Mobile Radiography, Fluoroscopy and Digital Fluoroscopy

for portables, they automatically engage the highest ___ available

mA

For 100 cm (40"), average person can use

fingertip-to-opposite axilla

From 100 cm (40"):
125 cm (50"):
150 cm (60"):
180 cm (72"):

125 cm: 1 ½ times increase in technique
150 cm (60"): Double technique
180 cm (72"): Triple technique

For mobile chests, always check the angle of the tube from ____ perspectives, while standing back as far as possible

two

If the anatomy of interest includes joint spaces, it is always more important to keep the CR perpendicular to the ____ rather than to the cassette or IR

anatomy

do not ever angle CR if looking at

fluid levels

if your pt is sitting at 20 degrees from vertical and back of bed is 10 degrees from vertical, how much angle for CR if looking for fluid levels

angle CR horizontal

For mobile radiography of large body parts, use ___ ratio grids for wide positioning latitude when grids are used

low

recommended approach to technique with portables is to have

manual technique chart

fluoroscopy was developed to radiologists could view ____ images

dynamic

image intensifier improved fluoroscopy by

• Improved fluoroscopy by increasing image brightness
Dramatically reduced the mA required, saving patient dose

fluoroscopic tubes operate between

1-5 mA

Due to low exposure rate, fluoroscopic images are statistically inferior to overhead images and demonstrate more

noise

ABC

automatic brightness control

purpose of image intensifier tube

Convert the remnant radiation beam into an amplified light image

The output phosphor (left, arrow) is always ___ cm in diameter

2.5

Concentration of the beam from the input to the output phosphor increases ___ by thousands of times

brightness

Increasing the physical diameter of the input phosphor results in increased

image resolution

the input phosphor converts x-rays into

light

Upon absorbing light energy, the photocathode emits

electrons

Concentrating the electrons increases output intensity. This process is called

minification

A thin photoemissive metal layer, made of a combination of antimony and cesium compounds

photocathode

A layer of fluorescent crystals of cesium iodide

input phosphor

A series of positively-charged metal rings that become narrower toward the anode end of the tube

The Electrostatic Focusing Lens

Made of cesium iodide
Converts the kinetic energy of the electrons striking it into light

output phosphor

The ratio of the number of light photons emitted by the output phosphor to the number of X-rays striking the input phosphor

flux gain

as output phosphor gets smaller, what happens to minification gain?

decreases

The product of the minification gain and the flux gain

brightness gain

a smaller region of the input phosphor is projected onto the output phosphor by moving the what where?

focal point of the electron beam closer to the input phosphor

Magnification mode can be used to improve what feature in the image?

spatial resolution or sharpness in the image

To avoid the appearance of noise from a poor SNR, the what increases the what to compensate for the loss of minification gain

Automatic Brightness Control
mA

Patient exposure increases by the ratio of the

change in area of the active input phosphor used

Using magnification mode in fluoro has what bad quality?

increases patient dose

As the patient rolls onto her side, the increased tissue thickness must be_____ to maintain fluoroscopic image brightness

compensated for

brightness of a fluoroscopic is _____ to the mA

directly proportional

brightness of a fluoroscopic image is to the what power of kvp

5th power

Generally, what kind of technique is preferred with fluoro?

high kVp / low mA

No form of electronic intensification can improve the image above the

statistical level of the absorbed x-ray photons

no amount of electronic intensification can overcome the mottle or noise produced when an

insufficient amount of x-rays is reaching the image intensifier

Small, momentary defects in the distribution of brightness ("twinkling") in a dynamic image

This noise pattern appears to be drifting across the image, creating the appearance of "crawling ants" or "snow"

scintillation

what is the best solution to improve scintillation

raise the mA

Image intensifiers are generally poor at

preserving high contrast in the transmitted image

Contrast deteriorates with aging of the intensifier -deterioration can be as high as ____% per year

10

Slight magnification and increased blur around the periphery of the image

pincushion distortion

Scattered random light from the output phosphor

veiling glare

Loss of brightness toward the periphery of the image

vignetting

A contributing factor to vignetting is

pincushion distortion

High-resolution TV cameras that use an ADC to turn the electronic signal into digital numbers

Digital Photospot Cameras

what piece of equipment in the OR allows for significant reductions in patient exposure

Carbon fiber tables

A series of short visual checks, rather than continuous fluoroscopy, dramatically reduces cumulative exposure to the patient

Intermittent Fluoroscopy

This is the most important way to limit patient exposure during fluoroscopic studies

Intermittent Fluoroscopy

Keeping the last image displayed on the monitor

"Last Image Hold" Devices:

feature that automatically turns the x-ray beam on and off during operations

pulsed fluoroscopy

with Pulsed-Progressive Mode, the fluoro tube is being run in

radiographic mode

refers to the length of each pulse

pulse width

refers to how many pulses occur per second of operation

pulse rate

if pulse width is reduced from 6 to 3, how much is patient dose decreased?

1/2

The _____ detector uses a cesium iodide phosphor coupled to an active matrix array (AMA) of amorphous silicon thin-film transistors (TFTs)

indirect

The ____ detector uses an AMA of amorphous selenium TFTs

direct

Dual-Use FPD systems convert from radiographic to fluoroscopic mode by grouping sets of 4 small pixels together to form a larger effective pixel

binning

DFPDs can be operated either in

continuous or pulsed fluoroscopy mode

• Changing from fluoroscopic mode to DF mode requires an increase in tube current of 20 to 100 times the mA

• Nonetheless, a net decrease in patient exposure can be achieved compared to continuous fluoroscopy because why

the extremely short pulse times for exposures

The time it takes for the x-ray tube to be switched on

Interrogation Time:

The time it takes for the x-ray tube to be switched off

Extinction Time

Grids for DFPDs have their lead lines running in which direction to prevent aliasing artifacts

diagonal