Concept Generation

Mechanical Actuator for Magnetic Resonance Elastography of the Lumbar Spine

Overview

Background Information

Project Scope

Metrics

Design Process

AcknowledgementsOur team would like to thank our sponsor, Dr. Cortes, our

advisor, Dr. Wang, along with the BMEG design staff

Prototype

Final Design

Validation

Christian Aurup, Caitlin Banks, Brittany King & Kenneth Warren

The project scope is to design a functioning MRI compatible mechanical apparatus with the ability to displace a patient’s lumbar intervertebral discs to measure disc mechanical properties. An end goal is to have the apparatus available for use in a research facility.

Dr. Cortes has partnered with the Spine Biomechanics Lab in using Magnetic Resonance Elastography (MRE) to vibrate intervertebral spine tissue in-vitro. Vibrating the soft tissue creates a displacement that can be measured in an MRI scan. This displacement assesses the degradation and mechanical properties of the tissue.

Research was conducted on different types of actuators that are currently being used with MRE to vibrate and measure different types of tissue. Our sponsor had used a copper solenoid coil, which relied on the magnetic waves generated by the MRI machine to induce a vibrational movement (Figure 1). An amplifier and waveform generator was connected as a power source. We followed his basic design of the copper solenoid coil for our design.

The complete device consists of the mechanical actuator with its housing, a body RF coil, wave generator, and amplifier. The actuator and housing rests under the patient’s lumbar spine and on top of the MRI table. The wave generator and amplifier are outside of the MRI room, connected to the actuator via a cable. Four coils, each with 700 turns, are connected on opposite corners by two long arms. Each arm is connected to each other by a center rod, which holds two back supports and a rectangular frame with two contact points. Three different heights were created for the contact point, depending on tissue thickness variability. The magnetic current of the MRI machine creates a torque in the coils, causing them to vibrate. The center framing acts as

Once this was decided, calculations were performed to see how many coils and turns of copper wire were need. Safety and force generated had to be considered.

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Coil Temperature Test

Time (min)

Tem

pera

ture

(°F)

Load cell testing was done, where 125lbs was applied to each back support without any deformation. For the temperature testing (shown left), the coils were in parallel with 8V and 0.2A of current

pine

Design

Figure 1

Actuator TypeSolenoid actuatorPiezoelectric actuator

Motor actuatorAcoustic actuatorHydraulic actuatorPneumatic actuator

Force DeliveryLever mechanism

“See-saw” mechanism

Eccentric disks Rotating camPistons

Coil TypeSingle, R/F Coil

Body Coil

Testing

x

y

Displacement X Direction

Displacement Y Direction

Displacement Z Direction

the see-saw mechanism, and causes the contact points to hit the spine, causingintervertebral disc displacement.