Transcript Physical & Psychophysical Evaluation of a New Digital

Physical & Psychophysical
Evaluation of a New Digital
Specimen Radiography System for
Use in Mammography
Elizabeth Krupinski, PhD
Hans Roehrig, PhD
University of Arizona
William Schempp, PhD
MedOptics Corporation
Rationale

Specimen radiography of excised breast
tissue is critical to ensure that an
appropriate tissue sample has been
obtained or that complete removal of
the lesion has been successful.
Objectives

To physically characterize the new highresolution digital specimen radiography
system from MedOptics Corporation.
 To evaluate human observer detection
performance using images acquired with the
new system.
The Digital System

Camera
• 1024 x 1024, 1” x 1” large area high-res CCD
• 2:1 fiber optic taper bonded to CCD (2”x2” FOV)
• standard Lanex Regular screen coupled to large end of
taper
• image data digitized at 500 Kpix/sec, 12-bits

Faxitron MICRO 50 x-ray source
• 15-50 kVp range
• 1-90 sec time selection
• SID = 50 cm
Faxitron HVL & Eeff
Energy
20 KeV
Filtration Carbon
20 KeV
Al-filter
25 KeV
Carbon
25 KeV
Al-filter
30 KeV
Carbon
30 KeV
Al-filter
HVL
(mm Al)
0.088
0.0833
0.104
0.0898
0.110
0.091
(/)Al
(cm2/g)
29.3
30.8
24.7
28.6
23.3
28.2
Eeff
(KeV)
9.55
9.38
10.1
9.63
10.3
9.67
Camera X-radiation Response
10000.00
Camera Response (Mean and Stdv (rms) in Digital
Units [ADU]) to X-radiation (mR)
25 kVp
Corrected Mean [ADU]
or RMS [ADU]
1000.00
30 kVp
Corrected Mean
Curve Fit for 30 kVp
log(Y) = 1.04655*log(X) + 1.7888
20 kVp
100.00
25 kVp
20 kVp
Corrected RMS
Curve Fit for 30 kVp
10.00 log(Y) = 0.50577*log(X) - 0.291
30 kVp
1.00
1.00
10.00
100.00
Exposure [mR]
1000.00
Camera Dark Signal & Noise
1000.00
Uncorrected Dark-Signal and Dark-Noise
of Uncooled CCD as Function of Time
Mean or Stdev [GL]
Dark Signal
100.00
Dark Noise
10.00
1.00
0.01
0.10
1.00
Time [sec]
10.00
100.00
Noise Power Spectrum 25 kVp
100.00
Noise Power Spectra for Exposures at 25 kVp
Noise Power (mm^2)
10.00
Exposure Time 4 sec
1.00
Exposure Time 1 sec
0.10
0.01
0.00
2.00
4.00
6.00
Spatial Frequency (lp/mm)
8.00
10.00
Noise Power Spectrum 30 kVp
10.00
Noise Power Spectra for Exposures at 30 kVp
Noise Power (mm^2)
Exposure Time 3 sec
1.00
Exposure Time 1 sec
0.10
0.00
2.00
4.00
6.00
8.00
Spatial Frequency (lp/mm)
10.00
Comparison NPS & Square MTF
100.00
Noise Power Spectrum and MTF for
Specimen Radiography System
Noise Power (mm^2) or MTF^2
10.00
Noise Power Spectrum
25 kVp, 4 sec
1.00
0.10
Scaled MTF^2
from Curve Fit
0.01
0.00
0.00
2.00
4.00
6.00
8.00
Spatial Frequency (lp/mm)
10.00
MTF
1.00
MTF of the CCD-based Camera of the MedOptics
Specimen Radiography System; derived from the
Fourier Transform of profiles of x-ray images of a
10 micron wide x-ray slit ("Line-Spread-Function")
MTF (rel. Units)
0.80
0.60
Dashed Line 25 kVp
Solid Line
30 kVp
0.40
0.20
Polynomial Coefficients
Curve Fit: Polynomial of degree 2
Degree 0:
0.997419
Degree 1:
-0.220671
Degree 2:
0.0125387
0.00
0.00
2.00
4.00
6.00
8.00
Spatial Frequency (lp/mm)
10.00
MTF from Square Wave Response
1.00
MTF of the CCD-based Camera of the MedOptics
Specimen Radiography System; derived from the
Fourier Transform of x-ray images of a lead-bar pattern
("Squarewave Response")
MTF (rel. Units)
0.80
0.60
Dashed Line 25 kVp
Solid Line
30 kVp
0.40
0.20
0.00
0.00
2.00
4.00
6.00
8.00
Spatial Frequency (lp/mm)
10.00
Observer Performance Study

2 CDMAM contrast-detail phantoms
• Commercially available large version
• Small experimental version
 Imaging conditions
• Traditional plain film
• Fuji Computed Radiography (CR)
• MedOptics Digital System
 25 kV & 30 kV @ High (3600 GL), medium (2400 GL) &
low (1200 GL) exposures
Film Image Optical Densities
Condition
High
Medium
Low
Plain Film
25 kV
Plain Film
30 kV
Fuji Film
25 kV
Fuji Film
30 kV
1.60
1.20
0.80
1.60
1.20
0.80
1.34
1.32
1.30
1.36
1.36
1.31
Viewing Conditions

Traditional film & Fuji CR film
• standard viewbox @ 1100 ft-L
• extraneous light masked

Fuji CR digital & MedOptics Digital
•
•
•
•
DataRay DR110
1728 x 2304
140 ft-L
Perceptually linearized with Barten curve
Observers & Task




10 undergrad students in each condition
On outline of phantom indicate location of all
disks visible in the phantom(s)
Window/Level & zoom available on monitor
Ambient lights turned off in
all conditions
Large Phantom Results
100
Plain Film 25
80
Fuji Film 25
Fuji Monitor 25
60
%
MedOptics Monitor 25
Plain Film 30
40
Fuji Film 30
Fuji Monitor 30
20
MedOptics Monitor 30
0
Low
Medium
High
F = 68.44, p < 0.0001
Small Phantom Results
100
Plain Film 25
Fuji Film 25
Fuji Monitor 25
60
MedOptics Monitor
25
Plain Film 30
40
Fuji Film 30
20
Fuji Monitor 30
ig
h
H
M
ed
iu
m
0
Lo
w
%
80
F = 52.62, p < 0.0001
MedOptics Monitor
30
Performance Summary






Increases monotonically low to high exposures
25 kV > 30 kV
MedOptics Digital System Best
Traditional plain film worst
Fuji CR monitor & film in middle
Minor differences between phantoms
Conclusions


MedOptics Digital Biopsy System yields high
detection performance
Currently mammographers image core biopsy
samples with either traditional systems or
stereotactic units
• Traditional takes too long
• Stereotactic requires patient to get out of unit to image
sample

Digital avoids these problems & is fast