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In order to meet the vibration reduction requirement, the cradle was designed to be supported entirely by the bore of the machine, which vibrates at a frequency of 45Hz, a safe distance away from our targeted avoidance frequencies of 5 Hz and 1 kHz. The cradle was originally designed so that it sits in the center of two rings, each of which holds an air bladder on the outside that was inflated in order to isolate the vibrations of the cradle.
Objective
The goal of this project was to design and fabricate a cradle for a mouse subject to lie in as pictures of its brain are taken. The cradle had to be small enough to fit inside the bore of the fMRI machine, a Bruker 7T Biospec system. It also needed to be adjustable to allow for optimal positioning of the subject, and to enable the use of subjects of all shapes and sizes. The primary concern in designing this cradle was vibration reduction. If the mouse cradle moved too much while tests were being run, the images would appear blurry and be useless to the study. In order to obtain an optimal image, the cradle needed to be designed so that it did not vibrate at 5 Hz or 1 kHz. It also needed to be made completely of non-metallic or magnetic material in order to keep from interfering with the 7-tesla magnetic field produced by the machine. Additionally, the cradle had to incorporate a means of positioning the optical fiber so that it would rest securely atop the mouse’s head.
Additionally, a sliding apparatus at the head of the cradle was installed in order to accurately position and hold the optical fiber used to stimulate the mouse. In order to avoid the use of any metallic or magnetic materials, the base of the cradle was fashioned out of PVC, the adjustable components were formed out of Delrin, and nylon fasteners attached any parts that needed to be joined together.
After testing the design, we found that, the two-ring system was not enough to balance the bore in the machine. There was an excess of material that reached out of the bore, that threw off the balance of the cradle, yet was necessary in order to safely remove the cradle from the machine. To counter this, we thought it prudent to add a third ring and air bladder to the end of the cradle, that would support the cradle in the bigger opening just outside the bore itself, and add a handle to the end of the cradle for ease of grasping. Unfortunately the time limits of the class prevented us from actually adding this piece to our design, but we provided the sponsor with Solid Works drawings and dimensions so that they could accomplish it in the near future.
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