Accuracy of stereotactic localisation using magnetic resonance imaging: a comparison between two- and three-dimensional studies

Use of Frameless Stereotactic Navigation System Combined with Intraoperative Magnetic Resonance Imaging and 5-Aminolevulinic Acid

OBJECTIVE

We have described the integrated use of a neuronavigation-guided system for frameless stereotaxy (VarioGuide [Brainlab AG, Munich, Germany]) with intraoperative magnetic resonance imaging (iMRI) and 5-aminolevulinic acid (5-ALA) and report the advantages and disadvantages that the use of these tools together can have in the treatment of various types of intracerebral lesions.

METHODS

After the skin incision, creation of a burr hole at the entry point, and dura opening, the VarioGuide procedure was started. Initially, the wizard software will require positioning of the stereotactic arm over the burr hole and provides feedback regarding the correct position. The procedure is performed in an iMRI theater furnished with a surgical microscope (Kinevo [Carl Zeiss AG, Oberkochen, Germany]) supplied with a violet-blue excitation light for 5-ALA fluorescence. At the end of the surgery, iMRI was performed. We present 2 exemplary cases to describe the application and workflow of these tools.

RESULTS

When used for traditional biopsy, the possibility of performing a new iMRI scan could be of paramount importance because the brain shift can be compensated for and an alternative trajectory can be calculated from the new images and fiber tracking reconstruction. The fluorescence of the tissue sample examined under the microscope filter can provide immediate information about the nature of the lesion, allowing for the possibility of converting the procedure to open craniotomy and tumor removal.

CONCLUSION

The use of combination frameless stereotaxy with iMRI and 5-ALA has shown benefits in terms of safety and precision. Moreover, the use of these tools can simplify tumor removal after simple biopsy, widening the spectrum of indications.

Stereotactic Placement of Intratumoral Catheters for Continuous Infusion Delivery of Herpes Simplex Virus -1 G207 in Pediatric Malignant Supratentorial Brain Tumors

OBJECTIVE

The engineered herpes simplex virus-1 G207, is a promising therapeutic option for central nervous system tumors. The first-ever pediatric phase 1 trial of continuous-infusion delivery of G207 via intratumoral catheters for recurrent or progressive malignant brain tumors is ongoing. In this article, we describe surgical techniques for the accurate placement of catheters in multiple supratentorial locations and perioperative complications associated with such procedures.

METHODS

A prospective study of G207 in children with recurrent malignant supratentorial tumors is ongoing. Preoperative stereotactic protocol magnetic resonance imaging was performed, and catheter trajectories planned using StealthStation planning software. Children underwent placement of 3-4 silastic catheters using a small incision burr hole and the Vertek system. Patients had a preinfusion computed tomography scan to confirm correct placement of catheters.

RESULTS

Six children underwent implantation of 3-4 catheters. Locations of catheter placement included frontal, temporal, parietal, and occipital lobes, and the insula and thalamus. There were no clinically significant perioperative complications. Postoperative computed tomography scans coupled with preoperative MRI scans demonstrated accurate placement of 21 of 22 catheters, with 1 misplaced catheter pulled back to an optimal location at the bedside. One patient had hemorrhage along the catheter tract that was clinically asymptomatic. Another patient had cerebrospinal fluid leak from a biopsy incision 9 days after surgery that was oversewn without complication.

CONCLUSIONS

The placement of multiple intratumoral catheters in pediatric patients with supratentorial tumors via frameless stereotactic techniques is feasible and safe. Intratumoral catheters provide a potentially effective route for the delivery of G207 and may be employed in other trials utilizing oncolytic virotherapy for brain tumors.

Accuracy of VarioGuide Frameless Stereotactic System Against Frame-Based Stereotaxy: Prospective, Randomized, Single-Center Study

INTRODUCTION

Frameless stereotactic brain biopsy systems are widely used today. VarioGuide (VG) is a relatively novel frameless system. Its accuracy was studied in a laboratory setting but has not yet been studied in the clinical setting. The purpose of this study was to determine its accuracy and diagnostic yield and to compare this with frame-based (FB) stereotaxy.

MATERIAL AND METHODS

Overall, 53 patients (33 males and 20 females, 60 ± 15 years old) were enrolled into this prospective, randomized, single-center study. Twenty-six patients were randomized into the FB group and 27 patients into the VG group. Real trajectory was pointed on intraoperative magnetic resonance. The distance of the targets and angle deviation between the planned and real trajectories were computed. The overall discomfort of the patient was subjectively assessed by the visual analog scale score.

RESULTS

The median lesion volume was 5 mL (interquartile range [IQR]: 2-16 mL) (FB) and 16 mL (IQR: 2-27 mL) (VG), P = 0.133. The mean distance of the targets was 2.7 ± 1.1 mm (FB) and 2.9 ± 1.3 mm (VG), P = 0.456. Mean angle deviation was 2.6 ± 1.3 deg (FB) and 3.5 ± 2.1 deg (VG), P = 0.074. Diagnostic yield was 93% (25/27) in VG and 96% (25/26) in FB, P = 1.000. Mean operating time was 47 ± 26 minutes (FB) and 59 ± 31 minutes (VG), P = 0.140. One minor bleeding was encountered in the VG group. Overall patient discomfort was significantly higher in the FB group (visual analog scale score 2.5 ± 2.1 vs. 1.2 ± 0.6, P = 0,004).

CONCLUSIONS

The VG system proved to be comparable in terms of the trajectory accuracy, rate of complications and diagnostic yield compared with the "gold standard" represented by the traditional FB stereotaxy for patients undergoing brain biopsy. VG is also better accepted by patients.

Discrepancies between the MRI- and the electrophysiologically defined subthalamic nucleus

BACKGROUND

The aim of our study was to evaluate discrepancies between the electrophysiologically and MRI-defined subthalamic nucleus (STN) in order to contribute to the ongoing debate of whether or not microelectrode recording (MER) provides additional information to image-guided targeting in deep brain stimulation.

METHODS

Forty-four STNs in 22 patients with Parkinson's disease were investigated. The three-dimensional MRI-defined STN was derived from segmentations of axial and coronal T2-weighted images. The electrophysiological STNs were generated from intraoperative MERs in 1,487 locations. The stereotactical coordinates of positive and negative STN recordings were re-imported to the planning software, where a three-dimensional reconstruction of the electrophysiological STN was performed and fused to the MRI data set. The estimated borders of the MRI- and MER-STN were compared. For statistical analysis Student's t, Mann-Whitney rank sum and Fisher's exact tests were used.

RESULTS

MER-STN volumes, which were found outside the MRI-STN, ranged from 0 mm(3) to 87 mm(3) (mean: 45 mm(3)). A mean of 44% of the MER-STN volumes exceeded the MRI-STN (maximum: 85.1%; minimum: 15.1 %); 53.4% (n = 793) of the microelectrode recordings were concordant and 46.6% (n = 694) discordant with the MRI-defined anatomical STN. Regarding the dorsal borders, we found discrepancies between the MER- and MRI-STN of 0.27 mm (= mean; SD: 0.51 mm) on the first operated side and 1.51 mm (SD: 1.5 mm) on the second (p = 0.010, t-test).

CONCLUSIONS

MER provides additional information to high-resolution anatomical MR images and may help to detect the amount and direction of brain shift.

VARIOGUIDE: A NEW FRAMELESS IMAGE‐GUIDED STEREOTACTIC SYSTEM—ACCURACY STUDY AND CLINICAL ASSESSMENT

OBJECTIVE

VarioGuide (BrainLAB AG, Feldkirchen, Germany) is a new system for frameless image-guided stereotaxy. In the present study, we aimed to assess target point accuracy in a laboratory setting and the clinical feasibility of the system.

METHODS

Using the phantom of our frame-based stereotactic system (Riechert-Mundinger; Inomed Medizintechnik GmbH, Teningen, Germany), target points were approached from different angles with the frameless system. Target point deviation in the x, y, and z planes was assessed. Furthermore, patients harboring intracranial lesions were diagnostically biopsied using VarioGuide.

RESULTS

Phantom-based accuracy measurements yielded a mean target point deviation of 0.7 mm. Between February 2007 and April 2008, 27 patients were diagnostically biopsied. Lesion volumes ranged from 0.2 to 117.6 cm3, trajectory length ranged from 25.3 to 64.1 mm, and the diagnostic yield was 93%.

CONCLUSION

Concluding from the phantom measurements with ideal image-object registration, assumed spherical lesions with a volume of 0.524 cm3 can be biopsied with 100% target localization. Early clinical data revealed VarioGuide to be safe and accurate for lesions of 0.2 cm3 and larger. Thereby, the system seems feasible for the biopsy of most intracranial lesions.

Error Analysis of MRI and Leksell Stereotactic Frame Target Localization in Deep Brain Stimulation Surgery

Stereotactic deep brain stimulation (DBS) is the surgical treatment of choice for medication-refractory patients with Parkinson's disease and essential tremor. The subthalamic nucleus and ventral intermediate nucleus of the thalamus appear to be effective targets for electrode placement. Because these targets are small and encased in fiber tracts, their localization can be exceedingly difficult. However, the precision of electrode placement is crucial for obtaining successful results. Currently, surgeons rely on preoperative MRI or CT images to derive stereotactic coordinates for targeting sites such as the subthalamic nucleus and ventral intermediate nucleus of the thalamus coupled with microelectrode recordings during surgery for proper electrode placement. However, it has been argued that the stereotactic head frame produces detrimental artifacts during MRI. We examined MRI images taken from 11 patients undergoing repeat DBS surgery, and determined the coordinates of the previously placed electrode. We then set the Leksell G stereotactic frame to these coordinates and obtained fluoroscope-localizing images. Using MATLAB image analysis tools, we were able to quantify the 3-dimensional error in target localization by measuring the distance from the electrode tip to the targeted coordinate. The mean errors were 0.09 +/- 0.34 mm perpendicular, lateral to medial, 0.01 +/- 0.32 perpendicular, posterior to anterior, and -0.08 +/- 0.33 mm parallel to the electrode, superior to inferior. According to statistical analysis, the error was random and did not seem to move in any predictable fashion. Therefore, we conclude that preoperative MRI images can be safely used in DBS surgery, and they do not negatively affect its accuracy.

Does new magnetic resonance imaging technology provide better geometrical accuracy during stereotactic imaging?

Object.The authors sought to compare the accuracy of stereotactic target imaging using the Siemens 1T EXPERT and 1.5T SYMPHONY magnetic resonance (MR) units.

Methods.A water-filled cylindrical Perspex phantom with axial and coronal inserts containing grids of glass rods was fixed in the Leksell stereotactic frame and subjected to MR imaging in Siemens 1T EXPERT and Siemens 1.5T SYMPHONY units. Identical sequences were used for each unit. The images were transferred to the GammaPlan treatment planning system. Deviations between stereotactic coordinates based on MR images and estimated real geometrical positions given by the construction of the phantom insert were evaluated for each study. The deviations were further investigated as a function of the MR unit used, MR sequence, the image orientation, and the spatial position of measured points in the investigated volume.

Conclusions.Larger distortions were observed when using the SYMPHONY 1.5T unit than those with the EXPERT 1T unit. Typical average distortion in EXPERT 1T was not more than 0.6 mm and 0.9 mm for axial and coronal images, respectively. Typical mean distortion for SYMPHONY 1.5T was not more than 1 mm and 1.3 mm for axial and coronal images, respectively. The image sequence affected the distortions in both units. Coronal T2-weighted spin-echo images performed in subthalamic imaging produced the largest distortions of 2.6 mm and 3 mm in the EXPERT 1T and SYMPHONY 1.5T, respectively. Larger distortions were observed in coronal slices than in axial slices in both units, and this effect was more pronounced in SYMPHONY 1.5T. Noncentrally located slice positions in the investigated volume of the phantom were associated with larger distortions.

Does new magnetic resonance imaging technology provide better geometrical accuracy during stereotactic imaging?

Object. The authors sought to compare the accuracy of stereotactic target imaging using the Siemens 1T EXPERT and 1.5T SYMPHONY magnetic resonance (MR) units.

Methods. A water-filled cylindrical Perspex phantom with axial and coronal inserts containing grids of glass rods was fixed in the Leksell stereotactic frame and subjected to MR imaging in Siemens 1T EXPERT and Siemens 1.5T SYMPHONY units. Identical sequences were used for each unit. The images were transferred to the GammaPlan treatment planning system. Deviations between stereotactic coordinates based on MR images and estimated real geometrical positions given by the construction of the phantom insert were evaluated for each study. The deviations were further investigated as a function of the MR unit used, MR sequence, the image orientation, and the spatial position of measured points in the investigated volume.

Conclusions. Larger distortions were observed when using the SYMPHONY 1.5T unit than those with the EXPERT 1T unit. Typical average distortion in EXPERT 1T was not more than 0.6 mm and 0.9 mm for axial and coronal images, respectively. Typical mean distortion for SYMPHONY 1.5T was not more than 1 mm and 1.3 mm for axial and coronal images, respectively. The image sequence affected the distortions in both units. Coronal T2-weighted spin-echo images performed in subthalamic imaging produced the largest distortions of 2.6 mm and 3 mm in the EXPERT 1T and SYMPHONY 1.5T, respectively. Larger distortions were observed in coronal slices than in axial slices in both units, and this effect was more pronounced in SYMPHONY 1.5T. Noncentrally located slice positions in the investigated volume of the phantom were associated with larger distortions.

Combining stereotactic angiography and 3D time-of-flight magnetic resonance angiography in treatment planning for arteriovenous malformation radiosurgery

PURPOSE

This study was initiated to evaluate the advantages of using three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA), as an adjuvant to conventional stereotactic angiography, in obtaining three-dimensional information about an arteriovenous malformation (AVM) nidus and in optimizing radiosurgical treatment plans.

METHODS AND MATERIALS

Following angiography, contrast-enhanced MRI and MRA studies were obtained in 22 consecutive patients undergoing Gamma Knife radiosurgery for AVM. A treatment plan was designed, based on the angiograms and modified as necessary, using the information provided by MRA. The quantitative analysis involved calculation of the ratio of the treated volume to the MRA nidus volume (the tissue volume ratio [TVR]) for the initial and final treatment plans.

RESULTS

In 12 cases (55%), the initial treatment plans were modified after including the MRA information in the treatment planning process. The mean TVR for the angiogram-based plans was 1.63 (range 1.17-2.17). The mean coverage of the MRA nidus by the angiogram-based plans was 93% (range 73-99%). The mean MRA nidus volume was 2.4 cc (range 0. 6-5.3 cc). The MRA-based modifications resulted in increased conformity with the mean TVR of 1.46 (range 1.20-1.74). These modifications were caused by MRA revealing irregular nidi and/or vascular components superimposed on the angiographic projections of the nidi. In a number of cases, the information from MRA was essential in defining the nidus when the projections of the angiographic outlines showed different superior and/or inferior extent of the nidus. In two cases, MRA revealed irregular nidi, correlating well with the angiograms and showed that the angiographically acceptable plans undertreated 27% of the MRA nidus in one case and 18% of the nidus in the other case. In the remaining 10 cases (45%), both MRI and MRA failed to detect the nidus due to surgical clip artifacts and the presence of embolizing glue.

CONCLUSIONS

The 3D TOF MRA provided information on irregular AVM shape, which was not visualized by angiography alone, and it was superior to MRI for defining the AVM nidus. However, when imaging artifacts obscured the AVM nidus on MRI and MRA, angiography permitted detection of AVM. Utilizing MRA as a complementary imaging modality to angiography increased accuracy of the AVM radiosurgery and allowed for optimal dose planning.

Evaluation of the spatial accuracy of magnetic resonance imaging-based stereotactic target localization for gamma knife radiosurgery of functional disorders

PURPOSE

This study was undertaken to determine the impact of geometric distortions on the spatial accuracy of magnetic resonance imaging (MRI)-guided stereotactic localization for gamma knife functional radiosurgery.

METHOD

The spatial accuracy of MRI was evaluated by comparing stereotactic coordinates of intracranial targets, external fiducials, and anatomic structures defined by computed tomographic and MRI studies of the Radionics skull phantom (Radionics, Inc., Burlington, MA), the Rando head phantom, and 11 patients who underwent gamma knife functional radiosurgery. The distortion in MRI was assessed from computed tomographic and MRI fusion studies for these patients, as well as from MRI studies acquired by swapping the direction of the magnetic field gradients for five patients who underwent gamma knife radiosurgery and three patients who underwent MRI-guided frameless surgery. A follow-up program to compare the location of the created lesion with the intended target complemented the analysis.

RESULTS

The average difference between computed tomographic and MRI stereotactic coordinates of external fiducials, intracranial targets, and anatomic landmarks was of the order of 1 pixel size (0.9 x 0.9 x 1 mm3) along the x, y, and z axes. The average linear scaling along these axes as determined by fusion studies was approximately 0.8% and consistent with a single pixel. The follow-up studies, available for seven patients, revealed good agreement between the location of the created lesion and the intended target.

CONCLUSION

The spatial accuracy of an MRI-based localization system can be comparable to computed tomography-based localization with the added benefit of MRI resolution. Both machine- and object-related MRI distortions can be reduced to an acceptable level with contemporary scanners, optimized scanning sequences, and distortion-resistant stereotactic instruments.