Abstract
Image-guided surgery has developed on the basis of navigation-technology born in the late 1980s, enhanced by improvements in various imaging modalities. Intraoperative MRI (iMRI) plays an important role in accurate navigation that is free from the influence of brain shift, allows fine resection control during the tumor surgery, and provides early detection of intraoperative complications. Thus, the role of iMRI is to visualize the intraoperative brain structure and function, namely, to serve as quality assurance (QA) for the neurosurgery. There are increasing number of reports related to iMRI, up to 290 at last count, with at least 200 units installed in ORs throughout the world at present.
Diffusion tensor imaging (DTI) and tractography enables visualization of the pyramidal tract intraoperatively. High magnetic-field MRI units are capable of conducting DTI to compensate for brain shift during surgery. Lower magnetic-field MRI units, however, are not as powerful. We have developed an advanced imaging technique, “reshape & fuse” in which preoperative images are fused appropriately to deformed intraoperative images using a non-rigid registration algorithm. Using this technique, we were able to successfully estimate the intraoperative shift of the pyramidal tract both toward the inside and outside of the brain.
Intraoperative hemorrhagic complications can be detected with iMRI, although characterization of the super acute hemorrhage on MRI has not been established yet. We investigated the relationship between blood concentration and MR signals, comparing among the values yielded by T1, T2 and fast FLAIR on various blood concentrations using artificial blood samples. Values of fast FLAIR had the best linearity among the three, suggesting that fast FLAIR is sensitive enough to detect a small amount of blood, and at the same time, able to estimate the concentration of blood in a mixture with CSF. This finding could lead to better visualization of intraoperative super acute hemorrhagic events.
Expanding iMRI and developing related imaging technologies would contribute greatly to the QA of neurosurgery, pushing forward the frontier for intraoperative visualization of the brain.
