The effect of extending femur scan length on BMD results on the Hologic Discovery-W scanner.

A longer dual-energy X-ray absorptiometry scan field of the hip may be useful for the detection of atypical subtrochanteric femur fractures. It has been demonstrated in a Prodigy GE/Lunar scanner that extending the scan length does not affect bone mineral density (BMD) results at the total hip or femoral neck. We hypothesized that extending the scan field on a Hologic Discovery scanner would also have no effect on BMD results at the hip. Thirty subjects who presented for standard of care dual-energy X-ray absorptiometry scans underwent paired default (15.2 cm) and extended (24.1 cm) length hip scans. There was no significant difference in the total hip or any of the component subregions of femoral neck, greater trochanter, or intertrochanteric (shaft) BMD between the default and extended length scans.

Association of the presence of bone bars on radiographs and low bone mineral density.

OBJECTIVE: Bone bars (BB) are struts of normal trabecular bone that cross the medullary portions of the metaphysis and diaphysis at right angles to the long axis of the shaft. The purpose of this investigation was to determine whether the presence of bone bars (BB) identified on radiographs of the proximal femurs and tibia, predict lower bone mineral density (BMD) as evaluated with dual-energy x-ray absorptiometry (DXA) in the lumbar spine, total hip, or femoral neck. MATERIALS AND METHODS: A total of 134 sequential DXA patients underwent radiography of the pelvis, hips, and both knees. The radiographs were evaluated for the presence of BB by two musculoskeletal radiologists who were blinded to DXA results. A t test was used to evaluate the relationship of BB to BMD and a Chi-square test was used to determine if BB were equally distributed among the categories of normal BMD, low bone mass (osteopenia), and osteoporosis. RESULTS: BB were associated with lower BMD at all measured sites. BB at the intertrochanteric and proximal tibial sites were the most predictive of low BMD while supraacetabular and distal femur BB were less predictive. Osteoporosis or osteopenia is seen in 60-91% of those with BB depending on the side and reader. It is only seen in about 40% of those without BB. CONCLUSIONS: We conclude that the presence of BB suggest decreased BMD and when correlated with other clinical information, might support further evaluation of BMD.

The effect of peritoneal dialysate on DXA bone densitometry results in patients with end-stage renal disease.

The bone mineral density of patients undergoing peritoneal dialysis (PD) is low compared to a healthy population. No studies have been conducted to investigate whether the presence of peritoneal dialysate affects dual-energy X-ray absorptiometry (DXA) results. We hypothesized that the presence of peritoneal dialysate would not affect the measurement of bone mineral density (BMD) or bone mineral content (BMC) in the spine. Thirty patients on PD had DXA scans of the lumbar spine and hip completed before and after the drainage of peritoneal dialysate. A paired t-test was used to compare the difference in area, BMC, and BMD before and after drainage of dialysate. A significant difference was found in the BMC of the spine before and after the drainage of dialyzate. We recommend that peritoneal dialyzate be removed prior to scanning patients on PD and that densitometry technologists should be observant about the presence of peritoneal dialysate.

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 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.

Nonprogression of vertebral area or bone mineral content on DXA does not predict compression fractures.

The 2003 International Society for Clinical Densitometry consensus guidelines recommend exclusion of vertebral bodies for lack of increase in bone area (BA) or bone mineral content (BMC), or an unusual T-score discrepancy (>1 standard deviation [SD]) between adjacent vertebrae. It is unclear how often nonprogression in BA, BMC, and T-score discrepancies predicts abnormal vertebral morphology, such as compression fractures. We prospectively studied 101 individuals sent for clinical dual-energy X-ray absorptiometry (DXA) scanning, including 20.8% males and 79.2% females. The population was 85% Caucasian, 13% African-American, and 3% Hispanic. The mean age was 65.6 yr; 20.2% were currently on steroids and 22.7% were taking drugs for osteoporosis. All subjects underwent the usual posteroanterior (PA) spine DXA scan PA and lateral vertebral fracture analysis (VFA). The presence of vertebral compression fractures and/or scoliosis of the lumbar spine by VFA were correlated with nonprogression of area or BMC, and/or a difference of >1 SD in T-scores using Fisher's exact test. By VFA, we detected 22 lumbar compression fractures among 101 subjects, which was 16% of the population. Nonprogression of BA, BMC, and T-score discrepancy were not statistically associated with the presence of vertebral compression fracture as assessed by VFA. Thirty percent of subjects had lumbar spine scoliosis. The presence of scoliosis was significantly related to a T-score discrepancy at L1-L4.