CTXA Hip—An Extension of Classical DXA Measurements Using Quantitative CT

Abstract

Bone mineral density (BMD) estimates for the proximal femur using Dual Energy X-ray Absorptiometry (DXA) are currently considered the standard for making a diagnosis of osteoporosis in an individual patient using BMD alone. We have compared BMD results from a commercial Quantitative CT (QCT) BMD analysis system, “CTXA Hip”, which provides clinical data for the proximal femur, to results from DXA. We have also used CTXA Hip to determine cortical and trabecular contributions to total BMD. Sixty-nine patients were scanned using 3D QCT and DXA. CTXA Hip BMD measurements for Total Hip and Femoral Neck were compared to DXA results. Twenty-two women were scanned at 0,1,2 years and CTXA Hip and DXA results analyzed for long-term reproducibility. Long-term reproducibility calculated as root-mean-square averages of SDs in vivo was 0.012 g/cm2 (CV = 1.8%) for CTXA Total Hip and 0.011 g/cm2 (CV = 2.0%) for CTXA Femoral Neck compared to 0.014 g/cm2 (CV = 2.0%) and 0.016 g/cm2 (CV = 2.7%), respectively, for DXA. The correlation of Total Hip BMD CTXA vs. DXA was R = 0.97 and for Femoral Neck was R = 0.95 (SEE 0.044 g/cm2 in both cases). Cortical bone comprised 62±5% (mean ± SD) of total hipbone mass in osteoporotic women. CTXA Hip provides substantially the same clinical information as conventional DXA and in addition provides estimates of BMD in separate cortical and trabecular bone compartments, which may be useful in evaluation of bone strength.

Application of quantitative computed tomography for assessment of trabecular bone mineral density, microarchitecture and mechanical property

“…The QCT volumetric density assessment in the hip has also shown a very low (b2%) precision error [84,85]. All studies indicated that there was a significant association between the hip CTXA and DXA (rN0.95) with a high precision (CV b 2%) [13,20].…”

“…The QCT X-Ray Absorptiometry (CTXA) analysis at the hip using pelvis CT images with a calibration phantom and software system was developed by Cann et al (Mindways Software, Inc, Austin, TX) [13,20]. This technique uses a two-dimensional projection (anterior-posterior) of CT three-dimensional formation with software to calculate the area bone density (mg/cm 2 ) in hip and femoral neck integral bone, just like the DXA method.…”

“…The hip CTXA are difficult to use routinely for the assessment of fracture risk due to it's high radiation dose and limitation of two-dimensional assessment. It can be used in cases with a restricted DXA availability or as an additional measure in cases already obtaining a pelvic CT study [13,20,75].…”

“…Compared to DXA, QCT offers superior sensitivity in diagnosing osteoporosis, monitoring the bone density changes, and evaluating the bone trabecular microarchitectural and mechanical property simultaneously, but still considered a supplemental method due to its high radiation [12]. Two-dimensional QCT BMD measurement of the spine tended to show a lower precision, which lead to limited employment [13]. In the U.S., there are over 12,000 multidetector CT (MDCT) scanners [14].…”

Focal osteoporosis defects play a key role in hip fracture

“…Even though the overall prediction of hip fractures using CBM and DXA was similar [20], identifying focal osteoporosis through imaging techniques such as CBM might help in the proactive prevention of hip fracture given that targeted implantation of locally acting pharmaceuticals via the greater trochanter is technically feasible [21]. Traditional QCT measures of femoral neck and ‘total hip’ areal Bone Mineral Density (for example CTXA™, Mindways Austin, Texas, USA [22]) are now in routine clinical usage for hip fracture prediction by incorporation in the WHO FRAX™ tool. Several important questions remain; i) is focal osteoporosis present in the cortical and trabecular bone of women with hip fracture, and ii) do the CBM measures discriminate hip fractures better than traditional QCT measures of femoral neck and ‘total hip’ density (Fig.…”