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PubMed1998

[Age-related changes of densitometric and strength parameters evaluated with QCT method in healthy women].

In the present study the age-related changes of pQCT values in normal Polish women were examined. The volumetric bone mineral density, trabecular density, cortical density and Strength Strain Index was measured using peripheral quantitative computed tomography (Stratec XCT 960) in 459 healthy women aged 18-60 years. Bone mineral measurement of the distal and proximal radius may be useful in evaluation of age-related bone loss, fracture risk and for diagnosis of osteoporosis.

Absorptiometry, Photon↗
PubMed1994

[Influence of bone marrow fat on the determination of bone mineral content by QCT].

Single-energy quantitative CT (SEQCT) is thought to be suitable for long-term observation of changes in bone mineral content in individual patients. However, in patients with osteoporosis, an increase in bone marrow fat cannot be ignored. The relationship between bone marrow fat and bone mineral density (BMD) at different tube voltages of 80 kV and 120 kV was investigated using a set of solution phantoms that we devised, and was also studied in healthy volunteers. On the basis of the results obtained using the solution phantoms, the influence of bone marrow fat accounted for a decrease of 8.9 mg/cm3 in BMD value at 80 kV and of 10.8 mg/cm3 at 120 kV in the presence of 10 vol% fat. These findings suggested that the influence of fat was less at a lower tube voltage. The formulas used to estimate the true bone mineral and fat contents from the BMD values at low and high tube voltages were derived by eliminating the influence of beam hardening. Using these formulas, we studied healthy volunteers, and found that the difference between the true BMD value and the BMD value calibrated for beam hardening averaged 17.8 mg/cm3 at 80 kV and 22.6 mg/cm3 at 120 kV. Moreover, the estimated concentration of bone marrow fat in the volunteers averaged 25.0 vol%. In conclusion, because SEQCT performed at a low tube voltage is less influenced by bone marrow fat, it should be selected for assessment of the clinical response to therapy and for studying sequential changes. However, in patients with a low bone mineral content indicated by SEQCT, it would be worthwhile trying to estimate both true mineral and fat contents in bone using the formulas obtained in this study in order to differentiate decrease in bone mineral from interference by bone marrow fat.

Adult↗
PubMed2006

Cumulative reaction probabilities: A comparison between quasiclassical and quantum mechanical results.

This article presents a quasiclassical trajectory (QCT) method for determining the cumulative reaction probability (CRP) as a function of the total energy. The method proposed is based on a discrete sampling using integer values of the total and orbital angular momentum quantum numbers for each trajectory and on the development of equations that have a clear counterpart in the quantum mechanical (QM) case. The calculations comprise cumulative reaction probabilities at a given total angular momentum J, as well as those summed over J. The latter are used to compute QCT rate constants. The method is illustrated by comparing QCT and exact QM results for the H+H2, H+D2, D+H2, and H+HD reactions. The agreement between QCT and QM results is very good, with small discrepancies between the two data sets indicating some genuine quantum effects. The most important of these involves the value of the CRP at low energies which, due to the absence of tunneling, is lower in the QCT calculations, causing the corresponding rate constants to be smaller. The second is the steplike structure that is clearly displayed in the QM CRP for J = 0, which is much smoother in the corresponding QCT results. However, when the QCT density of reactive states, i.e., the derivatives of the QCT CRP with respect to the energy, is calculated, a succession of maxima and minima is obtained which roughly resembles those found in the QM calculations, although the latter are considerably sharper. The analysis of the broad peaks in the QCT density of reactive states indicates that the distributions of collision times associated with the maxima are somewhat broader, with a tail extending to larger collision times, than those associated with the minima. In addition, the QM and QCT dynamics of the isotopic variants mentioned above are compared in the light of their CRPs. Issues such as the compliance of the QCT CRP with the law of microscopic reversibility, as well as the similarity between the CRPs for ortho and para species in the QM and QCT cases, are also addressed.

Journal Article↗
PubMed1998

Vertebral bone density evaluated by dual-energy X-ray absorptiometry and quantitative computed tomography in vitro.

Vertebral bone density is evaluated mainly by dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Densitometry is used as an estimator of bone strength and forms the basis for choice of treatment. DXA expresses bone density in grams per square centimeter (area density) and QCT expresses bone density in milligrams per cubic centimeter (volumetric density). The aim of this study was to identify the differences between the two techniques, DXA and QCT, when applied to a group of female and male subjects over a wide age range. The data consisted of 221 lumbar vertebral bodies (L3 and L4) excised at autopsy. There were 90 females with a mean age of 65.6 (range 18-94) years and 131 males with a mean age of 62.0 (range 21-94) years. The vertebrae were scanned en bloc in demineralized water in Plexiglas containers with both DXA and QCT. DXA was performed using posteroanterior (PA) and lateral projection. QCT was performed in the center of each vertebra with 1 cm slice thickness. Both methods showed decreasing bone density with age. Lateral DXA showed a decrease in bone density with age from approximately 0.8 g/cm2 to approximately 0.4 g/cm2. QCT showed a decrease in bone density with age from approximately 180 mg/cm3 to approximately 30 mg/cm3. Lateral DXA bone mineral densities (BMD) were correlated with QCT densities in both females (r2 = 0.68, p < 0.00001) and males (r2 = 0.53, p < 0.00001), but females had constantly lower DXA BMDs than males at a given QCT density. QCT and width-adjusted midlateral DXA (g/cm3) were significantly correlated, with r2 = 0.64 (p < 0.00001) for females and r2 = 0.61 (p < 0.00001) for males. In conclusion, age- and gender-related differences in human vertebral bone density were shown to be dependent on the scanning method used. DXA bone mineral content (BMC) and BMD showed that females had lower values than males at all ages. When the "volumetric" DXA measurements and QCT were used, the females had the highest densities in the younger decades and males had the highest densities in the oldest decades. Finally, the area density (BMD) measured by DXA was lower in females than in males with identical QCT volumetric bone densities.

Absorptiometry, Photon↗
PubMed2006

Volumetric quantitative computed tomography of the proximal femur: relationships linking geometric and densitometric variables to bone strength. Role for compact bone.

INTRODUCTION: In assessing cervical fractures of the proximal femur, this in vitro quantitative computed tomography (QCT) study had three objectives: to compare QCT to dual-energy X-ray absorptiometry (DXA) for predicting the failure load of the proximal femur, to compare the contributions of density and geometry to bone failure load, and to compare the contributions of cortical and trabecular bone to bone failure load. A novel three-dimensional (3D) analysis tool [medical image analysis framework (MIAF-Femur)] was used to analyze QCT scans. METHODS: The proximal ends of 28 excised femurs were studied (1) using QCT to separately measure bone mineral density (BMD) and geometric variables of trabecular and cortical bone, (2) using mechanical tests to failure in a stance configuration, and (3) using DXA to measure BMD. The variables were described with mean, standard deviation, and range. Correlation matrix and multivariate linear models were computed. RESULTS: Among correlations, cortical thicknesses of the femoral neck were significantly correlated with femoral failure load, especially of the inferoanterior quadrant (r2=0.41; p<0.001), as was cortical volume at the "extended neck" (r2=0.41; p<0.001). Femoral failure load variance was best explained by a combination of QCT variables. Combining densitometric and geometric variables measured by QCT explained 76% of femoral failure load variance compared with 69% with the DXA model. Geometric variables (measured by QCT) explained 43% of femoral failure load variance compared with 72% for densitometric variables (measured by QCT). A model including only trabecular variables explained 52% of femoral failure load variance compared with 59% for a model including only cortical variables. CONCLUSION: The QCT-MIAF reported here provides analysis of both geometric and densitometric variables characterizing cortical and trabecular bone. Confirmation of our results in an independent sample would suggest that QCT may better explain failure load variance for cervical fracture than the gold standard DXA-provided BMD.

Absorptiometry, Photon↗
PubMed2000

Interaction of the antioxidant flavonoid quercetin with planar lipid bilayers.

Our capacitance and conductance measurements on reconstituted planar lipid bilayers (BLM) suggest an insertion of the flavonoid quercetin (QCT) in the membranes, which is concentration- and pH-dependent. Interaction of the flavonoid with the membrane has no impact on either structure or integrity of the lipid bilayer. The QCT molecules penetrate the lipid bilayer by intercalating between the flexible acyl chains of the phospholipids, the deepest insertion occuring in acidic medium, when QCT is neutral and completely liposoluble. Results indicated that aggregation of QCT within the hydrophobic core is accompanied by an increase of the transmembrane conductance following an alteration of the hydrophobic barrier for small electrolytes. By contrast, within alkaline media where QCT is deprotonated, the reaction site of the flavonoid is restricted to the hydrophilic domain of the membrane. This significantly changes the double layer capacitance as the negatively charged QCT molecules become sandwiched between polar headgroups at the bilayer surface. At highest alkaline pH, the transmembrane conductance was not affected, since QCT did not perturb the molecular packing of the hydrocarbonic acyl chains of the phospholipids. Results also demonstrated that changes in physical properties of the lipid bilayers following interstitial QCT embedding within either the hydrophobic domain or the polar headgroup domain may be related to both its lipophilic nature and interactions with the electric dipole moments of the polar headgroups of phospholipids. Data also demonstrated that translocation of QCT in the polar part of the lipid bilayer, at physiological pH and salt conditions, may be correlated with its optimized radical scavenging activity. This paper discusses the significance of the free radical scavenging capacity and antioxidant efficiency of QCT.

Antioxidants↗
PubMed2001

Quantitative ultrasound of the tibia depends on both cortical density and thickness.

This study investigated whether tibial speed of sound (SOS; SoundScan 2000, Myriad Ultrasound Systems, Israel) reflects not only bone mineral density (BMD) but also tibial cortical thickness, as assessed by dual-energy X-ray absorptiometry (DXA) and Quantitative CT (QCT) at a site-matched location. The secondary focus of the study was how tibial SOS compares with BMD at the spine and the hip, the most widely used locations for densitometry. Twenty-two young normal (N) and 23 postmenopausal women with spinal fractures (Fx) (mean (SD) age 35 (8) and 70 (5) years) underwent quantitative ultrasound (QUS) SOS measurement at the left tibial midshaft. From site-matched QCT scans (three 3-mm slices spaced along the QUS measurement region), BMD and cortical thickness were computed (QCT-cBMD, QCT-cTh). The cortex in the CT images was then subdivided into three concentric and equally spaced bands, and QCT-cBMD was computed separately for each band. DXA was performed at the mid-tibia (TIB BMD), at the spine (SPINE BMD) and the hip (total hip, HIP BMD). Correlation coefficients between parameters were determined with least-square linear fits. Intergroup differences were assessed by analysis of covariance, whose r2 value reflects the percentage variation in the data explained by group assignment. SOS correlated significantly with site-matched parameters (QCT-cBMD, OCT-cTh and TIB BMD, all r = 0.6, p < 0.001), SPINE BMD and HIP BMD (both r = 0.5, p < 0.001). Multiple regression with both QCT-cBMD and QCT-cTh against SOS yielded r = 0.7 with both parameters contributing significantly. For the cortex band subdivision, SOS correlated better with QCT-cBMD in the outermost band of the cortex (r = 0.67) than with the more central bands (r = 0.59 and r = 0.53). Group assignment could best explain SPINE BMD (r2 = 0.62) and HIP BMD (r2 = 0.51). SOS was comparable to TIB BMD (r2 = 0.3 vs. r2 = 0.35).: Our findings suggest that the tibial SOS measurement depends on both the thickness and density of the tibia, but is more strongly influenced by the density of the cortex near the surface than by its interior parts. The power of tibial ultrasound to discriminate between normal and fracture patients was less than that of spinal and femoral DXA BMD and comparable to site-matched DXA BMD.

Absorptiometry, Photon↗
PubMed2003

Finite element models predict in vitro vertebral body compressive strength better than quantitative computed tomography.

The correlation between bone mineral density and vertebral strength is not based on mechanical principles and thus the method cannot reflect the effects of subtle geometric features and densitometric inhomogeneities that may substantially affect vertebral strength. Finite element models derived from quantitative computed tomography (QCT) scans overcome such limitations. The overall goal of this study was to establish that QCT-based "voxel" finite element models are better predictors of vertebral compressive strength than QCT measures of bone mineral density with or without measures of cross-sectional area. QCT scans were taken of 13 vertebral bodies excised from 13 cadavers (L1-L4; age: 37-87 years; M = 6, F = 7) and used to calculate bone mineral density (BMD(QCT)). The QCT voxel data were converted into linearly elastic finite element models of each vertebra, from which measures of vertebral stiffness and strength were computed. The vertebrae were biomechanically tested in compression to measure strength. Vertebral strength was positively correlated with the finite element measures of strength (r(2) = 0.86, P < 0.0001) and stiffness (r(2) = 0.82, P < 0.0001), the product of BMD(QCT) and vertebral minimum cross-sectional area (r(2) = 0.65, P = 0.0008), and BMD(QCT) alone (r(2) = 0.53, P = 0.005). These results demonstrate that highly automated "voxel" finite element models are superior to correlation-based QCT methods in predicting vertebral compressive strength and therefore offer great promise for improvement of clinical fracture risk assessment.

Adult↗
PubMed2005

Quasi-compulsory treatment of drug dependent offenders: an international literature review.

This paper reports on a review of the literature on the quasi-compulsory treatment (QCT) of drug dependent offenders in five languages; English, German, French, Italian and Dutch. The findings of this review on previous reviews and on the availability, process, and outcomes of QCT are summarized. The review found that previous, anglophone reviews have tended to present positive outcomes from QCT, but that there are some problems with this research. QCT is increasingly available internationally, but may be applied at different stages of the criminal justice process, and to different types of offender. Research on the process of QCT is comparatively rare. The available research does suggest problems of system integration between criminal justice and treatment agencies in implementing QCT. The research in languages other than English shows a wider range of outcomes (including negative effects) for QCT than was found in the English literature. We conclude that the international literature shows that QCT does not inevitably produce worse outcome than voluntary treatment, but that we need more multimethod, multisite studies of QCT in order to inform policy and practice, which is currently being made in the absence of reliable evidence in many countries.

Crime↗
PubMed1990

Dual energy radiography versus quantitative computer tomography for the diagnosis of osteoporosis.

In this study we compared dual energy radiography (DER), a new, highly precise x-ray densitometric technique recently devised for measurements of vertebral mineral density and quantitative computer tomography (QCT), a densitometric technique that selectively measures the trabecular compartment of the vertebra. DER and QCT measurements were obtained in 56 healthy (H) and 48 fractured osteoporotic (OP) women using a Hologic QDR 1000 bone densitometer and a GE 9800 scanner, respectively. DER was significantly correlated with QCT in both the H (r = 0.75; P less than 0.0001) and the OP subjects (r = 0.58; P less than 0.0001). DER decreased significantly with age in the H (P less than 0.05), but not in the OP women, whereas QCT was related to age in both the H (P less than 0.0001) and the OP subjects (P less than 0.01). The rate of bone loss with age was also higher with QCT than with DER in both normal and osteoporotic women. The difference in bone density between the H and the OP subjects was larger (P less than 0.05) with QCT than with DER. Receiver operating characteristic analysis revealed that QCT was a better predictor of vertebral fractures than DER. A larger percentage of OP subjects were 2 SD or more below the normal predicted value with QCT (41%) than with DER (29%). Furthermore, the slopes of the regressions of bone density with age for normal and osteoporotic women were significantly different (P less than 0.05) with QCT but not with DER. These findings are consistent with a disproportionate loss of trabecular bone with age in osteoporosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

Spinal bone mineral assessment in postmenopausal women: a comparison between dual X-ray absorptiometry and quantitative computed tomography.

We compared quantitative computed tomography (QCT) and dual X-ray absorptiometry (DXA) with respect to their ability to discriminate subjects with and without prevalent vertebral fractures. In 240 post-menopausal women (mean age 63.7 +/- 6.9 years) lateral spine radiographs (T4-L4) were reviewed for the presence of vertebral fracture. Using a semiquantitative technique to grade the severity of vertebral deformities, we classified fractures as mild, moderate or severe (grade 1 to 3, respectively). Postero-anterior DXA (PA-DXA) and lateral DXA (L-DXA) measurements (L2-4) as well as QCT measurements of the lumbar spine (T12-L3 or L1-14) were obtained in all women. Seventy-two women were diagnosed with at least one fracture, and of these 40 were graded as mild. Comparing normal women with fractured women, we found the area under the receiver operating characteristics (ROC) curves to be greatest for QCT (0.81), followed by L-DXA (0.72) and PA-DXA (0.65). The differences among all three techniques were significant. Comparing the normal women with women having only mild fractures, the areas under the ROC curves were 0.79, 0.73 and 0.63 for QCT, L-DXA and PA-DXA, respectively. Significant differences existed between QCT and PA-DXA as well as between L-DXA and PA-DXA. Logistic regression analysis also revealed the highest age-adjusted odds ratios for QCT (3.67; 2.25-5.97) while L-DXA and PA-DXA showed substantially lower odds ratios (2.00; 1.39-2.87, and 1.54; 1.11-2.15, respectively). We conclude that low bone density as measured by QCT, PA-DXA or L-DXA is significantly associated with the prevalence of vertebral fractures. Of the methods studied, QCT of trabecular bone offered the best discriminatory capability. L-DXA proved to be superior to PA-DXA in its diagnostic sensitivity, particularly in women with mild fracture. Mild vertebral fractures are associated with decreased spinal bone density and may be regarded as osteoporotic deformities.

Absorptiometry, Photon↗
PubMed2000

Quantitative computed tomography in the evaluation of spinal osteoporosis following spinal cord injury.

Disuse osteoporosis occurs in the lower extremities of patients with spinal cord injury (SCI). However, spinal osteoporosis is not usually observed in these patients. We investigated lumbar spine bone mineral density (BMD) in SCI patients using single energy quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA). Our study population consisted of 64 patients with long-standing SCI. Spine BMD (g/cm3) was assessed by QCT at four vertebrae ranging from T11 to L4 with single mid-vertebral CT slices 1 cm thick parallel to the vertebral end-plates. Confounding variables affecting normal trabecular bone pattern, such as compression fractures, surgical hardware or fat replacement, were excluded. For a subset of 29 patients, DXA values of the spine and femoral neck were also measured, and QCT and DXA Z-scores were compared On the average, the 64 SCI patients had Z-scores 2.0 +/- 1.2 below those of age-matched controls. In the subset of 29 patients with both QCT and DXA measurements, the QCT and DXA Z-scores were 2.4 +/- 1.1 below and 1.3 +/- 2.3 above the mean, respectively (p < 0.0001). Our results indicate that QCT reveals osteoporosis of the spine after SCI, in contrast to DXA. We postulate that QCT is more valuable for evaluating spinal osteoporosis following SCI than DXA and thus recommend QCT for spinal BMD studies in SCI.

Absorptiometry, Photon↗
PubMed2004

Validation of thoracic quantitative computed tomography as a method to measure bone mineral density.

The purpose of this study was to measure precision of thoracic quantitative computed tomography (QCT) bone mineral density (BMD) and correlation to lumbar spine QCT bone density. We measured the reproducibility of thoracic QCT; two consecutive thoracic QCT scans of the T9, T10, and T11 vertebrae were performed on 95 subjects (49 females, 46 males; mean age, 62.5 years) undergoing coronary scanning. In order to correlate the thoracic to standard lumbar measurement, the subjects also underwent a lumbar QCT scan of the L1, L2, and L3 vertebrae as part of an abdominal aortic scanning study. The variation of thoracic BMD was assessed in different ethnic subgroups. Consecutive thoracic QCT measurements showed good agreement (r=0.98; RMS CV=5.78%). Thoracic bone density was significantly higher than lumbar bone density results (paired t-test, P=0.003), but the two methods correlated well (r=0.86). The regression equation for the relationship between lumbar (X) and thoracic (Y) QCT was Y=0.87X + 22.97. The standard error of estimate was 19.0 mg/cm3. Thoracic QCT from coronary calcium thoracic scans is able to measure BMD with rescan precision and regression errors that are small compared to the biologic variability in the population. Given the relatively small precision error and the reasonable correlation to lumbar BMD, an ancillary assessment of thoracic BMD in a cardiac scan is likely to be a useful assessment of bone mineral status in the general population.

Bone Density↗
PubMed1994

Quantitative computed tomography detects air trapping due to asthma.

OBJECTIVE: The purpose of this study was to prospectively see if quantitative computed tomography (QCT) could separate asthmatic patients from normal control subjects. The QCT results were also correlated with the pulmonary function tests (PFT) that were done on both the asthmatic patients and control subjects. SUBJECTS AND METHODS: Eighteen adult nonsmoking asthmatics and 22 adult control subjects were entered into the study. Quantitative CT was performed at the level of the transverse aorta and just above the diaphragm at both end inspiration and end expiration in all patients and control subjects: 10-mm and 1.5-mm collimation using a high spatial frequency algorithm was used to obtain the QCT examinations. The percent of pixels below -900 Hounsfeld units, pixel index, in each of the QCT axial images of the lungs was calculated for each asthmatic and control subject in the study. Pulmonary function testing was performed on both the asthmatics and control subjects and included determination of FEV1, FVC, FRC, RV, and TLC. Unpaired Student's t test analysis of the QCT data was done to statistically compare the asthmatics with the control subjects. Linear regression analysis was done to compare the QCT results with PFT data on the asthmatics and control subjects. RESULTS: When scans were performed at end expiration, at a level immediately superior to the diaphragm, the mean pixel index was significantly higher in asthmatic subjects compared with normal individuals on both CT (mean for normal subjects 0.16 vs 4.45 for asthmatics, p < 0.004) and high-resolution CT (HRCT) images (mean for normal subjects 1.04 vs 10.03 in asthmatics, p < 0.0001) indicating more areas of low attenuation in asthmatics. The CT and HRCT images from the lower lung zones that were performed at end expiration provided the best separation between the groups. The pixel index on expiration correlated with the degree of air trapping and airflow limitation in the asthmatic group based on FEV1, FRC, RV, and to a lesser extent, FVC. CONCLUSION: Expiratory QCT is a useful method to assess air trapping in asthmatic patients. The percent of abnormal lung in asthmatics as determined by QCT has a significant correlation with the PFTs that reflect air trapping in asthmatic patients. Quantitative CT may be helpful in assessing degrees of air trapping present in other diseases affecting the airways.

Adult↗
PubMed1991

[The early changes in bone mineral metabolism due to radiation--measurement of bone mineral density in lumbar vertebra by quantitative computed tomography].

Osteosclerosis, osteonecrosis and compression fracture are commonly observed several years after radiation. Since lumbago usually occurs several months after radiation, the possibility that bone mineral metabolism is disturbed during and immediately after radiation cannot be ruled out. However, there have been no reports concerning early changes in bone mineral metabolism due to radiation. The bone mineral density was measured by QCT (Quantitative Computed Tomography) in 30 normal non-radiated cases and 14 radiated cases to investigate the changes in bone mineral metabolism due to radiation. The bone mineral density (QCT-Value: QCT-V) in the 3rd lumbar vertebra (L3) of normal non-radiated subjects decreased linearly with age (Y = 291.114447-3.01473X). The QCT-V of the 5th lumbar vertebra (L5) of normal cases also decreased linearly with age (Y = 309.641397-3.03986X), resembling that of L3. The ratio of the QCT-V of L5 to L3 (L5/L3, expressed as a percentage) definitely increased with age (Y = 86.5657441 + 0.58885064X). In radiated cases, the QCT-V of L3 in the non-radiated field did not change appreciably. The QCT-V of L5 in the radiated field was decreased from 20GY and reached 53.08 +/- 17.37% of the pre-radiation value after 50GY. The L5/L3 ratio was also decreased from 20GY and reached 55.47 +/- 15.32% of the pre-radiation value after 50GY. It becomes apparent that the QCT-V of the radiated lumbar vertebra is decreased during radiation. It is suggested that bone mineral metabolism may be disturbed in the early phase of radiation.

Bone Density↗
PubMed2001

A comparison of spinal quantitative computed tomography with dual energy X-ray absorptiometry in European women with vertebral and nonvertebral fractures.

Quantitative computed tomography (QCT) was compared to dual X-ray absorptiometry (DXA) measured in the lumbar spine of 508 European women defined as normal without fracture (NoF), or osteoporotic (OP), with either vertebral fracture (VF), or peripheral fracture (PF). The correlations between QCT and DXA BMD measurements were significantly different in normal and in osteoporotic patients, indicating that the two exams do not measure the same bone aspects. According to ROC curves results, QCT Z-scores separate OP from NoF with better sensitivity than all other measurements. A threshold to differentiate OP from NoF was chosen at Z-score = -1 for DXA-BMD and -1.5 for QCT-BMD. VF patients showed a highly significant decrease in BMD by DXA or QCT. PF patients revealed measurements lower than those of normal subjects but greater than those of VF, calling into question the idea of a diffuse osteoporosis causing nonvertebral fractures that is measurable by spinal DXA or QCT. DXA is weakly dependent upon age, and T-score or Z-score are equivalent for evaluating osteoporosis. QCT depends greatly upon age, and Z-score appears to be more efficient.

Absorptiometry, Photon↗
PubMed1999

[Quantitative computer tomography].

Quantitative computed tomography (QCT) can determine the true volumetric bone density of trabecular and cortical bone separately and at any skeletal site. QCT, because of its sensitivity to changes in bone status, is widely accepted as the superior method for the axial skeleton because of the high responsiveness of spinal trabecular bone to osteoporotic changes. The precision and accuracy of QCT at this site are somewhat lower than the respective values of other densitometric techniques. Nevertheless, because QCT measures a higher rate of bone loss at early premenopausal age, it allows better estimation of risk of vertebral fracture and smaller time intervals between follow-up measurements. The clinical acceptance of QCT is constrained by limited access to CT scanners for bone densitometry, the higher degree of operator dependence and the inability of QCT to measure the femur. New developments currently in scientific trial show that using volumetric CT can increase precision of QCT at the spine and allow highly accurate, precise and meaningful measurements at the femur.

Female↗