Fluoroscopy is an imaging technique that
uses low level energy of X-rays to obtain real-time moving images of the
interior of the body. The primary function of fluoroscopy is real time imaging, a
fluoroscope allows a physician to see the internal structure and function of a
patient’s body. Fluoroscopy got its name from the use of
fluorescent screens that previously displayed the moving image before the use of
cameras. The fluoroscope is based on the x-ray beam.
Fluoroscopy
A schematic of an image-intensified fluoroscopy system consists an X-ray
tube, spectral shaping filters, collimator, an anti-scatter grid, an image
receptor, an image processing computer and a display device. Supplementary but necessary components
includes a high-voltage generator, a patient table and hardware to allow
positioning of the X-ray source assembly and the image receptor assembly
relative to the patient. A fluoroscope consists of an x-ray source and a
fluorescent screen between which patient is placed.
Schematic
Diagram of a fluoroscopic system
Fluoroscopy
is used to position the patient for subsequent image recording or devices for
interventional procedures.
- Plain
Radiography: good SNR, poor Temporal Resolution
- Fluoroscopy:
poor SNR, good Temporal Resolution
Angiography, a
specific use of fluoroscopy, allows physicians the ability to look at blood
flow through the blood vessels using fluoroscopy. Cardiac
catheterization and angioplasty use the real-time images to view coronary
blood flow and treat blockages.
C-arm devices are fluoroscopic x-ray machines,
which can be portable or fixed. Many times, these are digital devices and are
useful in many applications including during surgical cases.
FLUOROSCOPY AND RADIOGRAPHY
Fluoroscopy
and radiography share some of the same imaging chain components, but
differences exist. The primary difference is that the radiation exposure
rate is much lower for fluoroscopy compared with radiography. But, the total
exposure for a radiograph is much lower than a typical fluoroscopic
examination because the fluoroscopic exposure time is extended. To avoid
radiation injury to the patient, low fluoroscopic exposure rates are required.
HISTORICAL DEVELOPMENT
The first
fluoroscopes consisted of an x-ray tube and fluorescent screen. Fluorescence
is a material that immediately emits visible light in response to some stimuli.
A lead glass layer was involved to reduce exposure to the radiologist.
Early
fluoroscope screens were held by the radiologist or worn on the head like
goggles. The major problem with first-generation fluoroscopes was production of
an image with sufficient brightness.
THE FLUOROSCOPE AND ITS COMPONENTS
Parts of fluroscopy
X-ray generator
X-ray generator
X-ray generator converts
AC current from the wall outlet to high voltage DC current within
the fluoroscope. It produces electrical energy and allows for adjustment of
mA and kVp and tube current (mA) that is delivered to x-ray tube.
The
design of the generator is like that of generators used for radiography, consisting
either low continuous tube current or rapid pulsed exposure and
automatic brightness control (ABC).
Another
important feature of a fluoroscopic x-ray generator is ABC, which acts
to keep the image brightness seen on the monitor at a constant level as
the image intensifier is criticized over body parts of differing thickness and
attenuation. Fluoroscopic equipment agrees the radiologist to select an image
brightness level that is subsequently maintained automatically by varying the
kVp, the mA, or sometimes both.
ABC
The ABC
circuitry controls the X-ray intensity measured at the Image-Intensifier so
that a clear image can be displayed on the monitor when the ABC mode is selected.
The ABC compensates the brightness loss caused by decreased radiation reception by
generating more X-rays and/or producing more penetrating X-rays. The ABC
compensates by reducing mA and decreasing kVp when the image is too bright.
Two
methods are used to energize the x-ray tube for fluoroscopy:
- Continuous exposure
- Pulsed exposure.
For
continuous fluoroscopy, the generator provides a steady tube current while the fluoroscope
is activated. For pulsed fluoroscopy, the exposure is delivered in short pulses.
Advantage of pulsed fluoroscopy is improvement in temporal resolution, making
pulsed fluoroscopy useful for examining rapidly moving structures such as those
seen in cardiovascular applications. Pulsed fluoroscopy can be used as a method
of reducing radiation dose, particularly when the pulse rate is reduced.
X-ray tube
x-ray tube
The x-ray
tube converts electrical energy provided by the generator into an x-ray beam.
Within the x-ray tube, electrons are produced by a heated filament and accelerated
toward a positively charged tungsten anode. Vacuum tube that contains the
cathode and anode. DC current flows from the cathode to the positively-charged
tungsten anode. The interaction of the electrons with the anode results in the
emission of x rays. The whole assembly
is placed within an evacuated envelope and shielded housing.
The area
of the anode that is struck by electrons is mentioned to as the focal spot. To
reduce the effective size of the focal spot, the anode surface is angled. X-ray tubes are produced with anode angle
ranges of 7°–20°. The selection of x-ray
tube characteristics varies, depending on the specific clinical application. Effect
of anode angle on heat capacity and effective focal spot size.
focal
spot
COLLIMATOR
The
collimator contains multiple sets of radiopaque shutter blades that move into
the path of the x-ray beam. Two sets of blades are generally present within the
collimator:
- A round
iris: It conforms the x-ray beam to the circular FOV.
- Rectangular
blades: It can be brought in manually to further reduce the beam size.
Collimation
reduces the exposed volume of tissue, resulting in reduced scatter production
and improved image contrast. It also reduces regions of glare from unattenuated
radiation near the edge of the patient's body.
Most
fluoroscopy systems used for angiography and interventional applications
also contain equalization filters. These filters, also called contour or
wedge filters, are partially radiolucent blades used to provide further
beam shaping in addition to collimation.
The filters are made from tapered lead-rubber or lead-acrylic sheets
Collimator
FILTERS
Filtration
material is added to attenuate low-energy x rays from the beam. Aluminum is the most common added
filtration material. Copper can also be used for improved low-energy
x-ray filtering. The use of copper
filtration material has become more prevalent in fluoroscopy systems used for high dose procedures such as
angiography and interventional applications.
PATIENT TABLE AND PAD
Patient
tables
Patient
tables for fluoroscopic systems must provide adequate strength to support large
patients and, at the same time, result in minimal x-ray attenuation. Carbon
fiber composite material satisfies both these requirements. Patient support
pads should also be made of a material that provides minimal x-ray attenuation.
Thin foam pads are generally acceptable,
but thick gel pads have been found to result in excessive attenuation.
GRID
Anti-scatter
grids are used to improve image contrast by reducing the scattered x rays that
reach the image receptor. However, use of grids requires an increase in
radiation exposure. Grids may be circular (XRII systems) or rectangular (FPD
systems) and are often removable by the operator. Typical grid ratios range
from 6:1 to 10:1
IMAGE
INTENSIFIER
X-ray image intensifier
The X-ray image intensifier is an
electronic device that converts the X-ray beam intensity pattern into a visible
image suitable for capture by a video camera and displayed on a video display
monitor. It converts X-rays into light photons. It amplifies brightness
from 5,000 to 20,000-fold.
The major
components of an image intensifier include an input layer to convert x rays to
electrons, electron lenses to focus the electrons, an anode to accelerate them,
and an output layer to convert them into a visible image. All the components
are contained within an evacuated bottle. When installed, the tube is mounted
inside a metal container to protect it from rough handling and breakage.
OPTICAL COUPLING
Optical coupling
The
optical coupling system issues light from the image intensifier output window
to a video camera and other image recording devices. The native x-rays are converted to voltage
signals that are viewable on closed circuit television. Typical C-arm system
has a second TV monitor to display static image.
The
optical distributor may include a partially silvered, beam-splitting mirror,
which directs a portion of the light from the image intensifier output window
to an accessory device for image recording and passes the remainder to the
video camera. Aperture controls the
amount of light passes through to the TV camera.
TELEVISION SYSTEM
television system
A
closed-circuit television system is used to view the image intensifier output
image. The television system consists of a video camera that converts the image
to a voltage signal and a monitor that receives the signal and forms the image
display.
The
television system allows for real-time viewing of the fluoroscopic image by
several people at once from one monitor or multiple monitors. The video signal
is amplified and is transmitted by cable to the television monitor.
IMAGE
RECORDING
A
fluoroscopic imaging system may include additional devices to record images
during an examination. Recording methods include spot film devices, film
changers, photospot cameras, cine cameras, and digital photospots.
In
newer fluoroscopic systems, other methods are replaced with a digital image
recording. Digital
photospots are acquired by recording a digitized video signal and storing it in
computer memory. The operation is fast and convenient, plus image quality can
be enhanced by the application of various image processing techniques.
FLUOROSCOPIC
EQUIPMENT CONFIGURATION
Several
different equipment configurations have been developed to meet the requirements
of specific diagnostic and interventional applications. The basic
configurations include radiography/fluoroscopy (R/F) tables with either an
under-table or over-table x-ray tube and fixed C-arm, mobile C-arm, and mini
C-arm positioners.
R/F Units
with Under-Table X-ray Tube
R/F system
The R/F
system is the most common fluoroscopic equipment configuration. It is used for a wide range of diagnostic and
interventional procedures, including gastrointestinal, genitourinary,
arthroplasty, myelography, and device placement. The x-ray tube and collimator are mounted
below the tabletop with the image intensifier tower mounted above the table on
a carriage that can be panned over the patient.
R/F Units with Over-Table X-ray Tube
R/F configuration
Another
R/F configuration includes an x-ray tube mounted over the table with the image
intensifier below. The x-ray tube can be angled to acquire angulated
projections or tomograms.
C-ARM POSITIONERS
C-arm positioners
C-arm positioners allow angulation of the fluoroscopic imaging chain about the patient in all directions. The C-arm configuration has been incorporated into a number of different types of fluoroscopy systems. The system includes a patient table with a floating tabletop, which allows the operator to move the patient easily while the C-arm positioner remains fixed. Common applications for fixed C-arm units include cardiac, peripheral, and neuroangiographic and interventional procedures.
APPLICATIONS OF FLUROSCOPY
v
Fluoroscopy is
used in many types of examinations and procedures, such as barium X-rays, cardiac catheterization, arthrography , lumbar puncture, placement of intravenous (IV) catheters, intravenous pyelogram, hysterosalpingogram, and biopsies.
v Fluoroscopy may be used alone as a diagnostic
procedure, or may be used in conjunction with other diagnostic or therapeutic
media or procedures.
v
It can be used to Orthopedic Surgery
-Observe fractures and healing bones and Blood Flow Studies - View blood flow
to organs
v
In barium X-rays, fluoroscopy used alone allows the doctor to see the
movement of the intestines as the barium moves through them. (Observe
movement through GI tract)
v
In cardiac catheterization, fluoroscopy is used as an adjunct to enable
the doctor to see the flow of blood through the coronary arteries in
order to evaluate the presence of arterial blockages. (Direct
catheter placement (Angiography/Angioplasty)
v Electrophysiologic
procedures. During clinical electrophysiologic procedures,
fluoroscopy is used to treat patients with arrhythmias.
v Hysterosalpingogram. X-ray
of the uterus and fallopian tubes.
v
For intravenous
catheter insertion, fluoroscopy assists the doctor in guiding the catheter
into a specific location inside the body.
v
Other uses of
fluoroscopy include, but are not limited to, the following:
·
Locating
foreign bodies
·
Image-guided
anesthetic injections into joints or the spine
·
Percutaneous
vertebroplasty. A minimally
invasive procedure used to treat compressed fractures of the spine
FUNCTIONS
OF THE FLUROSCOPE
v Provide a
stream of high velocity electrons
v Focus
these electrons on a metal target
v Direct
the resulting x-rays through tissue
v Capture
x-rays after leaving tissue
v Process
the resultant image for viewing
How does the fluoroscope control the x-ray
radiation?
v The
fluoroscope can control the number
of x-rays produced. The x-ray generator controls the amount of electrical
current delivered to the x-ray tube. Amount of current is measured in amps (mA)
v The
fluoroscope can control the energy
of x-rays produced. The x-ray generator also controls the voltage of the
current in the x-ray tube which determines the energy and penetrating ability
of the x-rays.Voltage is measured in volts –Kilovolt peak (kVp)
How do I
prepare for a fluoroscopic exam?
PRECAUTIONS: If you are
pregnant or think you may be pregnant, please check with your doctor before
scheduling the exam.
CLOTHING: You may be
asked to change into a patient gown. A gown will be provided for you. Lockers
are provided to secure your personal belongings. Please remove all piercings
and leave all jewelry and valuables at home.
EAT/DRINK: Specific
instructions will be provided based on the examination you are scheduled for
eat.
ALLERGIES: Notify the radiologist
or technologist if you are allergic or sensitive to medications, contrast dyes
or iodine.
RISKS/BENEFITS OF FLUOROSCOPY
v Because
Fluoroscopy is an x-ray machine, it has the same risks as other x-ray machines.
v Two major
risks
·
There is a small possibility of developing cancer
due to the exposure to the radiation
·
Injuries such as burns caused by the radiation
v Benefit o
If a patient needs a Fluoroscopy, the benefit outweighs the minute risks
FLUOROSCOPY PROCEDURES
- v Insertion
of an IV into patient’s hand or arm
- v Patient
moved onto x-ray table
- v Additional
line may be inserted for catheter procedures
- v X-Ray
scanner used to create fluoroscopic images of the body
- v Dye may
be injected into the IV at this point
- v Type of
care will be decided on after the procedure has finished
IN DEPTH PROCEDURE
• Continuous x-ray passes through the body
• Beam passes onto a television monitor
• Body part and motion can be seen in detail
During the procedure
Generally,
fluoroscopy follows this process:
- You will be asked to remove any clothing or
jewelry that may interfere with the exposure of the body area to be
examined.
- If you are asked to remove clothing, you will
be given a gown to wear.
- A contrast substance may be given, depending
on the type of procedure that is being performed, via swallowing, enema,
or an intravenous (IV) line in your hand or arm.
- You will be positioned on the X-ray table.
- For procedures that require catheter
insertion, such as cardiac catheterization or catheter placement into a
joint or other body part.
- A special X-ray machine will be used to
produce the fluoroscopic images of the body
- structure being examined or treated.
- A dye or contrast substance may be injected
into the IV line to better visualize the organs or structures being
studied.
- After the procedure has been completed, the
IV line will be removed.
After the procedure
v The type
of care required after the procedure will depend on the type of fluoroscopy
that is performed.
v If you
notice any pain, redness, and/or swelling at the IV site after you return home
following your procedure, you should notify your doctor as this could
indicate an infection or other type of reaction.
v Your doctor
will give more specific instructions related to your care after the examination
or procedure.
