Final Design

Figure 1: Annotated CAD image of the Catheter Measuring Device

Figure 2: Catheter Measuring Device on cart. In practice, the device will rest on this cart.

1. Locking Mechanism

Figure 3: CAD drawing of locking mechanism and sensor mount

Figure 4: Locking mechanism hand sketch of actual performance

The main idea behind the Locking Mechanism is to constrain the movement of the catheter during the measurement procedure and have the catheter plugged in so that its entrance is adjacent to the Sensor Mount holes (Fig. 3). In previous tests, it was observed that the driven wire would enter the catheter only to push it away from the device due to friction between the wire and the inner walls of the catheter. Therefore, the Locker was designed to secure the catheter.

After the Locker is pressed down onto the catheter, it pushes the catheter down slightly, creating a deviation of roughly 0.008727 mm between the theoretical wire entrance and the actual wire entrance (Fig. 4). This deviation is very small, and therefore not factored into the program calculation of catheter length.

2. Sensor Mount

The sensor consists of an LED and a phototransistor, which are mounted onto holes in the Sensor Mount (Fig. 5). When the wire, represented as the brown bar, blocks the light between the LED and phototransistor, the controller knows that the wire is adjacent to the catheter entrance. Similarly, when the wire retracts from the catheter and eventually and unblocks the light, the controller knows that the wire is back in the device.

Figure 5: Cross section of Sensor Mount if looking from above.

3. Friction Drive

Figure 6: CAD image of Friction Drive Figure 7: Live image of Friction Drive

Figure 8: CAD drawing of Friction Drive.

The friction drive consists of two pinch rollers: a drive roller and a follower (Fig. 6). The drive roller is connected to a stepper motor which drives the Friction Drive and contains the controller that tracks the distance the wire is inserted into the catheter (Fig. 7). The drive roller features a groove that ensures that the contact between the rollers and wire is consistent (Fig. 8). The follower is pressed down onto the wire by springs to ensure sufficient friction for accurate measurement.

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4. Wire Storage

Figure 9: CAD image of Wire Spool Figure 10: Live image of Wire Spool

Figure 11: CAD drawing of Wire Spool

The Wire Spool is a key innovation that allows for even feeding of the wire into the Friction Drive. With the Wire Spool, the length of wire that was previously managed and stored by the person measuring catheter length is now completely managed and stored by the Catheter Measuring Device.

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Test Results

Figure 12: Testing during calibration of device measurement Figure 13: Test results after calibration and adjustments to Friction Drive

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Early Conceptual Design

Figure 14: A simple 2D representation of the proposed Catheter Measuring Device. The device is shown from the side and the device casing is represented as transparent so inner components can be observed.

Figure 15: The device as it is intended to be used in the brachytherapy operation room. The measuring wire is inside the catheter and being driven to the end of the catheter by the device.