pei-jan paul lin department of radiology beth israel deaconess medical center and

Technical Advances of Fluoroscopy with Special Interests in Automatic Dose Rate Control (ADRC) Logic of Cardiovascular

Angiography Systems(Modified For MCAAPM Meeting, November 2007)

Pei-Jan Paul LinDepartment of Radiology

Beth Israel Deaconess Medical Centerand

Harvard Medical SchoolBoston, MA 02215

Beth Israel Deaconess Medical center Harvard Medical School

PART I-(a).

Review of Basic Automatic Brightness Controlled Fluoroscopy

Systems.

And

Some historical overview.

Review of Fluoroscopy Equipment

1) Conventional Fluoroscopy Unit2) 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 fora) Cardiac Catheterization.b) Neuro Angiography.c) Visceral Angiography.d) Electrophysiology Laboratory.

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

Typical Upper and Lower GI Fluoroscopy Equipment .

100 mmPhoto Spot Camera

TV Camera

ImageIntensifier

OpticalDistributer

Cassette Compartment

Image Intensifier Tower

15/90, 30/90, 90/90 Tilting Examination Table

Four way motorized tabletop

35 mm CineCamera


TV Camera

ImageIntensifier

OpticalDistributer

Examination Pedestal

X-ray Tube Assembly

Four way floating tabletop / Stepping capable

C-arm connection

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.

Examination Pedestal

X-ray Tube Assembly

Flat Panel Image Detector

Mechanical Structure forMounting on the C-Arm

C-arm connection

Four way floating tabletop / Stepping capable

“Gains” of Image Intensifier

Brightness Gain = Intensifier LuminancePatterson B-2 Luminance

Conversion Factor =Luminance (cd/m2)

Radiation Input (mR/sec)

Minification Gain =Input PhosphorOutput Phosphor

2

Flux Gain: Electrons are accelerated (~30kV) Typical flux gain values; 50~60

Total Brightness Gain of Image Intensified Fluorocopy System

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.

• 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.

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.

4) Or, combinations of (1) through (3).

• System (3), “Exposure Time system” is similar to the radiographic automatic exposure control (AEC), it “phototimes” each fluoroscopic 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.

PART II-(b).

kVp-primary ABC Circuit

TV Camera

ImageIntensifierOptical Sensor,Photomultiplier.

X-ray Tube

PatientTabletopCollimatorHigh Tension Cable

TV Video Signal TrainTV CameraPre-amplifier TV Monitor VideoAmplifierPhotomultiplierAmprefier Reference VoltageVoltage Comparator Automatic Gain Control Lock-in Memory kVp- Controller mA-ControllerlGenerator Control Panel/Interface LogicHigh Tension TransformerSchematic Block Diagram of kVp-primary Automatic Brightness Control Fluoroscopy System

ImageIntensifier

TV Camera Amplifier

Video AmplifierTV Monitor

Photomultiplier Amplifier

Voltage Comparator

TV

Ca

me

raOptical Distributer

Reference Voltage

Automatic Gain Control

Lock-in Memory

"kVp" Control Module "mA" Control Module

X-ray Tube Characteristic Table

Generator Characteristic Table

Generator Power TrainX-ray Tube

Optical Sensor

Adapted from Reference #1

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.

TV Camera


X-ray Tube




(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.]

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me

ra

Optical Distributer

Reference Voltage


Lock-in Memory





Optical Sensor

TV Camera


X-ray Tube




(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.

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me


Reference Voltage


Lock-in Memory





Optical Sensor

TV Camera


X-ray Tube




(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.

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me


Reference Voltage


Lock-in Memory





Optical Sensor

TV Camera


X-ray Tube




(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.

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me


Reference Voltage


Lock-in Memory





Optical Sensor

PART II-(c).

mA-primary ABC Circuit

TV Camera


X-ray Tube



ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me


Reference Voltage


Lock-in Memory

"mA" Control Module "kVp" Control Module




Optical Sensor


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.

• 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.

PMMA Phantom

Ionization Chamber #1

Examination Tabletop

X-ray Tube Assembly

2.07

inSID= 110 cm


35 mm CineCamera


TV Camera

ImageIntensifier

OpticalDistributer

Flat Panel Detector

PMMA Phantom



X-ray Tube Assembly

2.07

in

SID= 110 cm


38 cm 38 cm

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.

PMMA PhantomOr, Copper Sheets



X-ray Tube Assembly

3.9

7 in

1.3

1 in

SID= 110 cm

38 cm


TV Camera

ImageIntensifier

OpticalDistributer

The geometry of experimental arrangementIs not critical as long as “clinical” situationIs simulated.

The phantom material may have been(1) aluminum, (2) copper, and (3) PMMAPlastic. Pressed wood had also been Employed without consistent results.

The accuracy of the fluoroscopic “kVp” &“mA” should be assessed with appropriatemeasurement devices so that the “power Loading” can be correctly calculated.

Evaluation of the characteristics of anABC controlled “legacy” fluoroscopy system.

Fluoroscopic Parameters (Normal Level)

40

50

60

70

80

90

100

110

120

0 1 2 3 4 5 6 7 8 9 10 11

Nominal PMMA Phantom Thickness (inches)

Tube P

ote

ntial (k

Vp)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Tu

be

Cu

rre

nt

(mA

)

Tube Potential

Tube Current

Power Loading Rate

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12


Po

we

r L

oa

din

g R

ate

(W

/se

c)

Power LoadingRate

Fluoroscopy Loading Curves

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

40 50 60 70 80 90 100 110 120Tube Potential (kVp)

Tub

e C

urre

nt (

mA

)

Fluoroscopy Curve, Normal Level

Fluoroscopy Curve, High Level

These two fluoroscopy loading curves can be compared to verify the system operation against the manufacturer supplied Technical Data Sheets.

Exposure Rate vs. PMMA Phantom Thickness

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10


Pa

tien

n E

ntr

an

ce E

xpo

sure

Ra

te

(R/m

in)

50

60

70

80

90

100

110

120

130

140

Ima

ge

Inte

nsi

fier

Inp

ut E

xpo

sure

R

ate

(mR

/se

c)

Patient Entrance Exposure Rate

Image Intensifier Input Exposure Rate

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

• Let us conduct the same test on a typical “Upper/Lower GI” Study fluoroscopy system (Philips Eleva System).

• With Phantom Materials of; PMMA Plastic, Copper and Aluminum.

• Compare the data to find out what thickness aluminum is equivalent to what thickness of copper.

• NOTE: PMMA Plastic phantom data will be employed as the “standard” since it is more “tissue equivalent than aluminum or copper.

PART II.Evaluation of ABC Logic

• The Philips Eleva System evaluated in this study was equipped with the following features;

1) Image Intensifier Format: Tri mode I.I.a) 17/25/31 cm active phosphor sizes. (3)

2) Fluoroscopy Operation:a) Continuous Fluoroscopy Mode. (2)

b) Pulsed Fluoroscopy Mode. (2)

c) Low Dose Level & High Dose Level Modes. (2)

3) Anti-scatter Grid may be removed.(2)

• The permutation of available modes under fluoroscopic operation configuration ~ 48

• Not all available modes of combination were evaluated.

PMMA PhantomOr, Copper Sheets



X-ray Tube Assembly

3.9

7 in

1.3

1 in

SID= 110 cm

38 cm


TV Camera

ImageIntensifier

OpticalDistributer

The geometry of experimental arrangementIs not critical as long as “clinical” situationIs simulated.

The phantom material may have been(1) aluminum, (2) copper, and (3) PMMAPlastic. Pressed wood had also been Employed without consistent results.

The accuracy of the fluoroscopic “kVp” &“mA” should be assessed with appropriatemeasurement devices so that the “power Loading” can be correctly calculated.

Evaluation of the characteristics of anABC controlled “legacy” fluoroscopy system.

Tube Potential vs. Phantom Thickness

40

50

60

70

80

90

100

110

120

0 2 4 6 8 10 12 14 16


Tube

Pot

entia

l (kV

p)

17 cm Mode, (N)

25 cm Mode, (N)

31 cm Mode, (N)

17 cm Mode, (L)

25 cm Mode, (L)

31 cm Mode, (L)

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.

Tube Currentl vs. Phantom Thickness

0.0

1.0

2.0

3.0

4.0

0 2 4 6 8 10 12 14 16


Tube

Cur

rent

(mA)

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)

The x-ray current graphs show similar trends as that of the previous slide on “kVp”.

Image Intensifier Input Air Kerma Rate vs. Phantom ThicknessWith Anti-scatter "Grid-".in

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 2 4 6 8 10 12 14 16

Nominal Phantom Thickness (inches)

Ima

ge

In

ten

sifie

r In

pu

t A

ir K

erm

a R

ate

(mG

y/s

ec)

17 cm Mode, (N)

25 cm Mode, (N)

31 cm Mode, (N)

17 cm Mode, (L)

25 cm Mode, (L)

31 cm Mode, (L)

Low level IIIAKR is approximately 0.7~0.75 mGy/sec, and the Normal level IIIAKR is 1.1 mGy/sec for the 31 cm active phosphor size, and 1.25 microGy/sec, and 1.35 mGy/sec for the 25 cm and 17 cm active phosphor sizes, respectively.

Air Kerma Rate

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16Nominal Phantom Thickness (inches)

Air

Ke

rma

Ra

te (

mG

y/m

in)

17 cm Mode (N)

25 cm Mode (N)

31 cm Mode (N)

17 cm Mode (L)

25 cm Mode (L)

31 cm Mode (L)

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.

Fluoroscopy Loading Curve

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

40 50 60 70 80 90 100 110 120

Tube Potential (kVp)

Tub

e C

urre

nt (

mA

)

Aluminum PhantomCopper PhantomPMMA Phantom

Phantom Thickness Equivalence

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90

Phantom Thickness (mm for Al, X0.1 mm for Cu, "inches" divide by 6 for PMMA)

Air

Ker

ma

Rat

e (m

Gy/

min

)

Aluminum

Copper

PMMA

Thickness Equivalence (Philips Eleva System)

Air Kerma Rate

(mGy/min)

Copper (mm)

Aluminum (mm)

Aluminum (inches)

PMMA (inches)

10 0.8 19 3/4 3.67[3-3/4]

20 1.6 38 1-1/2 5-1/2

40 3.2 58 2-1/4 7.3[7-1/2]

80 5.6 76 3.0 9.3[9-1/2]

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV

Ca

me


Reference Voltage


Lock-in Memory

"mA" Control Module "kVp" Control Module




Optical Sensor

“mA-primary” ABC Logic

• 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”.

Fluoroscopic Parameters (With Grid)

40

50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12 14Nominal PMMA Phantom Thickness (inches)

Tub

e P

oten

tial (

kVp)

0

1

2

3

4

5

6

7

8

9

Tub

e C

urre

nt (

mA

)

Tube Potential (60)

Tube Potential (75)

Tube Current (60)

Tube Current (75)

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.

Air Kerma Rate vs. Phantom Thickness

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12 14

Nominal PMMA Phantom Thickness

Air

Ker

ma

Rat

e (m

Gy/

min

)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Imag

e In

tens

ifier

Inp

ut A

ir K

erm

a R

ate

(mG

y/se

c)

PAKR (60)

PAKR (75)

IIIAKR (60)

IIIAKR (75)

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.

Phantom Thickness Equivalence

0

10

20

30

40

50

60

70

80

90

100

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)

Air

Ker

ma

Rat

e (m

Gy/

min

)

Aluminum

CopperPMMA

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.

Philip Eleva GE Advantx Philip Eleva

GE Advantx

Cu

(mm)

Al

(mm)

Al

(inches)

Al

(mm)

Al

(inches)

PMMA (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)

0

2

4

6

8

10

0 1 2 3 4 5 6 7Copper Thickness (mm)

PM

MA

Thi

ckne

ss (

inch

es)

0

1

2

3

4

5

Alu

min

um T

hick

ness

(in

ches

)

PMMA

Aluminum

Linear (PMMA)

Linear (Aluminum)

This chart may be used to convert the phantom thickness from one material to another, amongst copper, aluminum, and PMMA plastic.

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.

Excerpt from Reference #2

New Generation of Cardiovascular Fluoroscopy Systems are equipped with;

1) High Frequency Inverter Type Generatora) Precise switching time ( 1 msec)b) Better Pulse Shape (less over/under shoot)

2) Spectral Shaping Filtersa) 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

Automatic Dose Rate Control (ADRC) Logic

(a) A sophisticated software programming to control the copper filter thickness in response to x-ray attenuation.

(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.

(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.

Automatic Dose Rate Control (ADRC) Logic

(a) The fluoroscopy system employed is a Siemens Bi-plane angiography system AXIOM Artis dBA.

(b) Operated under 22 cm flat panel image receptor mode. [It is a 48 cm flat panel.]

(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.

Evaluation of the Automatic Dose Rate Control (ADRC) Logic

Geometrical Arrangement

Flat Panel Detector

PMMA Phantom



X-ray Tube Assembly

2.75

in

.95

in

Ionization Chamber #2.

105 cm

Iso-center

15 cm45 cm


120

100

80

60 0.2

0.4

0.6

0.8

1.0


Copper Filter (mmCu)

Co

pp

er F

ilter (mm

)T

ub

e P

ote

nti

al (

kVp

)

0 2 4 6 8 10 12 14


Tube Potential (kVp) and Filter Thickness (mmCu) vs. PMMA Thickness (inches)

0 2 4 6 8 10 12 14


100

80

60

40

20

Tu

be

Cu

rren

t (m

A)

Tube Current (mA) vs. PMMA Thickness (inches)

0 2 4 6 8 10 12 14


10

12

14

16

8Pu

lse

Wid

th (

mS

ec)

Pulse Width (mSec) vs. PMMA Thickness (inches)

120

100

80

60 0.2

0.4

0.6

0.8

1.0



Co

pp

er Filter (m

m)

Tu

be

Po

ten

tia

l (kV

p)

0 2 4 6 8 10 12 14


100

80

60

40

20

10

12

14

16

Tu

be

Cu

rre

nt

(mA

)

8Pu

lse

Wid

th (

mS

ec)

10 cm 20 cm 30 cm

0.9

0.8

0.7

0.6In

pu

t S

en

sit

ivit

y (m G

y/s

ec

)


0 2 4 6 8 10 12 140.1

1

10

100

En

tra

nc

e E

xp

os

ure

ra

te (

mG

y/m

in)

10 cm 20 cm 30 cm

Input Sensitivity in front of the Flat Panel Image Detector

Patient Skin Dose (Air Kerma)

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.

Tube Potential & Copper Filter vs. PMMA Thickness (3 kW)

50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12 14 16 18

PMMA Thickness (inches)

Tube

Pot

entia

l (kV

p)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Copp

er F

ilter (

mm

Cu)

Tube Potential

Copper Filter

Fluoroscopy Curve 70kV10RAF3kW

Data Source: AAPM TG 125

Pulse Width & Tube Current vs. PMMA Thickness (3kW)

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14 16 18PMMA Thickness (inches)

Tube

Cur

rent

(mA)

4

6

8

10

12

Pulse

Widt

h (m

Sec)

Tube CurrentPulse Width






50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12 14


Tube

Pot

entia

l (kV

p)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Cop

per F

ilter (

mm

Cu)

Tube Potential

Copper Filter



Tube Current & Pulse Width vs. PMMA Thickness (2 kW)

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14


Tube

Cur

rent

(mA)

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Pulse

Widt

h (m

s)

Tube Current

Pulse Width (mSec)

Fluoroscopy Curve 70kV10RAF2kW (Pediatric)



40

50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12


Tu

be

Po

ten

tia

l (k

Vp

)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Co

pp

er

Th

ickn

ess (

mm

Cu

)Tube Potential (kVp)


Fluoroscopy Curve 70kV10RAF2kW (Pediatric)


Tube Current & Pulse Width vs. PMMA Thickness (2 kW)

10

20

30

40

50

60

70

0 2 4 6 8 10 12


Tu

be

Cu

rre

nt

(mA

)

3

4

5

6

7

8

9

10

Pu

lse

Wid

th (

ms)

Tube Current (mA)

Pulse Width (ms)

What’s beyond the ADRC Logic?

• 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.

ImageIntensifier

TV Camera Amplifier Video Amplifier

TV Monitor


Voltage Comparator

TV

Ca

me

ra

Op

tical

Dis

trib

uter

Reference Voltage


Lock-in Memory

"kVp" Control Module

"mA" Control Module

Generator

X-ray Tube

Cine Camera Control &Synchronization Control

Cine Camera Filming Rate Selector

Pulse Width Control Module

Focal Spot Size Selector

Pulse Width Selector

Cine Run Time Selector

Controller Block A

Controller Block B

Power Rating Check

Anode Heat capacityPre-exposure CalculatorDuty Cycle CompensationOverload Protection



Anode Heat Sensor

N/A7-12 mR/frameDigital CinePhotofluorography

15-30 mR/frame10-20 mR/frame35 mm Cine Camera

500-1000 mR/frame100-500 mR/frameDigital SubtractionAngiography

100 mR/frame25-100 mR/frameDigital Photofluorography

100-200 mR/frame 50-100 mR/frame 100 mm Photospot Camera

N/A75 mR/secHigh Level Fluoroscopy

75-100 mR/sec50 mR/secNormal Level Fluoroscopy

50 mR/sec25 mR/secLow Level Fluoroscopy

Used To BeCurrent Practice

23/25 cm Image Intensifier Input Phosphor (Active) Size

Due primarily to the better image intensifier, television chain.

Comparison of Input Sensitivities

Data Date: 2001

N/A20~60 R/minDigital CinePhotofluorography

70~160 R/min30~80 R/min35 mm Cine Camera

500 mR/frame100~300 mR/frameDigital SubtractionAngiography

200 mR/frame75~100 mR/frameDigital Photofluorography

200 mR/frame 100 mR/frame 100 mm Photospot Camera

N/A5 R/minHigh Level Fluoroscopy

6 R/min3 R/minNormal Level Fluoroscopy

3 R/min> 1 R/minLow Level Fluoroscopy

Used To BeCurrent Practice

23/25 cm Image Intensifier, Patient Exposure Rate

Due primarily to the better image intensifier & television chain.Data Date: 2001

Comparison of Patient Exposure/Air Kerma Rate

Rotational Angiography

3D Imaging CT-like

Scan Parameters For CT 16 cm CTDI Phantom 70 kVp/20 mA per frame (AEC)

Siemens File Name 5S-1KDR 10S-1KDR

Angle of Rotation 192o 204.8o

Angles Per Frame 1.5o 0.8o

Number of Frames 128 256Peripheral Dose (reference only @

12 O’clock)

mR 452 947

mGy 3.84 8.05

Center Dose (reference only)

mR 9 12

mGy 0.077 0.102

Matrix Size 1024 X 1024 1024 X 1024

The C-arm frontal plane is employed for the raw data acquisition.

Simplified Basic Principle of CT-like Image and 3D Image Reconstruction with Rotational Angiography

EquipmentFlat Panel Image Detector

X-ray Tube

Patient atiso center

One projection image is obtained every 1.5o of rotation resulting in 128 images in 5 seconds.

Each image has a matrix size of 1024 X 1024.

Through back projection image reconstruction the CT-like images can be generated.

For a 512 X 512 CT-like image, two pixel rows of the projected image is “binned” together for processing.

The original DR images are in matrix size of, say, 1024 X 1024.

There are 128 projected images. Each image is composed of 1024 slices.

To save processing time, two rows and two columns of data may be binned together to form a 512 X 512 matrix CT-like image.

This is illustrated in the next slide.

Digitized values are assigned to each pixel.(in one dimension only is shown.)In the case of Flat Panel Detector, the signalis digitized in the internal structure of flat panelassebly while the analog TV signal from the image intensified system is put through a digitizer.

Pixel (1, 512) -------------------------------- Pixel (xxx, 512)

Clinical Images; Courtesy of Arra S. Reddy, M.D.

This is a simulated image.

128 images of 512 X 512 matrix size CT-like images are reconstructed.

These images are further processed to generate 3D images.

Acquisition of CT-like & 3D Images with Rotational Angiography Unit

Left Side: Rotaional Angiography Equipment | Right Side: CT-scanner

Projection “Raw” Fluoroscopy Image;

Notice the divergent beam of CONE shaped fluoroscopy beam causing distortion. (negative image)

Scout View of CT scanner shows minimal distortion, or almost distortion less image. (positive image)

Left Side: Rotational Angiography Equipment | Right Side: CT-scanner

Slice width ramps in the center of image with four plastic pins for linearity test are clearly shown.

Notice the similarity of the artifacts next to the slice width aluminum ramps.

#3

#2#1

#4

#5

Teflon Acrylic

PolyethyleneAir

Water

AluminumRamps


This is the high contrast resolution section of CT phantom. The 0.75 mm square holes are resolved.

The resolution of this CT scanner under Standard Reconstruction algorithm resolves 0.65 mm square holes, and better with “BONE” reconstruction algorithm.

0.40.6

0.650.750.85

1.0(mm)


While CT scanners are designed for resolving “low contrast objects”, the angiography equipment is able to show the nominal 2% contrast group under the CT scanner. Notice that the contrast level will not be the same due to the photon energy differences and the partial volume effect.

2.0%

0.62%

0.4%

5

43

21.5

The 3D images are best appreciated when presented in “Motion”.Clinical Images; Courtesy of Arra S. Reddy, M.D.

Photo: Courtesy of Siemens Medical Systems

We have come a long way from this!

1. 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)

2. 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)

3. 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)

4. AAPM TG 125 Home Page.

References & Other Reading Material

E-mail Address: [email protected]

pei-jan paul lin department of radiology beth israel deaconess medical center and

Documents

pulsed fluoroscopy system

legacy fluoroscopy equipment

image intensifier tower1590

mode image intensifier

automatic gain control

tube current ma

lower gi fluoroscopy

method of brightness