Vanderbilt University
Department of Biomedical Engineering
Phantom Simulation of Liver Motion
During Normal Breathing
Group 17: Team ITI
Ian Dallmeyer
Tuta Guerra
Ian Henderlong
Advisor:
Dr. Robert Galloway
Date of Submission:
April 26, 2004
Abstract
Image-guided liver surgery is a minimally invasive therapy to treat primary and
metastatic liver cancer with little damage to healthy tissue. It involves the use of tomographic
analysis such as CT, MR, and PET to create registered images of the abdomen. Current methods
of liver surgery only use these images preoperatively. Application of these imaging techniques
to surgical procedures during operations will improve not only the standard therapy for treatment
of liver cancer, but will also advance targeting accuracy that is critically needed in ablative
therapy of liver tumors. This design project focuses on creating a phantom simulation of liver
motion during normal breathing in order to provide an accurate, reusable device to practice and
perfect image guided-liver surgery techniques. This model consists of two different components;
a cart design with base and vehicle that support the silicon phantom liver and a circuit design
which produces the cyclic power output. Muscle Wire, a shape memory alloy, which contracts
when heated with applied current and relaxes when cooled without applied current, connects the
two components and creates the simulated liver motion during normal breathing. Our model
generated comparable displacement (10.4 mm ± 0.54 mm) and frequency (f = 0.112 Hz) to
documented human liver motion, but differed in generating the exact documented waveform
(Figure 3).
This is most likely attributed to the muscle wire’s contraction and relaxation
characteristics not being alterable.
Introduction
The American Cancer Society estimates that 17.550 new cases of primary liver cancer
and 200,000 cases of metastatic liver cancer will be diagnosed in the U.S. in 2005 and that
another 15,420 people will die of liver cancer. In contrast to many other types of cancer, the
number of people who get liver cancer and die from it is increasing. Liver cancer is about twice
as common in men as in women. This cancer is about 10 times more common in developing
counties in East Asia, Africa, and Asia than in the U.S and in many of these countries it is the
most common type of cancer. China is has one of the largest incident rates of liver cancer
reporting over 250,000 cases last year alone.
Current therapies for liver cancer
are incredibly invasive (Fig1).
Often
cancer is large, is found in many
different parts of the liver, or has spread
beyond the liver so liver resection or
transplantation
is
not
possible;
furthermore, many people with cirrhosis
do not have enough healthy liver tissue
to make surgery an option, leaving
radiation and chemotherapy as one of a
few alternatives. The majorities (80-90%) of the metastatic
Figure 1: Open Liver Resection
cancer patients has multiple tumors in their liver and are often not candidate for traditional
surgery. Image-guided liver surgery makes many more metastatic tumor cases operable and
offers the possibility of a more effective therapy with fewer side effects.
Image guided surgery uses tomographic imaging techniques such as CT, MR, and PET to
create a registered image that define the spatial extent, location and structure of the diseased area
and the location, function and topology of the normal anatomy about the disease areas. Using
these images as maps, surgeons can effectively guide the delivery of therapy in space and time to
localized regions of the liver.
These therapies include radio-frequency ablation,
chemoembolization, and other localized minimally invasive therapies.
Chemoembolization is an example of an image guided therapy that is improving the
survival rates of liver cancer patients. Under the guidance of X-ray angiography, physicians
insert a catheter through the patient's arteries to the liver and inject a high-dose of chemotherapy
into the cancerous tissue. This augments the anti-cancer effects of chemotherapy beyond the
effects offered by systemic (full body) delivery through a few mechanisms: 1) the chemotherapy
agent does not become diluted by mixing with the rest of the blood from the body prior to
reaching the cancer, 2) the chemotherapy agent is not broken down in the body through
biochemical processes prior to reaching the cancer, 3) larger amounts of the chemotherapy agent
can reach the cancer with fewer associated systemic side effects (Llovet 1734). Following intraarterial chemotherapy administration, embolization is performed, which involves the placement
of a small gelatin sponge into the hepatic artery to block blood flow to the cancer. This reduces
the volume of blood in the cancer, which allows the chemotherapy agent to spread throughout
the cancer and remain there in sufficient concentrations. The result: the chemotherapy is trapped
inside the tumor, and the tumor dies (Dusik). In a systematic review of chemoembolization,
which is also much less invasive than alternative care, including chemotherapy, transplantation,
or surgery, 61 randomized clinical trials concluded that chemoembolization improves survival of
patients with unresectable HCC [inoperable liver cancer] and may become the standard of
treatment as seen in Table 1 (Llovet 429).
Table 1:
1 and 2-Year Survival Rates with Chemoembolization
A Comparison of Two 2002 Clinical Trials
STUDY
AUTHOR
SURVIVAL % AT 1 YEAR
SURVIVAL % AT 2 YEARS
With image-guided
chemoembolization
Without
With image-guided
chemoembolization
Without
Llovet
82
63
63
27
Lo
57
32
31
11
Sources: "Randomized controlled trial of transarterial lipiodol chemoembolization for unresectable hepatocellular carcinoma," Lo et al in
Hepatology; 35; 1164-1171, 2002; and "Arterial embolization or chemoembolization versus symptomatic treatment in patients with unresectable
hepatocellular carcinoma: a randomized controlled trial," 359:1734-1739, The Lancet, 2002, as reported in "Systematic Review of Randomized
Trials for Unresectable Hepatocellular Carcinoma: Chemoembolization Improves Survival," by Josep M Llovet and Jordi Bruix, Hepatology, Vol.
37, No. 2, 2003.
Radio Frequency Ablation (RFA) was primarily developed for treating hepatocellular
carcinoma. HCC have poor response to chemotherapy and radiotherapy. Radiofrequency
ablation is virtually "Cooking tumors with Needles". It is based on the High frequency induced
thermo therapy (HiTT). A high frequency current alternating rapidly at approximately 480 KHz
(with in range of radio transmission) is delivered to the tumor tissue via a needle electrode. As
the current alternates, the ions in the vicinity of the needle tip rapidly change direction (ionic
agitation), which causes frictional heating of the tissue (resistive heating) and cell death by
coaggulative necrosis. Thus, the tissue itself is the source of heat rather than the electrode tip
(McGahan).
RFA has many advantages over surgery including low complication rate, reduced cost
and increased patient compliance. It is simple, safe, and an effective treatment modality. It is less
risky and has low morbidity & mortality as compared to surgery. Most of these procedures are
performed without general anesthesia on outpatient basis. Hospital stay is short and most patients
can resume normal activities within a few days. The procedure can be repeated if necessary and
can be combined with other available treatment modalities. After RFA treatment for HCC,
median survival is 44 months with 10% local recurrence. The overall survival rate after RFA for
liver metastasis is 86-94% at one year and 89% at 1.5 years. Fifty-three percent of patients
remain disease free at one year and thirty-three percent at 18 months (Nazir).
Current methods for treating liver cancer employ the use of computerized tomographic
images preoperatively. During the actual procedure, an intraoperative ultrasound probe is used
to determine tumor location in real time, but these images are of poor spatial quality and are not
very effective in more precise localization. In order to continue to develop and improve imageguided therapeutic surgical applications to liver cancer, accurate models of the liver and its
motion due to breathing need to be created so they can be used during surgical procedures. This
can be done with mathematical formulae, computer imaging, and physical modeling. As early as
1997, computer imaging techniques were found to be very helpful in volume estimations of the
kidney and liver.
Helical CT scans were conducted with regularly and irregularly shaped
polyvinylchloride bags containing saline of varying volumes immersed in peanut oil during
various rates of movement of 0, 10, 15, and 20 cycles/min, using a motorized platform, designed
to simulate respiratory motion. Results indicate that helical CT is a highly accurate technique for
estimating volume, even in the presence of simulated respiratory motion (Nawaratne).
Anthropomorphic phantoms have been used to validate the accuracy of the registration
algorithm created by techniques that try to accurately register the CT and the SPECT scans of the
liver of patients treated with radioactive microspheres.
While studies have confirmed the
accuracy of the algorithm for CT-SPECT registration under controlled conditions, the technique
is rather insensitive to the non-uniform activity distribution within the liver, measured by the
microsphere. Furthermore, movement of the liver did not afford for the phantom model to be
used in the same position, leaving speculation as the accuracy of the rigid registration. Further
testing on phantom models that more accurately recreate structure deformation, and motion of
the liver is necessary is needed for more accurate successes of tumor targeting (Sarfaranz).
Use of various different types of tomographic images to map the liver has evolved to
include different technologies. For example, in order to compensate for tissue deformation in the
organ, procedures will rely more frequently on anatomical surfaces for the basis of image
alignment and will require intraoperative geometric data. This can be accomplished using a laser
range scanner based on the optical principle of triangulation which acquires a dense set of threedimensional point data in a very rapid, noncontact fashion. Phantom studies were performed to
test the ability to link range scan data with traditional modes of image-guided surgery data
through localization, registration, and tracking in physical space. The experiments demonstrate
that the scanner is capable of localizing point-based fiducials to within 0.2 mm and capable of
achieving point and surface based registrations with target registration error of less than 2.0 mm
(Cash).
Mathematical Cardiac Torso (MCAT) Phantom models uses mathematical formulae, the
size, shape and configurations of the major thoracic structures and organs, such as the heart,
liver, breasts, and rib cage, to be realistically modeled for imaging purposes. However, normal
respiration causes a complex motion of different structures present in the abdomen and thorax,
making it difficult to register combination images of CT and PET scans Accurate representation
of activity and attenuation distribution conclude that the portrayed geometry is not enough and
reveals that respiratory motion precludes the detection of the smallest lesion inserted into the
liver using these numerical models. Differences between simulated and physical version of
phantoms can account for certain variables such as thickness of tissue wall, and underscore the
need for accurate physiological models that are required for both normal and pathological
subjects (Isoardi).
Currently porcine livers provide the majority of physiological models to simulate liver
surgery (Fig 2). They are used because their position and function most closely resembles that
of humans. While this may be the closet representation of
human livers, porcine livers do not accurately model the size,
structure, deformation, and movement of human livers.
Furthermore, porcine liver simulation requires extensive funds
to house, kill, remove the liver, and dispose of animal subjects
which end up costing roughly 1,000 and 2,000 dollars for an
inaccurate model that can only be operated on once. Therefore,
the cost, reusability, and incompatibility in terms of structure and
Figure 2: Procine Liver
motion render this model insufficient in providing an accurate and affordable simulator. Thus, it
is necessary to develop a phantom simulation of liver motion during normal breathing using an
anatomically correct phantom.
Alternatives to modeling liver motion include the use of high-frequency jet ventilation
that would ventilate the lungs without moving the diaphragm and the liver. However, the
duration of this therapy lasts a maximum of 45 minutes, where liver surgeries often take hours.
Moreover, HFJV has been shown to result in cardiovascular complications in the form of a high
airway pressure that can be transmitted to the heart. HFJV does not produce consistent patient
response especially at the extreme ends of the age spectrum. The most limiting factor for HFJV
is its inability to be affordable for low end hospitals to purchase and operate (Tarcsy-Hornoch).
The market potential for a physical, anatomically correct, reusable phantom liver
simulator is immense. The sheer numbers of cases and the frequency of incidence for liver
cancer around the world make the liver market almost 10x larger than the current neurosurgery
market, estimating the potential market for image guided liver surgery systems to be at $3.0-7.5
billion. Currently, the estimated cost of constructing and operating this phantom liver simulation
is approximately $100, compared to the porcine liver which is 10 times that and cannot be used
again. Currently there are no image-guided liver surgery systems on the market that actively use
medical images to guide tumor resections and probe placements for ablative therapies. This
design project of phantom liver simulation during normal breathing represents the first step in
creating a highly innovative technical advance in surgical guidance for abdominal procedures.
Methodology
The main goal of our project involved the creation and design of a physical model in
which an anatomically correct phantom liver moves in accordance to the actual motion of a
human liver. From our advisor, Dr. Bob Galloway, we were provided with an anatomically
correct phantom, silicon model of the human liver, which was molded at the Art Department
here at Vanderbilt University. Also, we were provided with a PVC pipe with diameter of 26 cm
and length of 29 inches to house our model. There is no risk associated with the operation of our
device; therefore, designsafe was not applicable to our project.
In order to initially evaluate our design goals, Innovation Workbench (IWB) (Appendix
II) was used to break down the process into brainstorming and prioritization of design tasks.
From IWB, our project design process was separated into 3 basic steps: design of sliding
mechanism and housing for the phantom liver, implementation and construction of a linear
actuator, and designing a circuit to control the required oscillation.
To accurately simulate the motion of
the liver due to the respiratory cycle, several
design constraints were necessary. The two
most notable being the limitations of the
design specs are the anatomical cranialcaudal motion of the liver at a displacement
of 10.8  2.5 mm and the frequency of the
oscillating
force
application,
which
Figure 3: Graph of liver motion due to respiratory cycle
simulates the respiratory cycle.
MRI
studies suggest that cranial-caudal movement alone could approximate clinically significant liver
motion effectively, completely neglecting other axes of motion (Korin). The average frequency
of normal human breathing is approximately one breath cycle for every 9 seconds, or 0.11 Hz
(Herline).
Figure 3 illustrates the actual
motion of a human liver with these specs.
Initial brainstorming was done to
create a system that holds the phantom liver
and provides a sliding mechanism limited to a
unidirectional motion simulating the cranialcaudal motion of the liver.
After gaining
consent from our advisor, the decision was
made to construct a cart system sliding on four
wheels with tracks that provide the desired
Figure 4: Cart System Design
motion. In order to keep costs down and since there were no materials provided; plywood was
used to construct the cart surface to hold the phantom liver with dimensions of 25 cm x 26.5 cm.
Four 1.25-inch plastic wheels with steel bases were purchased and screwed onto the plywood
surface. A base made of plywood was also cut long enough (32 cm) to hold the cart and allow
for room for the actuating system. A backing block made of oak was cut and secured through
two hinges to the base also.
The need for a recoil mechanism, which serves the purpose of simulating the liver’s
motion during the exhale, was noted and implemented as well. To provide this recoiling force,
two springs (k = 9 x 10^6 N/m2) were purchased along with 4 1-inch metal hooks to attach the
springs to the cart and the backing block. Two hooks were screwed into both the side of the cart
and the top of the backing block, respectively. Figure 4 illustrates our cart system.
Probably the biggest design consideration for our project was the decision
regarding the linear actuator device. Our advisor initially proposed the idea of using a shapememory alloy called muscle wire, which maintains a crystal structure that can be altered through
an increase in temperature. Basically the muscle wire contracts a variable amount, which is
determined through applied current. To choose the correct diameter and type of muscle wire, the
force necessary to move our cart the required 10.8 mm  2.5 mm was determined to be
approximately 3 N, which equates to about 0.30 kgf. It was determined that the Flexinol 150 LT
(150 m diameter/ 70 C activation temperature) muscle wire provided enough pulling force to
achieve our goal. Other linear actuators were considered, but the muscle wire provided the best
control and simulation of muscle fibers.
Implementing the muscle wire into our cart involved determining the necessary length of
wire and voltage necessary to achieve our goal. For muscle wire to contract and return to its
original length, it must not contract more than 5% of its length. A 30 cm piece of muscle wire
was used to produce 10.8 mm of contraction. This equates to a contraction of 3%, which is well
under the designated 5% cutoff for maintaining structural integrity. The muscle wire has an
internal resistance of 50 /m. Therefore, a 30 cm piece has a resistance of 15 . For optimal
contraction speed, a current of 400mA is required.
Using Ohm’s Law (V = IR), it was
determined that the muscle wire needed to see a voltage drop of 6 V.
Figure 5: Circuit Schematic
To oscillate the voltage across the muscle wire, a circuit was constructed as shown in
Figure 5. To achieve the specified frequency of voltage application, a TLC555 timer integrated
circuit was used. This device is capable of producing an “on” time (T1), “off” time (T2), and
frequency (F) of desired values. The equations that govern these specifications are as follows:
T1 = 0.693 x (R1 + R2) x C
T2 = 0.693 x R2 x C
F = 1/(0.693 x (R1 + 2R2) x C)
For our desired frequency of 0.11 Hz, we chose R1 = 1 k, R2 = 1 M, and C = 5.4 F.
The corresponding specifications are T1 = 4.44 s, T2 = 4.43 s, and F = 0.1124 Hz. Therefore,
the design constraints were met. The timer was powered by a 5 V DC source, which caused
oscillation output voltages of 0.91 V during T1 and 0 V during T2.
To apply these changes to control the muscle wire and allow it to oscillate from 6V
(heating/contraction) to 0V (cooling/relaxation), a PN222a Bipolar Junction transistor was used
to act as a switch for the applied current. As shown in the schematic in Figure 5, a 6 V DC
voltage was applied to the muscle wire, which connects to the collector of the BJT. The output
of the timer was attached to the base and the emitter was grounded. By having the base node
oscillating voltages, the BJT is switched between cutoff and saturation mode. When the timer
output is 0 V, no current flows through the muscle wire, and when the timer output is above 0.7
V (0.91 V actual), the muscle wire sees the 6 V and contracts accordingly.
A great deal of circuit work was required to fine-tune the oscillating specifications.
Initially, an operational amplifier was implemented to amplify the 0.91 V to 6 V.
Upon
realization that the maximum current an op-amp provides is 20mA, the BJT was designed and
proved to be very successful.
Results
With the length of wire we used (30
Cart Displacement vs Time
cm), the average displacement of the
phantom was 10.4 mm + 0.54 mm. Over an
8-9 second interval, our phantom moved
~10 mm in about half the cycle time or 4-5
seconds, and returned to rest in about the
Displacement (mm)
12
10
8
6
4
2
0
-2 0
20
40
Time (s)
Figure 6 – Cart motion vs. time
60
same amount of time producing a frequency of approximately 0.112 Hz. A plot of the cart
motion vs. displacement is shown in Figure 6.
There are noticeable differences between the documented liver motion shown in Figure 3
and our model’s data in Figure 6. These slight dissimilarities are most likely attributed to the
inability of the muscle wire to speedily and functionally change positions accurately. It’s crystal
structure contracts and relaxes with great sensitivity, but to accurately replicate the waveform
shown in Figure 3, possibly another more complicated circuit design or variable linear actuator
would produce the desired waveform. Also, it must be said that each human being’s liver motion
is not the same. Therefore, slight error in motion and displacement might be desired depending
on the application.
Conclusions
The two major specifications were that the 1-dimensional average total liver motion be
about 10.8 + 2.5 mm, and that the motion occurs at the same interval as that of the liver due to
the breath of a human subject. The amount of shortening it could demonstrate when the
activation current of 400 mA was passed through it was very close to the expected amount, about
3-4% of the total wire length, and the same amount of contraction was still observed after many
cycles. Muscle Wire therefore met the first design specification nicely. It was more difficult,
however, to meet the second specification. We found that the Muscle Wire shortening and
lengthening occurred a little too slow. The liver normally moves the entire 10 mm and back to its
original position in about 4 seconds, with about 5 seconds of relatively little motion, whereas our
model essentially broke up the motion evenly over the whole, reaching its greatest displacement
after carrying current for about 4.5 seconds, and returning to the initial length in the same time.
The rate of cycling was still equivalent to 1 breath every 9 seconds, our target breathing rate, but
either the Muscle Wire took too long to cool or we supplied it with its activation current for too
long. If T1 refers to the time during which the Muscle Wire is supplied with current and T2 = 9 –
T1 = time during which no current flows in the wire, then our T1 was a bit too long. The timer
circuit we used can produce T1 > T2, and even approximately T1 = T2, but not T1 < T2, which
may have allowed the Muscle Wire to relax more quickly. The contraction time might need to be
decreased a little bit as well, but that is more difficult to control without risking over-shortening
the Muscle Wire (putting a larger input voltage across the wire could shorten it past the 5% limit
for shape memory).
Suggestions for Future Work
As mentioned above, it is possible that a more complex timer circuit could supply the
necessary input to the Muscle Wire to return it to its initial length more quickly, by using a
shorter T1 and longer T2. Another way to increase the rate at which the Muscle Wire returns to its
initial length is to increase the cooling rate. Since the change in crystal structure that causes
shortening is caused by an increase in temperature, returning to a low temperature more quickly
should result in a faster return to the initial length. To increase the cooling rate, the Muscle Wire
could be surrounded by water or another liquid. In addition, the design specifications allowed for
as much as 23% variation in the amount of liver motion, so the motion produced by Muscle Wire
was probably too uniform to accurately represent the variability in the motion of the liver as a
person breathes, noting also that most people have frequent sighs that differ from normal breaths.
One class of materials that could be used as linear actuators is conductive polymers. This class of
polymers is receiving increased attention because of their ability to mimic the behavior of
biological muscles. These polymers may offer a more sensitive alternative to shape memory
alloy wires and might be able to contract and relax more quickly. An additional suggestion might
be rather than to move to more sophisticated materials like electroactive polymers, perhaps a
simple actuator such as a stepper motor could be used to create the desired oscillation. Overall
system performance may also have been improved by the employment of less crude components.
For example, to reduce friction we might have chosen different wheels or a more sensitive
sliding mechanism for the cart, but given our limited funds and materials, we chose to create the
cheapest model that achieves our given displacement and frequency specifications.
APPENDIX I: References
Dusik D, Morley M, Chemoembolization Helping Patients with Liver Cancer Live Longer,
Radiological Society of North America, June 19, 2003.
Llovet J, Real M, Montana X, et al. Arterial embolization or chemoembolization versus
symptomatic treatment in patients with unresectable hepatocellular carcinoma: a
randomized uncontrolled trial. The Lancet. 2002;359:1734-1739.
Llovet JM and Bruix J, Systematic Review of Randomized Trials for Unresectable
Hepatocellular Carcinomas: Chemoembolization Improves Survival, Hepatology, Vol.
37, No. 2, pp.429-442, 2003
McGahan JP, Browning PD, Brock JM, Tesluk H. Hepatic ablation using radiofrequency
electrocautery. Investigative Radiology 1990; 25:267-270
Nazir B, Chaturvedi AK, Rao A. ImageGuided Radiofrequency Ablation of Tumors: Current
Status Independent Journal of Radiology Imaging 2003 Vol.13; Iss.3:315- 322.
Nawaratne, Sumith; Fabiny, Robert; Brien, Joanne E.; Zalcberg, John; Cosolo, Walter; Whan,
Andrew; Morgan, Denis J. Accuracy of Volume Measurement Using Helical CT. Journal
of Computer Assisted Tomography. 21(3):481-486, May/June 1997.
Sarfaraz M, Wu X, Lodge MA, Yu CX. Automatic CT-SPECT registration of livers treated with
radioactive microspeheres. Physics in Medicine and Biology. Vol 49, May 4, 2004.
Isoardi RA, Comtat C, Frouin V, Delzescaux T, Trebossen R. Simulating Respiratory Motion in
Whole-Body PET Imaging with the MCAT Phantom. IEEE Transaction on Image
Processing. May, 2003
Cash DM, Sinha TK, Chapman WC, Terawaki H, Dawant BM, Galloway RL, Miga MI.
Incorporation of a laser range scanner into image-guided liver surgery: surface
acquisition, registration, and tracking. Med Phys. 2003 Jul;30(7):1671-82.
Tarczy-Hornoch P, Jones D, Zerom B, Woodrum D, and Berk R. Mechanical
Ventilators. [Online] Available http://weber.u.washington.edu/~neonatal/NICUWEB/vents.html, 1998.
Korin HW, Ehman RL, Riedere SJ, Felmlee JP, Grimm RC. Respiratory kinematics of the upper
abdominal organs: A quantitative study. Magnetic Resonance Medicine 1992;23:172178
Bar-Cohen, Yoseph. Electroactive Polymers as Artificial Muscles – Reality and Challenges.
2001. Proceedings of the 42nd AIAA Structures, Structural Dynamics, and Materials
Conference (SDM), Gossamer Spacecraft Forum.
APPENDIX II: Innovation Workbench
Innovation Situation Questionnaire
1. Brief description of the problem
Many minimally invasive surgical procedures are designed so that the surgeon can employ imageguided surgical techniologies to perform the required manipulation without the necessity of opening of
the body cavity. These technology guided procedures require exact placement of probes and that the
image accurately represents the patient so that it can be used as a surgical map. While in surgery, the
patient is kept under anesthetic and is breathing normally. The liver is a large organ lying in the
abdomen just below the diaphragm. Motion of the liver due to the respiratory cycle needs to be
accounted for in order to have accurate and precise placement of probes during surgery. This project
will provide a physical model of the human liver's motion during breathing to be used in preliminary
testing for technology guided surgical procedures.
2. Information about the system
2.1 System name
Phantom Simulation of Liver Motion during Normal Breathing
2.2 System structure
Anatomically correct physical model of the human torso containing the mechanical system of the
liver's motion
2.3 Functioning of the system
Exactly simulate the liver's motion during breathing
2.4 System environment
Initial PVC pipe (that may be upgraded to plastic human torso model) containing the phantom liver,
sliding mechanism, muscle wire/mechanical system to generate motion. Possible addition of lungs/
other anatomical entities
3. Information about the problem situation
3.1 Problem that should be resolved
Provide model for pre-operative testing of imaging systems and surgical procedures involving the
human liver
3.2 Mechanism causing the problem
Normal motion of the human liver due to the respiratory cycle
3.3 Undesired consequences of unresolved problem
Inaccurate images, inaccurate placement of probes, general inaccuracy of surgical techniques due
to liver motion
3.4 History of the problem
Failed attempts to properly image the liver during surgery and hence inaccurate insertion of probes
(ablators, scopes, etc.) to desired positions
3.5 Other systems in which a similar problem exists
General non-invasive surgical techniques involving the liver where there is a need for pin-point
accuracy in imaging and probe placement
3.6 Other problems to be solved
Providing an anatomically correct model of the human torso, determining best mechanism to
simulate liver motion (muscle wire/ gear system), maintaining exact average movements of the liver
due to respiratory cycle
4. Ideal vision of solution
Provided we can create a working model inside the PVC pipe construct, ultimately, we would like to
have a human torso shell where the model liver and the mechanism for movement can be stored
having a cosmetically pleasing and functionally sound system for the liver motion
5. Available resources
PVC Pipe, silicon pahntom liver, muscle wire (purchased from vendor)
6. Allowable changes to the system
Shell (either PVC pipe or human torso model) coudl be altered, working mechanism for motion of liver
(either muscle wire or gear system) can be altered but has not been determined yet
7. Criteria for selecting solution concepts
Successful replication of anatomical motion of liver due to the respiratory cycle, successful housing of
liver and stability of model
8. Company business environment
Markets include physicians, companies involved in imaging technology, companies involved in
providing equipment/techniques for non-invasive surgery involving the human liver
9. Project data
Name - Phantom Simulation of Liver Motion during Normal Breathing
Team Members - Ian Henderlong, Tuta Guerra, Ian Dallmeyer
Website - http://vubme.vuse.vanderbilt.edu/srdesign/2004/group17/
Problem Formulation
1. Build the Diagram
2. Directions for Innovation
12/2/2004 1:42:59 PM Diagram3
» 1. Find an alternative way to obtain [the] (Liver Surgery) that offers the following: provides or
enhances [the] (Image-Guided Surgery), (Non-invasive probe placement) and (Liver Motion during
breathing), does not cause [the] (Inaccurate imaging) and (Inaccurate probe placement).
2. Try to resolve the following contradiction: The useful factor [the] (Liver Surgery) should be in place in
order to provide or enhance [the] (Image-Guided Surgery), (Non-invasive probe placement) and (Liver
Motion during breathing), and should not exist in order to avoid [the] (Inaccurate imaging) and
(Inaccurate probe placement).
3. Find an alternative way to obtain [the] (Image-Guided Surgery) that does not require [the] (Liver
Surgery).
4. Consider transitioning to the next generation of the system that will provide [the] (Image-Guided
Surgery) in a more effective way and/or will be free of existing problems.
5. Find an alternative way to obtain [the] (Non-invasive probe placement) that does not require [the]
(Liver Surgery).
6. Consider transitioning to the next generation of the system that will provide [the] (Non-invasive probe
placement) in a more effective way and/or will be free of existing problems.
7. Find a way to eliminate, reduce, or prevent [the] (Inaccurate imaging) under the conditions of [the]
(Liver Surgery).
8. Find an alternative way to obtain [the] (Liver Motion during breathing) that offers the following:
provides or enhances [the] (Working Phantom Model), does not require [the] (Liver Surgery).
9. Find an alternative way to obtain [the] (Working Phantom Model) that offers the following:
eliminates, reduces, or prevents [the] (Inaccurate probe placement) and (Inaccurate imaging), does not
require [the] (Liver Motion during breathing), (Silicon Phantom Liver), (Muscle Wire/mechanical system)
and (Human Torso Model/Shell).
10. Find a way to eliminate, reduce, or prevent [the] (Inaccurate probe placement) under the
conditions of [the] (Liver Surgery).
11. Find an alternative way to obtain [the] (Silicon Phantom Liver) that provides or enhances [the]
(Working Phantom Model).
12. Find an alternative way to obtain [the] (Muscle Wire/mechanical system) that provides or enhances
[the] (Working PhantomModel).
13. Find an alternative way to obtain [the] (Human Torso Model/Shell) that provides or enhances [the]
(Working Phantom Model).
Prioritize Directions
1. Directions selected for further consideration
1. Find an alternative way to obtain [the] (Liver Surgery) that offers the following: provides or
enhances [the] (Image-Guided Surgery), (Non-invasive probe placement) and (Liver Motion during
breathing), does not cause [the] (Inaccurate imaging) and (Inaccurate probe placement).
1.1. Improve the useful factor (Liver Surgery).
1.3. Increase effectiveness of the useful action of [the] (Liver Surgery).
1.4. Synthesize the new ystem to provide [the] (Liver Surgery).
1.5. Apply universal Operators to provide the useful factor (Liver Surgery).
1.6. Consider resources to provide the useful factor (Liver Surgery).
2. List and categorize all preliminary ideas
Mechanical System: purchasing of muscle wire to provide force necessary to simulate liver motion
along with an appropriate power source.
Sliding Mechanism: cart with wheels and track, wax paper, or metal track system
Construct: Cut PVC tube and configure placement of phantom liver
Develop Concepts
1. Combine ideas into Concepts
Completion of testing of methods for mechanical system for movement of the liver will provide us with
pros and cons for each idea. Testing of various sliding mechanisms will allow selection of the most
effective method. Initial completion of model in PVC will allow possible transfer of model to a more
anatomically correct human torso model.
2. Apply Lines of Evolution to further improve Concepts
Our advisor stressed the importance of this device in pre-operative testing for imaging of the liver and
surgical procedures involving the human liver. By improving the concepts we can create a sensitive
and functional simulation of the liver due to respiration.
Evaluate Results
1. Meet criteria for evaluating Concepts
Concepts directly relate to criteria for creation of model
2. Reveal and prevent potential failures
Potential failures include wearing down of muscle wire system as mucle wire can only be used for a
specified period of time, breakdown of sliding mechanism
3. Plan the implementation
Acquistion of prodcuts from vendors will allow testing of methods, but until then plans will be
implemented as parts are received.
Creation of a Concept Map and Use of Innovation Workkbench:
Creation of a concept map gives us an opportunity to visualize the problem in terms of its place
in the big picture as well as in terms of the relevant details, such as the required components and
system parameters. Using Innovation Workbench is a good test of whether or not we know what
our problem is, why it needs to be solved, and what directions we intend to take in order to solve
it. Combining the two will be a good aid in developing a timeline, ensuring that we can complete
the required tasks and test our solution in time to present our results