Koller, Adam L

Abstract Concerns about declining gray fox (Urocyon cinereoargenteus) populations in the Midwest, United States, prompted a petition to list the prairie gray fox subspecies (Urocyon cinereoargenteus ocythous) under the US Endangered Species Act. Although previous studies identified a deep phylogenetic break between eastern and western lineages of the gray fox at the Great Plains Suture Zone, population structure within the Midwest remains poorly understood, complicating subspecies classification. To address this, we genotyped 339 individuals from the eastern lineage of the gray fox using single nucleotide polymorphisms (SNPs) generated from 2bRAD genomic sequencing to assess genetic diversity and structure. Bayesian clustering and principal component analysis supported three genetic clusters (K = 3), revealing a cryptic break within Missouri that subdivides the morphologically defined range of U. c. ocythous and a secondary break coinciding with the Mississippi River and the currently accepted subspecies boundary. However, low pairwise FST values and admixture indicate weak overall genetic differentiation with ongoing gene flow, whereas declining genetic diversity at northern latitudes is reflective of founder effects from post-glacial population expansion. Consistent with prior mitochondrial DNA (mtDNA) results, nuclear SNP data suggest that U. c. ocythous and Urocyon cinereoargenteus cinereoargenteus are unlikely to represent distinct evolutionary units. However, because 2bRAD detects primarily neutral variation, whole-genome sequencing will be needed to test for adaptive divergence that might persist despite gene flow. Our findings provide an important step toward a comprehensive understanding of population structure and refining subspecies boundaries within the eastern lineage of the gray fox.

Abstract Objective. Modern stereotactic neurosurgery increasingly relies on bilateral and multi-trajectory workflows (e.g. deep brain stimulation (DBS), stereoelectroencephalography (sEEG)), which can exceed the reach and flexibility of conventional frame-based systems. Building on our skull-mounted Navinetics D1 platform, we present a stereotactic frame (Navinetics E1) intended to expand the reachable work envelope, enable independent bilateral targeting, and preserve mechanical accuracy and patient comfort. Approach. We designed the Navinetics E1 stereotactic frame using a center-of-arc architecture with five degrees of freedom per hemisphere ( X, Y, Z , Arc, Collar) and two operating modes: Double Arm (independent left/right arms for simultaneous bilateral targeting) and Single Arm (mechanically coupled arms). The system was designed in CAD and fabricated via carbon fiber-reinforced polylactic acid (PLA-CF) additive manufacturing. Collision-aware MATLAB simulations quantified work volume and admissible approach directions. Mechanical targeting accuracy was evaluated on a ground truth fixture (GTF) platform, with mixed-effects modeling to assess target- and trajectory-dependent effects. Operative feasibility was assessed through an intraoperative entry-point replication test relative to the D1 system. Main results. Compared to the D1, the E1 frame significantly expanded key geometric ranges, including, most notably, 0°–360° Collar rotation and posterior Y -axis reach, thereby increasing the work volume and trajectory range by factors of 3.39 and 8.42, respectively. Mean GTF targeting deviation was 0.78 ± 0.38 mm in Single Arm mode and 1.23 ± 0.36 mm (right) and 1.65 ± 0.47 mm (left) in Double Arm mode. Entry-point replication across 17 clinical cases achieved 76.5% success in overlapping the reference points, providing preliminary evidence of feasibility under real operative conditions. Significance. The E1 frame extends a compact skull-mounted platform to support broader stereotactic reach and trajectory while enabling independent bilateral workflows. These features may reduce intraoperative reconfiguration for complex DBS and sEEG cases. Future work will focus on increasing structural stiffness, improving angular readout/setting, and developing MRI-compatible implementations.

OBJECTIVE Achieving submillimetric accuracy in stereotactic neurosurgery remains critical for safely targeting deep brain structures. Current workflows rely on intraoperative CT to register stereotactic frames to preoperative imaging, but this introduces additional radiation exposure, cost, and workflow complexity. Three-dimensional surface scanning (3DSS) potentially offers a fast radiation-free alternative capable of capturing detailed craniofacial anatomy and frame geometry. Therefore, the aim of this cadaveric study was to evaluate the feasibility, accuracy, and navigational compatibility of integrating 3DSS into stereotactic workflows as a potential replacement for intraoperative CT. METHODS A human cadaveric head was imaged with both thin-slice CT and structured-light 3DSS after mounting stereotactic frame components. CT, 3DSS, and computer-aided design (CAD) models were registered using a multistep point cloud alignment pipeline involving the fast point feature histogram, the random sample consensus method, and the iterative closest point algorithm. Accuracy was assessed using surface deviation error, root mean square error (RMSE), and fiducial registration error within a commercial neuronavigation platform. RESULTS Fusion of the 3D facial scan with CT provided a mean surface deviation error of approximately 0.4 mm. Registration of the 3DSS-derived N-bar localizer to its CAD reference model produced a frame alignment RMSE of 1.3 mm. Within the navigation system, the 3DSS-based workflow achieved a mean fiducial registration error of 0.14 mm (range 0.02–0.20 mm), outperforming the conventional CT-based method (mean error 0.20 mm, range 0.09–0.40 mm). CONCLUSIONS The 3DSS-based method enabled precise submillimetric stereotactic registration without the need for intraoperative CT, reducing radiation exposure and operative complexity. This workflow is fully compatible with existing navigation systems and could serve as a practical radiation-free alternative in stereotactic neurosurgery. Future work will focus on automating frame detection, incorporating artificial intelligence–driven fusion methods, and validating this approach in live surgical settings.