Projection Ultrasound and Ultrasound CT using A CMOSBased Sensor: A Preliminary Study

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Projection Ultrasound and Ultrasound CT using A
CMOS-Based Sensor A Preliminary Study
Chu Chuan Liu1,2, Shih-Chung B. Lo1, Matthew T.
Freedman1, John Kula3, Bob Lasser3 and Marvin E.
Lasser3
1. ISIS Center, Georgetown University Medical
Center, Washington, DC 2. Department of Electric
Engineering, Virginia Polytechnic Institute and
State University (Virginia Tech), VA 3.
Imperium Inc. Rockville, MD
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Introduction
The purpose of this study is to demonstrate the
ability of the CMOS-based ultrasound detector
array. It can generate ultrasound images with
projection and/or reflective geometry. It can
produce attenuation ultrasound image
ultrasound computed tomography (3D ultrasound
computed tomography)
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• System Performance in Projection Geometry

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Projection Ultrasound - Data Acquisition
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Hybrid Microelectronic Sensor Array
Schematic of the array
A 128 X 128 assembled array
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Projection Ultrasound - Laboratory Setup
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Compensation of inactive pixels
A point detector was used to automatically detect
inactive pixels followed by a bilinear
compensation processing. (A) Background
image (B) Marked background image. (C) Original
test images. (D) Fixed images.
(A)
(B)
(C)
(D)
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A C-Scan Image Sequence of A Human Finger
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Performance of Contrast Resolution on 3mm Lesions
Definition of CNR
Foreground - Background
Noise (SD of background)
Background ZerdineTM 0.22dB - 0.05dB /cm/MHz
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Microcalcifications as Test Targets
710-850µm
425-450µm
300-355µm
Intensity
122
147
3
2
140
2
169
167(11)
1
170(8)
CNRs
177(11)
158(8)
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Fan Line Pattern as a Test Target
A fan pattern is constructed by 7 stainless steel
wires. Each wire is 250 microns thickness.
Custom Made by CIRS (Norfolk VA)
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Profile Analysis of the Fan Sector Lines
320 microns space
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The Step Wedge for the Evaluation of Dynamic Range
Attenuation 0.7dB/cm/MHz - 0.07dB/cm/MHz
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Dynamic range
I100 chip
I300 chip
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Attenuation vs. Intensity (I100 and I300)
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• The PUCT Experiment

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Projection Ultrasound Computed Tomography (PUCT)
Setup
Micro-stepping motor controller
Micro-stepping motor
Micro-stepping motor power supply
Testing target
5-MHz transducer
Compound acoustic lens
The sensing camera
Water tank
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Test target
The test target is made by A plastic tube
Silicone Pearl shape object Stainless
wire
Center section of target No.1 (T1)
Center section of target No.2 (T2)
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The Projection Images W/ W/O Target
Image W/O Target
Target images
Inversed images
T1
T2
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PUCT System Scan Parameters

• In this experiment,
• Ultrasound transducer
• 1.5 plane wave ( Parallel beam)
• Angle increment 0.45 degree
• Ultrasound lens Yes
• Imperium 2-D ultrasound array Yes

Projections of T2
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Raw Data Acquired - PUCT Scan

• Each image acquired at 1/30 second
• An image was acquired without any target as
  initial intensity Io(x,y)
• 400 projection images (0.45 degree/increment)
• Iq(x,y)
• Ultrasound Projection Attenuation

Aq(x,y) - log( Iq(x,y)/Io(x,y))
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Exponential Attenuation of Ultrasound An
Assumption
No
Nx
m
No input intensity of X-ray Nx output intensity
of X-ray m linear attenuation
?x
No
Nx
??
??
??
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Intensity Correction
Ultrasound Projection Attenuation Aq(x,y) - log(
Iq(x,y)/Io(x,y))
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Filtered BP for PUCT Reconstruction
Magnitude response of backprojection filters. 
1Ram-Lak (ramp), 2Shepp-Logan, 3Cosine, and
4Hamming.
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PUCT Profile and Images
Ultrasound plane waves
Silicone
Plastic
Attenuation effect
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Initial Reconstruction Results (T1)
Each image represents the slice of the target.
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Initial Reconstruction Results (T2)
Each image represents the slice of the target.
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Correction of the Circular Shadow due to
Scattering
CT reconstruction results from base-line
scattering
Intensity model for correction
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Procedure to Correct the Sinogram

• Computer reprojection
• (Lo 1988 IEEE TMI)
• Correction of the sinogram
• FBP reconstruction based on corrected sinogram

Note This approach is different from paper
5368-41 at this conference (Soft-Tissue contrast
resolution within the head by means of flat
detector based cone-beam CT by Wiegert et al)
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PUCT W/O and W/ Intensity Correction(T1)
Sequence w/o correction
Sequence w/ correction
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PUCT W/O and W/ Intensity Correction(T2)
Sequence w/o correction
Sequence w/ correction
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PUCT Reconstruction with Scattering Correction
(T1)
Display direction
PUCT images (corrected)
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PUCT Reconstruction with Scattering Correction
(T2)
Display direction
PUCT images (corrected)
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Other Technical Issues

• Accuracy of the object center during the rotation
• 1-2 mm shift ? ring artifacts
• Beam hardening effect
• max 5 MHz, mean 4.7 MHz
• Scattering
• 2-D deblurring can be used (to be
  investigated)

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Conclusions

• The preliminary study shows that the CMOS-based
  ultrasound sensor is capable of producing
  transmission tomographic images.
• The circular shadow due to ultrasound scattering
  can be corrected up to a high degree of accuracy.
• Beam hardening effect shows on metal material and
  potential plastic tube.
• High precision for the center of the rotation is
  needed to avoid ring artifact in the center.
• Dead pixels or uneven sensitivity of pixels
  should be corrected before the reconstruction.