How to make a phantom ===================== ![Phantom head][1] Bill of materials ----------------- ### Consumables - Ballistic gelatin, 900 g (we use Custom Collogen VYSE Professional Grade) - Pure NaCl (e.g. kosher salt or non-iodized salt without anti-caking agents), 40.5 g - Optional: defoaming agent ### Reusable parts - Silicone o-ring cord stock 1/8" square, min. 36" - 3/8" threaded rod, qty. 8 - 3/8" x 2" hex head bolt, qty. 6 - 3/8" hex nut, qty. 16 - 3/8" washer, qty. 8 - Sealant for printed parts (e.g. XT30, Plasti-dip, Flex-Seal or Varethane Triple Thick polyurethane). Needs to cover 2 s.f. - If printing 4-piece design for each side, acetone for gluing pieces together - Several 3.5 mm stereo male-male wires; 1 per internal dipole source you intend to create. Our design files are based on UMECORE Nylon braided wire by LANSUNS, part number 4330104098, which can be purchased on amazon. * Note - any wire should work, BUT the nylon coating around the base of teh connector must be small in order to fit the caps we have included here. - Epoxy or hot glue for making solder joints water resistant - Paint or electrical tape for marking wire guides - > 6 L container for water and gelatin - Funnel for pouring gelatin ``` Notes: We use 3/8" SAE fasteners for their ready availability in US home improvement stores. The holes in printed parts are also designed to take M10 fasteners with some reaming. ``` ### Fabricated (3-D printed) parts 1. Left mold case 2. Right mold case 2. Inner post 3. Outer ring base 4. Electrode wire guides ("straws") 5. Electrode wire guide caps Procedure --------- ### Printing Parts were designed for printing with minimal support material required, though some post-processing of holes may be needed if printing without support. For users with smaller printers, 4 part mold case halves can be printed within a print bed volume of 125 x 114.3 x 97.5 mm. This option requires gluing and more careful sealing to ensure water tightness. Electrode wire guides can be printed using minimal support due to the diamond shaped interior cross section. The design is open on one side, allowing for thin 3.5 mm audio cables (up to approximately 3.5 mm in cable diameter) to be inserted into the guide without needing to remove connectors. ![Wire guides with audio cable][2] ### Model design, fabrication, and assembly The scalp surface was extracted from a male volunteer’s T1 MP RAGE MRI sequence using FreeSurfer. A mold case negative of the head along with interlocking inner parts were created for 3-D printing using Blender. There are six 3-D printed mold parts (see Bill of materials above). Prior to casting, surfaces must be sealed to prevent gelatin mixture from leaking out of the mold or into printed parts. Spray-on polyurethane rubber helps fill in gaps and layering artifacts from 3-D printing. ``` Poor adhesion and globbing can be an issue with brush-on sealants. We recommend spray-on sealants for better surface properties. ``` Silicone gaskets within channels provide additional sealing for the gaps between mold case halves and the inner post. Electrodes are fabricated from 3.5 mm TRS stereo audio cables by inserting them into a wire guide and sealing the end using a 3-D printed cap and a space-filling sealant such as epoxy or hot glue. The exposed end of the cable allows for a dipole to be created by polarizing the tip and ring. The inner post holds a maximum of 37 electrodes at fixed orientations for repeatable positioning. Wire guides can be rotated in 30 degree increments and locked into place by sliding into a hex channel of the inner post. The mold case halves are clamped together with threaded rod, holding the inner post and electrodes inside the head volume during gelatin casting. [1]: https://files.osf.io/v1/resources/qrka2/providers/osfstorage/5c939f832ea47a001b7817a6?mode=render [2]: https://files.osf.io/v1/resources/qrka2/providers/osfstorage/5c939f9f34062c001b1ee13d?mode=render