David Wikler

This study looks into the rigid-body registration of pre-operative anatomical high field and interventional low field magnetic resonance images (MRI). The accurate 3D registration of these modalities is required to enhance the content of interventional images with anatomical (CT, high field MRI, DTI), functional (DWI, fMRI, PWI), metabolic (PET) or angiography (CTA, MRA) pre-operative images. The specific design of the interventional MRI scanner used in the present study, a PoleStar N20, induces image artifacts, such as ellipsoidal masking and intensity inhomogeneities, which affect registration performance. On MRI data from eleven patients, who underwent resection of a brain tumor, we quantitatively evaluated the effects of artifacts in the image registration process based on a normalized mutual information (NMI) metric criterion. The results show that the quality of alignment of pre-operative anatomical and interventional images strongly depends on pre-processing carried out prior to registration. The registration results scored the highest in visual evaluation only if intensity variations and masking were considered in image registration. We conclude that the alignment of anatomical high field MRI and PoleStar interventional images is the most accurate when the PoleStar's induced image artifacts are corrected for before registration.

We compared the contributions of the labeled tracers (11)C-methionine (Met) and (18)F-FDG for PET-guided stereotactic biopsy of brain gliomas. In 32 patients with glioma, stereotactic Met PET and (18)F-FDG PET were integrated in the planning of stereotactic brain biopsy. PET images were analyzed to determine which tracer offered the best information for target definition. The stereotactic coregistration of PET images allowed accurate comparison of the level, distribution, and extent of uptake for both tracers according to tumor location and grade. A histologic diagnosis was obtained for all patients. All gliomas had an area of abnormal Met uptake, and 27 showed abnormal (18)F-FDG uptake. (18)F-FDG was used for target selection when its uptake was higher in tumor than in gray matter (14 gliomas). Seven were in the basal ganglia or brain stem. Met was used for target selection when there was no (18)F-FDG uptake or when (18)F-FDG uptake was equivalent to that in the gray matter (18 gliomas). Thirteen were in the cortex. Sixty-one of the 70 stereotactic trajectories obtained from the 32 patients were based on PET-defined targets and had an area of abnormal Met uptake. These 61 Met-positive trajectories always yielded a diagnosis of tumor. All nondiagnostic trajectories (n = 9) were obtained in areas with no increased uptake of Met. In all patients with increased uptake of both tracers, the focus of highest Met uptake corresponded to the focus of highest (18)F-FDG uptake. However, the extent of uptake of both tracers was variable. Distributions of highest Met and (18)F-FDG uptake are similar in brain gliomas. Because Met provides a more sensitive signal, it is the molecule of choice for single-tracer PET-guided neurosurgical procedures in gliomas.

We developed a technique that allows the routine integration of PET in stereotactic neurosurgery, including radiosurgery. We report our clinical experience with the combined use of metabolic (i.e., PET) and anatomic (i.e., MRI and CT) images for the radiosurgical treatment of brain tumors. We propose a classification describing the relative role of the information provided by PET in this multimodality image-guided approach. Between December 1999 and March 2003, 57 patients had stereotactic PET as part of their image acquisition for the planning of gamma knife radiosurgery. Together with stereotactic MRI and CT, stereotactic PET images were acquired on the same day using either (18)F-FDG or (11)C-methionine. PET images were imported in the planning software for the radiosurgery dosimetry, and the target volume was defined using the combined information of PET and MRI or CT. To analyze the specific contribution of the PET findings, we propose a classification that reflects the strategy used to define the target volume. The patients were offered radiosurgery with PET guidance when their tumor was ill-defined and we anticipated some limitation of target definition on MRI alone. This represents 10% of the radiosurgery procedures performed in our center during the same period of time. There were 40 primary brain lesions, 7 metastases, and 10 pituitary adenomas. Abnormal PET uptake was found in 62 of 72 targets (86%), and this information altered significantly the MRI-defined tumor in 43 targets (69%). The integration of PET in radiosurgery provides additional information that opens new perspectives for the optimization of the treatment of brain tumors.