Skull-fixated fiducial markers improve accuracy in staged frameless stereotactic epilepsy surgery in children.
ABSTRACT Surgery to monitor and resect epileptogenic foci may be undertaken in 2 stages, providing an opportunity to use skull-fixated fiducials implanted during the first stage to improve the accuracy of cortical resection during the second stage. This study compared the intrinsic accuracy of skin-based and skull-fixated fiducial markers in registering frameless stereotaxy during pediatric epilepsy surgery. To the authors' knowledge, these modalities of registration have not previously been directly compared in this population.
The authors undertook a retrospective review of pediatric patients who underwent resection of epileptogenic foci in 2 stages with frameless stereotactic assistance, performed by a single surgeon at Oregon Health & Science University. For the first stage (subdural grid implantation), 9 skin fiducial markers were used to register anatomical data in a frameless stereotactic station. Intraoperatively, four 3-mm screws were placed circumferentially around the craniotomy. Postoperatively, thin-slice brain MR and CT images were obtained and fused. For the second stage, the 4 screws were used as fiducial markers to register the stereotactic anatomical data. For both stages, accuracy (difference in millimeters from zero of the manual fiducial registration compared with the computer model) was determined using navigation software. The intrinsic accuracy of these 2 methods of fiducial registration was compared using a paired Student t-test.
Between 2004 and 2009, 40 pediatric patients with epilepsy underwent frameless stereotactic surgical procedures. Fourteen patients who had 2-stage procedures using skin-based and skull-fixated registration with complete accuracy data were included in this retrospective review. Mean registration error was significantly lower using skull-fixated fiducials (1.35 mm, 95% CI 1.09-1.60 mm) than using skin-based fiducials (1.85 mm, 95% CI 1.56-2.13 mm; p = 0.0016).
A significantly higher degree of accuracy was achieved using 4 skull-fixated fiducials compared with using 9 skin-based fiducials. This simple and accurate method for registering frameless stereotactic anatomical data does not involve the potential time, expense, discomfort, and morbidity of extraoperative skull-fixated fiducial placement. The method described in this paper could also be extrapolated to other planned 2-stage cranial surgical procedures such as combined skull base approaches.
Article: Frameless stereotaxy in children.[show abstract] [hide abstract]
ABSTRACT: Frameless stereotaxy provides stereotactic localization without a standard stereotactic frame. Other reference points on the patient are linked to radiographic images by means of a three-dimensional (3D) digitizer. We report the use of a frameless stereotactic system to assist in 53 procedures in 52 children using the ISG Viewing Wand system (ISG Technologies, Missasauga, Ont.). This device uses surface landmarks as well as random surface points as the reference system. The three-dimensional digitizer consists of a six-jointed articulated arm to which pointers, a rigid ventriculoscope, or stereotactic biopsy probe guide can be attached. Image reconstruction is performed on standard CT or MRI (3D volume acquisition) images, with typically 3-mm slice thickness. The tip of the probe can be displayed on 3D surfaced objects which can be cut away to reveal reformatted gray scale displayed on the cut surface, or in a triorthogonal view where simultaneous reformatted coronal and sagital views at the level of the tip of the probe are displayed. Cases for which the viewing wand was used included craniotomies for tumor (30), vascular malformation (6), epilepsy surgery (5), other lesions (3), rigid ventriculoscopy (9), and stereotactic biopsy (2). The accuracy of the system was measured by placing 20 fiducial markers on a plastic head of which 3-mm thickness CT images had been made. The average error using 4 fiducials as reference points was 1.5 mm when the fiducials were distributed around the circumference of the head. Using random surface points of 10, 20 and 40 in number gave average errors of 2.3, 1.6, 1.5 mm, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)Pediatric Neurosurgery 02/1994; 20(2):152-9. · 0.42 Impact Factor
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ABSTRACT: A new system of fiducial stereotactic markers that can easily be adapted to various imaging modalities without losing image registration was developed and tested. Utilizing MR and CT imaging the accuracy of the new system was evaluated with phantom studies and preliminary patient studies. The markers are clearly visible without artifacts on both imaging modalities. The clear delineation of the marker dots on the images enables an accurate automated marker detection. Using the marker system, image registration was found to yield an accuracy of up to 1 mm, depending on the imaging modality and the employed marker arrangement. The presented marker system shall improve patient comfort in comparison to conventional fixed stereotactic frames if repeated, highly accurate registrations are necessary over longer periods.Magnetic Resonance Imaging 02/1997; 15(5):579-85. · 2.06 Impact Factor
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ABSTRACT: The overall accuracy of neuronavigation systems may be influenced by (1) the technical accuracy, (2) the registration process, (3) voxel size and/or distortion of image data and (4) intraoperative events. The aim of this study was to test the influence of the registration and imaging modality on the accuracy. A plexiglas phantom with 32 rods was taken for navigation targeting. Sixteen fiducials were attached to the surface of the phantom forming two different attachment patterns (clustered vs. diffusely scattered). This model was scanned by MRI and CT (1-mm slices). Registration was performed using different numbers and attachment patterns of the fiducials. Using CT or MRI, the localization error was measured in image space as the Euclidean distance between targets defined in image space and those detected in the physical space. Accuracy was measured with two commercial systems, the Zeiss MKM and the StealthStation. The mean localization error varied between 1.59 +/- 0.29 mm (MKM, 8 scattered fiducials, CT scanning) and 3.86 +/- 2.19 mm (MKM, 4 clustered fiducials, MRI). The worst localization error was 9.5 mm (MKM). In case of an optimal registration, the 95th percentile for the localization error was 2.2 (MKM) and 2.75 mm (StealthStation). The imaging modality has only minor influence on the localization error, with CT increasing accuracy minimally. Both the fiducial number and the attachment pattern critically influence the localization error: 8 fiducials and a generalized attachment pattern increase the accuracy significantly. No correlation between the calculated registration accuracy and the measured localization accuracy was found. The application accuracy of different neuronavigation systems critically depends on the registration. The calculated registration accuracy provided by the system does not correspond to the localization error found in reality. The accuracy of frameless neuronavigation systems is comparable to that of classical frame-based stereotactic devices.Stereotactic and Functional Neurosurgery 02/2000; 75(4):188-202. · 1.46 Impact Factor