Abstract

This report describes three prototypes for a device that can rotate and flex/hyperextend the neck in CT and MRI scanners. This device must situate the head in positions of a known degree of rotation. Positions must be reproducible, allowing for accurate rescanning. The chosen design provides continuous isocentric rotation that can be isolated at any given angle. A reliable measuring system allows for the positions of the head to be replicated in future scans. At the current stage, half of the device is built, but more pieces are needed.

Background and Motivation

• Focus OneBackground:– Nerve roots run through the neural

foramen– Cervical motion may compress the

neural foramen and shear the nerve roots

Goal:– To measure the degree of

compression in the neural foramen in order to detect the pinching of the nerve roots during rotation

Background and Motivation

• Focus TwoBackground:– Degree of rotation of each

vertebra differs among patientsGoal:– Compare the stability of

segmented motion in the vertebrae of normal patients with that of patients with instability (Neck Reference)

Background and Motivation

• Focus ThreeBackground:– A disorder called Chiari I malformation– The cerebellum alters the flow

waveform of CSF

Goal:– Analyze the effect of flexion and

hyperextension on the flow rate of CSF in patients with Chiari I malformation

(The Chiari Clinic)

Rotation in the cervical vertebrae

Imaging

• The foci of this study can be evaluated with magnetic resonance imaging (MRI) and computed tomography (CT)

• MRI will be used for a high degree of resolution in detecting vascular significance

• CT will be used more often because of its ability to image bone

MRI Scanner

MRI

• Takes images by sending radiofrequency pulses into the body and detecting the signal off of the body’s protons

• Because of the large magnetic field, ferromagnetic materials—iron, cobalt, and nickel—cannot be brought close to the scanner

• Electrical wires and non-ferromagnetic materials can act as antennae and distort the images

• The MRI scanner being used is a GE Signa 1.5 T

CT

• Transmits x-rays into the body in a radial fashion

• Metallic objects are not hazardous, but can cause blurring in the images

• The CT scanner being used is a GE Lightspeed

Design Criteria

• Design a device that:• Allows for isocentric movement

– Flexion/hyperextension about the temporo-mandibular joint

– Left/right rotation about spinal axis

• Has the ability to reproduce positions• Is made of MRI- and CT-compatible

material• Is light and portable• Looks aesthetically pleasing

Decision MatrixDesign Rotating

ArmHelmet Design

U-shape design

Continuous rotation

3 2 1

Isocentric Left/right rotation

3 2 1

Isocentric flexion/extension

2 3 1

Ergonomics 2 3 1Patient Adaptability 3 2 1Compatible material

2 3 1

Total 15 15 61=Best rating 2=Second best rating 3=Third best rating

Preliminary Design

Advantages– The helmet design featured a rotating locking

hinge (Design 1)– Head cradle shaped like a helmet– Easily compatible with both MRI and CT

scanner stretchers

Disadvantage– It could not achieve isocentric

flexion/hyperextension.

Intermediate Design

Advantages– Based on client feedback and suggestions– U-shaped bar enables isocentric

flexion/hyperextension (Design 2)– A pin joint allows for simple rotation– Both flexion/hyperextension and device elevation

adjust with a single joint– Improved shape of head cradle

Disadvantages– Excessive stress on the U-shaped bar– The design has an imbalanced weight distribution

Final Design

Advantages– Consulted stresses and stability of design with

professors and within the team– Performed a basic finite element analysis on the back

pin with CosmoWorks, a sub-program of SolidWorks– Added a back support for the reinforcement of the U-

shaped bar (Design 3)– Can now adjust the degree of flexion/hyperextension at

the back support– Added clamp around rotation pin for stationary

positioningDisadvantage– No reliable method for attaching to both the MRI and CT

stretchers

Final Design: Results

• Continuous motion with stationary positioning• Compatible with CT and MRI• Material selection

– Polyvinyl chloride (PVC)– Nylon screws

• Basic finite element analysis• Detailed Solid Works® drawings• Video presentation• Prototype representation

Finite Element Analysis

• Performed FEA on the head cradle• On the restraint, the support rod was

immovable (no translation) at the clamp• Given a force of 8 lb orthogonal to the

head cradle surface• Used a solid mesh, 8998 elements, and

17114 nodes• Used a von Mises stress analysis• Minimum factor of safety = 19

Final Design: Progress

• Milled side supports• Constructed U-shaped

bar with PVC glue• Back of the head

support• Clamp over the rod

through the U-bar• Back joint support• Makeshift base Future head cradle

The Building Process

Future Work

• Continue research on materials• Insert a support mechanism for the side

supports• Accommodate prone scans• Perform an advanced finite element

analysis• Improve manufacturing capabilities• Scan patients and evaluate the accuracy

of reproducible positions

A Special Thanks to:

Professor Osswald-Material Selection

Professor Manner-Finite Element Analysis

Professor Fronczak-Joint design

References

Chiu, L.C., Liteamon, B.S., Yiu-chiu, B.S. 1995. Clinical Computed Tomography for the Technologists. Raven Press, New York.

Hashemi, R.H., Bradley, W.G. 1997. MRI The Basics. Williams & Wilkins, Baltimore, MD.

“Hospital for Joint Diseases.” Spine Center. Accessed: 5 Oct. 2003. URL: http://www.hjd.org/hospitals/hjd/hjdspine/muscleandligaments.htm.

“Spine Universe.” Accessed: 4 Oct. 2003. URL: http://www.spineuniverse.com/displayarticle.php/article1442.html.

“The Center for Spinal Disorders.” Accessed: 4 Oct. 2003. http://www.centerforspinaldisorders.com/disorders.htm.

“The Chiari Clinic.” Accessed: 7 Oct. 2003 URL: http://tribble.missouri.edu/ns/chiari/.

“The Neck Reference.” Accessed: 4 Oct. 2003. URL: http://www.neckreference.com/anatomy.html.