Fluoroscopic Equipment Design:
What’
What’s Different with Flat Panel?
John Rowlands
Financial disclosure statement
• Research supported by Anrad Corp
• Anrad Corp is a manufacturers of selenium
based flat panel imagers
Sunnybrook Heath Sciences Centre
University of Toronto
Concept of flat panel imager
Flat Panel Array Design
1000 rows
x
1000 columns
System Architecture
TOSHIBA
Automatic Exposure Control
in fluoroscopy
TOSHIBA
X-ray tube
Acquisition Workstation
X-Ray Generator Control
Detector
A
Low Voltage
Power Supply
B
Real Time
Image Processor
Fiber Optic Links
Image Processing Chain
Flat Panel
Detector
Real Time
Data
Correction
Real Time
Image
Processing
Correction of:
• Temporal
• Offset
and spatial filter
• Gain
• Image Resizing
• Pixel defect
•Gamma correction
• Horizontal noise
X-ray and
Acquisition
Control
Acquisition
Workstation
and
X-ray generator
CRT operation and
characteristic curve of monitor
- Need for gamma correction
Offset and gain corrections
• Dark field
Enlarged
“bad”
region
– offset correction
Bright field – gain corrections
As acquired image
Gain and Offset
corrected with
Bright field and Dark
Field images
respectively
Bad lines and points
replaced by
interpolation
Distortion in an XRII
Pincushion
distortion
Gamma and sharpness
corrected image
S-distortion
Complete XRII imaging system
Quantum accounting diagram
for XRII video system
Flat panel detector types
Indirect conversion
(CsI)
Quantum accounting diagram
for flat panel system
Direct conversion
(a-Se)
Intrinsic sources of blurring in
x-ray imaging systems
Phosphor blurring sources
Components of MTF in an XRII
Photoconductor blurring sources
1.0
output screen
0.8
0.6
MTF
electron lens
0.4
CsI input
screen
XRII
0.2
0.0
0
1
2
3
4
spatial frequency (lp/mm)
Components of MTF in an
XRII and flat panel
MTF of XRII and flat panel
1.0
1.0
output screen
0.8
1.0
(a)
(b)
0.8
0.8
0.6
0.6
0.6
CsI flat panel
MTF
MTF
MTF
electron lens
0.4
XRII
0.4
CsI flat panel
XRII
0.4
Nyquist 1.6 lp/mm
XRII
CsI input
screen
Nyquist 3.2 lp/mm
0.2
0.2
XRII zoom
0.2
Flat panel
0.0
0.0
0
1
2
spatial frequency (lp/mm)
0
1
2
spatial frequency (lp/mm)
3
3
4
0.0
0
1
2
3
4
spatial frequency (lp/mm)
4
Normal mode
Zoomed mode
5
Principle of photolithography
TFT+Photodiode Pixel Design
Thin film transistor or TFT
Array Design Rules
• Distance between neighboring features
127
µm
(Courtesy of Dr. R. Weisfield, dpiX
• Width of control lines
• Thickness of different layers
Fill Factor vs Pixel Size
Readout of a flat panel detector
Photodiode Fill Factor
1
0.8
0.6
0.4
Conservative Design Rules
0.2
Aggressive Design Rules
" Diode on Top " Design
0
0
50
100
150
200
250
Pixel Size (microns)
Data Lines
Data Lines
-5 V
Switch Line 3
-5 V
Switch Line 3
-5 V
Switch Line 2
-5 V
Switch Line 2
-5 V
Switch Line 1
-5
+10
VV
Switch Line 1
External Electronics
External Electronics
Data Lines
Data Lines
-5 V
Switch Line 3
+10
-5 VV
Switch
Switch Line
Line 33
-5
+10VV
Switch Line
Line 22
Switch
-5
+10
-5 V
VV
Switch Line
Line 22
Switch
-5
+10
VV
Switch
Switch Line
Line 11
-5
+10
VV
Switch
Switch Line
Line 11
External Electronics
External Electronics
Data Lines
-5 VV
+10
Switch Line 3
-5 V
Switch Line 2
Artifacts arising from inadequate
corrections
• Regions of different intensity
• Blurring
Switch Line 1
-5 V
External Electronics
• Line correlated noise
Image Courtesy of Dr. U Neitzel,
Neitzel, Philips
Image Courtesy of Dr. U Neitzel,
Neitzel, Philips
Cardiac cine
DQE of XRII and flat panel
1.0
1.0
(b)
(a)
0.8
XRII
0.8
CsI flat panel
0.6
DQE
DQE
0.6
0.4
CsI flat panel
0.4
XRII zoom
0.2
0.2
XRII
0.0
0
1
2
3
spatial frequency (lp/mm)
As a function of spatial frequency
4
0.0
1
10
100
1000
input dose (nGy)
As a function of dose to detector
CsI XRII/video
CsI flat panel
Advantages of flat panel imagers
Future developments
• Corrections for monitor non linearity
• Not yet quantum noise limited at low exposures
•Amplifier per pixel
•High conversion efficiency photoconductor
•Avalanche gain
• Compact form factor
• System on glass
• High dynamic range
•Suitability for advanced applications