Multi-Channel GustometerMulti-Channel Gustometer

Kevin A. JohnsonKevin A. Johnson**††

Instructor: Dr. Paul H. KingInstructor: Dr. Paul H. King**

Advisor: Dr. David H. ZaldAdvisor: Dr. David H. Zald††

Neuroimaging Engineer: Patrick HenryNeuroimaging Engineer: Patrick Henry††

*Vanderbilt University Department of Biomedical Engineering† Vanderbilt University Department of Psychology

Introduction

Gustometer Defined• A gustometer is a device to deliver taste

stimuli in a controlled manner.– Gustometers are typically used in experimental

applications.

Design Objective• The goal of this design is to create a device

that presents an array of taste stimuli for functional neuroimaging studies.– Intended specifically for research involving fMRI (3T).– Adaptable to a variety of experimental protocols.

Background

• Multi-channel gustometers have been utilized for psychophysical measurements on animal models.(1)

– At least 10 channels available.– Delivery controlled by computer.– Output stimuli tested for cross-contamination between

channels.

• Single-channel gustometers have been used in functional neuroimaging studies.(2,3,4,5,6)

– To examine multiple stimuli: Two gustometers have been operated in parallel, or unique stimuli have been presented in separate scanning trials.

• Novelty: Multi-channel gustometer applied to neuroimaging.– Facilitates a broad range of experimental protocols.

(taste discrimination, taste preference, etc.)

Design Specifications: Demands

• fMRI Friendly– No ferrous material within 10 ft. of participant (preferably farther

than 10 ft.)– Minimal electronics close to subject.

→ Note: In past experiments, this demand has been achieved by delivery fluid stimulus through extended tubing.

• Ability to deliver up to 10 different fluids.• Ability to deliver from 0.5 – 5 ml discrete boluses of liquid.

– Accuracy: ± 15%• Ability to switch in a relatively constant flow (no more than

250 ms pause) from one stimulus to another.– Note: It is fine if there is a time lag (< 1s) between a stimulus

pulse (stimulus switch) and the time it reaches the participant, as long as the timing is consistent (± 250 ms).

• A fixed flow rate of 0.5 ml/s is acceptable.• Ability to deliver up to 50 cc in a session for each stimulus,

with one stimulus (saline) able to deliver more (up to 200 cc).

• Ability to exchange stimulus containers quickly (exchange all 10 in less than 5 min).

Design Specifications: Wishes

• Expandable to deliver more than 10 different fluids.• Ability to vary flow rate (as low as 0.25 ml/s and as

high as 1 ml/s).• Easy to sanitize (contamination resistant).• Easily portable.• Include protective covering for device.• User-friendly.• Quick development time of device.• Reasonable cost.

Innovative Approaches

• Use electrical simulation of taste.+ Allows for more precise control of stimuli.+ Eliminates challenges of fluid flow.- There would be general design difficulties.- Perceptual problems of accurately simulating taste may be virtually impossible to overcome.

• Use only one pump to drive the gustometer.→ Preload multiple stimuli into single tubing according to protocol pattern.+ Drastically reduces the cost of the devices.- Cross-contamination between stimuli fluid likely. → Use solid stimuli.- Chewing motions distort image and chance of choking increases. → Freeze stimuli into solid pellet for transport in tubing. Convert stimuli to liquid form upon delivery to participant.- Perhaps too labor-intensive and complex.

Tubing Merging Unit

(7)

(7)

Force Assessment

• Maximum Pump Force at Maximum Pumping Speed = 10 lbs.(8)

• Assume frictional and valve forces are negligible.• Assume fluid stimuli is twice the weight of water (probably an

over estimation).• Fluid Weight = (Inner Tubing Volume)(2.0g/ml fluid)

• Pump appears to provide adequate force.• Verification to be completed during prototyping.

Function of Tubing Inner Diameter (ID)

ID (in.) Force (lbs.)

0.25 1.06

0.50 4.26

0.75 9.58

Delay Calculations

• Maximum Pumping Speed (using 60 cc syringe) = 1272 ml/hr.• Delay = Volume To Travel/Maximum Pumping Speed

– Delay dependent upon distance to participant and tubing size.

• Delay decreased by minimizing distance to participant and minimizing tubing size.

2 4 6 8 10 12

0.0625 0.284 0.569 0.853 1.138 1.422 1.707

0.125 1.138 2.276 3.414 4.553 5.691 6.829

0.1875 2.561 5.122 7.683 10.24 12.80 15.36

0.25 4.553 9.106 13.65 18.21 22.76 27.31

Delay (s)

Distance to Participant (in.)

Tube ID (in.)

Delay Analysis

• Delay is also dependent upon pump speed. A more expensive pump, provides greater pumping speed.(9) However, this is accomplished with with a larger syringe. Upgrading the 60cc syringe to a 120cc syringe would double the output volume, effectively cutting the delay in half.

• In order for stimuli delivery to be consistent in timing, the pumping rate of each individual pump can be graded to generate equivalent delays.

2 4 6 8 10 12

0.0625 0.142 0.284 0.426 0.569 0.711 0.853

0.125 0.569 1.138 1.707 2.276 2.845 3.414

0.1875 1.280 2.561 3.841 5.122 6.402 7.683

0.25 2.276 4.553 6.829 9.106 11.38 13.65

Delay (s) @ 2544 ml/hr Pump SpeedDistance to Participant (in.)

Tube ID (in.)

Safety Considerations

1. High Magnetic Field Environment– fMRI images are acquired with the use of strong magnetic

fields.

– Dangerous component interactions are eliminated by placing the device outside a shielded room, with only nonferrous tubing entering the environment.

2. Choking Hazard– The participant is susceptible to choking while passively

receiving fluid in a horizontal resting state.

– This risk can be minimized by using fluid quantities comparable to previous trials and performing testing and practice prior to actually scanning. The participant should also be monitored during scanning.

3. Sanitation Issues– Care should be taken to prevent participant exposure to harmful

substances from pertinent components and prior use.

Conclusions: Demands

• Device is fMRI friendly.• 10 different fluids can be delivered via a 10 pump-merging

system.• Pumps can deliver discrete boluses over a broad volumetric

range.• Timing remains a critical factor.

– While demands are apparently achievable, particular attention should be paid to timing issues in future design work and in the establishment of experimental protocols.

• A fixed flow rate of 0.5 ml may be achieved by the pump model selected (BS 8000).– The flow rate ranges from 1.62 nl/s to 0.3533 ml/s for syringes up

to 60 cc in size. If a 120 cc syringe can be employed, the flow rate would be increased to 0.7066 ml/s).

• It is possible to deliver in excess of 60 cc per stimulus.– More could be achieved by larger syringes, longer tubing, or

merging or multiple pumping systems.

• Stimulus containers (syringes) can be exchanged quickly.

Conclusions: Wishes

• Additional pumps could be added to increase the number of stimuli delivered.– The computer network can support 100 pumps. The conduit

diameter is a limiting factor that could be worked around.– Timing must be taken into account when adding additional pumps.

• A variable flow rate is possible (see Conclusions: Demands for maximum rate).

• Components are available that make sanitization easier.– Swabable valves and contaminant-resistant tubing exist.– Depending upon cost analysis, some components may be disposed

of after use, rather than sanitized.• The gustometer is easily portable if built on a shelved-cart.• Additionally, a removable protective covering would not be

significantly challenging to build/purchase.• A users-manual should be developed to aid in protocol design

and operation.• Quick development time of device and Reasonable cost:

→ Apparently achievable.

Future Work

• Explore possibility of increasing pumping volume rate to reduce delay times.

• Finalize timing issues and order appropriate components.

• Build and evaluate prototype using two pumps.• Modify design and pursue alternatives as

necessary.• Build final device and reevaluate efficacy and

safety.• Create user’s manual.• Implement in experiments.

References

1. Reilly, S., Norgren, R., and Pritchard, T. C. (1994). A new gustometer for testing taste discrimination in the monkey. Physiology and Behavior 55: 401-406. 

2. Zald, D. H., and Pardo, J. V. (2000). Cortical Activation Induced by Intraoral Stimulation with Water in Humans. Chemical Senses 25: 267-275.

3. Zald, D. H., Hagen, M. C., and Pardo, J. V. (2002). Neural Correlates of Tasting Concentrated Quinine and Sugar Solutions. Journal of Neurophysiology 87: 1068-1075.

4. Zald, D. H., Lee, J. T., Fluegel, K. W., and Pardo, J. W. (1998). Aversive gustatory stimulation activates limbic circuits in humans. Brain 121, 1143-1154.

5. O’Doherty, J., Rolls, E. T., Francis, S., Bowtell, R., and McGlone, F. (2001). Representation of Pleasant and Aversive Taste in the Human Brain. Journal of Neurophysiology 85: 1315-1321.

6. Cerf-Ducastel, B., Murphy, C. (2001). FMRI Activation in Response to Odorants Orally Delivered in Aqueous Solutions. Chemical Senses 26: 625-637.

7. Halkey-Roberts. (1999). Online Product Listings: Check Valves. http://www.halkey-roberts.com/products.htm.

8. Braintree Scientific Inc. (1998). BS-8000: Multi-PhaserTM: Programmable Syringe Pump. Publication #1200-01.

9. Harvard Apparatus (2001). Model ‘22’: Syringe Pump Series: User’s Manuel. Publication 5381-001.