© International Commission on Radiation Units and Measurements 2009
6. Quantitative Computed Tomography
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6.1 Introduction
In the context of the present Report, quantitative computed tomography (QCT) is referred to as a dedicated computed tomography (CT) technique to determine bone mineral density (BMD). Quantitative computed tomography was introduced shortly after the first CT scanner had been realized (Hounsfield, 1973) and was developed in parallel for the lumbar spine (Genant and Boyd, 1977) using clinical scanners and for the proximal radius (Rüegsegger et al., 1974) using smaller dedicated forearm scanners. All of these scanners worked in single-slice mode. For each acquired slice, a CT image is reconstructed in which dedicated regions of interest (ROIs) are analyzed. The linear attenuation coefficients within the ROI are calibrated to BMD. As decisive advantages, QCT offers an exact three-dimensional localization of the
6.2 CT Physics Relevant to QCT
6.2.1 Single-Energy QCT
6.2.2 Dual-Energy QCT
6.2.3 Scan Modes
6.3 QCT of the Lumbar Spine
6.3.1 Equipment and Data Acquisition
6.3.1.1 Localizer Radiograph
6.3.1.2 CT Images
6.3.2 Quantitative Image Analysis
6.3.2.1 Regions of Interest
Trabecular Bone
Cortical Bone
6.4 Peripheral QCT
6.4.1 Equipment and Data Acquisition
6.4.2 Quantitative Image Analysis
6.5 Volumetric QCT
6.6 Performance Measures
6.6.1 Sources of Error
6.6.1.1 Trueness
Spatial Resolution
Fat Error
Beam Hardening, Scatter, and Field Inhomogeneities
Patient Obesity
6.6.1.2 Precision
Image Noise
Patient Position and Movement
Data analysis
Recommendations to Improve Precision
6.6.2 Reference Data
6.7 Standardization