A method of acquiring and reconstructing a computed tomography (CT) image is provided. A first scan of the full field of view (FOV) is acquired. A second scan of a smaller target FOV is then acquired by using a collimator to narrow the X-ray beam width. The CT image is iteratively reconstructed by replacing a key-hole region of the full FOV projection data with the target FOV projection data. An exemplary embodiment comprises imaging a heart (target FOV) within a torso (full FOV) over multiple heart beat cycles. A computer readable medium is further provided, including a program configured to reconstruct a CT image using the key-hole method.