Inventive Problem Solving
Ideation Process
Project Initiation
1. Project objectives
Our primary objectives are to miniaturize the Raman Spectroscopy-Optical Coherence
Tomography probe for potential endoscopic use in disease diagnosis, develop novel approach
for fiber optic RS-OCT, increase sensitivity and specificity of probe. The objectives were
established by Dr. Anita Mahadevan-Jansen and Dr. Chetan Patil. The current medical device is
the work of Dr. Patil's discertation. Our primary objectives have been established in order to
increase the mobility of the sample arm of the current medical device to aid the capability of
detecting cancer in endothelial tissues. The objectives were established in October 2010 and do
not need to be updated yet. Yes, they are realistic. The project is ambitious since it has never
been done before. Although, since we are combining two current working techniques these
objectices are obtainable. We believe we are not overestimating our capabilies or the
capabilities of others.
2. Importance of the Situation
Since this medical device will allow for image guided cancer detection, doctor's will benefit
from this device by being able to identify endothelial tissue in a practical and safe manner. The
current RS-OCT probe has a sample arm that is too bulky that is difficult to move and can only
detect skin cancer. This device is selected for improvement to increase the mobility of the sample
arm and to decrease the sample arm size for potential endoscopic use. Failure to improve the
sample arm of the RS-OCT probe will result in limited cancer detection. This device requires
improvement since the current device is hard to use now, but it has great potential for cancer
detection in all endothelial tissue, not just the skin. Initially, a lot of research had to be done to
understand the complexities of Raman Spectroscopy and Optical Coherence Tomography.
Through the guidance of Dr. Patil, we have obtained enough information to start the project.
Using the combined resources of our advisors and research, we have developed prilimanary
design to tackle this project. By improving image guided cancer detection, cancer detection will
be quicker and safer for everyone. This device minimizes the need for tissue biopsy in order to
distinguish whether the tissue is cancerous or not.
Innovation Situation Questionnaire
1. Brief description of the situation
Miniaturize the sample arm of the current image guided cancer detection device in order to
improve mobility and have potential endoscopic use.
2. Detailed description of the situation
2.1. Supersystem - System - Subsystems
2.1.1. System name
Redisigned fiber optic Raman Spectroscopy and Optical Coherence Tomography sample arm
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2.1.2. System structure
The curent structure measures 5x8x3 inches. The sample arm is redesigned to fit inside a pipette
by using a combination of fiber optics, piezoelectric scanning mechanism, and a GRIN lens. The
The piezoeletric scanning mechanism measures 49x1.9x0.6 mm. It is centered into a rubber
insert in a fiber optic housing. A SMF 28 fiber used for OCT is fitted through the smae slot and
runs atop the 49 mm piezoelectric. It extends off the piezoelectric mechanism ___ mm. There is
a GRIN lens that sits ____ mm away from the tip of the fiber. This is all housed inside a pipette.
This constitues the OCT portion. The Raman fibers extend off the walls of the pipette ___ mm.
Currently, there are Raman fiber being used, one as a light source and the other as a collection
fiber. The fibers are placed 180 degrees away from each other.
2.1.3. Supersystems and environment
RS is limited by light. In order to perform RS, the environment will have to be completely dark.
2.1.4. Systems with similar problems
This system has never been made before therefore the trouble of combining RS-OCT into one
fiber optic probe has never been tackled. Individually though, advances have been made to
improve the devices.
2.2. Input - Process - Output
2.2.1. Functioning of the system
The OCT single fiber mode is driven by a constant voltage source to scan selected tissue to
aquire real-time image. The RS multi mode fibers are present to aquire biochemical composition
of selected tissue. Since OCT detects elastic scattering and RS detects inelastic scattering, both
OCT and RS cannot be run at the same time. Therefore once OCT aquires an image, OCT will be
turned off and RS will be turned on and directed at the area of interest base on the image
required.
2.2.2. System inputs
The system inputs are am AC voltage power supply running at ____ V and a 1310 nm light
source for OCT and 785 nm light source for RS.
2.2.3. System outputs
The sytem outputs are the data from the OCT and the data from the RS to be sent from the sample
arm to the computer to create an image and identify biochemical composition, respectively.
2.3. Cause - Problem - Effect
2.3.1. Problem to be resolved
The sample arm of current RS-OCT probe is too bulky. The sample arm is 5" x 8" x 3".
2.3.2. Mechanism causing the problem
Also the complex design of the medical device which involves both broadband light and Raman
excitation light along with collimating lenses.
2.3.3. Undesirable consequences if the problem is not resolved
If problem is not resolved and sample arm cannot be miniturized then image guided cancer
detection will be limited to tissue outside of the body (skin). This will also inhibit a non-invasive
technique to be developed that can detect cancer in internal tissues without a biopsy.
2.3.4. Other problems to be solved
The weak nature of Raman scattering (inelastic scattering) makes probe placement an important
variable when using RS to evaluate spatially confined tissues in vivo. The combination of OCT
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and RS in the device should first detect an area of interest using OCT and then coregister RS to
that area of interest. RS and OCT cannot be turned on simulateously. Also we must ensure that
both techniques do not limit or interfere with eachother.
2.4. Past - Present - Future
2.4.1. History of the problem
It is possible to modify the developemental direction to change the events leading to the
problem.If during the original design of the probe, Dr. Patil would have thought to use fiber
optics instead of a systems based on lenses then this problem would have been avoided.
2.4.2. Pre-process time
No there is nothing that could have resolved this problem. Raman scattering is weak and thus is
difficult to measure spatially confined tissues in vivo. Tissues could have been taken out of the
body and then tested with RS; however this would not be beneficial since it would no longer be a
non-invasive technique to diagnose cancer. Thus the sample arm should be miniaturized by
using fiber optics to use the device endoscopically.
2.4.3. Post-process time
Yes. Dr. Patil has already designed an RS-OCT probe that was designed with lenses and light
sources. This design can be improved upon. The combination of RS and OCT should be
continued, but fiber optics should be used instead of lenses in order to increase the cancer
detection capability of the device. Once the fiber optics are used to create a smaller sampling
arm, this design can further be improved upon by methods such as different orientation of the
fibers or different location of the light sources on the probe to further miniaturize the sampling
arm or increase the efficiency of the device.
3. Resources, constraints and limitations
3.1. Available resources
Information resources: Dr. Anita Mahadevan-Jansen, Dr. Chetan Patil, textbooks, Online
Science, Pub Med
Field Resource: Dr. Anita Mahadevan-Jansen (IP)
Material Resources: Online stores that sell necessary equipment to build probe (power supply,
polymer, platinum coil, Teflon tubing), material already at Vanderbilt (multi-mode and single
mode fibers)
Financial Resources: funded by Advisors
Space Resource: We are allowed to access the lab with the current probe in the FEL building
with our adviser, Dr. Patil
Functional Resource: the lab at FEL, provides a dark room with windows - important for RS
3.2. Allowable changes to the system
Small changes - the probe should work in theory. The probe could always be further miniaturized
and sensitivity and specificity could also be improved
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3.3. Constraints and limitations
OCT uses single mode fibers so it requires a broad bandwidth to acquire data. It uses a scanning
technique and only requires one fiber. RS uses multi-mode fibers so it requires a narrow
bandwidth to acquire data. It requires extra detection fibers to detect the emitted light. Therefore,
our challenge was to figure out a design that would be a happy middle configuration of the
different types of fibers since they have opposing uses. These conditions cannot be changed.
3.4. Criteria for selecting solution concepts
Compared to the existing probe, we want to decrease the size of the sample arm to make it more
usable (handheld) and increase the potential for endoscopic use to detect other cancers besides
skin cancer. The RS-OCT is used for image guided cancer detection. OCT acquires the image.
Raman Spectroscopy is able to identify malignant from non-malignant tissue. Decreasing the
probe size is an achiveable criteria since we will be using fiber optics instead of lenses. However,
miniaturizing enough that it will be able to be used endoscopically might be farfetched. This
criteria is long term.
Problem Formulation and Brainstorming
Diagram
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Miniaturize Probe
Possible
endoscopic use
Accuracy of
Diagnosis
Expensive
Fiber Optics
Durability
Single-Mode
Fibers
Multi-Mode Fibers
single phase
passes
Higher Numerical
Aperture
Useful for Optical
Coherence
Tomography
Greater Collection
Efficiency
Useful for Raman
Spectroscopy
4/25/2011 3:45:45 PM.
1. Find an alternative way to obtain Single-Mode Fibers that offers the following:
provides or enhances single phase passes does not influence Multi-Mode Fibers does not
require Fiber Optics.
2. Resolve the contradiction: Single-Mode Fibers should be provided to produce single
phase passes and shouldn't be provided to avoid counteracting Multi-Mode Fibers.
3. Find an alternative way to obtain Multi-Mode Fibers that offers the following:
provides or enhances Higher Numerical Aperture does not require Fiber Optics is not
influenced by Single-Mode Fibers.
5. Find an alternative way to obtain Greater Collection Efficiency that offers the
following: provides or enhances Useful for Raman Spectroscopy does not require Higher
Numerical Aperture.
9. Find an alternative way to obtain Miniaturize Probe that provides or enhances Fiber
Optics and Possible endoscopic use.
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10. Find an alternative way to obtain Fiber Optics that offers the following: provides or
enhances Single-Mode Fibers, Multi-Mode Fibers and Accuracy of Diagnosis eliminates,
reduces, or prevents Durability does not cause Expensive does not require Miniaturize
Probe.
11. Resolve the contradiction: Fiber Optics should be provided to produce Single-Mode
Fibers, Multi-Mode Fibers and Accuracy of Diagnosis and should be provided to
counteract Durability and shouldn't be provided to avoid Expensive.
12. Find a way to eliminate, reduce, or prevent Durability.
13. Find a way to eliminate, reduce, or prevent Expensive under the conditions of Fiber
Optics.
4/25/2011 1:32:03 PM.
Develop Concepts
1. Categorize preliminary ideas
Function 1: OCT laser emission - OCT optical fibers should be single-mode fibers.The beam of
light leaving the optical fiber must be able to be scanned axially. One needs to be exactly aware
of how the beam is scanned so that the 2-D image can be reconstructed. Laser source must be a
broadband laser source. The coherence length of the broadband laser beam must be low for
high resolution. We will use 1310 nm light source. The beam spot size on the tissue of interest
must be approximately the same as the resolution of the beam. Additionally you want a large
depth of focus, which is defined by the lens used.
Function 2: OCT collection -The collection of the reflected light during the OCT sampling must
filter out inelastic scattering. The collection should ideally be instantaneous, and confined to
the region of interest.
Function 3: Raman laser emission - You want to direct the beams to the same area of interest as
the OCT was scanning. This could possibly be done by angle-polishing the optical fibers.
Raman optical fibers should be multi-mode fibers. 785 nm laser source is to be used.
Function 4: Raman collection - The size of the cone of collection should be much wider than the
spot size of OCT to ensure efficient collection of the returning photons. This can be partially
determined by the numerical aperture of the optical fiber. A higher numerical aperture
corresponds to a larger cone of collection which corresponds to more efficient collection.
Additionally, elastic scattering must be filtered out.
2. Combine ideas into concepts
Single-mode fibers are required over multi-mode fibers for OCT because single-mode fibers do
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not allow multiple phases to pass through the fiber. Due to the principles of interferometry, it is
very important that the light leaving the fiber and the light returning to the fiber are of the same
phase.
In contrast, multi-mode fibers are preferred over single-mode fibers for Raman Spectroscopy
because multi-mode fibers are capable of higher numerical aperture. They have a greater
light-gathering ability than single-mode fibers. This is very important because the photons
returning in Raman spectroscopy are quite rare and hard to collect.
For these reasons, we proposed to use multi-mode fibers for RS, but have them in such close
proximity to the OCT single-mode fibers that the two sets of fibers will be sampling over the
same area. This close proximity is quite easily accomplished since the two sets of optical fibers
will be within several hundred micrometers of each other. A slight angle polishing of the
multi-mode RS fibers can account for that small distance.
Evaluate Results
1. Meet criteria for evaluating Concepts
The concept does meet the criteria for evaluating concepts. The fiber-optic size of the design is
miniaturized compared to the current probe and there should still be proper RS/OCT
functionality.
2. Reveal and prevent potential failures
It is necessary to produce all possible undesired effects or failures that can occur during the
implementaiton of the device miniaturization concept.
Event 1.We need to create a fiber optic RS system. To do this, we must align a raman excitation
fiber with a raman collection fiber so that the light emitted by the excitation fiber can be detected
by the collection fiber. Ideally, the raman fibers should be directly parallel to each other.
Event 2.We need to create a fiber optic OCT scanning technique.To make this OCT scanning
technique, we must focus the laser beam through a lens so that the beam width is set. Ideally,
we must align the beam so that it travels through the lens properly and can be reflected back
through the lens directly back into the fiber optic.
Event 3.These two mechanisms must not interfere with each other, but also be situated in a
manner such that they can ideally be housed together in a probe smaller than 1 cm in diameter.
Event 1 Failure Scenarios:
1. The raman fibers are very fragile, and if they are bent too much or dropped then they will be
useless. Additionally, the collection is very difficult to gather and it will not be possible to place
the raman fibers directly next to each other. Additionally, typical raman fiber setups use more
than one collection fiber, but we only have one so there could not be enough collection to
generate a raman spectrum.
2. The junction between the raman system and the OCT system could create a conflict because
the OCT scanning will take up space that would ideally place the raman fibers right next to each
other.
3. The raman light source is very fragile and can potentially be broken any time it is moved. If
the light source or raman fibers are bumped into or dropped, then the entire raman system will
potentially be ruined.
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4. The raman laser is powerful enough to damage eyes, so that could have a negative impact.
5. If there is a newcomer or visitor, or general stress, then the likelihood that someone
accidentally drops a raman fiber or bumps into the spectrograph and excitation laser is going to
be much more likely.
Event 2 Failure Scenarios:
1. The frequency cannot exceed the resonant frequency due to the fragility of the piezoelectric.
The piezo must not be bent either and should be handled with care. The leads coming off the
piezo accuator must not be exposed in order to reduce risks.
2. The interaction between the raman system and the OCT system could create a conflict because
the OCT scanning system needs to be aimed at the same area of interest as the raman detection
fibers. Additionally, the raman fibers extend beyond the GRIN lens so you need to make sure
the OCT laser beam doesn't hit the raman fibers.
3. The piezoelectric setup relies on the assumption that the optical fiber will remain firmly
attached to the piezoelectric actuator at all times so that the optical fiber undergoes a smooth
scanning motion. But the optical fiber can potentially be detached over time. Additionally, the
fiber optic cables being used throughout this system are very fragile and any index mismatching
from one cable to the other could result in poor OCT performance.
4. The OCT laser can harm eyes, so there it is dangerous. The piezoelectric leads may also
become shorted accidentally and create an electrical hazard and potentially overheat the system.
5. It is difficult to adjust the OCT system without throwing off the alignment of the laser and the
GRIN lens. Every time a test is done with the scanning fiber, it is possible that the fiber has
moved slightly off axis and is no longer aligned with the lens as well as it originally was.
Event 3 Failure Scenarios:
1. The two systems must be combined so that they are assessing the same exact area of tissue.
It is possible that during the testing the raman fibers will be bumped or liquid will enter the
device if it is being used endoscopically, and this will throw off the performance of the probe.
Additionally, as stated above the physical separation between the raman excitation fiber and the
raman collection fiber may be too large to generate raman spectrum graphs.
2. This event deals entirely with the junction of different systems in a space approximately 5
mm wide. There is little room for error in the placement of the raman fibers and the OCT fiber
alignment. For example, if the tip of a raman fiber obstructs the scanning of the OCT beam,
then the probe will not work correctly.
3. If a raman fiber is nudged, the GRIN lens that it is next to would be placed out of alignment.
4. The 1310 nm laser is harful to the users eye. Exposed leeds have 16 V.
5. The lights must be off while acquring data for raman, this could pose a problem if a
disturbance were to occur during this time.
Step 4.
1. Train user to avoid the laser at eye level
2. Tape all exposed leeds with electrical tape
3. Train user to handle the piezo accuator, GRIN lens, raman and OCT fibers with care
4. Create a rigid housing for all the componenets to eliminate interaction between user and
potentially harmful mechanisms in the design.
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3. Apply Patterns/Lines of Evolution
Increasing ideality
The ideality of this design is already quite high. It has very useful applications because the
probe can potentially noninvasively detect various types of epithelial cancer. It does not present
much danger to patients, so it doesn't have any important undesired features.
Segmentation
Segmentation is an important part of what still needs to be done in the future, especially in terms
of the final housing. It would be very helpful if the piezoelectric system within the housing
could be dismounted so that it can be repaired without altering the location of the GRIN lens.
Then the repaired piezoelectric system could just snap back into place and you could be sure it is
already aligned with the GRIN lens.
Dynamization
Dynamization is another aspect which this probe needs to improve upon. It would be easier to
eventually navigate this probe endoscopically if the probe could be more flexible. Additionally,
the tail end of the probe involves very fragile fibers running from the probe back to the laser and
spectrograph. This portion of the probe should be able to be detached from the rest of the probe
so mobilization is easy until the probe is finally in place and ready to diagnose.
Increasing controllability
The controllability could also be improved. Currently the probe is designed to simply image
tissue and then take the biochemical composition of the tissue. If the doctor already knows
which type of cancer they are attempting to detect, then perhaps in the future he or she could
switch a button and then the OCT imaging and RS detection could be more specialized towards
detecting the physical features and biochemical composition associated with that type of cancer.
Matching and Mismatching elements
Additionally, the matching and mismatching of elements could use improvement because the
materials we selected for the housing and the opto mechanics we used were not ideal. A
finalized housing system with micromachined mounts and optomechanics would be much more
preferable. Also, the current housing being used is rubber, but a more rigid material may be
desired to protect the fibers. Then the tip of the fiber may need to be flexible.
4. Plan the implementation
The first step of the implementation process is developing the OCT scanning technique. This
has potential failures relating to the alignment of the OCT scanning fiber and the GRIN lens.
The alignment can be prevented from going off-axis by utilizing micromachining in order to
precisely control the position of the piezoelectric actuator and the GRIN lens. Additionally, the
fiber optic cable can be permanently glued to the piezoelectric actuator.
The next step of the implementation process is setting up the raman spectroscopy portion so that
it is spatially registered with the OCT scanning portion of the probe. This can be done by
inserting the raman fibers in the plastic lumen that contains the GRIN lens. Then the ends of the
raman fibers can be angle polished or situated with miniature mirrors so that the excitation light
and the collection area align with the center of the OCT scanning section.
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The final step of the implementation process is converting the bench top design to a handheld
prototype. This has potential failures such as misalignment within the housing and the structure
must be strong enough to protect the fragile fibers from bending or being damaged.
Additionally, if a problem arises within the housing, the technician should be able to easily
access the inside of the housing to solve the problem without causing damage to the parts.
These repair problems can be prevented by designing a housing system that has multiple
connections so that if one part of the device is experiencing problems you don't have to take apart
the entire device and put it all back together piece by piece. The misalignment problems can be
prevented by utilizing micromachining to create miniature mounts and alignment rails within the
housing.
Questions That Require Experts:
1. How can the housing be micromachined so that the fiber and lens can remain aligned, and
allow for repairs to be made. Dr. Anita Mahadevan-Jansen has spoken to us about a new
professor at Vanderbilt who focuses on miniaturizing mechanical apparatuses.
2. How is alignment between the GRIN lens and the optical fiber maintained while the fiber is
scanning? We have previously contacted Xingde Li about utilizing piezoelectric actuators with
GRIN lenses, and he has successfully implemented them to create OCT scaning. So we will
just need to speak with him again.
3. In what ways can we improve raman accuracy other than moving the excitation and detection
fibers closer together? We can discuss this with Dr. Chetan Patil or other similarly qualified
raman experts.
R&D Experiments:
The first experiment could be to create a large model of what we hope our final housing to look
like, or to create a SolidWorks model. Then we could take these models to the professor
mentioned and seek his input for how he thinks we could miniaturize certain parts of the model
to cut down the overall size of the housing. He could tell us whether the housing could be less
than 1 cm in diameter or not. If that is possible, then the next step would be to develop the
housing. If it is not possible, then the next step would be to comporomise between the design
criteria and the functionality we want the housing to offer.
The second experiment we could do is to replicate the work of Xingde Li in his paper titled
"Rapid-scanning forward-imaging miniature endoscope for real-time optical coherence
tomography." By replicating his work we should develop a better idea of how GRIN lenses
work, and how the light is refracted when it enters at different angles. This would not really
provide us with a yes or no answer, but it is very important tot he scanning part of our project.
The third experiment could involve researching different fiber optic raman spectroscopy papers
and finding out which methods were the most accurate and whether they had any special types of
filters or excitation fibers to increase the accuracy. Then we could test a raman spectroscopy
setup alone, without any OCT components and see if the accuracy is improved. If the accuracy
is greatly improved, then we can repeat the test with the OCT components in place. If the
accuracy is not any better then we will need to find another way to improve the raman accuracy.
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