Ultrasound Imaging Capability for Otologic Surgical Drills

Julianna IanniMeher Juttukonda

David MorrisAdvisor: Dr. Jadrien Young,

M.D.

What is Otologic Surgery?Surgery of the earMastoidectomy

Mastoid air-filled spaces behind the ear

Uses to remove cells from the mastoid to treat anti-biotic resistant infections in the region to insert a cochlear implant

30,000 to 60,000 performed annually in the U.S. [1]

Anatomy of the Ear

Mastoidectomy Clip

ObjectivesTo find and attach an

ultrasound transducer to an otologic surgical drill.

To calculate the thickness of the mastoid bone using US

To shut off the drill when the mastoid bone has been drilled or provide the surgeon with enough information to stop at the correct distance.

Why Ultrasound?Category CT - Method Ultrasound

Safety Ionizing Radiation No Ionizing RadiationReal-time Data

Time Drilling Platform Not necessary

Invasiveness Invasive Non-invasive

Past Work Studied ultrasound equipment in order

to determine the most effective way to produce accurate images

Researched the best transducer frequency for imaging that region of the skull

Developed the website Observed use of otologic drills &

identify design constraints Identified potential design obstacles Generated design ideas concerning

mechanism of attachment Restructured design goals focusing

more on finding an ultrasound transducer compatible with an otologic drill.

Performed some proof of concept tests for ultrasound depth measurements through bone.

Solidworks PrototypeSide View

Top View Bottom View

The PrototypeThe ultrasound transducer is placed so that it

allows for the surgeon to quickly move the transducer into place to perform quick ultrasound scans.

When not in use the transducer can be moved back out of the way and will allow the surgeon to quickly return to work.

This set up allows for the surgeon to work quickly and prevents them from wasting a lot of time during surgery while also adding a safer means of cutting through the bones.

Model of MastoidBone -> Acrylic

Speed of Sound = 2750 m/s [4]Soft Tissue -> Gel

Speed of Sound ~ 1540 m/s

Analysis of Simulation

Results of simulation(gradient plots matched well w/ built-in edge

detection)Worked really well with 1 layer of acrylic:

Actual thickness= 2.03mmMeasured thickness= 2.23mm w/o tissue &

2.35mm w/tissueFor 4MHz: 2.13mm & 2.23mm respectivelyWant accuracy w/in 1mm

Multiple layers of acrylic?Harder to readMultiple peaks (including ones at the correct

thickness)Not as distinct from noise

Able to discern correct peaks knowing thickness, but can’t back them out just from data

Most likely due to small air-pockets between layers of acrylic caused more echoes & attenuation @ ea.

intersection

Multiple layers

Depth(cm)

y-gr

adie

nt a

mpl

itude

1 2 3 4 5 6 7

-20

-15

-10

-5

0

5

10

15

20Y gradient

• Example with 2 layers of acrylic

• (total thickness= 4.06mm)• w/tissue layer• 8.89MHz

StatisticsNo. Layers f (MHz) Tissue Thickness(cm) Thickness(cm) error(mm) error(mm) % Error % Error

Layer 1 Layer 2 Layer 1 Layer 2 Layer 1 Layer 2

1 1 8.89 N 0.2275 0.243 11.96

2 1 8.89 Y 0.2398 0.366 18.01

3 1 4 N 0.2164 0.132 6.50

4 1 4 Y 0.2272 0.24 11.81

5 2 8.89 N 0.2023 0.4298 -0.009 0.234 -0.44 5.76

6 2 8.89 Y 0.2398 0.4543 0.366 0.479 18.01 11.79

7 2 4 N 0.2023 0.4298 -0.009 0.234 -0.44 5.76

8 2 4 Y 0.2394 0.4283 0.362 0.219 17.81 5.39

Actual 1st Layer 0.2032 cm

Thickness 2nd Layer 0.4064 cm

Tissue 0.2 cm

Future Work• Getting transducers in & testing (high

frequency and low frequency)• building prototype & attachment for drill• calibrating/signal processing and analysis

References1. French, LC et al. “An estimate of the number of

mastoidectomy procedures performed annually in the United States”. Ear Nose Throat J. 2008 May; 87(5): 267-70.

2. Ear Anatomy: http://www.umm.edu/imagepages/1092.htm

3. Clement, GT et. Al. “Correlation of Ultrasound Phase with Physical Skull Properties”. Ultrasound in Medicine & Biology. 2002 May; 28(5): 617-624.

4. http://www.signal-processing.com/tech/us_data_plastic.htm