0:02

Hello and welcome to Case Crunch Rapid case review

0:04

for the core exam hosted by modality.

0:07

In this rapid fire format,

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faculty will show key images along

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with a multiple choice question,

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and you'll respond with your best answer via

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the live polling feature.

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After a quick answer explanation, it's onto the next case.

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You'll be able to access a recording of today's case review

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and previous case reviews

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by creating a free account using the link

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provided in the chat today.

0:28

We are honored to welcome Dr.

0:30

M Mahesh for a physics board review

0:31

and radiography and fluoroscopy.

0:34

Dr. Mahesh is professor of radiology

0:36

and cardiology at Johns Hopkins School

0:38

of Medicine in Baltimore, Maryland.

0:41

Additionally, he's chair of the Radiation control Committee

0:43

president of a A PM board, member

0:46

of a CR subject matter expert for U-N-I-A-E-A

0:50

and an elected member of NCRP

0:52

and ICRP questions will be covered at the end

0:55

of time allows, so please remember to use the q

0:58

and a feature to submit your questions.

1:00

With that, we are ready to begin today's board review. Dr.

1:03

Mahesh, please take it from here.

1:06

Wonderful. Uh, welcome to this board review.

1:09

Um, unlike other case review, this is for physics, so every,

1:13

everything will not be images.

1:15

There'll be, um, questions

1:17

and I'm also gonna take time to explain some

1:19

of these questions, uh, in a way so

1:22

that we are also covering the physics aspect of it.

1:25

I'm not, uh, sure how much of the physics, uh,

1:29

teaching you have during your residency program,

1:31

but here at Hopkins I do teach our residents twice a month

1:36

or the whole year on different topics of, uh, physics.

1:40

So let me start with this one.

1:42

Here's my introduction

1:44

and I'm gonna talk today focus on only radiography physics

1:49

and fluoroscopy physics.

1:50

Uh, do you want to post the first question? Ashley,

1:58

this is wonderful.

2:00

So I know majority of you are preparing for your exam,

2:03

which is a good thing, and I hope also to convey that

2:07

after the exam also you'll retain some of these materials

2:11

because when you become a radiologist, you'll be exposed

2:15

to some of these concept in your practice.

2:17

It'll be nice to remember, continue to remember.

2:20

So let me start off with a very basic question.

2:24

Brain strong radiation is the predominant type

2:27

of x-rays used in radiography.

2:36

Thank you. The answer is,

2:41

answer is true and here is the way of x-ray production in,

2:45

uh, in radiography are in fluoroscopy.

2:48

So the, in these three graphs, I want to explain what, why,

2:51

what is brain strong and what characteristic x-rays are.

2:55

If you're looking as a neutral atom,

2:57

surrounded nucleus surrounded by electron, roding it out.

3:00

If there is an external radiation

3:02

or external energy passing through this atomic cloud, if

3:07

that energy does not have a capability to knock off any

3:11

of the electron, but simply get rebounded

3:13

and change the direction in the process, it loses the energy

3:18

because it has to prevent the problem.

3:20

Conservation of momentum

3:22

and also conservation of energy has to be, uh, respected.

3:25

Therefore, when these energy change the direction,

3:29

the difference in the energy comes out as a, as a radiation

3:34

and we call that as a ban, strong radiation.

3:37

And on some time these external external energy

3:41

can knock off an electron

3:44

and this electron, usually the electron held in the closest

3:48

to the nucleus are the most strongly binding,

3:52

and if the energy, the binding energy,

3:54

the energy interacting is greater than the binding energy

3:58

that can knock off an electron,

4:00

these electron are moving out of this thing environment

4:04

and electron from the adjacent shell will jump into

4:08

the occupy the space.

4:10

When they jump in, they lose an energy

4:13

between the difference between the binding energy

4:15

and we call that as a characteristic x-ray.

4:19

So if we look in here, this is a graph, we shall the energy

4:23

of the coming out of this type of interaction

4:26

and the relative output of this energy coming out.

4:29

You can see there's variety of photo energy coming out

4:33

of all different energies except the characteristic X-rays

4:38

are very unique to energy.

4:40

They don't, they come out exactly at the energy of the level

4:44

between the, the keal and the electron.

4:46

That's what it's called, the characteristic

4:48

X-ray and dressed up.

4:49

It is called prem strong radiation.

4:52

It is also called a breaking radiation brain.

4:55

Strong goes after the French physicist

4:57

who do explain the phenomena.

4:59

Let me launch the next question.

5:03

Fil increasing filtration of an x-ray beam

5:09

likely reduces exposure time, beam intensity,

5:14

average energy of half value layer.

5:23

Wonderful. So we have a variable answer here.

5:27

First of all, you need to know each of them what they are.

5:30

So here is exposure time is the amount of MA at the time

5:34

where the electrons hit the anode to create an x-ray

5:38

and we talk about beam density every day.

5:40

Let me show you what is the right answer, the right answer.

5:43

If you increase the filtration of an x-ray beam,

5:46

it likely reduces the beam intensity.

5:49

Usually the increasing filtration

5:52

reduces the x-ray tube intensity approximately, for example,

5:56

three millimeter or

5:57

so will likely reduce the x-ray tube output.

6:01

Why? Here's a situation.

6:03

So this particular graph,

6:04

I'm gonna show again for other questions.

6:06

It has, it can be explained a lot of things.

6:10

So as I said, brain stroke radiation come

6:12

with all different energies

6:14

and the maximum energy is equal

6:17

to the maximum tube voltage set.

6:19

When you're exposing a patient RNA on a protocol,

6:23

let's say a hundred KVP is the maximum tube voltage.

6:27

So the x-rays coming out have all these energies lower than

6:31

thus and they all vary like this.

6:34

Now if you put some filters, means put some material in

6:39

between aluminum, copper

6:40

or a glass, it's going to absorb some

6:43

of the low level radiation.

6:45

We don't want low energy radiation

6:47

because they do not penetrate through the body

6:50

and create a signal.

6:52

They get just surface absorbed at the surface.

6:55

Because of that, we want to filter out some

6:58

of the low energy beam.

7:00

When we do that,

7:01

what happen is the other remaining intensity will go down.

7:05

Therefore, as you can see here,

7:07

average increasing average photon energy will increase the

7:11

photon average energy, but the intensity is slower.

7:15

Let me show you this example here on this side.

7:18

These two panels are the same.

7:20

They were set at 110, a hundred, a hundred KVP

7:24

with 250 ma.

7:25

That's the tube current of the x-ray tube.

7:28

A hundred KVP is the tube potential

7:31

to attract the electron towards the

7:33

anode to create an x-ray.

7:35

If there is no filtration, this is the typical,

7:38

uh, x-rays coming out.

7:40

If you map all the x-ray beam coming out of the tube

7:43

and measure the energy and plot it, this is how it'll be.

7:46

There are some characteristic x-ray,

7:49

but rest up it is brain strong radiation.

7:51

If you add a one millimeter of aluminum

7:54

immediately you can see here the average intensity goes down

7:58

because the, the, some

8:00

of the low energies are absorbed and take it out.

8:03

Therefore, the result, the it we,

8:05

we call the term called beam hardening.

8:08

We are hardening the beam to remove the low energy photons,

8:12

which are not useful for creating an image.

8:15

That's the idea. I can go into more details later.

8:18

Um, this is,

8:19

so increasing filtration reduces x-ray tube intensity.

8:24

Um, so let me launch the next question.

8:29

What is the most likely bulky factor

8:32

in adult radiography exam?

8:41

Answer here again is all about all over the place

8:44

and the correct answer is why, which is okay, that's

8:47

what this whole LA lecture is gonna be.

8:50

So first of all, you need to know what is Bucky.

8:52

Bucky is named after a physicist called Gustav Bucky,

8:55

a German physicist who created this one who came up

8:59

with the concept, the i the correct answer is why.

9:02

And here's the explanation.

9:04

So the Bucky factor we call, is a ratio

9:07

of the entrance exposure with grid to the entrance

9:12

exposure without grid.

9:14

So therefore, what is the purpose

9:15

of adding grid to the x-ray?

9:17

Um, to the in front of the detector?

9:20

The purpose of the grid is to award scatter radiation

9:24

reaching the detector, which basically

9:26

degrades the image quality.

9:28

So that's one of the reason why we put grid in the beam.

9:31

When we put grid in the beam,

9:33

the grid is basically imagine a, a lead septum, a series

9:38

of left septum back together in a compact way.

9:41

So you can imagine, um, a straw has straws, uh,

9:45

two straws separated by a lead piece

9:48

and the same thing goes across the whole thing.

9:51

Imagine when the x-ray is coming out of the patient

9:54

hits the grid, some of it can also hit the lead area that

9:59

that uh, that x-rays would not be detected.

10:02

Therefore that is wasted because of that.

10:05

Whenever we introduce a grid,

10:07

we call it a concept called a bucky factor,

10:09

which is basically, sorry, which is basically the ratio

10:12

of the entrance exposure with grid

10:15

to the entrance exposure without grid.

10:18

Typically bucky factor range from three to five

10:20

and average bucky factor is five

10:22

and here are the typical grid ratio.

10:26

Why is this important? Because you want

10:28

to eliminate the scatter radiation reaching the detector,

10:31

which basically degrade the image quality

10:33

and then you also want

10:35

to design the grid in such a way they don't block too much

10:38

primary radiation coming off or the patient.

10:41

So that's why we have different ratios is called

10:45

eight to one.

10:46

The ratio or the weight is dis decided is eight is the

10:50

height of the septum

10:52

and one is the suppression between the septum.

10:54

So eight is to means if it is eight millimeter,

10:57

there's a one millimeter gap between the next lid.

10:59

That's the ratio. If you look in here, what I want

11:02

to show you is like the relative number of photons

11:07

mapped versus different scatter angle.

11:10

And this is for a 20 centimeter thick patient.

11:13

If the field size is 25 by 25 centimeter field of view

11:17

for a hundred KVP, this is the typical number

11:20

of X-ray reaching out the detector with no grid.

11:24

If you insert the grid, it'll block off lot of these scatter

11:28

and that will come out to lower this

11:31

because it's the relative number shrink, you may have

11:34

to increase the dose and that's

11:35

where the bucky factor comes into picture.

11:38

Again, this is basically showing the field of view

11:41

and how the scatter is impacted

11:44

or changes with respiratory patient thickness.

11:47

This is called SPR scattered to primary ratio,

11:52

scattered to primary ratio.

11:53

How much scatter is coming outta the patient compared

11:56

to the primary radiation coming out

11:57

of the coming outta the patient.

12:00

Larger the patient thickness greater the scatter

12:03

to primary ratio and that can impact the the image quality.

12:08

That's why we insert grids to block off

12:11

and make the image quality better.

12:13

There are instances where we recommend to take the grid out,

12:18

especially in a pediatric fluoroscopy case

12:21

or a pediatric uh, x-ray imaging case

12:24

where the pediatric body is so small the scatter is so less

12:28

so we don't need the GI uh, the grids

12:31

because the grids will automatically lead

12:33

to a higher radiation dose to the patient.

12:36

Therefore we select,

12:37

selectively remove the grid when we are

12:39

doing pediatric imaging.

12:40

That's the general consensus between the B factor

12:43

and the grid ratio.

12:45

If you have any question, um, please feel free

12:49

to pose it in the q

12:50

and a, I'll be happy to answer the question.

12:53

The next question, Average x-ray

12:58

energy decreases with higher beam filtration.

13:08

So the question was average decreases

13:11

with higher beam filtration.

13:16

I think some of you got the answers from the previous slide,

13:19

but the answer is false

13:24

Because it's going to increase.

13:26

Thank you. The reason is like imagine here this is the type

13:31

of x-ray coming out of the tube

13:33

and if you plot each of the energies on the,

13:36

based on the number of photon, here it is,

13:39

this is the maximum energies that you voltage.

13:42

But if you look in here, the average energy

13:45

of the upper envelope is somewhere here,

13:49

but if a beam hard on the filter,

13:51

the average energy will increase.

13:54

And that's why the question was average energy decreases

13:57

with higher beam filtration

13:59

and the correct answer was false.

14:01

No, the average energy actually increases with tube

14:06

with the beam filtering and

14:08

and one of the ways to we calculate the average energy is

14:12

as follows, whatever the tube voltage we select

14:15

that is called the peak tube voltage.

14:18

Let's say a hundred KVP.

14:21

The average energy of the x-rays coming out

14:23

of the tube voltage is usually between one third

14:26

and two third of the peak tube voltage.

14:30

If it is a hundred KVP, the one third

14:32

of the tube voltage is 33 KEV and 2 30 66 KEV.

14:37

So the average energies is in between these things

14:40

and I also want to make sure tube voltage is expressed at

14:43

KVP tube.

14:45

Energies are expressed at KEV

14:47

kilo electron ALT is the average energy, energy

14:50

of the x-rays coming out.

14:52

So one third to two third more beam filtering.

14:55

It'll be more closer towards two third.

14:57

That is 66 AAV or so for a hundred KVP beam.

15:05

Next question, Smaller the focus spot size,

15:10

greater the image unharness,

15:19

the answer is false.

15:21

I'm glad. Now you may need to answer why it is so focal.

15:25

Spot size is the size

15:27

where the x electrons are hitting the anode

15:30

and x-rays are produced

15:32

and the x-ray produced there are reaching the patient

15:35

and the detector smaller.

15:37

The point of hitting the anode greater will be the sharpness

15:42

because smaller the focal spot size,

15:44

there's a less light spread of the energy beam spread.

15:48

Because of that the images will be very sharp,

15:51

but the other is smaller.

15:54

The focal spot size greater the chance

15:56

of x-ray tube getting burnt out

15:58

because the same spa get really high tube

16:02

tube loading.

16:04

So there are chances where are situation where we prefer

16:07

to use the smaller focal spot such as um, pediatric,

16:11

such as in mammography.

16:13

We always typical to use the smallest focus spot size

16:16

because we want to have the highest

16:19

spatial resolution in the image.

16:21

But if we are doing a longer time where we are not

16:24

so much in inclined to have the sharpest spatial resolution,

16:28

we can balance a trade off

16:30

with a slightly larger focal spot site.

16:34

When I say focal spot size, the magnitude

16:36

of the focal spot site is 0.3 millimeter to 1.5 millimeter.

16:41

Not anything greater than that.

16:43

So in CT

16:45

or in intermental fluoroscopy,

16:47

the focus spot size are usually larger

16:50

and in interventional fluoroscopy size, uh, fluoroscopy,

16:53

they usually have one or two focus spots size small

16:56

and large focus spot.

16:58

The smallest focus spot size is in used in mammography in

17:02

order to get the greatest facial resolution.

17:09

Next question. Scatter radiation increases

17:14

with x-ray field size.

17:21

The answer is true. And do you know why?

17:24

Because that can I, let me explain this situation.

17:27

This is the three panels

17:29

of a fluoroscopy uh, imaging system.

17:33

If you observe here the patient is the same,

17:36

a technique is the same except the field size hitting

17:40

the patient is different.

17:42

Larger the patient,

17:44

the larger the x-ray field hit entering the patient

17:47

every instant there is some scattering happen, some

17:50

of it is scattering, some of it is passed

17:52

through the patient and a lot of it is scattered

17:55

outside the patient and that scattering is each dot.

17:59

So if you look in here, this is a half a meter block

18:02

and this is also explain why we need

18:06

to wear a lead apron when we are working around a patient is

18:10

to block off the scatter radiation.

18:12

We don't have to worry about the primary radiation.

18:15

The main thing is we want

18:16

to block ourself from scatter radiation

18:18

and that scatter radiation is directly

18:21

dependent on the field size.

18:23

So imagine here if this field size is 30 centimeter

18:27

by 30 centimeter, if this is decreased to 15 by 15

18:31

by 50% for example, if you're exposing the entire

18:35

abdomen versus you're only focusing on the spinal cord,

18:38

look in how much disa advantage you get.

18:41

You decrease the scatter radiation plus

18:44

the patient dose is also reduced by 50%

18:47

but it's also have an advantage

18:48

of decreasing the scatter radiation

18:50

and if you go further down to the column

18:52

to the exact size, you have more further.

18:55

So I'm just trying to share with you not only the exam,

18:58

answer to the exam, but I also want to know the practicality

19:02

of what this impact of scatter radiation

19:05

and what it does to the personal standing around.

19:07

And that's one of the reason why we advise our clinician

19:11

to focus to the area what they're actually doing,

19:14

the fluoroscopy when they do a long procedure

19:16

because they're not only reducing the patient to the BA dose

19:21

but they're also reducing their exposure

19:23

to scatter radiation.

19:28

Next question, a grid ratio used in typical

19:32

table bucky radiography is which one?

19:43

I'm glad majority of you got it correct.

19:45

The answer is it should be eighties to one.

19:48

So again, as I said, um, the grid ratio is the height

19:52

of the grid plate versus the space between the septum.

19:56

So this is eighties to one is what typically used

19:59

for table bucky for a mammography since the distance

20:02

between the source to the buck receptor is short,

20:06

we use a shorter phase to one and for chest radiography

20:10

and other place we sometimes use 12 to one

20:13

or one 16 is to one.

20:16

Next question, What is the dynamic range

20:21

of digital detectors?

20:31

The answer is 10, 10,000 to one.

20:33

Now the next question is what is dynamic range?

20:36

Dynamic range is the range of x-ray exposure,

20:41

which can be used in the images.

20:44

The reason is like this is in compared

20:46

to film screen system which you are not used to.

20:49

It's historically before the digital detector we had film

20:53

screen system, which means if you,

20:55

if you use too much radiation, the film will become too dark

20:59

or if you use too too less of a radiation,

21:02

the film would become too light

21:04

and you would not able to see the images.

21:07

So there in the film screen system,

21:09

the dynamic range was very limited.

21:11

About a hundred is to one.

21:13

With the digital detector,

21:14

what happens is like even though you can expose a patient

21:17

very high radiation, the images can be manipulated

21:21

and still, uh, we can chain the windows and um, window width

21:26

and processing and still the image

21:28

that see the image, the same thing.

21:30

If the radiation is too low, the images can be salvaged

21:33

by adjusting the windowing and centering.

21:36

Because of that, the digital detector gave us a wide

21:39

application of using quite a range, still able

21:43

to salvage the images.

21:45

Only one drawback is if the images were,

21:48

you would use too much radiation in the fill screen system,

21:51

radiologists would know they had used too much radiation,

21:55

but now if the technologist used too much radiation,

21:58

they would not know

21:59

because the technologies can window down in the proper way

22:03

and send the right only images which is showing up properly.

22:06

So that is a disadvantage.

22:07

That's a, that's a different thing for discussion

22:09

for radiation protection next time,

22:13

what is the most likely x-ray absorber material

22:17

used in a indirect flat panel detector?

22:26

CCI think you guys are reading the books

22:29

correctly and thank you.

22:30

This is true and the correct answer is CCMR.

22:34

The reason when you say, uh, the question here is there,

22:38

let me see, I said indirect flat

22:42

panel x-ray detector.

22:45

So indirect flat panel X-ray detector means these digital

22:49

detectors go through two PA two, two steps.

22:52

One is x-rays when they come out of the patient

22:55

don't directly create image images.

22:57

They interact with the scintillator

23:00

and the scintillator is typically CCM added crystals.

23:03

They convert the x-rays into light

23:06

and the light internal interact

23:08

with the more folic silicone detector which create an

23:12

electrical signal to create an image.

23:14

So the most common one is the CCM added crystal

23:17

because these crystals can be grown in the lab

23:20

very unilaterally,

23:22

therefore the light hit,

23:23

the light produced is not spread the they go,

23:27

they produced light and

23:28

that light enters a channeled towards the detector.

23:32

Sodium added is one

23:33

of the common common detector used in nuclear medicine.

23:36

That's where we call it a gamma camera Barium.

23:39

Fluoro is used in the in the film screen system

23:43

and selenium is a material used in a direct flat panel xray

23:47

detector, which I'll explain later in a different question.

23:52

What is the effect of narrowing the window width

23:55

in digital imaging?

24:02

That's correct. It's increases the contrast

24:05

because what I meant is na window width is like this is the

24:09

scale is expressed.

24:11

Images expressed with gray scale zero

24:13

to 2 56 level gray scale.

24:15

If it's such a wide window then the structure in the image

24:19

can all appear washed out.

24:21

That's why we narrow it down to the area of

24:23

what we interested between zero to a hundred zero to 200.

24:27

Thereby we can narrow increase the image contrast.

24:32

So let me give some questions In fluoroscopy,

24:39

fluoroscopy time is the only indicator of total dose

24:42

to patient during fluoroscopy.

24:50

False. I'm glad you answered this fall

24:53

because historically everybody thought fluoroscopy time is

24:56

the only one which indicate the total dose to patient

24:59

during fluoroscopy.

25:00

If you're observing the clinic, a lot

25:02

of the time technologists

25:03

and nurses record the fluoroscopy time

25:06

during fluoroscopy unfortunately.

25:09

Now if we don't just do fluoro,

25:12

we also do recording like the DSA like this.

25:16

Because of that the DSA

25:17

and other things can be even higher dose.

25:20

So fluoroscopy time is not the only

25:22

indicator of the total dose.

25:26

Which of the following delivers the highest radiation dose

25:29

to patient undergoing fluoroscopy, syn imaging,

25:34

fluoroscopy spot film or digital subtraction angiography?

25:44

The answer is DSA correct.

25:48

Um, majority said DSA is correct. And here's the reason.

25:52

This is a graph just to show you a given idea.

25:55

What is the typical dose required at the image receptor

26:00

for an average size patient?

26:02

What is this graph basically telling like for different mode

26:06

of fluoroscopy, how much radiation is required at the

26:10

receptor to create a good images?

26:12

This is called in micro or micro ranking per frame.

26:16

For a standard fluoro it requires one and a half to two

26:20

and a half micro R per frame.

26:22

And in fluoroscopy we don't do one frame,

26:25

we do 30 frame per second or 15 frame per second

26:28

and we do five minutes, 10 minutes

26:29

and so forth so it can add up.

26:31

However, if we look at the D-S-A-D-S-A is one

26:35

of the largest radiation, um, contributor

26:38

to the patient patient dose

26:40

because each DSA frame can be as high as 500

26:45

to thousand micro or per frame.

26:47

And in DSA we don't do one image, we always do a series

26:51

of DSA run five run tendon.

26:54

Each of them are three per three frame per second,

26:57

so it can add sub.

26:58

Therefore if we just record the fluoroscopy minute,

27:02

that is not an indicator of the two patient dose.

27:05

In fact, we had to account all of them, especially

27:08

for a intermental fluoroscopy.

27:10

If you're doing a DSA, one of our, my suggestion

27:13

for our resident is to minimize the number

27:15

of DSA run they do

27:17

because it can add to the patient dose very fast.

27:23

In fluoroscopy, which of the following image receptor

27:27

has higher penalty with magnification?

27:35

Correct. Your image I tensor has the highest

27:38

penalty and I'll tell you why.

27:41

Again, this is just to show you a trick,

27:43

this was incorrectly answered

27:45

but the correct answer is the image intensifier.

27:48

Look at this graph. When you do magnification image,

27:52

intensifier has a greater penalty compared to the uh, the

27:56

advanced technology, the flat panel detector.

27:59

What shown here is like this is a image intensifier,

28:03

this is a phantom entrance skin dose rate

28:06

milli grape per minute.

28:07

You can see here, if you go down the in the magnification

28:11

means that the field size is smaller, the penalty is more

28:15

compared to the flat panel technology.

28:17

So this is how it works.

28:19

In a typical image intensifier field,

28:21

it is usually circular.

28:23

You hardly probably,

28:24

you hardly see image intensifier these days except some uh,

28:29

crs but most of the clinic are now has flat panel detector

28:33

where the penalty with magnification is far less compared

28:37

to the penalty with the image intensifier.

28:39

Because here when you decrease, when you go

28:42

to the mag field, mag mode, the field of view decreases

28:46

because the field of view decreases the number of x-rays.

28:50

Reaching the outside of the output

28:52

of the intensifier also decreases.

28:55

In order to maintain the image brightness,

28:57

the scanner will automatically push greater

29:00

radiation to come through the patient.

29:02

Therefore magnification means it increases the radiation

29:06

dose to the radia to the patient with image intensifier.

29:09

And that's, and there's the ratio of the ratio

29:12

of the image intensifier size versus the amount of radiation

29:16

and required with magnification.

29:18

So the penalty is greater with the image intensifier

29:23

compared to the, uh, the recent advanced technology

29:25

of flat panel detector.

29:30

Most appropriate radiation dose metric to evaluate skin dose

29:35

for patient undergoing fluoroscopy.

29:45

So majority had chosen dose area product, none

29:49

of you chosen amount of curie.

29:50

I'm glad because the amount

29:52

of activity is usually for nuclear medicine.

29:54

But the answer, the correct answer is community dose. Why?

29:58

I'll tell you because generally, sorry, this is

30:02

how typically different dose metrics are measured in

30:06

fluoroscopy or radiography.

30:08

There are so many different factors which,

30:10

which results in calculating the x-ray output

30:13

and this is called the entrance skin dose amount

30:17

of x-rays entering the patient.

30:19

Medical physicist has a unique way to measure that

30:22

and it is checked on a regular basis and all those things.

30:26

This is the exit dose and this is the entrance dose.

30:30

So with respect to um, the entrance dose,

30:33

that which is also important for calculating the skin dose

30:37

to the patient because if the skin dose is very high

30:41

that can show up with skin injury.

30:43

The way the skin dose is measured is we are we,

30:47

we are two main dose descriptors in

30:49

fluoroscopy or radiography.

30:51

One is the community dose,

30:53

the other one is a dose area product for those

30:56

who chose those area product.

30:58

It is also a current dose descriptor,

31:00

but that is not use

31:01

so much useful in evaluating the skin dose.

31:04

It is useful for estimating the risk

31:06

of the whole body, which is a different area.

31:09

So the correct answer is community dose

31:11

and the way it's measured is you can actually measure on the

31:14

skin surface how much x-ray x-rays are entering.

31:17

That's one of the reason why we filter the beam

31:20

because we want x-rays.

31:21

Don't just deposit in the skin surface and not go through

31:25

and create an image, co create a signal.

31:28

And that's why we filter by putting filters in the, in the,

31:32

in the, in the output of the x-ray tube to block a lot

31:34

of the low radiation filter and so forth.

31:37

So the correct answer is cumul dose

31:39

and is expressed in milli gray.

31:42

That is the SI unit conventionally we also call it a

31:46

rad milli radiation dose absorb.

31:52

So for mammography,

31:54

what is the most common target filter combination

31:57

to image a death dense breast?

32:06

So this is all over the place and the,

32:08

and the most highest chosen is rhodium rhodium,

32:11

which is the correct answer,

32:12

but I'm gonna explain to you there's also a one question in

32:15

the question in the question area.

32:17

If air camera was an option, would

32:18

that be a correct over community dose?

32:20

You are correct as as long

32:22

as the Air Karma is expressed at milli gray, that's

32:25

how we track on the patient air karma dose,

32:28

which is explained, which is displayed on the scanner.

32:30

So that is also, that is a correct one also.

32:33

So in mammography it's it's, it's a different type

32:37

of radiation used for mammography, we generally,

32:40

we don't use brem strong radiation,

32:42

we use characteristic x-rays

32:44

and that's one of the reason why mammo

32:47

for mammography we need

32:48

to have a mammography dedicated unit.

32:50

And the correct answer here

32:52

for dense breast is rhodium rhodium, that's the target

32:55

and the filter, here's an explanation.

32:58

So generally in mammography we are working

33:01

around in the lower energy.

33:03

You may ask the question, aren't we worried about me?

33:06

The lower en radiation absorbed just on the skin surface

33:10

don't pass through the body.

33:11

That's correct. However,

33:12

you don't need too much energetic x-rays in the to to memo

33:16

to image the mammos breast,

33:18

because breast is a soft tissue, there is no bones.

33:21

So because of that we can get away

33:24

with the lower energy still able to penetrate the breast.

33:28

The, and also it is important to differentiate

33:30

between the muscle and the fatty tissue

33:33

and the glanular tissue in breast.

33:35

Therefore if you use a higher energy,

33:38

the energy just washes out the image.

33:41

So now let's look at here.

33:42

This is a typical moly, molybdenum target

33:46

with the rhodium spa molybdenum and rhodium spectra.

33:50

But now here is molybdenum target

33:53

with the moly spect filtration.

33:55

The reason we use the same filtration is to block off lot

33:59

of these um, energies, low energies

34:01

and the high energy which is not used.

34:03

So that only characteristic x-rays of molybdenum, which is

34:06

around 1819, which is, is coming out of the x-ray tube

34:10

and that is the typically the type of target used

34:14

for a general breast tissue.

34:16

But if the breast tissue is dense,

34:17

the system automatically try to go for a larger target

34:21

because you need a little bit more energetic x-ray.

34:24

With the rhodium rhodium, it's usually the characteristic is

34:27

around 20 KEV which is suitable for mammo

34:31

for imaging the dense breast.

34:36

So typical voltage two voltage used in screening mammogram.

34:41

I think this is a easy giveaway question.

34:43

Um, everybody should be able to get this correct.

34:52

I'm glad majority card but still some of you got 55 to 75.

34:57

No, we are using typically the low energy.

35:00

We are not using this energy.

35:01

This is the typical energy of a radiography 55

35:06

to 75 on an average patient.

35:08

1 25 is usually used

35:10

for chest x-ray one 20 kvp is typically used for um, a lot

35:15

of the CT exams,

35:16

which we are gonna discuss in the next lecture.

35:18

So typically is between 25 to 30 39 KP.

35:22

Remember we are using characteristic x-rays

35:25

and also we want to image the best contrast

35:28

between the fatty tissue, glandular tissue

35:30

and the breast tissue, which is only

35:33

possible if you use characteristic x-ray

35:35

and at the lower energy range, which is what it is possible.

35:41

Why is compression key in screening mammogram?

35:50

And you have chosen all of the above.

35:53

Majority of you chosen all of the above. Perfect.

35:55

That's exactly the answer. The answer is all of the above.

35:59

And the reason is as follows.

36:02

So unfortunately in mammography, breast are compressed

36:07

and in fact that's one of the very negative

36:10

of screening mammogram.

36:11

Women hardly sometime hate to come back from annual checkup

36:15

because they can remember the previous year when they had

36:18

such a painful um, compression.

36:22

But compression is essential for a number of reason.

36:25

One is it is essential to reduce the x-ray scatter,

36:28

otherwise the pressed if is not compressed,

36:31

there is lot more scatter produced

36:33

that can image image quality more than that,

36:37

even though you do a such a fast x-ray in mammography

36:40

imaging still about one second or three second exposure.

36:44

If it is not compressed, they can always reduce, um,

36:48

motion artifact.

36:49

That will also reduces the geometric unharness

36:52

because the breast, the 3D breast image is trying

36:56

to compress as much as possible to a wide overlap.

37:00

And also to have this reduce unharness

37:04

that is also important.

37:06

It also reduces the patient dose when you compress

37:08

and it also reduce the motion unharness, unfortunately, uh,

37:12

the compression is very hard.

37:14

When I teach my residents

37:15

or my physics graduate students, I take them to the clinic,

37:19

especially male students.

37:21

I want to put their hand underneath the compression

37:24

and compress 35 or 40 pounds.

37:26

They know how it, it feels the pain

37:29

and that will, I wanna convey that

37:31

because it's the pain the patient, the the tech,

37:34

the patient experiences when they're doing mammogram

37:37

and uh, that's why we want to teach

37:39

or uh, to appreciate what the patient goes

37:42

through when they go through imaging sometime.

37:45

So the next question, brainstorm radiation

37:49

interaction results in

37:54

The following,

38:01

correct?

38:03

There may be some confusion of characteristic x-rays.

38:06

Um, it usually the interaction can result in characteristic

38:11

but the bem strong radiation means it is always associated

38:14

with the poly energetic x-rays.

38:16

Of course the heat is also produced

38:18

but it takes too much x-rays to create a

38:20

to raise the temperature by one degrees of the heat.

38:23

We have done some experiment to show that it takes lot of,

38:26

so heat is the last of this one,

38:28

but the answer is brand strong radiation interaction results

38:31

in poly energetic x-rays

38:34

as I I showed you the spectrum there are poly energetic when

38:38

it interact and it create, it can interact

38:40

and produce characteristic x-ray of unique energies.

38:49

The ans the choice a good choice, the answer is four

38:53

because I also mentioned here this is the,

38:57

the x-ray tube is under the x-ray table.

39:00

That's important because

39:01

that will tell you which exactly is coming.

39:03

The x-ray is hitting the patient

39:05

through under the table here, pass through the patient

39:08

x-ray table, pass through the padding

39:11

and pass through the patient

39:13

and every interaction result in tic absorption count

39:16

and scattering and PU is transmitted

39:18

through the tissue you capture

39:20

but lot of it is scattered back also.

39:23

Some of it is called back scatter

39:25

and that's why the number four has the highest uh, um,

39:29

or scatter in this direction.

39:31

And probably I also wanna draw your attention uh,

39:34

at sometime in the airport we used

39:35

to have an airport scanner.

39:37

They use the phenomena back scatter to create a fuzzy image

39:40

of the surface and that's

39:42

how they just used in the security.

39:44

Um, these days we don't use that scanner.

39:47

We are using more of a radio frequency scan, um, uh,

39:51

type of scanner in the airport.

39:52

And again that is also used as the concept

39:55

of scatter coming out and capturing and creating an image.

39:58

That's why they ask patient travelers

40:00

to remove everything on the surface so that it,

40:03

I don't show up on the images.

40:06

So, so according to us federal regression,

40:10

what is maximum skin entrance exposure rate load

40:14

during normal fluoroscopy?

40:22

The answer is 10 r per minute. Why?

40:25

And the people are chosen different numbers

40:27

but the regulation as

40:29

of now the correct answer is 10 R per minute.

40:32

In fact, that is the only limitation we have on the

40:35

fluoroscopy system.

40:37

There are two limited. One is during normal fluoro,

40:41

no matter how much the patient sizes when we measure at a

40:44

certain point it cannot exceed 10 r per minute.

40:48

In fact, that's one of the tests medical physicists does on

40:51

a annually to make sure the x-ray tube is not

40:53

producing too much radiation.

40:55

The second one is there is when you do on a high dose fluoro

40:59

mode or a boost level, it can go up to 20 r per minute.

41:03

That's where the question was 20 r per minute was there.

41:06

Other than that for senior DSA, there is no limit.

41:10

That's why we emphasize any of the fluoroscopy system

41:13

evaluated and tested

41:15

by a qualified medical businesses on an ongoing basis

41:18

to make sure the radiation levels are within the,

41:22

within the regulatory requirement.

41:26

Which of the following setup results in the lowest skin dose

41:30

to patient during fluoroscopy?

41:39

This is a difficult question

41:40

because there is a scenario changes all over the place,

41:42

but the correct answer is four.

41:45

And now I'm gonna explain why.

41:47

And before that there is one question posed in the qa

41:50

and the question is what filter combination we use

41:53

for normal density screen mammogram

41:55

for a normal density screen mammogram typical

41:59

technique is Molly, Molly and that's what it's system

42:03

and actually most of the mammography system

42:05

pre-select it which technique to use it.

42:08

When the pressed, when you select the uh, auto auto filter

42:12

technique, the system will send, give it three milliseconds

42:16

or less than a fraction to to sense the density

42:19

of the breast and it changes the technique for a normal um,

42:23

a normal density typically is molly Molly

42:27

and if it is slightly higher than we go into molly rhodium,

42:30

so that goes that that's the choice between Molly, Molly,

42:33

molly rhodium and if the density is even more higher than it

42:37

go to molly rhodium and then switch to mo rhodium rhodium

42:41

and then it even go into rhodium aluminum.

42:43

There are all these new things are happening

42:46

with the contrast mammography coming into clinic,

42:48

we're gonna see even more higher technique used

42:51

because it has to penetrate to the contrast.

42:54

So now the question here is the answer is D, two things.

42:58

First of all, what you want

42:59

to make make sure is like the patient is as far away

43:03

as possible from the x-ray tube

43:06

because only then you'll have less

43:09

radiation reaching the patient.

43:11

That's why we advise sometime a tall, a short radiologist

43:15

who are doing a fluoroscopy to stand on top of a table

43:19

to bring the patient away from the x-ray tube because

43:22

otherwise they can be in this scenario

43:24

where the short radiologist can,

43:26

because of the height the patient is automatically very

43:30

close to the x-ray tube that can lead

43:31

to higher uh, entrance dose to the patient.

43:35

Ideally this is the best case scenario.

43:38

This is what happen if we do this one.

43:40

There's lot of these um,

43:42

wasted in a way sometimes it's helpful

43:44

but mostly this is the most idealistic where the patient is

43:49

as close as possible to the image receptor.

43:51

Otherwise in this scenario the object can get magnified

43:55

and larger and so forth.

43:57

Uh, so this is the best scenario. Question number 2 22.

44:03

Automatic brightness control in fluoroscopy attempts

44:06

to maintain what

44:14

the correct answer is image brightness.

44:17

And that is one of the greatest um, feature

44:20

of the fluoroscopy because that's the one modality.

44:23

What we use these days is truly, truly um,

44:27

automatic brightness

44:28

because when we do the fluoro moment,

44:31

you put the foot on the pedal

44:33

or you can observe the image getting adjusted the brightness

44:36

because the image receptor will sense the patient thickness.

44:40

How much of the x-ray are coming outta the patient

44:43

to create then there is a requirement on how much brightness

44:47

to maintain depending on what we have set.

44:50

So that will automatically redirect to get more radiation

44:54

to pass through to reach the same brightness.

44:57

So you can also see sometime when you're doing a fluoro,

44:59

you move from a thicker portion

45:01

to the thinner area like a arm

45:03

or a leg, immediately the brightness changes

45:06

and it automatically flow immediately adjust

45:09

by adjusting tube voltage, sorry,

45:12

adjusting tube voltage or tube current.

45:15

It automatically interplay those things

45:17

and still to in order to maintain the image brightness.

45:20

Next question. What is the single radiation dose threshold

45:25

for onset of temporary appellation?

45:33

The answer is all over the place.

45:35

I understand there is some ity, the correct answer.

45:38

What we use is three gray.

45:41

The reason is like this is the approximate trend.

45:44

We have the the table for an average side patient,

45:48

if the entrance skin dose at the same point

45:52

exceeds more than two

45:53

or three gray, three grays, 3000 milligram of dose,

45:58

you can expect temporary appellation

46:00

and the onset is less than a week.

46:03

So, and if you go higher it, if it is more than seven gray

46:08

that when it can create a permanent appellation,

46:11

most probably you're going to hear from the patient back.

46:14

And this is what happens.

46:15

Why during intermental fluoroscopy we emphasize training

46:19

of the staff and the user very much

46:21

to understand these things.

46:23

Here are an example of radiation induced car injuries

46:26

after coronary procedure.

46:28

These are a cath procedure performed by the cardiologist.

46:32

If you look in here, the size

46:34

of the injury will tell you this is a biplane system

46:38

and this dose was estimated to close to a 10 grade.

46:41

10 gram means you're talking about inro innovative fibrosis

46:46

and it's more, it's gonna be a permanent injury here is

46:49

after two months in another patient

46:52

and that the injury was trying to heal itself

46:54

and the system loses the capacity to repair

46:57

and here it came out a necrosis of the area.

47:00

So these are very rare cases,

47:02

but it's happen in interven oscopy.

47:07

What percentage of patient entrance exposure rate is scatter

47:11

exposure rate at one meter?

47:19

So again, this is has all a variety

47:23

of question, but here is the answer.

47:26

Generally this is a general, as I said,

47:29

for an average size patient undergoing fluoroscopy,

47:33

the scatter coming out of the patient

47:35

at one meter is one 1000 of what he

47:39

or she's getting that's equal to 0.1 percentage.

47:43

So if the patient is getting sir X amount,

47:46

the scatter coming out at one meter is approximately

47:49

1000 of it.

47:52

And this is important to understand

47:54

that is also impact scatter radiation exposure

47:56

to the personal working around the fluoroscopy system.

48:00

So greater the radiation dose of the patient,

48:02

greater the scatter radiation hitting the at one meter.

48:05

And this is approximately number,

48:08

I think this is the last question.

48:09

Smaller the field of view

48:11

in fluoroscopy system results in what?

48:21

And the answer is it's higher patient radiation dose.

48:24

That's where it becomes we want to decrease the um, we want

48:28

to uh, increase the magnification and so forth.

48:31

There is, there is one question posed here,

48:33

isn't there generally a lot more scattered?

48:36

I agree there's a lot more scatter,

48:38

but the weight it's related to the entrance exposure

48:41

to the patient is what I'm mentioning.

48:43

At one meter not very adjacent to the patient.

48:46

Approximately one meter is 1000th of

48:49

what the patient is getting.

48:51

That's what we have observed, measured these things.

48:54

But if you're closer to the patient, it'll be a lot more.

48:56

So at one meter is what is 1000th.

49:01

I think this is all the questions I wanted to share

49:03

with you, but I think as we still have four minutes,

49:06

if you have any questions, um, uh,

49:09

pose this question I'll try to answer.

49:11

Otherwise I wish you all the best

49:13

and I think two weeks from now I'm gonna come back

49:16

and talk about ct.

49:19

Well thank you so much Dr.

49:20

Mahesh for this wonderful case review.

49:23

We will hold for a minute.

49:24

I think there's a couple questions coming in.

49:27

Sure. Now, oh, I, I see that.

49:30

Couple more questions coming in.

49:32

Um, explain the last question. Thanks.

49:35

So the last question is, uh, is it leads

49:39

to the magnification when you're doing a smaller field

49:41

of you, you want to increase the dose

49:44

because you want to get the same image brightness.

49:47

Therefore if you make it too small

49:49

and you automatically have a penalty to increase the dose,

49:51

that's the, that's the reason why we have

49:54

this higher patient dose.

49:57

Any other question? I also

50:02

for, for, for those who are participating, I also want

50:05

to draw your attention to excellent physics

50:07

articles in Radiographics.

50:10

Um, I was part, um, and this is what if it is flat panel.

50:14

So with flat panel detector,

50:16

what is happening is like when you decrease the field

50:18

of view, there is some electronic, uh,

50:21

magnification is done,

50:23

therefore the dose is not so much penalized.

50:26

So you that part is, you're right.

50:29

So what I meant to say is like if you check the

50:31

radiographics, there is a series

50:33

of physics tutorial articles which is available for free

50:37

and you can actually download, I have about five

50:39

or six of my own article

50:41

and they are go with the very straightforward topics, ct,

50:44

cardiac CT mammography and all those things.

50:46

So I'll advise you to take a look at those things can be a

50:50

very easy study guide

50:51

because each image with that legend behind itself will,

50:55

will, so will this spatial resolution increase?

50:59

Probably yes. There is so many factors, um,

51:01

which is a trade off going all, all the places.

51:04

So we have to be careful to give a one straight answer

51:07

for this particular question.

51:08

Smaller the field of you will increase the predation dose

51:11

but there is a chances it'll increase the spa,

51:14

you'll not lower the spatial resolution. That's correct.

51:18

Great. I think you got 'em all.

51:20

Thank you very much. Thank you Dr. Mahesh.

51:23

Yes, we will see you back in a couple of weeks

51:25

for another review specifically regarding ct. Yes.

51:29

Um, Yes. Thank you all for participating.

51:31

You can access the replays of our previous reviews

51:33

by creating a free account.

51:35

You can join us next week, Monday, April 7th with uh,

51:38

Dr. Aaron Gomez.

51:39

She's gonna lead us in a GU imaging board review.

51:42

And then the following week we'll have Dr. Mahesh back on.

51:44

He'll be back from France. You can register that the link

51:47

provided in the chat and follow us on social media

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for future meetings.

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Thanks again for learning with us and we will see you soon.