Vertebral mineral determination by quantitative computed tomography (QCT): accuracy of single and dual energy measurements.

Quantitative CT (QCT) studies of trabecular vertebral bone tissue have been carried out in vitro on a GE CT/T 9800 scanner. Results of both single energy (SE) 80 kVp and dual energy (DE) 80/140 kVp QCT data are compared with chemical mineral analysis to determine accuracy. We examined 62 vertebral specimens, from 28 cadavers (19 male and 9 female with an age range of 19-93 years, mean = 60.4). Averaging the results of all vertebral bodies of the same individual for SEQCT versus ashweight, we found a correlation coefficient (r) of 0.94 (p less than 0.0001), a standard error of the estimate (SEE) of 12.2 mg/cm3 (calibrated to K2HPO4), with a coefficient of variation (CV) of 13.2% and an average underestimation of bone mineral content of 18.7 mg/cm3. The corresponding DEQCT results were r = 0.98 (p less than 0.0001), SEE = 7.4 mg/cm3, CV = 7.0%, and an average underestimation of 4.9 mg/cm3. The SE and DE results are correlated with r = 0.98 (p less than 0.0001), SEE = 8.0 mg/cm3, and CV = 8.7%. From our SEQCT data and the results of the chemical analysis of bone mineral and fat content we calculated a fat sensitivity of 7.7 mg/cm3 K2HPO4 per 100 mg/cm3 fat change for our scanner. Using an average fat variability of 87.5 mg/cm3, this leads to a fat-related uncertainty for the normative SEQCT data of 6.7 mg/cm3, which is far lower than the normal biological variation of 29.4 mg/cm3. Using tabulated normative data on fat content versus age and versus mineral content of 188 vertebral specimens from five collaborating centers, we derived a correction algorithm for QCT measurement that reduces our average underestimation to 0.88 mg/cm3 with an SEE of 12.1 mg/cm3. Hence, this correction procedure can be used to estimate the fat corrected absolute mineral density for research purposes or for scanners with high fat sensitivity. For the GE CT/T 9800 scanner, with a relatively low fat to mineral sensitivity at 80 kVp, the correction procedure is generally not recommended for clinical studies since it minimizes the average fat induced error but does not reduce the residual, partially fat related uncertainty. Finally, since the fat related uncertainty is small compared to biological variation, the correlation is high between SEQCT and DEQCT, and the radiation dose is lower and the precision higher for SEQCT, we suggest that most clinical diagnostic studies using the GE CT/T 9800 scanner for bone mineral determination employ SEQCT at 80 kVp.

Bone mineral content in early-postmenopausal and postmenopausal osteoporotic women: comparison of measurement methods.

To investigate associations among methods for noninvasive measurement of skeletal bone mass, we studied 40 healthy early postmenopausal women and 68 older postmenopausal women with osteoporosis. Methods included single- and dual-energy quantitative computed tomography (QCT) and dual-photon absorptiometry (DPA) of the lumbar spine, single-photon absorptiometry (SPA) of the distal third of the radius, and combined cortical thickness (CCT) of the second metacarpal shaft. Lateral thoracolumbar radiography was performed, and a spinal fracture index was calculated. There was good correlation between QCT and DPA methods in early postmenopausal women and modest correlation in postmenopausal osteoporotic women. Correlations between spinal measurements (QCT or DPA) and appendicular cortical measurements (SPA or CCT) were modest in healthy women and poor in osteoporotic women. Measurements resulting from one method are not predictive of those by another method for the individual patient. The strongest correlation with severity of vertebral fracture is provided by QCT; the weakest, by SPA. There was a high correlation between single- and dual-energy QCT results, indicating that errors due to vertebral fat are not substantial in these postmenopausal women. Single-energy QCT may be adequate and perhaps preferable for assessing postmenopausal women. The measurement of spinal trabecular bone density by QCT discriminates between osteoporotic women and younger healthy women with more sensitivity than measurements of spinal integral bone by DPA or of appendicular cortical bone by SPA or CCT.

Osteoporosis: assessment by quantitative computed tomography.

The results presented in this article indicate that quantitative computed tomography provides a reliable means of evaluating and monitoring the many forms of osteoporosis and its various treatments. The greatest advantages of spinal QCT for noninvasive bone mineral measurement are its high precision, the high sensitivity of the vertebral spongiosa measurement site, and the potential for widespread application.

Quantitative computed tomography for spinal mineral assessment: current status.

Quantitative CT (QCT) is an established method for the noninvasive assessment of bone mineral content in the vertebral spongiosum and other anatomic locations. The potential strengths of QCT relative to dual photon absorptiometry (DPA) are its capability for precise three-dimensional anatomic localization providing a direct density measurement and its capability for spatial separation of highly responsive cancellous bone from less responsive cortical bone. The extraction of this quantitative information from the CT image, however, requires sophisticated calibration and positioning techniques and careful technical monitoring.

Assessment of metabolic bone diseases by quantitative computed tomography.

Advances in the radiologic sciences have permitted the development of numerous noninvasive techniques for measuring the mineral content of bone, with varying degrees of precision, accuracy, and sensitivity. The techniques of standard radiography, radiogrammetry, photodensitometry, Compton scattering, neutron activation analysis, single and dual photon absorptiometry, and quantitative computed tomography (QCT) are described and reviewed in depth. Results from previous cross-sectional and longitudinal QCT investigations are given. They then describe a current investigation in which they studied 269 subjects, including 173 normal women, 34 patients with hyperparathyroidism, 24 patients with steroid-induced osteoporosis, and 38 men with idiopathic osteoporosis. Spinal quantitative computed tomography, radiogrammetry, and single photon absorptiometry were performed, and a spinal fracture index was calculated on all patients. The authors found a disproportionate loss of spinal trabecular mineral compared to appendicular mineral in the men with idiopathic osteoporosis and the patients with steroid-induced osteoporosis. They observed roughly equivalent mineral loss in both the appendicular and axial regions in the hyperparathyroid patients. The appendicular cortical measurements correlated moderately well with each other but less well with spinal trabecular QCT. The spinal fracture index correlated well with QCT and less well with the appendicular measurements. Knowledge of appendicular cortical mineral status is important in its own right but is not a valid predictor of axial trabecular mineral status, which may be disproportionately decreased in certain diseases. Quantitative CT provides a reliable means of assessing the latter region of the skeleton, correlates well with the spinal fracture index (a semiquantitative measurement of end-organ failure), and offers the clinician a sensitive means of following the effects of therapy.

Study of bolus geometry after intravenous contrast medium injection: dynamic and quantitative measurements (Chronogram) using an X-ray CT device.

An X-ray computed tomographic (CT) scanner was used to measure and image transmission profiles of a single 8 mm thick object slice digitally with a high temporal (up to 20 ms), spatial (1.1 mm), and density (0.5%) resolution. This special digital radiography imaging mode is called a Chronogram. It produces a time-history of measured attenuation values but not a normal anatomical image. After intravenous bolus injection of contrast medium, bolus shape as a function of time and bolus passage times can be imaged. Absolute iodine concentrations in blood vessels and soft tissue can be evaluated at any time in all body regions. The Chronogram has the potential to quantify physiological parameters such as enhancement, passage times, and relative blood flow through pairs of arteries or symmetrically arranged organs and to measure absolute iodine concentrations. As a disadvantage, patient motion can prevent quantitative evaluation. This drawback can, however, be turned into an advantage in that all kinds of motion can be measured, for example, movement and pulsation of the heart.

Computed tomography of the adrenal glands.

Whole body CT opens a third dimension-in addition with the advantage of being a non-invasive method with relatively negligible risk. Both, the normal CT findings of the adrenal gland and the normal variants in shape and position are described. With help of morphometry and image processing measurements of the size of the adrenal gland of 20 healthy patients were made and are listed; not only the respective normal variants but also hypo-hyperplasia are pointed out. Some examples are suitable for the illustration of pathologic conditions, such as inflammation and benign and malignant primary and secondary neoplasis. Finally, the value of adrenal gland CT is discussed with reference to the other radiologic methods.

[CT and conventional radiography in the evaluation of bony lesions (author's transl)]. / Computertomographische und koneventionelle radiologische Untersuchungen bei Knochenerkrankungen.

Several cases selected from a group of 67 patients with bony lesions (primary benign and malignant neoplasia, secondary neoplasia and metabolic disorders) serve to demonstrate the significant information gained by CT compared to that gained by conventional radiographic methods including angiography and bone scanning. CT is advantageous in showing the exact intra- and extraosseous extent of the lesion--helpful for further diagnosis and therapy. Measurements of length, area, volume and density can help to narrow down the differential diagnosis and they aid in follow-up examinations. CT supplements conventional radiographic methods and in some cases may even replace them, e.g. angiography.

[Investigations of the mineral topography in human vertebral bodies. A comparison of results derived from bone-ashing, photodensitometry and attenuation coefficients by CT (author's transl)]. / Untersuchungen der Mineraltopographie am menschlichen Wirbelkörper mit der Röntgen-Computer-Tomographie.

A method for the in vivo investigation of the mineral distribution in human vertebral bodies by the aid of computed tomography is presented. The attenuation coefficients resulting from transversal tomograms of vertebral spongiosa are compared with the results of bone ashing from in vitro investigations. Computed tomography values, ash weights and photodensitometric values show a high degree of correlation.

[Effect and quantification of respiratory movement of abdominal organs on x-ray computer tomography (author's transl)]. / Einfluss und Quantifizierung der Atemverschieblichkeit von abdominellen Organen bei der Röntgencomputertomographie.

The effect of respiratory movement of abdominal organs on computer tomography is illustrated. Methods for an objective evaluation of the reproducibility of tomograms are presented. A procedure for the quantitative determination of the respiratory movement of abdominal organs using computer tomography is described.

[Computer assisted tomography of the normal and abnormal adrenal gland (author's transl)]. / Die gesunde und kranke Nebenniere im Röntgen-Computer-Tomogramm.

Initially, the hitherto existing radiographic methods of investigating the adrenal gland are demonstrated. Whole body CT opens a third dimension--in addition to being a non invasive method without risk. The normal CT findings of the adrenal gland are described, as well as the normal variants in shape and position. With help of morphometry and image manipulation, measurements of the size of the adrenal gland in 20 healthy patients were made and are being listed; and the respective normal variants as well as hypo- and hyperplasia are pointed out. Some examples serve to illustrate pathologic conditions, such as inflammation and benign and malignant primary and secondary neoplasia. Finally, the value of adrenal gland CT is discussed in reference to the other existing respective radiographic methods.