Subthalamic nucleus deep brain stimulator placement using high-field interventional magnetic resonance imaging and a skull-mounted aiming device: technique and application accuracy

Deep brain stimulation surgical techniques

Stereotactic techniques for placement of deep brain stimulation (DBS) electrodes have undergone continuous refinement since the introduction of human stereotaxis in the 1940s. Volumetric imaging techniques, including magnetic resonance imaging and computed tomography, have replaced ventriculography, and increasingly sophisticated computer systems now allow highly refined targeting of subcortical structures. This chapter reviews the underlying principles of stereotactic surgery, including imaging, targeting, and registration, and describes the surgical approach to DBS placement using both framed and frameless techniques.

An optimized system for interventional magnetic resonance imaging-guided stereotactic surgery: preliminary evaluation of targeting accuracy

BACKGROUND

Deep brain stimulation electrode placement with interventional magnetic resonance imaging (MRI) has previously been reported using a commercially available skull-mounted aiming device (Medtronic Nexframe MR) and native MRI scanner software. This first-generation method has technical limitations that are inherent to the hardware and software used. A novel system (SurgiVision ClearPoint) consisting of an aiming device (SMARTFrame) and software has been developed specifically for interventional MRI, including deep brain stimulation.

OBJECTIVE

To report a series of phantom and cadaver tests performed to determine the capability, preliminary accuracy, and workflow of the system.

METHODS

Eighteen experiments using a water phantom were used to determine the predictive accuracy of the software. Sixteen experiments using a gelatin-filled skull phantom were used to determine targeting accuracy of the aiming device. Six procedures in 3 cadaver heads were performed to compare the workflow and accuracy of ClearPoint with Nexframe MR.

RESULTS

Software prediction experiments showed an average error of 0.9 ± 0.5 mm in magnitude in pitch and roll (mean pitch error, -0.2 ± 0.7 mm; mean roll error, 0.2 ± 0.7 mm) and an average error of 0.7 ± 0.3 mm in X-Y translation with a slight anterior (0.5 ± 0.3 mm) and lateral (0.4 ± 0.3 mm) bias. Targeting accuracy experiments showed an average radial error of 0.5 ± 0.3 mm. Cadaver experiments showed a radial error of 0.2 ± 0.1 mm with the ClearPoint system (average procedure time, 88 ± 14 minutes) vs 0.6 ± 0.2 mm with the Nexframe MR (average procedure time, 92 ± 12 minutes).

CONCLUSION

This novel system provides the submillimetric accuracy required for stereotactic interventions, including deep brain stimulation placement. It also overcomes technical limitations inherent in the first-generation interventional MRI system.

The subthalamic nucleus at 3.0 Tesla: choice of optimal sequence and orientation for deep brain stimulation using a standard installation protocol: clinical article

OBJECT

Reliable visualization of the subthalamic nucleus (STN) is indispensable for accurate placement of electrodes in deep brain stimulation (DBS) surgery for patients with Parkinson disease (PD). The aim of the study was to evaluate different promising new MRI methods at 3.0 T for preoperative visualization of the STN using a standard installation protocol.

METHODS

Magnetic resonance imaging studies (T2-FLAIR, T1-MPRAGE, T2*-FLASH2D, T2-SPACE, and susceptibility-weighted imaging sequences) obtained in 9 healthy volunteers and in 1 patient with PD were acquired. Two neuroradiologists independently analyzed image quality and visualization of the STN using a 6-point scale. Interrater reliability, contrast-to-noise ratios, and signal-to-noise ratios for the STN were calculated. For illustration of the anatomical accuracy, coronal T2*-FLASH2D images were fused with the corresponding coronal section schema of the Schaltenbrand and Wahren stereotactic atlas.

RESULTS

The STN was best and reliably visualized on T2*-FLASH2D imaging (in particular, the coronal view). No major artifacts in the STN were observed in any of the sequences. Susceptibility-weighted, T2-SPACE, and T2*-FLASH2D imaging provided significantly higher contrast-to-noise ratio values for the STN than standard T2-weighted imaging. Fusion of the coronal T2*-FLASH2D and the digitized coronal atlas view projected the STN clearly within the boundaries of the STN found in anatomical sections.

CONCLUSIONS

For 3.0-T MRI, T2*-FLASH2D (particularly the coronal view) provides optimal delineation of the STN using a standard installation protocol.

Clinical outcomes of PD patients having bilateral STN DBS using high-field interventional MR-imaging for lead placement

OBJECTIVE

Recently, an iMRI-guided technique for implanting DBS electrodes without MER was developed at our center. Here we report the clinical outcomes of PD patients undergoing STN DBS surgery using this surgical approach.

METHODS

Consecutive PD patients undergoing bilateral STN DBS using this method were prospectively studied. Severity of PD was determined using the UPDRS scores, Hoehn and Yahr staging score, stand-sit-walk testing, and the dyskinesia rating scale. The primary outcome measure was the change in UPDRS III off medication score at 6 months. DBS stimulation parameters, adverse events, levodopa equivalent daily dose (LEDD), and DBS lead locations were also recorded. Seventeen advanced PD patients (9M/8F) were enrolled from 2007 to 2009.

RESULTS

The mean UPDRS III off medication score improved from 44.5 to 22.5 (49.4%) at 6 months (p=0.001). Other secondary outcome measures (UPDRS II, III on medication, and IV) significantly improved as well (p<0.01). LEDD decreased by an average of 24.7% (p=0.003). Average stimulation parameters were: 2.9V, 66.4μs, 154Hz.

CONCLUSION

This pilot study demonstrates that STN DBS leads placed using the iMRI-guided method results in significantly improved outcomes in PD symptoms, and these outcomes are similar to what has been reported using traditional frame-based, MER-guided stereotactic methods.

Deep brain stimulation: Subthalamic nucleus electrophysiological activity in awake and anesthetized patients

OBJECTIVE

The purpose of this study was to evaluate changes in subthalamic nucleus (STN) neuronal activity in Parkinson's disease (PD) patients during deep brain stimulation (DBS) surgery under general anesthesia, and to compare these data with those recorded in the same subjects during previous surgery under local anesthesia.

METHODS

Five patients with advanced PD, who had previously undergone bilateral STN-DBS under local anesthesia, underwent re-implantation under general anesthesia (with an anesthetic protocol based on the intravenous infusion of remifentanyl and ketamine) owing to surgical device complications. The microelectrode recording (MER) data obtained were analyzed by an off-line spike-sorting software. Neurophysiological data (number of spikes detected, mean firing rate, pause index and burst index) obtained under local and general anesthesia were then evaluated and compared by means of statistical analysis.

RESULTS

We found no statistically significant difference between the first and second surgical procedures in any of the neurophysiological parameters analyzed.

CONCLUSIONS

Bilateral STN-DBS for advanced PD with MER guidance is possible and reliable under a ketamine-based anesthetic protocol.

SIGNIFICANCE

General anesthesia can be proposed for those patients who do not accept an "awake surgery" for clinical reasons, such as excessive fear, poor cooperation or severe "off"-medication effects.

Intraoperative 3D fluoroscopy in stereotactic surgery

BACKGROUND

Intraoperative localisation of a stereotactic probe remains challenging. Stereotactic X-ray, the "gold standard", as well as intraoperative magnetic resonance (MRI) and computed tomography (CT), require a dedicated operating room (OR). Fluoroscopy with crosshairs confirms only grossly the target position. An alternative would be a mobile three-dimensional (3D) fluoroscopy C-arm. To our knowledge, this is the first report on 3D C-arm fluoroscopy to verify stereotactical trajectories. The objective was to assess the feasibility of using a 3D C-arm to verify the intraoperative trajectory and target.

METHODS

A total of 12 stereotactic trajectories in 10 patients were analysed, comprising 8 biopsies and 4 electrode trajectories. The fluoroscopic scan was performed after implantation of the deep brain stimulation electrode or after advancing the biopsy needle to the tumour. An image set is acquired during a rotation of the 3D C-arm. The image set is reconstructed and merged to the preoperative CT scan. Calculating the vector error and the deviation assesses target and trajectory accuracy.

RESULTS

The mean trajectory deviation was 0.6 mm (±0.54 mm) and the mean vector error was 1.44 mm (±1.43 mm). There was no influence on the surgical time and the mean irradiation dosage was 401.9 cGycm(2).

CONCLUSIONS

This target and trajectory verification is feasible. Its accuracy seems comparable with MRI and CT. There is no additional time consumption. Irradiation is comparable with stereotactic X-ray.

Pitfalls in precision stereotactic surgery

Precision is the ultimate aim of stereotactic technique. Demands on stereotactic precision reach a pinnacle in stereotactic functional neurosurgery. Pitfalls are best avoided by possessing in-depth knowledge of the techniques employed and the equipment used. The engineering principles of arc-centered stereotactic frames maximize surgical precision at the target, irrespective of the surgical trajectory, and provide the greatest degree of surgical precision in current clinical practice. Stereotactic magnetic resonance imaging (MRI) provides a method of visualizing intracranial structures and fiducial markers on the same image without introducing significant errors during an image fusion process. Although image distortion may potentially limit the utility of stereotactic MRI, near-complete distortion correction can be reliably achieved with modern machines. Precision is dependent on minimizing errors at every step of the stereotactic procedure. These steps are considered in turn and include frame application, image acquisition, image manipulation, surgical planning of target and trajectory, patient positioning and the surgical procedure itself. Audit is essential to monitor and improve performance in clinical practice. The level of stereotactic precision is best analyzed by routine postoperative stereotactic MRI. This allows the stereotactic and anatomical location of the intervention to be compared with the anatomy and coordinates of the intended target, avoiding significant image fusion errors.

Deep brain stimulation of the subthalamic nucleus for advanced Parkinson disease using general anesthesia: long-term results

Object

The authors analyze long-term outcome in a substantial number of patients who underwent subthalamic nucleus (STN) deep brain stimulation (DBS) surgery under general anesthesia.

Methods

Eighty-two patients underwent bilateral placement of DBS electrodes under general anesthesia for advanced Parkinson disease; the STN was the target in all cases. All patients underwent intraoperative microelectrode recording of the STN. No intraoperative macrostimulation was performed. Unified Parkinson's Disease Rating Scale (UPDRS) data were recorded in 28 patients. Assessment of outcome was performed using the UPDRS (in 28 cases), the electrophysiological recordings (in all 82 cases), medication reduction (in 78 cases), and complications (in 82 cases).

Results

There was improvement in UPDRS scores across all measures following surgery. The total UPDRS score, off medication, improved from 68.78 (geometrical mean, 95% CI 61.76–76.60) preoperatively to 45.89 (geometrical mean, 95% CI 34.86–60.41) at 1 year postoperatively (p = 0.003, data available in 26 patients). Improvements were obtained in UPDRS Part II (Activities of Daily Living) off medication (p = 0.001) and also UPDRS Part III (Motor Examination) off medication (p < 0.001). Results for the on-medication and on-stimulation states also showed a statistically significant improvement for UPDRS Part III (p = 0.047). Good microelectrode recording of the STN was obtained under general anesthesia; the median first-track length was 4.0 mm, and the median number of tracks passed per patient was 3.0. The median reduction in levodopa medication was 58.1% (interquartile range 42.9%–73.3%). One patient had an intracerebral hemorrhage in the track of 1 electrode but did not require surgical evacuation. One patient had generalized convulsive seizures 24 hours postoperatively and was intubated for seizure control. Unified Parkinson's Disease Rating Scale scores were obtained in 26 patients at 1 year, 28 patients at 3 years, 17 at 5 years, and 7 at 7 years postoperatively. Up to 7 years postoperatively, there was sustained improvement in the total UPDRS score. The results in these patients showed minimal deterioration in the motor section of the UPDRS over time, up to 7 years following the operation. The authors found no evidence that the UPDRS Part II scores changed significantly over the period of 1–7 years after surgery (p = 0.671, comparison of mean scores at 1 and 7 years using generalized estimating equations).

Conclusions

Long-term outcomes confirm that it is both safe and effective to perform STN DBS under general anesthesia. As part of patient choice, this option should be offered to all DBS candidates with advanced Parkinson disease to enable more of these patients to undergo this beneficial surgery.

Fiducial registration with spoiled gradient-echo magnetic resonance imaging enhances the accuracy of subthalamic nucleus targeting

BACKGROUND

A variety of imaging strategies may be used to derive reliable stereotactic coordinates when performing deep brain stimulation lead implants. No single technique has yet proved optimal.

OBJECTIVE

To compare the relative accuracy of stereotactic coordinates for the subthalamic nucleus (STN) derived either from fast spin echo/inversion recovery (FSE/IR) magnetic resonance imaging MRI alone (group 1) or FSE/IR in conjunction with T1-weighted spoiled gradient-echo MRI (group 2).

METHODS

A retrospective analysis of 145 consecutive STN deep brain stimulation lead placements (group 1, n = 72; group 2, n = 73) was performed in 81 Parkinson disease patients by 1 surgical team. From the operative reports, we recorded the number of microelectrode recording trajectories required to localize the desired STN target and the span of STN traversed along the implantation trajectory. In addition, we calculated the 3-dimensional vector difference between the initial MRI-derived coordinates and the final physiologically refined coordinates.

RESULTS

The proportion of implants completed with just 1 microelectrode recording trajectory was greater (81% vs 58%; P < .001) and the 3-dimensional vector difference between the anatomically selected target and the microelectrode recording-refined target was smaller (0.6 ± 1.2 vs 0.9 ± 1.3; P = .04) in group 2 than in group 1. At the same time, the mean expanse of STN recorded along the implantation trajectory was 8% greater in group 2 (4.8 ± 0.6 vs 5.2 ± 0.6 mm; P < .001).

CONCLUSION

A combination of stereotactic FSE/IR and spoiled gradient-echo MRI yields more accurate coordinates for the STN than FSE/IR MRI alone.

Improving targeting in image-guided frame-based deep brain stimulation

BACKGROUND

Deep brain stimulation (DBS) is commonly used in the treatment of movement disorders such as Parkinson disease (PD), dystonia, and other tremors.

OBJECTIVE

To examine systematic errors in image-guided DBS electrode placement and to explore a calibration strategy for stereotactic targeting.

METHODS

Pre- and postoperative stereotactic MR images were analyzed in 165 patients. The perpendicular error between planned target coordinates and electrode trajectory was calculated geometrically for all 312 DBS electrodes implanted. Improvement in motor unified PD rating scale III subscore was calculated for those patients with PD with at least 6 months of follow-up after bilateral subthalamic DBS.

RESULTS

Mean (standard deviation) scalar error of all electrodes was 1.4(0.9) mm with a significant difference between left and right hemispheres. Targeting error was significantly higher for electrodes with coronal approach angle (ARC) ≥10° (P < .001). Mean vector error was X: -0.6, Y: -0.7, and Z: -0.4 mm (medial, posterior, and superior directions, respectively). Targeting error was significantly improved by using a systematic calibration strategy based on ARC and target hemisphere (mean: 0.6 mm, P < .001) for 47 electrodes implanted in 24 patients. Retrospective theoretical calibration for all 312 electrodes would have reduced the mean (standard deviation) scalar error from 1.4(0.9) mm to 0.9(0.5) mm (36% improvement). With calibration, 97% of all electrodes would be within 2 mm of the intended target as opposed to 81% before calibration. There was no significant correlation between the degree of error and clinical outcome from bilateral subthalamic nucleus DBS (R = 0.07).

CONCLUSION

After calibration of a systematic targeting error an MR image-guided stereotactic approach would be expected to deliver 97% of all electrodes to within 2 mm of the intended target point with a single brain pass.

Clinical safety of brain magnetic resonance imaging with implanted deep brain stimulation hardware: large case series and review of the literature

BACKGROUND

Over 75,000 patients have undergone deep brain stimulation (DBS) procedures worldwide. Magnetic resonance imaging (MRI) is an important clinical and research tool in analyzing electrode location, documenting postoperative complications, and investigating novel symptoms in DBS patients. Functional MRI may shed light on the mechanism of action of DBS. MRI safety in DBS patients is therefore an important consideration.

METHODS

We report our experience with MRI in patients with implanted DBS hardware and examine the literature for clinical reports on MRI safety with implanted DBS hardware.

RESULTS

A total of 262 MRI examinations were performed in 223 patients with intracranial DBS hardware, including 45 in patients with an implanted pulse generator. Only 1 temporary adverse event occurred related to patient agitation and movement during immediate postoperative MR imaging. Agitation resolved after a few hours, and an MRI obtained before implanted pulse generator implantation revealed edema around both electrodes. Over 4000 MRI examinations in patients with implanted DBS hardware have been reported in the literature. Only 4 led to adverse events, including 2 hardware failures, 1 temporary and 1 permanent neurological deficit. Adverse neurological events occurred in a unique set of circumstances where appropriate safety protocols were not followed. MRI guidelines provided by DBS hardware manufacturers are inconsistent and vary among devices.

CONCLUSIONS

The importance of MRI in modern medicine places pressure on industry to develop fully MRI-compatible DBS devices. Until then, the literature suggests that, when observing certain precautions, cranial MR images can be obtained with an extremely low risk in patients with implanted DBS hardware.

Accuracy of magnetic resonance imaging-directed frame-based stereotaxis

BACKGROUND

Accurate placement of a probe to the deep regions of the brain is an important part of neurosurgery. In the modern era, magnetic resonance image (MRI)-based target planning with frame-based stereotaxis is the most common technique.

OBJECTIVE

To quantify the inaccuracy in MRI-guided frame-based stereotaxis and to assess the relative contributions of frame movements and MRI distortion.

METHODS

The MRI-directed implantable guide-tube technique was used to place carbothane stylettes before implantation of the deep brain stimulation electrodes. The coordinates of target, dural entry point, and other brain landmarks were compared between preoperative and intraoperative MRIs to determine the inaccuracy.

RESULTS

The mean 3-dimensional inaccuracy of the stylette at the target was 1.8 mm (95% confidence interval [CI], 1.5-2.1. In deep brain stimulation surgery, the accuracy in the x and y (axial) planes is important; the mean axial inaccuracy was 1.4 mm (95% CI, 1.1-1.8). The maximal mean deviation of the head frame compared with brain over 24.1 ± 1.8 hours was 0.9 mm (95% CI, 0.5-1.1). The mean 3-dimensional inaccuracy of the dural entry point of the stylette was 1.8 mm (95% CI, 1.5-2.1), which is identical to that of the target.

CONCLUSION

Stylette positions did deviate from the plan, albeit by 1.4 mm in the axial plane and 1.8 mm in 3-dimensional space. There was no difference between the accuracies at the dura and the target approximately 70 mm deep in the brain, suggesting potential feasibility for accurate planning along the whole trajectory.

Assessment of hippocampal adeno-associated viral vector gene delivery via frameless stereotaxis in a nonhuman primate

BACKGROUND/AIMS

Expression of the neuropeptide galanin in hippocampal neurons reduces seizures in the kainic acid rodent model of epilepsy. In order to translate these findings into a human clinical trial, the safety and feasibility of hippocampal adeno-associated viral (AAV) vector expression must be demonstrated in a nonhuman primate model.

METHODS

The Stealth Frameless Stereotactic System and Navigus Biopsy Appliance (Medtronic) were used to inject self-complementary AAV2 carrying the gene for green fluorescent protein (GFP) into monkey hippocampi. Using a single occipital trajectory per side (n = 8 trajectories), multiple injections spaced by 5 mm were delivered to each hippocampus.

RESULTS

GFP was expressed in both neuronal and glial cells. Injections led to nonhomogeneous gene expression, suggesting closer spacing of injections may lead to more gene expression. Increasing injection volumes entailed a general increase in volume of expression, but there was no overlap of expression within the 5-mm injection interval. Efforts to avoid the occipital horn failed to prevent leaking of vector into the ventricle, and resulted in deviation of the trajectory at proximal points from the hippocampus.

CONCLUSION

Using the occipital approach, adequate cannulation of the monkey hippocampus will require transventricular trajectories.

Frameless deep brain stimulation using intraoperative O-arm technology

Object

Correct lead location in the desired target has been proven to be a strong influential factor for good clinical outcome in deep brain stimulation (DBS) surgery. Commonly, a surgeon's first reliable assessment of such location is made on postoperative imaging. While intraoperative CT (iCT) and intraoperative MR imaging have been previously described, the authors present a series of frameless DBS procedures using O-arm iCT.

Methods

Twelve consecutive patients with 15 leads underwent frameless DBS placement using electrophysiological testing and O-arm iCT. Initial target coordinates were made using standard indirect and direct assessment. Microelectrode recording (MER) with kinesthetic responses was performed, followed by microstimulation to evaluate the side-effect profile. Intraoperative 3D CT acquisitions obtained between each MER pass and after final lead placement were fused with the preoperative MR image to verify intended MER movements around the target area and to identify the final lead location. Tip coordinates from the initial plan, final intended target, and actual lead location on iCT were later compared with the lead location on postoperative MR imaging, and euclidean distances were calculated. The amount of radiation exposure during each procedure was calculated and compared with the estimated radiation exposure if iCT was not performed.

Results

The mean euclidean distances between the coordinates for the initial plan, final intended target, and actual lead on iCT compared with the lead coordinates on postoperative MR imaging were 3.04 ± 1.45 mm (p = 0.0001), 2.62 ± 1.50 mm (p = 0.0001), and 1.52 ± 1.78 mm (p = 0.0052), respectively. The authors obtained good merging error during image fusion, and postoperative brain shift was minimal. The actual radiation exposure from iCT was invariably less than estimates of exposure using standard lateral fluoroscopy and anteroposterior radiographs (p < 0.0001).

Conclusions

O-arm iCT may be useful in frameless DBS surgery to approximate microelectrode or lead locations intraoperatively. Intraoperative CT, however, may not replace fundamental DBS surgical techniques such as electrophysiological testing in movement disorder surgery. Despite the lack of evidence for brain shift from the procedure, iCT-measured coordinates were statistically different from those obtained postoperatively, probably indicating image merging inaccuracy and the difficulties in accurately denoting lead location. Therefore, electrophysiological testing may truly be the only means of precisely knowing the location in 3D space intraoperatively. While iCT may provide clues to electrode or lead location during the procedure, its true utility may be in DBS procedures targeting areas where electrophysiology is less useful. The use of iCT appears to reduce radiation exposure compared with the authors' traditional frameless technique.

Intraoperative magnetic resonance imaging findings during deep brain stimulation surgery

OBJECT

Deep brain stimulation (DBS) is an established neurosurgical technique used to treat a variety of neurological disorders, including Parkinson disease, essential tremor, dystonia, epilepsy, depression, and obsessive-compulsive disorder. This study reports on the use of intraoperative MR imaging during DBS surgery to evaluate acute hemorrhage, intracranial air, brain shift, and accuracy of lead placement.

METHODS

During a 46-month period, 143 patients underwent 152 DBS surgeries including 289 lead placements utilizing intraoperative 1.5-T MR imaging. Imaging was supervised by an MR imaging physicist to maintain the specific absorption rate below the required level of 0.1 W/kg and always included T1 magnetization-prepared rapid gradient echo and T2* gradient echo sequences with selected use of T2 fluid attenuated inversion recovery (FLAIR) and T2 fast spin echo (FSE). Retrospective review of the intraoperative MR imaging examinations was performed to quantify the amount of hemorrhage and the amount of air introduced during the DBS surgery.

RESULTS

Intraoperative MR imaging revealed 5 subdural hematomas, 3 subarachnoid hemorrhages, and 1 intraparenchymal hemorrhage in 9 of the 143 patients. Only 1 patient experiencing a subarachnoid hemorrhage developed clinically apparent symptoms, which included transient severe headache and mild confusion. Brain shift due to intracranial air was identified in 144 separate instances.

CONCLUSIONS

Intraoperative MR imaging can be safely performed and may assist in demonstrating acute changes involving intracranial hemorrhage and air during DBS surgery. These findings are rarely clinically significant and typically resolve prior to follow-up imaging. Selective use of T2 FLAIR and T2 FSE imaging can confirm the presence of hemorrhage or air and preclude the need for CT examinations.

Novel platform for MRI-guided convection-enhanced delivery of therapeutics: preclinical validation in nonhuman primate brain

BACKGROUND/AIMS

A skull-mounted aiming device and integrated software platform has been developed for MRI-guided neurological interventions. In anticipation of upcoming gene therapy clinical trials, we adapted this device for real-time convection-enhanced delivery of therapeutics via a custom-designed infusion cannula. The targeting accuracy of this delivery system and the performance of the infusion cannula were validated in nonhuman primates.

METHODS

Infusions of gadoteridol were delivered to multiple brain targets and the targeting error was determined for each cannula placement. Cannula performance was assessed by analyzing gadoteridol distributions and by histological analysis of tissue damage.

RESULTS

The average targeting error for all targets (n = 11) was 0.8 mm (95% CI = 0.14). For clinically relevant volumes, the distribution volume of gadoteridol increased as a linear function (R(2) = 0.97) of the infusion volume (average slope = 3.30, 95% CI = 0.2). No infusions in any target produced occlusion, cannula reflux or leakage from adjacent tracts, and no signs of unexpected tissue damage were observed.

CONCLUSIONS

This integrated delivery platform allows real-time convection-enhanced delivery to be performed with a high level of precision, predictability and safety. This approach may improve the success rate for clinical trials involving intracerebral drug delivery by direct infusion.

Human/nonhuman primate AC-PC ratio--considerations for translational brain measurements

This comparative magnetic resonance imaging (MRI) analysis evaluated the ratio of AC-PC (anterior commissure to posterior commissure) distance measures in selected groups of humans and nonhuman primates (NHPs). An understanding of the basis of this ratio between primate species may allow more accurate translation of NHP stereotactic targeting measurements to upcoming human trials. MRI datasets of adult humans [n=21], and juvenile and adult NHPs (Macaca fascicularis [n=40], and Macaca mulatta [n=32]), were evaluated in a mid-sagittal plane to obtain the AC-PC distance measure for each examined subject. Two trained evaluators, blinded to each other's results, carried out three separate measurements of the AC-PC length for each subject. Each observer carried out measurements of the entire dataset [n=93] before repeating the measurements two additional times. Previous dataset measures were not available for review at the time of subsequent measures. Inter- and intra-observer variabilities were not statistically significant. Minimal intraspecies variation was found in the AC-PC measurement of our human and NHP groups. We found significant interspecies differences, however, more between humans and NHPs, and less between the NHP groups. Regression analysis confirms the strong linear relationship of AC-PC distance based primarily on species in our study groups. Human/NHP AC-PC ratios varied between 2.1 and 2.3 based on the compared NHP species groups. We conclude that the scale differences in brain measurements between NHPs and humans described in this study allows improved translation of stereotactic targeting coordinates in future human clinical trials, which may lead to improved efficacy and safety.