Design and Performance Characteristics
of Digital Radiographic Receptors
J. Anthony Seibert, Ph.D.
University of California, Davis Medical Center
Sacramento, California
Learning Objectives
• Describe digital detector technologies for
radiography and mammography
• Review functional attributes
• Compare detectors in terms of IQ and dose
• Summarize advantages/disadvantages
Presentation Outline
• Acquisition System Overview
• Digital Detector Attributes
• Digital Detector Technologies
• Factors affecting Image Quality & Dose
• Clinical Implementation and QC
1
Image acquisition, display, & interpretation
X
-rays
X-rays
Patient Detector Computer
kVp
Size
Efficiency
Digitization
kVp
Size
Efficiency
Digitization
mAs
Restraints
mAs
Restraints Resolution
Resolution Preprocessing
Preprocessing
Tube
Tube filtration
filtration Exam
Exam type
type Scatter
Scatter grid
grid Postprocessing
Postprocessing
Collimation
DQE
Configuration
Collimation ESE,
ESE, dose
dose
DQE
Configuration
PACS
Human
Data
Radiologist
Data delivery
delivery Radiologist
Data
Physician
Data display
display Physician
Experience
Data
storage
Experience
Data storage
Condition
Workflow
Condition
Workflow
Acquisition to Interpretation: Image Quality
• Image quality is an indicator of the relevance
of information presented in the image to the
task we seek to accomplish using the image
• Considered in terms of portrayal of
– Normal anatomy
– Depiction of potential pathology
• Not necessarily the ““same”
same”
same” in all images
• A constraining factor is radiation dose
Image Quality
• Screen-film radiography
Screen
Screen-film
–
–
–
IQ ““built
built in”
in” to the characteristics of the film
Film is acquisition, display and archive medium
Dose is determined by screen-film speed
screen
screen-film
• Digital radiography
–
–
–
IQ dependent on Signal to Noise Ratio (SNR)
Separation of acquisition, display, and archive
Dose is variable and dependent on required SNR
2
Presentation Outline
• Acquisition System Overview
• Digital Detector Attributes
• Digital Detector Technologies
• Factors affecting Image Quality & Dose
• Clinical Implementation and QC
Conventional screen/film detector
Transmitted xx-rays
through patient
Optical Density
1. Acquisition, Display, Archiving
Log Relative Exposure
Film processing:
light to optical density
Film
Gray Scale
encoded on
film
Intensifying Screens
x-rays → light
Digital XX-ray Detector
1. Acquisition
Digital Pixel
Matrix
2. Display
Digital to Analog
Conversion
Transmitted xx-rays
through patient
Digital
processing
Analog to Digital
Conversion
Charge
collection
device
X-ray converter
x-rays → electrons
3. Archiving
3
Analog versus Digital
Spatial Resolution
Exposure Latitude
M o d u latio n
MTF of pixel aperture (DEL)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
100 µm
Film
Signal output
Detector
Element,
“DEL”
DEL”
Sampling
Pitch
200 µm
Digital
100:1
1000 µm
10000:1
0.1
0
0
1
2
3
4
5
6
7
8
9
10
11
Log relative exposure
Freque ncy (lp/mm)
Digital Detectors
• Separation of acquisition, display and archive
• Digital acquisition is not contrast limited
– Image processing
• Signal to Noise Ratio (SNR) and Contrast to
Noise Ratio (CNR) impacts ““image
image quality”
quality”
• Detector DQE determines the exposure required
to achieve a required SNR
Digital Detectors
• Sampling and quantization (new noise sources)
• Detector pre-processing (correct imperfections)
pre
pre-processing
• Image post-processing (enhance image contrast)
post
post-processing
4
Presentation Outline
• Acquisition System Overview
• Digital Detector Attributes
• Digital Detector Technologies
• Factors affecting Image Quality & Dose
• Clinical Implementation and QC
Digital Detector Technologies
• Photostimulable Storage Phosphor (PSP or CR)
• Charge Coupled Device (CCD)
• Complementary MetalOxide Semiconductor (CMOS)
• Thin-FilmThin
Film-Transistor array (TFT)
Thin-Film-Transistor
• Photon counters (not discussed)
Computed Radiography (CR)
...is the generic term applied to an imaging system
comprised of:
Photostimulable Storage Phosphor
to acquire the x-ray projection image
xx-ray
CR Reader
to extract the electronic latent image
Digital electronics
to convert the signals to digital form
5
CR Detector
• Photostimulable Storage Phosphor (PSP)
• Direct replacement for S/F; positioning flexibility
Phosphor Plate
Cassette Holder
CR Image Acquisition
1. X-ray Exposure
Patient
5.
unexposed
2.
Image
Reader
X-ray
system
3.
Image
Scaling
Computed
Radiograph
4.
Image
Record
exposed
Phosphor plate
Image Acquisition
CR QC
Workstation
Patient information
Latent image produced
CR
Reader
Latent
image
extracted
DICOM / PACS
Laser film printer
Display / Archive
6
CR: How does it work?
Photostimulated Luminescence
τ
phonon
Conduction band
tunneling
τ recombination
4f 6 5d
Laser
stimulation
F/F+ e-
PSL
3.0 eV
Energy
Band BaFBr
8.3 eV
2.0 eV
τ Eu
4f 7
/
Eu 3+ Eu 2+
e
Valence band
PSLC complexes (F centers) are
created in numbers proportional to
incident xx-ray intensity
Incident
x-rays
Stimulation and Emission Spectra
Relative intensity
BaFBr: Eu2+
Stimulation
1.0
Emission
Optical
Barrier
0.5
Diode
680 nm
0.0
800
1.5
700
1.75
600
2
500
2.5
400
300 λ (nm)
3
4
Energy (eV)
Photostimulated Luminescence
Incident Laser
Beam
Light guide
PSL
Signal
PMT
Exposed
Imaging
Plate
Light
Scattering
Photostimulated
Luminescence
Protective Layer
Phosphor Layer
Laser Light Spread
"Effective" readout diameter
Base Support
7
CR: Latent Image Readout
Reference
detector
f -θ
lens
Cylindrical mirror
Light channeling guide
Laser
Source
Output Signal
Polygonal
Mirror
ADC
ADC
PMT
Laser beam:
Scan direction
x= 1279
image
y=To1333
z=processor
500
Plate translation:
SubSub-scan direction
SubSub-scan Direction
Plate translation
Typical CR resolution:
35 x 43 cm -- 2.5 lp/mm (200 µm)
24 x 30 cm -- 3.3 lp/mm (150 µm)
18 x 24 cm -- 5.0 lp/mm (100 µm)
Screen/film resolution:
Scan Direction
7-10 lp/mm (80 µm - 25 µm)
Laser beam deflection
Phosphor Plate Cycle
PSP
x-ray exposure
Base support
plate exposure:
create latent image
reuse
laser beam scan
plate readout:
extract latent image
light erasure
plate erasure:
remove residual signal
8
CR Innovations
• High-speed line scan systems (<10 sec)
High
High-speed
• Dual-side readout capabilities (increase DQE)
Dual
Dual-side
• Structured phosphors
• Mammography applications ????
• Low cost table-top CR readers
table
table-top
CR “lineline-scan”
scan”
Laser Line
Source
Linear CCD
Array
Shaping
Lens
Lens
Array
Sub-scan
Direction
Line excitation
Linear
Laser
Source
PSL
Stationary IP
5 sec scan
Linear CCD
Array
Side View
Light Collection Lens
Charge Coupled Device: CCD
•
•
•
•
•
•
X
-rays on scintillator
X-rays
Light collection: optical or fiberoptical
Emitted light to CCD photo-sensor
photo
photo-sensor
Electronic charge created on silicon
Charge transfer moves packets
Charge to voltage conversion & amplification
9
CCD Charge Collection
Light photons
-Vo
+Vo
-Vo
Transparent
polysilicon
“gate”
gate” electrode
Silicon dioxide
PhotoPhotogenerated
electrons
e-
Potential
Potential
Barrier
Barrier
Potential
eeWell
eee
ee- eeee-
Silicon substrate
CCD charge transfer
• Voltage potential of gate electrode pushes
electrons towards collection amplifiers
•
•
•
24 volts bias for good transfer efficiency
Larger pixel dimension has inefficient transfer
Pixel dimensions:
– 8, 10, 15, 20 micron
• Form factor of CCD array very small
Light emission & Optical coupling
Scintillator
Light
Large loss of light!!!
Optical coupling inefficiency
X-rays
CCD
Detector
Lens
Demagnification >10:1
10
CCD detector
• Silicon chip with photosensitive layer
High fill factor ~ 100 %
Good light conversion
efficiency (~85%)
2.5 cm
Scintillator
5 cm
5 cm
2.5 cm
35 cm x 43 cm
Larger CCD
arrays
Optical de-magnification
Lens efficiency?
Secondary Quantum Sink
CCD acquisition and readout
Parallel
CCD
clocks
Masking
Pixel
Electrode
Silicon
dioxide
Horizontal
Readout Register
Serial clocks
Serial Register
CMOS
Complementary Metal Oxide Semiconductor
• ““RAM”
RAM”
RAM” with photodiode converter
• Random access readout
• Low voltage operation (5V)
• ? NOISE ……
• Large FOV detector available (tiled CMOS)
• High sampling resolution possible
11
DECODER
LATCHES
COUNTER
ROW DRIVERS
CMOS detector on a chip
PIXEL
ARRAY
COLUMN SIGNAL CONDITIONING
CLK
RUN
DEFAULT
LOAD
ADDRESS
DATA
+5V
TIMING
AND
CONTROL
VS_OUT
VR_OUT
DECODER
READ
COUNTER
FRAME
LATCHES
Available:
“Tiled” matrix array of CMOS in large FOV
Array of tiled CMOS sensors
Xrays
Scintillator
Fiberoptic plate
Microlens optics
CMOS sensors
Controller electronics
7000x7000 element array, 17”
17” x 17”
17” FOV for one implementation
Amorphous Silicon
TFT active matrix array
Amplifiers – Signal out
G1
Active
Area
G2
Dead
Zone
G3
D1
Data lines
CR1
D2
CR2
D3
CR3
Gate
switches
ThinThin-Film
Transistor
Storage
Capacitor
Charge
Collector
Electrode
Charge
Amplifiers
Analog to
Digital
Converters
12
Amorphous Silicon
TFT active matrix array
Amplifiers – Signal out
G1
Expose to xx-rays
G2
Store the charge
G3
Active Readout
Activate gates
Amplify charge
Convert to Digital
Indirect detector:
a-Si TFT/ CsI phosphor
X-ray
Structured XX-ray
phosphor (CsI)
Light
Source
Gate
Drain
G
S
+
D
Adjacent gate line
TFT
Photodiode
Charge
Storage capacitor
X-rays to light to electrons to electronic signal
Direct detector:
a-Se / TFT array
Incident xx-rays
High
voltage
+
-
- - -
-
+
-
+
+
-
+
+
+
+++
+
-
Top electrode
Dielectric layer
Selenium photoconductor
Charge collection electrode
(pixel size)
ThinThin-FilmFilm-Transistor
Storage capacitor
Glass substrate
Stored charge
X-rays to electrons to electronic signal
13
Presentation Outline
• Acquisition System Overview
• Digital Detector Attributes
• Digital Detector Technologies
• Factors affecting Image Quality & Dose
• Clinical Implementation and QC
Image acquisition and display
Acquisition
Uncorrected
“Raw”
Raw”
PostPost-processing
PrePre-processing
Corrected
“Raw”
Raw”
X-ray system
- Spectrum
- Detector
“For display”
display”
enhanced
Outside
images
Display
?
Image
comparisons
Enhancement:
- Equalization
- Contrast/Detail
Dead pixels
Column/line defects
Shading/flatShading/flat-fielding
Signal amplification
Hard/Soft Copy
Perceptual linearization
VOI LUT -- DICOM GSDF
Hanging / Viewing
Signal to Noise Ratio (SNR)
• Determines detectability of an object
• The signal is derived from the x-ray quanta
xx-ray
• The noise is from a variety of sources:
–
–
–
–
–
X
-ray quantum statistics
X-ray
Electronic noise
Fixed pattern noise
Sampling noise (aliasing)
Anatomical noise
• System pre and post processing are crucial
14
Pre-Processing
Pre
Pre-Processing
Two major steps correct and adjust for:
• Detector / x-ray system flaws
xx-ray
– Pixel defects
– Sensitivity variations
– Offset gain variations
• Wide detector dynamic range
–
–
–
Identify image location
Scale image data
Optimize quantization levels for ““post-processing”
postpost-processing”
processing”
Preprocessing, Step 1: correct flaws
• Detector origin
–
–
–
–
stationary patterns (structured), fixed-point noise
fixed
fixed-point
thickness non-uniformities
non
non-uniformities
drop-outs, dead pixels, dead columns
drop
drop-outs,
dark current variation
• Equipment origin
– heel effect
– stationary patterns/artifacts (e.g., tube filter, grid)
Pre-processing schemes
Pre
Pre-processing
• 11-D
-D shading correction
– Computed Radiography (CR)
– Linear CCD
• 22-D
-D flat-field correction
flat
flat-field
– Area CCD, CMOS
– TFT arrays
15
Shading correction techniques: 11-D data
Apply offset correction to uniform exposures, n averages:
IO (x) = I(x)i - O(x)i ; i = 1, n
Create normalized shading correction array:
Sh(x) =
IO
x
IO (x)
Implement shading correction (line by line):
C(x) = (I(x) - O(x) ) × Sh ( x)
1
-D shading correction
1-D
Response
PrePre-processing
Corrected response
Scan Direction
Low noise, inverted, normalized correction trace
2
-D flat-field correction
flat
2-D
flat-field
• Non-functioning components:
Non
Non-functioning
– Dead pixels in columns and/or rows
• Intensity variations:
– Uneven phosphor coating
– Optical coupling (vignetting, barrel distortion)
– Converter sensitivity
• Variation in offset and gain of sub-panels
sub
sub-panels
• Variation in black-level correction
black
black-level
16
Uncorrected flat-panel image
flat
flat-panel
Background
signal
+,column defects
row defects
pixel defects
SubSub-panel offset gain variation
FlatFlat-field techniques: 2D image
(fixed detector)
Apply offset and average of <n> uniform exposures:
IO (x, y) = I(x, y) i - O(x, y) i ;
i = 1, n
Create normalized flatflat-field correction matrix:
IO
FF(x, y) =
IO (x, y)
Implement flatflat-field correction on acquired image:
C(x, y) = (I(x, y) - O(x, y) ) × FF ( x, y)
2
-D Flat-field correction
Flat
2-D
Flat-field
PrePre-processing
Raw, Raw
Background variations
Column, line defects
“Del”
Del” dropouts
Correction “mask”
mask”
Avg, inverted background
Column, line, pixel repair
Normalized values
Raw
PrePre-processed image
Image pixel value to
exposure relationship?
Processed
Contrast, resolution
enhancement; proprietary
processing
17
Preprocessing, Step 2: find / scale image
Determine Collimation
Collimation
Border
Shift and Subtract
Create / analyze Histogram Distribution
Collimated
area
Direct
x-ray
area
Frequency
Anatomy
Pixel value
Useful signal
The shape is dependent on radiographic study,
positioning and technique
Data conversion
Grayscale transformation
Input to output digital number
1,000
Output digital number
Relative PSL
Exposure into digital number
102
101
100
10-1
511
1023
10-1 100 101 102 103 0
Raw Digital Output
Exposure input
800
600
400
200
0
200 600 1,000
Raw Input digital number
Histogram
min
max
1. Find the
signal
2. Scale to
range
3. Create film
looklook-alike
18
Histogram: pediatric image
to 8323
to 9368
Frequency
800
600
400
200
0
0
200
400
600
800
1000
Digital value
Useful image range for anatomy
PrePre-processed
“raw”
raw” image
Scaled and inverted:
“For Processing”
Processing” image
Data conversion for overexposure
Exposure into digital number
Relative PSL
Reduce overall gain
102
101
100
10-1
Exposure
input
10-1 100 101 102 103
0
511
1023
Raw Digital Output
overexposure
min
max
(scaled and log amplified)
19
Screen – Film
Identical exposure
Digital
Data conversion for wide latitude
Exposure into digital number: less kV dependence
Change gradient
(auto mode)
Relative PSL
102
101
100
10-1
Exposure
input
10-1 100 101 102 103
0
511
1023
Raw Digital Output
low kVp
(scaled and log amplified)
(broad histogram)
min
max
Contrast Enhancement
• Optimize image contrast via non-linear
non
non-linear
transformation curves
• Unprocessed images: ““subject
subject contrast”
contrast”
• Proprietary processing:
–
–
–
–
““Gradation
Gradation processing”
processing” (Fuji)
““Tone
Tone scaling”
scaling” (Kodak)
““MUSICA”
MUSICA”
MUSICA” (Agfa)
……..
…….. And others by the various manufacturers
20
Look-upLook
up-table transformation
Look-up-table
Output digital number
1,000
M
L
E
A
800
600
Fuji System
Example LUTs
400
200
0
0
200
400
600
800 1,000
Input digital number
Types of image output:
Raw
“PrePre-processed”
processed”
No scaling
No flatfield
Unprocessed
“For processing”
processing”
CAD
VOI LUT
Contrast
Enhanced
“For presentation”
presentation”
Proprietary
Limited variability
VOI LUT: a more flexible approach
• Value Of Interest Look-UpLook
Up-Table (DICOM)
Look-Up-Table
• Adjustment of contrast, brightness with non-linear
non
non-linear
LUT adjustment
• Provides for manipulation of raw data
((“For
“For Processing”
Processing” images)
• Universal support (modalities, PACS) not available
• Future universal image processing workstation?
21
DICOM VOI LUT
• Configure CR/DX modality to send specific VOI LUT
– Eliminates ““burned-in”
burnedburned-in”
in” LUT
LUT and potential information loss
• PACS must be able to use and vary VOI LUT
Adjustable VOI LUT
4095
0
Raw image histogram values
P - values
Adapted from Mike Flynn presentation
Spatial Frequency Processing
““Edge
Edge Enhancement”
Enhancement”
Solid:
original response
response
MTF:
original
Edge
Enhanced:
Difference:
Response
Response
Dash:
low- pass
filtered
Difference
+filtered
Original
Original
low
low
low
low
Sum
Original
Blurred
high
high
high
high
Spatial frequency
Difference Edge enhanced
Multi-band Frequency Processing
Multi
Multi-band
NonNon-linear
weighting
Optimize subsubband weighting
NonNon-linear
weighting
NonNon-linear
weighting
NonNon-linear
weighting
“Multi frequency”
frequency”
enhanced image
22
Standard Processing
MultiMulti-frequency Processing
Compliments of Keith Strauss, Boston Childrens Hospital
SNR and CNR (dSNR
dSNR))
((dSNR)
• SNR: Average value / Std Dev of background
• CNR: ∆ Attenuation / Std Dev of background
– Contrast: tissue differences, tissue/bone differences
– Subject contrast: X-ray energy
X
X-ray
• Detection: CNR of 3 to 5
– Size (diameter); image processing
SNR and CNR
Background
420.3 ±3.3
Object
411.8 ±3.3
SNR =
420.3
= 127.4
3.3
CNR =
420.3 - 411.8
= 2.6
3.3
23
Noise Sources
• Incomplete x-ray absorption: η
x
x-ray
• Secondary quantum noise: quantum sink
– # secondary quanta ≤ incident q
• Spatial gain variation (flat-field)
(flat
(flat-field)
• Aliasing (insufficient sampling)
• Swank Factor
– Different x-ray photons produce variable signal
xx-ray
• Lubberts Effect
– Different x-ray photons
’s
xx-ray
PSF
photons produce
produce variable
variable PSF’
PSF’s
• Additive system noise
– Electronic, quantization, shot, etc.
Visual Detection of Object
• SNR (CNR) is x-ray quanta dependent
xx-ray
• Detection is determined by CNR and object size
• k = SNR × d × C
C = contrast
d = diameter
k = 3 to 5 for detection
Low Contrast Response: Leeds TO-16
TO
TO-16
3.5 mR
70 kVp
0.5 mR
24
What determines necessary dose?
• Patient thickness
• X
-ray technique; GRID or NO GRID
X-ray
• Detector absorption AND conversion efficiency
• Detector electronic and stationary noise
• Detector Detective Quantum Efficiency (DQE)
• Required SNR / CNR of examination
• Pre and post processing algorithms
• Display and viewing conditions
X-ray absorption Efficiency: CsI, BaFBr, Gd2O2S
% Absorption Fraction
100
CsI: 175 mg/cm2
90
80
Gd2O2S: 120 mg/cm2
70
60
50
BaFBr: 100 mg/cm2
40
30
20
10
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140
Energy (keV)
Detective Quantum Efficiency (DQE)
DQE(f ) =
22
SNR out
MTF(f ) 22
out
=
22
SNR inin NPSNN ( f ) × q
• A measure of the information transfer
efficiency of a detector system
• Dependent on:
–
–
–
–
–
–
Absorption efficiency
Conversion efficiency
Spatial resolution (MTF)
Conversion noise
Electronic noise
Detector non-uniformities / pattern noise
non
non-uniformities
25
““Pre-sampled”
PrePre-sampled”
sampled” MTF
1.0
0.9
a-Selenium: 0.13 mm
0.8
Modulation
0.7
0.6
CsICsI-TFT: 0.20 mm
0.5
0.4
CR: 0.05 mm
0.3
ScreenScreen-film
0.2
0.1
CR: 0.10 mm
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 4.0
4.5 5.0
Frequency (lp/mm)
Noise Power Spectrum
• Noise transfer characteristics of detector
• Analyze sub-images, Fourier Transform, average
sub
sub-images,
– (IEC 62220-1 standard, AAPM Task Group on NPS)
62220
62220-1
• Output is the noise power estimate as a function
of spatial frequency, NPS(f
f) in 2 dimensions
NPS(
NPS(f)
CR Image NPS
Scan direction
Detective Quantum Efficiency, Radiography
0.8
DQE( f )
CsI - TFT
0.6
a-Se - TFT
0.4
CR “dual-side”
Screen-film
0.2
CR Conventional
0.0
0.0
0.5
1.0
CCD
1.5
2.0
2.5
Spatial Frequency (cycles/mm)
26
ScreenScreen-Film
FlatFlat-field prepre-processing
MDACC: Chris Shaw, et al
aSi/CsI
aSi/CsI FlatFlat-Panel
Low contrast
resolution
CR
125 kVp
2 mAs
Image quality depends on more than
quantum mottle!
FlatFlat-field, absorption efficiency, scatter …
Shading, Flat-Field correction
Flat
Flat-Field
• Reduce structured noise
• Eliminate variable background
DQE(f)
• Increase DQE( f )
0.5
0.4
0.3
0.2
0.1
0
Flatfield
Raw
0
2
4
6
8
10
f (mm -1)
Digital Radiography: Radiation Exposure
• CR and DR tolerate poor radiographic technique
• Dose is dependent on DQE and ““required”
required”
required” SNR
• Dose is roughly proportional to inverse of DQE
27
Exposure issues
• Incident exposure can be ““hidden”
hidden”
hidden”
• Low exposures have excessive image noise
• High exposures lead to saturation signal loss
• Technique complacency, instead of ““just
just enough”
enough”
• Feedback is necessary!!
– S number, Exposure Index, LgM,
-number, other?
LgM, fff-number,
Characteristic Curve:
Response of screen/film vs. digital detectors
5
Useless
10,000
FilmFilm-screen
(400 speed)
Digital
1,000
3
2
Overexposed
Useless
100
Correctly exposed
1
10
Relative intensity
Film Optical Density
4
Underexposed
0
0.01
20000
0.1
1
10
100
1
Exposure, mR
2000
200
20
2
Sensitivity (S)
How do manufacturers indicate
estimated exposure?
• Fuji: ““S”
S” – sensitivity number
•• S
S ≅≅ 200
200 // Exposure
Exposure (mR)
(mR)
• Kodak: ““Exposure
Exposure Index”
Index” – EI
•• EI
EI ≅≅ 1000
1000 ×× log
log (Exposure
(Exposure [mR]
[mR] )) ++ 2000
2000
• Agfa: ““lg
lg M
M”” – relative exposure database
• IDC: ““f-number”
f-number”
number” – provides analogy to camera speed
•• +1
+1 == 2x
2x exposure;
exposure; +2
+2 = 4x
4x exposure
• DR: most systems currently do not have a feedback
signal…
signal… but use phototiming (AEC)
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CR vs DR and dose efficiency
• CR ~ 2X more exposure than a 400 speed film
~200 equivalent speed
• DR DQE(0) values vary substantially (20 - 80%)
• Dose efficiency related to DQE for given SNR
• Slot-scan systems most efficient
Slot
Slot-scan
Presentation Outline
• Acquisition System Overview
• Digital Detector Attributes
• Digital Detector Technologies
• Factors affecting Image Quality & Dose
• Clinical Implementation and QC
CR/DR implementation
• Modality interface: DICOM & HL-7
HL
HL-7
– PACS, RIS connections, Modality Worklist
• Image Size & Storage considerations
• 8 - 32 Mbytes Uncompressed
– 10 - 12 Pixels/mm
– Up to 4000 x 4000 x 2 Bytes
• 3 - 13 Mbytes: ~2.5:1 Lossless Compression
• Network Transmission
• 100 Mbit/sec
Mbit/sec minimum
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CR/DR implementation
• Uniformity for CR/DR images and Display
– Acceptance Testing
• Measurement of Performance
• Correction of Substandard Performance
– Calibration of CR/DR Response (presentation state)
– Calibration of Monitors
• Maximum brightness
• Look-upLook
up-Tables, DICOM GSDF, Part 14
Look-up-Tables,
– Periodic Quality Control
• Evaluation of resolution, contrast, artifacts
• Monitor technologist performance, exposure indices
CR/DR implementation
• Image Processing optimization
–
–
–
Establish Contrast Scale
Balance Edge Enhancement with perceived noise
Multi-frequency Enhancement parameter
Multi
Multi-frequency
adjustments
– Determine DC offset (brightness) for display
monitors
• Provide processing ““looks”
looks”
looks” to Radiologists
• Verify image display conditions
– Soft copy and hard copy
What is emerging as the lead technology?
Attribute
CR
DR
CCD
Positioning flexibility
****
**
**
Replacement for S/F
****
**
**
DQE / dose efficiency
**
***
**
Patient throughput
*
***
**
X-ray system integration
**
****
****
PACS integration
**
****
****
Cost per pat. throughput
***
**
***
Technologist ease of use
*
***
***
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Digital Radiography Considerations
• Replacement of S/F, aging CR
• High throughput, ambulatory imaging
• Advanced image acquisition and processing
– Digital tomosynthesis and CT
– Dual energy radiography
– Replacement of image intensifiers
• Low dose screening devices with CAD
– Lung cancer screening with dual energy
– Quantitative bone density analysis?
Conclusions
• CR is the most flexible and costcost-effective technology
• Direct digital radiographic devices have advantages in
efficiency and throughput
• The distinction between CR and DR is blurring
– Portable versus integrated; active versus passive
– “Cassette”
Cassette” versus “Cassetteless”
Cassetteless”
• All technologies are becoming faster, better, cheaper
• The digital solution is best accomplished as a
complementary mix of technologies
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