Image Tubes/ Image intensified fluoroscopy

Fluoroscopy is a … radiographic examination, compared to
diagnostic, which is static

dynamic

Radiographers should perform fluoroscopy only for…examinations, where
diagnosis is not involved

static

Image intensification tubes were developed in 1948 and they resulted in video camera and monitor systems which began to replace

Mirror systems

Currently used only for studies that require observation of dynamic physiological function

Fluoroscopy

Types of fluoroscopic equipment

C-arm mounted

Carriage

A fluoro carriage typically includes what?

intensification tube or x-ray tube

Fluoro x-ray tubes are similar to diagnostic x-ray tubes but how do they differ?

operate at longer periods of time w/ much lower mA

Fluoroscopic mA range

0.5-5.0 mA

A fluro tube target must be fixed at what SID?

15” (38cm)

Until when was image intensification technology developed

1948

Design to electronically amplify the brightness of an image

Image intensification tube

Modern image intensifiers are capable of increasing the image brightness to what?

5000-8000x

The input screen consists of a 0.1 - 0.2 mm layer of …. coated on the concave surface of the image intensification tube

Cesium iodide

The input screen surface may be made of glass, steel, or aluminum and ranges from … in diameter, depending on the manufacturer and use

6”-23”

What does the Input screen do?

Absorbs x-ray photons & emits light photons

What does the photocathode do?

Absorbs light photons & emits electrons

The process of converting x-rays to light to electrons is called

Photoemission

a negatively charged electrode that converts light into electrons using the photoelectric effect

Photocathode

What charge is the anode?

Positive

How much kV is the anode normally supplied w/?

+25 kV

Where is the anode positioned?

Inside glass envelop in front of output screen

What permits the accelerated electrons to pass through the anode field and onto the output screen

A hole in the center

The output screen is what type of screen?

glass fluorescent screen

What type of phosphor is the output screen?

silver-activated zinc cadmium sulfide

The electrons that strike the output screen are converted into what that exit the tube?

light photons

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

Brightness gain

Brightness gain formula

minification gain x flux gain

Calculated as the ratio between the area of the input and output screens

Minification gain

Minification gain formula

input screen diameter² / output screen diameter²

Flux gain formula

#of output light photons / #of input x-ray photons

Provides greater flexibility in all fluoroscopic exams and is standard in digital fluoroscopy

Multifield Image Intensification

When switching to a smaller mode, the image appears

Magnified

In magnification mode, minification gain is…, and fewer photoelectrons are incident on the output phosphor – a dimmer image results

reduced

To maintain the same level of brightness in magnification mode, the x-ray tube mA is… by the ABC which … the PT dose

increases

By increasing dose in magnification mode what is improved?

contrast & spatial resolution

Sensitive to low light (color blind), use for night vision (scotopic vision)

Rod

Are less sensitive to light, response for daylight vision, perceives (photopic vision)

Cones

Accelerate and Focus electrons and directs them toward the output screen

Electrostatic lenses

Leakage radiation must be less than …. at a distance of… from the protective housing

1 mGya/h & 1m

The control panel must indicate the conditions of exposure and must … when the x-ray tube is energized

positively indicate

The SID indicator must be accurate to within…of the actual SID.

2%

How much filtration for exposures using above 70kvp? 50-70kvp? below 50kvp

1. 2.5mm

2. 1.5mm

3. .5mm

The SSD must be not less than… on stationary fluoroscopes and not less… than on mobile fluoroscopes

38cm & 30cm

The fluoroscopic image receptor assembly serves as a primary protective barrier and must be how much lead equivalent?

2mm Pb

The fluoroscopic exposure control should be of what kind

Dead man

Where is the bucky slot moved during exam & how much of an opening is left?

moved to end of table & 5cm (12.7”)

The bucky slot should be how much lead equivalent?

0.25 mm Pb

The protective curtain should be how much lead equivalent

0.25 mm Pb

The cumulative timer produces an audible sound when time exceeds?

5min