Exposure Factors ( 5 relationships you need to know kVp, mA, s, Bucky, SID)

Summary

This video covers the relationship between various technical factors in x-ray imaging, including kVp, mA, exposure time, SID, and the bucky factor. It explains how these factors impact x-ray exposure and image quality, focusing on their importance and interdependence. The video emphasizes the kVp as the most critical parameter and discusses how changing one factor affects others. The content is designed to help technologists understand and control exposure settings effectively, using practical examples and a simplified approach to mastering the equations involved.

Takeaways

• 🔬 The script discusses the relationship between various technical factors in X-ray exposure, including kVp, mAs, time, SID (Source to Image Distance), and the Bucky factor.
• 📐 kVp (kilovolt peak) is the most crucial parameter for X-ray exposure and is sensitive to changes, affecting both contrast and penetration.
• 🔍 The SID is the second most important parameter, inversely proportional to the intensity of X-rays reaching the image receptor, with changes affecting the exposure quadratically.
• ⏱️ Time, mAs (milliamperage seconds), and the Bucky factor are considered to have equal importance and are linearly related to X-ray exposure.
• 📉 The Bucky factor measures the attenuation of X-rays after passing through the patient but before reaching the image receptor, with an increase in the Bucky factor leading to a decrease in exposure.
• 📚 Understanding the relationship between these parameters is essential for a radiology technologist to adjust one parameter and compensate by changing another to maintain consistent exposure.
• 📉 The script introduces the '15% rule' for kVp, which states that a 15% increase in kVp results in a doubling of exposure due to its exponential relationship.
• 🔄 The inverse relationship between SID and exposure is highlighted, emphasizing that increasing the SID results in a quadratic decrease in the number of X-rays reaching the detector.
• 🔄 The mAs is directly proportional to exposure, with a higher mAs resulting in more X-rays being produced in the same amount of time.
• 📝 The script encourages memorization of the relationship between these parameters by writing down the equation multiple times, which will help in adjusting exposure settings.
• 🔧 The final equation provided can be used to solve for the time in seconds, which is often the parameter adjusted to fine-tune exposure settings on X-ray equipment.

Q & A

What are the key technical parameters discussed in the script that affect X-ray exposure?

The key technical parameters discussed are kVp (kilovolt peak), mA (milliampere), time, SID (source to image distance), and the Bucky factor.

Why is kVp considered the most sensitive parameter for X-ray exposure?

kVp is considered the most sensitive parameter because it controls the penetration and contrast of the X-ray beam, and even a small change in kVp can significantly affect the exposure.

What is the 15% rule in radiography and how does it relate to kVp?

The 15% rule in radiography states that if you change the kVp by 15%, the exposure changes by a factor of two, because exposure is sensitive to the fifth power of kVp.

How does SID (Source to Image Distance) affect the intensity of X-rays measured on the image receptor?

SID is inversely proportional to the intensity of X-rays measured on the image receptor. As SID increases, the intensity decreases due to the spreading out of X-rays over a larger area.

What is the relationship between the Bucky factor and the exposure measured on the image receptor?

The Bucky factor measures the fraction of X-rays that are blocked or attenuated before reaching the image receptor. As the Bucky factor increases, the exposure measured on the receptor decreases.

How does mA relate to the exposure in X-ray imaging?

mA is directly proportional to the exposure in X-ray imaging. A higher mA results in more X-rays being produced, thus increasing the exposure.

What is the significance of the relationship between mA and time in X-ray exposure?

mA and time are directly proportional to the number of X-rays produced. A higher mA or longer exposure time results in more X-rays being measured at the image receptor.

How can one compensate for a change in one technical parameter by adjusting another?

One can compensate for a change in one technical parameter by adjusting another according to their inverse or direct proportional relationships with exposure, ensuring the overall intensity on the image receptor remains the same.

What is the purpose of understanding the relationship between these technical parameters and X-ray exposure?

Understanding these relationships allows a technologist to make informed adjustments to the X-ray settings to maintain optimal exposure and image quality, even when changing one or more parameters.

Why is it important to be able to write down the equation for X-ray exposure from scratch?

Being able to write down the equation from scratch ensures a deep understanding of the relationships between the parameters and exposure, enabling a technologist to solve for different relationships and make necessary adjustments during imaging.

Outlines

00:00

🔬 Understanding X-ray Exposure Parameters

This paragraph introduces the key technical factors in X-ray imaging: kVp (kilo-voltage peak), mAs (milliampere-seconds), and time. It emphasizes the importance of understanding how these parameters interact to affect X-ray exposure. The speaker uses an analogy to 'Chicka Chicka Boom Boom' to illustrate the concept of parameters affecting exposure intensity and explains that kVp is the most critical parameter due to its direct impact on contrast and penetration. The paragraph also introduces the SID (source to image distance) and the Bucky factor, which are physical factors in the room that influence exposure by attenuating X-rays.

05:02

📐 The Mathematical Relationship of X-ray Parameters

The second paragraph delves into the mathematical relationships between the X-ray parameters. It explains the '15% rule' for kVp adjustments, which states that a 15% increase in kVp results in a doubling of exposure due to its exponential effect. The paragraph also discusses the inverse relationship between SID and exposure, emphasizing that increasing SID leads to a quadratic decrease in the number of X-rays reaching the detector. The mAs and time are directly proportional to exposure, with mAs representing the flow rate of electrons and thus the number of X-rays produced. The speaker encourages the audience to practice writing the equation that relates these parameters to exposure intensity multiple times for memorization.

10:03

🔧 Adjusting Technical Parameters for Optimal Exposure

The final paragraph focuses on how to adjust technical parameters to maintain optimal exposure when changes are necessary. It provides examples of how changes in kVp, SID, Bucky factor, and mAs affect the required exposure time. The speaker illustrates the practical application of the previously discussed relationships, such as doubling the SID resulting in a quadrupling of exposure time, or increasing the mAs by a factor of two allowing for halving the exposure time. The paragraph concludes with a teaser for upcoming videos that will include an online calculator and more examples, encouraging viewers to subscribe for updates.

Keywords

💡KVP (Kilovoltage Peak)

KVP, or Kilovoltage Peak, is the peak kilovoltage used in an X-ray tube. It is a measure of the maximum voltage applied across the X-ray tube and is crucial for determining the quality of the X-ray beam. In the video, KVP is highlighted as the most sensitive parameter affecting X-ray exposure and is directly related to the contrast and penetration of the X-ray beam. The script mentions the '15 rule' in radiography, which is a simplified way to understand the impact of changes in KVP on exposure, where a 15% increase in KVP results in a doubling of the exposure due to its exponential relationship.

💡mA (Milliampere)

mA stands for milliampere and is a measure of the electric current flowing through the X-ray tube. It is one of the primary technical parameters that determine the quantity of X-rays produced. The video emphasizes that mA is directly proportional to the exposure, meaning that an increase in mA will result in an increase in the number of X-rays and thus the exposure, assuming all other factors are constant.

💡Time

In the context of X-ray exposure, 'Time' refers to the duration for which the X-ray beam is on. It is a critical parameter because it directly affects the total number of X-rays that reach the image receptor. The script explains that time is directly proportional to the mA, and together they determine the total exposure received by the image receptor.

💡SID (Source to Image Distance)

SID is the distance from the X-ray source to the image receptor. The video script explains that SID is inversely proportional to the intensity of the X-rays reaching the image receptor, meaning that increasing the SID will result in a decrease in the number of X-rays hitting the detector due to the spreading out of the X-ray beam.

💡Bucky Factor

The Bucky factor is a measure of the attenuation of X-rays after they pass through the patient but before they reach the image receptor. It is related to the use of grids or other devices that can block some of the X-rays. The script mentions that as the Bucky factor increases, the exposure measured on the receptor decreases, indicating an inverse relationship.

💡Exposure

Exposure, in the context of X-ray imaging, refers to the amount of X-ray energy that reaches the image receptor. The video script discusses how different technical parameters, such as KVP, mA, time, SID, and the Bucky factor, can affect the exposure. Understanding these relationships is essential for radiographers to adjust settings appropriately to achieve the desired image quality and diagnostic information.

💡Attenuation

Attenuation is the reduction in the intensity of a wave as it passes through a medium. In the script, attenuation is discussed in relation to the Bucky factor, which measures the fraction of X-rays that are blocked or absorbed after passing through the patient but before reaching the image receptor.

💡Contrast

Contrast in X-ray imaging is the difference in X-ray absorption between different tissues or structures within the patient's body. The script explains that KVP has a significant impact on contrast because it affects the penetration and energy of the X-ray beam, which in turn affects the visibility of different structures within the image.

💡Penetration

Penetration refers to the ability of X-rays to pass through tissues or objects. The script emphasizes that adequate penetration is necessary for X-rays to reach the image receptor. If the KVP is set too low, the X-rays may not penetrate the patient sufficiently, resulting in an ineffective image regardless of the mA or time settings.

💡15 Rule

The '15 Rule' is a simplified guideline in radiography that relates to the sensitivity of exposure to changes in KVP. The script mentions that if the KVP is increased or decreased by 15%, the exposure will approximately double or halve, respectively. This rule helps radiographers to quickly estimate the impact of KVP adjustments on exposure.

💡Image Receptor

An image receptor is the part of an X-ray system that captures the X-ray image. In the script, the image receptor is the surface or device that records the pattern of X-rays after they have passed through the patient, and the intensity of these X-rays is influenced by various technical parameters discussed in the video.

Highlights

Understanding the relationship between technical factors like kvp, ma, time, sid, and bucky factor is crucial for mastering x-ray exposure.

Kvp is the most sensitive parameter affecting x-ray exposure and controls contrast and penetration.

The 15% rule in radiography is explained, relating kvp changes to a factor of two in exposure.

Sid (source to image distance) is the second most impactful parameter on exposure, inversely proportional to exposure intensity.

The bucky factor and sid are physical room factors that inversely affect x-ray intensity.

Ma (milliamperage) is directly proportional to x-ray exposure, affecting the flow rate of electrons and thus x-ray production.

Time is directly related to the number of x-rays measured at the image receptor.

A method to calculate the new exposure time when changing technical parameters is introduced.

The importance of understanding the inverse square law as it applies to sid and its impact on x-ray exposure.

The concept of kvp to the fifth power and its significance in calculating exposure changes is discussed.

An example calculation is provided to demonstrate how changes in sid affect required exposure time.

The impact of changing kvp on exposure time, using the 15% rule for easy calculation.

How the bucky factor can affect exposure, with an example of grid changes and their effect on required exposure time.

The direct relationship between ma and exposure time, and how increasing ma can reduce the necessary exposure time.

The need to memorize the exposure equation for practical application in radiography.

An upcoming online calculator is teased for simplifying the calculation of exposure parameters.

The transcript concludes with an invitation to subscribe for more educational content and a reminder of the importance of understanding these technical factors.

Transcripts

so you know him we're talking about

kvpma

time bucky factor and sid we want to put

all those together see how they're

related to the exposure once you've

mastered this you're going to know

everything you need to know about how

these different technical factors are

related to your x-ray exposure so that

if you need to change one of these

technical parameters you will know how

it will affect your exposure and how you

can compensate that by changing another

technical parameter first off we're

going to talk about the different

parameters the ones that you're

typically setting on the interface are

the ones that are affecting the

x-ray generation

and the duration of time that those

x-rays are on so the kvp the ma and the

time we want to think about these all as

one bucket right these are a set of

technical parameters they're all related

to one another

and we can think about that because

those are the ones that we're all

setting on the interface and we have a

couple other parameters that are related

to the physical things that are in the

room so the sid is the source to image

distance so that's how far from our

x-ray tube to our image receptor and

then the final one we have is the bucky

factor

so the bucky factor is related to

the amount of x-rays that are being

blocked or attenuated

after they pass through the patient but

before they get to the image receptor

and we've got videos on every one of

these things separately that i'll have

linked below in the description i also

want you to remember

these two things are going to go

together the sid and the bucky factor we

can remember they go together because

they're both things that happen in the

room they also are going to go together

as far as the relationship or the

directionality when we look at the

relationship between these parameters

and the exposure or the intensity of

x-rays that are being measured on the

image receptor here we're just talking

about how we can put it all together to

get the real understanding that we need

as a technologist to know how these

things are affecting the exposure

and i'm not going to ask you to just

blanketly memorize a big equation so

rather we're going to take a kind of fun

way at least i think it's fun of

building up this a relationship if

you've ever read the book chicka chicka

boom boom this is a kids classic that i

particularly love with my two kids this

is written by a wisconsin native and all

the letters climb up the tree they all

fall down and splat there's just a big

pile

so what would you do if your professor

told you

here's a pile of letters on the ground

here or a pile of parameters in this

case on the ground

and asks you a question let's think

about these parameters and the first

question is

how important are these parameters to

the exposure and specifically what we

mean is if we change one parameter is it

going to have a big impact or a small

impact so let's put these in order of

ones that are going to have a big impact

at the top and then a smaller impact at

the bottom

so from everything we've talked about so

far we know

number one with the bullet is kvp right

kvp

the exposure in x-ray imaging is

exquisitely sensitive to kvp

additionally there's more reasons why

it's important because it controls the

contrast it controls the penetration

if you have a beam you really want to

set that kvp first make sure you have

adequate penetration because if you're

not getting x-rays through

zero times 100 is still zero so if you

have a beam that's not penetrating your

patient and you turn your enemy up by a

hundred times you're like oh yeah we're

really gonna get some through now

if you're not getting a good penetration

that's still zero right so no x-rays are

still making it through

so from the importance of the

penetration the contrast

and also the importance of changes in

this parameter

we really know number one with the

bullet kvp is at the top

then sid is actually our number two sid

is very important we've talked about one

over r squared finally the rest of the

three parameters they all have equal

importance and we're gonna go through

that now but they all are linearly

related to the

x-ray exposure and we're going to see

that now imagine we put them back in

that pile and we want to say the exact

impact so if i make a change to these

parameters how is that going to affect

my exposure or the intensity that we

have measured on the image receptor

there are approximates for some of these

parameters such as the kvp because you

can have different sizes of anatomy at a

high level the kvp goes like the fifth

power

so this is why we've talked about our 15

rule in radiography namely if we change

the kvp by 15

that's a factor of two

so

fifteen percent or one point one five we

raise that to the fifth power and we get

two that's where a fifteen percent rule

comes from because

exposure is exquisitely sensitive to the

kvp next sid is actually like we said

our second most important thing

it's actually inversely proportional to

sid so this makes sense because as we

move further away it's one over r

squared so as we move further away

they're going to be less

x-rays hitting that detector because

they're going to be spreading out mas is

going to be directly proportional to the

exposure

and then finally the bucky factor so

remember what we talked about

these are the two things that are in the

room the bucky factor and the sid

and the bucky factor measures the

x-rays

the fraction of x-rays that are blocked

essentially that are not making it to

the image receptor

so as the bucky factor increases

the exposure measured on the receptor

decreases

so

i want you to remember these two things

the bucky factor in the sid

because

we're talking about an inverse

relationship for both of those so the

two things that are the physical things

that are in the room

the intensity of the x-rays is inversely

proportional to both of them

and for sib it's inversely proportional

to the sid squared for mas that's the

easiest one because it's just directly

related to the mas

we've talked about the m a being like

the flow rate of electrons meaning the

rate at which the x-rays are going to

come out so

ma and time are directly proportional to

how many x-rays you're going to have

measured at the image receptor so when

we put all these things together this is

what our intensity is so you need to be

able to write that down you need to be

able to start with a blank sheet of

paper

you can make flash cards if you want for

each of these things separately but you

need to be able to start with a blank

sheet of paper and come up with this

equation not just look at this video but

start with a blank sheet of paper and be

able to come up with this equation

do it seven times and you'll have it

committed to memory at least for a

little while so that's important because

once you can write this down then we can

solve it also for other relationships

i'm going to go through the most

important way that we want to solve this

now is when you're operating your

equipment you're actually going to be

solving for the time in seconds usually

that's the thing that you're most often

going to be using as the final knob to

dial in our exposure so let's imagine we

want to solve for the time in seconds

imagine the case where we need to change

some of our technical parameters but we

have dialed in a good radiation dose so

the

exposure on the

image receptor is good we don't want to

change that

and so if we have our original set of

parameters and then what we're calling

our new set of parameters we want the

intensity to be the same

so we will set our initial intensity

equal to our new intensity now don't be

intimidated because it's a lot more

variables here but all we've done is

just write that twice i wanted to keep

the letters big here so i've got like a

top and a bottom but the things here on

the top are just like the left-hand side

of our equation then here's our equal

sign and then these things over here are

just like the right-hand side of our

equation we're going to go through and

each of the variables if you want to

essentially cancel out a variable right

if we want to move it from one side to

the other side so imagine we want to

start with our kvp so if we have kvp to

the fifth power on this side

then essentially what we do is we

multiply

by one over

kvp new to the fifth power on both sides

so what that's going to do is

essentially drag it down to the other

side

so we'll do that here

so now we have kvp over kvp new to the

fifth power

so for sid we're gonna end up taking sid

from the bottom on this side it's gonna

go over to the top on this side likewise

for the lucky new it's gonna go from the

bottom on this side over to the top on

this side

see that now we have the sid new squared

and the

bucky factor new over here

then finally we're going to take the m a

and we're going to bring it down over

here for the m a new so

let's now

consolidate this onto one line so we

have our s new which is our new time

our s new and we're going to go through

again just quickly

each of the sets of parameters

because we can now put parentheses here

so we can do the division or the ratio

first

and again this is our 15 rule

so in general we don't usually want to

do that

taking things to the fifth power in our

head so that's why we approximate it

with that 15 percent rule we've got

separate videos about the 15 rule

then we have our sid which remember the

directionality is going to be flipped

here for the sid this is second most

important because this goes as the

square

and then we have our bucky factor which

has the same directionality as the sid

those are the two things we group

together because those are the physical

things that are in the room

and then we have the

m a where again the m a is

the same relationship as the kvp

and finally the

original time so this is our final

equation that we could end up

calculating

if we want to determine for some given

set of parameters we want to change

something so if we end up moving the sid

further away so imagine we take the sid

and we move the sid from 40 to 80 and we

don't change anything else

so

what that's going to tell us here our

new sid is 80 and our original sid is 40

80 divided by 40 is 2

and then 2 squared

is

4.

so if we move the

sid twice as far and don't change

anything else

our time is actually going to be four

times longer so if we started with a

time that was .25 seconds we're now

going to need a time that is one second

a change in the kvp is the same as our

15 rule so if we leave everything else

the same just change the kvp we want to

determine what the impact is on the time

if our kvp went up by 15

that means we can reduce the time by a

factor of two start off with a 0.25

second acquisition it's going to be a

.125 acquisition guys for the bucky

factor if you end up putting a grid in

there which has a bucky factor of four

and you originally had a grid with a

bucky factor of two it's two times more

absorbing so imagine you start out with

an acquisition time of 0.25 seconds

you now need an acquisition time of 0.5

seconds only for the m a if you started

with an ma of 100

and then you went to an ma of 200

then in that case

the

flow of the

electrons is going to be increased so in

the same amount of time you're going to

get more x-rays so because you have more

x-rays in the same amount of time

the actual time that you have the

exposure on for can go down so if you

turn up that m a by a factor of two you

can

reduce the time by a factor of two so if

you start with 0.25 seconds you turn

your ma up from 100 to 200 then you're

back down to 0.125 seconds they're all

direct examples that you can do we're

going to have additional videos coming

up where we actually are going to have

an online calculator for this we're

going to be going through some examples

just like that so stay tuned for that

make sure you subscribe to the channel

so that you can see that also give us a

like below so we can spread this rad

love to more folks check out our video

on the 15 rule if you haven't seen that

one