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Hello, and welcome to Noon Conference hosted by Modality.

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Noon Conference connects the global radiology community through

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free live educational webinars that are accessible for all, and is an

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opportunity to learn alongside top radiologists from around the world.

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Today, we are honored to welcome Dr.

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Alka Singhal for a lecture entitled Ultrasound Physics.

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Dr. Singhal is an associate director of radiology at

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Medanta, the Medicity Hospital in Delhi NCR, India, and

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has over 28 years of experience in radiology.

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She has authored several publications and talks for leading national and

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international conferences and is the author of "Atlas of Parathyroid

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Ultrasound."

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At the end of the lecture, please join Dr.

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Singhal in a Q&A session where she will address

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questions you may have on today's topic.

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Please remember to use the Q&A feature to submit your questions so we can get to as

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many as we can before our time's up.

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

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Singhal, please take it from here.

1:02

Perfect. Thank you so much. So today's topic of our discussion is

1:06

ultrasound physics. So basically,

1:10

we've learnt through many advanced topics that

1:14

many a times it's really good to go back

1:18

to grassroots and really learn how we

1:21

actually create it.

1:23

So we can understand how pathology alters what we

1:27

see and how to really use our

1:30

equipment as our tool to enhance

1:34

when we are currently faced with various

1:37

challenges of size, dimension, and different

1:40

pathologies. And I

1:43

know AI is coming up, but still,

1:46

to understand how things work so

1:50

you can understand that this is how things look, and you are

1:54

in a better position to correlate between various

1:58

radiological imaging modalities,

2:01

CT, MR, ultrasound, everything. It's just

2:06

basically image is a creation of the dynamics of the sound with the

2:10

tissue, and once we understand that wholly,

2:14

our experience in scanning will become really complete and thorough.

2:19

So with that note, I begin

2:22

my

2:23

talk of ultrasound physics today.

2:26

Now, as we all know, basically it's a knobology, and of

2:30

course, we can make things appear right, and we can make things appear

2:34

different than what we were expecting as artifacts.

2:38

And of course, artifacts are, again, a tool of

2:42

diagnosing pathology, so as you will understand.

2:46

Now, the most important criteria, of course, is transducer selection, the

2:49

presets, and image optimization, and we'll run through grayscale,

2:53

color Doppler, and spectral Doppler setting. Okay?

2:57

So why do we need to understand ultrasound imaging physics?

3:01

Because eventually, ultrasound is a highly

3:05

operator-dependent modality,

3:09

much more than CT and MR are standards.

3:13

There's a standard protocol, there's a guideline.

3:16

Ultrasound, everybody kind of tends to follow their own protocol.

3:20

However, even though we set the

3:24

protocols, the dynamics of the patient, the depth

3:28

adjustment, the area of interest, everything is so

3:31

dynamic that you need to be aware constantly as

3:35

which parameters are you going to alter so you can get the best out of

3:39

the given situation in the patient.

3:42

Right. So this is how a high-end ultrasound machine looks like.

3:46

It's got various tools, hardware, and

3:50

various software and touch panels and great tools

3:54

for us to play around, right?

3:56

So knobologies are the knobs and how do we understand as we get a

4:00

new phone, new laptop, new machine, we are

4:03

all fumbling with the controls

4:07

initially. However, once we are used to, so we know

4:10

even in the darkest of the room, okay, that's where my hand goes to

4:14

adjust this parameter. And we have done a lot of complex

4:18

analysis as to what we wanted to change and what outcome we receive.

4:23

Okay?

4:24

So basically, all machines are similar, like any phone, like

4:28

any laptop. Basically, our ultrasound machine is the most high-end

4:32

sophisticated laptop or computer as we can understand, right?

4:36

Now, how do we get the best out of it?

4:38

Initially, we used to have toggles and control knobs, and these days,

4:42

most machines have touch panels, right?

4:45

Now, what are the

4:48

rules of knobology? Basic fundamental principle is the

4:52

same, right? So we need power, we

4:56

need ALARA, we need optimization in various

5:00

areas, right?

5:02

And what looks good to you to be able to diagnose is the way

5:06

your eyes have adjusted to the image.

5:08

So again, that is a very subjective experience and

5:12

varies from people to people. Often in your machine, you'll have presets

5:16

saved by a particular doctor, okay?

5:18

This is my preset, and this is your preset.

5:21

This is the way I like to look at the things, and I can

5:25

then closely discern where is the pathology and where it's

5:29

appearing as normal, right?

5:31

Now,

5:33

so

5:34

basically, let's understand. Of course, we'll use a

5:38

coupling medium to allow the sound waves to enter the

5:42

body, which is normally an ultrasound jelly.

5:46

Now, we're studying the B mode configuration.

5:48

B mode, B, the letter word B stands for the brightness

5:52

mode. So there is basically the sound waves have gone through the

5:56

tissue, and there is a reflected echo that's returned, and

6:00

brightness of that reflected echoIs what is

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giving us the information. Now, depending upon where it's

6:07

mapping in the field and how it's appearing, we are able to

6:11

get useful information on what is happening inside the body.

6:16

Right. Now, how do we understand this?

6:19

What are the common controls? There's a long list of controls.

6:22

If you have spent some time with your application specialist,

6:26

they really explain to you a lot more in detail because

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our generation is now trying to bypass all that, because

6:35

everything is kind of AI generated.

6:38

There is sophisticated tools, auto optimization

6:41

tools, and everything. So, I've written a chapter for

6:45

IRI textbook on-- visits some advanced

6:49

topics, right? So to understand the basic and then to

6:53

really go about it is the next level.

6:57

So understanding the fundamental image, harmonics, frame rate, all

7:01

these words we'll understand in detail for the color, hue, velocity,

7:05

persistent, gain, priority, and for the spectral Doppler,

7:09

again, broad frequency, filter, PRA,

7:13

zoom, aliasing. And then of course, 3D has its own

7:17

great

7:19

parameters that we have to work around to create

7:23

a good image. Now, the common factors at which we are

7:26

everyday

7:28

really toggling between our everyday practice currently are the

7:32

depth,

7:33

the focus, and the gain. Predominantly these three are

7:37

the factors. If you have selected the right transducer, selected the right

7:41

preset, what you really are working through is the

7:45

correct use of the depth, the gain, and the focus, right?

7:49

So of course, there is an auto scan optimization, which has got everything

7:53

calculated, inbuilt for you.

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You do take cine loop, and then you scroll back

8:00

to see where the pathology is, subtle hernias, subtle

8:04

VSDs, ASDs, and other abnormalities that

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you often pick up in the cine loop,

8:11

because our eyes sometimes do not

8:14

register it. As I said, one tenth of a second is the

8:19

moment that the image registers. So if it's a fast

8:24

moving area, like a septal defect or a tiny little

8:28

window where you had the hernia, so then you need to scroll

8:32

back to see it. So cine loops are not just

8:36

for

8:37

glorifying your work, they are diagnostic tools.

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Because then when you go step by step and thread by

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thread, you can really analyze and get more information.

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And of course, you've taken, chosen the right preset and right transducer

8:53

that you required for the area.

8:57

So we have to have the proper depth

9:01

for the area of interest. The gain settings have to be optimal.

9:04

The sector size, depending upon what you want to look at.

9:08

So example, you're doing a 3D. You have to have a sector that includes the

9:12

head of the baby. You have want to do a 3D of the endometrial

9:16

cavity. You have a sector width that includes the uterus.

9:19

So accordingly, we will work on these.

9:23

The most important is which transducer you are going to select.

9:27

Now you know that for abdomen, I'm going to select the curvy C2-4.

9:32

But who told you that you have to select that transducer?

9:35

Why can't you select the linear transducer to do it?

9:38

Why can't you select the transvaginal transducer to do abdominal

9:42

scan? Because of

9:46

the frequency requirement, the sector width requirement,

9:50

and the depth requirement that has been calibrated and

9:53

programmed to give you the image for that wider perspective,

9:58

and it's all been curated for you, right?

10:02

So if you were to do an abdominal scan with a linear transducer, which has a depth

10:06

of hardly four or five centimeters, you won't be able to see

10:10

the whole girth or the depth of the abdominal scan, which is about, say,

10:14

15 centimeters, right? So you need the depth, and of course,

10:17

you need the wider field of view as well.

10:20

And

10:21

a linear transducer would have that straight

10:25

field of view, right?

10:28

So accordingly, when you're doing an obs, so you also need

10:32

a wider view and not so much deeper, but we are

10:36

looking at the babies usually superficial.

10:39

So we are looking at that area. So accordingly,

10:42

adjusting the frequency allows us to increase the resolution at the expense of

10:46

penetration. So the fundamental basic

10:51

equation is that you go deeper in depth,

10:55

but the frequency goes down, the resolution goes down,

10:59

and you can use the highest frequency transducer that gives you the

11:03

best

11:04

depth of resolution for that area. That's the one transducer you choose.

11:09

So if you want to really reach up to the posterior

11:12

surface of the liver, so I will use a selected

11:16

transducer that gives me that

11:19

clear. So if I have a pediatric patient, I can definitely

11:23

use a linear transducer because even that might give me a depth

11:26

up to the posterior surface of the liver and will give

11:30

me great heightened resolution. So often, if I

11:34

cannot see the little triangle, the

11:39

fibro triangle anterior to the portal vein in bilary

11:43

cirrhosis, and when I go to the linear transducer, I can really

11:47

find it and see it.

11:49

So the trade-off between the depth and the resolution, we remember.

11:53

Next comes the preset. So you've selected the right transducer,

11:57

but then again, the preset comes into play.

11:59

So example, I've selected the curvy C2-4 transducer,

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but I can select abdominal preset or an obs preset

12:07

depending upon what is it that I'm intending to do.

12:10

If I'm doing an obs scan, because then I know that I really need a

12:14

depthDeep to the posterior spine, right?

12:17

I need to see a psoas abscess and retroperitoneal lymph nodes and

12:21

other pathology as well. And if I'm doing an obs, I know the

12:25

baby is usually anteriorly, right?

12:29

So then I don't need that much of depth, but I'll get more resolution

12:32

out of it by having my appropriated

12:35

settings that have been set as ideal

12:39

and fed into the machine, right? And created a combination of

12:43

factors labeled as a preset. These are

12:47

customized. Some come as factory settings, and you can

12:51

always customize them with your application specialist as per

12:55

your own personal needs.

12:57

Clear? So these can be customized.

13:00

Now, for example, this is an abdominal-- This is the same

13:04

transducer, C2-4. However, scan in the

13:08

above image, we've done with an obs preset, so it's only going to look at

13:12

certain range. The lower part, the kidney,

13:15

which is

13:17

the deeper part, is not well visualized.

13:21

However, when I change the preset to abdomen, it

13:25

has automatically adjusted the focal zone to include

13:29

reach to the posterior surface of the dome of the diaphragm, and

13:33

I'm able to visualize the entire kidney

13:41

very well.

13:43

Clear so far? So here we have a

13:46

block out or a loss of information, and here

13:50

we have more detailed information.

13:53

So that's the role of the correct presets.

13:55

And however, you can always manually change the settings even if the preset

13:59

is not correct. You can play up with the focus key and the depth

14:03

to adjust them,

14:06

though it makes your task much more

14:09

time effective, right? So when you choose the right preset

14:13

and you work with it.

14:15

Next, of course, depth, to be able to see to the required depth

14:19

of penetration, as we discussed. So like we discussed, the

14:22

equation, we have depth versus resolution trade-off,

14:26

and that we know.

14:28

Now, just a certain example. So we are trying to look at the pancreas, and

14:32

we have

14:34

depth and zoom. So we can have more, reduce the depth,

14:38

and we can reduce the depth and to portray the more pancreas in more

14:42

bigger zoom.

14:44

Okay, so we can use a post zoom or a pre zoom to

14:47

magnify our area of interest. If you are looking

14:51

at calculi in this common bile duct or any subtle

14:54

areas or a GB polyp, we can use that feature.

14:58

Now, what is gain? Gain is simply amplification.

15:02

Simple words. It's just increasing the volume.

15:06

Right? So the

15:08

echo that returned, we just amplifying it, right?

15:12

So everything gets amplified, right?

15:14

So we have to understand what level to

15:17

amplify it so we can understand and get the

15:21

required information without losing the information.

15:25

So it has to be optimum

15:27

so when we can identify the areas. So example,

15:31

so simply, if you have a gain too low, my

15:35

image will be like black, black. If I have gain too high, my

15:39

image will be all like white, white, too much of brightness.

15:43

So this is like a low gain, the first image.

15:46

The second image is like too high a gain.

15:49

Again, I have loss of information.

15:52

But when I have an optimal gain settings, I have good contrast

15:56

between the vessels, the muscles, the subcutaneous tissues, the muscles, and

16:00

every other tissue, and I can identify normal

16:03

anatomy and pathology subsequently.

16:07

Okay? So that's about the gain. So again, another example

16:11

in a urinary bladder, which shows low gain, high gain, and

16:14

optimum gain. Again, example of a liver, where we have

16:18

low gain, high gain, and optimum gain settings.

16:22

Coming to next, focus. Focus simply is

16:26

where you want to focus. Where do you want to look?

16:29

Where is your area of interest? So that area of interest will

16:33

change, even in the same area. So

16:37

example, I'm scanning abdomen. Now I see a calculus.

16:40

I want to take my area of focus to where that calculus is so that I can

16:44

get the maximum beam width over there, the maximum

16:47

energy, and really have a dense acoustic shadow and really

16:51

confirm it. For example, I have an ovarian lesion, which has

16:55

got a subtle internal mural nodule.

16:59

So I'm going to take my focus right there at the level at which that

17:02

mural nodule is in the ovarian lesion.

17:05

So I can, if at all, demonstrate more detail of it,

17:09

or if there's any vascularity, I can pick it up, or any other subtle

17:13

signs that can give me further clue whether I'm looking at a

17:17

benign or a malignant pathology or any further information that

17:21

I can add value to my test, to my

17:24

scan. Right? So that's the logic of using focus.

17:28

And by default, by the preset that you've chosen, it automatically

17:32

selects, assuming a population for the median

17:36

percentile, what depth it's

17:40

set to.

17:42

So this is just an example of a focus.

17:44

So wherever you want to look at, you put your focus.

17:49

Right? So wherever you want to see the best, you will set it up.

17:52

Now, the next is the TGC, the time gain compensation.

17:57

Now, what is that, is time gain compensation?

18:00

So we have to understand that the liver volume of

18:03

parenchyma, supposing it's on this anterior capsule and

18:07

the posterior capsule, is all the same volume of tissue, right?

18:11

Same volume. However, the ultrasound beam that

18:15

just entered the anterior capsule and the amount of energy

18:19

that was left after it was got absorbed, some by the parenchyma,

18:23

reaching the posterior capsule would be

18:26

diminished.Now, the echoes that are returning,

18:30

again, would be in that intensity, because already a

18:34

lot of sound energy is getting absorbed at all the layers.

18:37

So they will give us a different appearance of the amount, though

18:41

we know that it's the same volume of tissue anterior, posterior.

18:46

To correct for that, we have a time gain

18:49

compensation. So we adjust for that so that

18:53

our tissue looks uniform.

18:57

Right? And if there is any abnormality or pathology in

19:01

any area, we can discern, differentiate

19:05

it

19:06

easily.

19:08

Easy to understand time gain compensation,

19:12

right?

19:13

Okay.

19:15

So we have to do it optimally. Again, don't overdo it, don't

19:19

underdo it, so that you have a uniform optimal image

19:23

that you have from top to bottom, anterior to

19:27

posterior. Right? Balanced gains, right?

19:30

Output power, of course, machines have inbuilt.

19:33

If you have an ops preset, they would have inbuilt limit to

19:37

which it can do. Of course, when you're using contrast

19:41

ultrasound for any

19:44

other

19:46

imaging modalities, it gets vary. Right?

19:51

So we use the principle ALARA, as low as reasonably

19:55

achieved, and

19:57

AI has got lot more wonderful features in most machines

20:00

these days now.

20:02

Coming to the next level features of dynamic range is

20:06

another feature which is

20:09

really a very helpful tool sometimes.

20:12

When you have a subtle hepatic or metastasis

20:16

or a subtle nodule that you really want to

20:19

differentiate.

20:22

Spatial compounding, tissue harmonics, frequency compounding.

20:25

So tissue harmonics is one which is kind of normally on in most

20:29

presets. You might have to just turn it off to see how the image looks like

20:33

without it. Dynamic range is one I would really like to focus

20:37

upon because it's a very

20:39

helpful tool, especially in MSK ultrasound, and even

20:43

in finding out subtle nodular abnormalities.

20:46

So what does dynamic range mean?

20:50

The range in which it will

20:53

display the tissues,

20:55

the contrast, right? So if you

21:00

have a lower dynamic range, that means it can only have, say,

21:04

certain numbers of brightness that it can display.

21:08

But if you have a wider dynamic range, you'll have more smoother

21:12

image because you have a more gradation to

21:16

the

21:18

brightness that you've given. Right?

21:20

So if there is a subtle pathology and it is getting

21:24

merged with the adjacent parenchyma, so when you

21:28

narrow the dynamic range,

21:31

right, so it will increase the contrast, and you may be

21:34

able to identify it better, right?

21:37

Next time when you're looking for subtle hepatic metastasis or any other

21:40

abnormality. So example, we have an image of pancreas.

21:44

This is with a

21:47

dynamic range of 30 dB, where you have lower

21:51

dynamic range, so you have more contrasty image.

21:54

And this is the second image, which have the dynamic range of 70 dB,

21:58

which is wider dynamic range, so it's a softer and a

22:02

smoother image.

22:04

Clear? So similarly, look at the liver.

22:07

We have a dynamic range which is optimal.

22:10

We have a dynamic range which has been narrowed,

22:13

right? So of course, we use optimum dynamic range to do our

22:17

ND scans and other scans, right?

22:21

Coming to next.

22:24

Post-processing and different color maps we can use.

22:27

I use that frequently because sometimes in the routine

22:31

grayscale, maybe it's just a freshness of how our eyes

22:35

see in different color. So when you use the different color

22:38

hues, we can sometimes

22:41

perceive pathology differently and identify it.

22:45

So it's a really helpful tool to

22:50

demonstrate. Edge enhancement, again, if you just play

22:54

with it. And how to play with it, ask your application people to show

22:58

you. It's there up in the advanced features, but it's not played around

23:01

frequently. But seeing subtle MSK

23:04

pathologies and subtle nodular lesions, it can really give you

23:08

further more cues.

23:11

So frame averaging is something like a slice averaging.

23:15

We'll come to that more. So tissue harmonic imaging, as it's normally

23:19

on, like in gallbladder and everywhere, but we can turn it on.

23:23

Auto gain, auto optimization are the tools which are existing,

23:27

and, of course, if you've changed your settings too much,

23:31

you do not know what to do, just go back to your original preset and

23:34

restart from there. We can use a wider frame of

23:38

view,

23:39

especially just to take the measurement of a pathology that you get

23:44

or a normal anatomy that you can actually get to fit in one frame.

23:48

So use a trapezoid view is good. And often to

23:52

display a pathology, example, a foreign body or a

23:56

splint in the skin, you can have a trapezoid field

24:00

of view or an extended field of view to display the entire

24:04

pathology in one frame. That gives a nice

24:08

clinical information to the clinician, and it's very convincing

24:12

for the

24:14

patient also for counseling and other purposes, right?

24:18

So that's a panoramic view of the thyroid.

24:21

Cine loops, as I discussed, they are diagnostic, and

24:25

we can use them for cardiac, for hernias, for any

24:29

pathology, any area. When you go back and you scroll through, you

24:33

can look at a-And diagnose more new

24:37

information that you could not have picked up otherwise.

24:41

Coming next to color and to power and to

24:45

spectral Doppler. Again,

24:49

it's best not to use much of the AI and to do

24:52

it yourself is better. And on the spectral, when you

24:56

do it yourself, you are in more control and more

25:00

accurate, I feel. But however, if you've really taken

25:04

a perfect picture, perfect scan, and then you could depend on

25:08

the AI tool to do auto measurements as well.

25:12

So

25:13

again, the fundamental principles are the same.

25:16

So you choose the color box as

25:21

suiting the region of interest as appropriate as to the

25:25

size, and you accordingly have a beam width, steering, gate

25:29

size, angle, adequate depth, and zooming.

25:33

Now, again, the similar principles will apply.

25:39

And you also have to be aware of the Doppler-related artifacts, right?

25:44

Now coming to color, power, or HD power Doppler, and

25:48

there are various new names for that.

25:52

Perfusion imaging.

25:54

You name it, every manufacturer's got their own unique names,

25:58

B-flow, and you don't know.

26:01

So everything is there. The fundamental is that

26:05

you have to use the

26:08

velocity range,

26:11

know which tissue has what velocity range, and

26:14

accordingly--

26:16

So example, portal vein has got a low flow velocity.

26:19

Now, if I'm wanting to see the flow in that, my settings are at

26:23

lower. If I'm looking at renal arterial

26:27

Doppler. So I have to have a range where I can pick up the renal

26:31

arterial stenosis completely in the frame.

26:34

So accordingly, I have to know the anatomy, know the

26:38

area of interest, and adjust my parameters, right?

26:43

Spectral gives us added dimension of direction,

26:47

and then we can also do the calculations and measurements.

26:52

Like I said, the color box has to be as

26:56

small, and we try move the area of interest

27:00

to as superficial by rotating the patient or whatever

27:04

maneuvers you can do so that you have lesser depth in the

27:08

area that you are wanting to look at.

27:10

Appropriate size, of course, like we said here in the first

27:14

image, the box is bigger, and we have lots of

27:18

information in the color pixels. And at the same, when the box size is

27:22

adjusted, we have a good flow of color information.

27:26

Now, the color baseline, when we have

27:29

a color baseline, which is set as very high

27:34

or very low,

27:36

accordingly, it will pick up low flow velocities or high flow velocities.

27:40

So depending upon what you want to look at, you will adjust

27:44

your color baseline. And velocity scale,

27:48

what you want to see. You want to see the low velocity

27:52

scales as well, or you just want to see the higher velocity scales.

27:56

So example, if I'm doing a carotid arterial Doppler, I'm

28:00

looking at usually higher velocities, so I will have my scale

28:04

adjusted in that range. And if I'm looking at

28:07

a venous Doppler in the leg, when you select the preset,

28:11

observe what it says for the velocity range.

28:14

You will automatically see the velocity ranges have from

28:18

20 to 30 both the sides, centimeters per second.

28:22

But if I select a carotid arterial Doppler, then I'll

28:25

automatically see that the velocity range that it had selected is

28:29

100, or 100 up and down, 200

28:33

is the velocity range.

28:35

So this has been inbuilt in the machine, but you can manually change it as

28:39

well once you understand the concepts.

28:43

Same way for color gain, so not to do over gain so that it spills

28:46

beyond the

28:48

velocity, beyond the anatomy of the vessel.

28:51

It has to be just adequate to fill the vessel completely.

28:54

Of course, first you have scanned it in B-mode to know where

28:58

is the vascular anatomy, and you've noted calcifications and

29:02

other abnormalities to account for it. Right.

29:06

So like this is a thrombus in jugular vein.

29:09

We can see the artery here, and that's a thrombus.

29:11

So accordingly, we have to see that my first, the

29:15

color gain is adjusted so that I'm filling the lumen of the artery very

29:19

well. And now I'm going to assess the vascular areas

29:24

until then now. This is again a case of

29:28

carotid artery

29:31

tumor. So this is the bulb field where they have a

29:35

lesion in the carotid bulb, and this is how you

29:39

can see both the carotid arteries on the side and the

29:42

mass very well.

29:44

Color inversion, so normally we are used to or whatever.

29:48

So red and blue simply indicates the direction of flow

29:52

towards or away from the transducer.

29:54

It doesn't mean artery or the vein, so that has to be remembered.

29:58

Now, the beam steering is very important.

30:01

Now, what is this angle, and what is this angle between

30:05

which two things?

30:08

So is it the vessel wall

30:11

and the flow of blood,

30:13

or is it the direction of the flow and the beam?

30:17

What are the two things in which this angle is that you are

30:20

adjusting?

30:22

So many times this has been misinterpreted as being between

30:26

the wall and the beam. No. So this angle

30:30

actually exists between the direction of blood

30:34

flow

30:35

and theBeam.

30:38

So this is the ultrasound beam, and that's the direction of the blood flow.

30:42

So that must be remembered. So accordingly, we adjust it and

30:46

align it.

30:48

It applies in cardiac echoes and other areas as well,

30:53

all the Doppler settings.

30:55

To do the spectral calculations, our Doppler settings have to be

31:00

accurate. Then we've done the tracing, and we

31:03

receive a tracing when we've done that.

31:07

Now, what does a typical waveform comprise of?

31:11

Now, our typical waveform will match the

31:15

cardiac cycle from which it came from.

31:18

True?

31:19

A cardiac cycle includes a systole and a

31:23

diastole. True?

31:25

So depending on which part of the body blood

31:29

vessel you're looking at, it will have different

31:33

waveform in systole and diastole.

31:37

Easy to understand? So

31:40

what are the components? There's a time that is on the X-axis,

31:45

and there's a velocity component that is on the Y-axis.

31:49

Clear?

31:50

Now, how are things changing with time, the

31:53

velocity? That is what we are recording in spectral

31:57

term.

31:59

So we have a rise to

32:02

systole, peak systolic velocity.

32:05

Then this is a systolic velocity, then you have

32:09

the diastolic component, and then you have the

32:12

end-diastolic velocity. So this is one

32:16

cycle complete, and then the next cycle begins.

32:20

So from the beginning to the peak, that is the systolic

32:24

acceleration time that we record.

32:28

So this little area is called the systolic acceleration time,

32:32

and we will record the RI. That's the peak

32:36

systolic and divided by the peak diastolic.

32:40

We do the PI, is the peak systolic minus peak diastolic

32:44

divided by the mean,

32:46

and so on. We'll have the peak velocity and other

32:49

parameter. So understanding of this helps

32:53

us in understanding how things will appear.

32:57

Now,

32:58

typically, broadly, all the vessels in the body, the

33:02

arteries, we can put them into three typical waveforms.

33:06

One is the high pulsatility for the high resistance

33:10

waveform,

33:11

which is seen in cases of peripheral arteries for the arms and the

33:15

legs.

33:17

Basically, there is a forward flow in systole,

33:20

and there is a diminished or a

33:24

reverse flow in diastole. So these arteries, you can

33:28

say, are not the VIP or the very important arteries.

33:32

So they only get a forward flow in the systole, and they do not

33:36

get much diastolic flow. They are fine with that,

33:40

unless if there's a muscle and a lot of physical activity or an

33:43

athlete at the time of exercise.

33:47

Now, then next comes the important

33:50

arteries, which are the renal arteries, the carotid

33:54

arteries, the vertebral arteries, the celiac artery after means

33:58

especially. So these, because of their high

34:01

requirement all the time, the body has designed

34:05

how these work is the contraction, the

34:09

peripheral vascular resistance that is

34:14

by renin-angiotensin and vasoconstrictor and lot of

34:18

mediators. That's how it works. So broadly, the

34:22

waveform that we see is a systolic flow and a

34:26

maintained diastolic flow. Because these

34:30

organs are so important, they need a perfusion in both

34:34

systole and diastole, which is the kidneys, which is the

34:37

carotid arteries, the supply to the brain, the vertebrals, and the

34:41

celiac artery. Clear? And of course, we can have an

34:45

in-between pattern where we have a sharp systolic peak and

34:49

some flow in diastole, like the ECA and the SMA.

34:54

Clear? Now, let's understand. These can also turn

34:57

abnormal. It can be altered flow with

35:01

calcifications, plaques, or stenosis, or other

35:05

pathologies. When you have lots of range of

35:09

velocity, the spectral window will be

35:13

filling, because it's not clear now with a

35:16

particular range of velocity, but there are multiple range of velocity that are

35:20

filling in the window.

35:22

And of course, if there's turbulence, then again, you'll have various

35:26

waveforms, but no specific crisp waveforms.

35:31

So understanding that this is a normal triphasic peripheral arterial

35:35

waveform, which is narrow frequency-based, and there's a steep rise, quick

35:39

drop, an early diastolic reversal, and late forward flow.

35:43

Similarly to the color scale parameters or

35:47

to the B-mode parameters, we have the velocity scales.

35:50

If I'm looking at the carotid, and if I'm looking, my velocity range

35:54

is only 20 and 20, so it's only 40 or

35:59

50.

36:00

I'm just giving it.

36:02

But if I'm looking at the carotid, I do need to have at least 100,

36:05

120 centimeters up to. So I find I see the whole

36:09

waveform on one side of the tracing.

36:13

Baseline, I can move up and down depending on which portion I want to

36:16

display more.

36:19

Spectral aliasing, when I see a part of the waveform on the other

36:23

side, mixing with the colors. So again, that

36:28

ambiguity of the information is known as aliasing, and that

36:32

really helps us to pinpoint areas of stenosis,

36:36

areas where do we do the sampling for ductus venosus.

36:40

So how do we correct it? We can increase the velocity range,

36:44

change-All these three parameters will work.

36:48

What is PRF? It indicates the number of pulses emitted by the

36:52

transducer over a period of time, measured in hertz,

36:56

typically used between the ranges of one to 10 hertz.

37:00

And what is Nyquist limit? It represents a maximum Doppler shift

37:04

frequency that can be correctly measured without resulting

37:08

aliasing.

37:13

Normally, it's optimally set for all the ultrasound machines

37:17

for most pathologies, so you hardly have any

37:20

much

37:22

need to even change the parameters in the present

37:26

ultrasound scanners. Right?

37:28

So we've learned already about the transducers.

37:31

Then the angle is the important area that we need

37:35

to adjust. Why? Because of the factor

37:39

called cos theta,

37:41

so the angle has to be as

37:44

low, meaning as much in

37:47

alignment with the beam

37:50

for more accurate results.

37:53

Zero is better. Zero to 60 is good,

37:57

but anything more than 60, it leads to errors in the

38:01

velocity measurement and other parameters.

38:04

So ideally should be zero, and the angle is

38:08

between the beam and the direction of flow.

38:12

Okay, so aliasing is useful. It serves as lot of

38:17

value in diagnosing. The spectral wall filter,

38:21

if you have it too low, you will have loss of information

38:25

close to the baseline,

38:27

so you have to have it optimally adjusted.

38:30

If you have the spectral gain too high, you'll fill in the

38:35

spectral window.

38:37

And like I talked about the angle,

38:40

it has to be optimal. Sample volume, you usually keep it to the central

38:44

third of the blood vessel, the flow.

38:49

And

38:51

larger will lead to more wider range of

38:54

velocities and, again, errors. So in a nutshell,

38:58

how do we perform Doppler? You find a vessel in the grayscale

39:02

with the Doppler off to begin with.

39:05

You set your depth and focus to suit the vessel.

39:08

You turn on the color, then you adjust the color gain and the

39:12

PRF scale to see that vessel. Keep the color bar

39:15

small, as optimally required, and then you zoom it a bit.

39:20

You place your cursor. You turn on the pulse Doppler now.

39:23

When you get the cursor, you set it in the vessel.

39:26

You set

39:28

such that it covers only the width of the vessel, preferably the central

39:32

third, or as per pathology, if you're looking at septal

39:35

vascularity for an

39:37

ovarian lesion or any other area. If required, perform a little

39:41

angle correction here. Then you turn on

39:45

the update the spectral Doppler and get the tracing and

39:48

measure the waveform and quantify your results.

39:54

So this is, for example, a case example of a renal arterial

39:58

Doppler. So this is sampling of a middle segmental artery.

40:02

You have the artery, you've set it all up, and it's all reasonably

40:06

well-balanced superiorly above the baseline.

40:10

And then we've recorded the RI, PS, and ED.

40:13

So obs Doppler, you can see the aorta, you can see the

40:18

uterine artery as it's crossing the iliac vessels a

40:22

little above. And then we measure the

40:26

parameters. So RI is S minus D upon

40:30

S. PI is S minus D upon mean,

40:35

and SD ratio,

40:37

we do.

40:39

Right? So pulsatility index, RI index.

40:43

So machine has got the inbuilt formula.

40:46

When you select the preset, it's going to do the calculations automatically for

40:50

you and deliver them to you. You do need to measure the

40:54

AI,

40:55

the acceleration index, manually.

40:59

I think that's better. And then you can do the

41:02

various thing.

41:05

A little bit about ultrasound artifacts. I'll run through it.

41:09

So basically,

41:12

you see different echoes that do not correspond to

41:16

the tissue being imaged. So

41:19

why do we see that? So to

41:24

understand that, let's understand what is resolution.

41:27

So you have resolution. One is spatial resolution, and one is

41:31

lateral resolution.

41:33

So spatial is ability to distinguish between

41:37

the distant image points lying close to one each other.

41:41

And lateral is the amount of minimum separation of the

41:45

two reflectors in a direction perpendicular to the ultrasound beam.

41:49

So we have in one direction, and we have an other dimension.

41:53

There are two different dimensions that we are using to map the

41:57

information. So accordingly, we have a spatial

42:00

resolution and a lateral resolution.

42:03

So,

42:07

now we get different artifacts. How do we avoid, and how do

42:11

we use them to our diagnosis? The first, and the commonest we see everyday

42:15

practice, is acoustic shadowing.

42:17

So basically, we have a

42:19

area

42:23

of

42:25

low amplitude echoes, right, behind an area of

42:28

strongly attenuating tissue. Now, do you have a

42:32

shadowing kind of an area? Now, that doesn't mean that there is no

42:36

kidney tissue over here, or there is no normal parenchyma or abnormal

42:40

parenchyma here. Simply, that area

42:43

is being shadowed by a very high

42:47

density-Why? Because that has

42:51

absorbed all the beam

42:54

energy and it hasn't allowed any beam energy to

42:58

go, so that area is not insonated with ultrasound, so that

43:01

area has not created its own image.

43:05

Right?

43:06

So what is the thing we learn? We learn that, okay, we can

43:10

diagnose a structure, a bone, or a calcium, or a

43:13

calculi. However, supposing it's of a large

43:17

calculus, we have to work to move around so

43:21

we can see,

43:23

try and penetrate and scan the area that was

43:26

shadowed by the pathology to get more useful

43:30

information. That is also very important.

43:33

So subtle shadowing you can see in cases of appendiculitis, you

43:37

can see shadowing in cases of gallbladder,

43:40

and then it's cystic enhancement.

43:43

Now, this is just the converse of that thing.

43:46

Now, instead of a high energy, high absorbing structure, we

43:50

have a low attenuating structure.

43:52

So which didn't take that much of beam energy as compared to the

43:56

background parenchyma.

43:59

Right? So it let more sound energy to go through.

44:03

So as a result, the area is still in that

44:07

path,

44:09

glew up with light, or it became more brighter because it had

44:13

got more sound energy there.

44:16

Simple, easy to understand, helps us in diagnose.

44:19

Cis, it's an hallmark of cystic areas because that

44:23

indicates that that area is a fluid-filled, clear fluid because it's low

44:27

attenuating. Right? So we can

44:31

identify cystic enhancement. So this is just a summary,

44:35

increase through transmission so

44:38

we can identify cystic structures.

44:40

Now, beam width artifact is--

44:43

So we have a narrowing anus scattering of the-- or

44:47

widening of the beam.

44:49

So there can be a misinterpretation of the location of

44:53

the lesion, highly reflective object.

44:58

And this kind of an appearance you'll commonly see in cases of

45:01

urinary bladder when we are scanning.

45:04

A bowel shadow may just move in, and it may give us impression of a

45:07

pathology. So you have to have the correct frequency

45:11

zone placement to be able to overcome that.

45:15

Similarly, you can have side lobe artifacts and grating artifacts.

45:21

So these are both secondary lobe artifacts depending upon

45:24

the off-axis beam that is creating echoes that

45:28

are being put into the

45:31

central path of the area.

45:34

Right? How can you reduce them? By using

45:38

multiple advanced transducer design.

45:41

Now, what is slice thickness? Again, it also produces echoes, which are

45:45

not there or averages. It's similar concept as slice thickness

45:49

of raging in tissues. However, we have thinner slices.

45:53

So if you're doing very superficial area, you can use a

45:57

standoff. But these days, with the high

46:01

best equipment, it's hardly seen.

46:04

Now, reverberation is when you have a high

46:08

reflector. The sound waves, they just ricochet,

46:12

right? So you will get lines, lines, lines, lines, lines,

46:16

multiple areas. For example, you will see them in

46:20

cases of the rectus femoris when the abdominal wall.

46:24

That can give that appearance of that multiple reflectors in the...

46:27

and again, limit the visualization of the kidney.

46:31

So you simply have to move your transducer left and right, look in differently.

46:35

In cases of trachea, you can have that reverberation, which is

46:39

giving continuous shadowing onto the tracheal surface.

46:43

Comet tail is a tinier version of the reverberation

46:47

artifact, which you see a little triangular shadowing

46:51

behind the dense echogenic area.

46:54

Right. So then coming to ring down artifact,

46:57

again, the concept is due to the

47:01

vibrations of the fluid trapped between the air bubbles, you see a shadowing

47:05

behind the bowel gas.

47:08

And differentiation between ring down artifact and

47:12

acoustic shadowing, when you are clear of that, you are

47:15

unlikely to mistake a bowel shadow for a GB calculi and a GB

47:19

calculi for a bowel shadow. So once you're very

47:23

much focused, so here and

47:26

you have bowel shadow, which is outside, and you have GB calculi.

47:30

When you see this is dense and this is dirty ring down shadowing, you can clearly

47:34

differentiate between the two, which is very important.

47:38

Mirror artifact. Sometimes when you're scanning, say, the dome of the

47:42

diaphragm, a pathology which was

47:45

in the liver

47:47

appears as mimicking behind into the

47:53

pleural surface as if there's a pleural nodule.

47:56

That is because of the reflection of the

47:59

highly reflective diaphragmatic surface.

48:02

Twinkling artifact is a color artifact that you

48:06

see with calculi and helps us in

48:10

identification and localization of the calculi.

48:14

Right. Electrical interference, very rarely seen

48:18

in the high-end equipments that we have.

48:21

So artifacts definitely support us in diagnosis,

48:25

and we have to know how to apply them.

48:28

Simple questions just to summarize what we have learned.

48:31

Some quiz questions. So this is a 2D image, which looks pretty good,

48:35

I guess. A carotid vessel scan. Now look at the

48:39

arrow that has been placed here. It has been moved down.

48:43

So when the focus is looking too down, but I'm wanting to look at the carotid,

48:47

obviously my field of view is filled with echoes because I'm focusing

48:50

here.Now, again, with the focus adjusted, my area of

48:54

interest is clearer and better viewed.

48:57

Again, I change the depth setting to look at very

49:00

low, even in the carotid preset. Now again, my area

49:04

of interest is not well visualized. Then I corrected the depth.

49:08

It is better seen.

49:11

Now, if you're doing the color Doppler, but I used a box size that is too

49:15

large. So what happens is that my color image is

49:19

pixelated or you see it's broken, or

49:22

the beam energy is distributed on a larger

49:26

area, so I'm not able to get good information about the area

49:30

that I'm

49:31

focusing on. Again, this is incorrect beam steering,

49:35

so the beam angle is between the path of the beam

49:39

and the flow of the blood. And now this angle is more than 90,

49:43

which is not correct.

49:45

The angle is correct, which is between the

49:49

beam and the flow, but it's a very narrow

49:53

box size.

49:55

This is optimum box size, but there is an excess

49:59

of color gain here. There is less color gain, so it is

50:03

underfilling. So when you change these, you see how all these

50:07

factors here change. You'll be able to understand them.

50:10

So this is too much of Doppler gain, so it is filling up the window.

50:14

Correct your Doppler gain, so you have nice clear window.

50:17

Again, this is an image which has got lots of corrections that can be

50:21

done. You see the focus, you see this kind of thing.

50:25

Obviously, you correct all the parameters.

50:28

So just another quiz, which is this diagram.

50:32

Of course, we all know that's the reverberation artifact action.

50:36

So that example, the question, we have to correct the focus, the beam

50:40

steering, color gain, and the depth, almost everything.

50:44

Again, this is a example of a color Doppler for a aortic

50:48

aneurysm, and of course, both A and C are

50:51

correct.

50:53

Right. And

50:55

this is renal arterial Dopplers. These are all reasonably good

50:59

settings. Right? And of course, in this case of a

51:02

CFA and an SFA, we have a forward diastolic

51:06

flow. That means there is an obstruction

51:10

prior to this area that we are scanning,

51:13

because normally the waveform is triphasic, but it's

51:17

got a diastolic waveform.

51:20

Okay, so I really thank you for all your

51:23

attention and for your listening,

51:26

and if you have any questions, I'm more than happy to take them.

51:31

Awesome. Thanks for that lecture, Dr Singhal.

51:35

At this time, we will open the floor for any questions from our audience.

51:38

You can submit those through the Q&A feature.

51:41

So there is a question. Please, can you discuss the angle

51:45

more obviously?

51:48

So

51:49

the angle is, like I explained, the angle is angle

51:53

between the

51:55

beam direction

51:57

and the flow of the blood. So because

52:01

the vessels can be tortuous, vessels can be pointing this way or that

52:05

way, so don't look at the vessel wall.

52:07

Look at how the

52:11

flow is flowing. And I think it was well explained with all the quiz

52:14

questions towards the end that you have to keep the beam

52:18

direction and the direction of the flow and

52:22

keep that angle between zero to 60 degree.

52:25

So example, this is how my beam direction is coming, and this is

52:29

how the blood is flowing. So my this angle, which is now, is

52:33

less than 60 degrees. That is what I aim for to get more

52:37

accurate results for sampling. Because of the cos theta factor,

52:41

the error really increases significantly

52:44

erroneously post 60 degree angle.

52:49

Okay. Thank you. Hope that helps.

52:53

Next is twinkling artifact. Please explain.

52:57

So again, this is just like we have the acoustic

53:00

shadowing in B mode

53:03

due to the sound wave. So in the color,

53:07

when you have a high reflector, again, you have

53:11

that dense color shadowing or color

53:15

posterior to the

53:17

calculus area. And that has often been used to

53:21

actually measure the size of a small ureteric

53:25

stone or size of a small renal calculi,

53:29

because these can be...

53:33

You have another filter to differentiate because

53:36

sometimes the calcium, the stones, and the renal

53:40

central sinus echoes may be quite similar, and

53:44

you can have renal parenchyma echogenicity raised

53:48

due to, say,

53:51

medical renal disease or chronic kidney disease.

53:55

So again, use of that feature will still help you

53:59

differentiate or identify or delineate

54:02

the calculi area. So that's a added

54:06

tool that you can apply to get the diagnosis.

54:12

Thank you. So

54:16

yeah. Thank you.

54:18

Is there a technique to remove the mirror artifact?

54:21

So for the mirror artifact, you simply just

54:25

move the position, and you just scan in a

54:29

different way because it is when the

54:33

high beam reflector is directly posterior to the path

54:37

of the beam, when it's making that angle, then you'll see.

54:40

But supposing if you put the high reflector towards the

54:44

side, and then the beam is just going posteriorly, right?

54:48

So then you'll see that it's disappeared.

54:50

So then you'll know that it was just because

54:53

it was the highIntensity reflector was right

54:57

bang on perpendicular to the path of the beam.

54:59

So it just created an echo of the pathology

55:04

in the liver, in the pleural surface.

55:06

But when you just rotate or you turn around the patient or in a

55:10

manner that now the high reflector is

55:13

not sitting right against the path of the beam, but it's moved on the

55:17

side, you'll see it eliminate and disappear.

55:20

That will help you delineate and differentiate that that was a

55:24

artifactual pathology or artifactual appearance,

55:28

and not a real lesion in

55:30

pleural surface.

55:33

Okay. So thank you for that question from the

55:37

chat. That's been taken as well.

55:40

And

55:42

what is the normal RI for renal arteries and where exactly it is measured?

55:47

Oh, renal artery RI, you'll measure at every level.

55:50

So you'll measure at the origin, at the mid, at the

55:54

distal end, at the hilum end, and at the segmental arteries.

55:58

So you'll see the trend.

56:01

And you'll measure the aorta. So you

56:05

do RI ratios, and you see how the trends are

56:09

dropping or how the resistance is increasing in the renal

56:13

vascular bed. So you put all that together, that's like a

56:17

separate knock on renal arterial Doppler.

56:19

But yes, that's how you would do it. So you'll measure it at every level.

56:24

So you'll at least do renal artery sampling at the

56:28

origin, mid, and at the hilum, and the segmental

56:32

arteries for the upper, mid, and the lower pole, at least these six measurements,

56:35

and much more as the areas of

56:39

aliasing or pathology pinpoint to you.

56:43

Because aliasing are the areas of

56:47

spurts of high velocity. There could be areas of focal stenosis or

56:51

narrowing that must be sampled.

56:55

Okay. Thank you for the question from the chat.

56:58

Do we have any more questions in the chat?

57:02

Thank you. All questions have been answered. Thank you.

57:06

Beautiful.

57:08

Thank you all.

57:12

All right. I guess that's it.

57:15

Thank you, Dr. Singhal, for that lecture, and thanks to everyone for submitting

57:19

those questions.

57:22

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57:26

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57:27

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57:30

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57:33

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57:37

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57:40

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57:44

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57:48

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57:51

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57:54

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