Download Neck Rotator Final Paper - Computer-Aided Engineering

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Isocentric Neck Rotator for MRI and CT
Appel, B.L., Huser, A.J., Karas, A.L.,
Nadler, D.C., Pauls, S.J., Wentland, A.L.
BME 200/300
Department of Biomedical Engineering
University of Wisconsin-Madison
December 10, 2003
Client
Victor M. Haughton, M.D., Professor
Department of Radiology
Advisor
Robert G. Radwin, Ph.D., Professor
Department of Biomedical Engineering
Abstract
MRI and CT can be used to study the physiology of the neck and the hemodynamic significance
of cerebral spinal fluid when the neck is rotated and flexed/hyperextended. A device was needed
to move the neck into known degrees of rotation and flexion/hyperextension so that scans could
be repeated at a future time. Rotation must be performed about the isocentric axis. On the
device, a rod is centered about the spinal axis and can move freely to provide any rotational
degree. Flexion and hyperextension must be performed about the temporomandibular joint.
Side supports allow for flexion about this axis. The design has been tested with a finite element
analysis about the rotation pin. Currently, the device is half-finished and constructed out of
PVC.
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Table of Contents
Page
Abstract
1
Table of Contents
2
Problem Statement
3
Client Research
3
Background-MRI
3
Background-CT
5
Background-Anatomy
5
Current Devices
7
Literature Search
9
Design Constraints
10
Design 1—The Helmet Design
11
Design 2
12
Design 3
14
Meeting with Professors
19
Finite Element Analysis
19
Concerns
20
Future Plans
21
References
22
PDS
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Problem Statement
Our client needs a device that will rotate and flex/hyperextend the neck in both CT and
MRI scanners. Movements must be reproducible and isocentric about the spinal column.
Client Research
Our client, Dr. Haughton has three main objectives/hypotheses:
(1) Rotation narrows the neural foramen, which might cause compression in some patients. He
plans on collecting different measurements from scans of patients in a neutral and a rotated
position.
(2) Flexion increases the velocity of cerebrospinal fluid (CSF) flow in the foramen magnum
during the cardiac cycle. He intends on measuring CSF flow through the foramen magnum in
patients with Chiari I malformation (a neuromuscular deformation).
(3) With an interest in the cervical vertebrate (C1 – C5), he intends to discover how they are
affected when a patient rotates and flexes/hyperextends the neck.
In Dr. Haughton’s study, the ability to repeat particular positions is crucial because it
creates and provides another control in the study. Furthermore, if he wants to re-image a patient
he can replicate a specific position to detect a physiological change from the previous scan.
Background-Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) is an extremely helpful tool in the medical industry.
An MR scanner can display small differences in tissue density and it is especially advantageous
over other imaging techniques because of its extraordinary ability to show contrast in soft-tissues
(Figure 1). The scans (with contrast agent) are painless and have no known side effects.
Commercial scanners have been utilized since the early 1980’s and can be very effective in
diagnosing several different types of medical problems. MR images can be used to detect many
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different injuries including head trauma, aneurysms, strokes, and brain tumors. The contrast
agent (gadolinium) used in MRI makes the imaging technique useful in evaluating joints and
other soft-tissues.
Figure 1: An MRI scan of the brain (www.gemedicalsystems.com).
In MRI, radio-frequency pulses are transmitted to a patient’s body, whereby protons spin
and generate signals. These signals are then transformed to an image that radiologists use to
diagnose the various physiological conditions mentioned above. 1.5 Tesla MR imaging utilizes a
large magnet to produce a magnetic field 15,000 times the strength of the earth’s field. A
consequence of this fact is that ferromagnetic materials—cobalt, iron, and nickel—cannot be
placed in or near the MRI scanner. If inside of the scan’s field of view, a non-ferromagnetic
metal can cause a susceptibility artifact, a blurred and distorted appearance over a region of
interest. However, non-ferromagnetic metals can be used if they are outside of the field of view.
Scans typically range from one to ten minutes in duration, but could last as long as twenty
minutes for fMRI. The patient must lie totally still during the entire scan and must be able to
relax. This is extremely important since any movement by the patient could cause the image to
be distorted.
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Background Information on Computed Tomography
Computed Tomography (CT) allows physicians to obtain high-quality cross-sectional
images of structures within the body. CT images are put together from a large number of small
cross-sectional x-ray measurements that are taken from the patient. Adding these cross-sectional
views together allows for imaging in three dimensions.
CT scans can take approximately one half hour to one and a half hours for a specific part
of the body. The accuracy of this type of imaging is dependent on total immobilization of the
patient. The scans can be used for various situations and on various parts of the body. CT scans
may be used for analysis of head trauma, spine structure, tumor sites, osteoporoses, or specific
anatomy. Scans can also be used to assist in the guidance or placement of instruments or
treatments. Patients must have no metallic material on them while having a CT scan because it
can interfere with the image clarity.
There are low risks involved in CT scans. The worst possible adverse affect usually
comes from iodic material injected into the patient to help with picture contrast. There is also
minimal radiation exposure during these procedures.
Background Information on Anatomy, Basic Biomechanics, and Range of
Motion of the Head and Neck
The skull and spine are two of the most important protective bone structures of the
human body. The skull protects the brain, and the spine protects thirty-one pairs of nerve roots,
which branch out of the neural foramen and run throughout the body. The neck consists of
intricate vertebrae that have articulations, which are called amphiarthrodial joints. These joints
allow movement in three different planes. The overall structure of the spine allows for a large
variety of movements. Two of the most important joints are found in the neck where the spinal
column joins with the head. The atlantooccipital joint is between the first cervical vertebra (the
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atlas) and the occipital bone of the head. This joint allows for movements of the head in the
sagittal plane (flexion and hyperextension) and the frontal plane (lateral bending) (Nordin, 1999).
The first 10º-15º of flexion occurs at this joint, but further flexion occurs in all cervical vertebrae
(Banna, 1985). The atlantoaxial joint is between the atlas and the odontoid process of the head
and allows the head to rotate in the transverse plane (Nordin, 1999). The first 40º-50º of head
rotation occur at this joint while further rotation takes place in the facet joints in the lower
cervical spine (Banna, 1985). The movements of the neck are controlled and coordinated by a
large, complex group of muscles that are beyond the scope of this background information. It is
important to note that there is considerable variation between people in their neck’s range of
motion (Hay, 1988).
Figure 2. Head and neck model: (A) Neutral position (B) Full extension (C) Full rotation
(Vasavada, 1998).
The vertebrae of the cervical spine contain large openings in the bone called foramina.
These allow passage of arteries, nerve roots, and the spinal cord. These spaces will shift and
change when the neck is moved into different positions. The goal of this project was to create a
device that could allow doctors to investigate the changes in these spaces by allowing the head to
be supported in a variety of different positions during an MR or a CT scan. Our device should
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confine the neck and head to a specific movement at a time. This includes isocentric rotation
about the spinal axis and flexion/hyperextension about the coronal plane (Figure 2).
Current Devices Used and the Need for a Device to Rotate the Head and Neck
Accurately and Efficiently in MR and CT Imaging
Currently there are two head cradles in use in MR and CT imaging machines (Figure 3).
Both head cradles are designed solely for the purpose of supporting the head of the patient.
Neither cradle restricts movement of the neck about any axis. Although our proposed device
would allow for movement, it will lock in place for the scanning procedure and diminish patient
movement.
Figure 3: The current head cradle used in MRI. The patient lays on his/her back and simply rests
the head on the cradle. This cradle does not allow for rotation of the neck in any direction.
Currently there are no head cradle designs that provide for rotation and
flexion/hyperextension. However, there are designs for other parts of the body that have a
similar application relative to the site on the body in which they are used. One such design was
created by a biomedical engineering group in the spring of 2001 at the University of Wisconsin –
Madison. Their goal was to design a device that would create graded pelvic rotation about an
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axis passing through the spine (Asti, 2001). Their solution was to place rollers on the MRI and
CT stretchers. A backboard rests superjacent to these rollers and rocks back and forth to achieve
pelvic rotation in the desired direction (Figure 4, 5). Although this device is not in direct
competition with our potential design, it is important to note that there are other devices which
have been developed with similar applications focused on different parts of the body.
Figure 4. End view of the device designed to create graded pelvic rotations. The rollers
underneath the bench are unidirectional and are responsible for rotation (Asti, 2001).
Figure 5. Final drawing of the pelvic rotation device previously designed (Asti, 2001).
A device to accurately and efficiently lock the head and neck into various positions, other
than the comfortable straight resting position, could prove very useful in helping to explain
physiological changes that occur during motion. Changing the position of the head and neck
would allow for comparisons of spinal anatomy during those movements. Our client, Dr. Victor
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Haughton, plans to use a head and neck rotation device in order to research physiological
changes that occur both during flexion/hyperextension of the neck and during isocentric rotation
about the spinal axis.
Although the interest in building a head and neck rotation device is rooted in Dr.
Haughton’s research, such a device, if built, could have a much broader range of use. According
to our client, the full advantages of using such a device have not been realized partially because
such a device does not currently exist. A head and neck rotation device for use in MR and CT
imaging could eventually help radiologists to diagnose patients that have undergone serious
trauma, or even those with unusual neck pains that otherwise go undiagnosed. Much more
research on such a device is needed before the potential uses can be completely realized. Our
client envisions this device as something that could be used daily in a large hospital setting.
Literature Search
A great amount of research was conducted in order to understand the operating
environment of the device. Using Chiu’s work Clinical Computed Tomography for the
Technologist (Chiu, 1995) and Hashemi’s work MRI: The Basics (Hashemi, 1997), our team
began to understand the limitations that these radiographic techniques impose on engineering
design. To understand the osteological and muscular significance in rotation and
flexion/hyperextension, we consulted Gray’s anatomy (Gray, 1977).
Through a series of visits to UW-Madison’s Waisman Center and UW Hospital, we were
able to measure and sketch the components of the CT and MRI machines. Additionally, we
consulted a CT technician, who explained the effects of metals and how patients are brought into
the scanner.
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We consulted the US Patent and Trademark Office to find devices that pertained to our
design (U.S. Patent and Trademark Office, 2003). However, there were no devices that were
able to perform either rotation or flexion/hyperextension. General Electric Medical Systems had
two different designs for head and neck supports, but none of these designs had the ability to
rotate.
Design Constraints
The design must allow rotation to the left and right approximately 45° as well as flexion
and hyperextension approximately 25° about the mandible. The axis of rotation must be in line
with the spinal axis of the patient. A technician must manually move the neck to the desired
degree of movement. The device should be situated to this position, stable enough to prevent
deflections and small shifts that could affect reproducible positions. Movement should be
continuous and isolable at any position.
The device will be used more often in the CT scanner because of its ability to image
bone. However, the device should also fit in an MRI machine. The design must accommodate
for the MRI flex coil, which fits underneath the head and neck. This flex coil should be as close
to the head as possible, allowing for the clearest possible picture. The further away the coil is
from the region being scanned, the more unclear the image turns out.
Safety is an important factor to consider in this design. The safety of the technicians as
well as the safety and comfort of the patients is essential. The device must be lightweight and
portable so that technicians can easily attach and detach it from the stretcher. The structure will
accommodate all types of patients, regardless of size or physical ailments. Additionally, the
device should not enclose the head, because many patients suffer from claustrophobia.
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The materials in this design are extremely important. Because of the large magnetic field
of the MRI machine, the design cannot contain ferromagnetic materials. Because X-rays are
used in CT, radiolucent materials are essential about the region of interest. Plastics, such as
polyvinyl chloride (PVC), are ideal.
Design One – The Helmet Design
Rotation
The Helmet Design uses a rotating locking hinge (Figure 6A) for rotation about the spinal
axis. It rotates about the hinge in the back, which is approximated to be the spinal axis of the
patient lying within the head cradle. This is the only portion of the design that supports the head
cradle.
Flexion/hyperextension
The first design uses a telescoping joint (Figure 6B) for flexion/hyperextension about the
coronal axis. Since the head cradle is elevated by the locking hinge, it has the capacity to angle
up and down.
B
A
Figure 6. The Helmet Design. This design uses two very different methods of rotation. A. A
rotating locking joint. B. A telescoping joint.
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Advantages
The design makes use of the basic head cradle design currently used for CT scanners.
The Helmet Design rests on the table making it easily compatible with both MR and CT
scanners.
This design has the advantage that both methods of achieving rotation are very different
from each other. This makes rotations about the separate axes completely independent of each
other. That is, rotation around one axis can be locked while the head cradle is free to move about
the other. The use of the single pin attachment to the head cradle allows for the fixing of rotation
about the spinal axis. The proposed locking mechanisms allow for the head to be locked at
almost any angle.
Disadvantages
One disadvantage of the Helmet Design is that the two methods of rotation make the
design complicated. Since the head cradle is slightly elevated, patients may need to be propped
up to straighten the spine. This adjustment is necessary for the patient’s comfort and for
achieving a baseline for cervical physiology. Additionally, there is no mechanism to fix the
rotation about the coronal axis. The telescoping joint doesn’t necessarily rotate about the coronal
axis, but raises and lowers the head. This would provide some physiological changes, but not the
desired positions. This design was used as a building block from which the other design
alternatives were constructed.
Design Two
Rotation
Attached to the axle is a U-shaped bar (Figure 7) that is as wide as the slit-to-slit distance
on the bed and projects outwards towards the patient’s mandible. This U-shaped bar houses the
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head cradle. About the axle, the U, and therefore, the head cradle, rotates to the desired angle. A
clamping mechanism incorporated into the tower can maintain this angle and the angle can be
read by markings on the back of the tower. When switching to flexion/hyperextension, this
clamping mechanism can be locked down to the original neutral, isocentric position.
Figure 7. Design 2. The head cradle is held by a U-shaped bar that is attached by a pin to a tower
in the back of the structure.
Flexion/hyperextension
Near the mandible and about the temporomandibular joint for flexion/hyperextension,
pins from the U-shaped bar attach to the head cradle (these are the only two locations that the Ushaped bar is attached to the head cradle). About these pins, technologists can angle the head
cradle and lock the location in a fashion similar to the rotation axle (therefore, these pins are
locked during rotation). Again, markings indicate the angle that the head cradle is tipped.
Miscellany
There is a single tower near the top of the patient’s head and this piece is supported by
the base that runs a distance along the slits of the stretcher (the base’s latching mechanism being
compatible for both the CT and MRI stretchers). This tower has a series of pin holes where a
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single axle can be adjusted to a patient’s head. Ideally, this adjustment would align the vertebral
column and maintain a neutral position prior to any rotation or flexion/hyperextension.
Advantages
This design can provide for free rotation about a single isocentric axis. Additionally, this
design can provide greater degrees of flexion and hyperextension when compared to the helmet
design.
Disadvantages
However, there are quite a few flaws with this design. The adjusting rotation axel has a
limited amount of positions it can adjust to. This feature is merely as good as the number of axel
points, which in turn, is controlled by the diameter of the pin. There is a severe tradeoff between
this diameter and the number of holes in the tower. While a smaller diameter allows for a greater
number of holes and a greater number of positions for the U and head cradle, a smaller diameter
is far less stable than a thicker one. Hence, another flaw in this design is the great amount of
stress placed on the single pin near the top of the head. This location maintains the weight of the
patient’s head and of the entire structure. Additionally, the point of flexion/hyperextension is
constant. This isolation vastly underestimates the different sizes inherent in the population.
Without tailoring to each patient’s unique point of flexion/hyperextension, the neck may
experience variable changes in physiology unrelated to isocentric movements.
Design Three
The third design (Figure 8) was developed by combining ideas from each of the other two
designs. Pin joints were used for rotary motion. Clamping mechanisms were used to isolate
various positions.
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Figure 8. The third design. The third design can flex/hyperextend about the temporomandibular
joint and rotate about the isocentric axis of the spine.
Rotation
The third design consists of a pin-supported head cradle much like those of the two
earlier designs. The pin located at the back of the head cradle serves to set the spinal axis about
which the head can rotate. By manually rotating about this pin, continuous isocentric movement
can be achieved. Any position can be stabilized by a clamp in the back, which depends on
friction between the pin and U-shaped bar.
A scale around the rear pin can indicate the degree of rotation. The pin has a notch that
can line up with the scale. Therefore, when the head cradle is rotated, the pin’s notch will rotate
and indicate the angle on the scale. The scale will be critical in isolating different angles of
rotation. These positions can be repeated in future scans, increasing the accuracy of rescanned
positions. In other words, by specifying the position on the scale where a scan was first
performed, a technician can easily repeat this position in a future scan.
Flexion/hyperextension
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Like the helmet design, design three has a mechanism for rotation about the
temporomandibular joint for flexion and hyperextension. The U-shaped bar is supported by the
rear arm and two side supports (Figure 9). Pins from opposite sides of the U-shaped bar rest in
slits of parallel side supports. Since these pins freely rotate, they allow continuous motion for
flexion and hyperextension. By manually raising or lowering the entire U-shaped bar by sliding
the pins in the slits of the side supports (Figure 9), the height of the head cradle can be adjusted
for differently-sized patients. A scale on one of the side supports can measure the degree of
flexion or hyperextension. With a notch in the U-shaped bar, the degree of movement can be
annotated by following this notch on the scale.
Figure 9. Side support of the third design. Adjusting the pins into different notches can move the
U-shaped bar, and therefore, the head cradle, to different heights.
Miscellany
After consulting our client, the head cradle was reduced in size as compared to the helmet
design. By reducing this size, a patient’s head can move more freely because the top of the head
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cradle cannot hit the U-shaped bar as readily as the previous designs. Like the helmet design, the
head cradle still incorporates padding for patients’ comfort.
Another important aspect of the design is the base. This base must attach to both the
MRI and CT stretchers, which are not the same size. The MRI stretcher measures 39.5 cm in
width and the CT stretcher measures 42.0 cm in width. The most important aspect of the base is
that it keeps all three of the side supports in the same plane. The bottom edge of the base is
slightly curved to accommodate the different curvatures of the stretchers.
A
B
Figure 10. A. The back pin of the third design pushed nearly all the way back. B. The back pin
of the third design pushed nearly all the way forward. These adjustments can align a patient’s
head so that the temporomandibular joint is centered for flexion and hyperextension.
The ability to accommodate varying sizes of patients’ heads is very important, especially
since the spinal axis can vary from person to person. Design three compensates for these
variations by adjusting for head lengths and elevations. As previously mentioned, the side
supports can be adjusted to different levels, allowing for different elevations of the head (Figure
9). These adjustments are necessary for patients with varying shoulder sizes. For example, a
large person would have a spinal axis at a higher elevation from the stretcher than a small person.
Furthermore, patients’ heads are of varying lengths. The pin at the back of the head cradle not
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only serves to rotate the head cradle, but also to move the head cradle closer to or farther from
the U-shaped bar in order to properly align the axis of rotation about the temporomandibular
joint (Figure 10).
Advantages
As was described, design three provides for continuous rotation and
flexion/hyperextension. Design three can accommodate many different patients by adjusting the
position and height of the head cradle. The device is simple to use with clamps and screws
readily accessible to a technician, given that the stretcher is extraneous of the scanner’s bore.
These clamps and screws can be hand-tightened, allowing for quick and easy adjustments of
various positions.
Disadvantages
To provide for free rotation, the head cradle is supported by a single pin. However, the
materials are great enough to compensate for some of the stress on the back pin. Additionally,
near the front of the head cradle where the neck would be, a flex coil (MRI only) and padding
could support and counterbalance more of the stress. Disregarding these counterbalances, a
finite element analysis was performed to ensure the viability of this design.
The degrees of hyperextension are limited because the device cannot angle lower than the
plane of the stretcher. It is possible to extend the structure off of the CT stretcher, but there is no
room to do this in an MRI machine.
Our Chosen Design
Since design three was conceived by taking into account the flaws of the first two
designs, we chose design three as the final design. It satisfied the client’s requirements and was
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compatible with both MRI and CT scanners. Although the mechanism for attaching to the
stretchers still needs to be determined, the design shows great potential for its intended use.
Meetings with Professors
The team members consulted Professor Frank J. Fronczak in refining joint designs.
Professor Fronczak advised that the design was unstable because the structure was supported by
only the side supports. He recommended that a back support could compensate for this
instability.
Professor Tim A. Osswald recommended performing a finite element analysis on the
design to determine whether the material could support the load being applied. Professor Kim J.
Manner identified the area (rear axle) under the greatest amount of stress and suggested that a
finite element analysis be performed about this point.
Finite Element Analysis
The part of the design that will be under the most stress is the pin, from the clamp up to
the back of the head cradle. To ensure that the pin would adequately support the head cradle
without failure and with minimal deflection, a finite element analysis was performed on this
specific part. The analysis was done with a solid mesh, 8998 elements, and 17114 nodes. The
pin was restrained in all directions with no translation (immovable) where the clamp would be
affixed (given at 2 inches from the head cradle). A distributed load of eight pounds was applied
to the head cradle normal to the surface. A von Mises stress analysis was calculated and
diagrammed (Figure 11). The majority of the stress was concentrated in the pin between the
clamp and the head cradle. The minimum factor of safety was calculated to be nineteen. This is
a more than suitable factor of safety for the given application of the device.
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Figure 11. Finite element analysis of the rear pin of the head cradle. In a von Mises stress
analysis, the pin can hold a minimum safety factor of nineteen.
Concerns
Since scans can last up to several hours long, a patient lying on the neck rotator may
grow uncomfortable. Because our device is made of PVC and lends no comfort to the system,
we rely on the multitude of padding already available to CT and MRI technicians. Additionally,
padding can compensate for misalignment of the isocentric axis of rotation.
The weakest point of the design is the area around the axle of rotation. In addition to
supporting the majority of the structure’s weight and the average head weight of eight pounds,
this pin should ideally withstand a minimum safety factor of two (roughly thirty pounds).
Indeed, according to our finite element analysis, this point supports a minimum safety factor of
nineteen.
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Future Plans
Given our temporal and monetary constraints, our device is considerably stable. For
further development, we would continue to research different types of radiolucent materials to
make certain that we have found the strongest, most pliable, and most economical material(s) for
use in building the entire device. We would continue to run finite point analyses with different
materials until we determined which one was the best. Since aluminum is a non-ferromagnetic
material, we could look into incorporating aluminum pins and testing whether blurring and
susceptibility artifacts will obscure the region of interest in the field of view. Aluminum pins
would last considerably longer than plastic axles.
Upon completion of the material testing, we would further develop quality clamps that
would maintain the desired positions. This stability is very important for the design because it
ensures the reproducibility of exact head and neck positions. The degree of reproducibility has
extremely important implications when considering the need for accurate results in our client’s
research. The ability to prevent the device from moving during use is also important in attaining
accurate results for our client’s study. Further work should be done to develop a method to
maintain the stability and position of the device on the stretcher during scanning procedures.
One solution to this problem would be to fasten the device to the table.
Finally we would test the product in the hospital environment. Ideally, the device could
be tested on men and women in a range of ages to ensure the reproducibility, comfort, and
stability of the device. These tests should be performed in both the MRI and CT scanners.
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References
Asti, B. “Insert for an MRI Gantry that Provides Graded Rotation of the Spine’s Lumbar
Vertebrae.” University of Wisconsin-Madison Biomedical Engineering Design
Courses – Spring 2001 Archives. 2001.
Banna, Mohamed. 1985. Clinical Radiology of the Spine and the Spinal Cord. Aspen
Systems Corporation, Rockville, Maryland.
Chiu, L.C., Lipcamon, J.D., Yiu-Chui, V.S. 1995. Clinical Computed Tomography for the
Technologist. 2nd Edition. Raven Press, New York.
Gray, H. 1977. Anatomy. Random House, New York.
Hashemi, R.H., Bradley, W.G. 1997. MRI: The Basics. Williams & Wilkins, Baltimore, MA.
Hay, J.G., Reid, J.G. 1988. Anatomy, Mechanics, and Human Motion. 2nd Edition.
Prentice Hall, Englewood Cliffs, NJ.
Nordin, M., Ozkaya, N. 1999. Fundamentals of Biomechanics: Equilibrium, Motion, and
Deformation. Springer-Verlag New York, Inc.
U.S. Patent and Trademark Office. “Patent full-text and full-page image database.” 2003.
Accessed September 28, 2003. URL: http://www.uspto.gov/patft/
Vasavada, A.N., Siping, L., Delp, S.L. “Influence of Muscle Morphometry and Moment Arms
on the Moment-Generating Capacity of Human Neck Muscles.” Spine 23(4): 412-422,
1998.
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PDS: v. 3.0
Date: December 5, 2003
Title: Neck Rotator
Group Members:
 Betsy Appel
 Aaron Huser
 Anna Karas
 Dana Nadler
 Steve Pauls
 Andrew Wentland
Problem Statement: Our client needs a device that will rotate and flex/hyperextend the neck in
both CT and MRI scanners. Movements must be reproducible and isocentric about the spinal
column.
Client Requirements:
 A device with the ability to rotate the neck
 The ability to flex and hyperextend the neck
 Compatible with CT and MRI scanners
 Reproducible positions of rotation and flexion/hyperextension
 Able to secure the head in place
 Radiolucent/non-ferromagnetic materials
 Relatively light and portable
 Aesthetically pleasing
Design Requirements
1. Physical and Operational Characteristics
a. Performance requirements: This device needs to function in both a CT and MRI scanner.
Specifically, the scanner models are a GE Lightspeed CT scanner and a GE Signa 1.5 T MRI
scanner. The head support must allow isocentric spinal motion, including manual rotation of
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the head and flexion/hyperextension of the neck. The device should attach to the stretcher of
both machines. The size of the device cannot exceed the size of the opening in the CT or
MRI bore and an MRI flex coil must fit underneath the head cradle. The support must hold
the neck and spine stable and not inflict any more pain or anxiousness. It must be stable
enough to be used daily by technicians.
b. Safety: For the safety of technicians using the neck rotator, it must be lightweight and
easily movable to prevent long-term injury. The device must lock at the
rotated/hyperextended position to provide the necessary stability to the neck and spine of the
patients.
c. Accuracy and Reliability: The degree of motion must be known. This position can be in
actual degrees or based on a relative numbering system (to repeat the position in the future).
Therefore, technicians and doctors can replicate an image by knowing the exact position the
scan was taken in.
d. Life in Service: The device must endure a daily usage (four or more hours per day) for
twenty years.
e. Shelf Life: The device should last approximately twenty or more years in a clinical
atmosphere.
f. Operating Environment: The device will remain indoors under a medical/clinical
atmosphere (STP). A minimal amount of heat will be sent into the neck rotator from the
frequent cessations of the MRI’s RF pulses. X-rays will also be transmitted through it. Since
patients will be lying on it, any bacteria or fluids generated by them will also get onto the
device.
g. Ergonomics: In the extreme case, the neck rotator should support kyphotic patients. Let
us say that the average patient is 75 kg, or 165 lb. Also, let’s assume that 60% of the body
weight is in the torso, which is unsupported lumbarly, and that the average moment arm for
the center of mass of the torso is 0.28 m above the waist. This generates a moment arm of
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124 Nm that must be rigidly supported by the hinge joints. All screws should circumvolve
smoothly.
h. Size:
1. CT:
-The neck rotator must fit within the CT’s bore, measuring 67 cm in diameter.
-To latch onto the stretcher, the neck rotator should attach to the 42 cm between the two
slits (on the stretcher).
-The current neck piece has a tongue that locks into the bottom of the stretcher. This
tongue measures 17.7 cm in width and 13.5 cm in length. Our device should be similar to
this, if appropriate and not considering the extra length needed for kyphotic patients.
2. MRI:
-If the neck rotator attached to the stretcher, it must fit onto the 39.5 cm gap between the
slits.
-Our device should not measure more than 50 cm in length, as is the length of the current
head cradle.
i. Weight: Primarily, CT and MRI technicians will be lifting the neck rotator throughout the
day. Therefore, the device should weigh thirty pounds or less, but ideally the mass of an
MRI head coil (approximately 10-15 lbs).
j. Materials: The device should not contain ferromagnetic materials. The device will contain
PVC for its radiolucency and stability.
k. Aesthetics, Appearance, and Finish: The device should be off-white or black to match the
color of the CT and MRI scanners. It should also accommodate an attachment for padding,
which will support the patient’s neck.
2. Production Characteristics
a. Quantity: One main unit with the ability to move in rotation and flexion/hyperextension
b. Target Product Cost:
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 PVC Type I Rectangular Bar: 1” Thick, 2” Width: $12.48
 PVC Type I Square Bar: 1.5” Square, 5’ Length: $33.90
 Clear PVC Type I Rod: ¾” Diameter, 5’ Length: $11.15
 PVC Type I Sheet: 1” Thick, 12” x 12”: $23.23
 8 nylon 3/8”x2” bolts: $0.60/bolt
 8 nylon 3/8” nuts: $0.15/nut
 8 nylon 3/8” washers: $0.07/washer
 2 PVC 1”x12” long pipes: $2.99/pipe
 PVC primer and glue: $13.69
 4 industrial strength 3”x3” square Velcro sheets: $4.99/pack
Total Cost: $126.95
3. Miscellaneous
a. Standards and Specifications: None yet, but possibly some health code issues, e.g. the
device cannot absorb liquids or bacteria.
b. Customer: The customer prefers to use the CT scanner with his patients. Since we are
detecting physiological changes in the neck, radiologists must have the ability to see the
bones and spinal column. Because the bones do not have hydrogen, they are missing in MRI
images. Therefore, our project should conform to CT before MRI.
c. Patient-related concerns: There are two main patient concerns. The first is that patients
can become claustrophobic while being scanned. Therefore, the design should take into
account that a patient may not want his/her face covered in any way. The second concern is
comfort. The design should include a pad so a patient can rest his/her head comfortably.
d. Competition: There is no competition for a mechanistic way of rotating the head in MRI
and CT scanners. However, another design team created a device with a similar application,
but it was used to rotate the lower back instead of the head and neck.