TransScan R

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Quantitative TCT Challenges SK Patch, UW-Milwaukee
Images across modalities
Prototype TCT already competes w/conventional
scans!
EIT
TransScan RD
qualitative potentially quantitative
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Mathematical Representation (assumes constant
soundspeed)
S upper hemisphere
inadmissable transducer

• Integrate f over spheres
• Centers of spheres on sphere
• Partial data only for mammography

S- lower hemisphere
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FBP inversion (complete data)

• Backproject data (thanks to V. Palamodov!)
• Switch order of integration
• Use d-manifold identity (4x!) ?
• f ?Riesz potential ?
• f after high-pass filter

imaging object
Use co-area formula
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Reconstruct Idealized Data - many different ways
- series solutions Norton, NortonLinzer

• - other measurement geometriesKunyansky06/07
• minimal filtering Xu05
• even space dims Finch07
• regularization schemes Schuster05/07,
  Haltmeier05
• Neumann data FinchRakesh07
• injectivity proofs and range char. Finch06,
  Ambartsoumian05/06
• iterative reconstruction Anastasio

!! apologies to other authors !!
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TCT Wave Eq Model
mechanical
electrical
homog ICs
for I(t) ?(t)
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Quantitative Imaging Challenges

• partial scan data - iterative recon
• transducer aperture size - integrating
  detectors
• acoustic attenuation - corr. for aphysical
  model
• variable soundspeed
• E field pattern/optical fluence corr.
• broadband data required, including low freqs
• unwanted EM coupling to US measurements
• transducer response - freq
  dependent has limited sensitivity -
  anisotropic

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E-field pattern Acoustic Source
SOP to solve in frequency domain near carrier
frequency.

• 1) E is wave-like. At 100 MHz, ?air300cm,
  ?H20 33cm, ?fat70cm, ?muscle40cm
• 2) tangential BCs force continuity of E x n

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Rf coupling
Materials 434 MHz RF for 1?s pulse, 16kW peak
power 2.25? MHz Panametrics US transducer Phys
saline-filled straw lt 1mm diam
changed shape whenever big bags of salt water
walked into room
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E-field in TCT Testbed
Very nearly TE103 Aluminum walls DI water not
lossy, waves resonate I(t) 1.
acoustic window
E-field on central plane inside
Power in
50kW amp yields instantaneous SAR gtgtgt
12W/kg
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TCT Testbed - hardware
Translators - Sherry Yan, George Hanson, UWM-EE.
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BCs - object orientation critical
21 aspect ratio
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Imact on Rtct - qualitative
E in horizontal x-sections
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Transducer Freq Response

• frequency content of measured pressures critical.
  
• Freq content is a function of true pressure, -
  EM pulse, I(t) - transducer frequency
  response, kA(?)

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Transducer Freq Response

• Freq response filters image (Anastasio,et al)
• EM temporal profile also filters image
• Therefore, we characterize transducer frequency
  response independently of EM frequency content,
  using
• hydrophone
• 2 transducers at same CF

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Transd Freq Resp - measure

• Transmit w/transd A, receive w/hydrophone
• Transmit w/transd A, receive w/transd tct

TA Stiles (UW Madison) D Pachauri, N Purwar, P
Dey (UW-Milwaukee)

• far-field results
• broad- narrow-band pulses

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Data -
hydrophone transducercalibration
measured


transducer sluggish
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Frequency content response
Narrowband (NB)

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Impulse Response
Broadband (BB) freq resp
complex, Herm symm
Narrowband (NB) freq resp
real symmetric
acausal
acausal
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07 system - poor IOld RF pulse profile killed
frequency content
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Conclusions
Transd char RF shielding both critical. RF
deposition clearly patient dependent will
require per/patient correction. (like
high-field MRI) Have much to learn - thanks to
those who have already given suggestions.
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Backup slides
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Transducer shield - Rev 1 by M Mitchell J
Becker
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Rf shield - Rev 1 results
Nov 07
Jan - Mar 07
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EM shield
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Acoustic Attenuation Blurs
PNT Wells, Biomedical Ultrasonics

• where
• ?t are dual Fourier variables
• b1 in tissue b2 in fluids
• a0.1 MHz-1 cm-1
• L is distance in cm

• soundspeed c1540m/s

• EXP ill-posed physics
• Analytic correction by Anastasio/LaRiviere

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Acausal Absorption Model
No atten