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S Prevrhal

Publications and source records attributed to S Prevrhal.

4 recordsLinked to original sources
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↗
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↗
PubMed1999

Accuracy limits for the determination of cortical width and density: the influence of object size and CT imaging parameters.

In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness. Two different bone-mimicking phantoms with varying cortical thickness were scanned with single-slice CT on a Somatom Plus 4 scanner. Images were reconstructed with both a standard and a high-resolution convolution kernel. Two special operator-independent segmentation methods were used to automatically detect the edges of the cortical shell. We measured cortical thickness and density and compared the phantom measurements with theoretical computations by simulating a cross-sectional shape of the cortical shell. Based on the simulations, we calculated CT's power to detect small changes in cortical thickness. Simulations and phantom measurements were in very good agreement. Cortical thickness could be measured with an error of less than 10% if the true thickness was larger than 0.9 (0.7) mm for the standard (high-resolution) kernel which is close to the full width at half maximum (FWHM) of the point spread functions for these kernels and our scanner. Density measurements yielded errors of less than 10% for true cortical thickness values above two to three times the FWHM corresponding to 2.5 (2) mm in our case. The simulations showed that a 10% change in cortical width would not be detected with satisfying probability in bones with a cortical shell thinner than 1.2 mm. An accurate determination of the cortical thickness is limited to bones with a thickness higher than the FWHM of the scanner's point spread function. Therefore, the use of a high-resolution reconstruction kernel is crucial. Cortical bone mineral density can only be measured accurately in bones two to three times thicker than this number. In thinner bones, the measured density becomes dependent on the thickness. Changes in cortical thickness can only be assessed if the change is rather large or if the measured bone has sufficient thickness. Therefore, assessing density or thickness of the vertebral shell by CT should be treated with caution.

Bone Density↗