DEXA Measurement of spine density in the lateral projection. I: Methodology

Summary Bone mineral content and bone mineral density (BMC in g and BMD in g/cm²) were measured using dualenergy X-ray absorptiometry (DEXA). DEXA scans in the lateral decubitus position required about 12 minutes for the L2−L4 sequence at 0.75 mA (dose 5 mrem) and 4 minutes at 4.75 mA (7 mrem). The former scans were done with the Lunar DPX densitometer and the latter with the Lunar DPX-L One test of the algorithms used for measurement is the equality of BMC in both AP and lateral projections. BMC in the lateral projection averaged about 1% lower than in the AP projection in phantoms and for L2+L3 in 8 subjects, but the difference was not significant. Additional tests were done on the effects of tissue thickness and position from the tabletop. There was little or no influence of tissue thickness from 18 to 30 cm on BMD results, but there was a small influence of thickness below 18 cm (0.01 g/cm²;P=0.01) and of distance from the tabletop at extremes of positioning (0.02 g/cm²;P=0.06). The precisionin vivo was similar for both 4- and 12-minute scans; the standard deviation of repeat measurements was about 0.02 g/cm², which was about 2% relative to the mean BMD for a region within the vertebral body. The latter region included half the BMC of the body, or 24% of the entire vertebra. Results of 4-minute scans on the DPX and 12-minute scans on the DPX-L in 9 subjucts were highly correlated (r=0.98;P<0.001).     

The effect of overlying calcification on lumbar bone densitometry

Summary We studied bone mineral density (BMD) of the spine using dual photon absorptiometry, as well as standard anterior-posterior and lateral lumbar spine X-ray film in 113 ambulatory elderly male volunteers with a mean age of 72 years (range 66–91 years). Each subject had three measurements taken for lumbar vertebrae 1 through 4: BMD, length of aortic calcification (AC), and degenerative facet sclerosis graded 0–3. A separate statistical model was fit to BMD for each vertebra using analysis of covariance. AC did not contribute significantly to BMD. BMD was increased by 0.28–0.03 g/cm² (L1–L4) with a sclerosis score of 2, and by 0.47–0.25 g/cm² with a sclerosis score of 3,P<0.001. The association between increased BMD and overlying facet sclerosis may be related to the bone density within the sclerosis itself or to an association between degenerative joint disease and a generalized increase in subchondral bone.     

The Interference of Gamma Rays With Bone Mineral Density Measurements in 177Lu-PSMA and DOTATATE Therapy

The main purpose was to describe the interference of gamma radiation emitted by ¹⁷⁷Lu with simultaneous bone mineral density BMD measures for patients undergoing ¹⁷⁷Lu-PSMA and ¹⁷⁷Lu DOTATATE therapy. A cohort of 9 patients underwent ¹⁷⁷Lu-PSMA therapy were randomly selected to speculate the activity in the abdominopelvic region. So that, SPECT/CT scan at 24 h was used with attenuation and scatter correction. The activities were derived from the delineated ROIs over the abdominopelvic zone showing a range of 34?274 MBq. Next, a water path was placed under spine phantom mimicking L1-L4 vertebrae and followed by consecutive DEXA scans made by Hologic 4500 W and GE-Lunar DPX-NT systems. Five scans were performed without/and with different Lu-177 activities 37, 185, 370 and 555 MBq under the same geometric conditions. The obtained BMD readings of L1-L4 by the Hologic device were 1.027, 1.024, 1.021, 1.013, and 1.006 g/cm² with presence of 0, 37, 185, 370, and 555 MBq ¹⁷⁷Lu activity, respectively. Whereas, in Lunar device, it was found as higher as 1.163, 1.121, 1.09, 1.072, and 1.043, respectively. There was no statistically significant difference between both devices (p _value ≥ 0.05). The fluctuation ranges in the L1-L4 BMD readings at the presence of 37?555 MBq were 0.3%?2%, and 3.6%?10.3% for Hologic and Lunar systems, respectively. It was emphasized that gamma radiation emitted by ¹⁷⁷Lu relatively influence DEXA scans and the yielded BMD measures. Postponing DEXA scans as early as 8 d after ¹⁷⁷Lu-PMSA and 11 d after ¹⁷⁷Lu-DOTATATE therapies is recommended to avoid the erroneous contribution of gamma radiation and provide precise bone assessment.     

Dual-energy X-ray absorptiometry of the spine in anteroposterior and lateral projections

Dual-energy X-ray absorptiometry (DXA) of the lumbar spine provides an estimation of the bone mineral content (BMC) corrected by the projected area of the spine and expressed in g/cm². This two-dimensional estimate of the bone mineral density (BMD) is influenced by the skeletal size, assessed by the subject's height. In order to obtain an estimate of the volumetric BMD, we measured BMC with a new DXA device (Sophos L-XRA) equipped with 24 detectors and a rotating arm, thus allowing scanning of the lumbar spine in both an anteroposterior (AP) projection and a lateral (LAT) projection with the patient in a supine position. Comparison between the results obtained on the third (L3) and fourth (L4) lumbar vertebrae with automatic or manual analysis showed that the best precision was obtained with the lateral measurement of L3 alone with an automatic soft tissue baseline determination. Results were expressed in g/cm² and in g/cm³ (by dividing the g/cm² value by the width (AP area divided by the height of the vertebra) of L3), and were compared with those obtained by conventional AP scanning of L2–4 (g/cm²). The in vivo precision error evaluated by triplicate measurements on 10 controls was 17 mg/cm² (1.96%) and 5.2 mg/cm³ (2.31%) for LAT L3 as compared with 13 mg/cm² (1.15%) for AP L2–4. Volumetric BMD (g/cm³) measurement, assessed in vitro on a calibrated hydroxyapatite phantom, and the absolute values obtained in normal women were similar to those obtained by quantitative computed tomography (QCT). In 39 healthy adults (27±4 years) BMD expressed in g/cm² was correlated with height (r=0.36 for AP L2–4 andr=0.39 for LAT L3;p<0.05 for both) but not with LAT L3 BMD expressed in g/cm³ (r=0.02; NS). The age-related bone loss between 30 and 80 years of age, derived from the normal values for 101 healthy women (age range 19–73 years) was 36% for AP L2–4, 52% for LAT L3 (g/cm²) and 60% for LAT L3 (g/cm³). In a group of 22 women with untreated postmenopausal vertebral osteoporosis (one or more non-traumatic vertebral crush fractures) the mean decrease in BMD, expressed as a percentage of the age-adjusted normal value, was more pronounced (p<0.001) for LAT L3 BMD (–21% in g/cm²,Z-score –1.08; –22% in g/cm³,Z-score –0.94) than for AP L2–4 BMD (–9%,Z-score –0.66). We conclude that: 1) BMD measurement restricted to the vertebral body of L3 can be achieved with a low precision error with this new DXA device; 2) it allows an estimate of the volumetric density (g/cm³) which does not seem to be influenced by skeletal size; 3) lateral BMD appears to be more sensitive than conventional AP scanning for assessing age-related bone loss and should be useful in the investigation of trabecular osteoporosis.     

Precision of dual-photon absorptiometry

Summary Precision of dual-photon absorptiometry (DPA) measurements was determined in a lumbar spine phantom and in humans. Approximately half of the measurements were made before and half after a¹⁵³gadolinium source change. The phantom was measured with different amounts of acrylic, which simulates human soft tissue, in order to evaluate the influence of body thickness on bone mineral density (BMD). Results of scans analyzed with two software versions from Lunar Radiation Corp., the widely used 08B and a prototype 08C, are compared. DPA with a cold source significantly overestimated BMD in the phantom in the presence of large amounts (more than 25 cm) of soft tissue equivalent with version 08B but not with the newer version 08C. Similiarly, in nine subjects, there was a significant decrease in spine BMD after a source change when scans were analyzed with version 08B (mean difference 0.026 g/cm²,P=0.002) but not with 08C (0.01 g/cm²,P=0.234). No systematic effect of source change on femoral BMD measurements was observed. The SD of the mean difference of two measurements of the nine subjects was 0.019 g/cm² (1.6% of the mean value) for the spine with software version 08B and 0.024 g/cm² (2.0%) with version 08C, 0.03 g/cm² (3.3%) for the femur neck, 0.03 g/cm² (4.0%) for the greater trochanter, and 0.04 g/cm² (4.9%) for Ward's triangle region of the proximal femur. The spine phanton was scanned on two other commercial bone densitometers in order to assess inter-instrument variation. Phantom measurements of L2-4 BMD made on two Lunar Radiation Corp model DP3 scanners which differed by 2% were 10 and 12% higher than those with a Norland Corp. model 2600 scanner.     

Axial rotation component of thoracic scoliosis

The axial rotation (rotation about a vertical axis) of the vertebrae, of the ribs, and of the back surface are components of the deformity recognized clinically as the "rib hump" in thoracic scoliosis. Relationships of these rotations to the lateral deviation and lateral curvature of the spine were studied in 40 patients with idiopathic scoliosis. Stereoradiographs of the spine and rib cage were used to measure three components of axial rotation: rotation of the vertebrae, of the rib cage, and of the plane of maximum curvature of the spine. Stereotopographs of the back surface were digitized to measure the axial rotation of the back surface. In individual patients, there were high correlations of all components of axial rotation at each spinal level with the corresponding vertebral lateral deviation from the spinal axis. By regression analyses of the maximum values of each rotation in each curve, the rotation of the apex vertebra was found to be generally of lesser magnitude than the rotation of the plane of maximum curvature of the spine and in an opposite sense in kyphotic curves. The rib cage rotation was generally of lesser magnitude than the vertebra rotation, and the back surface rotation was less than both of these skeletal rotations. Vertebra rotation correlated most closely with lateral deviation of the spine. Simple segmental coupling of axial rotation and lateral bending could not be responsible for this axial rotation.     

腰椎各椎体骨密度的分析

目的分析腰椎各椎体骨密度（ＢＭＤ）的差异。方法对１２１４例在我科进行骨密度检查的２０～８９岁人群,男性３９０例,女性８２４例,除外各种器质性内分泌、消化系统及肿瘤等疾病,用双能Ｘ线骨密度仪（ＤＥＸＡ）测量腰椎ＢＭＤ,通过计算机分析比较各椎体ＢＭＤ值的差异与相互关系,用ＥＸＣＥＬ软件做统计学分析,计数资料进行配对ｔ检验。结果ＢＭＤ值以Ｌ１最低,Ｌ４最高,Ｌ１－２与Ｌ２－４ＢＭＤ女性在４０岁以上有显著差异（Ｐ＜０．００１）,男性在６０岁以上（Ｐ＜０．０５）,８０岁以后无明显差异,女性５０岁以后骨丢失明显快于男性。结论腰椎各椎体ＢＭＤ存在差异,尤以女性明显,其差异与增龄造成的腰椎退行性变的干扰有关     

Effect of increased axial rotation angle on bone mineral density measurements of the lumbar spine

Background contextOsteoporosis frequently occurs in elderly people and is commonly associated with neuromuscular diseases or severe cerebral palsy. Osteoporosis can cause pain via compression fractures or secondary neurologic deficits; thus, accurate evaluation of bone mineral density (BMD) is essential for the prevention and treatment of osteoporosis. However, spinal axial rotation caused by scoliosis may affect the outcome of BMD tests, such that BMD measurements may be significantly greater than actual BMD in patients with severe scoliosis of the spine.PurposeWe investigated the effect of axial rotation angle on BMD measurements of the phantom spine.Study design/settingInvestigation for the effect of axial rotation with aluminum phantom spine.MethodsA GE-Lunar Aluminum Spine Phantom was used to assess BMD. Bone mineral content (BMC), BMD, and cross-sectional area were measured 100 times at L1–L4 using a GE Lunar Prodigy Vision system. Dual-energy X-ray absorptiometry was performed at axial rotation angles of 0° to 25° (5° intervals).ResultsCross-sectional area decreased and BMD values increased as the axial rotation angle increased, whereas BMC did not change significantly. A fitting function was obtained to evaluate the relationships among axial rotation angle, cross-sectional area, and BMD. We obtained an equation to estimate BMD at L1–L4: 1.000?0.001674x+0.0001043x²?0.000005333x³, where x denotes the axial rotation angle. We found that the observed BMD needed adjustment when the angle was more than 5°.ConclusionsBone mineral density values may be overestimated in patients with even slight (>5°) axial rotation. When osteoporosis is suspected in a clinical setting, the degree of axial rotation should be measured on a lumbar spine X-ray.     

Correction of the effects of source,source strength,and soft-tissue thickness on spine dual-photon absorptiometry measurements

Summary Dual photon absorptiometry measurements of the spine are subject to drift associated with source, source strength, and truncal thickness. This study was conducted to determine the extent to which this drift in bone mineral density (BMD) measurements can be improved by analysis of scans with a new software version, 08C, and by applying external standard or phantom corrections to scans analyzed with the older version, 08B. A phantom, consisting of human lumbar vertebrae embedded in acrylic, and five clear acrylic plates to simulate a soft-tissue thickness range of 15.2–27.9 cm, was measured on a Lunar Radiation Corp DP3 scanner over the life of a 153-gadolinium (Gd) source and scans analyzed with software versions 08B and 08C. Phantom BMD was lower with 08C at both high [0.012±0.002 (SEM) g/cm²,P<0.001] and low (0.027±0.003 g/cm²,P<0.001) count rates than with 08B. Phantom BMD of scans analyzed with 08B increased with increasing source age and the source strength-related increment increased significantly as acrylic thickness increased (P=0.014). When the same scans were analyzed with 08C, the thickness-related effect was corrected whereas a small (0.011 g/cm²/year) source-strength effect persisted. The effects of source strength and truncal thickness on BMD were also evaluated in 40 humans scanned at two detector collimations to vary count rate. With 08B, mean BMD was 1% greater when measured with 8 than with 13 mm collimation (mean difference 0.011±0.003 g/cm²,P=0.001), whereas the version 08C, mean BMD was the same at the two collimations. Similarly, when phantom corrections were applied to the scans analyzed with 08B, the source strength effect was no longer significant. A truncal thickness effect, apparent in the 40 human scans analyzed with 08B, was not present with 08C. Finally, the phantom was scanned with three different Gd sources. With both 08B and 08C, BMD values were similar with two and significantly lower (by 0.012±0.002 g/cm²,P=0.011) with the third Gd source. Thus, with the new analysis software 08C, multiple thickness calibration is no longer needed, however, calibration with an external standard is still necessary.     

Navel Jewelry Artifacts and Intravertebral Variation in Spine Bone Densitometry in Adolescents and Young Women

Non-removable navel jewelry can increase the measured bone density of the underlying vertebra. We measured lumbar spine bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) in an observational study of 727 adolescents and young women aged 14–30 yr. We evaluated several methods of correcting BMD: manually erasing a small area, eliminating 1 or 2 vertebrae, estimating the BMD from 1 or 2 vertebrae using data from remaining vertebrae, and estimating the BMD using T-scores of the remaining vertebrae. Ten percent (n = 71) of the subjects were wearing navel jewelry. The areal BMD by DXA of L1 and L2 was similar in those with jewels as in controls without jewels, but L3–L4 showed higher bone density in those with jewelry, and the spine BMD of L1–L4 was significantly higher in the bejeweled women (1.043 ± 0.011 vs 1.006 ± 0.004 g/cm², p = 0.01). The estimated errors in accuracy (g/cm²) were 0.034 due to the jewels; 0.005 from erasing a small area; 0.019 from eliminating L4; 0.044 from eliminating both L3 and L4; 0.016 from predicting BMD using L1–L3; and 0.028 using L1–L2. The T-scores using the Hologic database were progressively lower in the caudal vertebrae, even in 96 local women aged 30–35 yr, whose average T-score was 0.35 at L1 but ?0.26 at L4. Thus, we found significant errors due to intravertebral variability. We suggest the optimal method of correcting for small artifacts is to erase the area under the artifact.     

Bone quality in the lumbar spine in high-performance athletes

Little is known about the influence of high-performance training on the bone quality of the lumbar spine, in particular, the effects on bone mineral density (BMD) in athletes with high weight-bearing demands on the spine. Measurements were therefore performed in internationally top-ranked high-performance athletes of different disciplines (weight lifters, boxers, and endurance-cyclists). The measurements were carried out by dual-energy X-ray absorptiometry, and the results compared with the measurements of 21 age-matched male controls. The BMD of the high-performance weight lifters was greater than that of the controls by 24% (0.252 g/cm²) on the AP view and by 23% (0.200 g/cm²) on the lateral view (P<0.01), while difference in BMD between the boxers and the controls was+17% (0.174 g/cm²) on the AP view and +19% (0.174 g/cm²) on the lateral view. The BMD of the lumbar spine in all endurance cyclists was lower than that in the controls (AP view-10%, 0.105 g/cm²; lateral view-8%, 0.067 g/cm²; P>0.05). The results show that training program stressing axial loads of the skeleton may lead to a significant increase of BMD in the lumbar spine of young individuals. Other authors' findings that the BMD of endurance athletes may decrease are confirmed. Nevertheless the 10% BMD loss of cyclists was surprisingly high.     

In vitro comparability of dual energy X-ray absorptiometry (DEXA) bone densitometers

Summary Six Hologic QDR-1000 DEXA bone densitometers at different centers across the USA were compared to determine the intermachine variability. Nine scans in succession were acquired on each machine using a single anthropomorphic lumbar spine phantom (manufactured by Hologic). Values for BMC, area, and BMD were recorded for each measurement. Means, standard deviations (SD), and coefficients of variation (CV) were calculated for each machine. All the CVs (BMC, area, BMD) were less than 1% (range 0.3%–0.6%). The CV of the means at the six sites were 0.4%, 0.6%, and 0.5% for BMC, area, and BMD, respectively. Although several significant differences for BMC, area, and BMD were noted by ANOVA between machines at different sites, the difference between the highest and lowest means of the individual machines was only 1.1%, 1.31%, and 1.07% for BMC, area, and BMD. The small variations between the DEXA systems are encouraging for researchers involved in multicenter trials in which data are pooled.     

A comparison of two dual-energy X-ray absorptiometry systems for spinal bone mineral measurement

Summary Two dual-energy X-ray absorptiometry (DEXA) systems—the Hologic QDR-1000 and the Norland XR-26 bone densitometers—were evaluated in terms of precision, accuracy, linearity of response, X-ray exposure, and correlation of in vivo spinal measurements. In vitro precision and accuracy studies were performed using the Hologic anthropomorphic spine phantom; linearity of response was determined with increasing thicknesses of aluminum slabs and concentrations of Tums E-X in a constant-level water bath. Both systems were comparable in precision, achieving coefficients of variation (CVs) of less than 1% in bone mineral content (BMC, g), bone area (cm²), and bone mineral density (BMD, g/cm²). Both were accurate in their determination of BMC, bone area, and BMD with reference to the Hologic spine phantom. Both systems also showed good BMC and BMD linearity of response. Measured X-ray skin surface exposures for the Hologic and the Norland systems were 3.11 and 3.02 mR, respectively. In vivo spinal measurements (n=65) on the systems were highly correlated (BMC: r=0.993, SEE=1.770 g; area: r=0.984, SEE=1.713 cm²; BMD: r=0.990, SEE=0.028 g/cm²). In conclusion, both systems are comparable in terms of precision, accuracy, linearity of response, and exposure efficiency.     

Changes in vertebral rotation after Harrington and Luque instrumentation for idiopathic scoliosis.

This study was carried out to analyze the three-dimensional and in particular the rotational correction obtained after spine instrumentation for idiopathic scoliosis. Preoperative and postoperative radiographs and computed tomographic scans with single axial cuts through each vertebral level were obtained for 14 patients: 4 Harrington, 7 Luque, and 3 Harrington-Luque. Rotation of vertebrae relative to the spinal axis and rotation between vertebrae (segmental rotation) were measured from computed tomographic scans of instrumented and uninstrumented segments. The derotation and changes occurring after surgery were calculated. Before operation, rotation was maximal at the apex, and close to 0 at the end vertebra; segmental rotation was greatest at the end of the curve, and minimal at the apex. After Harrington instrumentation the apical vertebrae showed a median derotation of 16%, after Luque instrumentation it was 12% and after Harrington-Luque instrumentation it was 13%. Segmental derotation did not uniformly occur. Major derotation was obtained at the end vertebrae and 39% of the total derotation occurred outside of the instrumented levels of the spine.     

“Black Hole Artifacts”—A New Potential Pitfall for DXA Accuracy?

Certain types of metallic objects apparently have high attenuation (a white image) on dual-energy X-ray absorptiometry (DXA) scan images, but instead show up as black (black hole artifacts). When small, these artifacts may easily be missed on visual inspection. We hypothesized that such “black hole” artifacts could have a significant effect on bone mineral density (BMD) results. Human use approval (Institutional Review Board [IRB]) was obtained to publish patient scans and an IRB waiver was obtained for nonhuman research. We placed individual surgical clips and cassettes of clips of tantalum, stainless steel and titanium, and a bullet over the third lumbar vertebra (L3) of a Hologic spine phantom. In addition, 4 or 8 individual tantalum or stainless steel clips and tantalum squares were placed over L3 of cadaveric spines (high-density spine L1–L4 BMD = 1.049 g/cm²) and low-density spine BMD (L1–L4 BMD = 0.669 g/cm²) with attached soft tissues. Stainless steel and titanium clips scanned as white objects with DXA. A bullet and tantalum clips scanned black (black holes). All clip types were visible on single-energy scans as white objects. Eight tantalum clips significantly lowered L3 BMD compared to 4 or 0 clips in the high-density spine. There were no significant differences in BMD L1–L4 between 0, 4, and 8 tantalum clips in the high-density spine. In the low-density spine, 8 tantalum clips over L3 had significantly lower BMD compared to 4 tantalum clips overlying L3 and 4 clips lateral to L3 and 4 clips over L3. All of these scenarios had lower L3 BMD than no tantalum clips overlying L3. The BMD of L1–L4 was lowest with 8 clips at L3, but was not significantly different than no clips overlying L3. Eight tantalum clips lateral to L3 was significantly higher than no clips over L3. Black hole artifacts can occur in DXA scans containing certain metals like tantalum surgical clips. Although these surgical clips could decrease BMD at a localized area, they do not significantly decrease the L1–L4 spine BMD in a high-density spine specimen. In a low-density spine specimen, tantalum clips do have the potential to alter BMD of a single vertebral body and L1–L4. Attention should be paid to the possibility of black hole artifacts on DXA scans and the effect they may have on spine results. Viewing scans in the single-energy mode can be used to verify the presence of tantalum clips.     

The accuracy of volumetric bone density measurements in dual X-ray absorptiometry

New developments in dual x-ray absorptiometry (DXA) allow the performance of high precision anteroposterior (AP) and lateral scans of spinal bone mineral density (BMD, units: g/cm²) without the patient moving from the supine position. Data from both projections may be combined to give an estimate of the true volumetric bone mineral density (VBMD, units: g/cm³) of the lumbar vertebral bodies. This report presents a cadaver study designed to validate DXA measurements of volumetric bone density. Sections of whole lumbar spine were scanned in AP and lateral projections in a water tank to simulate soft tissue. Individual vertebrae were then divided to separate the vertebral body from the neural arch, and vertebral body volume was measured using the displacement of sand. The bone mineral content (BMC) of vertebral bodies and neural arches was measured by ashing at 250°C for 60 hours followed by 500°C for a further 24 hours. The results showed that DXA scanning systematically underestimated ashing data by 14% for AP BMC, 33% for vertebral body BMC, 23% for vertebral body volume, and 12% for VBMD. Despite these significant systematic errors, the DXA measurements and ashing values were highly correlated (r=0.979-0.992). The results suggested that after allowing for the systematic errors, lateral DXA parameters related closely to true BMC, volume, and VBMD.     

Performance evaluation of a dual-energy X-ray bone densitometer

Summary We tested a dual-energy bone densitometer (LUNAR DPX) that uses a stable x-ray generator and a K-edge filter to achieve the two energy levels. A conventional scintillation detector in pulse-counting mode was used together with a gain stabilizer. The densitometer normally performs spine and femur scans in about 6 minutes and 3 minutes, respectively, with adequate spatial resolution (1.2×1.2mm). Total body scans take either 10 minutes or 20 minutes. The long-term (6 months, n=195) precision of repeat measurement on an 18-cm thick spine phantom was 0.6% at the medium speed. Precision errorin vivo was about 0.6, 0.9 and 1.5% for spine scans (L2-L4) at slow, medium and fast speeds, while the error was 1.2 and 1.5 to 2.0%, respectively, for femur scans at slow and medium speed. The precision of total body bone density was 0.5%in vitro andin vivo. The response to increasing amounts of calcium hydroxyapatite was linear (r=0.99). The densitometer accurately indicated (within 1%) the actual amount of hydroxyapatite after correction for physiological amounts of marrow fat. The measured area corresponded exactly (within 0.5%) to that of known annuli and to the radiographic area of spine phantoms. There was no significant effect of tissue thickness on mass, area, or areal density (BMD) between 10 and 24cm of water. The BMD values for both spine and femurin vivo correlated highly (r=0.98, SEE=.03 g/cm²) with those obtained using conventional¹⁵³Gd DPA. Similarly, total body BMD correlated highly (r=0.96, SEE=.02g/cm²) with DPA results.     

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.     

Segmental vertebral rotation in early scoliosis

Summary In order to investigate the development of the vertebral axial rotation in patients with early scoliosis, the vertebral rotation angle (VRA) was quantified on the basis of 132 anteroposterior radiographs obtained from patients with diagnosed or suspected scoliosis. The rotation was measured in the apical vertebra and in the two suprajacent and two subjacent vertebrae. The radiographic material was divided into a control reference group and three scoliotic groups with varying Cobb angle from 4° up to 30°. In the reference group a slight vertebral rotation was significantly more often seen to the right. In the scoliotic groups, the rotation was most pronounced in the apical segments. The mean VRA toward the convex side was significantly increased in the vertebrae just suprajacent to the apex in curves with a Cobb angle of 8°–15° and in the cranial four vetebrae in curves with a Cobb angle of 16°–30°. Atypical vertebral rotation to the opposite side of the major curve was observed in 12.8% of the cases. There was a significant positive correlation between the VRA and the Cobb angle. These results show that a slight VRA to the right is a common feature in the normal spine, and that the VRA increases with progressive lateral deviation of the spine. It is concluded that the coronal plane deformity in early idiopathic scoliosis is accompanied and probably coupled to vertebral rotation in the horizontal plane.     

Establishment of BMD reference curves at different skeletal sites in women, using a Cartesian coordinate numeration system

The BMD reference curve is the reference value used for diagnosing osteoporosis and assessing bone mass changes. Its accuracy would affect the correctness of T -score and Z -score values and thus the reliability of diagnostic results. In this paper, we report the use of a new method, a Cartesian coordinate numeration system, to establish BMD reference curves at different skeletal sites in women. In a reference population of 3,919 women ranging in age from 5–85 years, we used the dual X-ray absorptiometry (DXA) bone densitometer to measure BMD at the posteroanterior spine (PA; vertebrae L1–L4), followed by a paired PA/lateral spine scan of the vertebral bodies of L2–L4, expressed in g/cm² and g/cm³, and of the hip and forearm. We chose the cubic regression model to best fit BMD curves that varied with age at different skeletal sites. We then referred the BMD of the fitting curves established by the method of the coordinate numeration system as reference curves, compared them to BMD reference curves derived from the fitting curve equation or age cross-section, and calculated the deflection degrees of the BMD reference curves acquired from the fitting curve equation. At the PA spine, lateral spine (expressed in g/cm³), femoral neck, Wards triangle and radius + ulna ultradistal, the reference curves calculated from the equation were significantly lower than those confirmed by the method of the coordinate numeration system; whereas, at the lateral spine (expressed in g/cm²), total hip, and radius + ulna 1/3 sites, the reference curves derived from the equation were markedly higher than those acquired from the coordinate numeration system. The differences in the two kinds of reference curves calculated by these two different methods gradually increased along with the increment in ages of the women. At the peak value of the reference curves, the BMD calculated from the equation deflected from 2.02% to –10.0% from the BMD acquired from the coordinate numeration system at different skeletal sites, and from 21.5% to –121.8% until the age of 85 years. The highest positive deflection of 65.2% existed at the lateral spine (expressed in g/cm²) and the lowest positive deflection of 21.5% at the total hip. The maximum negative deflection of –121.8% was at the radius + ulna ultradistal, and the minimum negative deflection of –32.6% at the PA spine. The BMD curve acquired from age cross-section was highly positive compared with the one derived from the coordinate numeration system ( r =0.955–0.985 p =0.000) with no significant difference between them. Various analysts used such a method to obtain the coefficient of variance (CV) in BMD precision on each curve that was from 0.05–0.19%. Our study shows that the Cartesian coordinate numeration system is an accurate, precise and reliable method and can serve to reveal the serious drawbacks of using the fitting curve equation to calculate BMD. The BMD reference curves established by this coordinate numeration system maintained the authenticity of the fitting curve, whereas, using the fitting curve equation to obtain BMD reference curves at different skeletal sites led to distortion, and resulted in false increases or decreases in T -score and Z -score values.