Radiation Physics Test 5-Fluoro

who was credited for the discovery of fluoroscopy?

Thomas Edison

where is the xray tube located for fluoroscopy?

under the table

what is mounted like a c-arm and maintains alignment?

image intensifier

when is the xray tube activated in fluoro?

until image intensifier is pulled over and locked into place

what can the mA station range from because it is on continuously?

0.5 mA to 5 mA

why is a fluoroscopy machine xray tube considered "fixed"?

it is under the table and we cannot get it any further away from the patient

what is SOD?

source to object distance

what is the standard minimum distance between the fixed tube and the patient?

38 cm (15 in)

when in the OR using a C-arm, what is the standard minimum SOD?

30 cm (12 in)

how does an image intensifier work?

it intensifies the signal that is coming through the patient to allow for a brighter image so that there is more detail visible

what is the distance between the tube and the image intensifier called?

SID

what happens to image quality if you increase SID?

it decreases

what changes the SID during fluoro?

radiologists raising and lowering the image intensifier

what is the distance from the patient to the image intensifier called?

OID

what is it called an image intensifier?

it is intensifying the signal from the patient and projecting it onto a smaller area

what shape is the surface of the image intensifier?

concave

why is the image intensifier concave in shape?

to maintain the distance electrons have to travel at any point from input to output

what is the first thing x-rays are going to encounter when they leave the patient?

the input phosphor

what happens when x-rays strike the input phosphor?

it is going to kick out a ton of light photons in proportion to the x-ray it encounters (emits vertically)

how many light photons does the image intensifier produce when it absorbs each x-ray?

5,000

where are the light photons sent when they exit the input phosphor?

photocathode

it will take a lot of _____ _______ to produce one ________ (10-20%)

light photons, electron

what is made of photo-emissive material?

photocathode

what property of a material means that when it has encountered light, it is going to produce electrons through a process called photo emission?

photo-emissive

where do electrons get produced in the image intensifier?

photocathode

after electrons leave the photocathode, where to and how are they moved?

electrons are focused and accelerated towards the anode by electric lenses/focusing electrodes

what charge do electrons have?

negative

what creates the potential difference in the anode and what does it do?

the small amount of kV (25 kV) which helps accelerate electrons towards the anode

what happens in the anode when you apply more voltage during fluoro?

the electrons will travel further and closer to the output screen

what does the anode have that allows electrons to pass through to the output phosphor?

a hole

what is the hole for transmission of electrons made of?

zinc and cadmium

why is the hole in the anode small and thing?

we want it to produce a brighter image

what happens when electrons have been focused and hit the output phosphor?

they are converted to light photons

what are light photons converted to when they come through the output phosphor?

a digital signal

why does the output phosphor have a small aluminum plate?

to prevent any light from coming back into the output phosphor once it exits and to prevent the light from returning down to the photocathode

what is a CCD?

charged coupling device

what is the device after the output phosphor?

CCD

what was used before CCDs and what was the disadvantage?

video cameras, but there would be lag in the image

what is the main purpose of a CCD?

to convert light photons into electrons to form the digital signal

what happens when light photons hit the CCD?

it will emit electrons proportional to whatever light it encountered

what is an advantage of CCD?

it is extremely fast

while convergences are going on, what is the result?

a brighter image

what is the process of starting off with a few x-rays and making conversions to get a ton of light photons to end up in the CCD to produce the image?

total brightness gain

what is defined as an increase in image intensity by the image intensifier?

total brightness gain

what is calculated by multiplying 2 factors that we get from the image intensifier system?

total brightness gain

what two factors are multiplied to get total brightness gain?

minification gain and flux gain

what is the ratio between the areas on the input screen and the area on the output screen?

minification gain

what deals with the geometry of the image intensifier (how big the first thing is that is struck vs. the last thing that it struck)?

minification gain

what causes an increase in brightness or intensity?

minification gain

what is NOT a part of the final image?

the # of photons

how do you calculate minification gain?

input screen diameter^2/output screen diameter^2

what is more about how well the output phosphor converts electrons back to light?

flux gain

what is a measurement of the increase in light photons due to the efficiency of the output phosphor?

flux gain

what is the ratio of x-rays in vs. light out?

flux gain

what is the average flux gain?

3000-4000

what is the formula for flux gain?

light photons emitted by the output phosphor/x-rays striking the input phosphor

how do you calculate magnification?

input diameter/diameter used

what is the formula for dose change?

input diameter^2/diameter of screen used^2

what is controlled by electrostatic lenses?

magnification

what happens when the focal point is further away from the output screen?

magnification

what is the result of magnification on patient dose?

it increases patient dose

what is constantly changing while you are fluoroing?

mA and kV

why is mA and kV constantly changing during fluoro?

it is automatically adjusting the brightness of the image

how is brightness automatically adjusted on the image during fluoro?

by emitting more or less x-rays as you move over the tissues

what is automatic brightness control?

changing kV and mA to maintain the same brightness the entire time

what is the number one source of occupational dose in fluoro?

scatter from the patient

what is occupational dose measured in?

Gy

what are different variables in occupational exposure?

all staff, length of time, no exact distance so ISL is not used

what do you need to calculate exposure?

exposure time and rate

if the exposure rate is 25 mGy/min and the time is 40 seconds, what is the occupational exposure?

16.6 mGy

what is the relationship between SID and intensity?

inverse

the closer the image intensifier is to the patient, what happens to intensity?

it increases

what happens to image quality when intensity is increased?

it is improved

the patient does decreased due to ___

ABC

what is the relationship between OID and magnification?

directly related

what happens to magnification when you increase OID?

it increases

what happens to image quality when you decrease magnification?

it is better

what is higher is fluoroscopy because the source of x-rays is closer to the patient?

entrance skin dose

what is the general rule of thumb for entrance skin dose?

skin receives 2 R/min/mA

what are the table-top radiation intensity limits?

-2.1 R/min/mA @ 80 kV

-10 R/min

-20R/min when using high level fluoro

how do you calculate entrance skin dose?

multiple the duration of the dose by the mA it was performed at

what are some factors that cause an increase in entrance skin exposure?

short SID, low kV, decreased filtration

what can be used to calculate scatter radiation intensity?

entrance skin dose

at a distance of 1 meter from the "source" (patient), what is the intensity?

0.1% of the entrance skin exposure

how do you calculate entrance skin exposure?

multiple the Gy by 0.001

what happens to magnification if you decrease OID?

it is decreased, which increases image quality

when you increase mA, what happens to image quality and patient dose?

better image quality, increases patient dose

what kV and mA do you use for best quality and lowest dose?

high kV and low mA

what is the minimum source-to-skin distance for C-arm? stationary?

30 cm (12 in) for C-arm

38 cm (15 in) for stationary

what is the timer set on for safety during fluoroscopy?

5 min timer

what is last image hold?

maintains the last real-time fluoroscopic image until it is replaced by the unit being activated again

what do you want to make sure of for safety within fluoroscopy?

collimation and NO magnification

how thick do lead aprons have to be for fluoroscopy?

0.25 mm lead equivalent

what is the deadman switch?

a safety device designed to immediately stop operation when the operator releases their grip on the switch

what does ABC do?

ensures a consistent overall image brightness by automatically adjusting the X-ray tube's exposure parameters (kVp and mAs)

what is pulsed fluoro?

bursts of x-rays instead of a continuously flow