Ultrasound Imaging Capability for Otologic
Surgical Drills
Julianna
1Department
1
Ianni ,
Meher
1
Juttukonda ,
1
Morris ,
David
Jadrien
2
Young
of Biomedical Engineering, 2Department of Otolaryngology (Vanderbilt University, Nashville, Tennessee)
OTOLOGIC SURGERY
RESULTS
PROTOTYPE
8.89 MHz Simulation
40
150
•Otologic surgery: purpose of restoring hearing and balance
•Design
• Uses an annular (ring) ultrasound transducer for imaging
• Positions transducer to allow for quick imaging during surgery
• Allows the transducer to move to clear the surgical area when not in use
30
20
50
Echo Amplitude
Amplitude
100
Amplitude
•Mastoidectomy: type of otologic surgery
•Mastoid – air-filled space behind the ear
•Uses of surgery
•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 United States
10
0
-10
-20
-30
0
0
1
2
3
4
5
6
-40
7
0
1
2
3
4
Depth (cm)
5
6
7
Depth(cm)
Depth(cm)
Figure 4: These are (from left to right) the Ultrasound image, the magnitude plot, and the gradient plot
for a frequency of 8.89 MHz and an acrylic thickness of 1.91 cm.
•Problem: accidentally drilling too far through mastoid bone can cause
damage to critical structures behind the bone
4.00 MHz
Simulation (T)
4 MHz
Frequency
(T)
30
a
•Anatomy of the ear
8.89 MHzSimulation
Simulation (T)
8.89 MHz
(T)
20
4.00 MHz Simulation
4 MHz
Simulation (A)
40
c
15
e
30
20
10
20
0
-10
Echo Amplitude
Amplitude
Amplitude
Echo Amplitude
Echo Amplitude
Amplitude
10
5
0
-5
10
0
-10
-10
-20
-20
-15
-30
0
1
2
3
4
Depth(cm)
Depth (cm)
5
6
-20
7
MHz Simulation (NT)
4 MHz 4.00
Simulation
(A)
30
-30
0
1
3
4
Depth (cm)
Depth(cm)
5
6
7
8.89 MHz Simulation (NT)
8.89 MHz
Simulation (A)
20
b
2
1
d
2
3
4
Depth(cm)
Depth (cm)
5
6
7
MHz Simulation
8.89 8.89
MHz
Simulation (A)
40
15
20
0
f
30
Figure 6: Dimensions shown are in mm. The otologic drill
with the ultrasound transducer attached in side view (left), top
view (top), and bottom view (bottom).
20
10
0
-10
Echo Amplitude
Amplitude
Amplitude
Echo Amplitude
Echo Amplitude
Figure 1: The anatomy of the inner ear, showing the mastoid bone and the sensitive structures.
Amplitude
10
5
0
-5
FREQUENCY OPTIMIZATION
-20
-30
•Assumptions
•Only reflection, transmission & attenuation; no scattering
•Model
•Speed of sound in skull bone = 2700 m/s
•Attenuation in skull bone = 20 dB/(MHz*cm)
•Frequencies studied: 1 MHz, 4 MHz, 8.89 MHz
•Results
•The estimated amplitude of the signal of echoes received versus time:
•(a) 1MHz : 1.62 x 10-8 , (b) 4MHz: 1.70 x 10-20 , (c) 8.89MHz: 5.03 x 10-40
1
2
3
4
Depth(cm)
Depth (cm)
5
6
7
-15
0
-10
-20
-10
0
10
DISCUSSION & CONCLUSIONS
-30
-40
0
1
2
3
4
Depth (cm)
Depth(cm)
5
6
7
0
1
2
3
4
Depth(cm)
Depth (cm)
5
6
Figure 5: These are plots of the gradient of magnitudes vs. depth. For (a), (b), (c), and (d), the
thickness was 0.2 cm. For (e) and (f), the thickness was 1.91 cm. For (a), (b), and (e), the transducer
frequency was 4 MHz. For (c), (d), and (f), the transducer frequency was 8.89 MHz. For (a) and (c), the
interface was acrylic-gel (T). For (b), (d), (e), and (f), the interface was acrylic-air (A).
Table 1: Error in Measurements
Image Freq (MHz) Thickness (cm) Measured (cm)
a
8.89
0.203
0.228
b
8.89
0.203
0.240
c
4
0.203
0.216
d
4
0.203
0.227
e
4
1.905
1.849
f
8.89
1.905
1.827
Error (cm)
0.024
0.037
0.013
0.024
-0.056
-0.078
% Error
11.959
18.012
6.496
11.811
-2.940
-4.094
Table 1: This table contains
the errors (cm) as well as
the percent errors
associated with each
Ultrasound measurement.
As can be seen from the
data, every measurement is
accurate to within 1 mm.
7
•
•
•
•
MODEL
•Design
ADVANTAGES OF ULTRASOUND
•Current Method: Computed Tomography
•Method
•A CT scan is performed a few days before surgery
•A platform is drilled into the skull before procedure
•Location of drill is triangulated and shown on the CT
Category
CT - Method
Ultrasound
•Disadvantages
•Ionizing radiation
Safety
Ionizing Radiation
No Ionizing Radiation
Real-time Data
•Images not in real-time
•More invasive and more time-consuming
Time
Figure 3: The model consists of polyvinyl alcohol gel adhered to layers of acrylic Plexiglass
to model the elastic properties of bone and tissue. The thickness t was 0.2 cm.
•Methods
• MATLAB program was created to detect edges of the acrylic
• Gradient of image in y-direction was calculated & plotted vs. depth
• Assumption: Peak in gradient plot = edge of object
• Technique was compared to MATLAB’s Roberts edge-detection function
Figure 7: These images show
the device in the ‘rest’ (top) and
‘in-use’ (bottom) positions.
Drilling Platform
ACKNOWLEDGEMENTS
We would like to thank Dr. Michael Miga for allowing us to use his ultrasound machine, Dr.
Robert Galloway for his help in selecting the transducer type, and Dr. Paul King for advising.
REFERENCES
Not necessary
Invasiveness
Invasive
Non-invasive
•Proposed Method:
Ultrasound
•Method
•Preliminary thickness is measured
•Surgeon shuts off drill and measures thickness whenever necessary
•An image is taken and an algorithm is used to calculate thickness
•Advantages
•Real-time images
•No ionizing radiation
•Improved safety and reduced time of procedure
Functionality of Device
• Testing of similar transducers on model revealed that thicknesses from
2 to 19mm can be accurately measured
Transducer
• Custom transducers were built with a range of frequencies with a
hollowed opening for the drill bit
• Frequency affects resolution and depth penetration
Advantages of Design
• Does not require surgeon to change technique
• Can be moved into and out of place
• Can attach to existing drill bits
Future Directions
• Developing a way for the device to connect to the drill power supply
• Testing the transducer on cadaver models
• Designing a software to calculate thickness from Ultrasound images
1.
Labadie, Robert et al. "Automatic determination of optimal linear drilling trajectories for cochlear access
accounting for drill-positioning error". Int J Med Robotics Comput Assist Surg 2010; 6: 281–290.
2.
Moilanen, Petro et al. "Assessment of the cortical bone thickness using ultrasonic guided waves: modelling and in
vitro study". Ultrasound in Med & Biol. 2007. Vol. 33. No. 2. p254-62.
3.
Holscher, Thilo et al. "Transcranial Ultrasound Angiography (TUSA): A New approach for contrast specific imaging
of intracranial arteries". Ultrasound in Med. & Biol., 2005. Vol. 31, No. 8, pp. 1001–1006.
4.
Tretbar, Stephen et al. "Accuracy of Ultrasound Measurements for Skull Bone Thickness Using Coded Signals."
IEEE Transactions on Biomedical Engineering. Mar 2009. Vol. 56, No. 3.
5.
Majdani, O et al. "A robot-guided minimally invasive approach for cochlear implant surgery: preliminary results of
a temporal bone study." Int J Comput Assist Radiol Surg. Sep 2009. Vol. 4, No. 5, pp. 475-86.