Review of Fluoroscopy Equipment The “Legacy” Fluoroscopyaapm.org/meetings/amos2/pdf/29-7888-66277-421.pdf · Harvard Medical School Boston, MA 02215 ... automatic exposure control

1

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

Angiography Systems

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.

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 for

a) Cardiac Catheterization.b) Neuro Angiography.c) Visceral Angiography.d) Electrophysiology Laboratory.

The “Legacy” Fluoroscopy1) 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 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

2

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

Input Phosphor (-) Output Phosphor

Anode (+)

Image Intensifier TubeElectrode (Focusing)

Internal Structure of Image Intensifier

Electron Flux

Aluminum SubstrateFluorescent ScreenPhotocathode

X-ray Photons Electrons

Output Phosphor

Electrons Light Photons

Thin Aluminum LayerFluorescent Screen

Input Phosphor

(a) Fluorescent screens are made of Cesium Iodide (CsI) which has a higher absorption of X-rays than the older silver-activated zinc-cadmium sulfide.

(b) Photocathode is a photoemissive metal; a combination of antimony and cesium.

“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 minificationgain is (9/1)X(9/1)=81.

The Flux gain is approximately ~50.

Therefore, the total brightness gain is = 81 X 50 = 4050.

3

• 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.

Glass Substrate

AmorphousSilicon Array

Contact Fingers

Scintillator(CsI)

Contact LeadsFor Read-OutElectronics

Scintillator

aSi Array

Opticlad Reflector

Glass Substrate

Graphite Cover

Epoxy Seal

GE Detector Design

Courtesy of General Electric Heath Care Systems, Inc.

X-ray absorption

Light emission

Light absorption

Electron-hole generation

Conversion to digital signal

X-Ray Photons

Cesium Iodide (CsI)

Light

Amorphous Silicon Panel(Photodiode/Transistor Array)

Electrons

Digital Data

Read Out Electronics

DET

ECTO

R

IQ, fast readout, low noise, no significant image retention

Basic GE Detector Physics

Courtesy of General Electric Health Care Systems, Inc.

X-Ray Photons

Cesium Iodide (CsI)

Light

Amorphous Silicon Panel(Photodiode/Transistor Array)

Electrons

Digital Data

Read Out Electronics

DET

ECTO

R

IQ, fast readout, low noise, no significant image retention

Basic GE Detector Physics

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

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.

• 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.

4

kVp-primary ABC Circuit TV CameraImageIntensi fierOptical Sensor,Photomultiplier.TV Video Signal TrainTV CameraPre-amplifier TV M VideoAmplifierPhotomultiplie rAmprefier Reference VoltageVoltage Compara torAutomatic Gain Control Lock-in Memory

ImageIntensifier

TV Camera Amplifier

Video AmplifierTV Monitor

Photomultiplier Amplifier

Voltage Comparator

TV C

amer

a

Optical 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 CameraImageIntensi fierOptical Sensor,Photomultiplier.TV Video Signal TrainTV CameraPre-amplifier TV M VideoAmplifierPhotomultiplie rAmprefier Reference VoltageVoltage Compara torAutomatic Gain Control Lock-in Memory


(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 C

amer

a

Optical Distributer

Reference Voltage


Lock-in Memory





Optical Sensor



(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 C

amer

a

Optical Distributer

Reference Voltage


Lock-in Memory





Optical Sensor



(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 C

amer

a

Optical Distributer

Reference Voltage


Lock-in Memory





Optical Sensor



(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 C

amer

a

Optical Distributer

Reference Voltage


Lock-in Memory





Optical Sensor

5

mA-primary ABC Circuit TV CameraImageIntensi fierOptical Sensor,Photomultiplier.TV Video Signal TrainTV CameraPre-amplifier TV M VideoAmplifierPhotomultiplie rAmprefier Reference VoltageVoltage Compara torAutomatic Gain Control Lock-in Memory

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV C

amer

a

Optical Distributer

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 PhantomIonization Chamber #1


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

3.97

in

1.31

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

Pot

entia

l (kV

p)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Tube

Cur

rent

(mA)

Tube PotentialTube Current

6

Power Loading Rate

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12


Pow

er L

oadi

ng R

ate

(W/s

ec)

Power Loading

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)

Tube

Cur

rent

(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 10Nominal PMMA Phantom Thickness (inches)

Pat

ienn

Ent

ranc

e E

xpos

ure

Rat

e(R

/min

)

50

60

70

80

90

100

110

120

130

140

Imag

e In

tens

ifier

Inpu

t Exp

osur

eR

ate

( μR

/sec

)

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; Copper and Aluminum.

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

3.97

in

1.31

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.

7

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 16Nominal Phantom Thickness (inches)

Imag

e In

tens

ifier

Inpu

t Air

Ker

ma

Rat

e( μ

Gy/

sec)

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 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.

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

Ker

ma

Rat

e (m

Gy/

min

)

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 120Tube Potential (kVp)

Tube

Cur

rent

(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 90Phantom Thickness (mm for Al, X0.1 mm for Cu, "inches" divide by 6 for PMMA)

Air

Ker

ma

Rat

e (m

Gy/

min

) AluminumCopperPMMA

8

Thickness Equivalence (Philips Eleva System)

9.3[9-1/2]

3765.680

7.3[7-1/2]

2-1/4583.240

5-1/21-1/2381.620

3.67[3-3/4]

3/4190.810

PMMA (inches)

Aluminum (inches)

Aluminum (mm)

Copper (mm)

Air Kerma Rate

(mGy/min)

ImageIntensifier

TV Camera Amplifier



Voltage Comparator

TV C

amer

a

Optical Distributer

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)

Tube

Pot

entia

l (kV

p)

0

1

2

3

4

5

6

7

8

9

Tube

Cur

rent

(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 14Nominal PMMA Phantom Thickness

Air K

erm

a R

ate

(mG

y/m

in)

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

Inpu

t Air

Kerm

aR

ate

( μG

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 K

erm

a R

ate

(mG

y/m

in)

AluminumCopperPMMA

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.

9

99.33.2823765.6

PMMA (inches)Al(inches)

Al(mm)

Al(inches)

Al (mm)

Cu (mm)

7.37.32.7682.25583.2

4.35.51.42361.5381.6

2.53.650.87220.75190.8

GE Advantx

Philip Eleva

GE AdvantxPhilip Eleva Thickness Equivalence (Fussed)

0

2

4

6

8

10

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

PM

MA

Thic

knes

s (in

ches

)

0

1

2

3

4

5

Alu

min

um T

hick

ness

(inc

hes)

PMMAAluminumLinear (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.

10

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

Tube Potential (kVp)Copper Filter (mmCu)

Copper Fi lt er (m

m)Tu

be P

oten

tial (

kVp)

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

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


100

80

60

40

20Tube

Cur

rent

(mA

)

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


10

12

14

16

8Puls

e W

idth

(mSe

c)

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

120

100

80

60 0.2

0.4

0.6

0.8

1.0

Tube Potential (kVp)Copper Filter (mmCu)

Coppe r F il ter (m

m)Tu

be P

oten

tial (

kVp)


100

80

60

40

20

10

12

14

16

Tube

Cur

rent

(mA

)

8Puls

e W

idth

(mSe

c)

10 cm 20 cm 30 cm

0.9

0.8

0.7

0.6Inpu

t Sen

sitiv

ity (μ

Gy/

sec)

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

0.1

1

10

100

Entr

ance

Exp

osur

e ra

te (m

Gy/

min

)

10 cm 20 cm 30 cm

Input Sensitivity in front of the Flat Panel Image Detector

Patient Skin Dose (Air Kerma)

11

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

Cop

per 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

Puls

e W

idth

(mSe

c)

Tube CurrentP ulse Width






50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12 14PMMA 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

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

PMMA Thickness (inches)

Tube

Cur

rent

(mA)

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Puls

e W

idth

(ms)

Tube Current

Pulse Width (mSec)

12

Fluoroscopy Curve 70kV10RAF2kW (Pediatric)



40

50

60

70

80

90

100

110

120

130

0 2 4 6 8 10 12PMMA 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

1

Cop

per T

hick

ness

(mm

Cu

Tube Potential (kVp)

Copper Filter (mmCu)

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 12PMMA Thickness (inches)

Tube

Cur

rent

(mA)

3

4

5

6

7

8

9

10

Pul

se W

idth

(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 C

amer

a

Opt

ical

Dis

tribu

ter

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 μR/fram eD ig ita l C inePho to fluorography

15-30 μR/fram e10 -20 μR/frame35 m m C ine Cam era

500-1000 μR/fram100 -500 μR/fram eD ig ita l SubtractionAng iography

100 μR/fram e25-100 μR/fram eD ig ita l P hoto fluorography

100-200 μR/fram e50-100 μR/fram e 100 mm P hotospot Camera

N/A75 μR/secHigh Leve l F luoroscopy

75 -100 μR/sec50 μR/secNormal L eve l F luoroscopy

50 μR/sec25 μR/secLo w Leve l F luoroscopy

Used To B eCurren t P rac tice

23/25 cm Image In tens ifie r Inpu t Phosphor (Ac tive ) S ize

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

13

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]

Documents

Review of Fluoroscopy Equipment The “Legacy” Fluoroscopyaapm.org/meetings/amos2/pdf/29-7888-66277-421.pdf · Harvard Medical School Boston, MA 02215 ... automatic exposure control