This book is a multiauthored text edited by three senior authors who have a tremendous experience in the use of intraoperative MRI technology. The book is divided into five sections that describe the various iterations of iMRIs that are available, its application for minor procedures.
This book is a multiauthored text edited by three senior authors who have a tremendous experience in the use of intraoperative MRI technology. The book is divided into five sections that describe the various iterations of iMRIs that are available, its application for minor procedures, the resection of neoplastic lesions, and its role in the management of nonneoplastic disorders. The last section focuses on the future improvements in design that are likely to improve surgical access and utility of this burgeoning technology.
The first section describes the characteristics of iMRI machines that are available in the low, medium and high field strength. The reader gets a very good idea about the relative benefits and limitations of each of these machines. Hospitals that may be in the process of deciding which technology to go in for may use this information as a good guide. This section also highlights the optimal pulse sequences that may help differentiate tumor-brain interface, perform intraoperative fMRI and DTI tracking and detect complications related to brain ischemia and hematoma formation. The chapters in this section are well illustrated and show both the technology and the images obtained with various units. The chapter on optimal pulse sequences is very well written and discusses the specific pulse sequences that can help obtain the maximum intraoperative information with the least amount of time. These sequences can be tailored to provide not only anatomical details but also to help obtain both DTI and functional activation data for intraoperative neuronavigation, thereby accounting for brain shifts and movement of eloquent tracts during surgery. The authors describe the challenges of this methodology. Specific anesthetic challenges that restrict the use of standard monitoring equipment have been outlined. These include patient access, length of operative procedure, influence of magnetic field and RF currents on the functioning of the equipments and the images obtained, and risk of migration of ferromagnetic instruments, among others. This has led to the development of MR compatible anesthesia and monitoring equipment. Safety issues and steps needed to ensure reliability of equipment have been described.
The second section describes the use of intraoperative MR to perform biopsies of deep-seated tumors, insert catheters in patients with small ventricles, biopsy complex septated ventricular systems, drain cysts, place catheters in patients with slit-like ventricles. Intraoperative MRI has also been used to place deep brain stimulator electrodes precisely, although conventional techniques have relied on frame-based stereotaxy and physiologic microelectrode guidance. However, this methodology can be cumbersome as discussed by the authors.
The third section would be of special interest to the neurosurgeons, as it deals with resection of tumors with intraoperative MRI guidance. The different chapters have discussed the utility of iMRI on improving the extent of resection for gliomas, pituitary adenomas, and tumors near eloquent areas. IMRI also helps obtain real-time information to update the intraoperative neuronavigation, early detection of injury to eloquent cortex, or the development of hematoma at tumor bed. Mehdorn et al discussed the pitfalls of iMRI in their chapter on resection of high-grade gliomas. The ease of repeat scanning with the low-field systems wherein the unit can be brought up to the surgical field is definitely an advantage when compared with high-field systems. The sequences used can also be tailored to limit the amount of time spent under the scan. The use of contrast enhanced images should be limited, as the contrast may diffuse over time and limit the value of information on subsequent scans. The other chapters discuss the use of iMRI for intraoperative functional MRI and diffusion-weighted images with tractography to visualize eloquent structures during surgical resection.
The other sections deal with the use of intraoperative MRI for confirmation of satisfactory placement of depth electrodes, ensuring completeness of lesional resections and callosotomy in patients with intractable epilepsy, vascular lesions like cavernomas.
The world of intraoperative MRI technology is changing rapidly, and newer applications are on the horizon. This book highlights some of these which include the use of robotic devices and manipulators which help obviate the restrictions MRI imposes on the use of mechanical devices around scanners. These robots made from MRI compatible materials use hydraulic, pneumatic or ultrasonic motors that can be manipulated remotely. The technology in these areas is evolving. Intraoperative MRI may also be used for MRI guided laser probe delivered or ultrasound mediated thermal ablation of small brain tumors or focal putative epileptogenic foci. These new modalities can deliver focused energy resulting in thermal ablation of involved neural tissue. Temperature-sensitive imaging MR techniques can help monitor the extent of thermal injury created. The size and shape can be conformed to the 3D extent of the tumor or lesion under consideration. Other techniques include molecular imaging, PET scanning using newer isotopes, optical imaging using fluorescence-based agents. Use of these newer technologies has resulted in the need for integration of various imaging modalities in the same operating environment. Newer operating rooms are being developed to accommodate these evolving needs and facilitate the use of robotic devices in neurosurgery. The last few chapters describe these evolving concepts as they affect the operating environment of the future.