AbstractID: 9335 Title: Respiratory Gated Micro-CT Imaging The ability to obtain sequential high resolution CT images of laboratory animals provides researchers with a very powerful noninvasive tool that has not previously been available. This imaging technique can help scientists visualize treatment response in individual living animals, and avoid the current “snap-shot” limitations imposed by routine histopathological methods. The in-vivo CT approach also potentially allows for assessment of response patterns (progression of disease or healing) in true 3D, which is difficult or impossible to obtain using histopathology techniques. Our laboratory has acquired a cone-beam CT scanner suitable for scanning mice and rats. This system is able to acquire a 3D array of voxels (each voxel represents about 90 microns in each dimension) of a live animal during a specific portion of the respiratory cycle. The modified Feldkamp reconstruction process results in isotropic voxels, and provides consistent detail when viewed from any plane (axial, coronal or sagittal). This capability has been applied to several animal models of lung tumors, and to assess cancer treatment response to lung tissues (radiation and chemotherapy). Initial applications have focused on tissues with inherently high contrast (bone and lung); recent improvements in calibrated scanning techniques may ultimately prove successful for low-contrast applications as well. Radiation dose measurements have proved consistent with the vendor’s specification (1 Gy/100 mAs). Requirements for technical, veterinary and biologic expertise will be described. Assessment of image and measurement accuracy, and measurement precision will be addressed, and remaining challenges will be discussed.