Phantom and clinical studies. (a) The C-arm was used to acquire radiographs of a spine phantom at varying angular views. (b) Close-up of the instrumented spine phantom. (c) AP, OBL, and LAT views of the lumbar (L1–L5) section of the instrumented spine phantom. (d) Clinical studies in which intraoperative radiographs were obtained using the same C-arm. The projections show AP, OBL, and LAT views of a patient undergoing thoracolumbar spine surgery with screws delivered at T12–L4. Additional instruments (e.g., retractors) are also visible.