Beth Israel Deaconess Medical center
Harvard Medical School
PART I.
Technical Advances of Fluoroscopy with
Special Interests in Automatic Dose Rate
Control (ADRC) Logic of Cardiovascular
Angiography Systems
Pei-Jan Paul Lin
Department of Radiology
Beth Israel Deaconess Medical Center
and
Harvard Medical School
Boston, MA 02215
Review of Fluoroscopy Equipment
1) Conventional Fluoroscopy Unit
2) Special Procedures Fluoroscopy Unit
a) Extension of conventional fluoroscopy.
b) Pedestal Type examination table fluoroscopy and
over-head hanger synchronized lateral plane.
3) Fluoroscopy Systems with Positioners for
a)
b)
c)
d)
Cardiac Catheterization.
Neuro Angiography.
Visceral Angiography.
Electrophysiology Laboratory.
Review of Basic Automatic
Brightness Controlled Fluoroscopy
Systems.
And
Some historical overview.
The “Legacy” Fluoroscopy
1) Compartment for full size cassettes,
2) Either Conventional or Pedestal type examination table,
3) Image Intensifier,
a) Input Phosphor, and Output Phosphor.
b) Image intensifier is an Electron Optical Device.
c) Optical Distributor mounted on I.I. to accommodate
Cameras, i.e.;
• Photospot (photofluorographic) Camera,
• Cine (cinematographic) Camera, and
• Closed Circuit Television Camera
TV Camera
TV Camera
100 mm
Photo Spot
Camera
Optical
Distributer
Image Intensifier Tower
35 mm
Cine
Camera
Optical
Distributer
100 mm
Photo Spot
Camera
Image
Intensifier
Image
Intensifier
Cassette
Compartment
Four way floating tabletop / Stepping capable
Four way motorized tabletop
15/90 Tilting
Examination Table
Typical Upper and Lower GI Fluoroscopy Equipment .
C-arm connection
Examination
Pedestal
X-ray Tube Assembly
1
Up to this point may be considered
“Legacy Fluoroscopy” Equipment.
• Irrespective of the geometrical
configuration, the fluoroscopy is equipped
with “Automatic Brightness Control” (ABC)
circuit.
• The TV chain is equipped with “Automatic
Gain Control” (AGC).
• The primary imaging parameter may be
“tube potential”, “tube current”, or “pulse
width” for pulsed fluoroscopy.
Mechanical Structure for
Mounting on the C-Arm
Flat Panel Image Detector
Four way floating tabletop / Stepping capable
C-arm connection
Examination
Pedestal
X-ray Tube Assembly
Internal Structure of Image Intensifier
Input Phosphor (-)
Input Phosphor
Output Phosphor
Thin Aluminum Layer
Fluorescent Screen
Aluminum Substrate
Fluorescent Screen
Photocathode
Output Phosphor
X-ray Photons
Electrons
Electrons
Light Photons
Electron Flux
Anode (+)
Electrode (Focusing)
Image Intensifier Tube
Total Brightness Gain of Image
Intensified Fluorocopy System
“Gains” of Image Intensifier
Brightness Gain =
Intensifier Luminance
Patterson B-2 Luminance
Luminance (cd/m2)
Conversion Factor = Radiation Input (mR/sec)
Minification Gain =
Input Phosphor
Output Phosphor
(a) Fluorescent screens are made of Cesium Iodide (CsI) which has a
higher absorption of X-rays than the older silver-activated zinccadmium sulfide.
(b) Photocathode is a photoemissive metal; a combination of antimony
and cesium.
2
Flux Gain: Electrons are accelerated (~30kV)
Typical flux gain values; 50~60
For a 9” mode image intensifier with
1” output phosphor, the minification
gain is (9/1)X(9/1)=81.
The Flux gain is approximately ~50.
Therefore, the total brightness gain is
= 81 X 50 = 4050.
2
GE Detector Design
• The flat panel image detector
technology as a whole (at a minimum)
will have to; (1) have a similar
electronic gain in order to maintain
the input sensitivity enjoyed by the
image intensifier television chain, (2)
hence, a comparable input sensitivity
to maintain the same patient
exposure.
Contact Leads
For Read-Out
Electronics
Contact Fingers
Glass Substrate
Scintillator
(CsI)
Opticlad Reflector
Amorphous
Silicon Array
Graphite Cover
Scintillator
Epoxy Seal
aSi Array
Glass
Substrate
Courtesy of General Electric Heath Care Systems, Inc.
Basic GE Detector Physics
Basic GE Detector Physics
X-Ray Photons
X-Ray Photons
Cesium Iodide (CsI)
X-ray absorption
Cesium Iodide (CsI)
Light
Light emission
Amorphous Silicon Panel
(Photodiode/Transistor Array)
Electrons
Read Out Electronics
Light absorption
Electron-hole generation
Conversion to digital signal
Digital Data
IQ, fast readout, low noise, no significant image retention
Courtesy of General Electric Health Care Systems, Inc.
Automatic Brightness Control
•
There are there primary imaging
parameters that may be employed to
drive the ABC circuit, namely;
1) The tube potential “kVp”,
2) The tube current “mA”, or
3) The exposure time, more accurately;
“pulse width” for a pulsed fluoroscopy
system.
DETECTOR
DETECTOR
Light
Amorphous Silicon Panel
(Photodiode/Transistor Array)
Electrons
Read Out Electronics
Cesium iodide scintillator absorbs
X-Ray photons and converts them
to light
Low-noise photodiode array absorbs
light and converts it into an electronic
charge... Each photodiode represents
a pixel or picture element...
Charge at each pixel is read out by
low- noise electronics and turned into
digital data sent to an image processor
Digital Data
IQ, fast readout, low noise, no significant image retention
Courtesy of General Electric Health Care Systems, Inc.
• System (3), “Exposure Time system”
is similar to the radiographic
automatic exposure control (AEC), it
“phototimes” each fluorscopic pulse.
• Usually, the tube potential and tube
current are manually selected.
• This method of brightness control
has long been retired, and will not
be discussed further.
3
TV Camera
Let us go through the operation logic of a “kVp-primary” fluoroscopic ABC, as the
one shown here in this slide. (a) Suppose, the x-ray tube potential and current
are adjusted properly for a given steady situation.
Optical Distributer
TV Camera Amplifier
Video Amplifier
Optical Sensor
kVp-primary ABC Circuit
Image
Intensifier
Photomultiplier
Amplifier
TV Monitor
Reference
Voltage
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Automatic Gain
Control
Voltage Comparator
Lock-in Memory
"kVp" Control Module
"mA" Control Module
X-ray Tube Characteristic Table
Generator Characteristic Table
Generator
Power Train
X-ray Tube
Adapted from Reference #1
Optical Distributer
TV Camera Amplifier
Video Amplifier
Optical Sensor
Image
Intensifier
Photomultiplier
Amplifier
(d) The “mA-control module” receives a signal from the “kVp-control Module”, and will increase
the tube current in accordance to a preprogrammed value based on the “fluoroscopy loading
curve”. (e) As the x-ray tube current rises, the required increase in tube potential is reduced to
perhaps 5 kVp, rather than 10 kVp.
TV Camera
TV Camera
(b) Assume that a patient has swallowed a large amount of barium meal. Therefore, a sudden
increase in x-ray absorption had occurred. (c) The voltage comparator detects that a
decrease in voltage from the photomultiplier amplifier. A signal is sent to the “kVp-control
Module” to increase the tube potential by 10 kVp. [If the current remained the same.]
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Automatic Gain
Control
TV Camera Amplifier
Video Amplifier
Optical Sensor
TV Monitor
Reference
Voltage
Optical Distributer
Image
Intensifier
Photomultiplier
Amplifier
TV Monitor
Reference
Voltage
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Automatic Gain
Control
Voltage Comparator
Lock-in Memory
Voltage Comparator
Lock-in Memory
"kVp" Control Module
"mA" Control Module
"kVp" Control Module
"mA" Control Module
X-ray Tube Characteristic Table
X-ray Tube Characteristic Table
Generator Characteristic Table
Generator Characteristic Table
Generator
Power Train
X-ray Tube
Generator
Power Train
X-ray Tube
Adapted from Reference #1
Optical Distributer
TV Camera Amplifier
Video Amplifier
Optical Sensor
Image
Intensifier
X-ray Tube
Photomultiplier
Amplifier
(h) During this transition time, the TV monitor image brightness is maintained to a
constant by the Automatic Gain Control in the video chain. The reaction time of the AGC
is approximately 40~60 mSec. This short reaction time of the AGC circuit essentially
ensures a constant brightness level is presented to the human eyes.
TV Camera
TV Camera
(f) A newly established steady state is then presented to the output phosphor of the
image intensifier with a constant brightness again. (g) This whole process may take
somewhere around 1 to 2 seconds.
Adapted from Reference #1
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Automatic Gain
Control
TV Camera Amplifier
Video Amplifier
Optical Sensor
TV Monitor
Reference
Voltage
Optical Distributer
Image
Intensifier
Photomultiplier
Amplifier
TV Monitor
Reference
Voltage
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Automatic Gain
Control
Voltage Comparator
Lock-in Memory
Voltage Comparator
Lock-in Memory
"kVp" Control Module
"mA" Control Module
"kVp" Control Module
"mA" Control Module
X-ray Tube Characteristic Table
X-ray Tube Characteristic Table
Generator Characteristic Table
Generator Characteristic Table
Generator
Power Train
X-ray Tube
Adapted from Reference #1
Generator
Power Train
Adapted from Reference #1
4
TV Camera
Let us go through the operation logic of a “mA-primary” fluoroscopic ABC, as the
one shown here in this slide. (a) Suppose, the x-ray tube potential and current
are adjusted properly for a given steady situation.
Optical Distributer
TV Camera Amplifier
Video Amplifier
Optical Sensor
mA-primary ABC Circuit
Image
Intensifier
Photomultiplier
Amplifier
TV Monitor
Reference
Voltage
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m
a
C
V
T
S
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ln
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P
m
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ck-iA
lL
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m
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Automatic Gain
Control
Voltage Comparator
Lock-in Memory
"mA" Control Module
"kVp" Control Module
X-ray Tube Characteristic Table
Generator Characteristic Table
Generator
Power Train
X-ray Tube
Adapted from Reference #1
Irrespective of the image receptor system, i.e., whether the image receptor is an
image intensifier or a flat panel image detector, the subject of discussion does
not change. The primary theme of this presentation is on the Automatic
Brightness Control, or the updated version, called Automatic Dose Rate Control
(ADRC) Logic which is available and installed on either of these image receptors.
Optical
Distributer
TV Camera
100 mm
Photo Spot
Camera
35 mm
Cine
Camera
Image
Intensifier
Flat Panel Detector
Ionization Chamber #2
Ionization Chamber #2
PMMA Phantom
PMMA Phantom
38 cm
38 cm
Ionization Chamber #1
2.07 in
Ionization Chamber #1
2.07 in
Examination Tabletop
Examination Tabletop
SID= 110 cm
SID= 110 cm
X-ray Tube Assembly
X-ray Tube Assembly
TV Camera
Evaluation of the characteristics of an
ABC controlled “legacy” fluoroscopy
system.
Fluoroscopic Parameters (Normal Level)
Optical
Distributer
38 cm
Ionization Chamber #2
PMMA Phantom
Or, Copper Sheets
Ionization Chamber #1
3.97 in
Examination Tabletop
SID= 110 cm
X-ray Tube Assembly
The phantom material may have been
(1) aluminum, (2) copper, and (3) PMMA
Plastic. Pressed wood had also been
Employed without consistent results.
The accuracy of the fluoroscopic “kVp” &
“mA” should be assessed with appropriate
measurement devices so that the “power
Loading” can be correctly calculated.
110
Tube Potential (kVp)
1.31 in
Image
Intensifier
The geometry of experimental arrangement
Is not critical as long as “clinical” situation
Is simulated.
3.5
120
3.0
Tube Potential
100
2.5
Tube Current
90
2.0
80
1.5
70
Tube Current (mA)
• A few slides ago, it was mentioned that the
“mA-control module” receives a signal
from the “kVp-control Module”, and will
increase the tube current in accordance to
a preprogrammed value based on the
“fluoroscopy loading curve”.
• The fluoroscopy loading curve is at the
heart of the ABC, and verification and/or
evaluation of fluoroscopy ABC logic can
be obtained through a simple experimental
setup.
1.0
60
0.5
50
40
0.0
0
1
2
3
4
5
6
7
8
9
10
11
Nominal PMMA Phantom Thickness (inches)
5
These two fluoroscopy loading curves can be compared to verify the system
operation against the manufacturer supplied Technical Data Sheets.
Power Loading Rate
350
Fluoroscopy Loading Curves
3.5
Power Loading
Fluoroscopy Curve, Normal Level
3.0
250
Fluoroscopy Curve, High Level
Tube Current (mA)
Power Loading Rate (W/sec)
300
200
150
100
50
2.5
2.0
1.5
1.0
0.5
0.0
0
0
2
4
6
8
10
12
40
50
Nominal PMMA Phantom Thickness (inches)
The image intensifier input exposure rate (air kerma rate) beyond the 10” phantom
thickness will starts to fall down due to the ABC Logic that limits generator to 110
kVp/3.0 mA
Patient Entrance Exposure Rate
130
7
Image Intensifier Input Exposure Rate
120
6
110
5
100
4
90
3
80
2
70
1
60
0
50
0
•
2
4
6
8
Nominal PMMA Phantom Thickness (inches)
Image Intensifier Input Exposure
Rate (μ R/sec)
Patienn Entrance Exposure Rate
(R/min)
140
8
70
80
90
Tube Potential (kVp)
120
10
TV Camera
The Philips Eleva System evaluated in this
study was equipped with the following
features;
Evaluation of the characteristics of an
ABC controlled “legacy” fluoroscopy
system.
Optical
Distributer
a) 17/25/31 cm active phosphor sizes. (3)
Image
Intensifier
2) Fluoroscopy Operation:
1.31 in
a) Continuous Fluoroscopy Mode. (2)
b) Pulsed Fluoroscopy Mode. (2)
c) Low Dose Level & High Dose Level Modes. (2)
38 cm
3) Anti-scatter Grid may be removed.(2)
•
110
• Let us conduct the same test on a typical
“Upper/Lower GI” Study fluoroscopy
system (Philips Eleva System).
• With Phantom Materials of; Copper and
Aluminum.
• Compare the data to find out what
thickness aluminum is equivalent to what
thickness of copper.
The geometry of experimental arrangement
Is not critical as long as “clinical” situation
Is simulated.
1) Image Intensifier Format: Tri mode I.I.
The permutation of available modes under
fluoroscopic operation configuration ~ 48
Not all available modes of combination were
evaluated.
Ionization Chamber #2
PMMA Phantom
Or, Copper Sheets
Ionization Chamber #1
Examination Tabletop
3.97 in
•
100
PART II.
Evaluation of ABC Logic
Exposure Rate vs. PMMA Phantom Thickness
9
60
SID= 110 cm
The phantom material may have been
(1) aluminum, (2) copper, and (3) PMMA
Plastic. Pressed wood had also been
Employed without consistent results.
The accuracy of the fluoroscopic “kVp” &
“mA” should be assessed with appropriate
measurement devices so that the “power
Loading” can be correctly calculated.
X-ray Tube Assembly
6
These graphs show that (1) the “Low Level” modes employ lower “kVp” than the “Normal
Level” modes. And, the larger the active phosphor size employs lower “kVp” than smaller
active phosphor sizes, (2) at the same time the larger active phosphor size with “Lower Level”
fluoroscopy has a wider dynamic range in coverring the patient (phantom) thickness.
The x-ray current graphs show similar trends as that of the previous slide on “kVp”.
Tube Currentl vs. Phantom Thickness
4.0
Tube Potential vs. Phantom Thickness
120
T u b e C u r r en t (m A )
T ube P otential (k V p)
110
100
90
80
17 cm Mode, (N)
25 cm Mode, (N)
31 cm Mode, (N)
17 cm Mode, (L)
25 cm Mode, (L)
31 cm Mode, (L)
70
60
50
3.0
2.0
17 cm Mode, mA (N)
25 cm Mode, mA (N)
31 cm Mode, mA (N)
17 cm Mode, mA (L)
25 cm Mode, mA (L)
31 cm Mode, mA (L)
1.0
0.0
0
40
0
2
4
6
8
10
12
14
2
4
6
8
10
12
14
16
Nominal PMMA Phantom Thickness (inches)
16
Nominal PMMA Phantom Thickness (inches)
Low level IIIAKR is approximately 0.7~0.75 μGy/sec, and the Normal level IIIAKR
is 1.1 μGy/sec for the 31 cm active phosphor size, and 1.25 microGy/sec, and 1.35
μGy/sec for the 25 cm and 17 cm active phosphor sizes, respectively.
Image Intensifier Input Air Kerma Rate vs. Phantom Thickness
With Anti-scatter "Grid-".in
3.0
Air Kerma Rate
80
2.0
cm Mode,
cm Mode,
cm Mode,
cm Mode,
cm Mode,
cm Mode,
(N)
(N)
(N)
(L)
(L)
(L)
70
17
25
31
17
25
31
60
Air Kerma Rate (mGy/min)
17
25
31
17
25
31
2.5
(μGy/sec)
Image Intensifier Input Air Kerma Rate
The “Air Kerma Rate” graphs show and confirm the same trends described in previous
slides. Essentially, this fluoroscopy system is able to penetrate 10” to 14” of PMMA
equivalent patient thickness depending on the mode of operation. This is typical of
fluoroscopy systems employed for upper/lower GI studies.
1.5
1.0
0.5
0.0
50
40
cm Mode
cm Mode
cm Mode
cm Mode
cm Mode
cm Mode
(N)
(N)
(N)
(L)
(L)
(L)
30
20
10
0
0
2
4
6
8
10
12
14
16
0
Nominal Phantom Thickness (inches)
2
4
6
8
10
12
Nominal Phantom Thickness (inches)
14
16
Fluoroscopy Loading Curve
Phantom Thickness Equivalence
4.0
100
3.5
Air Kerma Rate (mGy/min)
3.0
Tube Current (mA)
90
Aluminum Phantom
Copper Phantom
PMMA Phantom
2.5
2.0
1.5
Aluminum
Copper
PMMA
80
70
60
50
40
30
20
10
1.0
0
0
0.5
10
20
30
40
50
60
70
80
Phantom Thickness (mm for Al, X0.1 mm for Cu, "inches" divide by 6 for PMMA)
90
0.0
40
50
60
70
80
90
Tube Potential (kVp)
100
110
120
7
“mA-primary” ABC Logic
Aluminum
(mm)
Aluminum
(inches)
PMMA
(inches)
3.67
[3-3/4]
5-1/2
10
0.8
19
3/4
20
1.6
38
1-1/2
40
3.2
80
58
5.6
76
3
• A GE Advantx fluoroscopy system is equipped
with the “mA-primary” ABC Logic.
• The tube potential may be pre-selected, and
defaulted to 75 kVp for fluoroscopy operation.
This is the minimum “kVp” unless the “kVp” is
manually selected at a lower value.
• The tube potential is increased by a preset value
(5, or 10 kVp) when the Patient Air Kerma Rate
approaches the regulatory limitation.
• The system is calibrated to work at a given “kVp”
while the “mA” is varied in accordance to the
attenuation the optical sensor “sees”.
TV Camera Amplifier
Video Amplifier
Optical Sensor
Photomultiplier
Amplifier
Image
Intensifier
7.3
[7-1/2]
9.3
[9-1/2]
2-1/4
Optical Distributer
TV Monitor
Reference
Voltage
Automatic Gain
Control
Voltage Comparator
Lock-in Memory
"mA" Control Module
"kVp" Control Module
X-ray Tube Characteristic Table
Generator Characteristic Table
Generator
Power Train
X-ray Tube
The same set of data obtained on the Philips System is also obtained. This
slide shows the Tube Potential and Tube Current as functions of the PMMA
Phantom Thickness. NOTE: the default “kVp” values for the 60 kVp, and
the 75 kVp are represented here.
Fluoroscopic Parameters (With Grid)
9
130
120
8
Tube Potential (60)
Tube Potential (75)
Tube Current (60)
Tube Current (75)
110
100
7
6
90
5
80
4
70
3
60
2
50
1
0
40
0
Note: This is a 10 year old system and the IIIAKR has been increased to account for
the decreased image intensifier efficiency. At the 6” of phantom thickness, there is a
singular point that corresponds to a jump in Tube Potential.
Tube Current (mA)
(mGy/min)
Copper
(mm)
Tube Potential (kVp)
Air Kerma
Rate
TV Camera
Thickness Equivalence (Philips Eleva System)
2
4
6
8
10
Nominal PMMA Phantom Thickness (inches)
12
14
The phantom thickness equivalence graphs are charted on this slide. The points of
discontinuity correspond to the phantom thickness that triggered the generator to
increase the tube potential.
Phantom Thickness Equivalence
Air Kerma Rate vs. Phantom Thickness
100
10.0
100
70
8.0
7.0
Air Kerma Rate (mGy/min)
80
80
70
60
60
6.0
50
5.0
40
4.0
30
3.0
20
2.0
10
1.0
10
0
0.0
0
0
2
4
6
8
10
Nominal PMMA Phantom Thickness
12
14
Aluminum
Copper
PMMA
90
9.0
PAKR (60)
PAKR (75)
IIIAKR (60)
IIIAKR (75)
Image Intensifier Input Air Kerma
Rate (μGy/sec)
Air Kerma Rate (mGy/min)
90
50
40
30
20
0
10
20
30
40
50
60
70
80
90
Phantom Thickness (mm for Al, X 0.1 mm for Cu, divide by 6 "inches" for PMMA)
8
This chart may be used to convert the phantom thickness from one material to
another, amongst copper, aluminum, and PMMA plastic.
Philip
Eleva
GE
Advantx
Cu
(mm)
Al
(mm)
Al
(inches)
Al
(mm)
Al
(inches)
0.8
19
0.75
22
0.87
3.65
2.5
1.6
38
1.5
36
1.42
5.5
4.3
3.2
58
2.25
68
2.7
7.3
7.3
5.6
76
3
82
3.2
9.3
9
Thickness Equivalence (Fussed)
PMMA (inches)
10
5
8
4
6
3
4
2
PMMA
Aluminum
2
1
Linear (PMMA)
Linear (Aluminum)
0
Aluminum Thickness (inches)
GE Advantx
PMMA Thickness (inches)
Philip Eleva
0
0
1
2
3
4
5
6
7
Copper Thickness (mm)
PART III.
The ADRC; new generation of ABC
•
•
•
•
Application of filters using aluminum, copper and high atomic
number elements for patient exposure reduction had been studied
for use in radiographic examinations.
On the other hand, the introduction of copper filters for spectral
shaping during fluoroscopic imaging procedures had been available
for the past decade,
However, extensive application of spectral shaping filters started in
its earnest as the interventional angiography procedures become
widely practiced in the US in the early 1990s.
Use of spectral shaping filters contributed to minimize the patient
(skin entrance exposure) air kerma dramatically while the image
quality is optimized and maintained.
New Generation of Cardiovascular
Fluoroscopy Systems are equipped with;
1) High Frequency Inverter Type Generator
a) Precise switching time ( 1 msec)
b) Better Pulse Shape (less over/under shoot)
2) Spectral Shaping Filters
a) 0.2 ~ 0.9 mm copper (beam hardening)
b) On a rotating wheel in collimator assembly
(interchangeable filters during fluoroscopy)
3) High Heat Capacity X-ray Tube
a) High Anode Heat Capacity (2 MHU)
b) High X-ray Tube Housing Heat Capacity (3 MHU)
c) To counter attenuation by spectral shaping filter
Excerpt from Reference #2
Automatic Dose Rate Control (ADRC) Logic
Automatic Dose Rate Control (ADRC) Logic
(a) A sophisticated software programming to control the
copper filter thickness in response to x-ray attenuation.
(a) The fluoroscopy system employed is a Siemens Biplane angiography system AXIOM Artis dBA.
(b) The ADRC is designed to control various imaging
parameters including; (1) focal spot size, (2) kVp, (3)
mA, (4) pulse width, etc. during fluoroscopy.
(b) Operated under 22 cm flat panel image receptor
mode. [It is a 48 cm flat panel.]
(c) The heavy copper filter preferentially removed low
energy photons and the mean x-ray beam energy is,
thus, increased.
(d) For the same applied tube potential this would require
a higher “tube current” to produce an acceptable image
quality. --- Hence, a “high power” x-ray tube is
required.
(c) Pulsed fluoroscopy rate @ 15 pulses/sec.
(d) Fluoroscopy curve name: 80kV10RAF2kW
(e) Equipped with spectral shaping filters of; 0.2, 03, 0.6,
and 0.9 mm of copper.
(f) The small focal spot (0.6 mm) is the default.
(g) SID = 105 cm, Source-to-chamber #1 = 60 cm.
9
Evaluation of the Automatic Dose Rate
Control (ADRC) Logic
Tube Potential (kVp) and Filter Thickness (mmCu)
vs. PMMA Thickness (inches)
Flat Panel Detector
120
Iso-center
Tube Potential (kVp)
PMMA Phantom
45 cm
Ionization Chamber #1
Examination Tabletop
2.75 in
15 cm
105 cm
Copper Filter (mmCu)
Tube Potential (kVp)
100
1.0
0.8
80
0.6
0.4
0.2
60
X-ray Tube Assembly
Geometrical Arrangement
0
2
Pulse Width (mSec)
60
40
20
6
8
10
12
14
16
14
12
10
8
0
2
4
30 cm
1.0
0.8
80
0.6
0.4
Input Sensitivity
in front of the
Flat Panel Image
Detector
0.2
60
100
80
60
40
20
Patient Skin Dose
(Air Kerma)
16
14
12
10
Input Sensitivity (μGy/sec)
Copper Filter (mmCu)
Tube Potential (kVp)
100
Tube Current (mA)
8
10 cm
Copper Filter (mm)
Tube Potential (kVp)
20 cm
Entrance Exposure rate (mGy/min)
10 cm
120
6
10
12
14
Nominal Phantom Thickness (inches)
Nominal Phantom Thickness (inches)
Pulse Width (mSec)
Tube Current (mA)
80
4
14
Pulse Width (mSec) vs. PMMA Thickness (inches)
100
2
4
6
8
10
12
Nominal Phantom Thickness (inches)
Adapted from Reference #2
Tube Current (mA) vs. PMMA Thickness (inches)
0
Copper Filter (mm)
.95 in
Ionization Chamber #2.
20 cm
30 cm
0.9
0.8
0.7
0.6
100
10
1
8
0.1
0
2
4
6
8
10
12
Nominal Phantom Thickness (inches)
14
0
2
4
6
8
10
12
14
Nominal Phantom Thickness (inches)
10
Why is it possible to have a “Better Image Quality” &
“Lower Patient Dose” at the same time?
• Image quality is “better” because of
consistently lower tube potential is
employed---higher image contrast!
• Radiation dose to the patients, especially,
small and average size patient, is
significantly reduced due to the use of
spectral shaping filters --- considerably
amount of low energy portion of spectrum
is removed before hitting the patient.
• There are many fluoroscopy curves designed by
the manufacturers tailored to fit specific types of
examination.
– Some 256 fluoroscopy curves are available.
– Cardiac vs. Neuro vs. Visceral angiography
– For adults ? Or for pediatric patients?
• Needs to verify the preprogrammed fluoroscopy
curves for the intended use of the system.
• Not only the acceptance testing of the hardware
is necessary, but also evaluation of the software
becomes increasingly important.
Fluoroscopy Curve 70kV10RAF3kW
Fluoroscopy Curve 70kV10RAF3kW
Tube Potential & Copper Filter vs. PMMA Thickness (3 kW)
Pulse Width & Tube Current vs. PMMA Thickness (3kW)
120
0.9
180
0.8
160
Copper Filter
100
0.6
90
0.5
80
0.4
70
0.3
60
0.2
50
T ube C urrent (m A)
0.7
C o p p e r F ilte r ( m m C u )
10
140
120
8
100
80
Tube Current
P ulse Width
0.1
0
2
4
6
8
10
12
14
16
40
18
4
0
2
4
6
PMMA Thickness (inches)
8
10
12
14
16
18
PMMA Thickness (inches)
Data Source: AAPM TG 125
Data Source: AAPM TG 125
Fluoroscopy Curve 70kV10RAF2kW
Fluoroscopy Curve 70kV10RAF2kW
Tube Potential & Copper Filter vs. PMMA Thickness (2 kW)
Tube Current & Pulse Width vs. PMMA Thickness (2 kW)
Tube Potential
0.8
110
Copper Filter
0.7
100
0.6
90
0.5
0.4
80
70
0.3
60
0.2
50
0.1
T ube C urrent (m A)
120
C o p p e r F ilte r ( m m C u )
0.9
130
T u b e P o te n tia l (k V p )
6
60
70
8.0
60
7.0
50
6.0
40
5.0
30
4.0
Tube Current
20
P u ls e W id th ( m s )
T u b e P o te n tia l ( k V p )
Tube Potential
110
12
P u ls e W id th ( m S e c )
130
3.0
Pulse Width (mSec)
0
2
4
6
8
10
12
14
10
2.0
0
2
4
6
8
10
12
14
PMMA Thickness (inches)
PMMA Thickness (inches)
Data Source: AAPM TG 125
Data Source: AAPM TG 125
11
Fluoroscopy Curve 70kV10RAF2kW (Pediatric)
Fluoroscopy Curve 70kV10RAF2kW (Pediatric)
Tube Potential & Copper Filter vs. PMMA Thickness (2 kW)
130
1
Tube Current & Pulse Width vs. PMMA Thickness (2 kW)
70
120
10
0.9
Tube Potential (kVp)
90
0.6
80
0.5
70
0.4
60
0.3
8
50
7
40
6
30
5
Tube Current (mA)
Pulse Width (ms)
20
50
Pulse Width (ms)
0.7
Tube Current (mA)
100
9
60
0.8
Copper Filter (mmCu)
Copper Thickness (mmCu
Tube Potential (kVp)
110
4
0.2
40
10
0.1
0
2
4
6
8
10
3
0
12
2
4
6
8
PMMA Thickness (inches)
PMMA Thickness (inches)
• The fluoroscopy is employed to find the passage
and manipulate the catheter and/or the guide
wire to the point of interests.
• The mission of the ADRC for fluoroscopy may
be accomplished but is just the starting point for
the acquisition of diagnostic information.
• In other words, the “acquisition mode” of the
examination, as opposed to the “fluoroscopic
mode” lies ahead.
TV Camera
What’s beyond the ADRC Logic?
12
Data Source: AAPM TG 125
Optical Distributer
Data Source: AAPM TG 125
10
TV Camera Amplifier
Video Amplifier
TV Monitor
Automatic Gain
Control
Cine Camera Control &
Synchronization Control
Lock-in Memory
Cine Camera Filming
Rate Selector
Image
Intensifier
Photomultiplier
Amplifier
Reference
Voltage
Focal Spot Size
Selector
Voltage Comparator
Pulse Width Selector
"kVp" Control Module
"mA" Control Module
Cine Run Time
Selector
Pulse Width Control
Module
Controller Block A
Power Rating Check
X-ray Tube
Anode Heat Sensor
Generator
Anode Heat capacity
Pre-exposure Calculator
Duty Cycle Compensation
Overload Protection
X-ray Tube Characteristic Table
Generator Characteristic Table
Controller Block B
Comparison of Patient Exposure/Air Kerma Rate
Comparison of Input Sensitivities
23/2 5 c m Im a ge In tens ifie r Inp u t Pho sp ho r (Ac tive ) S ize
Cu rr en t P r ac tice
Lo w Le ve l F luo r osc opy
No r m a l L ev e l F luo ros co py
2 5 μ R/s e c
5 0 μ R/s e c
23/25 cm Image Intensifier, Patient Exposure Rate
Current Practice
Used To Be
5 0 μ R/s e c
Low Level Fluoroscopy
> 1 R/min
3 R/min
7 5 -100 μ R/s e c
Normal Level Fluoroscopy
3 R/min
6 R/min
Us ed T o B e
Hig h Lev e l F lu oro sc opy
7 5 μ R/s e c
N/A
High Level Fluoroscopy
5 R/min
N/A
10 0 m m P ho to sp o t Ca m er a
5 0 -1 00 μ R/fr a m e
1 0 0 -2 00 μ R/fr a m e
100 mm Photospot Camera
100 mR/frame
200 mR/frame
1 00 μ R/fr a m e
Digital Photofluorography
75~100 mR/frame
200 mR/frame
Digital Subtraction
Angiography
100~300 mR/frame
500 mR/frame
35 mm Cine Camera
30~80 R/min
70~160 R/min
Digital Cine
Photofluorography
20~60 R/min
N/A
D ig ita l P ho to fluo r og r aphy
25 -10 0 μ R/fr a m e
D ig ita l Su b tr ac tion
An g iog r aphy
1 0 0 -5 00 μ R/fr a m e
3 5 m m C in e Ca m er a
1 0 -2 0 μ R/fr a m e
1 5-3 0 μ R/fr a m e
D ig ita l C in e
Ph o to flu or o gra phy
7 -12 μ R/fr a m e
N/A
50 0 -1 00 0 μ R/fr a m
Due primarily to the better image intensifier, television chain.
Data Date: 2001
Due primarily to the better image intensifier & television chain.
Data Date: 2001
12
We have come a long way from this!
References & Other Reading Material
1.
2.
3.
4.
PP Lin, “Acceptance testing of automatic exposure
control systems and automatic brightness stabilized
fluoroscopic equipment”, in Quality Assurance in
Diagnostic Radiology, AAPM Monograph No. 4, New
York: Am. Inst. Phys., pp 10-27 (1980)
PP Lin, “The operation logic of automatic dose control
of fluoroscopy systems in conjunction with spectral
shaping filters”, Med. Phys. Vol 34 no 8, pp 3169-3172
(2007)
PP Lin, “Cine and Photospot Cameras”, in
Encyclopedia of Medical Devices and Instrumentation,
John G. Webster Editor, John Wiley & Son, Publisher,
1st Edition, Vol. 2, pp 681-693 (1988)
AAPM TG 125 Home Page.
E-mail Address: plin@bidmc.harvard.edu
Photo: Courtesy of Siemens Medical Systems
13