Conventional Fluoroscopy Imaging System

Conventional Fluoroscopy
Imaging System
Muhammad Arif Afridi
Lecturer In Medical Imaging
Email: drarifafridi@gmail.com
MUHAMMAD ARIF AFRIDI | LECTURER IN MEDICAL IMAGING | DRARIFAFRIDI@GMAIL.COM 1

An Overview of Fluoroscopy
The Primary function of the fluoroscope is to provide real-time dynamic viewing of anatomic
structures.
Dynamic studies are examinations that show the motion of circulation or the motion of
internal structures.
During fluoroscopy, the radiologist generally uses contrast media to highlight the anatomy.
The radiologist then views a continuous image of the internal structure.
If the radiologist observes something during the fluoroscopic examination and would like to
preserve that image for further study, a radiograph called a spot film can be taken without
interruption of the dynamic examination.

Fluoroscopy is actually a rather routine type of x-ray examination except for its application in
the visualization of vessels, called angiography.
These angiography are now referred to as interventional radiology
“The fluoroscope is used for examination of moving internal structures and fluids.”

Fluoroscope and its associated parts.

Fluoroscopy Composition / Structure
Fluoroscopic imaging system, the x-ray tube is usually hidden under the patient table.
The image intensifier are set over the patient table.
With some fluoroscopes, the x-ray tube is over the patient table, and the image receptor is
under the patient table.
Some fluoroscopes are operated remotely from outside the x-ray room.
During image-intensified fluoroscopy, the radiologic image is displayed on a television monitor
or flat panel monitor.
Image intensifier that converts x-rays into visible light at high intensity

During fluoroscopy, the x-ray tube is operated at less than 5 mA.
Despite the lower mA, however, the patient dose is considerably higher during fluoroscopy
than during radiographic examinations because the x-ray beam exposes the patient constantly
for a considerably longer time.
The kilovolt peak (kVp) of operation depends entirely on the section of the body that is being
examined.
Fluoroscopic equipment allows the radiologist to select an image brightness level that is
subsequently maintained automatically by varying the kVp, the mA, or sometimes both.
This feature of the fluoroscope is called automatic brightness control (ABC).

Fluoroscope and its associated parts.

Special Demands of Fluoroscopy
Fluoroscopy is a dynamic process; thus, the radiologist must adapt to moving images that are
sometimes dim.
This requires some knowledge of image illumination and visual physiology.

1. Illumination
The principal advantage of image-intensified fluoroscopy over earlier types of fluoroscopy is
increased image brightness.
Just as it is much more difficult to read a book in dim illumination than in bright illumination.
It is much harder to interpret a dim fluoroscopic image than a bright one.
Illumination levels are measured in units of lumen per square meter or lux.
Radiographs are visualized under illumination levels of 100 to 1000 lux.

2. Human Vision
The structures in the eye that are responsible for the sensation of vision are called rods and
cones.
Light incident on the eye must first pass through the cornea, a transparent protective covering,
Then through the lens, where the light is focused onto the retina.
Between the cornea and the lens is the iris, which behaves similarly to the diaphragm of a
photographic camera in controlling the amount of light that is admitted to the eye.
In the presence of bright light, the iris contracts and allows only a small amount of light to enter.
During low-light conditions, the iris dilates and allows more light to enter.
When light arrives at the retina, it is detected by the rods and the cones.

The threshold for rod vision is approximately 2 lux and cones threshold is about 100 lux.
Cones are used primarily for daylight vision, called photopic vision, and rods are used for night
vision, called scotopic vision.

Fluoroscopic Technique
During fluoroscopy, maximum image detail is desired; this requires high levels of image
brightness.
The image intensifier was developed principally to replace the conventional fluorescent screen.
The image intensifier raises illumination into the cone vision region, where visual acuity is
greatest.
High kVp and low mA are preferred.

Image-Intensifier Tube
The image-intensifier tube is a complex electronic device that receives
the image-forming x-ray beam and converts it into a visible-light image of
high intensity.
The tube components are contained within a glass or metal envelope that
provides structural support but more importantly maintains a vacuum.
When installed, the tube is mounted inside a metal container to protect it
from rough handling and breakage.
X-rays that exit the patient and are incident on the image-intensifier tube
are transmitted through the glass envelope and interact with the input
phosphor, which is cesium iodide (CsI).
When an x-ray interacts with the input phosphor, its energy is converted
into visible light.

The CsI crystals are grown as tiny needles and are tightly packed in a layer of approximately 300
μm, Each crystal is approximately 5 μm in diameter.
The next active element of the image-intensifier tube is the photocathode, which is bonded
directly to the input phosphor with a thin, transparent adhesive layer.
The photocathode is a thin metal layer usually composed of cesium and antimony compounds
that respond to stimulation of input phosphor light by the emission of electrons.
This process is known as photoemission.
The number of electrons emitted by the photocathode is directly proportional to the intensity
of light that reaches it.
The photocathode emits electrons when illuminated by the input phosphor.

The image-intensifier tube is approximately 50 cm long.
A potential difference of about 25,000 V is maintained across the tube between photocathode
and anode so that electrons produced by photoemission will be accelerated to the anode.
The anode is a circular plate with a hole in the middle through which electrons pass to the
output phosphor,
which is just the other side of the anode and is usually made of zinc cadmium sulfide.
The output phosphor is the site where electrons interact and produce light.

For the image pattern to be accurate, the electron path from the
photocathode to the output phosphor must be precise.
The engineering aspects of maintaining proper electron travel are
called electron optics.
The interaction of these high-energy electrons with the output
phosphor produces a considerable amount of light.
Each photoelectron that arrives at the output phosphor produces
50 to 75 times as many light photons as were necessary to create it.

Ratio of the number of light photons at the output phosphor to the number of x-rays at the
input phosphor is the flux gain.
The ability of the image intensifier to increase the illumination level of the image is called its
brightness gain.

Summary
Glass envelope
Surrounds all of the components and provides mechanical support of internal
components has a vacuum tube.
Input phosphor
Receives incident x-rays from the x-ray tube and converts them into light
Composed of cesium iodide
Photocathode
Attached to the input phosphor by an adhesive layer, Converts light from input
phosphor to electrons by photoemission Negative portion of the tube
Anode
Positive portion of the tube. A circular plate with a hole in it in which electrons
are focused to which goes to the output phosphor
Electrostatic focusing lenses
Focuses electron path form photocathode to anode by means of repulsion
Output phosphor
Converts electrons from anode to light

Fluoroscopic Image Monitoring
Television Monitoring
Image Recording
Vidicon television camera tube
diameter of approximately 2.5 cm
length of 15 cm. The image-intensifier tube

Television Monitoring
With the television monitoring system of a fluoroscopic image, the output phosphor of the
image-intensifier tube is coupled directly to a television camera tube.
The vidicon is the television camera tube that is most often used in television fluoroscopy.
It has a sensitive input surface that is the same size as the output phosphor of the image-
intensifier tube.
The television camera tube converts the light image from the output phosphor of the image
intensifier into an electrical signal that is sent to the television monitor, where it is reconstructed
as an image on the television screen.

Advantage
A significant advantage of television monitoring is that brightness level and contrast can be
controlled electronically.
With television monitoring, several observers can view the fluoroscopic image at the same time.
It is even common to place monitors remote to the examination room for others to observe.
Television monitoring also allows for storage of the image in its electronic form for later playback
and image manipulation.
A television camera tube or CCD converts the light signal from
the output phosphor to an electronic signal.

Methods
Television Camera. Two methods are used to electronically convert the visible image on the
output phosphor of the image intensifier into an electronic signal.
These are the thermionic television camera tube and the solid state charge-coupled device
(CCD).

The television camera consists of cylindrical housing, approximately 15 mm in diameter by 25
cm in length, that contains the heart of the television camera tube.
It also contains electromagnetic coils that are used to properly steer the electron beam inside
the tube.
The glass envelope serves the same function that it does for the x-ray tube: to maintain a
vacuum and provide mechanical support for the internal elements.
These internal elements include the cathode, its electron gun, assorted electrostatic grids, and a
target assembly that serves as an anode.

The electron gun is a heated filament that supplies a constant electron current by thermionic
emission.
The electrons are formed into an electron beam by the control grid, which also helps to
accelerate the electrons to the anode.
At the anode end of the tube, the electron beam passes through a wire mesh–like structure and
interacts with the target assembly.
The target assembly consists of three layers that are sandwiched together. The outside layer is
the window, the thin part of the glass envelope.
Coated on the inside of the window is a thin layer of metal or graphite, called the signal plate.
The signal plate is thin enough to transmit light yet thick enough to efficiently conduct
electricity. Its name derives from the fact that it conducts the video signal out of the tube into
the external video circuit.

Image Recording
The conventional cassette-loaded spot film is one item that is used with image-intensified
fluoroscopes. The spot film is positioned between the patient and the image intensifier.
During fluoroscopy, the cassette is parked in a leadlined shroud so it is not unintentionally
exposed. When a cassette spot-film exposure is desired.
When the entire film is exposed at one time, it is called “one-on-one” Mode.
When only half of the film is exposed at a time, two images result—“two-on-one” mode.
Four-on-one and six-on-one modes are also available, with the images becoming successively
smaller.

Television Monitor. The video signal is amplified and is transmitted by cable to the television
monitor, where it is transformed back into a visible image.

FLUOROSCOPY QUALITY CONTROL
Fluoroscopic examination can result in high patient radiation dose.
The entrance skin dose (ESD) for an adult averages 30 to 50 mGyt/min (3 to 5 R/min) during
fluoroscopy
Approximate patient radiation dose can be identified through the performance of proper QC
measurements.
Some measurements may be required more frequently after significant changes have occurred
in the operating console, high-voltage generator, or x-ray tube.

Thank you!

Conventional Fluoroscopy Imaging System

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