Target definition and trajectory optimization for interactive MR-guided biopsies of brain tumors in an open configuration MRI system

We present an imaging strategy for planning and guiding brain biopsies in an open configuration MR system. Preprocedure imaging was performed in a 1.5-T MR system and was designed to provide, in a clinically efficient manner, high resolution anatomical and functional/physiologic information for precise definition and tissue characterization of the target, aiming at optimization of the biopsy trajectory for planning a safe and accurate procedure. The interventions were performed in a .5-T open bore magnet, and imaging was optimized to provide the imaging quality and temporal resolution necessary for performing the procedure interactively in near real time. Brain biopsies of 21 patients were performed in a 10-month period. Segmentation and surface rendering analysis of the lesions and vascular structures and dynamic MR perfusion and cortical activation studies provided an efficient and comprehensive way to appreciate the relationship of the target to surrounding vital structures, improved tissue characterization and definition of the tumor margins, and demonstrated the location of essential cortex, allowing appropriate placement of the burr hole and choice of optimal trajectory. Interactive protocols provided good visualization of the target and the interventional devices and offered the operator real-time feedback and control of the procedure. No complications were encountered. Advanced methods of image acquisition and processing for accurate planning of interventional brain procedures and interactive imaging with MR guidance render feasible the performance of safe and accurate neurointerventional procedures.

Hormones, radiosurgery and virtual reality: new aspects of meningioma management

The understanding and management of meningiomas is changing significantly today. One of the most striking features of their pathophysiology is their predominance in women. In a series of 517 patients with meningiomas seen by the Brain Tumor Group at Brigham and Women's Hospital, the female:male ratio was 24:1. The progesterone receptor appears to be the major candidate to explain this difference. Although meningioma cells variably express receptors for estrogen, androgen, platelet-derived growth factor, epidermal growth factor, and somatostatin, these molecules do not explain the differences because they are not differentially expressed or are not activated. Progesterone receptor can be shown to be expressed in 81% of women and 40% of men with meningiomas; it can also be shown to be activated by transfecting a construct with the progesterone responsive element and a reporter in it and using the cell's own receptors to activate this construct. Surgery remains the mainstay of meningioma management. At the Brigham and Women's Hospital three-dimensional reconstruction techniques have markedly improved the ability to visualize the tumor as well as its relation to vascular structures. With MRI reconstruction, it is possible to know the tumor's relation to the sagittal and other sinuses, to identify feeders and proximity to major arteries, and to establish its location and relation to cortex by frameless stereotaxis. These techniques can be used in a virtual reality format are some of the most powerful in neurosurgery both for teaching and for the surgical procedure itself. External beam radiation has been shown by others to be an effective adjunctive treatment to prevent meningioma recurrence. Recently, linear accelerator radiosurgery and stereotactic radiotherapy have changed the pattern of radiation at our institution. In a series of 56 skull base meningiomas, for example, 95% were controlled (i.e., showed no growth) over a four year period. Fractionated focal radiation potentially offers the same control rate with fewer complications. With increasing understanding and treatment possibilities, meningiomas remain one of the most intriguing and challenging tumors in the nervous system.

Computer-assisted surgical planning for cerebrovascular neurosurgery

OBJECTIVE

We used three-dimensional reconstructed magnetic resonance images for planning the operations of 16 patients with various cerebrovascular diseases. We studied the cases of these patients to determine the advantages and current limitations of our computer-assisted surgical planning system as it applies to the treatment of vascular lesions.

METHODS

Magnetic resonance angiograms or thin slice gradient echo magnetic resonance images were processed for three-dimensional reconstruction. The segmentation, based on the signal intensities and voxel connectivity, separated each anatomic structure of interest, such as the brain, vessels, and skin. A three-dimensional model was then reconstructed by surface rendering. This three-dimensional model could be colored, made translucent, and interactively rotated by a mouse-controlled cursor on a workstation display. In addition, a three-dimensional blood flow analysis was performed, if necessary. The three-dimensional model was used to assist in three stages of surgical planning, as follows: 1) to choose the best method of intervention, 2) to evaluate surgical risk, 3) to select a surgical approach, and 4) to localize lesions.

RESULTS

The generation of three-dimensional models allows visualization of pathological anatomy and its relationship to adjacent normal structures, accurate lesion volume determination, and preoperative computer-assisted visualization of alternative surgical approaches.

CONCLUSION

Computer-assisted surgical planning is useful for patients with cerebrovascular disease at various stages of treatment. Lesion identification, therapeutic and surgical option planning, and intraoperative localization are all enhanced with these techniques.

Use of cortical surface vessel registration for image-guided neurosurgery

OBJECTIVE

We have treated patients with brain surface tumors by using video registration of a three-dimensional image to the surgical field, to identify eloquent cortices, localize the lesions, and define the tumor margins. "Skin-to-skin" registration using the skin surface to produce alignment was performed earlier but was difficult in areas with few prominent registration landmarks. For this reason, "vessel-to-vessel" registration using the cortical vessels as fiducials was applied to 17 cases, to improve accuracy. This article presents the advantages and limitations of vessel-to-vessel registration, as determined from the data for these cases. The accuracy is also estimated.

METHODS

A three-dimensional model was reconstructed from magnetic resonance imaging data, and a two-dimensional projection was superimposed on the video image of the actual surgical field. The tumor was resected with guidance from the registered video image. The two-dimensional projection accuracy of vessel-to-vessel registration was compared with that of skin-to-skin registration by using a phantom study.

RESULTS

All 17 tumors underwent gross total resection, and the patients experienced no major permanent neurological deficits. In the phantom study, the two-dimensional, projected, target registration error of a tumor with skin-to-skin registration was estimated as 8.9 +/- 5.3 mm and that with vessel-to-vessel registration was 1.3 +/- 1.4 mm (99th percentile confidence intervals, 24.8 and 5.5 mm, respectively).

CONCLUSION

Video registration using cortical surface vessels is practical and improves two-dimensional projection accuracy significantly, compared with skin registration.

3D localization of surface 10-20 EEG electrodes on high resolution anatomical MR images

A method to visualize surface EEG electrodes on conventional high-resolution magnetic resonance (MR) images is presented. Because conventional silver or gold electrodes generate an insignificant artifactual signal signature in MR images, a plastic capsule filled with gadolinium-doped water was designed to mold onto each electrode, thereby outlining the electrode surfaces as a negative imprint on MR images. MR images of the head with capsules affixed clearly demonstrated the location and shape of the electrodes. Selected cranial tissues were identified by using semi-automatic image segmentation to determine their three-dimensional spatial relationship to the electrodes. Such representations could be used as a starting point for more precise EEG source localization modeling applicable to individual patients.

Frameless 3D volume registration of MR data sets for stereotactic pallidotomy

Frameless 3D volume registration of Magnetic Resonance (MR) and computed (CT) data sets has been described by Kummar et al. [11]. Its use in 3D volume registration for stereotactic planning in patients undergoing pallidotomy is presented. Pre-operative examinations with the stereotactic frame and postoperative examinations without the stereotactic frame can be co-registered and reviewed for accuracy of planned and lesional coordinates.

Neurosurgery and the Internet

The Internet is a global computer network which has recently become accessible for many reasons to the general public. The growth in its use for entertainment purposes is now being mirrored by its application to medical interests requiring rapid communication. Neurosurgery as a speciality has a tradition of adapting quickly to new technology and can benefit from these new communication techniques. The established methods used on the Internet to transfer information are discussed along with the medical applications of these methods. The ways in which the Internet is being used have important messages for the coming NHS wide network and the future potential of computer networks in neurosurgery and medicine.