INTERNALLY STABILIZED SPINE - OPTIMAL CHOICE OF FREQUENCY-ENCODING GRADIENT DIRECTION DURING MR-IMAGING MINIMIZES SUSCEPTIBILITY ARTIFACT FROM TITANIUM VERTEBRAL BODY SCREWS

In 18 vertebral bodies with titanium fixation screws and in a phantom model, visualization of the vertebral body marrow was improved and sus ceptibility artifact was reduced on T1-weighted spin-echo magnetic res onance images when the direction of the frequency-encoding gradient wa s parallel to the long axis of the screw. A perpendicular direction im proved image quality only when the region of interest was adjacent to the tip of the screw. In the phantom, the length of the screw was stat istically significantly increased and the width and area were reduced (P <.001) when the gradient was parallel to the long axis of the screw .