| Micro-CT has been mainly used to study the anatomical structure of small animals since it can provide complete anatomical information,owns high spatial resolution and simple system structure that can be readily combined with other functional imaging models.In addition,CT perfusion imaging can capture physiological function changes.Clinical CT perfusion imaging have been widely used in the diagnosis of acute cerebral ischemia and the evaluation of hepatic function.Micro-CT perfusion imaging would promote some preclinical studies that could not been implemented on human beings.For example,perfusion imaging during the tumor growth could facilitate observing the changes of angiogenesis and blood perfusion after drug treatments.Consequently,the drug efficacy could be evaluated.However,the combined challenges of high spatial and temporal resolution have made micro-CT perfusion imaging more difficult.As a result,micro-CT could not observe fast dynamic process or perform functional study as clinical CT does.Aiming at solving this problem,this thesis have studied on fast-scanning micro-CT imaging methods for small animal dynamic observation.In order to realize the dynamic observation in vivo for small animals,a fast-scanning gantry-rotated micro-CT system is developed.To keep the small animal in a natural position,the X-ray source and the detector are fixed on a gantry and rotate around the animal to perform in vivo imaging.Furthermore,in order to achieve high temporal resolution,a fast image collection mode is proposed.In this mode,the flat panel detector exposure and gantry rotation are implemented synchronously.The gantry keeps continuous rotation with a constant speed and trigger the detector exposure at a fixed distance interval.The fast collection mode can shorten scanning time and reduce radiation dose through omitting the repeated acceleration and deceleration of the rotary stage in image collection step by step.The temporal and spatial resolution,contrast resolution,imaging uniformity,linearity,and radiation dose are measured to evaluate the system performance.Furthermore,a phantom imaging and a small animal imaging in vivo are performed to verify the system imaing capability.The result reveals that the system can take only 8 s to finish a whole body scan.The spatial resolution of the system measured by a frequency-domain method is 100 μm.The imaging of standard electron density phantom indicates that except for the bone and lung,the contrast-to-ratio of other soft tissues are less than 1.00 with radiation dose of 91.2 mGy.In other words,the confidence level of distinguishing the soft tissues from the water is lower than 74%.The imaging of a uniform water phantom with a diameter of 30 mm shows that the error between the boundaries and the center of the phantom is lower than the image noise.The linearity of the system reaches 0.9994 measured by scanning contrast agent of different concentration.During the scanning,the radiation dose for the mice is lower than 4%of the half lethal dose.As to the operator,the radiation dose is less than 0.1 μSv/h.Based on the homemade fast-scanning micro-CT system,this thesis proposed a method to observe the dynamic metabolism of non-ionic iodine contrast agent in mice.Moreover,a novel segmentation method based on dynamic contrast enhanced micro-CT images is proposed.A series of dynamic contrast enhanced images are acquired by fast scanning after injection of a non-ionic iodinated contrast agent.Based on different dynamic contrast enhancement characteristics,the pixels of the image are classified to different categories.The heart,liver,spleen,lung,and kidney are extracted from separate categories by morphological processing.Seven mice have been segmented to evaluate this method.The results are highly consistent with manual segmentation. |
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