© International Commission on Radiation Units and Measurements 2009
5. X-ray Absorptiometry
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5.1 Introduction
In Sections 5, 6, and 7, the physics, techniques, and implementations of the three modalities absorptiometry, computed tomography, and ultrasound and their applications in bone densitometry are described. In order to better compare the modalities, the structure of the chapters is similar. Each starts with a review of the relevant physical concepts and then describes available equipment and modes of data acquisition. Afterwards, numbers for the performance measures introduced in the previous chapters are discussed for specific techniques and implementations of the modality under consideration. This is concluded with a section on reference data.
In the context of the present report, two meanings of the term absorptiometry are important. In general, absorptiometry refers to mechanisms of how photons or more specifically gamma
5.2 Physics of Absorptiometry
5.2.1 Sources of Systematic Errors
5.2.2 Single-Energy Absorptiometry
5.2.3 Dual-Energy Absorptiometry
5.3 Radiographic Absorptiometry
5.3.1 Equipment and Data Acquisition
5.3.1.1 Skeletal Sites
5.3.1.2 Image Formation
5.3.1.3 Image Calibration and Analysis
5.3.2 Performance Measures
5.3.2.1 Trueness
Calibration
Beam Hardening and Scatter
Soft Tissue
5.3.2.2 Imprecision
Patient Position and Movement
5.3.3 Reference Data
5.4 Radiogrammetry
5.4.1 Equipment and Data Acquisition
5.4.1.1 Image Formation
5.4.1.2 Image Analysis
5.4.1.3 Digital X-ray Radiogrammetry
5.4.2 Performance Measures
5.4.2.1 Trueness
Magnification
Assumption of Circular Geometry
5.4.2.2 Precision
Patient Position and Movement
Data Analysis
Recommendations
5.4.3 Reference Data
5.5 Single- and Dual-Energy X-ray Absorptiometry
5.5.1 Equipment
5.5.1.1 X-ray Sources
Voltage Switching
K-edge Filtering
5.5.1.2 Detectors
Photomultiplier Tubes
Solid-State Detectors
5.5.2 Data Acquisition
5.5.2.1 Imaging Geometry
Pencil Beam Systems
Fan Beam Systems
Cone Beam Systems
5.5.2.2 Skeletal Sites
Proximal Femur
Lateral Spine
Forearm
Whole Body
Other Applications of DXA
5.5.3 Performance Measures
5.5.3.1 Trueness
Soft Tissue Composition and Baseline Measurement
Beam Hardening
Patient Obesity, Weight Change, and Bone Size
Degenerative Changes
Strontium
Other Artifacts
Note on Trueness
5.5.3.2 Imprecision
Patient Position and Movement
Spatial Resolution
Data Analysis
5.5.4 Reference Data
5.5.5 Standardization
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