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0:28

Today we're honored to welcome back Dr.

0:30

Mahesh for a physics board review in ultrasound. Dr.

0:33

Mahesh is a professor of radiology

0:35

and cardiology at Johns Hopkins School

0:37

of Medicine in Baltimore, Maryland.

0:40

Additionally, he is chair

0:41

of the Radiation Control Committee, president

0:43

of A A PM Board, member of a CR subject matter expert

0:47

for N-I-A-E-A and an elected member of NCRP

0:51

and ICRP.

0:53

Questions will be covered at the end if time allows,

0:55

so please remember to use that q

0:57

and a feature to submit your question.

1:00

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

1:02

Mahesh, please take it from here.

1:05

Hi, good evening. Um, I'm happy to talk about the

1:09

physics of AL ultrasound.

1:13

So you wanna set up the first question.

1:18

Wonderful. Um, I know many of you're preparing

1:22

for the board exam

1:24

and this is the right, um, one

1:25

of the topic which we talk heavily.

1:28

So let me go through a couple of some of the basics, uh, um,

1:32

with the question and followed by some of the understanding

1:34

of why that question is done.

1:37

So let me start off with a very fundamental question.

1:41

Question number one, the wavelength

1:43

of three megahertz sound beam is sharpest in

1:48

which tissue

1:55

and the answer is between A and bone.

1:58

We have only few people responded,

2:00

we have 35 people attending.

2:03

And, uh, is there any problem with the response?

2:05

Please let us know. The answer is a,

2:10

because here is a formula, the velocity

2:14

of sound waves is equal to a product of frequency

2:17

and wavelength or wavelength is equal

2:20

to velocity development.

2:22

The frequency. So given here, the megahertz three megahertz

2:26

as a constant frequency, the EF factor is being the same.

2:30

If you look down on this table of velocity

2:32

for different material, the smallest,

2:35

the shortest velocity is in air.

2:38

That's about 330 meters per second.

2:41

Therefore, the vallen is proportional to um, velocity.

2:46

Therefore, the sharpest, the valent

2:48

of three megahertz is sharpest in air

2:51

because that's correspond to the velocity you can see here.

2:55

Um, bone has, uh,

2:56

higher velocity sound wave travels higher in, in bone metal,

3:01

um, is 44,000.

3:03

And in soft tissue,

3:05

the approximate is about 1540 meters per second.

3:08

And here's the following, um, there's also discussion

3:11

that the SAR tissue is 1540 meter per second.

3:14

Um, so in a is 330 meters per second is what you need

3:18

to remember, and that is the answer.

3:20

So now let me go down a little that level.

3:24

Question number two, why is gel applied to skin

3:27

during ultrasound imaging?

3:35

And the answer is to remove air.

3:37

That's correct, because gel is applied to the skin so

3:42

that you don't leave any gap

3:43

between the transducer and the skin.

3:47

That way the sound wave travel faster

3:49

through the soft tissue.

3:51

If there's air, as you saw that the

3:54

velocity is small there in the air,

3:56

therefore that can diminish the transmission

3:59

of the sound wave.

4:00

Therefore, to get clear image, you you prefer

4:04

to put the gel on the skin.

4:07

It fundamentally, the basic principle

4:09

of the pre high principle is, uh, it acts

4:12

as a coupling agent between the surface and the skin surface

4:16

and the transducer eliminating any air pockets, um,

4:20

between the ultrasound probe, I call it a transducer,

4:24

a probe in the skin because

4:26

otherwise that will interfere with the sound wave, create,

4:29

reflection, reflection, all those other things.

4:33

What does the Q factor of an ultrasound transducer describe?

4:44

The answer is, um, is all over the area here.

4:48

The correct answer is frequency response of crystal.

4:53

So what is Q factor?

4:56

Q factor is called, also called a quality factor

4:58

for ultrasound trans user.

5:00

It tells how efficiently it can

5:04

transmit and receive the signal.

5:06

That's, that's important.

5:07

That's a characteristic of a cure

5:09

of an ultrasound transducer probe.

5:12

It also require relates to bandwidth of frequencies.

5:16

So you can see here this is a typical, uh, uh,

5:19

ultrasound transducer.

5:21

You have a pizo electric effect element,

5:23

that's the one which produces, um, uh, sound base

5:27

and return back and connects it.

5:29

There is a caustic absorb that is sound base absorbed.

5:33

And there's also, this is actually a correction, is a

5:36

transmit receiver, um, cable which collects,

5:39

which we transmit the sound base

5:41

and also receive the sound base in a echo forum.

5:44

So here is a different scenario.

5:47

If it is a high queue, means it has longer spatial pulse,

5:52

pulse length as you can see, a longer pulse length.

5:55

Whereas a heavy damping means a very low queue,

5:59

means the sound is very short will,

6:01

and they won't transmit much.

6:03

And this is the broad bandwidth,

6:05

whereas this one is a narrow bandwidth so that it'll,

6:09

it'll penetrate through the material much more

6:11

longer 'cause of the iq.

6:13

So that's why the frequency response of a crystal is

6:18

what Q factor tells us.

6:23

Question number four, what is the attenuation?

6:26

If an ultrasound beam is attenuated by 99%,

6:36

the answer again is variable.

6:38

The correct answer is minus 20. So how, what is tonation?

6:44

Tonation means it's stopping of anything

6:47

in x-ray, we saw x-ray.

6:48

Tonation is the stopping power of a material

6:51

to block x-ray here, tonation is the stopping power

6:55

of the material to block us on wave.

6:57

So if an tonation ultrasound is alternated

7:01

by 99% means only 1% has passed through the material.

7:06

So we call it, we have a formula call

7:09

relative sound intensity.

7:11

This is expressed in desi bells.

7:13

That's the unit of relative sound intensity.

7:15

That's what we are, we are all these, uh, headphones are,

7:19

uh, when they see the power of the headphone,

7:21

the loud noise they express in decimal.

7:24

And that is also called

7:25

as like the decibel level reaches

7:27

more than a hundred decibel.

7:29

It is kind of like harmful the year and all those things.

7:32

Anyway. So here's the formula.

7:34

10 times 10 times longer than longer than week of base 10

7:39

to the ratio of these two i is the word a measured intensity

7:44

and inot is the internet original intensity.

7:47

So I means it ated by 99% means that trans

7:52

measured intensity is one,

7:53

whereas the version intensity is a hundred.

7:56

So if you put this into formula log

7:59

of 0.01 is minus two, minus two times 10 is minus 20.

8:04

Therefore, if a particular tissue has a negative decimal

8:08

value, it means it is attenuating the sound

8:11

waste very fast one.

8:13

If it is a positive decibel means it amplifies the sound.

8:17

For example, in a metal, if you click on one end,

8:21

the sound transmit and enhances that has a positive decibel.

8:25

Whereas in a soft tissue, another thing it get absorbed.

8:29

So if you have this ratio

8:32

of 0.1%

8:34

or 1% transmission, that's equal to a decimal of minus 20.

8:39

And if least 10% is minus 10 and 50 is minus three.

8:42

Again, it goes back to this, this formula

8:45

of log themic scale to 10 is in a calculated I by inot,

8:51

which of the following has the highest acoustic impedance?

9:01

Okay, the current answer is bone.

9:04

As you can see, caustic impedance means the, the stopping

9:08

or the resistance offered

9:10

by a particular tissue for the sound waste.

9:13

And you see that bone has one of the highest

9:16

caustic impedance, 7.8 kilogram per meter

9:19

square, uh, per second.

9:21

And you can see here air has the least

9:24

acoustic impotence and you can hear that.

9:27

And then the fatty tissue

9:29

and other tissues that the following, um, metal has the, one

9:33

of the even higher one, it's about 30.

9:35

So among the choices we are asked at the bone,

9:37

and that's the correct answer, which

9:42

of the two images was acquired with a sound

9:46

at shortest wavelength?

9:50

So image A is obtained at six megahertz,

9:53

image B is obtained at three megahertz.

10:02

The answer is, uh, a image and, and the, and the image a

10:07

and that is correct.

10:09

Why? Because you have the formula velocity called

10:12

to frequency time ent.

10:14

Therefore, if this is sick bag heart, uh,

10:18

and uh, with the shortest valent means

10:21

this should be the shortest

10:23

because the velocity of velocity of the subway tra

10:27

transport traveling through these two tissues the same.

10:30

So therefore the six megahertz will have the shortest well

10:34

compared to three megahertz will have a longer variant.

10:36

That's the, and that that comes out from this formulation

10:39

of weak equal frequency time lambda.

10:42

The wave length,

10:47

which of the following will

10:49

directly affect the frame rate in ultrasound?

10:53

Is it line density frequency selection, speckle reduction,

10:57

or harmonic imaging?

11:05

The answer is between these two

11:07

and the right answer is line density.

11:10

Sorry, because line density means it's the number

11:14

of scanned lines

11:15

or beams, which is used to create an image

11:18

within an angular width.

11:20

How many ways it to send and create pattern?

11:22

So higher provide better image resolution,

11:26

but will reduce frame rate because you, so

11:29

therefore the line density, um, will directly affect, uh,

11:33

which of the following will directly affect the frame

11:35

density is the line there.

11:36

Frame rate is the line density.

11:38

So if the higher level provides better image resolution,

11:42

but if, sorry, uh, lemme see.

11:46

But this will reduce the frame rate.

11:48

So the line density is inverse, is mostly affects the,

11:52

um, the frame rate.

11:57

Which of the following, um, transmit

12:02

setting will result in the best axial resolution?

12:12

So now here is again as a variable answer here,

12:16

the correct answer is four

12:19

transmit cycles at eight megahertz.

12:22

Why? Because for a, for a given transmit frequency,

12:27

XI resolution, um,

12:29

really degrade if there are greater number

12:32

of transit cycles are used.

12:34

Therefore, in order to have the best XI resolution, you want

12:38

to have a minimum number of transit cycle.

12:40

But for a given number of transit cycle,

12:44

axi resolution will improve if the transit

12:46

frequency is increased.

12:48

Therefore, between these two choices, the four,

12:51

the lower the transmit cycle is better

12:53

and higher, the frequency is better

12:56

to get the axi resolution.

12:58

Therefore, the choice was, uh,

13:00

four cycles at eight hertz is the right answer.

13:05

I think this is a, it's an error.

13:07

It should be C and uh, that's a type of error.

13:11

What is the axial resolution of an ultrasound beam

13:16

transmitting four cycles at one megahertz in soft tissue.

13:26

Again, this is a bit of a calculation.

13:29

I am hoping these type of

13:31

detailed calculations are not given,

13:32

but this is a little bit more complicated than the other

13:35

calculation, but other calculations you need to know.

13:38

But what is the right answer?

13:39

The right answer is three millimeter.

13:42

So what is, what is axial resolution?

13:45

Axial resolution is the ability of the, of the,

13:49

of the system to resolve object in the line of the beam.

13:54

This is the line of the beam.

13:56

So ability to down along the axis of the beam propagation,

14:01

also known as the depth is, uh, is one,

14:04

this is axi resolution is independent of the depth,

14:07

how depth, how many, it doesn't matter how deep they are,

14:10

it can resolve here.

14:11

So here for example, there is a, there is a, there is a,

14:15

there is a tradeoff.

14:16

Increasing transmit frequency will improve axial resolution,

14:20

but ation increases and so forth.

14:22

So let me show you the calculation.

14:24

This is a little bit more calculation.

14:25

I wanna go step by step.

14:27

So the axi resolution is calculated as form.

14:32

Axial resolution is one half of the spatial pulse length

14:36

because you are, you are in ultrasound,

14:39

we tra we transmit the sound wave

14:42

and wait for it to come back.

14:44

You collect the echo, that's the receiver.

14:46

So the total time of the travel,

14:48

you have to account both of them.

14:50

Therefore, axi resolution is half

14:53

of the spatial pulse length.

14:55

So at one megahertz of ultrasound, the len,

14:59

the wavelength is 1540, sorry 50, uh, I'm sorry,

15:05

1540 P millisecond one by one hertz

15:07

because we are using soft tissue, speed of length, speed

15:11

of velocity of sound in soft tissue is about

15:14

1540 meters per second.

15:16

And you divide that by the frequency one megahertz.

15:19

So you get at one megahertz, the wavelength is 1.54 you

15:25

now, now the spatial pulse length is what the, is the number

15:29

of cycles, times the wave length, that's about 6.16

15:34

and the axi resolution is one half of that.

15:37

That's why it's approximately three millimeter.

15:40

Now the science behind it is important

15:42

for a given frequency.

15:45

Um, you want to see axi resolution will degrade

15:49

if we have more transit cycles are used

15:52

because more transit cycle you incur use it,

15:56

that will increase the spatial pulse

15:58

length longer and longer.

15:59

Therefore the XI resolution will go down for a given number

16:03

of transit cycle.

16:04

If there are four transit cycle

16:06

or two transit cycle, the XI resolution will improve.

16:10

If the frequency is increased, like as you can see,

16:13

the frequencies increased, the variant will decrease

16:16

and that therefore the spa pulse plan is also decreases and

16:20

therefore there is a trade off

16:22

of increasing the transmit frequency.

16:25

Um, is increased ation, the ultrasound beam

16:28

and uh, generally this is not, it's independent of the depth

16:33

or depending no matter how deep the objects are,

16:36

that is doesn't matter for the actual resolution.

16:39

For axial resolution, it is important on the

16:41

transmit frequency and also the um, the spatial pulse length

16:46

of the beam and the,

16:48

and the frequency of the transducer

16:52

in real time be mode ultrasound,

16:56

the lateral resolution is improved with increased What

17:06

the answer is scan line line density.

17:10

So in a real mode,

17:12

real time V mode ultrasound higher line density

17:17

generates better lateral spatial resolution.

17:20

On the other hand, if you have more line lines are used,

17:24

the frame rate must be it is

17:25

because it needs some time to correct the it,

17:27

that's why the lateral resolution is increased

17:30

by increased scan length line density.

17:35

Question number 11, which performance parameters related

17:39

to ultrasound equipment's ability to resolve

17:42

in plain objects along the propagation axis

17:46

of an ultrasound B?

17:54

That's correct because we are talking about resolve in plain

17:59

object along the propagation axis of ultrasound beam

18:02

and that's, uh, that's, uh, axi resolution.

18:06

Next question, question number 12.

18:09

Lateral resolution in ultrasound is best achieved when the

18:13

objects are at above focus zone at focus zone

18:19

or below focus zone

18:27

at focus zone is correct.

18:29

And here's the thing, when you say lateral resolution,

18:33

you're talking about in this direction perpendicular to the,

18:36

uh, propagation.

18:38

So in the longitudal, uh,

18:39

axial resolution you're talking about object in this line.

18:42

Now the lateral resolution is object line across the beam.

18:46

So the lateral resolution is defined as the ability

18:50

of the ultrasound beam to resolve object on,

18:54

on particular direction to the people.

18:56

And this is depend on the width of the focal zone

18:59

and on the depth focal zone is if you, this is a

19:03

curve curl curve transducer

19:06

because it is a curve, curve career curve object.

19:09

You see the, say the beam focuses at this

19:12

is called the focal zone.

19:14

And the focal zone, it has the best resolution.

19:17

If the object were away from the focal zone,

19:20

you can see here it is almost joining together.

19:23

And if it is away from the focal zone,

19:25

again the resolution is very poor.

19:27

That's why it is it.

19:29

But another thing is this is depends on the width

19:32

of the focal zone and on the depth also.

19:36

So here the depth is much longer, whereas inal resolution,

19:40

it is independent of the depth in the,

19:43

in the depth beam direction, whereas lateral resolution, um,

19:47

it is dependent on the width and on on the depth.

19:53

So which of the following control provides greater depth

19:56

of visualization?

19:58

On the top image on the, on the depth

20:01

of top image is 124.7 millimeter.

20:05

And the bottom one is a hundred point 101 millimeter.

20:09

So the one is this is this is the, uh,

20:12

the phantom which we use as a medical physicist

20:15

to do the quality control.

20:17

And you can see here on the we, we can,

20:20

we can see different period point, sorry,

20:23

the correct answer is, uh, greater transmit power.

20:27

And I'm sorry, with the mouse modeling this a something

20:30

which I'm messing up with the, going back on the slide,

20:33

I apologize, but here the right answer is transmit power

20:36

created transmit power.

20:38

What I wanna show you in this particular phantom is

20:41

these phantom is commonly we use it here.

20:44

For example, if we see a line in this direction,

20:48

we can see the capacity of the axial resolution

20:51

and how far the deep it can go.

20:54

As you can see here, the resol axial resolution is same no

20:58

matter how deep the objects are here.

21:00

This one will measure the lateral resolution, how

21:04

how good the object,

21:05

the transducer can resolve object in the lateral plane.

21:09

And we count this and we can measure.

21:11

Then there are other things which we measure is like, um,

21:14

low, uh, high echoic point and low e echoic point

21:17

and also the uh, the distance measurement and so forth.

21:21

So there are a number of uc tests which we do on,

21:24

on a phantom, which is embedded by all sort

21:27

of these object inside it.

21:31

Which performance parameter related

21:34

to ultrasound equipment's ability

21:37

to resolve in plain objects perpendicular to access

21:41

of ultrasound being

21:49

I think this was an easy one.

21:50

It's a lateral resolution because we have seen that.

21:54

But in the,

21:55

in the PM direction is axial resolution perpendicular

21:58

to the axis of the resolution is a lateral resolution.

22:02

Again, the same figure I wanna show you,

22:04

the best resolution is obtained

22:06

and the focus zone of the particular transducer, um,

22:10

and away from it is more away from it has

22:13

all this other situation.

22:16

How long is the echo written time

22:19

for an interface at one centimeter depth

22:28

as I, as I mentioned, oh, this is six,

22:30

six microsecond and so forth.

22:33

The answer is 13 microsecond. Why? Here's the formula.

22:38

It is based on the range equation we have the time,

22:42

the echo time equal to two times the depth divided by the c,

22:47

c is the velocity we are assuming it's in soft tissue.

22:50

So it's therefore it's 1,540 meters per second

22:55

or 1.54 meter per microsecond.

22:59

The distance is calculated as C times G divided by two.

23:04

This is the depth at which the echo signal is formed.

23:07

That's the depth. So depth is calculated by the velocity

23:11

of the sound in a particular tissue

23:13

or in a multiplied by the time delay,

23:17

which include both the time for the fault to travel

23:20

and also refer back.

23:21

So time and divided by the two

23:23

because we, we always count time as the amount,

23:26

the time it took to transmit to particular region

23:29

and the reflection is held back, the echo is hard back.

23:32

So using this formula D equal CT by two, we are trying

23:36

to calculate what T is.

23:38

So if we interpose all these things, you get 2D divided

23:41

by C, therefore this comes out to 13th microsecond.

23:45

So this is another one of those things.

23:47

You just need to remember if the depth is equal

23:50

to the velocity times the time delay divided by two

23:55

because the time delays always takes into account twice the,

23:58

it is already taken into twice the time to go

24:01

and come back to, to transmit and HiTA interface

24:05

and reflect back, which is scattered by the transmitter.

24:08

And that's how it's calculating

24:14

which interaction of ultrasound wave

24:17

can result in artifacts marked by lateral displacement

24:22

of object in an ultrasound image relative

24:26

to their original locations.

24:34

Correct? It's a refraction

24:36

because as you can see here, um, this basically,

24:41

um, the way, um, um, it, the beam seemed

24:45

to be not reflected but out.

24:49

And this is typical artifact

24:51

because the structure appears

24:53

to be not in the current location

24:55

and it appears in the wrong location due to the bending.

24:59

And this is a classic example of this like Phil drop coin,

25:02

the coin appears almost lightly out.

25:05

Actually that can cause that is

25:06

because of the lateral displacement due to fraction

25:10

reflection is basically, um,

25:12

is the sound way getting reflected in a

25:14

particular, uh, interface.

25:16

And that is what we do in the um, uh, ultrasound.

25:20

We collect the reflection and create the object wa

25:22

and the in interface surface transmission is passing through

25:28

refraction is the one which causes the object to be appeared

25:31

as if it is displayed from a particular location.

25:34

And this is the classically we've seen in the ultrasound.

25:39

So now what is the maximum pulse reputation

25:43

frequency to penetrate 20 centimeter

25:48

of tissue using a three megahertz trans transducer?

25:58

And the answer is, um, let me show you the answer

26:04

and the answer is four megahertz.

26:06

Now we need to know what is pulse reputation, frequency,

26:10

pulse reputation, frequency is given for the transducer.

26:13

How much of this, um, wave cells sent per unit time?

26:18

And that is divided by that, that is, uh, given

26:21

by the formula C times 2D as you can see again

26:26

twice the distance PRF is the frequency.

26:29

Again, you can call it frequency equal

26:32

to velocity divided by the vallen.

26:34

Vallen here is color two times the depth, that's

26:37

what this 20 centimeter, 20 centimeter is 200 millimeter

26:41

and the C is gives as us 1 54,

26:44

that is assuming it's a soft tissue 1, 5, 4 0 meter per

26:48

second or 1.54 meter per microsecond.

26:52

So if we put this into this formula here, again,

26:55

that comes up to 3.85 kilohertz at approximately,

27:00

um, approximately four hertz is, so

27:05

if we, if we divide this by microsecond

27:08

or op can number to four hertz.

27:13

So again, these formula seems daunting

27:16

but simply the same formula C equals len, the frequency,

27:20

once you remember that it can change these things around.

27:26

Now what is an M mode display present?

27:35

That's correct, that's moving anatomy, um,

27:39

as a function of time.

27:41

And here MM mode stand for motion, um,

27:45

where B mode is like a more static one.

27:47

So in MO what happens is

27:49

echo signal amplitudes are modulated to brightness level.

27:53

So the echo signal coming out is, it varies depending on,

27:57

depending on the amplitude is coming.

27:59

Each of these are given a different brightness signal.

28:03

Therefore, um, the, the flow is actually showing the,

28:07

like a color how it's in the color in the docker are

28:11

or in more display.

28:13

So here's what happens is like ultrasound beam is not swept

28:17

across the plane of interest.

28:18

Instead the beam is fixed

28:20

because you're only targeting anatomy or,

28:23

or an object which is flowing through the beam area.

28:26

So as it moves through the area,

28:29

you're collecting the reflection

28:30

and the reflection,

28:32

the amplitude goes into different direction.

28:34

So the beam is fixed in one position,

28:37

but observer observe over scanning time

28:40

to graph a motion of moving structure.

28:43

So you're basically keeping there,

28:45

the beam is position at the same level like a carotid artery

28:48

or any of these blood vessels you want to image kept there

28:52

and you hold it in the same position where

28:54

and correct the echo signals

28:56

and the echo signal collecting it.

28:58

The amplitude depends on the, uh, the flow direction

29:02

and also the uh, going in

29:04

or out, it is mapped into a color scale

29:07

and that's what you get this, all these colors.

29:10

So let me see here. Next question.

29:16

Which information does the color doppler provides?

29:25

It's a mean flow velocity, that's correct. Um, let me see.

29:32

It's, and probably you heard right now in a doppler effect,

29:36

uh, from my, my, from my sound system

29:39

because there's an ambulance to call from hospital

29:43

as it moved away you could hear the

29:45

waning sound of the scene.

29:46

That's, that's the phenomena of the do sound effect

29:50

and that's mapped into a color phenomena.

29:52

We call it color doppler and that's it

29:54

because the sound wave where is hearing?

29:56

So this is information which in the color,

30:00

color doppler is we want to call

30:02

for the mean flow velocity is what is uh, recorded.

30:08

Which type of artifact does the arrow in the image

30:11

of a kidney cyst indicate?

30:20

The answer is ation.

30:22

You are correct because if we look in here closely, sorry,

30:26

if you looking closely here, this is the cyst means it is,

30:30

it is a air pocket, so it is dark,

30:32

there's all the soft tissue in the kidney area.

30:35

Um, probably this is reflecting from the, uh, darker, um,

30:39

bone or some other, other, other tissue.

30:41

But here, if you look here, this is,

30:44

you can see here almost like a line artifacts

30:47

and a bunch of parallel lines here.

30:49

And that is like hitting back and,

30:52

and we call this like a, it's called ation artifact

30:56

because it has equally spaced echoes

30:59

with decreasing brightness and length.

31:02

It's very classically nice one.

31:04

So the bar, the first one is larger, it's also brighter,

31:08

but if you go down the list, it's almost equally spaced,

31:11

but you have different, um, um, brightness

31:13

and also decreasing length.

31:15

And there these are called river reservation artifact.

31:22

And, and you were as per us FDA, what is the upper limit

31:26

for mechanical index for general ultrasound scanning?

31:37

The answer is, um, the answer is 1.9

31:42

and this is a mechanical index.

31:45

A MI is a value of a negative pressure divided

31:49

by the squire root at the center frequency.

31:51

It is also used in terms of like some type

31:53

of a harm in the ultrasound safety aspect,

31:56

also the mechanical index

31:58

and that's allocated here, pressure divided

32:01

by the squire root of the center frequency.

32:03

Um, there is a question in the,

32:06

the take on question number 17.

32:08

I had that at 3.8 kilohertz.

32:11

Um, but how come my answer was four?

32:13

Actually I think it's a typo,

32:15

which I have done in the question.

32:16

It should be four kilohertz

32:18

because I run it off to, um, it should be in hertz, not, uh,

32:22

it should be in kilohertz, not just hertz.

32:25

Um, um, so higher frequency resulted better

32:29

and worse axle resolution.

32:30

We can come back to you, I'll come back later to show back,

32:34

go back to the axle resolution

32:35

and you can discuss this frequency component of it.

32:40

Next question. The following information can be obtained

32:43

from the spectral Doppler evaluation except the following

32:54

that correct because you can actually, um,

32:57

by the doppler we can actually get the, sorry.

33:04

So you can see the main idea

33:06

of the D evaluation is to see the direction.

33:08

You can get the direction of the flow.

33:09

That depends on the color, what you see on the,

33:12

on the arteries or veins, the blood flow in

33:15

or out of the, uh, trans area.

33:18

You can, you can also get the spectrum

33:19

of flow velocity mapped on

33:21

and you can also see what type of flow,

33:23

but we cannot see the depth of the vessel.

33:25

That's correct. Which type

33:29

of artifact does the arrow in the image

33:31

of a kidney cy indicate?

33:40

The current answer is, um, a um, is a twinkle

33:45

creating a twinkle twinkle artifact.

33:48

This is because it's, it's characterized

33:51

by a mixture of colors.

33:53

And as you can see here, this is the probe going around the,

33:58

to the doppler doppler imaging.

34:01

You can see the scales here.

34:03

The, the red means it is indicating in your 15.4 centimeter

34:08

per second in one direction, minus 54 is a flow, uh,

34:12

in the opposite direction.

34:14

So that's how you can differentiate

34:16

the direction of the flow.

34:17

And uh, and here the artifact is actually caused, uh, sorry,

34:23

and this is because it is happened may probably,

34:26

there may be an object which reflect a very highly

34:29

reflective object and that signal gets signaled

34:32

and in this case, twinkle artifact is caused

34:34

by the kidney stone around it.

34:36

That's why we see the very brightness here.

34:38

That's the kidney stone is equal to calcium phosphate,

34:41

calcium equal like a bone.

34:43

So similar to bone, that's where they, it's the,

34:46

it's a loud signal you can,

34:47

because it is a maximum automation.

34:50

And when you have that reflection base mixed together,

34:53

you can have these type of, a combination of a mixture

34:57

of color and it's designed, it's called as, um, a twinkle,

35:01

uh, artifact based on the surface

35:06

reflection in the image.

35:08

Which two tissues have greatest impedance differences?

35:18

That's correct. The answer is, um, muscle, sorry,

35:22

muscle and bone.

35:24

And what, why this is here is what's shown

35:27

as the different tissues and this is the impedance

35:31

and the unit of influence is called als.

35:34

Time number six.

35:35

You can see here, lemme

35:37

see, you can see here.

35:43

Um, the bone has the highest impedance and muscle is less.

35:47

Therefore you can see, um,

35:50

the surface reflection in the image is so high

35:53

between the muscle

35:54

and the on the bone, which is the femur here in this case

35:59

compared to fluid and muscle.

36:03

Another question, the fetus of two image.

36:06

These are the images of fetus images, you can see the fetus,

36:10

um, forming here.

36:12

And you can see the idea here.

36:14

Caution is the fetus in these two images were exposed

36:18

to electromagnetic radiation, mechanical vibration,

36:22

ionizing radiation, uh, impedance oscillation.

36:31

The current answer is mechanical vibration.

36:34

And that's one of the reason why we, the,

36:38

we always warn about all these

36:41

boutique ultrasound centers trying to provide nice, uh, uh,

36:46

baby picture for the pregnant women.

36:48

Uh, especially in the malls.

36:50

You can, you might have seen this facility which advertise,

36:53

they can give you all these 3D images,

36:55

but every time you are doing it you can gonna create

36:58

mechanical vibrations that can harm the fetus of the baby.

37:03

And that's why we always caution as one of the, uh,

37:07

cautionary, uh, aspect we want, uh, not to lower

37:12

use ultrasound, pregnancy, use it only when essential not

37:16

for, uh, boutique factor.

37:19

The other one is like if there are any air cavity in the,

37:23

in the fetus area that can create what is called a say, uh,

37:26

like a temperature can increase in that area

37:29

because the reflection

37:30

that can also cause a little bit more harmful to the,

37:33

to the, to the fetus.

37:34

So all these things are part

37:36

of the ultrasound safety aspect.

37:40

So I have these, uh, these, I had these questions.

37:44

Let me see these,

37:45

the questions coming out on the under on the board.

37:48

So the second one I said, uh, I think it should be four, uh,

37:52

four kilowatts not, um, for hertz.

37:55

So that's fine. What is the image finding that shows

37:58

that there's more reflection between bone

38:00

and muscle on the period?

38:01

What is the imaging finding that part?

38:04

I don't know the answer. What is the, uh, finding,

38:08

I think you guys need to know.

38:09

I'm not a ultrasound radiologist.

38:11

So what is the, this is, I'm just talking about the, um,

38:15

reflection, but I don't wanna,

38:17

I don't know the answer to that one.

38:19

So the other question you had was

38:24

higher frequency results in better

38:27

or worse action resolution.

38:28

Let's go back to the, uh, axial resolution question.

38:37

So let me stop, let me, let me, let me here, come back here.

38:40

Let me go back to the axial part resolution.

38:43

So this is what we are talking about.

38:45

Um, let me see, where is there acceleration?

38:49

Uh, we can go back here to the next one.

38:53

Let me see.

38:59

So as we can see here, the

39:05

transmit the frequency will improve a acceleration

39:07

however tion increases

39:09

and also ability

39:10

to resolve on the axis along the depth

39:13

is independent of the depth.

39:14

Let me see what, what else?

39:15

Like, you know, you're talking about the frequency.

39:17

Um, let's say how do we calculate the frequency?

39:21

We are calculating the frequency, um, with it.

39:25

So this is the XI resolution was calculated as follows.

39:29

Let's say here, if we use this, this formulation

39:34

resolution is 3.02.

39:35

That is three millimeter XI resolution.

39:38

If you increase the frequency here,

39:41

the variant becomes smaller,

39:43

therefore the spatial LE length becomes smaller,

39:46

therefore the resolution can also become smaller.

39:50

So therefore increasing the frequency will actually improve

39:54

the spatial XI resolution.

39:56

A better when it transmit frequency

40:01

al re degrade or the more tracking is used.

40:04

But on the other end, if the a trade off is increasing,

40:07

is increasing imagination, but if the, um,

40:14

because of the spatial

40:15

and going smaller, the AL resolution is increased.

40:18

So I would say the XI resolution will improve

40:22

with the higher frequency of this one transfusion.

40:25

Let me see other questions you

40:27

have for the lab.

40:31

Is thematic radiation wrong?

40:32

Yes, because ultrasound is not part

40:35

of the electromatic spectrum.

40:36

Ultrasound is a differently

40:39

because thematic spectrum works under the principle

40:41

of e equals mc square, all of the spectrum

40:45

present in the electromatic.

40:47

Radiation is part of this, uh, travel with speed

40:51

of light C equals the three point,

40:53

three point 10 point of eight meters per second.

40:55

Whereas ultrasound is the sound where

40:57

therefore it's not electromatic radiation.

41:00

What is the relationship between pulse reputation,

41:03

frequency and frequency?

41:04

They're pretty much the, they're they're the same.

41:07

Um, can you review your variation versus the ring

41:10

down artifact please?

41:12

Uh, the ring down artifact, again, that depends on the,

41:17

uh, um, I'm not very familiar with one.

41:21

I, the answer I can convey is like revelation is like there

41:24

is a reflective, uh, surface

41:26

and that's causing this, uh, reservation

41:29

and that creating a artifact whereas a ring down artifact is

41:32

like, like the, the, the whole um,

41:38

I don't want to guess this

41:39

because I had

41:40

to think about ring down artifact I'm not very familiar with

41:44

because I've not heard so much about the ring artifact.

41:47

Um, uh, so you need to check on that in the,

41:49

in the textbook, uh, for the check it out on this one.

41:52

So I'm, I'm sorry about that.

41:53

I want to give wrong information.

41:56

Whereas ation artifact, as you can see here,

41:59

uh, we saw that one.

42:01

What's the reason is like, uh, let see,

42:08

see this is the equally spaced decreasing brightness

42:11

that is sent from the surface, but this is

42:13

because of the interface.

42:14

There is a very high reflection point causes this one

42:18

and that is causing this all this uh, uh, uh,

42:24

so I think we answered the question.

42:28

Any other question? So I got this one done

42:34

answer, so thank you very much

42:37

and I think two weeks from now I wanna talk about the final

42:40

set of these questions.

42:41

That, and that's on radiation protection,

42:43

which is again a major portion of the, um,

42:47

board exam will be taking a lot of questions about

42:49

radiation protection and limitations and so forth.

42:53

So I look forward to sharing that information.

42:56

Uh, two weeks from now is that May 12th, uh, Ashley May

42:59

12th. Yes,

43:00

May 12th. And they're

43:01

gonna announce it and we're gonna have it so on.

43:05

Yes. Thank you so much Dr.

43:07

Mahesh for this case review. Appreciate it. Sure,

43:09

Appreciate, thank you very much for joining.

43:12

Yes, thank you for everyone for participating.

43:14

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43:17

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43:18

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43:20

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43:23

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43:26

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43:29

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43:30

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43:32

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43:34

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43:37

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