Abstract:
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Purpose: QCT is unique in giving separate volumetric density measurements of
cortical and trabecular bone. Volumetric density measurements are important in
children, as they are not influenced by growth and bone size. The main
limitations have been the inability to scan different anatomical sites, patient
movement due to long examination times and radiation dose. Spiral CT enables a
volume of image data to be acquired in approximately 60 seconds. Recent
developments in QCT software permit both conventional 2D and 3D QCT techniques.
Methods and Materials: 3D QCT was applied to children (n=20, aged 5-19 years)
with disabling conditions, ranging from hemiplegia, athetosis to severe
epilepsy who were part of two studies investigating the effects of weight-bearing
exercise on the skeleton. The tibial site was chosen because this is where the
effect of the interventions would be presumed to be the greatest. Scanning with
conventional DXA and pQCT proved impossible due to long scan times, involuntary
movement and limb contractures. Therefore 3D QCT (Philips Medical Systems
SR-400) was applied to the lumbar spine (L1-L3) and to the proximal tibia. Scan
analysis was performed using QCT-Pro (Mindways Software Inc) and BonAlyse
(Jyvaskyla, Finland). Scan protocol: The tibiae were placed over the
calibration phantom (Mindways), the limb to be scanned was wrapped in a gel
bag. This simulates soft tissue and reduces streak artefacts. A PA scan
projection radiograph was taken from the knee joint to the upper third of the tibia
and sections prescribed from the tibial plateau and 87mm distally (maximum
number of slices = 30). Scans were also performed on 2 or 3 lumbar vertebrae.
CT measurements were obtained at 120kV, 50mA, 2s scan time, 3mm slice width,
3mm table increment, spiral CT mode pitch =1, scan field of view = 420. The
radiation dose was 85 microSv for the two sites. Standardised precision for
repeat analysis of scans was 0.88% tibia; 0.9% spine.
Results: In 19 patients volumetric BMD (vBMD) of the spine and proximal tibia
and tibial diaphyseal cortical bone were measured. After 6 months of low
magnitude mechanical loading (vibrating plates) vBMD in the tibia increased by
18%; no significant changes were observed in the spine or the tibial diaphysis
Conclusion: 3D QCT enables bone density studies to be feasible where other
methods may be technically impossible, and this study has confirmed increase in
tibial vBMD through non-pharmacological intervention.
(C.T.R. is a consultant for Exogen Smith and Nephew.)
Questions about this event email: kate.ward@man.ac.uk
Adams MD, J,
Changes In Bone Mineral Density Using 3D QCT of the Tibia and Lumbar Spine in Children with Disabling Conditions Using Low Magnitude Mechanical Loading. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3106316.html
