Week 1: Fluoroscopy

Question 1

What is fluoroscopy and what might it be used for?

Answer 1

• Invented by Thomas Edison in 1896.
• Dynamic radiographic exam, compared to diagnostic radiography which produces static images.
• Provides real-time dynamic viewing of internal anatomic structures and fluids
• Often used in conjunction with contrast media to visualize vessels (angiography) or to visualize the GI tract where internal structures share similar subject contrast.
• A static image known as a spot film can be taken during a fluoroscopic exam without interrupting the live action fluoro exam.

Question 2

What is the radiographer’s role during a fluoroscopic exam?

Answer 2

• Generally, the radiographer’s role is to assist the radiologist during a fluoroscopy exam in the radiology department. Assisting can include:
• Taking a patient history & explaining the procedure to the patient.
• Setting up the room to include fluoroscopy equipment & technical factors as well as contrast media needed.
• Readying radiation protection equipment.
• Assisting the patient into various positions.
• Aiding in patient comfort during the fluoro exam.
• Taking overhead images.
• Note-Fluoroscopy should never be used as a positioning guide.

Question 3

What is fluoroscopy never used for?

Answer 3

As a positioning guide

Question 4

Under the Table Fluoroscopy Unit

Answer 4

• Most commonly used for gastrointestinal (GI) exams.
• The fluoroscopic x-ray tube and image receptor are mounted on a C-arm to be aligned at all times.
• The x-ray tube is positioned under the table with the image receptor (image intensifier (II)or flat panel detector) positioned over the table, attached to the carriage.
• In DF (digital fluoroscopy) these units generally contain at least 2 flat panel detectors (1 for general radiography and 1 for fluoroscopy).
• Occupational dose is most intense at the level of the table and below.

Question 5

Over the Table Fluoroscopy Unit

Answer 5

* X-ray tube is above the patient table with the image receptor below the table.
* These units can be fully controlled, including the table, at an operator’s console featuring a joystick controller in a shielded control booth.
* In digital fluoroscopy (DF), these units generally contain a single flat panel detector for both general radiography and fluoroscopy.
* Occupational dose is most intense at the level of the table and above.

Question 6

Describe the fluoroscopic carriage

Answer 6

• The arm that supports the equipment suspended over the table.
• Contains controls for power to drive the carriage, brightness, spot image selection, tube shutters for collimation, image orientation, magnification, and table tilting.
  * For under the table units, it supports the image intensifier or flat panel detector.
  * For over-table units, it supports the x-ray tube.

Question 7

Describe the fluoroscopic table

Answer 7

-Must provide strength to support patients and are rated by the manufacturer for a particular weight limit.
-It is important that the table not absorb much radiation to avoid shadows, loss of signal and loss of contrast in the image.
-Carbon fiber technology offers a good combination of high strength and minimal radiation absorption, making it an ideal table material

Question 8

What is the milliamperage (mA) range used in image intensified fluoroscopy as compared to the mA range used in diagnostic x-ray tubes?

Answer 8

-In Fluoroscopy: 0.5–5.0 mA (the tube target must be fixed to prevent an SOD of less than 15 in (38 cm))
-In X-ray: 50–1,200 mA

Question 9

What is the purpose of the image intensifier (II) and how much of an increase in brightness can be expected because of the II?

Answer 9

• The II is housed within a glass or metal envelope that maintains a vacuum and is mounted inside a metal container for protection.
• An II is an electronic device that converts the intensity pattern(remnant beam) that exits the patient into a visible image suitable for capture by a television camera (video camera) or charge coupled device (CCD) and displayed on a monitor.
• The II was designed to amplify the brightness of an image.
• The II can increase brightness 500-8,000 times

Question 10

Image intensifier (II): Input fluorescent screen (input phosphor)

Answer 10

• 0.1 - 0.2 mm layer of sodium-activated cesium iodide (CsI) coated onto a concave surface.
• The input phosphor is concave to maintain the same distance between each point on the input phosphor and its corresponding location on the output phosphor to inhibit distortion.
• When an x-ray interacts with the input phosphor, it is converted to visible light.
• The CsI phosphors are tightly packed and needle-like. They are microlight pipes allowing for minimal light dispersion and improved spatial resolution. They absorb about 66% of the incident beam, which results in a good conversion efficiency, or quantum yield.

Question 11

Image intensifier (II): Photocathode

Answer 11

• The photocathode is bonded directly to the input phosphor with a thin, transparent adhesive layer.
• The photocathode is a thin metal layer composed of cesium and antimony compounds.
• Through photoemission, the photocathode emits electrons when stimulated by visible light from the input phosphor. (The process is similar to thermionic emission except that the stimulation is visible light instead of heat)

Question 12

Image intensifier (II): Electrostatic focusing lenses

Answer 12

• Negatively charged electrodes located inside and along the length of the glass envelope of the II.
• Because electrons produced at the photocathode are negative, the negative charge of the lenses accelerates and focuses the electron stream, which carries the fluoroscopic image (The pattern of electrons emitted from the large cathode end of the image-intensifier tube must be reduced to the small output phosphor)

Question 13

Image intensifier (II): Anode

Answer 13

• Non-rotating, positively charged and is supplied with about 25 kV. This + charge causes an extreme attraction of the negative electrons produced at the photocathode.
• The anode is positioned immediately in front of the output phosphor.
• It has a hole in its center that permits the accelerated electrons to pass through the anode and onto the output phosphor.

Question 14

Image intensifier (II): Output fluorescent screen (output phosphor)

Answer 14

• The output phosphor is usually about 1” in diameter.
• Made of silver-activated zinc cadmium sulfide.
• Electrons produced at the photocathode have high kinetic energy and contain the image of the input phosphor in minified form.
• These electrons strike the output phosphor, converting the electrons into green light photons that exit the II tube. These green light photons produced at the output phosphor are the fluoroscopic image and must be collected for viewing on a monitor.
• Collection of the green light is done with a television camera (video camera) or a charge coupled device (CCD).

Question 15

Define minification gain

Answer 15

• Occurs as a result of the same number of electrons that were produced at the large input phosphor by the photocathode being compressed into the area of the small output phosphor. Most II tubes have input phosphors of 6”, 9”, or 12”. The typical output phosphor has a diameter of 1”.

-Simply an increase in brightness or intensity (not an improvement in the quality or number of photons making up the image)

Question 16

Minification Gain formula

Answer 16

minification gain= input screen diameter(squared)/ output screen diameter(squared)

Question 17

What is the minification gain for an image intensification tube with an input screen diameter of 6” and an output diameter of 1”?

Answer 17

6(squared) = 36
1(squared) = 1

Minification gain: 36/1 = 36

Question 18

Define flux gain

Answer 18

• Flux gain is a measurement of the increase in light photons due to the conversion efficiency of the output phosphor.
• Flux gain is the ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor.

Question 19

Flux gain formula

Answer 19

Flux gain= number of output light photons/number of input x-ray photons

Question 20

If the output fluorescent screen produces 75 light photons for each x-ray photon that strikes the input fluorescent screen, what is the flux gain?

Answer 20

Flux gain= 75/1= 75

Question 21

Define total brightness gain

Answer 21

• Measurement of the increase in image intensity achieved by an image intensification tube. It is determined by the product of minification gain and flux gain.

Question 22

Total brightness gain formula

Answer 22

Brightness gain= minification gain x flux gain

Question 23

Using the previous 2 questions you answered about the Minification gain(answer was 36) and Flux gain(answer was 75), calculate the brightness gain.

Answer 23

36 x 75 = 2,700

Question 24

Describe automatic brightness control (ABC)

Answer 24

• Also referred to as automatic brightness stabilization (ABS), automatic dose control (ADC), or automatic exposure rate control (AERC).
• Feature of fluoroscopic equipment that maintains proper image brightness automatically by varying the kVp, mA, pulse time, or all three depending upon the patient’s part thickness, position, and/or pathologies present.
• The ABC monitors the current (electron quantity) flowing between the photocathode and the anode of the II, or the intensity of the light at the output phosphor of the II. Adjustments are automatically made to technical factors to maintain proper image brightness.
• All analog ABC’s have a relatively slow response time (lag), which is noticeable while scanning a patient fluoroscopically from head to foot. Image brightness adjustment lags a moment behind rapid changes in tissue density.

Question 25

Describe the magnification tube and multifield image intensification and its effect on patient dose, contrast resolution, and spatial resolution

Answer 25

• The greater the voltage applied to the electrostatic lenses, the greater the electron acceleration and the closer the focal point moves toward the input phosphor, which magnifies the image. By selecting magnification on the fluoro carriage, you are changing the voltage applied to the electrostatic lenses. This reduces the FOV, magnifying the image.
• Depending upon the number of magnification options available, these tubes are called multifield, dual-field, triple-field, or quad-field intensifiers.
• Magnification tubes are capable of 1.5 - 4 magnification
• Resolution can be increased from about 4 lp/mm to 6 lp/mm when magnification mode is used.
• When magnifying an image, only a portion of the input screen is irradiated, the minification gain is reduced, and fewer photoelectrons are incident on the output screen, so the ABC responds by adjusting ma, kVp, and/or pulse time to maintain image brightness.
• With the II in magnification mode:
-Patient dose: increases
-Contrast resolution: increases
-Spatial resolution: increases

Question 26

Magnification formula

Answer 26

Magnification= input screen diameter/ diameter of input screen used during magnification

Question 27

What is the magnification for an image viewed with an image intensification tube with an input screen diameter of 9” that is using a 4” diameter during magnification?

Answer 27

9/4= 2.25

Question 28

Two methods used in image intensified fluoroscopy to electronically convert the visible image on the output phosphor into an electronic signal

Answer 28

• Television camera
• Charge Coupled Device (CCD)

Question 29

Television camera

Answer 29

• Coupled directly to the output phosphor and converts the visible image on the output phosphor of the II into an electronic signal.
• Coupling of the television camera to the output phosphor can be done by fiberoptics or a lens system.
• Vidicon and Plumbicon are television cameras used most often.
• This type of fluoroscopy is considered analog.

Question 30

Charged couple device (CCD)

Answer 30

• Sensitive component of the CCD is a layer of crystalline silicon. When the silicon is illuminated by the light from the output phosphor, a charge is generated, which is then sampled, pixel by pixel and manipulated to produce a digital image.
• Coupled to the output phosphor of the II via fiberoptics or lens system.
• CCD is much smaller and rugged than television camera.
•Converts the visible image on the output phosphor of the II into an electronic signal.

(Like the television camera except the newer way)

Question 31

CMOS (complementary metal oxide semiconductors)

Answer 31

Even newer than CCD

Question 32

Viewing & Recording Systems

Answer 32

• Fluoroscopy requires high-quality video display for fine details and subtle contrast differences in patient anatomy.
• Flat panel digital displays with high maximum luminance and high-contrast ratios are common.
• Flat panel displays should be calibrated with the DICOM part 14 Grayscale Standard for the widest range of gray levels.
• Recording dynamic images or digital spot images can be achieved with flash drives, cd’s, DVD’s, or a fluoroscope’s hard drive. Adequate memory is necessary.

Question 33

Fixed vs Mobile Fluoroscopy

Answer 33

-Fixed: can’t be moved to other rooms, SSD: 15 inches (38cm)
-Mobile: can be moved around to different rooms/areas, SSD: 12 inches(30cm)

Question 34

C-arm

Answer 34

A C-arm X-ray machine is a medical imaging machine and can be used flexibly in different surgical settings within any medical clinic or hospital. The device adopted the name because of its general appearance of a C-shaped arm that connects the X-ray detector and the x-ray source

Question 35

Mini C-arm

Answer 35

A mini C-arm is designed to scan patient extremities. The C-arm has a much smaller arc and lower generator power capacity, making it suitable for hands, feet, wrists, and elbows. A few models are even capable of some limited shoulder exams

Question 36

Hand-held x-ray device

Answer 36

Small and convenient, the X-ray detector used with the handheld fluoroscopy device is thin, flat and lightweight and can be easily positioned and moved behind the arm, leg or other extremity that is being examined. The extremity is placed on top of the detector, and the handheld is aimed at it

Question 37

O-arm

Answer 37

The O-arm is a cone beam imaging system designed primarily to support orthopedic surgery as well as for image-guided and vascular surgery. Using a gantry that can be opened or closed, the O-arm can function as a 2D fluoroscopy device or collect 3D volumetric imaging data like a CT system

Question 38

Multifield image intensification

Answer 38

Most image intensifiers are of the multifield type. Multifield image intensifiers provide considerably greater flexibility in all fluoroscopic examinations. Trifield tubes come in various sizes, but perhaps the most popular is 25/17/12 cm. These numeric dimensions refer to the diameter of the input phosphor of the image intensifier tube

Question 39

The __________ emits electrons when illuminated by visible light from the input phosphor

Answer 39

Photocathode

Question 40

If the radiologist observes something during the fluoroscopic examination and would like to preserve that image for further study, a radiograph called a ______ ______ can be taken without interruption of the dynamic examination.

Answer 40

Spot film

Question 41

Internal scatter radiation in the form of x-rays, electrons, and particularly light, can reduce the contrast of image intensifiers through a process called ________ _________

Answer 41

veiling glare

Question 42

How an image intensifier works

Answer 42

The primary x-ray beam exits the patient and strikes the input screen of the image intensifier tube, which is a vacuum tube with a cathode and an anode. The fluorescent screen is built into the image intensifier as its input screen. The fluorescent screen absorbs the x-ray photons and emits light photons, which immediately encounter the photocathode (the cathode of the tube) that is in contact with the input screen to prevent divergence of the light beam. The photocathode absorbs the light photons and emits electrons. The electrons are then accelerated from the cathode toward the anode and the output screen by the potential difference that exists between the cathode and the anode. At the same time, the electron beam is focused onto the output screen, which is much smaller than the input screen. Electrostatic lenses are used to accelerate and focus the electrons. The primary brightness gain occurs from the acceleration and focusing of the electron beam. The acceleration of the electron beam increases its energy and its ability to emit light at the output screen. The focusing of the electron beam intensifies the image into a smaller area. The output screen absorbs the electrons and emits light photons, which are then available for viewing or further electronic processing by a video system. Note the changes in the quantity of photons and electrons in the image intensification tube at each stage of the intensification process. The entire image intensification tube is encased in a lead-lined housing that effectively absorbs the primary beam while permitting the intensified light photon image to be transmitted to the viewer. An ion pump device called a getter is used to remove ions produced during operation and to maintain the vacuum within the tube.

Question 43

For the Automatic Brightness Control, regulation of the primary beam can be accomplished by

Answer 43

varying kVp, mA, and pulse time

Question 44

The output phosphor absorbs ______________ and emits ______________

Answer 44

Electrons, light photons

Question 45

The input phosphor of the image intensifier converts _______________ to _______________

Answer 45

X-rays, light

Question 46

Reduction of brightness seen at the periphery of the image because objects positioned furthest from the center of the input phosphor are inherently unfocused. This type of distortion is called

Answer 46

-vignetting (pincusion distortion)
(causes image intensity to be greater at the center of the image and less at the edges)

Question 47

The invention of the fluoroscope is credited to

Answer 47

Thomas A. Edison in 1896

Question 48

Most image intensification tubes have input screens of

Answer 48

6” (15 cm) or 9” (23 cm) or 12” (30cm)

Question 49

The typical output screen has a diameter of

Answer 49

1” (2.5 cm)

Question 50

Size distortion is caused by

Answer 50

OID

Question 51

Shape distortion is primarily caused by

Answer 51

-Geometric problems in the shape of the image intensification tube
(Although the image intensifier input screen is concave, it does not completely eliminate edge distortion at the output screen. Electrons at the outer edges of the image tend to flare outward as they are electrostatically focused.)

Question 52

Most commonly used fluoroscopic viewing system is

Answer 52

flat-panel digital displays with high maximum luminance and high contrast ratios

Question 53

Magnification image intensifiers cause _________ patient dose because the automatic brightness control (ABC) will increase the tube output to compensate for the loss of electrons within the image intensification tube during magnification

Answer 53

Increased

Question 54

angiography

Answer 54

visualization of vessels

Question 55

_______ kVp and _______ mA are preferred

Answer 55

High, low

Question 56

The numeric dimensions, such as a typical multifield tube which is 25/17/12, refers to the diameter of the ________ ___________ of the image-intensifier tube

Answer 56

input phosphor

Question 57

In the magnified mode, the ___________ gain is reduced, and fewer photoelectrons are incident on the output phosphor. A dimmer image results.

Answer 57

Minification

Question 58

A television camera tube or CCD converts the light signal from the _________ __________ to an __________ __________

Answer 58

Output phosphor, electronic signal

Question 59

Glass envelope

Answer 59

Maintains vacuum and provides mechanical support for the internal elements