacia. The causes of rickets include conditions that lead to hypocalcemia and/or hypophosphatemia, either isolated or secondary to vitamin D deficiency. In osteomalacia, Vit. D deficiency leads to impairment of the mineralisation phase of bone remodeling and thus an increasing amount of the skeleton being replaced by unmineralized osteoid. The relationship between Vit. D and bone mineral density and osteoporosis are still controversial while new evidence suggests that Vit. D may play a role in other bone conditions such as osteoarthritis and stress fractures. In order to maintain a “good bone health” guidelines concerning the recommended dietary intakes should be followed and screening for Vit. D deficiency in individuals at risk for deficiency is required, followed by the appropriate action.

The effect of common artifacts lateral to the spine on bone mineral density in the lumbar spine

Artifacts such as surgical clips, gallstones, and kidney stones are often present in the soft tissue stripe lateral to vertebral bodies. Using cadaveric specimens, we placed bra wires, gallbladder clips, a large gallstone, a calcium carbonate or a calcium citrate pill lateral to L1, or a large or small calcium-containing kidney stone lateral to L3 and compared the mean bone mineral density (BMD) of individual vertebral bodies and L1-L4 with and without the soft tissue artifact. The specimens used had high BMD (L1-L4 BMD=1.049 g/cm2) and low BMD (L1-L4 BMD=0.669 g/cm2) and were scanned with a Hologic Discovery W scanner with 12.7 software in the array mode. None of the artifacts affected L1 or L3 BMD or L1-L4 BMD significantly in the high BMD spine. However, bra wires, a large calcium citrate pill lateral to L1, 3 calcium citrate pills lateral to L1, a calcium carbonate pill over L1, and 3 calcium carbonate pills lateral to L1 did affect L1-L4 BMD in low BMD torso. Gallbladder clips or gallstone did not affect L1-L4 BMD in either specimen. We conclude that artifacts lateral to the spine, particularly in a low BMD spine, can affect the interpretation of L1-L4 BMD using a Hologic Discovery W scanner with 12.7 software in array mode.