Final Design

Final Phantom Design

Figure 1: CAD Model of individual components of the final design

• The Inner core, which was made of Polycarbonate, consists of 14 plugs, 7 tubes and 2 plates.

• The Outer shell was made from Soft (Masterkleer) PVC tubing along with a small plug for air-sealing.

• The tubes and plates were sealed with 3M Instant-Bonding Adhesive and Loctite Silicone RTV glue.

• Outer shell was sealed to plates with RTV glue and Nylon Worm Clamps.

Signal Introducing Plugs:

• ⅜-24 Male thread with Buna-N O-ring at base of threading portion to help with sealing.

• Thread relief, similar to kind in standard machine screws, where O-ring resides.

• Hole in center about 0.01 cm bigger than wire shielding (22 AWG wire with 0.15 cm diameter shielding) for each plug.

• Wires glued in with acrylic cement to form an air and water-tight seal and to introduce the current into the fluid.

Tubes:

• 7 tubes of 15.24 cm length, 0.953 cm ID, and 1.27 cm OD.

• Each tube has ⅜-24 Female thread.

• Filled with a kosher salt/DI water solution. Concentration of solution is 48 g/L.

Plates:

• 8.26 cm outer diameter with 7 holes of 1.27 cm diameter for tubes to run through for each plates.

• 1.43 cm diameter hole drilled concentrically with aforementioned holes 0.254 cm down from both surfaces to allow for glue placement. Large hole can be seen around tubes.

• Grooves were created on outer diameter of plate to allow for grip-like feeling for nylon clamps.

Outer Shell:

• 15.24 cm length, 8.26 cm ID, and 9.53 cm OD.

• Shell has hole of 0.48 cm located 5.08 cm from edge for the evacuation of air.

• Filled with same kosher salt/DI water solution as tubes

How it Works:

Figure 2: Block Diagram of the electrical signal path

• The signal is produced by the FG085 Function Generator and first travels to a soldered PC board, whereby a 10 kΩ resistor helps to modulate the signal to the required current amplitude. Tests with this resistor modulation with the final phantom have yielded 68 ± 2 μA through each individual straw.

• The current then exits the PC board and resistor to travel into a 25-pin DB port in a patch panel that connects the MRI control room to the MRI scanning room. The patch panel, besides connecting the control room to the operating room, also serves the purpose of filtering out Radio Frequency (RF) noise from outside of the scanning room that may distort MRI scans.

• While normal wires may be used up to this point, once the current enters the MRI scanning room, it must incorporate RF shielding to prevent the current in the wire from distorting MRI scans. This is achieved through the use of coaxial cables, which have an additional layer of copper shielding which blocks RF waves.

• The coaxial cable then carries the current to the acrylic box, which has been shielded from RF noise with a layer of copper foil. Inside of the box, a PC board splits the incoming current into seven separate, but equal currents that exit the box through a bundle of seven coaxial cables.

• These seven cables carry their respective currents to their individual tubes in the phantom, whereby the current passes through the salt water solution in each tube. This salt water solution has been tested and specified to be 48 g/L in order to attain a resistance value of 1 kΩ per tube.

• The current then exits the tube through another seven coaxial cables, which pass back into the acrylic box in a bundle and follow a similar path back through the patch panel and to the ground in the PC board and the signal generator.