Full transcript
0:00okay so Chapter four
0:04what we need to do now is now that we
0:06understand what sound is some of the
0:09parameters that we use to measure some
0:11to understand that it is a cyclical
0:13pressure energy that is propagated
0:15through a medium we know that in order
0:22for sound to travel we need a
0:26compressible deformable medium and that
0:29as it travels we experience something
0:32called this emulation in addition to
0:35some of the other interactions such as
0:37reflection refraction all these
0:39interactions with matter now we need to
0:42start talking about how diagnostic
0:43ultrasound actually works so what we
0:46discussed up until now is simply how
0:48sound works but in order for us to see
0:51echoes off from a ultrasound system we
0:57need to send out pulses so let me show
1:02you what I'm talking about
1:03so if we have whoops ETA transducer and
1:07we have an object that we are going to
1:10image we will send pressure waves from
1:13this transducer out as it bounces off
1:16this interface it reflects back that
1:19information back to the transducer and
1:21on our screen and a distance equal to
1:27how far it traveled out and back we will
1:30see an object in the middle of our
1:32screen the only way that we can see or
1:37hear that echo is to send a short pulse
1:42of energy of sound and then wait and
1:45listen so on a scale it sort of kind of
1:49looks like on there comes that thing
1:51again we send a short pulse and then we
1:55listen and then we listen some more and
1:57then we send another short pulse it is
2:00estimated that sound actually
2:03transmitted ultrasound actually
2:04transmitted about 0.1% of the time and
2:07listens 99.9 percent of the time in
2:10order to pick up the
2:13reflections so we send a short pulse of
2:18energy and we listen for these echoes to
2:21come back at different locations the
2:23longer it takes for an echo to return to
2:25the ultrasound system and deeper these
2:28echoes are in our image if you think of
2:35it this way if you went into a cave and
2:37you yelled your name really loud very
2:41shortly you could wait and listen for
2:43those echoes to come back and you'll
2:45also notice that the farther away they
2:47are the less strong they are
2:50it's just hey and it fades off because
2:54of attenuation it's less strong every
2:59echo that comes back from the further it
3:01goes out the strongest signal is the
3:05initial signal you screaming your name
3:08is going to be louder than any echo
3:10returning from a distance that went out
3:13bounced off something and came back so
3:16if you simply screamed your name
3:18continuously you would never hear any
3:21echo come back which is why we pulse and
3:24then listen alright we pulse and then we
3:29listen for those echoes to come back if
3:31we don't pulse we can't we interfere
3:34with every echo coming back and we'll
3:36never see any of these interfaces on our
3:39screen that makes sense okay so some of
3:42the ways that we actually look at our
3:44pulse sequence so let's say we have a
3:49two cycle pulse there and a two cycle
3:51thoughts here and a two cycle pulse here
3:55there's parameters that we can look at
3:57like we looked at frequency light we
3:59looked at period these are ways of
4:01measuring waves and how big they were
4:06and how they determined how how long
4:09they would bring or how short they would
4:11bring these little pulses in themselves
4:13have specific parameters for example the
4:17first one how long a pulse is actually
4:20on is known as the pulse duration
4:25the pulse duration is equal to n which
4:31is the number of lines or sorry which is
4:34n which is the number of cycles in the
4:36pulse in this case we have two cycles
4:39and that pulse two cycles and that also
4:42two cycles in that pulse
4:43what's that the number of cycles on the
4:48pulse and then the other part of that
4:55formula is a period remember the period
4:59is how long does it take for one cycle
5:01to occur the pulse duration is how long
5:04is the pulse so taking the number of
5:09cycles in that pulse multiplying by how
5:11long it takes for one cycle to occur
5:12we'll get our pulse duration so just for
5:15example let's say looking at this
5:18particular problem the pulse duration in
5:21this case n would be two because there
5:23are two cycles in each of these pulses
5:25and let's say the period was one
5:27millimeter simply multiplied by one
5:30minute one millimeter the pulse duration
5:33would be two millimeters long that's
5:35it's that simple another way we can
5:46measure the size of a pulse is something
5:51called the spatial pulse length the
5:56spatial pulse length looks very similar
5:58to the pulse duration it is the number
6:01of cycles in that pulse multiplied by
6:04the wavelength as you remember is the
6:06length of one cycle and I realize they
6:13did ulceration incorrectly this should
6:15be one second because it's a time frame
6:17not a measurement so that would be two
6:20seconds and the same thing if we wanted
6:22to calculate a spatial pulse length from
6:24this example again n would equal to
6:26let's say the one wavelength in this
6:28case was one millimeter so the spatial
6:31pulse length would equal two millimeters
6:33sorry about that that's up so one
6:35measures how long it takes
6:37for that pulse t wants to occur the
6:39other one is how long in length is that
6:43or how big is that pulse everybody okay
6:52with this so let's look at what happens
6:59let's take this to that okay so what we
7:10have here is two separate pulses both of
7:16them having two cycles which one has the
7:19larger pulse duration A or B the largest
7:27yet which one has the largest pulse
7:30duration which one's bigger
7:35Sammy huh is it a I just because it I
7:41feel like it's gonna greet laughter so
7:42you're saying this one that has a pulse
7:47duration that is this big okay that's
7:50compared to this which one has a longer
7:53pulse duration obviously a right yes but
7:58what you also notice is that a also has
8:01a longer spatial pulse length when
8:03compared to B as well right so you'll
8:07find that pulse duration is
8:11approximately if that supposed to be
8:12approximate to the spatial pulse length
8:15not in units but whatever happens to one
8:19will happen to the other there are two
8:23ways that we can increase the size of
8:28the pulse duration or spatial pulse
8:30light one is in this case we make the
8:33wavelengths longer the size of one cycle
8:37is decreased in wave form be a has a
8:44longer wavelength therefore it has a
8:47longer pulse duration and a longer
8:48spatial pulse length the other way to
8:51increase the size of a pulse is to give
8:55it more cycles right regardless of what
9:01the frequency is when compared back to
9:04their originals more pulses means bigger
9:08spatial pulse length and bigger pulse
9:09durations which is why their formulas
9:13pulse duration equals n times period and
9:16spatial pulse length equals n times
9:18wavelength look very similar so they are
9:25directly tied to each other every time
9:29that pulse increases in size or in
9:33length of time the spatial calls like
9:37and pulse duration will increase and the
9:40opposite any way that we decrease the
9:42spatial pulse length Impala station they
9:45will both decrease that makes sense
9:47hey so let's look at some other
9:50parameters okay so starting here okay so
10:17so far we've discussed pulse duration
10:21its spatial pulse length we need to
10:27start talking about the space in between
10:29the pulses so starting here going to
10:33different colors starting here at the
10:37beginning of this pulse this entire
10:40pulse sequence does not stop until he
10:42hits the beginning of the next pulse the
10:46time it takes from the beginning of the
10:48pulse to the end of the pulse and it's
10:51listening time here to here is known as
10:56its pulse repetition period from the
11:04beginning of
11:05Hulse to the beginning of the next pulse
11:07that is your pulse repetition period it
11:15includes the pulse the time that
11:17ultrasound is on and it's listening time
11:20waiting for echoes to come back in
11:31addition a number of pulses and that
11:38makes it worse doesn't it that's not a
11:40green I wanna let's try it purple there
11:46we go there's a pulse here there's a
11:50pulse here
11:51how many pulses occur per second is
11:54known as the pulse repetition frequency
12:02yes how many pulses occur per second is
12:06known as as pulse repetition frequency
12:20so Holt repetition frequency units are
12:24Earth's because it's something that
12:26happens per second the units for pulse
12:29repetition period are in seconds because
12:33it's how long something is taking to
12:36occur the one thing you should notice is
12:42that they are reciprocals of each other
12:44so the pulse repetition period is equal
12:49to 1 over the P R F and the PRF our
12:58pulse repetition frequency is equal to 1
13:00over the pulse repetition period what
13:07much already
13:10PRP yeah which one oh you mean this one
13:14yeah yeah here P is equal to 1 over the
13:18PRF PRF is equal to 1 over the PRP all
13:35right so there is no other formula for
13:39calculating the pulse repetition period
13:41but there is another formula for
13:43calculating the false repetition
13:44frequency the PRF our fault repetition
13:51frequency is equal to velocity at two
13:54fifteen forty meters per second divided
13:56by two times the depth down in back
14:18so an ultrasound system let me explain
14:21what this means so if this is our
14:23transducer and this is our depth of
14:26interest in order to create an
14:30ultrasound image we have to send
14:32multiple lines of sight to gather
14:34information so we will send out a beam
14:37wait for it to return and then send
14:40another beam of information wait for it
14:43to return and back and forth all the way
14:46until we move all the way across and
14:48create one frame and at that point we've
14:51created one frame of information but it
14:55turns out how often we pulse since we
14:58have to wait for it to return from the
15:00depth you've chosen as an operator until
15:04it returns we can't send the next pulse
15:06out because it will interfere with it
15:08with the echoes coming back from the
15:10first Falls so we have to wait for it to
15:13return so primarily our pulse repetition
15:15frequency or how frequently we pulse is
15:18determine on our depth because if I make
15:22the depth all the way down here our next
15:24transducer sanera we have to wait for it
15:26to go all the way down here all the way
15:28back remember it only travels a 15:49
15:31with your second so we have to wait for
15:33a limitation all the way back here so
15:36the farther away your depth is the
15:42longer it takes for us to update a pulse
15:46which means our pulse repetition period
15:49is longer so that slows down our pulse
15:53repetition frequency which means our
15:54pulse repetition frequency is slower
15:56which is clearly outlined by the formula
16:01that's an F here in the depth depth is
16:08inversely proportional to the frequency
16:10so the deeper the depth the longer it
16:15takes for us to update a pulse which
16:16means the slower our pulse repetition
16:18frequency so the deeper the depth the
16:24slower the pulse repetition frequency
16:29so the lower your PRF and inversely so
16:34the higher or more repulse repetition
16:38period because it takes longer to create
16:40one pulse sequence yes
16:48so the deeper your Duff be lower your
16:52pulse repetition frequency meaning it
16:54takes longer or each pulse to occur so
17:00the lower your PRF which means the
17:03longer or higher your PRP or how long it
17:08takes for each all sexy months to occur
17:11because PRF new PRP are inversely
17:13proportional everybody okay in this one
17:24if you say so
17:26well let's let's let's give it a test
17:27drive let's see tell me what is the
17:39pulse repetition frequency in Hertz I'll
17:44say in the soft issue and let's say the
17:56depth keep it simple this time the depth
17:58is 10 centimeters let's go with that
18:01let's give a shock
18:04remember the formula is PR F equals
18:07velocity divided by 2 D is that it's
18:14yeah so starting with velocity whoops
18:2215 40 meters per second divided by 2
18:27times the depth which is 10 centimeters
18:30that's what we're looking at right all
18:34right so do you want to convert the 15
18:37forty meters per second into centimeters
18:39per second
18:40or convert the 10 centimeters and meters
18:44really you guys never want to touch the
18:47velocity be so much easier if you did
18:56so 15 40 meters per second / it would be
19:0020 centimeters so 20 centimeters would
19:03be 1/2 right so that it would be point 2
19:08meters so now we just divide this out we
19:13can I'm gonna just go add 1 0 1 spot
19:16here and add a 0 here to divide it into
19:201 5 4 0 0 2 into 15 goes 7 times
19:26that's 14 with one left over 14 comes
19:30down at 7 again and it will be 14 and 0
19:34so that is 0 what okay so what we end up
19:42with the 7700 meters will cancel out
19:46left with 1 over seconds or Hertz 7700
19:51Hertz
19:52how'd you guys do yeah I did it right
19:54besides I wrote the wrong number okay
19:57all right now what I want you to do is
20:00calculate the pulse repetition period
20:03from that pulse repetition frequency now
20:11calculate the pulse repetition period
20:13now that you have the most repetition
20:14frequency you can calculate alt cert
20:16petition period yeah sure go ahead
20:28because my avid is always here and I
20:31added a decimal place here so now it's
20:34not 1540s it's about 15,000 won just to
20:39make my math a little easier for me I
20:42tend to lose decimal places if
20:45simple things for me if I don't do that
20:47I tend to lose my decimal place you have
20:58to change the Hertz two seconds so our
21:07hardware which one one has a teeny is
21:14not a clear tail on it that's an R for
21:17sure so RP equals one over seventy seven
21:24hundred Hertz or one over seconds right
21:28there's no way to get out of this one we
21:30just gonna have to divide that out so
21:337700 to 110 100,000 it will go into
21:3910,000 right our point is here we have
21:43one zero two zeroes three zeros and 7700
21:48goes into 10,000 once right zero zero
21:52will borrow from here turn that to ten
21:57but the nine ten and nine ten nine and
22:02wait no I don't have to go back that far
22:04do I I still have to borrow from there
22:10so it takes me there so zero zero the
22:14nine don't be ten here sorry
22:18I'm messing this really up so if there's
22:20three there and then nine from there so
22:22it'd be twenty three hundred left over
22:25dropping another zero twenty three
22:27thousand I'm guessing 7700 will go into
22:31twenty three thousand roughly three
22:33times I'm going to guess that's probably
22:36one to nine but roughly 1/3 will be
22:39close enough so we end up with point
22:41zero zero zero one three one over one
22:46over seconds or seconds how close did
22:51you come I did it
22:55a senator pray but I had
22:57I for some reason thought I had to
23:00change the hurts like you know like we
23:03need to change it to like been really
23:04the million right
23:05that would be megahertz yes okay yeah
23:10that's why you were saying it's gonna be
23:11a really big number small yeah
23:14a million to anything makes it figure
23:16small yeah Anna what did you say
23:18happened a winter than you probably more
23:21correct than I am I just didn't want
23:24carried out that far ballpark well what
23:29you should have learned from your
23:29midterm is that ballpark should be good
23:32enough to get you almost any answer so
23:35because you saw when they did a lot of
23:36those problems up here I was just kind
23:38of guesstimating and then seeing if any
23:40of the answers were close and most of
23:41the time we could find an answer that
23:43was close and go from there other
23:46questions on this one feel pretty good
23:48about calculating ultra repetition
23:50frequency and also a petition period all
23:56right let's try it one more time that
23:57won't work
23:58so let's calculate the ER f + y RP in
24:07soft tissue and let's say the depth is
24:17make it 5 centimeters let's get that
24:23shot alright so setting the pulse
24:30repetition frequency of sequel 1540
24:34meters per second divided by 2 times 5
24:39centimeters centimeters which would
24:43equal 15 forty meters per second divided
24:46by 10 centimeters converting that into a
24:50meter at the point 1 right so if we add
24:58a decimal place here we can add a
24:59decimal place here and now fifteen
25:02thousand four hundred divided by one
25:03meters cancel out left with 15 thousand
25:07four
25:08one over seconds or Hertz so that's our
25:11pulse repetition frequency calculating
25:14the PRP it is one over
25:1715400 one over seconds so again there's
25:22no easy way to do this or hundred into
25:25one doesn't go into ten hundred a
25:28thousand ten thousand but it will go
25:30into a hundred thousand good creep seven
25:34times maybe six times
25:37okay so 15 for all times six zero zero
25:43twenty four to thirty two three six nine
25:48two four nine two four zero zero so zero
25:56zero we gotta go ten nine ten nine ten
26:03so that's gonna be six seven eight seven
26:09six
26:10Oh add a zero why didn't put my number
26:14in here with six and decimal places one
26:19two three four zeros and the six and
26:23fifteen thousand four hundred into
26:25seventy six thousand would be four okay
26:34all right so 0.0064 and it was one over
26:42one over seconds so it was seconds would
26:44be the six well you usually just go here
26:51something we usually just go a couple of
26:54decimal places yes they should be fine
26:55just to give you an idea hey so how many
27:01you got that correct
27:02both altar petition frequency and period
27:04are we feeling a little bit better about
27:06how to calculate these two and
27:07understand that they're interrelated
27:09okay good
27:11[Applause]
27:13let's go back to
27:20one other parameter that we need to look
27:24at before we can go to lab and that is
27:29something called the duty factor which
27:31is based on the time really pulse
27:43duration which is the time that the
27:45pulse is on divided by the pulse
27:47repetition period which is that entire
27:51pulse sequence the time is on plus it's
27:53listening time the duty factor actually
27:56tells us the exposure to our patient
27:59like how much ultrasonic energy are we
28:02delivering to our patients that's
28:04ulceration and the cooldown time which
28:06is the pulse repetition period so just
28:10looking at this if we had a pulse
28:11duration of let's say 0.01 milliseconds
28:16and a PRP of let's say one millisecond
28:24what is our duty factor
28:53got it they thought this would be an
28:56easy one
28:57oh wait yeah that's all you do right
29:01there
29:02Lars you know 1/1 what is it really what
29:09is 0.01 divided by one point no thank
29:14you
29:15point O one and because the milliseconds
29:16cancel each other out Duty factors known
29:19as a unitless measurement it can be
29:22described as a fraction or it can be
29:25turned into a percentage by multiplying
29:27by a hundred percent and in this case
29:29multiplying this by a hundred would
29:31increase it by two preferred two decimal
29:34places or turn it into one percent so
29:37the duty factor of one percent is kind
29:39of consistent with what I said earlier
29:41is that we listen Oh point one percent I
29:44mean listen 99.9 percent I'm that's
29:47close but a duty factor of one percent
29:49would indicate 99 percent of time we're
29:52listening for for echoes to come back
29:56and only about one percent of the time
29:58are we actually delivering an ultrasound
30:00energy to our patient so that's how
30:04simple do B factor can be once you have
30:06those two numbers it's fairly easy to
30:09calculate does everybody feel okay with
30:12duty factor all right so let's recap we
30:19discussed facial pulse length which is
30:22the number of cycles on the pulse
30:23multiplied by the wave length we discuss
30:27pulse duration which is also the number
30:29of cycles in a pulse multiplied by the
30:31period we discussed pulse repetition
30:34frequency which is the velocity divided
30:38by two times the depth and is primarily
30:40controlled by the operator you by
30:42setting the depth of images that you
30:44want to see the pulse repetition period
30:48is calculated by the inverse of the PRF
30:51the PRF is also known to be inversely
30:54related to the PRP and lastly the duty
30:59vector which pulls it all together is
31:02the pulse duration divided by the pulse
31:04repetition period
31:05we've discussed all of that their
31:08meanings and we've worked all of these
31:10out in formulas so that you know how to
31:12work them right yeah I'm just
31:21reconfirming that that's what we did
31:23today right so the next lab we're going
31:31to look at requires you to understand
31:36the inter workings of all these as we
31:38discuss pulse repetition period and
31:40pulse repetition frequency go
31:42hand-in-hand we also said there's a
31:43correlation between spatial pulse length
31:45and pulse duration this next lab
31:47assignment is going to give you a
31:49scenario where you're going to calculate
31:50the spatial pulse length the pulse
31:52duration the pulse repetition frequency
31:53the pulse repetition period and the duty
31:56factor as well as anything that would
31:58lead into those calculations like wave
32:04length which we understood from before
32:06was velocity divided by frequency or the
32:09period which is the inverse of the
32:11frequency depth as we remember was
32:14velocity multiplied by time right you
32:17remember these formulas all of these
32:20have to go together in a certain way so
32:23the lab assignment actually is a story
32:26problem that gives you a scenario and
32:28from that you should be able to
32:30calculate all these what you'll find out
32:32from this lab assignment is that if you
32:34do not calculate one of these correctly
32:37the entire structure falls apart which
32:41means none of the numbers work so you
32:43have to calculate everything correctly
32:45in order to come up with the right Duty
32:48factor or ultimately the exposure to
32:50your patient second part that part two
32:53of your lab assignment is conceptual as
32:57this increases that decreases increases
33:00remains the same again that's all how
33:02these are interrelated that's how all
33:04these formulas are interrelated to each
33:06other this is the first of three lab
33:09assignments and the first one takes a
33:12little more time than most which is why
33:14we're going to quit a little early today
33:15and start working on this lab assignment
33:18we will see this again and again and
33:20again because it's extremely important
33:22for you understand how all of them are
33:23interrelated and how all of them work
33:25together ok so this is we the first lab
33:29assignment that being said are there any
33:30questions about what we covered here
33:31what's on this page so far no all right
33:43exposure here patient Kim do you have
33:47any questions or did any of your
33:48students have any questions you want me
33:50to address before I stop this recording
33:52nope we're good thank you
33:54Thanks