# Real Color Model of a Cadaver for Deep Brain Stimulation of the Subthalamic Nucleus
## 2 Methods  
The entire process for this study was approved by the institution review board of Ajou University Hospital in Korea (AJIRB-MED-MDB-18-315). In a previous study, the sectioned images of a male head (interval: 0.1 mm; pixel size: 0.1 mm \(\times\) 0.1 mm; color depth: 48 bits of color; file format: TIFF) were produced with the use of cryomacrodtome [14]. The segmented images of 294 structures (interval: 0.5 mm; pixel size: 0.1 mm; color depth: 48 bits of color) were produced manually [15]. The sectioned images and the segmented images of a small size can be downloaded online at neuroanatomy.kr, and the full-size images can be acquired directly from the authors. To produce a volume model that could be handled by a personal computer, the voxel size (intervals \(\times\) pixel size) of the sectioned images and segmented images was adjusted to 0.5 mm \(\times\) 0.5 mm \(\times\) 0.5 mm and converted to the DICOM format in Photoshop. The images of the DICOM format were reconstructed into a real color volume model and a segmented volume model. They were saved as neuroimaging informatics technology initiative (NIFTI) files using an MRIcroGL, which is MRI processing freeware available in the general personal computer environment (www.mccauslandcenter.sc.edu/mricrogl/home, accessed on 28 May 2021) [16; 17]. With this volume model, real color head structures could be observed in the arbitrary plane. For the comparison with the clinical data, 31 patients who were diagnosed with [PERSON]'s disease and underwent DBS surgery in Ajou University Hospital in Korea were employed for the study (16 male, 15 female). The age ranged from 31 to 76 years (mean: 62.3; standard deviation: 10.1), and the disease duration ranged from 3 to 19 years (mean: 8.9; standard deviation: 4.0). All the DBS surgeries targeted the bilateral subthalamic nucleus and used head frame and microelectrode recording, but only the left side was chosen for this study. The patient data could be obtained thanks to the help of Professor [PERSON] of the Department of Neurosurgery at the Ajou University School of Medicine. Preoperative MRIs (method: T1; field strength: 3 teslas; repetition time: 2500 ms; echo time: 8 ms; resolution: 224 \(\times\) 224) and postoperative CTs (Philips Healthcare, 16 detectors; 512 \(\times\) 512 matrix; bone series; spiral protocol; slice thickness: 2 mm) of the patients were obtained. On the MRIs, the brain structures were visible, whereas the electrode was not visible. On the CTs, the brain structures were not visible, whereas the electrode was visible. Therefore, the CT was registered to the MRI using Stealth VR (Medtronic plc, Ireland) to obtain the coordinates of the entry point and target point in the MRI. In the 31 patients, the entry point was the crown of the rostral middle frontal gyrus underneath the frontal bone. The target point was the dorsolateral part of the subthalamic nucleus. The entry and target points were indicated on the sectioned images so as to produce a virtual DBS electrode on the volume model (Figure 1). The coordinates of the entry point and target point were determined on the sectioned images based on the registration using the FSL nonlinear registration tool (FLIRT) of the FMRIB software library (FSL), which is freeware available in the general personal computer environment [18]. The registration detail was affine (12 parameter model) with linear interpolation. Considering the three-dimensional slope of the electrode, every point between the entry point and target point were calculated using Excel 2016 (Microsoft Corp., WA) and drawn using the Extend Script Toolkit of Photoshop CS6 (Adobe System Inc., CA). Two  
Figure 1: Entry point (yellow arrow head) and target point (green arrow head) of DBS. The entry point and target point acquired from the post-operative CT of a DBS patient as a representative were applied to the pre-operative MRI of a DBS patient through registration.