Helical multidetector row quantitative computed tomography (QCT) precision

Reproducibility of CT-based opportunistic vertebral volumetric bone mineral density measurements from an automated segmentation framework

BACKGROUND

To investigate the reproducibility of automated volumetric bone mineral density (vBMD) measurements from routine thoracoabdominal computed tomography (CT) assessed with segmentations by a convolutional neural network and automated correction of contrast phases, on diverse scanners, with scanner-specific asynchronous or scanner-agnostic calibrations.

METHODS

We obtained 679 observations from 278 CT scans in 121 patients (77 males, 63.6%) studied from 04/2019 to 06/2020. Observations consisted of two vBMD measurements from Δdifferent reconstruction kernels (n = 169), Δcontrast phases (n = 133), scan Δsessions (n = 123), Δscanners (n = 63), or Δall of the aforementioned (n = 20), and observations lacking scanner-specific calibration (n = 171). Precision was assessed using root-mean-square error (RMSE) and root-mean-square coefficient of variation (RMSCV). Cross-measurement agreement was assessed using Bland-Altman plots; outliers within 95% confidence interval of the limits of agreement were reviewed.

RESULTS

Repeated measurements from Δdifferent reconstruction kernels were highly precise (RMSE 3.0 mg/cm3; RMSCV 1.3%), even for consecutive scans with different Δcontrast phases (RMSCV 2.9%). Measurements from different Δscan sessions or Δscanners showed decreased precision (RMSCV 4.7% and 4.9%, respectively). Plot-review identified 12 outliers from different scan Δsessions, with signs of hydropic decompensation. Observations with Δall differences showed decreased precision compared to those lacking scanner-specific calibration (RMSCV 5.9 and 3.7, respectively).

CONCLUSION

Automatic vBMD assessment from routine CT is precise across varying setups, when calibrated appropriately. Low precision was found in patients with signs of new or worsening hydropic decompensation, what should be considered an exclusion criterion for both opportunistic and dedicated quantitative CT.

RELEVANCE STATEMENT

Automated CT-based vBMD measurements are precise in various scenarios, including cross-session and cross-scanner settings, and may therefore facilitate opportunistic screening for osteoporosis and surveillance of BMD in patients undergoing routine clinical CT scans.

KEY POINTS

Artificial intelligence-based tools facilitate BMD measurements in routine clinical CT datasets. Automated BMD measurements are highly reproducible in various settings. Reliable, automated opportunistic osteoporosis diagnostics allow for large-scale application.

Incidental vertebral fracture prediction using neuronal network-based automatic spine segmentation and volumetric bone mineral density extraction from routine clinical CT scans

Objectives

To investigate vertebral osteoporotic fracture (VF) prediction by automatically extracted trabecular volumetric bone mineral density (vBMD) from routine CT, and to compare the model with fracture prevalence-based prediction models.

Methods

This single-center retrospective study included patients who underwent two thoraco-abdominal CT scans during clinical routine with an average inter-scan interval of 21.7 ± 13.1 months (range 5-52 months). Automatic spine segmentation and vBMD extraction was performed by a convolutional neural network framework (anduin.bonescreen.de). Mean vBMD was calculated for levels T5-8, T9-12, and L1-5. VFs were identified by an expert in spine imaging. Odds ratios (ORs) for prevalent and incident VFs were calculated for vBMD (per standard deviation decrease) at each level, for baseline VF prevalence (yes/no), and for baseline VF count (n) using logistic regression models, adjusted for age and sex. Models were compared using Akaike's and Bayesian information criteria (AIC & BIC).

Results

420 patients (mean age, 63 years ± 9, 276 males) were included in this study. 40 (25 female) had prevalent and 24 (13 female) had incident VFs. Individuals with lower vBMD at any spine level had higher odds for VFs (L1-5, prevalent VF: OR,95%-CI,p: 2.2, 1.4-3.5,p=0.001; incident VF: 3.5, 1.8-6.9,p<0.001). In contrast, VF status (2.15, 0.72-6.43,p=0.170) and count (1.38, 0.89-2.12,p=0.147) performed worse in incident VF prediction. Information criteria revealed best fit for vBMD-based models (AIC vBMD=165.2; VF status=181.0; count=180.7).

Conclusions

VF prediction based on automatically extracted vBMD from routine clinical MDCT outperforms prediction models based on VF status and count. These findings underline the importance of opportunistic quantitative osteoporosis screening in clinical routine MDCT data.

Impact of GH administration on skeletal endpoints in adults with overweight/obesity

OBJECTIVE

Overweight/obesity is associated with relative growth hormone (GH) deficiency and increased fracture risk. We hypothesized that GH administration would improve bone endpoints in individuals with overweight/obesity.

DESIGN

An 18-month, randomized, double-blind, placebo-controlled study of GH, followed by 6-month observation.

METHODS

In this study, 77 adults (53% men), aged 18-65 years, BMI ≥ 25 kg/m2, and BMD T- or Z-score ≤ -1.0 were randomized to daily subcutaneous GH or placebo, targeting IGF1 in the upper quartile of the age-appropriate normal range. Forty-nine completed 18 months. DXA, volumetric quantitative CT, and high-resolution peripheral quantitative CT were performed.

RESULTS

Pre-treatment mean age (48 ± 12 years), BMI (33.1 ± 5.7 kg/m2), and BMD were similar between groups. P1NP, osteocalcin, and CTX increased (P < 0.005) and visceral adipose tissue decreased (P = 0.04) at 18 months in the GH vs placebo group. Hip and radius aBMD, spine and tibial vBMD, tibial cortical thickness, and radial and tibial failure load decreased in the GH vs placebo group (P < 0.05). Between 18 and 24 months (post-treatment observation period), radius aBMD and tibia cortical thickness increased in the GH vs placebo group. At 24 months, there were no differences between the GH and placebo groups in bone density, structure, or strength compared to baseline.

CONCLUSIONS

GH administration for 18 months increased bone turnover in adults with overweight/obesity. It also decreased some measures of BMD, bone microarchitecture, and bone strength, which all returned to pre-treatment levels 6 months post-therapy. Whether GH administration increases BMD with longer treatment duration, or after mineralization of an expanded remodeling space post-treatment, requires further investigation.

Automatic phantom-less QCT system with high precision of BMD measurement for osteoporosis screening: Technique optimisation and clinical validation

Background

Objective

Methods

Results

Conclusion

Translational potential statement

Sources of error in bone mineral density estimates from quantitative CT

Bone mineral density (BMD) estimates from quantitative computed tomography (QCT) have proven useful for opportunistic screening of osteoporosis, treatment monitoring, and bone strength measurement. These estimates are subject to bias and variance from a variety of sources related to the imaging equipment, methods applied in the estimation procedure, and the patients themselves. In this article, we review the literature to describe the sources and sizes of error in spine and hip BMD estimates from single-energy QCT that can result from factors related to the scanner, imaging techniques, imaging subject, calibration phantom, and calibration approach. We also describe the baseline variance that can be expected based on repeatability and reproducibility studies. Though reproducible BMD estimates may be achievable with QCT, a thorough understanding of the potential sources of error and their size relative to the diagnostic task is essential to their appropriate and meaningful interpretation.

Bone and joint enhancement filtering: Application to proximal femur segmentation from uncalibrated computed tomography datasets

Methods for reliable femur segmentation enable the execution of quality retrospective studies and building of robust screening tools for bone and joint disease. An enhance-and-segment pipeline is proposed for proximal femur segmentation from computed tomography datasets. The filter is based on a scale-space model of cortical bone with properties including edge localization, invariance to density calibration, rotation invariance, and stability to noise. The filter is integrated with a graph cut segmentation technique guided through user provided sparse labels for rapid segmentation. Analysis is performed on 20 independent femurs. Rater proximal femur segmentation agreement was 0.21 mm (average surface distance), 0.98 (Dice similarity coefficient), and 2.34 mm (Hausdorff distance). Manual segmentation added considerable variability to measured failure load and volume (CV_RMS > 5%) but not density. The proposed algorithm considerably improved inter-rater reproducibility for all three outcomes (CV_RMS < 0.5%). The algorithm localized the periosteal surface accurately compared to manual segmentation but with a slight bias towards a smaller volume. Hessian-based filtering and graph cut segmentation localizes the periosteal surface of the proximal femur with comparable accuracy and improved precision compared to manual segmentation.

CT Phantom Evaluation of 67,392 American College of Radiology Accreditation Examinations: Implications for Opportunistic Screening of Osteoporosis Using CT

OBJECTIVE. The purpose of this study was to investigate whether systematic bias in attenuation measurements occurs among CT scanners made by four major manufacturers and the relevance of this bias regarding opportunistic screening for osteoporosis. MATERIALS AND METHODS. Data on attenuation measurement accuracy were acquired using the American College of Radiology (ACR) accreditation phantom and were evaluated in a blinded fashion for four CT manufacturers (8500 accreditation submissions for manufacturer A; 18,575 for manufacturer B; 8278 for manufacturer C; and 32,039 for manufacturer D). The attenuation value for water, acrylic (surrogate for trabecular bone), and Teflon (surrogate for cortical bone; Chemours) materials for an adult abdominal CT technique (120 kV, 240 mA, standard reconstruction algorithm) was used in the analysis. Differences in attenuation value across all manufacturers were assessed using the Kruskal-Wallis test followed by a post hoc test for pairwise comparisons. RESULTS. The mean attenuation value for water ranged from -0.3 to 2.7 HU, with highly significant differences among all manufacturers (p < 0.001). For the trabecular bone surrogate, differences in attenuation values across all manufacturers were also highly significant (p < 0.001), with mean values of 120.9 (SD, 3.5), 124.6 (3.3), 126.9 (4.4), and 123.9 (3.4) HU for manufacturers A, B, C, and D, respectively. For the cortical bone surrogate, differences in attenuation values across all manufacturers were also highly significant (p < 0.001), with mean values of 939.0 (14.2), 874.3 (13.3), 897.6 (11.3), and 912.7 (13.4) HU for manufacturers A, B, C, and D, respectively. CONCLUSION. CT scanners made by different manufacturers show systematic offsets in attenuation measurement when compared with each other. Knowledge of these off-sets is useful for optimizing the accuracy of opportunistic diagnosis of osteoporosis.

Measurements of volumetric bone mineral density in the mandible do not predict spinal osteoporosis

OBJECTIVE

The objective of this study was to determine whether the trabecular volumetric Bone Mineral Density (vBMD) of the middle, body and angle of the mandible correlates with vBMD of the cervical and lumbar vertebrae in a Chinese population.

METHODS AND MATERIALS

661 subjects (270 males, 391 females), ranging from 20 to 59 years of age, were recruited for vBMD measurements by quantitative CT (QCT). Basic information (age, height and weight), vBMD of the mandible (middle, body and angle sites), and vBMD of the cervical and lumbar vertebrae were recorded. Spearman's rank correlation test was used to investigate the association of mandibular with vertebral vBMD.

RESULTS

The study cohort comprised 661 subjects: 270 (41%) males, 391 (59%) females. Median age in males was 40 (range, 21-59) years. Median age in females was 41 (range, 20-59) years. Values of the Spearman correlation coefficient between mandibular and vertebral vBMD ranged from R = 0.048 to 0.141. In males, the three correlation coefficients between mandibular and cervical vBMD (middle: R = 0.138; body: R = 0.126; angle: R = 0.122) were all statistically significant (p < 0.05). In females, the correlation between the middle mandibular site and cervical site was statistically significant (R = 0.141, p < 0.01). None of the other correlations examined were statistically significant.

CONCLUSION

In this study population, mandibular vBMD was at best weakly correlated with cervical and lumbar vertebral vBMD, indicating that mandibular vBMD should be measured independently for the assessment of mandibular bone status.

Assessment of paraspinal muscle characteristics, lumbar BMD, and their associations in routine multi-detector CT of patients with and without osteoporotic vertebral fractures

PURPOSE

To investigate paraspinal muscle characteristics and lumbar bone mineral density (BMD) and their associations in routine abdominal multi-detector computed tomography (MDCT) as well as the impact of osteoporotic vertebral fractures on such associations.

METHOD

116 patients (69.7 ± 8.1 years, 72 males) who underwent routine abdominal MDCT (oncological staging and/or follow-up for tumor recurrence) were retrospectively included and assigned to a fracture and control group (age- and gender-matched), depending on the presence or absence of lumbar osteoporotic vertebral fractures. BMD was derived from lumbar vertebrae using a conversion equation, and the cross-sectional area (CSA), CSA ratio (CSA psoas muscles divided by CSA erector spinae muscles), and muscle attenuation were measured for the psoas and erector spinae muscles at the levels L2 and L4/5 without dedicated software.

RESULTS

Males showed significantly higher BMD, CSA, and CSA ratios at the levels L2 and L4/5, while females had decreased erector spinae muscle attenuation at L4/5 (p < 0.05). No significant differences between patients with versus without fractures were observed except for BMD (68.5 ± 37.2 mg/ml vs. 91.4 ± 26.8 mg/ml; p < 0.01). Age-adjusted partial correlation testing revealed significant correlations of BMD and the CSA ratio at level L4/5 (r = 0.20; p = 0.03), but not with muscle attenuation (p > 0.05).

CONCLUSIONS

Paraspinal muscle characteristics and lumbar BMD can be assessed seamlessly in routine abdominal MDCT without dedicated software. There are level-dependent interactions between paraspinal muscle characteristics as well as lumbar BMD. Vertebral fracture status was independent of paraspinal muscle characteristics.

X-ray-based quantitative osteoporosis imaging at the spine

Osteoporosis is a metabolic bone disease with a high prevalence that affects the population worldwide, particularly the elderly. It is often due to fractures associated with bone fragility that the diagnosis of osteoporosis becomes clinically evident. However, early diagnosis would be necessary to initiate therapy and to prevent occurrence of further fractures, thus reducing morbidity and mortality. X-ray-based imaging plays a key role for fracture risk assessment and monitoring of osteoporosis. Whereas over decades dual-energy X-ray absorptiometry (DXA) has been the main method used and still reflects the reference standard, another modality reemerges with quantitative computed tomography (QCT) because of its three-dimensional advantages and the opportunistic exploitation of routine CT scans. Against this background, this article intends to review and evaluate recent advances in the field of X-ray-based quantitative imaging of osteoporosis at the spine. First, standard DXA with the recent addition of trabecular bone score (TBS) is presented. Secondly, standard QCT, dual-energy BMD quantification, and opportunistic BMD screening in non-dedicated CT exams are discussed. Lastly, finite element analysis and microstructural parameter analysis are reviewed.

Liver Fat Content Measurement with Quantitative CT Validated against MRI Proton Density Fat Fraction: A Prospective Study of 400 Healthy Volunteers

Background Although chemical shift-encoded (CSE) MRI proton density fat fraction (PDFF) is the current noninvasive reference standard for liver fat quantification, the liver is more frequently imaged with CT. Purpose To validate quantitative CT measurements of liver fat against the MRI PDFF reference standard. Materials and Methods In this prospective study, 400 healthy participants were recruited between August 2015 and July 2016. Each participant underwent same-day abdominal unenhanced quantitative CT with a calibration phantom and CSE 3.0-T MRI. CSE MRI liver fat measurements were used to calibrate an equation to adjust CT fat measurements and put them on the PDFF measurement scale. CT and PDFF liver fat measurements were plotted as histograms, medians, and interquartile ranges compared; scatterplots and Bland-Altman plots obtained; and Pearson correlation coefficients calculated. Receiver operating characteristic curves including areas under the curve were evaluated for mild (PDFF, 5%) and moderate (PDFF, 14%) steatosis thresholds for both raw and adjusted CT measurements. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Results Four hundred volunteers (mean age, 52.6 years ± 15.2; 227 women) were evaluated. MRI PDFF measurements of liver fat ranged between 0% and 28%, with 41.5% (166 of 400) of participants with PDFF greater than 5%. Both raw and adjusted quantitative CT values correlated well with MRI PDFF (r2 = 0.79; P < .001). Bland-Altman analysis of adjusted CT values showed no slope or bias. Both raw and adjusted CT had areas under the receiver operating characteristic curve of 0.87 and 0.99, respectively, to identify participants with mild (PDFF, >5%) and moderate (PDFF, >14%) steatosis, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value for unadjusted CT was 75.9% (126 of 166), 85.0% (199 of 234), 78.3% (126 of 161), and 83.3% (199 of 239), respectively, for PDFF greater than 5%; and 84.8% (28 of 33), 98.4% (361 of 367), 82.4% (28 of 34), and 98.6% (361 of 366), respectively, for PDFF greater than 14%. Results for adjusted CT were mostly identical. Conclusion Quantitative CT liver fat exhibited good correlation and accuracy with proton density fat fraction measured with chemical shift-encoded MRI. © RSNA, 2019 Online supplemental material is available for this article.

Vertebral bone marrow fat content in normal adults with varying bone densities at 3T magnetic resonance imaging

BACKGROUND

Sex-related differences of vertebral bone marrow fat in relation to varying bone densities have not yet been evaluated although some studies have reported an inverse association of bone marrow fat and bone mineral density (BMD).

PURPOSE

To evaluate the relationship between bone marrow fat and BMD and to demonstrate the sex-related differences of the vertebral bone marrow fat in normal adults with varying bone densities.

MATERIAL AND METHODS

A total of 123 normal adult volunteers were enrolled in this study. ¹H-MRS of the lumbar spine was performed. The fat fraction (FF) values of vertebral bone marrow were measured. Volumetric BMD measurement was performed by quantitative computed tomography (QCT). All participants were divided into three groups according to BMD (normal, osteopenia, osteoporosis). The differences in the FF and body mass index (BMI) values of the three groups were compared, and partial correlation analysis was used to evaluate the correlation between FF values and BMD/BMI.

RESULTS

The FF values increased with decreasing BMD in both male and female participants. There were significant sex differences for the FF values in the normal bone density group ( P < 0.001). The FF values of the normal bone density group in male participants were significantly higher than those of the female participants ( P < 0.001). The FF values were significantly negative correlated with BMD for all participants (r = -0.820, P < 0.001).

CONCLUSION

The FF values of vertebral bone marrow correlated inversely with BMD. Sex-related differences of FF values was related to BMD.

Vertebral bone marrow diffusivity in normal adults with varying bone densities at 3T diffusion-weighted imaging

Background There has been controversy surrounding the relationship between diffusivity and bone mineral density (BMD) in vertebral bone marrow. Moreover, sex-related differences of vertebral bone marrow diffusivity in relation to varying bone densities have not yet been evaluated. Purpose To prospectively investigate the role of diffusion-weighted imaging (DWI) in assessing vertebral marrow changes in normal adults with varying bone densities. Material and Methods A total of 124 normal adult volunteers were enrolled in this study. Sagittal magnetic resonance (MR) DWI of the lumbar spine was performed. The ADC values of vertebral bone marrow were measured. Volumetric BMD measurement was performed by quantitative computed tomography (QCT) using Mindways QCT analysis software. All participants were divided into three groups according to BMD (normal, osteopenia, osteoporosis). The differences of the apparent diffusion coefficient (ADC) values of the three groups was compared, and partial correlation analysis was used to evaluate the correlation between ADC values and BMD. Results ADC values decreased as BMD decreased in female participants. When compared with the normal bone density group, ADC values were significantly decreased in the osteoporotic group and in the osteopenic group of female participants. ADC values of female participants were significantly higher than of male participants in the normal bone density group ( P < 0.001). ADC values correlated positively with BMD values (r = 0.307, P = 0.016) for female participants. Conclusion The diffusivity in vertebral bone marrow with varying bone densities differed by sex. ADC values correlated positively with BMD in women. DWI can quantitively evaluate osteoporosis in women.

Calcium isotope signature: new proxy for net change in bone volume for chronic kidney disease and diabetic rats

Herein, we measure the Ca isotope ratios (⁴⁴Ca/⁴²Ca and ⁴³Ca/⁴²Ca) in serum and bone samples collected from rats with chronic kidney disease (CKD) or diabetes mellitus (DM). For the serum samples, the isotope ratios are lower for the CKD (δ⁴⁴Ca/⁴²Ca_serum = 0.16 ± 0.11‰; 2SD, n = 6) and the DM (δ⁴⁴Ca/⁴²Ca_serum = -0.11 ± 0.25‰; 2SD, n = 7) rats than that for the control rats (δ⁴⁴Ca/⁴²Ca_serum = 0.25 ± 0.04‰; 2SD, n = 7). Bone samples from two distinct positions of 20 rats in total, namely, the center and proximal parts of the tibial diaphysis, are subject to Ca isotope analysis. The resulting δ⁴⁴Ca/⁴²Ca values for the bone of the proximal part are about 0.3‰ lower than that for the serum samples from the same rats. The larger isotope fractionations between the serum and bone are consistent with previously reported data for vertebrate animals (e.g., Skulan and DePaolo, 1999), which suggests the preferential incorporation of lighter Ca isotopes through bone formation. For the bones from the control and CKD rats, there were no differences in the δ⁴⁴Ca/⁴²Ca values between the positions of the bone. In contrast, the δ⁴⁴Ca/⁴²Ca values of the bone for the DM rats were different between the positions of the bone. Due to the lower bone turnover rate for the DM rats, the δ⁴⁴Ca/⁴²Ca for the middle of the diaphysis can reflect the Ca isotopes in the bone formed prior to the progression of DM states. Thus, the resulting δ⁴⁴Ca/⁴²Ca values show a clear correlation with bone mineral density (BMD). This can be due to the release of isotopically lighter Ca from the bone to the serum. In the present study, our data demonstrate that the δ⁴⁴Ca/⁴²Ca value for serum can be used as a new biomarker for evaluating changes in bone turnover rate, followed by changes in bone volume.

Asynchronously Calibrated Quantitative Bone Densitometry

Conventional quantitative computed tomography (QCT) uses a phantom scanned simultaneously with the anatomical region of interest. A newly developed method called asynchronous QCT does not require a phantom to be present during the patient scan. This allows the inclusion of computer tomography scans performed without any calibration standard in a different clinical context than bone densitometry, for example, in a screening context. In the present study, the asynchronous and the conventional quantitative computed tomographies were compared. Specifically, short-term precision, a phantom-induced bias, methodical equivalence of the asynchronous and the conventional methods, and interobserver variability were investigated. Ten phantom scans served for investigation of short-term precision. A prospective dataset of 43 study participants (44-80 years, mean 63.8 ± 8.6 years) was acquired over 3 clinical sites. Trabecular regions of the spine as well as cortical and trabecular regions of the hip (femoral neck, trochanter, intertrochanter, and shaft) were analyzed with respect to the presence or absence of a phantom and with regard to the synchronous and asynchronous calibration methods. Regarding precision, all variations of the mean areal and volumetric densities were lower for the asynchronous method than for the conventional method. The presence of the phantom resulted in a bias of 2.3 mg/cm³, and the choice of the asynchronously or synchronously calibrated analysis resulted in a bias of 3.7 mg/cm³ at the spine. Both were statistically, but not clinically, significant. The total hip was statistically, but not clinically, significantly different by 0.008 g/cm². The bone density values between the 2 techniques correlated highly with one another at all regions investigated. Interobserver variability between 2 trained observers showed a difference of 0.2 mg/cm³ (spine) and differences less or equal to 0.009 g/cm² (hip), which again was regarded as clinically nonsignificant. In summary, the asynchronously calibrated QCT provides results comparable to the established synchronously calibrated QCT.

Population-Stratified Analysis of Bone Mineral Density Distribution in Cervical and Lumbar Vertebrae of Chinese from Quantitative Computed Tomography

Objective

To investigate the bone mineral density (BMD) of cervical vertebrae in a population-stratified manner and correlate with that of the lumbar vertebrae.

Materials and Methods

Five hundred and ninety-eight healthy volunteers (254 males, 344 females), ranging from 20 to 64 years of age, were recruited for volumetric BMD (vBMD) measurements by quantitative computed tomography. Basic information (age, height, weight, waistline, and hipline), and vBMD of the cervical and lumbar vertebrae (C2–7 and L2–4) were recorded. Comparisons among sex, age groups and different levels of vertebrae were analyzed using analysis of variance. Linear regression was performed for relevance of different vertebral levels.

Results

The vBMD of cervical and lumbar vertebrae was higher in females than males in each age group. The vBMD of the cervical and lumbar vertebrae in males and the vBMD of lumbar vertebrae in females decreased with aging. In each age group, the vBMD of the cervical vertebrae was higher than that of the lumbar vertebrae with gradual decreases from C2 to C7 except for C3; moreover, the vBMD of C6 and C7 was significantly different from that of C2–5. Correlations of vBMD among different cervical vertebrae (females: r = 0.62–0.94; males: r = 0.63–0.94) and lumbar vertebrae (males: r = 0.93–0.98; females: r = 0.82–0.97) were statistically significant at each age group.

Conclusion

The present study provided normative data of cervical vertebrae in an age- and sex-stratified manner. Sex differences in vBMD prominently vary with age, which can be helpful to design a more comprehensive pre-operative surgical plan.

Comparison of femoral neck BMD evaluation obtained using Lunar DXA and QCT with asynchronous calibration from CT colonography

For patients undergoing screening computed tomography colonography (CTC), an opportunity exists for bone mineral density (BMD) screening without additional radiation exposure using quantitative computed tomography (QCT). This study investigated the use of dual-energy X-ray absorptiometry (DXA)-equivalent QCT Computed Tomography X-Ray Absorptiometry (CTXA) analysis at the hip obtained using CTC examinations using a retrospective asynchronous calibration of patient scans. A cohort of 33 women, age 61.3 (10.6) yr (mean [standard deviation]), had routine CTC using various GE LightSpeed CT scanner models followed after 0-9 mo by a DXA hip BMD examination using a GE Lunar Prodigy machine. Areal bone mineral density (aBMD) and T-scores of the proximal femur were measured from either prone or supine CTC examinations using Mindways QCT Pro software following standard workflow except that the CT scanners were asynchronously calibrated by phantoms scanned retrospectively of the CTC examination without the subject present. CTXA and DXA aBMD were highly correlated (R2=0.907) with a linear relationship of DXA_BMD=1.297*CTXA_BMD+0.048. The standard error of estimate (SEE) on the linear fit was 0.053 g/cm2. CTXA and DXA T-scores showed a linear relationship of DXA_T-score=1.034*CTXA_T-score+0.3 and an SEE of 0.379 T-scores. CTXA and DXA aBMD and T-score measurements showed good correlation despite asynchronous scan acquisition and retrospective QCT calibration. The SEE of 0.053 g/cm2 is on par with the literature comparing Hologic and Lunar DXA devices. The observed relationship between CTXA and Lunar DXA aBMD matches predictions from published cross-calibrations relating CTXA to DXA aBMD measurement. Thus, opportunistic use of CTXA T-scores obtained at the time of CTC could enhance osteoporosis screening.

Cortical bone assessed with clinical computed tomography at the proximal femur

Hip fractures are the most serious of all fragility fractures in older people of both sexes. Trips, stumbles, and falls result in fractures of the femoral neck or trochanter, and the incidence of these two common fractures is increasing worldwide as populations age. Although clinical risk factors and chance are important in causation, the ability of a femur to resist fracture also depends on the size and spatial distribution of the bone, its intrinsic material properties, and the loads applied. Over the past two decades, clinical quantitative computed tomography (QCT) studies of living volunteers have provided insight into how the femur changes with advancing age to leave older men and women at increased risk of hip fractures. In this review, we focus on patterns of cortical bone loss associated with hip fracture, age-related changes in cortical bone, and the effects of drugs used to treat osteoporosis. There are several methodologies available to measure cortical bone in vivo using QCT. Most techniques quantify bone density (g/cm(3)), mass (g), and thickness (mm) in selected, predefined or “traditional” regions of interest such as the “femoral neck” or “total hip” region. A recent alternative approach termed “computational anatomy,” uses parametric methods to identify systematic differences, before displaying statistically significant regions as color-scaled maps of density, mass, or thickness on or within a representative femur model. This review will highlight discoveries made using both traditional and computational anatomy methods, focusing on cortical bone of the proximal femur.

Relation of visceral and subcutaneous adipose tissue to bone mineral density in chinese women

The relationship between adipose and bone tissues is still being debated. The purpose of our study was to evaluate whether the distribution and volume of abdomen adipose tissue are correlated to trabecular bone mineral density in the lumbar spine. In this cross-sectional study, 320 Chinese women, being divided into two groups according to age ≥55 years and <55 years, were evaluated with quantitative computed tomography (QCT) of the spine to simultaneously evaluate the average trabecular BMD of L2-L4, VAT, and SAT. Possible covariates of height, weight, age, and comorbidities were considered. In the <55-year-old sample, multiple linear regression analyses indicated that VAT volume was negatively correlated to trabecular BMD (P value = 0.0003) and SAT volume had no correlation to trabecular BMD. In contrast, there was no significant correlation between VAT or SAT and BMD in the ≥55-year-old sample. Our results indicate that high VAT volume is associated with low BMD in Chinese women aged <55 years and SAT has no relation with BMD.

Assessment of technical and biological parameters of volumetric quantitative computed tomography of the foot: a phantom study

SUMMARY

Few studies exist for bone densitometry of the whole foot. A phantom study demonstrated the sources of error and necessary controls for accurate quantitative computed tomography of the foot. A loss in bone mineral density (BMD) in the small foot bones may be an early indicator of diabetic foot complications.

INTRODUCTION

Volumetric quantitative computed tomography (vQCT) facilitates the assessment of pedal bone osteopenia, which, in the presence of peripheral neuropathy, may well be an early sign of diabetic foot deformity. To date, sources and magnitudes of error in foot vQCT measurements have not been reported.

METHODS

Foot phantoms were scanned using a 64-slice CT scanner. Energy (in kilovoltage peak), table height, phantom size and orientation, location of "bone" inserts, insert material, location of calibration phantom, and reconstruction kernel were systematically varied during scan acquisition.

RESULTS

Energy (in kilovoltage peak) and distance from the isocenter (table height) resulted in relative attenuation changes from -5% to 22% and -5% to 0%, respectively, and average BMD changes from -0.9% to 0.0% and -1.1% to 0.3%, respectively, compared to a baseline 120-kVp scan performed at the isocenter. BMD compared to manufacturer-specified values ranged, on average, from -2.2% to 0.9%. Phantom size and location of bone-equivalent material inserts resulted in relative attenuation changes of -1.2% to 1.4% compared to the medium-sized phantom.

CONCLUSION

This study demonstrated that variations in kilovoltage peak and table height can be controlled using a calibration phantom scanned at the same energy and height as a foot phantom; however, error due to soft tissue thickness and location of bones within a foot cannot be controlled using a calibration phantom alone.

Converted lumbar BMD values derived from sagittal reformations of contrast-enhanced MDCT predict incidental osteoporotic vertebral fractures

We obtained baseline and follow-up bone mineral density (BMD) values of the lumbar spine from sagittal reformations of routine abdominal contrast-enhanced multidetector computed tomography (MDCT) using a reference phantom and assessed their performance in differentiating patients with no, existing, and incidental osteoporotic fractures of the spine. A MDCT-to-QCT (quantitative computed tomography) conversion equation for lumbar BMD measurements was developed by using 15 postmenopausal women (63 ± 12 years), who underwent standard lumbar QCT (L1-L3) and afterward routine abdominal contrast-enhanced MDCT. Sagittal reformations were used for corresponding lumbar BMD measurements. The MDCT-to-QCT conversion equation was applied to baseline and follow-up routine abdominal contrast-enhanced MDCT scans of 149 postmenopausal women (63 ± 10 years). Their vertebral fracture status (no, existing, or incidental osteoporotic fracture) was assessed in the sagittal reformations. A correlation coefficient of r = 0.914 (p < 0.001) was calculated for the BMD values of MDCT and standard QCT with the conversion equation BMD(QCT) = 0.695 × BMD(MDCT) - 7.9 mg/mL. Mean follow-up time of the 149 patients was 20 ± 12 months. Fifteen patients (10.1 %) had an existing osteoporotic vertebral fracture at baseline. Incidental osteoporotic vertebral fractures were diagnosed in 13 patients (8.7 %). Patients with existing and incidental fractures showed significantly (p < 0.05) lower converted BMD values (averaged over L1-L3) than patients without fracture at baseline and at follow-up. In this longitudinal study, BMD values of the lumbar spine derived from sagittal reformations of routine abdominal contrast-enhanced MDCT predicted incidental osteoporotic vertebral fractures.

Simulated increases in body fat and errors in bone mineral density measurements by DXA and QCT

Major alterations in body composition, such as with obesity and weight loss, have complex effects on the measurement of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA). The effects of altered body fat on quantitative computed tomography (QCT) measurements are unknown. We scanned a spine phantom by DXA and QCT before and after surrounding with sequential fat layers (up to 12 kg). In addition, we measured lumbar spine and proximal femur BMD by DXA and trabecular spine BMD by QCT in 13 adult volunteers before and after a simulated 7.5 kg increase in body fat. With the spine phantom, DXA BMD increased linearly with sequential fat layering at the normal (p < 0.01) and osteopenic (p < 0.01) levels, but QCT BMD did not change significantly. In humans, fat layering significantly reduced DXA spine BMD values (mean ± SD: -2.2 ± 3.7%, p = 0.05) and increased the variability of measurements. In contrast, fat layering increased QCT spine BMD in humans (mean ± SD: 1.5 ± 2.5%, p = 0.05). Fat layering did not change mean DXA BMD of the femoral neck or total hip in humans significantly, but measurements became less precise. Associations between baseline and fat-simulation scans were stronger for QCT of the spine (r(2)= 0.97) than for DXA of the spine (r(2)= 0.87), total hip (r(2) = 0.80), or femoral neck (r(2)= 0.75). Bland-Altman plots revealed that fat-associated errors were greater for DXA spine and hip BMD than for QCT trabecular spine BMD. Fat layering introduces error and decreases the reproducibility of DXA spine and hip BMD measurements in human volunteers. Although overlying fat also affects QCT BMD measurements, the error is smaller and more uniform than with DXA BMD. Caution must be used when interpreting BMD changes in humans whose body composition is changing.

Cervical spine bone mineral density as a function of vertebral level and anatomic location

BACKGROUND CONTEXT

Bone mineral density (BMD) measurements acquired from quantitative computed tomography scans have been shown to correlate with bone mechanical properties such as strength, stiffness, and yield load. There are currently no reports of BMD as a function of anatomic location within each vertebra.

PURPOSE

The overall objective of this study was to characterize BMD in the cervical spine as a function of level and anatomic location.

STUDY DESIGN

Cervical spine BMD was evaluated in vivo using a clinically relevant age group.

PATIENT SAMPLE

Twenty-two subjects (13 women and 9 men) were included with an average age of 48 ± 7 years (range, 35-61 years). Ten subjects were recently diagnosed with cervical radiculopathy (age 49 ± 8 years; six women and four men; and two smokers and eight nonsmokers), and 12 subjects were asymptomatic controls (age 46 ± 6 years; seven women and five men; and three smokers, three quit smoking, and six nonsmokers).

OUTCOME MEASURES

Physiologic measures included overall BMD for C3-C7, average BMD within 11 anatomically defined regions of interest for each vertebra, and density distribution (by volume) within each anatomic region and vertebral level.

METHODS

Subject-specific three-dimensional bone models were created from high-resolution computed tomography scans of the subaxial cervical spine (C3-C7). Custom software calculated the average BMD within 11 anatomically defined regions of interest for each three-dimensional bone model. Bone mineral density values for each voxel of bone tissue were binned into 50 mg/cc ranges to determine the density distribution by volume. Repeated-measures analysis of variance was used to test for differences within subjects by level (C3-C7) and anatomic location. The correlation between BMD in the central vertebral body and the pedicle and lateral mass regions was tested using Pearson correlation.

RESULTS

Average BMDs by level were 476, 503, 507, 473, and 414 mg/cm(3) for C3-C7, respectively. C3 and C6 BMDs were significantly less than those of C4 and C5 (p<.007). C7 BMD was significantly less than those of all other levels (all p<.001). Control and female subjects showed a trend toward higher BMD than radiculopathy and male subjects across all levels (p value: .06-.17). Wide variation in BMD was observed over anatomical regions, with the pedicles having significantly higher BMD than all other anatomic locations and the anterior portion of the central vertebral body having significantly lower BMD than all other anatomic locations. There was a significant positive correlation between central vertebral body BMD and lateral mass BMD at each level. Bone mineral density distribution by volume plots revealed women had a higher volume of very high-density bone than men but only in the posterior elements.

CONCLUSIONS

This study has characterized BMD in the cervical spine according to vertebral level and anatomic location within each vertebral level using live subjects from a clinically relevant age group. The results indicate significant differences in BMD according to vertebral level and among anatomical regions within each vertebra. The results suggest to the surgeon and device manufacturer that surgical procedures involving instrumentation attached to C7 may require a modification in instrumentation or in surgical technique to attain results equivalent to more superior levels. The results suggest to the basic scientist that computational models may be improved by taking into account the wide variation in BMD over different anatomical regions.

Assessing the clinical utility of quantitative computed tomography with a routinely used diagnostic computed tomography scanner in a cancer center

The purpose of this study was to characterize quantitative computed tomography (QCT) in our multi-detector computed tomography (MDCT) scanner with regard to the influence of the QCT phantom on dose and the influence of varying mA and CIRS phantom size on bone mineral density (BMD) measurements. We accomplish this by scanning a commercially available QCT phantom and a corresponding quality assurance phantom. To assess the feasibility of having the QCT phantom in place while patients are being scanned, we measured radiation dose difference in a CT body phantom with and without the QCT phantom on the CT table and also, with and without the use of dose modulation programs. We also analyzed reconstructed QCT phantom images with the manufacturer's software to measure BMD. Although patient characteristics may be different, leading to different mA values, the influence of the QCT phantom on the dose to patients was minimal when compared with doses measured without the phantom in place. Average BMD measurements were not significantly affected by varying mA, for a fixed-size phantom. The average BMD exhibited a weak dependence on computerized imaging reference systems (CIRS) torso phantom size, with a propensity for decreasing BMD with increasing size. Measurement precision was unaffected by varying CIRS size. Having the ability to measure bone density as part of the routine management of cancer patients, with no added cost, time, or radiation dose, will allow for the prospective evaluation of bone mineral changes. We believe that this ability will facilitate the detection of abnormal bone loss and will lead to better management of this loss and, thus, reduce the complications and associated morbidity in these cancer survivors.

BMD measurements of the spine derived from sagittal reformations of contrast-enhanced MDCT without dedicated software

PURPOSE

To assess QCT equivalent BMD of the lumbar spine in sagittal reformations of routine abdominal contrast-enhanced MDCT with simple PACS measurement tools and to apply this method to MDCT datasets for differentiating patients with and without osteoporotic vertebral fractures.

MATERIALS AND METHODS

Eight postmenopausal women (65±5 years) underwent standard QCT to assess BMD of L1-L3. Afterwards routine abdominal contrast-enhanced MDCT images of these women were obtained and apparent BMD of L1-L3 was measured using the sagittal reformations. The MDCT-to-QCT conversion equation for BMD was calculated with linear regression analysis. The conversion equation was applied to vertebral BMD datasets (L1-L3) of 75 postmenopausal women (66±4 years). Seventeen of the 75 patients had osteoporotic vertebral fractures.

RESULTS

BMD values of contrast-enhanced MDCT were on average 56 mg/ml higher than those of standard QCT. A correlation coefficient of r=0.94 (p<0.05) was calculated for the BMD values of MDCT and standard QCT with the conversion equation BMDQCT=0.69×BMDMDCT-11 mg/ml. Accordingly converted BMD values of patients with vertebral fractures were significantly lower than those of patients without vertebral fractures (69 mg/ml vs. 85 mg/ml; p<0.05). Using ROC analysis to differentiate patients with and without vertebral fractures, AUC=0.72 was obtained for converted BMD values (p<0.05). Short- and long-term reproducibility errors for BMD measurements in the sagittal reformations amounted 2.09% and 7.70%, respectively.

CONCLUSION

BMD measurements of the spine could be computed in sagittal reformations of routine abdominal contrast-enhanced MDCT with minimal technical and time effort. Using the conversion equation, the acquired BMD data could differentiate patients with and without osteoporotic vertebral fractures.

Phantom-less QCT BMD system as screening tool for osteoporosis without additional radiation

PURPOSE

Phantom-less bone mineral density (PLBMD) systems are easily integrated into the CT workflow for non-dedicated Quantitative CT (QCT) BMD measurements in thoracic and abdominal scans. This in vivo retrospective study aims to determine accuracy and precision of the PLBMD option located on the Extended Brilliance Workspace (Philips Medical Systems, Cleveland, OH, US) from both cross-sectional and longitudinal image data.

MATERIALS AND METHODS

The cross-sectional comparison with phantom-based QCT BMD was performed for 82 patients (61 female, 21 male) with a mean age of (63.0±11.8 SD) years on 197 vertebrae. This was followed by an interobserver variability analysis on 71 vertebrae. The longitudinal PLBMD study was carried out on 45 vertebrae from 10 patients (5 female, 5 male) with a mean age of (64.4±11.5 SD) years. They were re-scanned with standardized scan and contrast-injection protocols within a mean and median of (33±41 SD) and 8 days, respectively. All CT scans were acquired on an Mx8000 Quad (Philips) at Florence-Nightingale Hospital, Kaiserswerth, Germany, in a spiral acquisition mode.

RESULTS

A negligible BMD bias of -0.9mg/cm(3) for the PLBMD option was observed with respect to phantom-based QCT BMD. Applying CT number matching of muscle and fat ROIs, the analysis of cross-sectional interobserver and of longitudinal variability yielded precision values of 3.1mg/cm(3) (CV%=4.0) and 4.2mg/cm(3) (CV%=5.3), respectively.

CONCLUSION

Although the precision is inferior to phantom-based BMD systems, PLBMD is a robust clinical utility for the detection of lowered BMD in a large patient population. This can be achieved without additional radiation exposure from non-contrasted CT scans, to perform an ancillary diagnosis of osteopenia or osteoporosis.