Open MR imaging in spine surgery: experimental investigations and first clinical experiences

Introduction: The latest open MRI technology allows to perform open and clo sed surgical procedures under real-time imaging. Before performing spinal t rauma surgery preclinical examinations had to be done to evaluate the artif acts caused by the implants, Methods: The MRT presented is a prototype deve loped by GE. Two vertically positioned magnetic coils are installed in an o peration theater. By that means two surgeons are able to access the patient between the two coils. Numerous tests regarding the material of instrument s and implants were necessary in advance. The specific size of the artifact depending on the pulse sequence and the positioning within the magnetic fi eld had to be examined. Results: The magnifying factors of the artifact in the spin echo sequence regarding titanium are between 1.7 and 3.2, dependin g on the direction of the magnetic vector. Regading stainless steel they ar e between 8.4 and 8.5. In the gradient echo sequence the factors are betwee n 7.5 and 7.7 for titanium and between 16.9 and 18.0 for stainless steel. T he tip of an implant is imaged with an accuracy of 0 to 2 mm. Since Septemb er 1997 16 patients with unstable fractures of the thoracic and lumbar spin e have been treated by dorsal instrumentation in the open MRI. Percutaneous insertion of the internal fixator has proven a successful minimally invasi ve procedure. The positioning of the screws in the pedicle is secure, the d egree of indirect reduction of the posterior wall of the vertebral body can be imaged immediately. The diameter of the spinal canal can be determined in any plane. Discussion and conclusion: The open MRI has proven useful in orthopedic and trauma surgery. The size and configuration of the artifacts caused by instruments and implants is predictable. Therefore exact position ing of the implants is achieved more easily. Dorsal instrumentation of unst able thoracolumbar fractures with a percutaneous technique has turned out s afe and less traumatic under MR-imaging. Real-time imaging of soft tissue a nd bone in any plane improves security for the patient and allows the surge on to work less invasively and more precisely.