CT SCANNER WITH UNTRACKED MARKERS

A surgeon selects a volume of interest by placing an untracked "marker" in a patient near an area where an update is desired. During surgery, when an updated CT scan is requested, the CT scanner performs a scan of the patient using a full field of view to take a series of two-dimensional initial images of the patient from a plurality of angularly spaced positions about the patient. The position of the untracked marker is determined by the CT scanner in or more of the initial images. The volume of interest is defined as the position of the untracked marker, plus some margin. The CT scanner then collimates the x-ray source to scan only the volume of interest. The CT scanner then completes the update scan of the volume of interest and updates a previous CT scan(s) to create a fully updated CT image, reducing x-ray exposure of the patient.