Ch. 25 Study Guide (Conventional Fluoro)

Who invented Fluoroscopy?

Thomas A. Edison in 1896

Unit for illumination level:

Lamberts and Millilamberts (1L = 1000mL)

What is the function of rods and cones?

Structures of the eye responsible for the sensation of vision. When light arrives at the retina from the cornea then lens, it is detected by the rods and cones.

Photopic vision?

Human vision of intense light levels (daylight vision) used by cones

Scotopic vision?

Human vision of low light levels (night vision) used by the rods

What is visual acuity?

Ability to perceive small objects better

Cones have better visual acuity and contrast perception than rods.

Factors that affect the brightness of fluoroscopic images:

• Anatomy being examined

• kVp

• mA

What is the mA used in fluoroscopy?

less than 5 mA

Compare the patient dose of Fluoroscopy vs Conventional x-ray:

Fluoroscopy: Lower mA, continuous x-ray beam, longer exposure time (High patient dose)

Conventional x-ray: Higher mA, brief x-ray beam, shorter exposure time (Low patient dose)

Components of Image intensifier (Very important)

1. Metal Housing

2. Vacuumed Glass or metal envelope

3. Input phosphor

4. Photocathode

5. Electrostatic lens

6. Anode

7. Output phosphor

Materials/chemicals used in each component (Very important)

Input phosphor made of cesium iodide which convert x-ray into visible light

Photocathode convert visible into electrons

PMT multiply the electrons with the help of dynode

Output phosphor made of zinc cadmium sulfide convert e- to visible light

Focusing lens used to converge the light to CCD

CCD use to capture real time x-ray and display on monitor screen

Functions of each component of the Image intensifier (very important)

Metal Housing: Protection from rough handling and breakage

Vacuumed glass or Metal envelope: Structural support, maintains a vacuum

Input phosphor: Converts the x-ray energy into visible light

Photocathode: Emits electrons when stimulated by the light from the input phosphor (photoemission)

Electrostatic lens: Focuses the electron stream on the output phosphor.

Anode: Allow electrons to pass through to the output phosphor

Output phosphor: Accelerated electrons interact to produce visible light

What is Flux Gain?

The ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor.

What is Minification Gain?

The ratio of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor.

Calculation of Flux Gain?

Flux gain = number of output light photons

                   number of input x-ray photons

Calculation of Minification Gain?

Minification Gain= D1 squared

                              D2 squared

D1 = Diameter of the input phosphor

D2 = Diameter of the output phosphor

Calculation of total Brightness Gain?

Brightness gain = minification gain x flux gain

What is veiling glare?

Scattered radiation in the form of x-rays, electrons, and particularly light can reduce the contrast of image intensifier tubes.

What is vignetting?

The reduction in brightness at the periphery of the image.

What is a multi-field image intensifier?

Produces up to three different magnifications of the image

Which input phosphor size will produce the biggest magnification? (27, 17 or 12 cm)?

12 cm?

Advantages of magnification mode?

Better spatial resolution

Better contrast resolution

Which mode gives you more coverage of the anatomy?

25 cm?

What is the focal point?

Reduce the field of view (FOV)

What happens to the focal point as you change the mode from big (25) to small (12)?

Causes the electron focal point to move farther from the output phosphor, increases magnification (similar to increasing OID)

How can you calculate the magnification factor of a multi-field image intensifier?

MF = Initial diameter of the input phosphor

          New diameter of the input phosphor

Calculate the increase in radiation dose when you change from 36-inch mode to 12-inch mode.

???

What is the disadvantage of the magnification mode?

Higher patient dose

How the light from the output phosphor is converted to a visible image on the monitor? (Two different devices)

Thermionic television camera tube and charge-coupled device (CCD)

What is the function of television camera tube? Name the two common models.

Converts the light image from the output phosphor into an electrical signal.

Vidicon tube: Most common
Plumbicon tube: Modified version of vidicon

Components of television camera tube

Learn how each component of the television camera tube works.

three layers of the target assembly and their functions.

What are the chemicals used in signal plate and target plate?

A thin layer of metal or graphite
Antimony trisulfide

Which is the photoconductive layer of the television camera tube?

Target plate or material: Antimony trisulfide

What are the two systems used to connect the television camera tube to the image intensifier?

Fiber optics system

Lens system

Learn the advantages and disadvantages of each system.

How many lines per frame are used in CRT monitors used in regular fluoroscopy?

525 lines per frame

Learn the function of a photo spot camera. What is the advantage of using it?