Direct application of MR images to computer-assisted bone tumor surgery

We describe a method for the direct application of MR images to navigation-assisted bone tumor surgery as an alternative to CT-MRI fusion. Six patients with an orthopedic malignancy were employed for this method during navigation-assisted tumor resection. Tumor types included osteosarcoma (4), high-grade chondrosarcoma (1), and adamantinoma (1). Mean patient age was 25.3 years (range 18–52 years). Mean duration of follow-up was 25.8 months (range 18–32 months). Resorbable pin placement and rapid 3-dimensional spoiled gradient echo sequences made the direct application of MR images to computer-assisted bone tumor surgery without CT-MR image fusion possible. A paired-point registration technique was employed for patient-image registration in all patients. It took 20 min on average to set up the navigation (range 15–25 min). The mean registration error was 0.98 mm (range 0.4–1.7 mm). On histologic examination, distances from tumors to resection margins were in accord with preoperative plans. No patient had a local recurrence or distant metastasis at the last follow-up. Direct patient-to-MRI registration is a very useful method for bone tumor surgery, permitting the application of MR images to intraoperative visualization without any additional costs or exposure of the patient to radiation from the preoperative CT scan.