Estimation of bone mineral density and architectural parameters of the distal radius in hemodialysis patients using peripheral quantitative computed tomography

We analyzed bone changes in a series of hemodialysis patients followed up for a maximum of 299 months by assessing bone mineral density (BMD) and architectural parameters of the distal radius using peripheral quantitative computed tomography (pQCT), and determined the predictors of skeletal changes in these patients. No significant differences in trabecular BMD (BMD(T)) were found compared with BMD(T) of the normal control. In contrast, cortical BMD (BMD(C)) was significantly decreased compared with BMD(C) of the normal controls. Hemodialysis patients had significantly lower values for cortical bone area, cortical thickness, moment of inertia, and polar moment of inertia than the age-matched controls. From single and multiple regression analysis, the most significant predictor of metabolic bone disease in these cases was found to be duration of hemodialysis. In addition, increases in serum alkaline phosphatase and intact parathyroid hormone in secondary hyperparathyroidism were found to correlate with a decrease in pQCT values in cortical bone; as such, these increases were also found to be a predictive. The present study confirms that the reduction in both BMD(C) and architectural parameters in hemodialysis patients occurs partly because of prolonged hemodialysis and secondary hyperparathyroidism. In addition, immobilization, dietary factors, daily intake of calcium or vitamin D, and so on must be taken into account when clarifying the causes of skeletal complications resulting from hemodialysis.     

X-ray quantitative computed tomography: the relations to physical properties of proximal tibial trabecular bone specimens

Cylindrical bone specimens from the proximal epiphysis of ten normal human proximal tibiae were randomly assigned to a destructive axial compression test-series (N = 94) or to a protocol of standardized mechanical conditioning followed by non-destructive repeated testing to 0.6% strain and a final destructive test (N = 121). Specimen X-ray quantitative computed tomography (QCT) obtained at different scanning energies (100, 120 and 140 kVp) yielded closely related results (r = 1.00). Accordingly, predictions of physically measured densities or mechanical properties were not improved by using more than one scanning energy. QCT and physically measured densities were intimately related (QCT at 140 kVp to apparent density using linear regression: r = 0.94, and to apparent ash density: r = 0.95) and did not differ significantly in their ability to predict the mechanical properties, thus favouring the more easily implemented QCT for routine work. Evaluation of the relation of apparent density to Young's modulus and ultimate strength suggested that a power law regression model is preferable to a linear model, although linear model prediction of mechanical properties does not have significantly worse accuracy within the narrow density range investigated. The effect of conditioning on the behaviour of bone specimens subjected to destructive compression tests was to increase the stiffness and strength by approximately 50 and 20% respectively.     

Measurement of bone mineral density (BMD) with quantitative computed tomography (QCT) in postmenopausal osteoporosis: effect of estrogen.

To determine the efficacy of the estrogen replacement therapy (ERT) on the bone mineral density (BMD) measured with quantitative computed tomography (QCT) in postmenopausal osteoporosis 16 women aged 46-72 were examined. They were divided into two groups: 8 women treated with conjugated estrogens (Group I) and 8 who did not received ERT (Group II). In all 16 patients the serum hormonal concentrations (LH, FSH and estradiol) were measured with radioimmunological methods. The bone densitometry was performed in all of them using the single-energy computed tomography (QCT) with the computer Picker 1200. Bone mineral density was measured in three lumbar vertebra (L1-L3) and expressed in milligrams K2HPO4 per ml. The bone mineral density (BMD) was statistically significantly higher in the estrogen treated group (Group I) in every vertebra compared with that of controls (Group II). The serum FSH concentration was statistically significantly lower in the ERT group (Group I) and a statistically significant correlation between FSH level and average BMD (Lmean) was present. In conclusion: 1. the ERT is very efficacious in preventing bone loss in postmenopausal women; 2. measurement of BMD in lumbar vertebra L1 or L3 may be a sufficiently reliable and accurate, cost-effective and time-saving method of screening for osteoporosis; 3. the serum FSH determination seems to be useful in monitoring of the estrogen therapy for postmenopausal osteoporosis.     

Protocol for measurement of liver fat by computed tomography.

To develop a protocol for measurement of liver fat using computed tomography (CT), we conducted a preliminary study with 118 men and 76 women to determine a readily identifiable vertebral landmark at which the CT image displayed both liver and spleen. Analysis of five landmarks revealed that the CT image obtained at the T12-L1 level simultaneously displayed the liver and spleen in 90% of the men and women. The T12-L1 protocol was cross-validated on a sample of 130 men and 113 women. In this sample, we also assessed the regional characteristics of liver and spleen tissue attenuation at the T12-L1 level by subdividing each image into quartiles from anterior to posterior, each of which were further divided into medial and lateral regions. A similar analysis was performed on images located 12 mm above and below T12-L1. The T12-L1 image displayed both liver and spleen in 92% (403 of 437) of the combined study sample. There was a significant (P<0.005) stepwise increase in attenuation values [Hounsfield units (HU)] from the inferior to superior image. Although some significant (P<0.05) differences were observed between the eight regions by comparison to the whole liver or spleen, the average magnitude of the difference was <2.0 HU for liver and <3.5 HU for spleen. Acquisition of a single CT image at the T12-L1 level is a practical and reliable method for routine measurement of liver fat in research and clinical settings.     

High-resolution computed tomography for the comparative study of fossil and extant bone

Special methods have been developed to use computed tomography (CT) for 3-dimensional imaging of both fossil and extant bones. Most commercial CT scanners cannot display the internal structure of fossils because the very high density is beyond the upper limits of the normal CT number scale (Hounsfield scale) of the scanners. X-ray projections from CT scans of fossils were modified by scaling the data to provide an expanded CT number scale, allowing the internal structure of highly fossilized objects to be visualized. These images were compared with state-of-the-art, high-resolution CT images of extant bone. Special image reformatting software was used to provide qualitative and quantitative 3-dimensional imaging. The recent rapid advances in CT technology have made this imaging modality the procedure of choice in much of diagnostic radiology. Use of this tool in paleoanthropology has been limited in the past by restricted access to scanners. However, new developments in CT will make this technique available to many researchers in the near future.     

The bone behind a low areal bone mineral density: peripheral quantitative computed tomographic analysis in a woman with osteogenesis imperfecta

Areal bone mineral density (BMD) is the most widely used densitometric parameter. However, this approach makes it difficult to understand the structural basis of bone diseases, because a large number of bone properties are integrated into a single number. This is exemplified in the present case of a 27-year-old woman with osteogenesis imperfecta type I. Peripheral quantitative computed tomographic analysis at the radial metaphysis and at the radial diaphysis revealed a decreased areal BMD at both sites (z score -3.9 and -3.4, respectively). Yet, the structural basis for this decrease was different for the two locations: At the distal radius areal BMD was decreased because volumetric BMD was very low, whereas bone size was above the mean of the reference range. At the proximal radius areal BMD was decreased, because bone size was very low but volumetric BMD was above average. Bone mineral content of the radial diaphysis was very low for forearm muscle size, a finding which is compatible with Frost's hypothesis that the mechanostat setpoint is increased in osteogenesis imperfecta.     

Dual-energy X-ray performs as well as clinical computed tomography for the measurement of visceral fat

Visceral adipose tissue (VAT) is associated with adverse health effects including cardiovascular disease and type 2 diabetes. We developed a dual-energy X-ray absorptiometry (DXA) measurement of visceral adipose tissue (DXA-VAT) as a low cost and low radiation alternative to computed tomography (CT). DXA-VAT was compared to VAT assessed using CT by an expert reader (E-VAT). In addition, the same CT slice was also read by a clinical radiographer (C-VAT) and a best-fit anthropomorphic and demographic VAT model (A-VAT) was developed. Whole body DXA, CT at L4-L5, and anthropometry were measured on 272 black and white South African women (age 29 ± 8 years, BMI 28 ± 7 kg/m(2), waist circumference (WC) 89 ± 16 cm). Approximately one-half of the dataset (n = 141) was randomly selected and used as a training set for the development of DXA-VAT and A-VAT, which were then used to estimate VAT on the remaining 131 women in a blinded fashion. DXA-VAT (r = 0.93, standard error of the estimate (SEE) = 16 cm(2)) and C-VAT (r = 0.93, SEE = 16 cm(2)) were strongly correlated to E-VAT. These correlations with E-VAT were significantly stronger (P < 0.001) than the correlations of individual anthropometry measurements and the A-VAT model (WC + age, r = 0.79, SEE = 27 cm(2)). The inclusion of anthropometric and demographic measurements did not substantially improve the correlation between DXA-VAT and E-VAT. DXA-VAT performed as well as a clinical read of VAT from a CT scan and better than anthropomorphic and demographic models.     

A Monte Carlo simulation for the estimation of patient dose in rest and stress cardiac computed tomography with a 320-detector row CT scanner

PurposeTo estimate organ dose and effective dose for patients for cardiac CT as applied in an international multicenter study (CORE320) with a 320-Detector row CT scanner using Monte Carlo (MC) simulations and voxelized phantoms. The effect of positioning of the arms, off-centering the patient and heart rate on patient dose was analyzed.MethodsA MC code was tailored to simulate the geometry and characteristics of the CT scanner. The phantoms representing the adult reference male and female were implemented according to ICRP 110. Effective dose and organ doses were obtained for CT acquisition protocols for calcium scoring, coronary angiography and myocardial perfusion.ResultsFor low heart rate, the normalized effective dose (E) for cardiac CT was higher for female (5.6 mSv/100 mAs) compared to male (2.2 mSv/100 mAs) due to the contribution of female breast tissue. Averaged E for female and male was 11.3 mSv for the comprehensive cardiac protocol consisting of calcium scoring (1.9 mSv); coronary angiography including rest cardiac perfusion (5.1 mSv) and stress cardiac perfusion (4.3 mSv). These values almost doubled at higher heart rates (20.1 mSv). Excluding the arms increased effective dose by 6–8%, centering the patient showed no significant effect. The k-factor (0.028 mSv/mGy.cm) derived from this study leads to effective doses up to 2–3 times higher than the values obtained using now outdated methodologies.ConclusionMC modeling of cardiac CT examinations on realistic voxelized phantoms allowed us to assess patient doses accurately and we derived k-factors that are well above those published previously.     

Harmonizing finite element modelling for non-invasive strength estimation by high-resolution peripheral quantitative computed tomography

The finite element (FE) method based on high-resolution peripheral quantitative computed tomography (HR-pQCT) use a variety of tissue constitutive properties and boundary conditions at different laboratories making comparison of mechanical properties difficult. Furthermore, the advent of a second-generation HR-pQCT poses challenges due to improved resolution and a larger region of interest (ROI). This study addresses the need to harmonize results across FE models. The aims are to establish the relationship between FE results as a function of boundary conditions and a range of tissue properties for the first-generation HR-pQCT system, and to determine appropriate model parameters for the second-generation HR-pQCT system. We implemented common boundary conditions and tissue properties on a large cohort (N = 1371), and showed the relationships were highly linear (R² > 0.99) for yield strength and reaction force between FE models. Cadaver radii measured on both generation HR-pQCT with matched ROIs were used to back-calculate a tissue modulus that accounts for the increased resolution (61 µm versus 82 µm), resulting in a modulus of 8748 MPa for second-generation HR-pQCT to produce bone yield strength and reaction force equivalent to using 6829 MPa for first-generation HR-pQCT. Finally, in vivo scans (N = 61) conducted on both generations demonstrated that the larger ROI in the second-generation system results in stronger bone outcome measures, suggesting it is not advisable to convert FE results across HR-pQCT generations without matching ROIs. Together, these findings harmonize FE results by providing a means to compare findings with different boundary conditions and tissue properties, and across scanner generations.     

A method for the quantitative measurement of cell aggregation

It is demonstrated that formation of cellular aggregates in a slowly rotating suspension is accompanied by a decrease in total cell concentration in the top layer of the suspension. Both the average particle size and the initial cell concentration of the homogeneous suspension, are parameters which determine the magnitude of the effect.The method is exemplified by

1. 1. aggregation of HeLa cells after treatment with neuraminidase;

2. 2. agglutination of HeLa cells with concanavalin A;

3. 3. agglutination of human erythrocytes with poly- -lysine;

4. 4. agglutination of human erythrocytes with poly- -lysine following pretreatment with neuraminidase.

     

Peripheral quantitative computed tomography at the distal radius: cross-calibration between two scanners

Peripheral quantitative computed tomography (pQCT) is an important technique to study the interaction between the muscle and bone systems. We have recently established pQCT reference ranges for children, adolescents and young adults using a recent version (XCT 2000) of the Stratec scanners (Stratec Inc., Pforzheim, Germany). However, the previous version of this type of scanner (XCT 900) is still widely used and cross-calibration is needed to use these reference data. Therefore, both distal radii of 19 healthy subjects (age 21 to 59 years; 11 women) were analyzed at the "4% site" using both the XCT 900 and the XCT 2000. Cross-sectional area, total and trabecular bone mineral density (BMD), total bone mineral content (BMC) and polar Strength-Strain Index (SSI) results from the two scanners were compared using linear regression analysis. To achieve scanner calibration we used the intercept and slope of the correlations. The correlation coefficients between the two devices were 0.82 for the cross-sectional area, 0.81 for total BMD, 0.97 for trabecular BMD, 0.99 for total BMC and 0.86 for polar SSI. In conclusion, these data allow for the conversion of XCT 900 results at the distal radius to XCT 2000 values and vice versa.     

Non-invasive measurement of coronary heart disease using electron beam computed tomography

PURPOSE OF REVIEW: Electron beam computed tomography is a non-invasive investigation that can quantify calcification within the walls of coronary arteries. Coronary arteries remodel to maintain luminal integrity, so that significant plaque may be present before the development of luminal stenoses. This has led to interest in techniques that assess the coronary artery wall, rather than the lumen. This review examines the power of coronary calcification detected by electron beam computed tomography to predict coronary heart disease events, and outlines recent studies in which it has been used as a surrogate marker for coronary heart disease. RECENT FINDINGS: The predictive power of coronary calcification has been shown to exceed that of traditional coronary heart disease risk factors and possibly also coronary angiography. This may justify the use of coronary calcification as a surrogate marker for coronary heart disease, and studies have thus examined cross-sectional associations between coronary calcification and potential risk factors in healthy individuals and patients with diabetes, end-stage renal failure and familial hypercholesterolaemia. Intervention studies can use the rate of change of coronary calcification detected by serial electron beam computed tomography imaging as an end-point, rather than relying on coronary heart disease events. As every participant reaches an end-point, sufficient power can be attained with smaller numbers at substantially less cost. SUMMARY: Coronary calcification detected by electron beam computed tomography may prove an invaluable tool in the selection of at-risk individuals suitable for primary prevention, and a useful surrogate marker for coronary heart disease in clinical trials.     

A new cone-beam computed tomography dosimetry method providing optimal measurement positions: A Monte Carlo study

PurposeThe conventional weighted computed tomography dose index (CTDI_w) may not be suitable for cone-beam computed tomography (CBCT) dosimetry because a cross-sectional dose distribution is angularly inhomogeneous owing to partial angle irradiations. This study was conducted to develop a new dose metric (f(0)^CB_w) for CBCT dosimetry to determine a more accurate average dose in the central cross-sectional plane of a cylindrical phantom using Monte Carlo simulations.MethodsFirst, cross-sectional dose distributions of cylindrical polymethyl methacrylate phantoms over a wide range of phantom diameters (8–40 cm) were calculated for various CBCT scan protocols. Then, by obtaining linear least-squares fits of the full datasets of the cross-sectional dose distributions, the optimal radial positions, which represented measurement positions for the average phantom dose, were determined. Finally, the f(0)^CB_w method was developed by averaging point doses at the optimal radial positions of the phantoms. To demonstrate its validity, the relative differences between the average doses and each dose index value were estimated for the devised f(0)^CB_w, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ResultsThe relative differences between the average doses and each dose index value were within 4.1%, 16.7%, and 11.9% for the devised, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ConclusionsThe devised f(0)^CB_w value was calculated by averaging four “point doses” at 90° intervals and the optimal radial positions of the cylindrical phantom. The devised method can estimate the average dose more accurately than the previously developed CTDI_w methods for CBCT dosimetry.