Fluroscopy

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.