1. A method for imaging a tissue specimen excised during surgery, the method comprising, by a combined positron emission tomography (PET) and micro computed tomography (micro CT) scanner: scanning the surgically excised tissue specimen placed on a specimen stage with a computed tomography (CT) imaging system of the combined PET and micro CT scanner, the combined PET and micro CT scanner including an X-ray tube, an X-ray detector and at least one PET detector module, wherein each one of the X-ray tube, the X-ray detector and the at least one PET detector module are translatable along X, Y and Z axes relative to the specimen stage; scanning the surgically excised tissue specimen placed on the specimen stage with a positron emission tomography (PET) imaging system of the combined PET and micro CT scanner; constructing a PET image of the surgically excised tissue specimen based on data acquired by the PET imaging system; and constructing, during the surgery, a three-dimensional micro CT image of the surgically excised tissue specimen based on data acquired by the micro CT imaging system, wherein the three dimensional micro CT image includes at least one visualization of a lesion marker and illustrates tissue structure of a margin of the surgically excised tissue specimen.