Study On Bone Density Measurements With Fan-beam Dual Energy X-ray Sources

A method of bone density measurements utilizing dual energy X-ray absorptiometry is studied in details in this paper. X-rays from cathode-ray tube contain continuous photons and characteristic photons. Continuous photons are composed of photons with different energies. Different attenuations will happen in photons with different energies when they pass through objects. It is called beam-hardening effect. To correct the effect, ways using hardware and software are discussed in the paper. After the comparison of two ways, we choose the way using hardware. It is to get photons with approximately single energy through the prehardening process. So it is also called the equivalent energy way. In the mass thickness computations for dual component matter with X-rays, we need to solve a group of two integral equations. While the equivalent energy way will simplify the group into a new group of two linear equations and it increases the computing speed and accurancy. There are seven chapters in this paper.Chapter 1 mainly introduces the research background of DEXA (Dual Energy X-ray Absorptiometry). It introduces the concept of osteoporosis and its potential harmfuness. Several methods for bone density measurements are introduced and compared. Then the advantages of DEXA are concluded. At last, the development history of DEXA is introduced and the technical key points of fan-beam DEXA are discussed.Chapter 2 introduces the physical description of X-ray absorptiometry. Two ways utilizing hardware and software are discussed separately to correct the beam-hardening effect of X-rays. Then we advance the equivalent energy method to measure mass thickness of matter. Photon-counting and charge-integrating technologies are introduced. The feasibility of the second method is proven through numerical calculations. The optimal dual energy X-ray for mass thickness measurements of dual component matter is also discussed through the numerical calculations. To identify the equivalent energies for two materials in the real experiments, calibrations using standard material are introduced.Chapter 3 introduces the design of software framework of DEXA. The design includes the PCI card drivers and the application framework. During the introduction of the drivers, the hardware design of the PCI data grabbing card based on X-Scan array detector is also introduced. All of the function modules in the software are introduced and realized in the chapter. Chapter 4 mainly discusses the experiments for dual component sample mass thickness measurements. It includes the experimental performance test of X-Scan detector and the sample experiment of substitutes for human bone and soft tissue. The experiment of fish sample is also performed.Chapter 5 introduces the simulation experiments of X-ray source, fan-beam collimator and linear array detector using Geant4 software development kit. During the simulation of X-ray source, the energies and intensity distributions of exit photons are discussed under different situations containing different energies and angles of incident electrons, different target materials and thicknesses. During the simulation of fan-beam collimator, different lengths of the collimator, different heights of the narrow slit and different tilt angles are discussed. The design principles of fan-beam collimator for linear array detector are concluded based on the simulation results. At last, the crosstalk between Gd₂O₂S: Tb crystal array is simulated.Chapter 6 mainly introduces the measuring standard for Chinese bone density. A reference bone density database for people from all over China is established based on the clinical literatures.Chapter 7 concludes the finished work of DEXA and points out the next research plan of DEXA.