A Movable Phantom Design For Performance Test Of PET/CT Respiratory Motion Control

Lung cancer is one of the greatest threats to the health of human being.As the biggest developing country of the world,China has a more serious situation on prevention,diagnosis and treatment of lung cancer.Early diagnosis is benefit for improving the survival rate and the quality of life of cancer patients.Because the clinical feature of lung cancer in early stage is not obvious,a definite diagnosis is mostly made when the state of lung cancer is in late stage,so early diagnosis is particularly more important for lung cancer patients.Positron Emission Tomography/Computed Tomography?Hereinafter referred to as PET/CT?is a new type of medical imaging equipment,which organically combines the functional imaging,PET,and the anatomical imaging,CT,has both high sensitivity for discovering the metabolism of nidus in early stage as PET and high resolution for accurately displaying the anatomical structure of nidus as CT.It can realize the accurate qualitative and exact localization of tumor,thus improving reliability of early diagnosis of lung cancer.But the respiratory motion of human body has a significant impact on the imaging result of PET/CT.Various hardware equipment and software algorithms have being developed for respiratory control in clinical,PET/CT itself is achieving continuous improvement on performance,both can meliorate the impact of respiratory motion to the diagnosis of PET/CT.Mainly in academia,a method based on clinical case analysis is used for evaluating the impact of respiratory motion and the effect of various respiratory control methods.But it has many disadvantages,such as a high time cost,and clinical difference makes it unable to lateral comparison,poor repeatability and reproducibility,and so on.Furthermore,due to the lack of third-party testing result except of manufacturers and hospitals,it's difficult to ensure the fairness of clinical evaluation results.Simulating the human lung respiratory motion,this study designs a movable phantom to quantitatively analyze the PET/CT performance of respiratory motion control.Using a separate structure,the movable phantom consists of a chest base and embedded tumor simulants.The chest base refers to a large sample of human anatomy data;tumor stimulants are different sized hollow balls which can be filled with ¹⁸F-Fluoro-deoxy-glucose(Hereinafter referred to as ¹⁸F-FDG)inside,to be used for simulating pulmonary tumors of various sizes.The design divides the respiratory cycle into three stages:exhale?EX?,end-of-exhale?EOE?,inhale?IN?,establishes pulmonary tumor motion finite-state model,combining with clinical data.Two high-precision stepper motor under the control of microcontroller can realize the rotation and translation of tumor stimulants to simulate the lung tumor motion locus as the respiratory motion.Setting up different respiratory motion parameters?such as speed,amplitude,period?can make the movable phantom simulating different respiratory motions,and the PET/CT dynamically collects it for image fusion as performance evaluation images.We set the PET/CT image when the phantom is statical as the standard image,and compare the performance evaluation images with the standard one to estimate the deviations in three dimensions.Then the respiratory motion control performance of the PET/CT can be quantitatively evaluated.Clinical trials proved the feasibility of this evaluation method.In addition,the phantom can also be applied to correct the SUV value of moving focus in clinic.As the motions of chest base and tumor stimulants of the phantom are rigid,and the motion parameters are precisely controlled,therefore,the evaluation is repeatable and reproducible,which effectively makes up for the inadequacy of clinical data collection scheme.