Motion correction for augmented fluoroscopy - application to liver embolization

Hepatic embolization is a procedure designed to cut off blood supply to liver tumors, either hepatocellular carcinomas (HCC) or metastases from other parts of the body. While it often serves as a palliative treatment, it can also be indicated as a precursor to liver resection and liver transplants. The procedure itself is conducted under fluoroscopic X-ray guidance. Contrast agent is administered to opacify the vasculature and to indicate the arterial branches that feed the treatment target. These supply routes are then blocked by embolic agents, cutting off the tumor´s blood supply. While methods exist to enhance fluoroscopic images and reduce the dependency on contrast agent, they are typically confounded by patient respiratory motion and are hence not effective for abdominal interventions. This paper presents an appearance based tracking algorithm that quickly and accurately compensates for the liver´s bulk motion due to respiration, thereby enabling the application of fluoroscopic augmentations (i.e. image overlays) for hepatic embolization procedures. To quantify the accuracy of our algorithm, we manually identified vascular and artificial landmarks in fluoroscopy sequences acquired from three patients during free breathing. The average postmotion compensation landmark misalignment was 1.9 mm, with the maximum landmark misalignment not exceeding 5.5 mm.