USE OF SUBVOXEL REGISTRATION AND SUBTRACTION TO IMPROVE DEMONSTRATIONOF CONTRAST ENHANCEMENT IN MRI OF THE BRAIN

To assess the potential of registration of images before and after con trast medium for improving the demonstration of contrast enhancement, we compared conventional 2D T1-weighted spin-echo images with precisel y registered 3D volume images and subtraction images derived from them in 2 normal subjects and 30 patients with a variety of brain disease. The volume images were registered to subvoxel accuracy using a rigid body translation and rotation, sine interpolation and a least-squares fit; subtraction images were obtained from these. Normal contrast enha ncement was demonstrated better with positionally registered volume an d subtraction images than with conventional images in the meninges, ep endyma, diploic veins, scalp, skin, orbit and sinuses. Abnormal enhanc ement was seen better in meningeal disease, multiple sclerosis and tum ours as well as on follow-up studies. Subvoxel registration of images before and after contrast medium may be of considerable value in the r ecognition of contrast enhancement where there are small changes, or w here the changes affect tissues with high or low baseline signal value s. The technique also appears likely to be of value in demonstrating c ontrast enhancement in tissues at inferfaces and at other areas of com plex anatomy, and in follow-up studies.