AAPM 2004
“Modern Fluoroscopic Equipment
Design and Application”
Human
Vascular
System
Phillip L. Rauch, M.S.
Henry Ford Hospital
Detroit, Michigan
Human
Vascular
System
PVD
Claudation
(Exercise induced pain)
Deep Vein
Thrombosis
(Economy class
blood clot)
Peripheral
Vascular
Imaging
A. Bolus Chase
(Native)
B. Stepping
(Subtraction)
1
Bolus Chase (Native)
Human
Vascular
System
Stepping (Subtraction)
Human
Vascular
System
2
Human
Vascular
System
a
b
c
Inferior Vena Cava Filters
Human
Vascular
System
Department of Radiology - Division of Physics and Engineering
3
Stent with Balloon Angioplasty
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Human
Vascular
System
Basilar-tip Aneurysm
Stent with Balloon Angioplasty
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Human
Vascular
System
4 Coil
1
6
Coils
4
Human
Vascular
System
Occlusion Coils
Occlusion Micro-coil
Occlusion Micro-coil
Occlusion Micro-coil
5
Rotational Angiography
Fluoroscopic Imaging
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Fluoroscopic Imaging
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6
Fluoroscopic Imaging
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Fluoroscopic Imaging
Fluoroscopic Imaging
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Fluoroscopic Imaging
X-ray
Source
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7
Fluoroscopic Imaging
X-ray
Detector
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Fluoroscopic Imaging
Signal
Readout
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Fluoroscopic Imaging
Notes: Image Display Monitors
DO NOT DELETE!!!
Image
Display
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8
Text Monitor
Image Monitors
C-arm Control Module
Laser Imager
Module
Image Acquisition
Control Module
Mouse
Keyboard
Contrast Injector
Control Module
System
Documentation
THE FLUOROSCOPIC IMAGE
A radiation field of varying
intensity distribution present
at the input to the image
detector results in an output
distribution of visible light
which is spatially related to
and proportional in intensity
to the input radiation
distribution
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9
THE FLUOROSCOPIC IMAGE
Fluoroscopic Image
Fluoroscopic Image: Spatially Modulated Intensity
Detector Input
Detector Output
Iout Iin
Intensity I(x,y)
(kV, filter, tissue, dose)
Relative Contrast
(kV, filter, tissue, W/L)
(I2-I1) / (I2+I1)
Noise (Quantum Mottle-IIIER)
(Added Noise: Detector,
DAC, ADC, Processing)
I1/2 SNR
(Geometry, Detector
Sharpness I/ x
Blur, Processing)
(Detector, Processing)
Temporal Fidelity I/ t
Compensated (Motion, Persistence,
Artifact/Distortion I
Subtraction)
as needed
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Digital Sampling Artifact
Artifact
Distortion
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Aliasing
Nyquist frequency, fN
Equal to half of the sampling
frequency
(Represents the maximum frequency
that a sampled system can
accurately handle)
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To represent this continuous signal a
sample is taken at regular intervals
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10
Aliasing
Adequately sampled
Sampling at an appropriate frequency
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Aliasing
Aliasing
Sample
Original
Adequately sampled
Sampled signal adequately represents the
original signal
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Aliasing
Sampled Signal is
Lower Frequency
Undersampled
Under-sampling a periodic signal
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Undersampled
Sample
Original
Sampling a frequency at an inappropriate rate
produces low frequency artifacts (aliasing)
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11
Image Characteristics
Visual Perception
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Fluoroscopic Image
Noise
Noise
I1/2 SNR
Contrast
(I2-I1) / (I2+I1)
Contrast
Sharpness
I/ x
Sharpness
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12
Noise - Random
Low Contrast & Noise
Where are the 3’s
Integration
Level 3
1
2
No Integration
Frame Integration (Reduces Noise)
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Low Contrast & Noise
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Noise - Random
Where are the 3’s
Low Dose (No Frame
Integration)
Low Dose (Maximum
Frame Integration)
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13
Noise - Random
Noise - Random
Where are the 3’s
Where are the 3’s
4 Frames/sec
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8 Frames/sec
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Noise - Random
Noise - Random
Where are the 3’s
Where are the 3’s
15 Frames/sec
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30 Frames/sec
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14
Noise - Random
Noise - Random
Where are the 3’s
Where are the 3’s
4 Frames/sec
4 Frames/sec
(With Background Suppression)
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Artifact Reduction
Digital Subtraction
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+
=
Image Frame (Inverted)
Mask
(Native Image without Contrast)
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Subtracted Image Frame
Image Frame
(Native Image with Contrast)
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Digital Native
Digital Subtraction
Quantum Sink: Detector
Landmark (25%)
Quantum Sink: Detector
Noise
Contrast
What About Motion?
Sharpness
Fluoroscopy (0.74 BR/fr)
Digital Acquisition (353 BR/fr)
Fluoroscopy (0.74 BR/fr)
Digital Acquisition (353 BR/fr)
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Do You See Motion?
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Motion
Temporal
Fidelity
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17
Fluoroscopy – Pulsed vs Cont.
Pulsed Fluoro - 30pps
(Displayed at 7.5 fps)
Image Persistence (Lag)
Continuous Fluoro
(Displayed at 7.5 fps)
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Image Persistence (Lag)
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Recursive Filter
1/K
Input(n)
+
Output(n)
Z-1
(K-1)/K
y(n-1)
K = 1.n, 2, 3, 4, 8
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18
K=1
(1 Frames)
K=2
(10 Frames)
Frame 9
contributes 0.2%
Frame 5
contributes 3%
Frame 2
contributes 25%
Recursive Filter
K=4
(24 Frames)
Frame 18
contributes 0.2%
Frame 8
contributes 3%
Frame 2
contributes 19%
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19
Sharpness
Sharpness
X-rays from Point Source
Signal
Modulation
Decreases
with Spatial
Frequency
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Sharpness
Signal
Modulation
Decreases
with Spatial
Frequency
Detector
Signal
Detector
Signal
Signal
Modulation
Decreases
with Spatial
Frequency
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Sharpness
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Detector
Signal
Abrupt Intensity
Change at Edge
Detector
Signal
X-ray
Intensity
Square Wave
Resolution
Target
Signal
Modulation
Decreases
with Spatial
Frequency
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20
Edge Restoration
100
20
40
60
80
0%
%
%
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Contrast (Grayscale)
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Edge Restoration
0%
100 %
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Are the circles the same shade of gray?
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21
Are the circles the same shade of gray?
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Are the circles the same shade of gray?
Are the circles the same shade of gray?
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Fluoroscopy Imaging
It’s time for a
Pop Quiz….
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22
Imaging Quiz #1
What is the diffuse “cloudcloud-like”
like”
pattern overlying the grid image?
Imaging Quiz #1
Fluoroscopic Image
Pattern Recognition
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23
Imaging Quiz #2
Imaging Quiz #2
#1
#2
Which one is the quarter?
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Imaging Quiz #2
Which one is the quarter?
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Imaging Quiz #2
#3
Which one is the quarter?
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#1
#2
#3
Which one is the quarter?
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24
Imaging Quiz #2
#1
#2
Imaging Quiz #2
#3
Which one is the quarter?
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Pattern Recognition
#1
#2
#3
Which one is the quarter?
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Imaging Quiz #3
Does Orientation Matter?
Who are these persons?
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25
Imaging Quiz #3
Imaging Quiz #3
Bill Gates
Bill Gates
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Abraham Lincoln??
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Quiz #4 Which is a
darker shade of gray?
B
A
26
They are the same
shade of gray!!
They are the same
shade of gray!!
They are the same
shade of gray!!
27
Imaging
Quiz #5
What is
this?
They are the same
shade of gray!!
B
Noise
Contrast
Temporal?
A
Imaging
Quiz #5
What is
this?
Noise
Contrast
Temporal
Imaging
Quiz #5
What is
this?
Noise
Contrast
Temporal
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Imaging
Quiz #5
What is
this?
Noise
Contrast
Imaging
Quiz #5
What is
this?
Temporal
Imaging Task
What is this?
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Noise
Contrast
Temporal
Imaging Task
What is this?
This task is difficult because the image is
presented out of context
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29
Imaging Task
What is this?
Image presented in context
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Human Visual System
Able to recognize patterns of motion in the
presence of noise
Since fluoroscopy is utilized for motion
studies, we can allow greater amounts of
image noise while still being able to
recognize anatomical patterns in the image
It is important to assure that temporal fidelity
is maintained
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Imaging Task
What is this?
Same image,
different context
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Last Imaging Quiz
How can you increase the IIIER (and thereby
improve the quantum statistical noise), yet
simultaneously reduce the entrance exposure rate
to the patient?
How can you do the above, while preserving or
even improving tissue contrast, and overall image
quality?
How can image processing be detrimental to the
goals of the procedure?
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30
Last Imaging Quiz
Stay tuned……
Attend the other courses in
this series
Thank you for your
attention in my class
Best wishes in your continued studies and
for your career in Medical Physics
--Phil Rauch
(philr@rad.hfh.edu)
Department of Radiology - Division of Physics and Engineering
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