RAD 172 Final Review - Fluoroscopy

Dynamic

visualizing the motion and function of internal structures

Static

captures still images of the body

Dark adaptation

required to permit the RODS of the eye to become activated

Visual acuity

controlled by the CONES of the eye

Where are cones located in the eye?

Center of the retina

What are cones used for?

Used for perception of small objects and bright/high light level conditions

Scotopic

vision in dim light

Photopic

vision in daylight or other bright light

Photopic visual acuity is ____times greater than scotopic acuity

10

Typical basic fluoroscopic image chain and equipment used

Fluoro x-ray tube and IR are mounted on a C-arm to maintain alignment

What does the C-arm permit?

- Permits the IR to be raised and lowered to vary the beam geometry for max resolution while the x ray tube remains in position

- Permits scanning the length and width of the table

Carriage

the arm that supports the equipment suspended over the table

what does the carriage include?

- Image intensifier

- X-ray tube

- Controls for power to drive

- Spot image selection

- Tube shutters (collimation)

- on/off dead man switch

- Magnification selection

- Reverse image search

- Brightness

What must be done for an exposure be taken when using the carriage?

Exposure cannot be taken until the carriage is returned to a full beam intercept position

Fluoro xray tubes : mA range

0.5 - 5.0 mA

The tube target is fixed to prevent a SOD of...

less than 15 inches or 38 cm

Tube can be operated by a ...

foot pedal (dead man type)

What do the tube have that permit maintenance of close collimation?

electronically controlled shutters

How much can image intensifiers increase image brightness?

500- 8000 times

Brightness of fluoro depends on

anatomic part

kVp

mA

What kVp and mA is preferred?

high kVp

low mA

Size distortion is caused by

OID

Shape distortion is caused by

geometric problem in the shape of the image intensification tube

How does image intensifier work?

1. Beam exits patient

2. strikes input screen

3. input screen absorbs xray photons and emits light photons

4. light photons interacts with photocathode and absorbs the light photons and emits electrons (photoemission)

5. Electrons are then focused and accelerated from the photocathode toward the anode and output screen

6. Output screen absorbs these electrons and emits light photons

What is the input screen composed of?

cesium iodide

How much of the incident beam do Csl phosphors absorb?

66%

What shape is the input screen and why?

concave shape b/c helps minimize image distortion

What is the photocathode made of?

cesium and antimony compounds

Why is the photocathode in contact with the input screen?

to prevent divergence

How are the electrons focused and accelerated from the photocathode toward the anode and output screen?

potential difference (25 kV) that exists between each side

What are electrostatic lenses?

series of charged electrodes used to accelerates and focus electrons to the anode and output screen

What is the output screen made of?

Zinc cadmium sulfide

each photon electron that hits the output screen results in _____________more light photons than before

50 - 75 x

What part of the image intensifier output screen has better resolution?

center

(brighter image and less geometric distortion )

What is flux gain?

measurement of the increase in light photons due to the conversion efficiency of the output screen

Flux gain formula

output screen (light photons) / input screen (light photons)

What is minification gain?

result of the same number of electrons that were produced at the large input screen being compressed into the area on the small output screen

Minification gain formula

input screen diameter^2 / output screen diameter^2

What is brightness control?

used to automatically maintain satisfactory fluoroscopic image brightness and contrast

What does ABC stand for?

Automatic brightness control

What does ABC do?

Maintains the brightness of the image by automatically adjusting the exposure as necessary according to subject density and contrast

- has a slow response time

What maintains optimum fluoroscopic image brightness during fluoroscopic

operation - Very important in maintaining image quality?

Electronic feedback loop between image intensifier and xray tube

What is vignetting?

a fall off in brightness at the periphery of an image

Csl image intensifier capable of...

2lp/mm

Digital flouro capable of...

3lp/mm or better

What is interrogation time?

length of time required for the generator to come on and acheive the necessary kVp and mAs levels

What extinction time?

time required to shut the generator down in preparation for the next pulse

continuous fluoro

allows for real time imaging but delivers large dose for patient

pulsed fluoro

delivers bursts of radiation at set intervals, reducing fluoro times

duty cycle

the fraction of time between the interrogation and the extinction times (xray tube is energized)

thin film transistors (TFT)

combined with pulsed technology

replaces the image intensifier

most common viewing system

flat panel TFT system

Flat panel TFT system includes...

a charged coupled device (CCD) that stores from light photons then transmitting the image to a monitor for viewing

200 - 400 microns DEL size (2-3 lp/mm)

Pixel

smallest element of digital image

matrix

2d series of square boxes composed of pixels

Digital pixel size?

1024 x 1024 pixels

pros of digital flouro

- Post processing (results in enhanced contrast resolution)

- Speed of acquisition

- 1024 x 1024 image matrix (high resolution)

- Reduces patient dose with both dynamic and static images recorded at reduced doses

what are the two designs of digital flat panel fluoro systems?

Fluoro tube below patient

Fluoro tube above patient

Multiple detector flat-panel systems:

- Tube is under the table and detector is in carriage above table

- 2 additional detectors located to perform both upright and recumbent

- Can switch electronically between fluoro and static

Single Detector flat- panel system:

- Used for all imaging

- More cost effective

- Requires single x-ray tube to perform both static and dynamic images

- Tube is mounted above the table top

What is a feature of digital radiation protection that retains the last image?

Last-image hold feature

What are some post processing features in digital radiation protection?

Window level, window width, filtering

How much can digital radiation protection reduce patient exposure compared to conventional methods?

Up to 90%

Radiation protection for patient:

Use largest field of view to area of interest

Highest kVp

Low dose modes

Pulsed fluoro

Tabletop exposure rate should not exceed...

10R/min

(At that rate skin redding can happen after 20 minutes ( 10 minutes under boost mode))

Mobile minimum SOD

12 inches or 30 cm

Fixed minimum SOD

15 inches or 38 cm

Magnification mode __________ dose with image intensifier. (2x dose increase per mag field)

increases

Lead apron pb/eq

at least 0.5 mm

If hands must be placed in the primary beam, lead gloves of atleast ____________Pb/eq must be worn

0.5 mm pb/eq

Tech should keep what part of their body with the lead apron facing ______?

front of their body, facing the patient and tube

highest scatter happens @ _________ degree angle incident beam

90 degree angle

bucky slot cover

0.25 mm Pb/eq

Total brightness gain

measurement of the increase in image intensity achieved by a image intensification tube

total brightness gain formula

minification gain x flux gain

The greater the voltage, the greater the acceleration, what happens to the focal point?

closer the focal point moves toward the input screen

triple field intensifiers

14, 7, 5 inch fields

dual fields

9, 6 inch field

Patient exposure _________ when a __________ viewing mode is selected

increases, smaller

magnification formula

Input Screen Diameter / diameter of input screen used during magnification