AAPM Annual Meeting 2006
Abstract ID: 26-5971-9361
Digital Fluoroscopic Imaging:
Acquisition, Processing and Display
Barry Belanger, PhD
Outline
X-Ray Clinical Imaging Applications: Variety & Key
Considerations
Performance Metrics for Clinical Imaging
Modern X-Ray Imaging System Design:
Acquisition, Processing and Display
Key Points to Consider in the Purchasing Process
Disclosure: GE Healthcare Employee
Implementing Quality Assurance & Pitfalls to Avoid
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Fluoro X-ray Systems under discussion
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
X-Ray Clinical Imaging Applications:
Variety & Key Considerations:
Anatomy/object of interest: radiographic attenuation, size, motion:
Cardiovascular:
R&F “fluoro”
Bone: spine: vertebroplasty, needle placement
GI tract with barium contrast
Blood vessel or Heart chamber with iodine contrast
Guidewire, catheter, stent
• Background anatomy: attenuation variations, motion
Thorax: large attenuation variations, rapid cardiac motion
Abdomen: more uniform attenuation, less motion
Cranium: large attenuation variations, little motion
• Attenuation range: from pediatric to obese adult.
AP thorax: 6cm (ped) to 32cm (large adult) and growing, equivalent to
~9HVLs of ~3cm, ~500:1 difference in attenuation.
LAT thorax presents greater range and challenge
Range of Needs and Conditions is huge:
>> Need for Flexibility, Automation, Preset Protocols
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
1
Performance Metrics for Clinical Imaging:
Performance Metrics: Clinical Image Quality & Dose
Optimization Problem Statement:
Benefit
•Imaging Dose Efficiency:
Cost
Clinical Objective
=
Risk
~
=
Clinical Image Quality
Dose
=
Imaging Dose
Efficiency
Objectives:
• Maximize Imaging Dose Efficiency: Best clinical image quality for any dose
level clinician chooses to use, tailored to intended application.
• Provide range of Dose/IQ selections to operator to fit application needs and
preferences of clinicians.
• Provide Dose Readout/Feedback: clinician awareness for decision making.
• Automate the process as much as possible.
X-Ray Source Efficiency
Image Detector Efficiency
•Dynamic Range
•Temporal Response
Caveat:
• Dose = Dose Rate x Time, alternately Dose/Exposure x Number of
Exposures.
Need to consider impact of Image Quality on fluoro time, number of
exposures required to achieve clinical goals
•Image Artifacts
A Comprehensive Set of Relevant IQ Measures
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Performance Metrics for Clinical Imaging:
Requirement
Clinical Benefits
X-Ray Source Efficiency: High continuous
power capability, range of spectral filters
• High Dose Efficiency
• High fluoro penetration capability for
large patients
Image Detector Efficiency (DQE): High XRay Conversion Efficiency, Low Readout
Noise
• High Image Quality: Object detectability
• High Dose Efficiency
Consistent with ALARA (As Low As Reasonably Achievable) Dose Principle
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Performance Metrics: XRT: Spectral Filtration
Spectrum after 25 cm Water
Spectrum at patient entrance
4.00E+02
7.00E+04
3.50E+02
3.00E+02
5.00E+04
Photon Nr
Photon Nr
6.00E+04
4.00E+04
3.00E+04
2.00E+04
• Visualize contrast differences from thin
to dense anatomy.
• No Blooming in thin anatomy: robust,
forgiving to difficulties with positioning,
collimation, contour filters, etc.
Temporal Response: Fast Readout, low
lag, range of frame rates & exposure times
•High definition of moving objects
•Good rendering of dynamic events
A Comprehensive Set of Relevant IQ & Dose Efficiency Measures
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
2.00E+02
1.50E+02
1.00E+02
1.00E+04
Wide Dynamic Range: High min/max
signal range from image detector plus
specialized image processing to present
information effectively on display.
2.50E+02
5.00E+01
0.00E+00
0.00E+00
15
25
35
45
55
65
75
85
15
25
35
Energy (keV)
regular filtration
0.2 mm Cu additional filtration
45
55
65
75
85
Energy (keV)
regular filtration
0.2 mmCu additional filtration
• Softer radiation does not contribute significantly to image
• Spectral filtration eliminates this radiation before it reaches the patient
• Requires higher XRT power to be effective
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
2
Performance Metrics: Detector: Importance of DQE
DQE=1.0
DQE = 0.5
DQE = 0.25
CNR = 5
CNR = 3.5
CNR = 2.5
Performance Metrics: Temporal Response: Value
Pediatric Imaging
Protocol
4 msec max pulse
width
30 Frames/Sec
Options enabled
by higher DQE:
Better Image, Same Dose
Same Image, Lower Dose
DQE (Detective Quantum Efficiency) is judged the best index of object
detectability in contrast & dose-limited imaging, as in real clinical
imaging.
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
X-Ray Source Assembly: X-Ray Tube & Collimator
Modern X-Ray Imaging System Design
• XRT/Source Assembly
• Image Detector
• Automatic Exposure Control
X-Ray Tube:
• 3200 Watt continuous fluoro capability
• Metal envelope for reduced off focus radiation
• 0.3, 0.6, 1.0 Focal Spot (0.3 for DSA)
• Imaging modes: fluoro, dynamic record, Digital Spot, DSA,
Rotational/3D
Collimator with variable Spectral Filtration:
• Image processing & Display
•
• Procedure Protocol Driven Customization and Control
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
•
•
Contour Filters
0.1, 0.2, 0.3, 0.6 & 0.9mm Copper filters
Rectangular Blades
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
3
Detectors: Image Intensifier/TV >> Flat Panel
DFP Benefits:
“Birthright”
Camera
•200u Pixel 40x40cm Flat Panel
•State of the Art 40cm Image Intensifier + 1k x 1k CCD
• Brightness & MTF Uniformity
Across Entire Image
• No Veiling Glare
• No Geometric Distortion
• No Earth Field Distortion
Image Intensifier Chain
Image
Optical
Iris
Intensifier
Detector DQE: Flat Panel vs II/CCD
Analog
Processing
& A/D
Detective Quantum Efficiency
0.8
Innova 4100
0.7
II/CCD
0.6
Design-Dependent:
• 5-10x Improvement in
Dynamic Range: depends on
imaging mode and DFP &
Electronics Design
• Radiographic DQE: Typically
better
• Fluoro DQE: Depends on
Detector & Electronics Design
Digital
Flat Panel Detector
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
DQE
0.5
0.4
0.3
41cm
FOV
20cm
FOV
0.2
0.1
0
0
0.5
1
1.5
2
2.5
Spatial Frequency (cycles/mm)
40cm Flat Panel has Significant Advantage in DQE
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Detector DQE: X-Ray Detector/Imaging Chain
Detector: DFP: Binning in Larger FOVs
Innova 2100 Fluoro DQE @ 1 uR/Fr
Native 200 x 200 micron photodiodes
Summed 400 x 400 micron pixel (in blue)
Binning Principle:
Scan
• Scan Adjacent Lines in Pairs
• Digitally add adjacent columns in pairs
amp
amp
amp
• 4X signal/pixel: better SNR
• Limiting Spatial Resolution 1.25 instead of
2.5 lp/mm (comparable to II/Video)
• Good DQE at lower doses used in LFOV
imaging, exceeding II/Video chain
• Reduced image processing, storage and
display requirements.
amp
Performance Implications:
A/D
A/D
A/D
A/D
+
+
Binning Enables LFOV Imaging at Required Rates
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
0.80
To understand how well
an image chain works we
must consider:
The DQE curve of
the image chain
The spatial
frequency content of
the object being
imaged
DQE(f) at fluoro level
radiation exposure of
8 nGy/Fr (1 uR/Fr)
0.60
0.40
0.20
0.00
0.00
0.50
1.00
1.50
2.00
2.50
Spatial Frequency (cyc/mm)
Spatial frequency content
of a stent.
Note that there is
progressively less signal at
higher frequencies,
particularly beyond 2
lp/mm.
• The spectrum of the stent extends over a wide range of spatial frequencies.
• Therefore, the DQE response over this same range of spatial frequencies is
important to determining the quality of the image.
• Response at a single spatial frequency, e.g., spatial resolution limit, doesn’t tell the
story.
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
4
Detector Dynamic Range: DFP Versus II/TV
II/Video Chain Transfer
Function
Digital Detector Transfer
Function
Modern X-Ray Imaging System Design
Saturation Limit
Skin Line
Lung
Soft Tissue
Noise Floor
Spine, Diaphragm
• XRT/Source Assembly
Detector Signal
Video Signal
Saturation Limit
• Image Detector
• Automatic Exposure Control
• Imaging modes: fluoro, dynamic record, Digital Spot, DSA,
Rotational/3D
Noise Floor
X-Ray Intensity
X-Ray Intensity
• Image processing & Display
• DFP Provides 5-10x Improvement in Dynamic Range of Captured X-ray
Information.
• Display Dynamic Range Must Be Addressed Independently (later in this
presentation)
• Higher Dynamic Range Can Reduce Retake Rates (no burnout/blackout) and is
More Forgiving to Errors, Hence it is Dose Conservative
• Procedure Protocol Driven Customization and Control
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Automatic Exposure Control Systems
Automatic Exposure Control Systems:
“Trajectory” Table-Based
Image Data from Detector: Possibilities
Average
Area-Location Weighted
Histogram
Detector
Patient
Auto Ex
XRT
Generator
Exposure Control Algorithm: Possibilities
Automatic selection of kVp, mA, pulse
width, focal spot, spectral filter &
detector dose as a function of image
signal from detector and effective
patient attenuation (calculated from xray technique, SID, other system
parameters)
Desirable Objectives:
• Maximize Imaging Dose Efficiency: Best clinical image quality for
any dose level clinician chooses to use, tailored to intended
application, capitalizing on component characteristics.
• Provide range of Dose/IQ selections to operator to fit application
needs and preferences of clinicians.
Exposure
• Provide Dose Readout/Feedback: clinician awareness for
On
decision making.
Off
• Automate the process as much as possible.
Skin Dose
DAP
Rate
Total
Total
Total
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Effective Brightness is calculated from
digital image
Detector
Patient
Auto Ex
XRT
Generator
kVp
mA
Pulse width
Spectral Filter
Focal spot
Algorithm Calculates Effective Patient
Thickness (EPT), based on:
•Effective Brightness
•kVp, mA, Pulse Width
•Spectral Filter
•FOV, SID, Grid In/Out
Using new EPT, Determines Technique
& Spectral Filter for next exposure from
trajectory table, and sends to generator.
Fluoro: 30 PPS, Normal Detail, 'Smart IQ' Trajectory
EPT
Technique
Cm
kVp
pw
mA pk
Filt
15
73
8.0
8.3
0.2
20
73
8.0
27.4
0.2
25
77
11.8
36.6
0.1
30
95
12.4
34.3
0.1
Pat Dose
R/min
0.41
1.29
4.16
10.00
Det Dose
mR/min
3.6
3.6
3.6
3.6
Benefits: Flexibility, Optimization, Upgradeability
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
5
Automatic Exposure Control Systems:
“Trajectory” Table-Based: Trajectory Design Process
Automatic Exposure Control Systems: “Trajectory” TableBased: Typical Optimization Criteria
Object Contrast: Difference in x-ray intensity due to the
presence of the stent or other device, iodine in artery, barium in
colon, etc.
Background Noise: Normal statistical variation in background
intensity due to finite number of x-rays used to image
Contrast (more is better)
= CNR
Image Quality =
Noise (less is better)
Clinical Objectives
Anatomy, Motion
System Capabilities
Regulatory Requirements
Cost
Physics Model
Auto Exp Control
Trajectories
Patient Skin Dose
Significant dose savings on small patients & shallow angles
• Provide several levels of CNR (and therefore dose) to Operator:
Fluoro: 30 PPS, Normal Detail, RDL Trajectory
EPT
Fluoro: 30 PPS, Low
Technique
Pat Dose Det Dose
Detail, IQ Plus Trajectory
CmEPT
pw Detail,mA
Filt
R/min
Technique
Pat Dose mR/min
Det Dose
Cine: 30kVp
PPS, Normal
IQ pk
Plus Trajectory
pw
mA pk
Filt
R/min
mR/min
15 CmEPT
79 kVp
9.2
0.2 Trajectory
0.60
Technique
Pat Dose6.0
Det Dose
Fluoro:
15 PPS,8.0
Normal
Detail,
IQ Plus
20 15 Cm EPT
79
8.0
34.0
0.2
2.050.60
6.9 6.0
79
kVp
8.0
pw
9.2
mA
pk
0.2
Filt
R/min
mR/min
Technique
Pat Dose
Det Dose
Fluoro: 30 PPS, Normal
Detail, 'Smart IQ' Trajectory
25 20 15 Cm
92 EPT
10.98.0 8.0 38.4
0.1
9.94
9.4
79 79 kVp
34.0
0.2
2.05
6.9 6.0
pw
mR/min
9.2mA pk 0.2 Filt 0.60R/min
Technique
Pat Dose
Det Dose
30 25 20 120
12.5
32.1
0.0
10.00
7.1
92
10.9
38.4
0.1
9.94
9.4
79
8.0
34.0
0.2
2.05
R/min6.9 6.0
mR/min
15 Cm
79 kVp
8.0 pw
9.2mA pk 0.2 Filt
0.60
30 25 20 120
12.5
32.1
0.0
10.00
7.1
92
10.9
38.4
0.1
9.94
79 73
8.0 8.0
34.0 8.3
0.2 0.2
2.050.41 9.4 6.9 3.6
15
30 25 20 120 92 7312.510.9 8.032.138.427.40.0 0.1 0.210.009.941.29 7.1 9.4 3.6
30 25
120 77
12.511.8 32.136.6
0.0 0.1 10.004.16
7.1 3.6
30
95
12.4
34.3
0.1
10.00
3.6
Optimization
Algorithm
=
Design Strategy: One of several possibilities:
• Maintain near-constant CNR over range of patient thickness (within
limits)
Operator chooses level of IQ required for procedure: via protocols,
tableside control, initial system setup (trajectory family)
• Minimize patient dose required to achieve selected CNR by optimizing
x-ray technique and filtration.
• Pediatric: Limit Pulse width to 4 mSec max in fluoro and digital cardiac
record
Consistent with ALARA (As Low As Reasonably Achievable) Dose Principle
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Automatic Exposure Control Systems: “Trajectory” Table-Based:
Sample Trajectories for One Operating Mode of Pediatric Angiography
Automatic Exposure Control: “Trajectory” Table-Based:
Trajectory “Family” Options Example
0.6
8
0.5
PW (ms)
100
80
60
40
0.3
4
10
20
thickness(cm)
30
40
0
0
10
20
thickness(cm
)
30
40
0
10
20
thickness(cm)
30
40
kVp (upper left), Pulse Width (upper middle), Spectral
Filter thickness (upper right), mA (lower left) and
patient entrance dose as a function of EPT in cm of
PMMA for one fluoro AutoEx trajectory.
300
1000
regdose (mGy/min)
250
PeakmA
Target Values:
• kVp: 60-80 kVp for Iodine
imaging
• Pulse Width: 4 mSec max for
peds
200
150
100
50
0
0
10
20
thickness (cm)
Normal : 91.2
Low : 32.4
Normal : 293
Low : 146
Normal : 2.0
Low : 1.0
• Mode Selection 2
Normal : 25.2
Low : 10.4
Normal : 91.2
Low : 35.2
Normal : 293
Low : 146
Normal : 2.0
Low : 1.0
• Mode Selection 3
Normal : 14.9
Low : 5.7
Normal : 91.2
Low : 32.4
Normal : 293
Low : 146
Normal : 2.0
Low : 1.0
• Mode Selection 4
Normal : 18.7
Low : 7.7
Normal : 32.4
Low : 14.3
Normal : 293
Low : 146
Normal : 1.0
Low : 0.5
• Mode Selection 5
Normal : 9.7
Low : 4.0
Normal : 32.4
Low : 14.3
Normal : 293
Low : 146
Normal : 1.0
Low : 0.5
0.1
0
0
Cardiac
Normal : 21.8
Low : 9.4
Dyn 5 fps
DSA
0.2
2
20
0
Fluoro 30fps
• Mode Selection 1
0.4
6
30
40
Note log scale
Loweer Dose
Patient Thickness Control
Range:
• From 0 cm (bare table) to
>40cm of PMMA effective
patient thickness (EPT)
10
120
Spectral filter
Within limits of:
•XR Tube: filament, power, etc.
•Generator: Power, control
ranges
•Regulations
Typical Dose Levels: Fluoro (mGy/min), Cardiac & Innova Chase (µGy/fr) and DSA (mGy/fr)
140
kV
Independent control of:
• kVp
• mA
• Pulse Width (primary & Grid)
• Spectral Filter
• Focal Spot
100
Test conditions:
10
1
0.1
0
5
10
15
20
0.01
thickness(cm)
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
25
30
35
40
• Patient Entrance Dose
• 20 cm FOV
• 20 cm PMMA phantom
• Reference: Operator
Manual
• Fluoro Levels : 5:1 range in dose rate, @ 30 fps: (20:1 with 15 and 7.5 fps)
• Mode 2 and Mode 5 Trajectories have 5R/min limit in Fluoro Low Mode.
• Cardiac Record Levels : 6:1 range in dose/frame
• Dynamic 5 fps: 2:1 range in dose/frame
• DSA: 4:1 range in dose/frame
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
6
Automatic Exposure Control: Options for Dose
Change with Frame Rate
Two Options Seen on Current Systems:
1. Balanced Dose/IQ : Follows “Aufrichtig” or “Square Root”
Scale: Maintains static object detectability.
2. Minimize Dose: Dose rate drops directly with fluoro frame
rate.
Automatic Exposure Control: Options for Dose
Change with Field of View: DFP vs II
Output Phosphor
II: As FOV is reduced, II sensitivity decreases, because a smaller input area
of the scintillator is being projected to the same output phosphor area.
Required II entrance dose goes up inversely with area, or…
Compensations & compromises must be made (video camera iris), and …
Electron Trajectories
Smaller FOV’s may operate at higher than optimal entrance doses
Scintillator
Frame Rate
30
15.0
7.5
Balanced
Dose/IQ
100%
75%
50%
Minimize
Frame
Rate
Dose
30
100%
15.0
50%
7.5
25%
Balanced
Dose/IQ
10.4
7.8
5.2
Minimize
Dose
10.4
5.2
2.6
Data for
GE Innova
2100 in
mGy/min
Scintillator
FOV: 40
FOV: 17
Photodiode Array
FOV: 40
FOV: 17
DFP: Flat panel Sensitivity is
independent of FOV, because it
depends only on the size of the
detector elements, which is fixed:
Patient
Patient
X-Rays
X-Rays
Free to choose the optimal
dose for each FOV.
Best choice may depend upon application and user:
Select lowest frame rate tolerated by user for application
Select lowest usable dose at selected frame rate
No compromises with FP
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Automatic Exposure Control: Options for Dose
Change with Field of View
Automatic Exposure Control: Options for Dose
Change with Field of View
Illustration of FOV Change without Dose Change
12 cm
Illustration of FOV Change with Dose Change
30
cm
20
cm
16
cm
12
cm
Dose Increase from
30 cm
16 cm
20 cm
6x
30 cm
Inc
Dose
ea
1/Ar
with
rease
Dose Increase with 1/Length Between
Dose
Con
sta
2.5x
the two
nt
1x
How much does IQ improve with magnification alone?
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
How much does IQ improve with magnification + dose?
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
7
Automatic Exposure Control: Options for Dose
Change with Field of View
Modern X-Ray Imaging System Design
DoseRateChangewithFOV
35.0
mGy/min
30.0
25.0
NoChange
20.0
1/Area Change
15.0
1/Length Change
10.0
Actual Change
• XRT/Source Assembly
• Image Detector
5.0
0.0
0
10
20
30
40
FOV (length in cm)
Different Philosophies:
1/Area: Assume that smaller FOV indicates need
for better CNR and keep perceived Contrast/Noise
Constant
No Change: Accommodate Clinicians’ Vision Only
1/Length: Split the difference between the two
above
• Automatic Exposure Control
• Imaging modes: Fluoro, Dynamic Record, Digital Spot,
DSA, Subtracted Bolus Chase, Rotational Angio/3D/CT
• Image processing & Display
• Procedure Protocol Driven Customization and Control
GE Philosophy is Close to 1/Length.
Most manufacturers change less than 1/Area with FOV
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Rotational Angio/3D/CT on Flat Panel Angiography Systems
Rotational Angio/3D/CT on Flat Panel Angiography Systems
MIP
Volume Rendering
Sagittal cross-section
Vascular, bone and soft tissue 3D imaging in the intervention suite
3D Images
Cross-sections
Rotational
Acquisition
Automatic
3D Recon
3D Display
In Several Formats
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Oblique cross-section Axial cross-section
Coronal cross-section
Both 3D views and cross-sections
Can be automatically created at 3D volume loading
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
8
Rotational Angio/3D/CT on Flat Panel Angiography Systems
Oblique cross-section
Rotational Angio/3D/CT on Flat Panel Angiography Systems
Acquisition and Reconstruction Protocols
Axial cross-section
•
•
•
•
•
•
“Classical”
“3D” Mode
~5 second acquisition
One or two spins (for subtracted)
~200o at 35-40o/s
~150 frames
3D recon in 2563 and/or 5123
Display: MIP, VR, MPVR, etc.
Vascular, bone and
soft-tissue 3D imaging
Sagittal cross-section
Coronal cross-section
Full screen axial cross-section
Both 3D views and cross-sections
Can be automatically created at 3D volume loading
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
“CT” Mode
•
•
•
•
•
•
~5, 10 & 20 second acquisition
One single non-subtracted spin
~200o at ~40, 20 and 10o/s
~150, 300 or 600 frames
3D recon in 2563 or 5123
Display: MPVR ( + MIP, VR, etc. )
Increased contrast senstivity for
bone and soft-tissue imaging
Evolution toward better “CT” Capabilities:
Longer effective exposure times than CT in some cases
Higher spatial resolution capability than CT
Low contrast sensitivity less than CT
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Rotational Angio/3D/CT on Flat Panel Angiography Systems
Modern X-Ray Imaging System Design
Typical Reconstruction Algorithm Elements and Attributes:
• Full cone-beam tomographic reconstruction
• Based on Feldkamp algorithm
• Compensation/calibration for “Open Gantry”
dynamic mechanical behavior
• Processing of truncated views
• Beam hardening correction
• Ring artefacts removal
• Parallel implementation
• Reconstruction time depends primarily on
matrix, e.g., 2563, 5123.
• XRT/Source Assembly
• Image Detector
• Automatic Exposure Control
• Imaging modes: fluoro, dynamic record, Digital Spot, DSA,
Rotational/3D
• Image processing & Display
• Procedure Protocol Driven Customization and Control
Your CT knowledge should be transferrable!
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
9
Image Processing: Dynamic Range Management
Digital Spot Example: Simple Display LUT
Digital detector dynamic range covers the entire range of
exposure levels; more than can be displayed without
processing!
Image Brightness
Classic Contrast/Latitude Tradeoff
Image Processing: Dynamic Range Management
Desired Behavior
Breaking the Contrast/Latitude Constraint
Image Processing: Dynamic Range Management
Digital Spot Example: Multiresolution Processing
Transform
•Select Weights
Raw Input
Lung,
Lung,
Skin
Line
Line
Skin
Lung,
Skin Line
Skin
Skin Line
Line
Simple
Display
LUT
Can
Mimic
… or many
different
looks
suchLook
as a of
…or
a Bone
Look
Film...look
soft-tissue
But one LUT can’t do it all at once.
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Image Processing: Dynamic Range Management
Realtime Processing in Peripheral Runoff Sequence
Bolus Chase: Unsubtracted
•Spatially filter
A1
Soft Tissue
Dense Soft Tissue
Spine,
Spine,
Spine,
Breast
Spine,
Diaphragm
Diaphragm
Diaphragm
Diaphragm
X-ray Detected
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Decompose
Tissue
Soft Typical
Breast
Mass
Soft
Tissue
Reconstruct
•No contour/bolus filters used
•Weighted Addition
•Manually pan table to follow
contrast bolus.
Processed Image
•AutoEx automatically adjusts
technique on the fly.
•DRM handles wide dynamic
range of image data from
detector
A2
...
An
Wide Dynamic Range + DRM:
Get all the desired
information in one
image
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
• More diagnostic info in one run
• Robust: fewer retakes?
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
10
Image Processing: Fluoro Noise Reduction
Advanced Fluoro Noise Reduction (FNR)
Image Processing: FNR Motion Compensation
Impact of Motion Compensation at 30 fps
What is it?
16 frame recursive averaging 16 frame recursive averaging
with motion compensation
no motion compensation
none
•Temporal averaging of image data to reduce quantum noise (fluoroonly application)
What is advanced?
•Motion compensation is integrated into the algorithm:
reduces lag effects in the presence of anatomical motion
•Level of filtering is matched to frame-rate
Results:
•Significant improvement in clincial image quality > opportunity to
reduce dose.
•Sufficient noise reduction to allow (in certain cases) use of a lastimage hold in lieu of acquiring a spot image
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Modern X-Ray Imaging System Design
Motion Compensation is a Clear Benefit
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Procedure Protocol-Driven Customization and Control
Auto Exposure Control
Feedback signal
•Average
•Location Weighted
•Histogram
Protocol Selection:
•Acquisition Mode
•Low/Norm/High Dose
•Trajectory “Family”
•Frame Rate
•FOV
Algorithm
Positioner:
•SID
•Grid In/Out
• XRT/Source Assembly
• Image Detector
detector
• Automatic Exposure Control
• Imaging modes: fluoro, dynamic record, Digital Spot, DSA,
Rotational/3D
• Image processing & Display
FOV
kVp, mA, PW,
spectral filter,
focal spot
patient
table
collimation
spectral filter
• Procedure Protocol Driven Customization and Control
X-ray tube
kVp, mAs,
Focal spot
X-ray
generator
Acq Mode
Dose Traj
FR, FOV
DRM Contrast
FNR Strength
Edge Enhance
Operator Controls:
•Low/Norm/High Dose
•Frame Rate
•Fluoro/Record Mode
Realtime Digital
Image Processing:
DRM
FNR
Edge Enhance
Image Processing Can Use Protocol & Exposure Information for Optimization:
Beware of Interactions when Testing
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
11
Procedure Protocol-Driven Customization and Control
Key Points to Consider in the Purchasing Process
System Features for Dose Reduction
Pre-defined Procedure Protocols (fit dose & technique to procedure)
Automatic Spectral Filters
Pulsed, Variable Frame Rate Fluoro (linked to Procedure Protocols)
Virtual Collimation, Virtual Panning
Adjustable Contour (Wedge) Filters in Collimator
Last Image Hold
Fluoro Loop Replay & Store (with DICOM & DVD Record)
• Applications breadth required by clinical
department, both today and looking out ~5 years.
• Procedure/protocol capability/flexibility/performance
provided by equipment
• Imaging/Dose performance provided by equipment
Auto or Manual Grid removal
Patient Contouring (Automatic Minimization of patient-detector distance)
Dose reporting
The More Automatic/Programmable, the Better
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
Implementing Quality Assurance & Pitfalls to Avoid
• Prioritize by key clinical procedural needs.
• Work with Supplier’s Field Service Engineer and Applications
Specialists through installation and customer training to fully
understand capabilities and optimize to clinical needs and
preferences.
Thank You!
• Perform full verification test set at installation
•Consider “standardized” procedures:
•Manufacturer’s
•IEC 61223-3-1
•SCA&I?/NEMA XR-21 (Cardiac)
• Perform key functional & performance checks at periodic intervals.
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
AAPM 2006: Digital Fluoroscopic Imaging: Acquisition, Processing and Display. Abstract ID: 26-5971-9361. Belanger
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