Development Of A Cone Beam CT System For Extremity Imaging

Nowadays,human extremity diseases mainly include osteoarthritis,fractures,osteoporosis etc.,which seriously affect human health and bring considerable economic burden to families and society.Cone beam CT provides sub-millimeter resolution of high quality diagnostic images for screening extremity diseases with lower radiation doses and shorter scan times than conventional CT.The development of a dedicated extremity cone beam CT imaging system can compensate the shortcomings of traditional imaging modalities and can be optimized for specific imaging tasks in extremity imaging.At present,the research on extremity imaging modalities in China is under-developed.Therefore,the aim of this paper is to develop a dedicated extremity cone beam CT imaging system for the special needs of high resolution of extremity imaging.The descriptions of the dedicated extremity cone beam CT imaging system in this paper mainly includes hardware system,software system,and results and evaluation.The major contributions are summarized as follows:The entire hardware system is powered by 220 V power supply.During the working condition,the overall maximum power consumption of the system can be up to 3000 W.To reduce the radiation dose,the system adopts pulsed X-ray exposure mode,which contains strict timing synchronization control for X-ray exposure and detector.Before scanning,the system needs to be positioned,and then the 3600 full scan is conducted with the rotating disk and slider control system in the gantry.Considering the software system,the low-frequency Fourier component analysis based on the steel ball point projection orbit is used to determine the system geometric correction parameters due to the deviation caused by mechanical installation.Collecting multiple sets of dark field and flood field data,and obtaining a projection image obtained by threshold gain correction are uniform in brightness.Since the reconstructed images of objects that contains metallic substances will bring metal artifacts,and linear interpolation will be used for artifact removal.Moreover,MITK-based dedicated cone beam CT imaging software is developed.In terms of results and evaluation,the pen holder phantom,IQ phantom and animal limbs were scanned to conduct the experiments.The experimental results show that geometry artifacts of the pen holder phantom are removed by using the geometrically corrected parameters,and the refill structure is clearly displayed.Collecting multiple sets of dark field and light field data,projection image obtained by threshold gain correction is uniform in brightness;The reconstruction result of the IQ phantom metal artifact test module is performed by linear interpolation to eliminate metal artifacts.The corresponding results show that the dark band disappears and the strip artifacts are obviously removed.In the reconstruction of IQ phantom PMMA,the ROIs mean variance fluctuation is small,and the image has good uniformity.Under the same conditions,the IQ phantom is scanned twice successively,and the obtained noise power spectrums are no different,indicating that the system is promising in terms of maintaining noise stability;the FDK algorithm and the SIRT algorithm were used to reconstruct the limb of the animals.The corresponding results showed that the bone tissue reconstructed by FDK had better image resolution,and the SIRT reconstruction results had lower noise level.Both algorithms could clearly display the bone textures.Dedicated extremity cone beam CT can be used for imaging of extremities in human body,providing important clinical information for the diagnosis of orthopedic diseases such as osteoarthritis,fracture and osteoporosis.The development of such a system can effectively improve the accuracy of diagnosis and help doctors to diagnose diseases as soon as possible,and develop effective treatments to enable patients to get timely diagnosis and treatment,which promotes the recovery of extremity function and improves the quality of life.