Real-Time Fusion Imaging of Ultrasound and CT for Chest Wall Liposarcoma via Automatic Liver Registration as an Anchor

Abstract

Real-time fusion imaging can reconstruct pre-acquired CT or MR and fuse them with ultrasound to simultaneously display ultrasound and its corresponding CT or MR images. This method has been widely reported in the diagnosis and intervention of focal liver lesions, and its use has been demonstrated by studies for diseases of breast, extremities, and prostate. Recently, automatic registration can use algorithms to automatically extract 3D spatial coordinates from liver vasculature or surface contour, and simplify the work for a precise imaging fusion of liver. Liposarcoma is one of the most common soft tissue tumors but its involvement of chest wall is rare. Complete resection is usually considered the treatment of choice for liposarcoma to minimize local recurrence. However, precise preoperative localization can be challenging for inconspicuous lesions in chest wall. Pre-acquired contrast enhanced CT from chest to liver was imported, processed, and reconstructed by the ultrasound machine (EPIQ 7, Philips). A manual sweep with the ultrasound transducer (C9-2, Philips) was performed to acquire a partial liver volume. The shapes of the diaphragm and liver surface were extracted, and then automatically aligned with that from the CT volume. Then real-time ultrasound was performed in conjunction with fused CT images to characterize chest wall lesions. A 61-year-old man with history of liposarcoma was presented with recurrence in right posterior chest wall. He had multiple resections for repeated recurrence in the trunk where the skin surface was extensively scarred. Fusion imaging with automatic registration was attempted. Real-time fusion imaging of ultrasound and CT revealed two hypoechoic nodules in the chest wall. The locations of recurrence were marked on the skin. The tumors were successfully exposed and removed upon exploration at the marks. The histopathological findings suggested that the removed chest wall tumors were dedifferentiated liposarcoma. This case demonstrates success of fusion imaging with ultrasound and CT for chest wall liposarcoma. The novel use of automatic liver registration as an anchor point for fusion is a feasible approach to identify chest wall soft tissue tumors. This method can be helpful in characterizing inconspicuous chest wall lesions and providing precise guides for further intervention.