Stereotactic Imaging Research Articles

Arcuate fasciculus tractography integrated into Gamma Knife surgery

To prevent speech disturbances after Gamma Knife surgery (GKS), the authors integrated arcuate fasciculus (AF) tractography based on diffusion tensor (DT) MR imaging into treatment planning for GKS. Arcuate fasciculus tractography was retrospectively integrated into planning that had been previously performed by neurosurgeons and radiation oncologists. This technique was retrospectively applied to 12 patients with arteriovenous malformations adjacent to the AF. Diffusion tensor images were acquired before the frame was affixed to the patient's head and DT tractography images of the AF were created using the authors' original software. The data from DT tractography and stereotactic 3D imaging studies obtained after frame fixation were transported to a treatment planning workstation for GKS and coregistered so that the delivered doses and incidence of posttreatment aphasia could be assessed. The AF could not be depicted in 2 patients who initially presented with motor aphasia caused by hemorrhaging from arteriovenous malformations. During the median follow-up period of 29 months after GKS, aphasia developed in 2 patients: 30 Gy delivered to the frontal portion of the AF caused conduction aphasia in 1 patient, and 9.6 Gy to the temporal portion led to motor aphasia in the other. Speech dysfunction was not observed after a maximum radiation dose of 10.0-16.8 Gy was delivered to the frontal fibers in 4 patients, and 3.6-5.2 Gy to the temporal fibers in 3. The authors found that administration of a 10-Gy radiation dose during GKS was tolerated in the frontal but not the temporal fibers of the AF. The authors recommend confirmation of the dose by integration of AF tractography with GKS, especially in lesions located near the temporal language fibers.

CT/MR Image Fusion in the Postoperative Assessment of Electrodes Implanted for Deep Brain Stimulation

Background/Aims: Stereotactic postoperative imaging is essential for verification of the position of electrodes implanted for deep brain stimulation (DBS). MRI offers superior visualisation of the DBS targets relative to CT, but previous adverse incidents have heightened concerns about risks of postoperative MRI. Preoperative MRI fused with postoperative CT offers an alternative method for evaluating electrode position, but before this method can be clinically applied, the image registration accuracy must be established. The purpose of this study was to quantitatively assess the accuracy of three different image registration and fusion methods. Methods: Preoperative stereotactic MRI and postoperative stereotactic CT were acquired from 20 patients under- going DBS surgery (35 electrodes in total). The postoperative CT was registered and fused with the preoperative MRI, using three different registration algorithms. The position of each electrode tip was determined in stereotactic coordinates both in the (unfused) postoperative CT and the fused CT/MRI. The difference in tip position between the CT and fused CT/MRI was used to evaluate the registration accuracy. Results: The mean error along the lateral, anteroposterior, and vertical axes was 0.5, 0.5, and 1 mm, respectively. Conclusions: CT/MRI fusion provides a safe, practical technique for postoperative identification of DBS electrodes.

SU‐FF‐T‐346: Measurement of Surface Dose Increase From Patient Immobilization Thermoplastic Masks Using Gafchromic EBT Films

Purpose: To evaluate setup accuracy of the BrainLAB stereotactic radiotherapy head immobilization mask using orthogonal projections from on‐board imaging. Materials and Methods: Eight patients were simulated and treated with the BrainLAB stereotactic head immobilization masks and CT‐localizers for brain lesions using single and hypo‐fractions. Orthogonal pairs of kV projections were acquired using Varian Trilogy's on‐board imager. The kV projections were then registered with digitally‐reconstructed‐radiographs (DRR) obtained from treatment planning. Shifts between the kV images and reference DRR's were calculated: anterior‐posterior (A‐P), left‐right (L‐R) and superior‐inferior (S‐I). If the shifts were > 2 mm in any direction, the patient was reset within the immobilization mask until satisfying accuracy was achieved. Results: Shifts as large as 5 mm in the A‐P, L‐R and S‐I directions between kV projections and DRR's were found. These shifts represent offsets between the treatment and simulation setup using immobilization mask. The mean offsets of 0.1 mm, 0.7 mm, and −1.6 mm represent systematic errors in the A‐P, L‐R and S‐I directions, respectively, using the BrainLAB localizer. The mean of the radial shifts is about 1.7 mm. The standard deviations of shifts 2.2 mm, 2.0 mm, and 2.6 mm represent patient setup accuracy with the BrainLAB mask in A‐P, L‐R and S‐I directions. Conclusions: The BrainLAB mask provides less invasive immobilization system than the head ring. Relying on this system for patient setup might be associated with errors as large as 5 mm. Image‐guidance with the kV on‐board imager provides shifts that are required to setup patient prior to or during patient treatment. The patient may relax or move during treatment, and thus uncontrolled and undetected setup errors may be produced with patients that are not well immobilized. The combination of stereotactic immobilization and image guidance will achieve more controlled and accurate patient setup within 2 mm.

SU-FF-T-550: Evaluation of Setup Accuracy of a Stereotactic Radiotherapy Head Immobilization Mask Using KV On-Board Imaging

Purpose: To evaluate setup accuracy of the BrainLAB stereotactic radiotherapy head immobilization mask using orthogonal projections from on‐board imaging.Materials and Methods: Eight patients were simulated and treated with the BrainLAB stereotactic head immobilization masks and CT‐localizers for brain lesions using single and hypo‐fractions. Orthogonal pairs of kV projections were acquired using Varian Trilogy's on‐board imager. The kV projections were then registered with digitally‐reconstructed‐radiographs (DRR) obtained from treatment planning. Shifts between the kV images and reference DRR's were calculated: anterior‐posterior (A‐P), left‐right (L‐R) and superior‐inferior (S‐I). If the shifts were > 2 mm in any direction, the patient was reset within the immobilization mask until satisfying accuracy has been achieved. Results: Shifts as large as 5 mm in the A‐P, L‐R and S‐I directions between kV projections and DRR's were found. These shifts represent offsets between the treatment and simulation setup using immobilization mask. The mean offsets of 0.1 mm, 0.7 mm, and −1.6 mm represent systematic errors in the A‐P, L‐R and S‐I directions, respectively, using the BrainLAB localizer. The mean of the radial shifts is about 1.7 mm. The standard deviations of shifts 2.2 mm, 2.0 mm, and 2.6 mm represent patient setup accuracy with the BrainLAB mask in A‐P, L‐R and S‐I directions. Conclusions: The BrainLAB mask provides less invasive immobilization system than the head ring. Relying on this system for patient setup might be associated with errors as large as 5 mm. Image‐guidance with the kV on‐board imager provides shifts that are required to setup patient prior to or during patient treatment. The patient may relax or move during treatment, and thus uncontrolled and undetected setup errors may be produced with patients that are not well immobilized. The combination of stereotactic immobilization and image guidance will achieve more controlled and accurate patient setup within 2 mm.

Avoiding the ventricle: a simple step to improve accuracy of anatomical targeting during deep brain stimulation

The authors examined the accuracy of anatomical targeting during electrode implantation for deep brain stimulation in functional neurosurgical procedures. Special attention was focused on the impact that ventricular involvement of the electrode trajectory had on targeting accuracy. The targeting error during electrode placement was assessed in 162 electrodes implanted in 109 patients at 2 centers. The targeting error was calculated as the shortest distance from the intended stereotactic coordinates to the final electrode trajectory as defined on postoperative stereotactic imaging. The trajectory of these electrodes in relation to the lateral ventricles was also analyzed on postoperative images. The trajectory of 68 electrodes involved the ventricle. The targeting error for all electrodes was calculated: the mean +/- SD and the 95% CI of the mean was 1.5 +/- 1.0 and 0.1 mm, respectively. The same calculations for targeting error for electrode trajectories that did not involve the ventricle were 1.2 +/- 0.7 and 0.1 mm. A significantly larger targeting error was seen in trajectories that involved the ventricle (1.9 +/- 1.1 and 0.3 mm; p < 0.001). Thirty electrodes (19%) required multiple passes before final electrode implantation on the basis of physiological and/or clinical observations. There was a significant association between an increased requirement for multiple brain passes and ventricular involvement in the trajectory (p < 0.01). Planning an electrode trajectory that avoids the ventricles is a simple precaution that significantly improves the accuracy of anatomical targeting during electrode placement for deep brain stimulation. Avoidance of the ventricles appears to reduce the need for multiple passes through the brain to reach the desired target as defined by clinical and physiological observations.

The value of image coregistration during stereotactic radiosurgery

Coregistration of any neuroimaging studies into treatment planning for stereotactic radiosurgery became easily applicable using the Leksell Gamma Knife 4C, a new model of gamma knife. The authors investigated the advantage of this image processing. Since installation of the Leksell Gamma Knife 4C at the authors' institute, 180 sessions of radiosurgery were performed. Before completion of planning, coregistration of frameless images of other modalities or previous images was considered to refine planning. Treatment parameters were compared for planning before and after refinement by use of coregistered images. Coregistered computed tomography clarified the anatomical structures indistinct on magnetic resonance imaging. Positron emission tomography visualized lesions disclosing metabolically high activity. Coregistration of prior imaging distinguished progressing lesions from stable ones. Diffusion-tensor tractography was integrated for lesions adjacent to the corticospinal tract or the optic radiation. After refinement of planning in 36 sessions, excess treated volume decreased (p = 0.0062) and Paddick conformity index improved (p < 0.001). Maximal dose to the white matter tracts was decreased (p < 0.001). Image coregistration provided direct information on anatomy, metabolic activity, chronological changes, and adjacent critical structures. This gathered information was sufficiently informative during treatment planning to supplement ambiguous information on stereotactic images, and was useful especially in reducing irradiation to surrounding normal structures.

Cord Dose Specification and Validation for Stereotactic Body Radiosurgery of Spine

Effective dose to a portion of the spinal cord in treatment segment, rather than the maximum point dose in the cord surface, was set as the dose limit in stereotactic-body radiosurgery (SBRS) of spine. Such a cord dose specification is sensitive to the volume size and position errors. Thus, we used stereotactic image guidance to minimize phantom positioning errors and compared the results of a 0.6-cm 3 Farmer ionization chamber and a 0.01-cm 3 compact ionization chamber to determine the detector size effect on 9 SBRS cases. The experimental errors ranging from 2% to 7% were estimated by the deviation of the mean dose in plans to the chamber with spatial displacements of 0.5 mm. The mean and measured doses for the large chamber to individual cases were significantly (∼17%) higher than the doses with the compact chamber placed at the same point. Our experimental results shown that the mean doses to the volume of interest could represent the measured cord doses. For the 9 patients, the mean doses to 10% of the cord were about 10 Gy, while the maximum cord doses varied from 11.6 to 17.6 Gy. The mean dose, possibly correlated with the cord complication, provided us an alternative and reliable cord dose specification in SBRS of spine.

Image-Guided Titanium Implantation for Craniofacial Prosthetics

Osseointegration implants have revolutionized craniofacial prosthetic reconstruction. Implant placement relies on adequate thickness and quality of bone to permit osseointegration. Positioning the implant is critical in craniofacial reconstruction because surface contours of the prosthesis must be preserved while housing attachment components securely and discretely. Also, the position of the final prosthesis must transition to native tissue smoothly. We report on the use of intraoperative stereotactic image guidance in the placement of implants for orbital, nasal, and auricular prosthetic reconstruction. Clinical data, intraoperative images, and postoperative rehabilitated results are presented to demonstrate the utility of the application of stereotactic image guidance for implant placement. In our experience, stereotactic image guidance facilitates optimal implant site selection if there is abnormal bone quantity or quality.

Relative Cerebral Blood Volume Values to Differentiate High-Grade Glioma Recurrence from Posttreatment Radiation Effect: Direct Correlation between Image-Guided Tissue Histopathology and Localized Dynamic Susceptibility-Weighted Contrast-Enhanced Perfusion MR Imaging Measurements

Differentiating tumor growth from posttreatment radiation effect (PTRE) remains a common problem in neuro-oncology practice. To our knowledge, useful threshold relative cerebral blood volume (rCBV) values that accurately distinguish the 2 entities do not exist. Our prospective study uses image-guided neuronavigation during surgical resection of MR imaging lesions to correlate directly specimen histopathology with localized dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging (DSC) measurements and to establish accurate rCBV threshold values, which differentiate PTRE from tumor recurrence. Preoperative 3T gradient-echo DSC and contrast-enhanced stereotactic T1-weighted images were obtained in patients with high-grade glioma (HGG) previously treated with multimodality therapy. Intraoperative neuronavigation documented the stereotactic location of multiple tissue specimens taken randomly from the periphery of enhancing MR imaging lesions. Coregistration of DSC and stereotactic images enabled calculation of localized rCBV within the previously recorded specimen locations. All tissue specimens were histopathologically categorized as tumor or PTRE and were correlated with corresponding rCBV values. All rCBV values were T1-weighted leakage-corrected with preload contrast-bolus administration and T2/T2*-weighted leakage-corrected with baseline subtraction integration. Forty tissue specimens were collected from 13 subjects. The PTRE group (n = 16) rCBV values ranged from 0.21 to 0.71, tumor (n = 24) values ranged from 0.55 to 4.64, and 8.3% of tumor rCBV values fell within the PTRE group range. A threshold value of 0.71 optimized differentiation of the histopathologic groups with a sensitivity of 91.7% and a specificity of 100%. rCBV measurements obtained by using DSC and the protocol we have described can differentiate HGG recurrence from PTRE with a high degree of accuracy.

HEARING PRESERVATION AFTER INTRACANALICULAR VESTIBULAR SCHWANNOMA RADIOSURGERY

Tumor control, facial function preservation, and hearing preservation are important criteria for successful management of intracanalicular vestibular schwannomas, whether observation, microsurgery, or radiosurgery is chosen. We collected data prospectively to assess hearing preservation after intracanalicular vestibular schwannoma radiosurgery. Between 1987 and 2003, 96 patients (65 men and 31 women) underwent gamma knife stereotactic radiosurgery (SRS) for intracanalicular tumors. The median patient age was 54 years (range, 22-80 years). Hearing was graded using the Gardner-Robertson (GR) and the American Academy of Otolaryngology-Head and Neck Surgery classifications. Dose planning was performed on intraoperative stereotactic images using multiple 4-mm isocenters. The median tumor volume was 0.112 mm3 (range, 0.05-0.447 mm3), and the median margin dose was 13 Gy (range, 10-18 Gy). The mean and median audiologic follow-up periods were 42 months and 28 months (range, 12-144 months), respectively. Serviceable hearing was preserved in 31 of 40 (77.5%) patients with initial American Academy of Otolaryngology-Head and Neck Surgery Class A hearing. Serviceable hearing was preserved in 40 of 79 (64.5%) patients with GR Grade I or II pre-SRS hearing. Ninety-two patients had GR Grade I, II, or III hearing before SRS, and GR Grade I, II, or III hearing was maintained in 78 patients (85%). Hearing grades improved in 7 patients. Facial and trigeminal nerve function was preserved in all patients. The tumor control rate (freedom from additional intervention) was 99.0% (95 of 96) at a median follow-up of 28 months (range, 12-144 months). One patient underwent tumor resection 18 months after radiosurgery. SRS is a minimally invasive first-line management option for patients with intracanalicular tumors and provides high rates of hearing preservation with minimal morbidity.

Evaluation of alignment error due to a speed artifact in stereotactic ultrasound image guidance

Ultrasound (US) image guidance systems used in radiotherapy are typically calibrated for soft tissue applications, thus introducing errors in depth-from-transducer representation when used in media with a different speed of sound propagation (e.g. fat). This error is commonly referred to as the speed artifact. In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through layers of simulated body fat, and we compared the results with calculated/predicted values. A general purpose US phantom (speed of sound (SOS) = 1540 m s−1) was imaged on a multi-slice CT scanner at a 0.625 mm slice thickness and 0.5 mm × 0.5 mm axial pixel size. Target-simulating wires inside the phantom were contoured and later transferred to the US guidance system. Layers of various thickness (1–8 cm) of commercially manufactured fat-simulating material (SOS = 1435 m s−1) were placed on top of the phantom to study the depth-related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using commercially manufactured tissue-simulating material (SOS = 1540 m s−1) for the top layers. For the fat-simulating material used in this study, we observed the magnitude of the depth-related alignment errors resulting from the speed artifact to be 0.7 mm cm−1 of fat imaged through. The measured alignment errors caused by the speed artifact agreed with the calculated values within one standard deviation for all of the different thicknesses of fat-simulating material studied here. We demonstrated the depth-related alignment error due to the speed artifact when using US image guidance for radiation treatment alignment and note that the presence of fat causes the target to be aliased to a depth greater than it actually is. For typical US guidance systems in use today, this will lead to delivery of the high dose region at a position slightly posterior to the intended region for a supine patient. When possible, care should be taken to avoid imaging through a thick layer of fat for larger patients in US alignments or, if unavoidable, the spatial inaccuracies introduced by the artifact should be considered by the physician during the formulation of the treatment plan.

Stereotactic model of the electrical distribution within the internal globus pallidus during deep brain stimulation

Deep brain stimulation (DBS) of the internal globus pallidus (GPi) is an established surgical technique for the treatment of movement disorders. The objective of this study was to propose a computational stereotactic model of the electrical distribution around the electrode within the targeted GPi in order to optimize parameter adjustment in clinical practice. The outline of the GPi can be defined precisely by using stereotactic magnetic resonance imaging (MRI) and from this it is possible to model its three-dimensional structure. The electrode and the distribution of the patient-specific parameters can then be co-registered with the GPi volume. By using this methodology, it is possible to visualize and measure the relationship between the electrical distribution of patient-specific parameters and the morphology of the GPi. The model could be applied in clinical practice to help determine the threshold for achieving a therapeutic effect and consequently may aid in optimizing parameter settings for individual patients.

Solitary Nocardia farcinica brain abscess in an immunocompetent adult mimicking metastatic brain tumor: rapid diagnosis by pyrosequencing and successful treatment

Background Nocardia brain abscess carries a higher morbidity and mortality rate than other bacterial cerebral abscesses, with reported mortality rates of 55% and 20% in immunocompromised and immunocompetent patients, respectively. To prevent a delay in diagnosis and treatment, an aggressive therapeutic approach is required. In the present study, a rapid and accurate molecular diagnostic approach using pyrosequencing (PS), a semiautomated molecular genotyping method of nucleotide sequencing-by-synthesis, was performed. Case description A 53-year-old man developed word-finding difficulties, followed by confusion and disorientation. On examination, the patient had a mixed aphasia; the receptive component was greater than the expressive component. The remainder of his neurologic examination findings was normal. Gadolinium-enhanced magnetic resonance imaging of the brain revealed a 2.0-cm multilobular, partially cystic, peripheral-enhancing mass in the posterior left temporal-parietal region with significant vasogenic edema and localized mass effect. A detailed laboratory investigation revealed that this patient was immunocompetent. An awake left posterior temporal-parietal craniotomy with cortical motor and speech mapping, using frameless stereotactic image guidance and intraoperative real-time ultrasound, was performed. Frozen section was consistent with cerebral abscess and methenamine silver staining revealed many beaded, thin-branching gram-positive bacilli. Colonies suspicious for Nocardia sp were seen within 2 days, and PCR followed by pyrosequencing (PS) identified Nocardia farcinica. Conclusions We report a nocardial cerebral abscess mimicking a metastatic brain tumor, and we demonstrate that PS technology can be used for the accurate and rapid identification of N farcinica isolated from a brain abscess—facilitating a rapid diagnosis and successful, durable treatment.

TU‐C‐351‐02: Alignment Error Due to Speed Artifact in Stereotactic Ultrasound Image Guidance

Purpose: US image guidance systems which are calibrated for soft tissue applications will introduce errors in depth‐from‐transducer representation when used in media with a different speed of sound propagation (e.g. fat). In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through simulated layers of body fat, and compared the results with calculated/predicted values. Method and Materials A General Purpose Ultrasound Phantom (speed of sound‐SOS = 1540 m/s) Model ATL 040 (CIRS, Norfolk, VA) was imaged on a LightSpeed RT CT scanner (GE Health Care, Waukesha, WI) at 0.625‐mm slice thickness and 0.5mm pixel. Target‐simulating wires inside the phantom were contoured and later transferred to the BAT Sxi unit (Nomos Corp., Cranberry, PA). Various thicknesses (1–8cm) of fat simulating material (SOS = 1435 m/s), manufactured by CIRS, were placed on top of the phantom to study the depth‐related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using tissue simulating material (SOS=1540 m/s) for the top layers. Result and Discussion: For the fat simulating material used in this study, we observed the magnitude of the depth‐related alignment errors resulting from this speed artifact to be 0.73 mm per cm of fat imaged‐through. The measured alignment errors caused by the speed artifact agreed with the calculated values within measurement uncertainties for the five different thicknesses of fat simulating material studied here. Conclusion: We demonstrated the depth‐related alignment error due to speed artifact when using US image guidance for radiation treatment alignment. When possible, care should be taken to avoid imaging through a thick layer of fat for larger patients in US alignments.

Stereotactic MRI in Dyt1 Dystonia: Focal Signal Abnormalities in the Basal Ganglia Do Not Contraindicate Deep Brain Stimulation

Aims: To study stereotactic magnetic resonance imaging (MRI) features of the basal ganglia in DYT1 primary dystonia. Methods: Twenty-five genetically confirmed DYT1 dystonia patients (age range, 8–66 years; mean age, 22 years) underwent brain MRI under general anesthesia at the time of globus pallidus internus (GPi) deep brain stimulation (DBS) surgery. MR images were retrospectively reviewed for signal intensity alterations. Clinical improvement of patients was assessed by comparing pre- and postoperative Burke-Fahn-Marsden Dystonia Rating Scale scores. Results: Seventeen patients out of 25 (68%) exhibited T₁-weighted hypointense/T₂-weighted hyperintense signal abnormalities in the putamen and globus pallidus on MR images. Signals were isointense with cerebrospinal fluid in all sequences. The mean volume of focal signal abnormalities was 15 mm³ (maximum, 154.5 mm³). The total volume of focal signal abnormalities in the basal ganglia was correlated with the duration of the disease (p = 0.01). Although clinical outcome did not differ as a function of the presence of focal signal abnormalities overall, patients with signals within the GPi tended to show lesser improvement (p = 0.04). Conclusions: T₁-hypointense/T₂-hyperintense signal abnormalities are common findings in the putamen and globus pallidus of DYT1 patients but do not contraindicate DBS. However, their presence within the GPi may reduce the efficacy of DBS treatment.

QUANTITATIVE ANALYSIS OF EXPOSURE OF STAGED ORBITOZYGOMATIC AND RETROSIGMOID CRANIOTOMIES FOR LESIONS OF THE CLIVUS WITH SUPRATENTORIAL EXTENSION

A two-stage approach using orbitozygomatic (OZ) and retrosigmoid (RS) craniotomies is one option for the management of petroclival lesions with supratentorial extension. The goal of this study was to investigate the supratentorial and infratentorial exposures of the clivus obtained through this staged approach. Formalin-fixed, silicon-injected specimens underwent stereotactic imaging. Six paired OZ and RS craniotomies were performed. Neuronavigation was used to determine the areas and limits of exposure and to plot these areas on three-dimensional reconstructions of the skull base. The mean area of exposure of the parasellar region and clivus through the OZ craniotomy was 640 +/- 75 mm. Visualization of the parasellar region, cavernous sinus, and upper cranial nerves was achieved. The ventral brainstem corresponding to the cranial quarter of the clivus was visualized. The mean area of exposure of the clivus and petrous bone through the RS was 1930 +/- 250 mm. In the cranial quarter of the clivus, there was a small region of overlap in exposure between the two craniotomies. The limits of exposure are described. OZ and RS craniotomies provide complementary exposure with limited redundancy. Significant visualization of the parasellar region, clivus, and surrounding bony landmarks is obtained. The primary limitation is exposure of the contralateral half of Zones II and III of the clivus. This strategy represents a reasonable option for accessing paracentral petroclival lesions with a supratentorial extension.

EUS-Guided Fiducial Placement (EUS FNF) Prior to Targeted Radiation Therapy in Abdominal and Pelvic Tumors: A Case Series

Introduction: Stereotactic radiosurgical techniques, such as CyberKnife, and image guided radiation therapy (IGRT) deliver precisely aimed radiation beams to tumors while minimizing radiation to adjacent normal tissue. Internal radiographic markers, or fiducials, serve as reference points to accurately delineate tumors and guide radiation therapy. Published reports describe fiducials placed surgically or percutaneously under US or CT guidance, as well as EUS-guided placement of thoraco-abdominal fiducials, but there have been no reports of gastroenterologists using EUS to guide fiducial placement in the prostate. We describe a case series of EUS-guided placement of fiducials (EUS FNF), which provides not only an alternative to invasive surgical methods, but allows access to structures that may be difficult to reach percutaneously. Methods: Five patients scheduled for CyberKnife or IGRT were evaluated for tumor localization and fiducial placement via EUS. 3 mm × 0.8 mm gold seeds were backloaded into a 19G FNA needle, and a linear array echoendoscope was used to deploy the fiducials into the area of interest under EUS and fluoroscopic guidance. Post-procedure abdominal X-rays or CT scans were performed to confirm fiducial positioning. All patients received intravenous antibiotics prior to EUS FNF and completed up to five days of oral antibiotics following the procedure. Results: A total of sixteen fiducials were used in five patients; one was lost in the stomach during attempted placement. Seven were placed in three abdominal tumors: one pancreatic uncinate adenocarcinoma, one metastatic melanoma in the uncinate process, and one metastatic cholangiocarcinoma in a periduodenal lymph node. Eight gold seeds were deployed in two patients with prostate cancer in four quadrant fashion to delineate the prostate. There was no reported migration of the fiducials at the time of radiation therapy and no complications were noted due to fiducial placement. Conclusions: EUS FNF to facilitate stereotactic radiosurgical and image guided radiation therapy is a new and safe alternative to traditional surgical or percutaneous approaches. In addition to being less invasive, EUS FNF provides the advantage of targeting lesions in difficult, more posterior locations such as the uncinate process. Moreover, we describe the use of a linear array echoendoscope for EUS FNF placement in the prostate, thus adding to the expanding list of indications for EUS.

PRETARGETING FOR THE IMPLANTATION OF STIMULATION ELECTRODES INTO THE SUBTHALAMIC NUCLEUS

The optimal imaging modality for preoperative targeting of the subthalamic nucleus (STN) for high-frequency stimulation is controversially discussed. Commonly used methods were stereotactic magnetic resonance imaging (MRI), stereotactic ventriculography, and fusion between MRI and stereotactic computer tomography. All of these techniques not only have their own advantages but also specific limitations and drawbacks. The purpose of this study was to evaluate the accuracy of the preoperative MRI targeting as compared with ventriculography in terms of both the STN target as well as the internal landmarks.Thirty patients with Parkinson's disease who underwent bilateral surgery for STN-high-frequency stimulation received both stereotactic ventriculography and stereotactic MRI. The theoretical target was determined by each of these two imaging modalities. The final electrode placement was performed after extensive electrophysiological evaluation using microrecording and microstimulation. The real target was assumed to be given by the electrode contact with the best clinical result assessed by the United Parkinson's Disease Rating Scale in the postoperative follow-up. In addition, the coordinates of the two landmarks, anterior commissure and posterior commissure, were determined using both imaging methods.The mean targeting error was 4.1 +/- 1.7 mm (mean +/- standard deviation) for MRI and 2.4 +/- 1.1 mm for ventriculography (P< 0.0001). The mean target mismatch between the two imaging methods was 2.9 +/- 1.2 mm. The length of the anterior commissure-posterior commissure distance differed significantly (P < 0.0001) between MRI (27.6 +/- 1.6 mm) and ventriculography (25.0 +/- 1.3 mm). The mismatch was mainly induced by an anterior displacement of the anterior commissure by 1.9 +/- 2.2 mm (P < 0.0001) in MRI determination, as compared with ventriculography.Our findings show that the indirect targeting of the STN using coordinates based on radiological landmarks is more accurate than the direct targeting using anatomic visualization of the target structure. Regardless of the imaging procedure, electrophysiological mapping is required for optimal electrode placement, although in 20% of cases, the target determined by MRI falls out of the radius explored by electrophysiology.

Stereotactic image‐guided navigation in the preoperative imaging of perforators for DIEP flap breast reconstruction

Preoperative imaging is sought prior to DIEA (Deep Inferior Epigastric Artery) perforator flaps due to the potential for maximizing operative success and minimizing operative complications. Recent advances include the use of computed tomography (CT) angiography (CTA) and magnetic resonance angiography. Image-guided stereotactic surgery is a recent technique that has been used with success in several fields of surgery. The variability of perforator anatomy makes DIEA perforator flap surgery a suitable candidate for such technology, but as yet this has not been described. A study was undertaken to determine the feasibility of CT-guided stereotaxy technique in DIEA perforator flap surgery and to compare findings with both conventional CTA and operative findings. Five consecutive patients planned for an elective DIEA perforator flap were recruited. Each patient underwent preoperative imaging of the anterior abdominal wall vasculature with both conventional CTA and CT-guided stereotactic imaging. Imaging findings were compared to operative findings. In all cases, all the major perforators were accurately localized with stereotactic imaging and with conventional CTA. Stereotactic navigation demonstrated a slightly better (nonsignificant) correlation with perforator location than conventional CTA. As such, CT-guided stereotactic imaging is an accurate method for the preoperative planning of DIEA perforator flaps, providing additional and potentially more accurate data to conventional CTA. With no additional scanning required, the method described in this paper allows the combined use of both methods for preoperative planning.

Use of polymer gel for bypassing the stereotactic imaging step prior Gamma Knife radiosurgery in small animals

Object. Accurate targeting is crucial for the irradiation of a small volume in an animal model, such as lesions produced in the rat brain by Gamma Knife. We propose an original method based on a polymer gel dosimeter to determine the accuracy and reproducibility of irradiation using a new stereotactic frame. Methods. A in-house designed rat stereotactic frame compatible with the Gamma Knife Automatic Positioning System was constructed. Initial spatial coordinates to target the right frontal lobe were acquired by X-ray imaging of the rats positioned in the stereotactic frame using the Gamma Knife angiographic fiducial box. The rat brain was then removed through a small burr hole and the intracranial cavity was washed and filled with the polymer gel dosimeter. This “gel brain” was irradiated at a dose of 15 Gy using 4 or 8 mm collimator helmets. The irradiated volumes coordinates were measured non-invasively by magnetic resonance imaging (MRI) or visually after excision of the polymer gel. Results. The position of the polymerized areas revealed that the stereotactic frame is able to accurately reproduce the same position of irradiation in each animal. The average location of the center of the polymerized areas was as follows: X = 3.07 ± 0.31 mm, Y = 5.50 ± 0.26 mm and Z = 0.90 ± 0.45 mm when using 8 mm collimators; and X = 2.86 ± 0.18 mm, Y = 6.00 ± 0.22 mm and Z = 0.58 ± 0.39 mm for 4 mm collimators. The small standard deviation demonstrated that assessment of the irradiated volume performed with the gel dosimeter was highly reproducible. Conclusion. The polymer gel dosimeter confirmed the ability of the rat stereotactic frame to accurately and reproducibly position a small animal for precise radiosurgery procedures. These characteristics eliminate the need of stereotactic imaging before irradiation.