Development Of Adjustable Spatial Resolution Small Animal Cone Beam CT(CBCT)

Modern preclinical studies mostly use CT to achieve in vivo imaging of small animals to observe disease states or treatment effects.Cone Beam Computed Tomography(CBCT),as a kind of CT,is more suitable for small animal in vivo imaging because of its advantages of high spatial resolution,low radiation,and fast imaging speed,and has attracted much attention and research.The spatial resolution and field of view(FOV)size of most CBCTs are fixed,and it is difficult to achieve overall imaging of the area of interest when scanning large animals with high spatial resolution CBCTs,while it is difficult to achieve image quality standards for small animal imaging with low spatial resolution CBCTs,and domestic CBCTs with this function are still in the laboratory development period.At present,the domestic CBCT with this function is still in the laboratory research and development period,and the productized and commercialized domestic CBCT is still in the blank stage.A small animal CBCT with continuously adjustable spatial resolution has been designed and developed for this current situation:(1)A "step-focus-rotation" image acquisition model is proposed.The stepping is the smallest motion system,which can transport the object to be measured to the "focus" in a stepping horizontal motion;the translation system,which is responsible for the "focus",is the second,and changes the distance from the ray source to the object to be measured in the "rotation" to complete the adjustable spatial resolution;the rotation is the largest system,which drives the rotation of the translation system to achieve the scanning of the object to be measured.The pan system,which is responsible for the "focus",is second,and in the "rotation",the distance from the source to the object to be measured is changed to complete the spatial resolution adjustment;the rotation is the largest system,which drives the rotation of the pan system to achieve the scanning of the object to be measured.This acquisition mode can choose the appropriate spatial resolution and field of view according to different experimental needs,providing more accurate image support for experimental research and positioning detection;reducing the movement of the object to be measured and improving the image quality;at the same time,the "embedded" structure design reduces the pressure of space shortage in the subsequent self-shielding design.(2)An "all-in-one" adjustable spatial resolution system is developed.The hardware design is based on STM32F091VCT6 as the core,and the communication circuit and GPIO input/output circuit are designed according to the specific functional requirements;the software design is based on Keil5 to write the focus logic of the pan system and the block motion rotation reset instruction of the rotation system.The whole system can realize the "integrated" control of focus,rotation,hard limit,etc.,so that the action of each division is completed in an orderly and close manner,which significantly improves the work efficiency,significantly reduces the R&D and production costs,and simplifies the later maintenance and repair work.(3)The "steel ruler method" is used to calculate the spatial resolution parameters and the deflection error of the flat detector.Due to the existence of processing and assembly errors,the actual position of the flat detector is not consistent with the theory,so the actual spatial resolution parameters and the deflection error of the flat detector are solved by using a steel ruler with scale,which is a simple and efficient method.(4)The final experiment shows that the variable spatial resolution range of small animal CBCT is 27-50μm,the FOV range reaches 38.5-86 mm,the conversion time of the ultimate spatial resolution is 5.625 s,and the fastest image scanning takes only 36 s,which can accurately reconstruct the normal mice in 3D at different resolutions with high repeatability.The selfdeveloped product has been put into production and sales,bridging the gap of commercialization of domestic adjustable spatial resolution small animal CBCT.