The document is a detailed overview of fluoroscopy technology, including its components, imaging chain, and advancements in detector systems, such as the replacement of image intensifiers with flat panel detectors. It discusses various configurations of fluoroscopy systems, improvements in imaging quality, and the importance of dose monitoring for radiation safety. Additionally, it explains technical aspects of brightness gain, distortion effects, and automatic exposure rate control in modern fluoroscopy setups.

1. Fluoroscopy
Eyasu Altamo(PCR1)
Moderator :Dr Seife.T Medical Physicist

2. Content of session
Introduction
Fluoroscopy imaging chain components
Fluoroscopy detector system
Automatic exposure rate control
Fluoroscopy modes of operation
Imaging quality in fluoroscopy
Fluoroscopy suites
Radiation dose

3. Introduction
Fluoroscopy is an imaging modality that allows real-time x-
ray viewing of a patient with high temporal resolution.
 Its works based on an x-ray image intensifier coupled to a
still/video camera.
But curently ,Flat panel detectors have been replacing the
image intensifiers(II).

4. Introduction …
Fluoroscopy are commonly used
To position the imaging system for the recording of
images (e.g., angiography)
To provide imaging guidance for interventional
procedures (e.g., angioplasty).

5. St.paul’s Hospital fluoroscopy room

6. St.paul’s Hospital fluoroscopy room

7. St.paul’s Hospital fluoroscopy room

8. St.paul’s Hospital fluoroscopy room

9. TechnologicalAdvancementoffluoroscopy inrecentyears
• The II has increased in size from 15-cm -40-cm.
• Analog television (TV) cameras have been replaced
with CCD or CMOS cameras(high resolution, low
noise ).
• Flat panel detector technology has led to
• larger rectangular FOV systems
• high spatial resolution
• improved image fidelity

10. Cont….
 Improvements in fluoroscopic systems with:-
Increased x-ray beam filtration,
Higher x-ray detection efficiency phosphors,
Lower acquisition frame rates, and
Electronic image guidance and
Enhancement
This improvement led to lower dose operation
• Since June 10, 2006, dose-monitoring technology
become a component of all interventional fluoroscopy
systems manufactured

11. Functionality
• Real-time” imaging is usually considered to be 30 frames per
second (FPS) and this sufficient to provide the appearance
of continuous motion.
• Modern general-purpose fluoroscopy systems use a pulsed x-
ray beam in conjunction with digital image acquisition(allow 3
to 30 FPS ).
• Lower frame rates reduce radiation dose when high temporal
resolution is not needed.

12. Cont..
• Digital fluoroscopy systems allow the recording of a real-
time sequence of digital images.
• Unrecorded fluoroscopy sequences are used for advancing a
catheter (positioning) during angiographic procedures
• In gastrointestinal fluoroscopy, much of the diagnosis is
formulated during the unrecorded fluoroscopy sequence.

13. • Fluoroscopy produce real-time x-ray images with high frame rates
and a low-dose of radiation per image.
• In general, five configurations of fluoroscopy systems are available:
I. Gastrointestinal/genitourinary (GI/GU) systems (with the x-ray tube under the
patient table);
II. Remote fluoroscopy (over-table x-ray tube);
III.Interventional vascular (vascular surgery, radiology);
IV. Cardiology and interventional electrophysiology, and
V. Mobile C-arm configurations (surgery, pain medicine).
All configurations have the same basic components.
9.2 Fluoroscopic Imaging Chain Components

14. Fluoroscopic Imaging Chain Components

15. Fluoroscopic Imaging Chain Components
X-ray tube
Filters :Copper filtration combined with lower kV values allows
angiography systems to provide lower dose operation while still
delivering high image contrast for angiographic applications.
Collimators (circular diaphragms for II and rectangular for
FPF)
operator adjustable attenuating wedges
image intensifiers(II)
flat panel detectors operate
several thousand times more sensitive than a
standard radiographic detector and, in principle,
can produce images using several thousand
times less radiation

16. 9.3 Fluoroscopic Detector Systems
The Image Intensifier, Based Fluoroscopy Systems
There are four principal components of an II:
1. Vacuum housing to keep air out and allow unimpeded electronflow,
2. Input layer that converts the absorbed incident x-rays into light,
which in turn releases electrons,
3. Electron optics system that accelerates and focuses the
electrons emitted by the input layer onto the output layer
4. output phosphor that converts the accelerated electrons into a
visible light image.

17. A Diagram of the modern II

18. Input Screen
• The input screen of the II consists of four different layers,

19. 1,vacuum window
• The first layer is the vacuum window, a thin (typically 1 mm)
aluminum window that is part of the vacuum containment
vessel.
• Its keeps the air out of the II,
• Curvature is designed to withstand the force of the air
pressing against it.
• The vacuum window of a large FOV (35-cm) II supports over a
ton of force from atmospheric air pressure.
• A vacuum is necessary in all devices in which electrons are
accelerated across open space.

20. 2,Support layer
•Its supports the input phosphor and
photocathode layers.
•Commonly 0.5 mm of aluminum
• The first component in the electronic lens
system.
• Its curvature is designed for accurate
electron focusing.

21. 3,Input phosphor
• Function is to absorb the x-rays and convert their energy
into visible light.
• All modern IIs use cesium iodide (CsI) for the input
phosphor.
• The CsI crystals have a trace amount of sodium, causing it
to emit bluelight.
• For a 60-keV x-ray photon absorbed in the phosphor,
approximately 3,000 light photons (at about 420 nm
wavelength) are emitted.

22. 4,Photocathode
• The fourth layer of the input screen is the photocathode,
• Thin layer of antimony and alkali metals (such as Sb2 S3 ) that
emits electrons when struck by visible light.
• Approximately 400 electrons are released from the photocathode
for each 60-keV x-ray photon absorbed in the phosphor.
• With 10% to 20% conversion efficiency

23. III, Electron Optics
• Focusing the electrons is accomplished by the several
electrodes in the electron optics chain
• Five-component electronic lens system:
• G1, G2, and G3 electrodes
• Input phosphor substrate (the cathode) and
• The anode just proximal to the output phosphor,
• The kinetic energy of each electron is dramatically
increased by acceleration due to the voltage difference
between the cathode and anode, resulting in electronic gain

24. IV, The Output Phosphor

25. Anode
• The anode is a very thin (0.2 mm) coating of aluminum on the
vacuum side of the output phosphor.
• which is electrically conductive to carry away the electrons
once they deposit their kinetic energy in the phosphor.

26. output phosphor
• Made of zinc cadmium sulfide doped with silver (ZnCdS: Ag),
• ZnCdS: Ag has a green (530 nm) emission spectrum.
• The ZnCdS phosphor particles are very small (1 to 2 mm),
and the output phosphor is quite thin (4 to 8 mm), to
preserve high spatial resolution.
• Each electron causes the emission of approximately
1,000 light photons from the output phosphor.

27. output window
• The last stage in the II that the image signal passes through is
the output window
• The output window is part of the vacuum enclosure and must be
transparent to the emission of light from the output phosphor.
• Some fraction of the light emitted by the output phosphor is
reflected inside the glass window.
• This contribute veiling glare, which can reduce image contrast.
• This glare is reduced by using a thick (about 14 mm) clear glass
window

28. Brightness Gain
• Brightness gain is a measurement of the increase in
image brightness or intensification achieved by the
conversions in the image intensification tube.
• Two factors are used to determine the total
brightness gain: flux gain and minifi cation gain.
• The total gain in brightness comes from a
combination of acceleration of the
photoelectrons, called flux gain, and compression
of the image size, called minification gain.

29. Flux Gain
• Flux gain is the ratio of the
number of light photons at
the output phosphor to the
number of x-ray photons at
the input phosphor,
• Thus producing the
conversion of the electron
energy into light energy.

30. Minification gain
• Minifi cation gain is the ratio of
light from input phosphor to light
at the output phosphor,
• Thus producing concentrated light
from the larger input phosphor
onto the smaller output phosphor.
• Minification is an increase in
brightness or intensity of the
image;

31. Total Brightness Gain
• Total brightness gain is obtained by multiplying flux
gain by minifi cation gain.
• The image intensifier will have decreased
brightness as it ages, resulting in increased patient
dose to maintain brightness.
Brightness gain = flux gain × minifi cation gain

32. Optical Coupling to the Video Camera
•camera tube or CCD may be coupled to the
output phosphor of the image intensifier by
either a fiber-optic bundle or an optical lens
system.
•The fiber-optic bundle is simply a bundle of
very thin optical glass filaments.
• This system is very durable and simple in design
but does not allow spot filming.

34. optical lens system
• The optical lens system is a series of optical lenses that focus the
image from the output phosphor on the television camera (camera
tube or CCD).
• When spot filming is desired, a beam splitting mirror (a partially
silvered mirror that allows some light to pass through and reflects
some in a new direction) is moved into the path of the output image
and diverts some of the light to the desired spot-filming device
• This system, although allowing spot filming of this type, is more
susceptible to rough handling, which may cause maladjustment of
the mirror and lenses and result in a blurred image

35. Lens adjustment
• Includes an adjustable aperture in which adjusting its size
dictates how much light gets through the lens system.
• f= focal length/aperture diameter. Area is determinant
• Standard f-numbers increment by multiples of √2: 1.0, 1.4, 2.0,
2.8, 4.0, 5.6, 8, 11, and 16.
• Changing the diameter of the hole by a factor of √2 changes
its area by a factor of 2,
• Thus, increasing the f-no by one f-stop reduces the amount of
light passing through the aperture by a factor of 2.

36. Cont…
• Lower gain by increasing f- number -> higher x-ray exposure
rate , lower noise images and higher patient dose
• Higher gain -> lower x-ray exposure rate, reduced image
quality, lower dose

37. Video Cameras
•A light-sensitive camera such as :
1.Analog vidicon
2. Solid-state CCD (Charge coupled device)
3. CMOS system (complementary metal oxide
semiconductor)
•They optically coupled to the output screen of
the II and is used to relay the output image to
a video monitor for viewing by the operator.

38. Analog vidicon
• Its function on the principle
of photocondutivity,where
resistance of photoconductive
surface decrease with
increase in light intensity
• Vidicon is short tube with
length of 12 to 20cm and
diameter between 1.5to 4cm.
• Its no longer used in modern
fluoroscopy

39. 2,CCD (Charge coupled device)&CMOS system
(complementary metal oxide semiconductor
• They are solid-state electronic arrays that convert a
projection image into a digital image and then into a video
signal.
• Such a device uses photodiode semiconductor materials in an
array to convert incident light intensity incident into
corresponding electronic charge (electrons), and locally
store the charge for electronic readout.

40. Cont..
• Both CCD and CMOS cameras have very small pixel
dimensions, on the order of 10–20 micron (0.01 to 0.02 mm),
incorporated into a 2.5 by 2.5 cm area that replaces an
analog TV camera.
• The typical matrix comprises 1,000 by 1,000 or 2,000 by
2,000 detector elements, but there is a wide variety and
selection of sizes that a manufacturer might choose to
include in a system.

41. Cont..
• In either output (CCD or CMOS) a digital projection image
is produced, and then converted to a video signal that is
used to drive one or more monitors in the fluoroscopy suite.
• Solid-state cameras are preferred because of their
stability, reproducibility, and linearity.

42. charge-coupled device (CCD)
• The CCD consists of a series of semiconductor capacitors, with
each capacitor representing a pixel.
• Each pixel is composed of photosensitive material that
dislodges electrons when stimulated by light photons.
• The CCD reads out the stored charge in a “bucket brigade” fashion,
causing locally stored electrons to be transferred from one row to the
next row, along defined columns, to eventually be deposited onto a charge
amplifier at the end of each column.

45. CMOS system (complementary metal oxide
semiconductor
• The CMOS device has
independent detector elements,
each comprised of a storage
capacitor and transistor switch.
• Charge to voltage conversion as
well as amplification is carried
out in the pixel
• itself : speed is higher.
• The signal from a CMOS device
is accessed, as is the signal from
a TFT flat panel detector.

46. Characteristics Unique to Image Intensifier Systems
•1,Brightness Gain
•2 ,Pincushion Distortion
•3,S Distortion

47. 1,Brightness Gain
• The brightness gain is the product of the electronic and
minification gains of the II.
• The electronic gain of an II is roughly about 50,
• The minification gain is variable depending on the electronic
magnification
• As the effective diameter (FOV) of the input phosphor
decreases ,the brightness gain decreases.

48. 2 ,Pincushion Distortion
• It is the result of projecting the image with a
curved input phosphor to the flat output phosphor .
• Pincushion distortion worps the image by stretching
the physical dimensions in the periphery of the
image.
• Therefore, for improved accuracy with distance
measurements,
• it is best to position the desired anatomy in the central
area of the FOV

50. 3,S Distortion
• S distortion is a spatial warping of the image in an S shape
through the image.
• This type of distortion is usually subtle.
• It is the result of stray magnetic fields and the earth’s
magnetic field affecting the electron trajectory from the
cathode to the anode inside the II.

51. Cont..
On fluoroscopic systems
capable of rotation.
the S distortion will
generally shift in the image
during rotation due to the
change in the II’s
orientation with respect to
the earth’s magnetic field.

52. Flat Panel Detector Based Digital Fluoroscopy
Systems
• Flat panel detectors are comprised of thin film transistor (TFT) arrays of individual
detector elements (dexels) that are packaged in a square or rectangular area.
• Each detector element has :-
Capacitor, which accumulates and stores the signal as an electrical charge,
Transistor which serves as a switch
• There are two modes of TFT:-
• Indirect
• Direct x-ray conversion modes

53. cont’d
Indirect detection TFT systems,
The absorbed x-rays are initially converted to light in the adjacent
layered phosphor
Each dexel has a transistor and a capacitor, in addition to a
photodiode, which converts the x-ray induced light from the
phosphor into a corresponding charge.
Direct detection fluoroscopy detectors
 Semiconductor (selenium) produces x-ray induced charge directly,
which is collected under a voltage to ensure that the signal is
captured within the same dexel as the x-ray absorption event.

55. Cont..
• For fluoroscopic applications, the flat panel image receptor
replaces the II, lenses, and camera system, and directly
records the real-time fluoroscopic image sequence.
• The size of a detector element (dexel) in fluoroscopy is usually
larger than in radiography.
• some flat panel systems have the ability to adjust the dexel
size by binning four dexels into one larger dexel.

57. 9.4 Automatic exposure rate Control
• In modern fluoroscopic systems the exposure rates are controlled
automatically.
• This enabled by Automatic exposure rate control (AERC) circuit
(formerly referred to as Automatic Brightness Control – ABC)
• This system help to provide a consistent optical density/
signal-to-noise ratio between images, regardless of patient-centric
factors such as size and density.

58. • It does this by regulating the x-ray exposure rate incident on the
input phosphor of the II or flat panel detector.
• When the system is panned from a region of low attenuation to one of
greater attenuation of the patient, fewer x-rays strike the detector.
An AERC sensor measures the x-ray intensity and the AERC sends a
signal to the x-ray generator to increase the x-ray exposure rate .
Cont…

59. cont...
• Its maintain a consistent overall appearance of the image by
automatically adjusting the kVp and/or mAs.
• How the mA and kV change as a function of patient thickness has an
important influence on the compromise between patient dose and
image quality
• When the fluoroscopist pans to a thicker region of the patient, the
AERC circuit requests more x-rays from the generator.

60. AERC
• When the generator responds by increasing the kV, the
subject contrast decreases, but the dose to the patient is
kept low because more x-rays penetrate the patient at
higher kV.
• In situations where contrast is crucial (e.g., angiography),
the generator can increase the mA instead of the kV; this
preserves subject contrast at the expense of higher patient
dose

62. Reference