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Spring 2014 MAE 156B Project #6

MRI Positioning System

BACKGROUND

The Center for Functional Magnetic Resonance Imaging (CFMRI) houses three imaging systems: two 3 tesla short bore scanners--GE Discovery MR750--for human studies; and one 7 tesla scanner--Bruker Biospec 70/20 USR--for small animal imaging. MRI scanners produce a rapidly changing magnetic field which aligns the hydrogen nuclei within the sample body. These hydrogen nuclei absorb energy from an applied radio frequency (RF) pulse, which then creates a brief and faint electromagnetic field signals that are detected by the RF coils in the MRI system. Samples are positioned at the bore’s isocenter, the optimal position for producing high-resolution images. Our sponsor, Robert Bussell, is an associate development engineer at the CFMRI specialized in the 7 Tesla scanner, Bruker Biospec, used for animal and tissue imaging. The current positioning system used at the center comprises of tooling manually positioned along a dovetail shaped guide. Our goal is to design an automated positioning system with high accuracy and repeatability to replace their existing setup.

The belt-driven linear slider is comprised of a NEMA 23 stepper motor, a 1/2" wide timing belt, two timing pulleys, and the carriage itself. The motor was chosen based upon its high torque capabilities, and its ability to achieve high resolution microstepping when used with a stepper motor driver. Using timing pulleys with a 1.432" pitch diameter, we were able to achieve a step size of approximately 0.2 mm.