Authors
Timothy Eng
Team Leader
Mary Lim
BWIG
Lauren Hensley
BSAC
April Zehm
Communicator
Client & Advisor
Dr. Victor Haughton, M.D.
UW Department of Radiology
UW Medical School
Professor Justin Williams
Department of Biomedical Engineering
Abstract
A physical model of the human hindbrain and
upper cervical spinal canal was desired to study the
effects of varying dimensions and obstructions on
pressure changes within the spinal canal. A
prototype was assembled to roughly mimic the
Chiari I malformation. The final design is a multi-
piece module, which houses a funnel-like cavity.
The module will be used with an electronically
controlled piston pump and pressure will be
quantified using a transducer. Future work
includes increasing the complexity of the cavity
within the module by replicating CT scans of this
part of the spinal canal.
Problem Statement
The goal of this project was to create a
life-size physical model of the human
hindbrain and upper cervical spinal canal.
This will be used to study how varying
dimensions and obstructions affect
cerebrospinal fluid (CSF) flow in terms of
pressure. Oscillatory flow is required in
the model, and pressure must be
quantifiable.
Background Information
Chiari I Malformation
– Brainstem and cerebellar tonsils (brain
tissue) lower into cranial vault
Obstructs CSF flow
Causes increased PRESSURE on brain and in
spinal canal
– Symptoms: headaches, pain, dysphagia,
numbness, motory and sensory inhibition,
loss of consciousness
– Treatment: surgery (physical enlargement)
Anatomy of Chiari I
http://tribble.missouri.edu/ns/chiari/aboutchiarimalformation.htm#chiari
Bernoulli’s Law
P + ½ ρv2 = constant
Pressure is proportional
to diameter of tube
Velocity is inversely
proportional to
diameter of tube
Design Constraints
Must replicate anatomical size of human
spinal canal and cranial vault
Requires oscillatory flow that mimics actual
CSF flow
Pressure measured accurately along various
points
Ability to interchange pieces
Must attach to provided pump
MRI compatible
Chosen Design
Two working modules
– Replicate CT scans of
normal patients and
Chiari I malformation
– Oscillatory flow
induced by piston
pump
– Interchangeable,
polycarbonate pieces
– Pressure quantifiable
via transducer
Problems Encountered
Budget Constraints
– Expected cost exceeded $200 limit
Time Constraints
– 3-4 hours/block; 20 blocks needed
Available Equipment Constraints
– Shop machinery inadequate for small scale
design
– Accuracy and precision would be compromised
Design Modifications
CT scan images replaced with range of
cylinders
– Form inner funnel-like shape in module
Pressure measured in same fashion
Maintains interchangeability of pieces
Meets design specifications; approved by
client as acceptable (but temporary)
solution to problem
Prototype Construction
Acquired materials
– Polycarbonate sheet
– Non-magnetic stainless
steel screws
– Adaptors for pump
– Flexible tubing
Piecewise Construction
Testing for functionality
Schematic of Prototype
Side view schematic
Functional Prototype
Polycarbonate
Inexpensive
Measures pressure
changes at various
points within module
Easy to assemble and
interchange pieces
Simple design can be
modified to utilize CT
scans/improve
accuracy of model
Piston Pump
Will be used by
client
Generates
oscillatory flow
Electronically
controlled
Compatible with
multiple modules
Placement of the Module
Module connected
to pump via plastic
adaptors
Fluid flows
through module in
oscillatory manner
(sine function can
be generated)
Cost Analysis
3/8” 12”x24” polycarbonate sheet $29.76
6” non-magnetic stainless steel
screws with 1/4” diameter (4)
+ wing nuts (4) $ 5.06
1/4” flexible plastic tubing (3 ft) $ 0.87
Plastic Adaptors $ 0.00
Goop Marine (rubber sealant) $ 4.39
TOTAL: $40.08
Future Work
Present to client
Increase accuracy of design
– Alter inner cavity by replicating CT scans of
normal and Chiari I patients
– Increase size of pieces for anatomical
correctness
– Increase number of pressure points measured
Assist in data collection
– Monitor pressure changes
References
Arnett, B. 2002. Arnold-Chiari malformation. History of Neurology: reprinted 2003.
Automation Creations, Inc. 2004. “Material Property Data.” Accessed 12 March
2004. URL: www.matweb.com
Chang, H.S. and Nakagawa, H. 2003. Hypothesis on the pathophysiology of
syringomyelia based on simulation of cerebrospinal fluid dynamics. Journal of
Neurology, Neurosurgery and Psychiatry 74: 344.
Haughton, V. Personal Interview. Jaunary 6, 2004.
Haughton, V. Personal Interview. February 13, 2004.
Haughton, V. Personal Interview. April 14, 2004.
Haughton, V. Personal Interview. April 16, 2004.
Loth, F., Yardimci, M.A., and Alperin, N. 2001. Hydrodynamic modeling of
cerebrospinal fluid motion within the spinal cavity. Journal of Biomechanical
Engineering 123.
Mueller, D. “The adult chiari I malformation.” The Chiari Clinic . Accessed: 01 March,
2004. URL: http://tribble.missouri.edu/ns/chiari/aboutchiarimalformation.htm
Hoffman, R.D. 2003. Piston Pump. The Internet Glossary of Pumps. Accessed: 15
February 2004. URL: http://www.animatedsoftware.com/pumpglos/pistpump.htm
The Ventricular System and CSF. Accessed 08 March 2004. URL:
http://faculty.washington.edu/chudler/vent.html