hi learners it's em from sano nerds and this video is on transducer anatomy unit eight transducer anatomy a transducer is any device that changes one form of energy into another there are tons of examples of transducers in everyday life like an engine takes in gas or chemical energy and then converts it into kinetic or motion energy light bulbs take electrical energy and convert the energy into light and some heat our bodies can even act like transducers the muscles can take chemical energy and change it into motion the transducers that are part of an ultrasound system are special kinds of transducers they are considered bi-directional all those previous examples show energy conversion that only happen in one direction here's a drawing of a basic transducer to better understand the very complex transducers used with the modern ultrasound system we can begin by deconstructing a simple single element transducer in a single element transducer the pct is disk shaped we're going to learn more about each piece in the next section section 8.1 pzt element the ultrasound transducer is capable of changing electrical energy into sound and sound energy into electrical the part of the transducer that is responsible for the bi-directional conversion is called the piezoelectric element the act of turning sound which are pressure waves into electrical volts is called the piezoelectric effect the piezoelectric effect occurs during reception when echoes are coming back from the body so during reception the piezoelectric element will change shape when sound pressure is applied the shape change produces the electrical voltage and this is the piezoelectric effect a material changing shape creating a voltage recall that sound is a mechanical wave which is also known as a pressure wave and when that sound is coming back from the body it interacts with the piezoelectric material to produce that voltage and then that voltage is sent to the machine to be processed and turned into an ultrasound image the act of turning electrical votes into sound waves is called the reverse piezoelectric effect the reverse piezoelectric effect occurs during transmission and that is when the transducer is emitting sound waves into the body so during transmission the piezoelectric material is going to receive a voltage that's applied from the machine that voltage is going to change the shape of the piezoelectric material and then a sound wave is produced the reverse piezoelectric effect is voltage to sound where the normal piezoelectric effect is sound to voltage it's going to be very important they remember when a piezoelectric effect occurs and when reverse piezoelectric effect occurs as sonographers we get to see the piezoelectric effect happen all the time because that's our job that's what's happening in the machine so we can create our ultrasound waves but there's actually this really cool thing that you can even try on your own lifesavers makes the lifesaver the wintergreen lifesavers and they have these little crystally pieces within the lifesaver that when you chew on them create the piezoelectric effect the pressure of you chewing on these crystals creates a voltage so sometimes you can see a little spark if you're in the dark when you chew on these wintergreen lifesavers so i actually have a little gift that i found on the internet here in slow motion they are destroying this lifesaver and you can see this blue spark that's the voltage that's real that's a little tiny little bit of voltage that occurred from the pressure condensing those crystals and creating a voltage because they are piezoelectric material so just like piezoelectric material can occur in lifesavers it actually does occur quite a bit in nature as well so some examples of piezoelectric material which is also known as ferroelectric material is going to include quartz topaz cane sugar and tourmaline so as you can see these are all mostly crystals when these crystals are compressed they will create an electric volt that's the piezoelectric piece of it and it would be fantastic if we could just take these elements from nature and turn them into crystals for our ultrasound machine but as you can kind of see from these examples these aren't perfect crystals they have imperfections in them and when that happens we wouldn't be able to get pure sounds and predictable sounds from these materials therefore we've got man-made materials that act as piezoelectric materials the most common man-made material is called lead zirconate titanate or abbreviated to p z t now you might be thinking why pzt if you think back to your table of elements lead is represented by the letters p b which stood for the latin term plum bum so lead is abbreviated p c zinc for the zirconate and t titanium for the titanate so lead zirconate titanate gets abbreviated to pct crystal quite often problem with man-made materials though is that they do have some pitfalls first off when you make man-made materials they're not naturally piezoelectric so to make it piezoelectric we're going to put the material in a magnetic field and then we have to heat everything up to an extremely high temperature by doing so this creates kind of a magnetism within the material that will react to those voltages as they come down and the sound pressure waves now this might not seem initially like a pitfall but the problem is is if this man-made material once it's been treated to have its piezoelectric properties if this element is exposed to really high levels of heat after its construction it's going to lose all of its piezoelectric properties so this really high temperature has a name it's called the curry point thankfully though the curry point is extremely high over 500 degrees fahrenheit or about 300 degrees celsius and the odds of encountering these extreme temperatures during our everyday clinical use is extremely low but it's still something to consider that these piezoelectric materials can lose their properties in the right conditions another pitfall of the man-made pzt material is that it has a very high impedance remember that means resistance to sound so the pct material has a high resistance to sound compared to the low impedance of skin so the skin is more accepting of that sound wave the problem is though when we have that large of a mismatch that means that less sound is actually going to enter into the body if we were just put pct crystal onto skin so one of the ways that they kind of bring down the impedance level of the pzt is to mix it with a resin and this piezo composite is made just right so we can improve the element's bandwidth its sensitivity and its resolution so if we look at these images here we can see that we have the pzt elements there's square in this bottom example here and then they're encased in a resin it's an example of more rectangular shaped this is smaller rectangle shaped and then these are even smaller i believe these ones have been sub-diced or broken down into little pieces that work together so it's interesting to see what those materials look like when they're not inside of our transducer however whatever the material is made out of for ultrasound we typically refer to the element as either pct the ceramic active element or crystal so you'll hear a lot of different terms to describe the actual so you'll hear a lot of different terms describing the actual piece of the transducer that is creating the sound waves so let's take a little bit of a closer look at how the pct crystal actually creates the frequency first thing we need to know is that at least one element is needed to create a 2d image or a pulsed wave however most of our transducers do have hundreds of crystals at the transducer phase contrary to this then continuous wave transducers need at least two elements one is always transmitting one is always receiving either way though each crystal is connected to a wire that connects back to the machine when voltages come down the wire they will cause the pzt crystal to resonate or change shape the contraction and expansion of the material is what creates the sound wave in this image i've got a little diagram of what it looks like when the pct crystal contracts and expands so at rest we have the pct crystal here the magnetic poles within it are just kind of chilling out nothing's really being applied so this is the normal size of that element as those voltages come down one is going to be a negative voltage and the other is going to be a positive voltage and those are applied to either side of the face now if you remember back to magnets the negative is attracted to positive and positive is attracted to negative and because of that it's going to kind of spin these atoms around and by doing so it kind of stretches them out which causes the pzt crystal to expand another voltage is going to be applied then and it's going to be the opposite and when those voltages flip the magnetic properties don't like being matched up with its own they try to get away from it and by doing so it makes the whole pct crystal compress so we end up with something that kind of looks like this we have a crystal that expands and contracts beyond its normal size those expansions and contractions create a pressure wave which results as a sound wave or ultrasound wave into the body upon reception then those sound waves are going to come back cause the crystal to do the same thing but this time it's going to cause a voltage then to head back to the machine how does the pzt crystal affect the frequency then well in continuous weight transducers it's actually pretty easy whatever the electrical voltage frequency is that is produced by the machine is what the acoustic frequency is so an electrical frequency of three megahertz comes down the wire interacts with the crystal and a three megahertz acoustic frequency is produced so in the continuous wave transducer the electrical frequency is equal to the acoustic frequency remembering continuous wave transducers that the wave is always being transmitted and received and these types of transducers do not produce images creating a frequency in a pulse wave transducer however is a little bit more complicated so in the pulse wave transducer the sound is pulsed meaning that it has an off and on time remember that during those pulses multiple pct elements are going to be activated the waves that are created are very small wavelets remember huge ins waves and these wavelets are going to construct and destruct creating the propagating pulse and instead of just getting a constant stream of voltages the pct crystals are getting blast of voltages so they create those pulses so it's a little bit of voltage pulse goes out and then we have that prp a little bit of voltage pulse goes out and then we wait again so it's with those kind of bursts of voltages those pulsings now we end up getting some different properties created by our pzt element so in the pulse wave transducer the frequency at which the pzt crystal resonates or expands and contracts at is based on two things it's going to be the thickness of the pzt crystal and the propagation speed of the pct crystal and we know this because the formula for the operating frequency of the transducer is related to the pct element and that the frequency of the transducer is going to be equal to the speed in the element divided by 2 multiplied by the thickness of the element most of our pct material has a propagation speed of about four to six millimeters per micro second and the elements are going to range anywhere from 0.2 millimeters to about one millimeter thick let's take a look at the relationships that we can pull from this formula the first one is that frequency and element thickness are going to be inversely related thicker elements create low frequencies and thinner elements are going to create higher frequencies so a very thick element will give us that low frequency long wavelength where our thin element will create a higher frequency with shorter wavelengths so as thickness increases the frequency is going to decrease if we take a look at a couple examples by plugging in some numbers into our formula let's take a look at this green one first we see that the pzt element has a thickness of one millimeter if we're given that this is a four millimeter per micro second propagation speed we'll plug our one millimeter in and we can see that this transducer is going to produce a two megahertz frequency now let's jump over to the pink one which only has a 0.2 millimeter thickness everything remains the same except we're going to change the thickness of the pzt element and we see that it creates a 10 megahertz frequency so by plugging in some very basic numbers into our formula we can see that as the thickness increases the frequency is going to decrease making them inversely related remember that we can also figure that out based on the formula knowing that the denominator is going to be inversely related to the quotient another relationship that we can see from that formula is that frequency and propagation speed are going to be directly related so slower propagation speeds are going to create lower frequencies where fast propagation speeds are going to create higher frequencies again we have a pzt crystal with a propagation speed of one millimeter per microsecond versus our pzt crystal that has a four millimeter per micro second our slow propagation speed our low numerical value propagation speed is going to create the lower frequency and the high propagation speed or higher numerical value propagation speed is going to create the high frequency so if we plug in one millimeter per microsecond in our 0.2 millimeter thickness pct crystal we get a 2.5 megahertz frequency keeping everything the same but changing to a four millimeter per microsecond propagation speed increases that frequency to 10 megahertz so now we can see that when propagation speed increases it's going to create a higher frequency making these directly related again we know this because the numerator is directly related to the quotient now if we take a look at our operating frequency formula and a formula that we learned way back where wavelength is equal to the propagation speed divided by the frequency we can kind of combine these together and what we end up seeing is that the thickness of the pct crystal is equal to half of the wavelength so this again tells us that as the frequency increases we know that our wavelength is going to decrease therefore our thickness is going to decrease because wavelength and thickness are going to be directly related as far as math goes for any of these formulas the biggest thing with frequency formula up here is to just know that the propagation speed is directly related to the frequency and the thickness is inversely related to the frequency so if the thickness of the pzt crystal is doubled then we'll see a doubling of the operational frequency and as that pct crystal gets thinner we should see an increase in the frequency that it creates the formula on the bottom here is going to be more likely the one that you may actually have to calculate you may be given that the frequency of a wave is five millimeters what is the thickness of the pct crystal you would know that five multiplied by half is 2.5 so you should be able to say that it is a 2.5 thick pct crystal so to summarize some of the main points of how pulsed wave pzt crystals affect the frequency of the transducer we see that with high frequency transducers we're going to see short wavelengths thin pzt crystals and faster pzt propagation speeds where low frequency transducers are going to have longer wavelengths thicker pzt crystals and slower pct propagation speeds continuous wave remember is our easy one just the electrical frequency is going to be equal to the acoustic frequency you will see in your workbook that i gave you three different scenarios in which you have been given frequencies and wavelengths and pct crystal thicknesses and you'll compare the two transducers to answer the question i've also asked you to use a formula to prove why your answer is correct so go ahead and work through those scenarios and when you're ready un-pause the video and we'll go over the answers our first scenario tells us that transducer a has a propagation speed of six millimeters per microsecond and a thickness of 0.4 millimeters transducer b has a propagation speed of three millimeters per microsecond and a thickness of 0.4 millimeters based on this information which transducer should have the higher frequency looking back we can see that both pct elements have the same thickness 0.4 millimeters so thickness is not what we are looking at we're looking at the propagation speeds one has a six millimeter per microsecond the other has a three millimeter per micro second knowing our formula and knowing the relationships that we pull from it the higher the numerical value of propagation speed the higher the frequency should be so in this example we can say that transducer a is going to have the higher frequency on the bottom you can see how i have plugged those numbers into our formula we put in our six millimeters per microsecond over two multiplied by the thickness of the pct element plug in that math and we get seven and a half megahertz frequency for transducer a transducer b ends up with the 3.75 megahertz so we can see with increased propagation speed we get an increased frequency lower propagation speed decreases the frequency the next scenario says transducer a has a propagation speed of 6 millimeters per microsecond and a frequency of 12 megahertz transducer b has a propagation speed of 4 millimeters per microsecond and a frequency of 10 megahertz based on this information which element will be thicker for this example the answer again is transducer a and if you got to the math of this awesome because we did have to go through a couple extra steps on this one the first thing we needed to figure out is what was the wavelength of the 12 megahertz transducer and then secondly we needed to use our thickness multiplied by half of the wavelength to figure out the thickness of the pzt element to be able to answer this question so for transducer a we took our six millimeters per microsecond and divided it by 12 megahertz that gave us a wavelength of 0.5 millimeters multiplied by half and we see that we get a 0.25 millimeter thickness for transducer a we do the same thing then with transducer b where we plugged in our four millimeters and divided by 10 megahertz to get a wavelength of 0.4 multiply it by half and we get a thickness of the pct crystal at 0.2 millimeters 0.25 millimeters is bigger than 0.2 so transducer a has the thicker element so the element thickness is directly related to the wavelength our last scenario then says that transducer a has a propagation speed of six millimeters per microsecond and a thickness of 0.3 millimeters where transducer b has a propagation speed of 6 millimeters per microsecond and a thickness of 0.8 millimeters based on this information which will have the higher frequency so now we have the exact same propagation speed in our transducers but we have different thicknesses of the pct element and we know that the thickness of the pct element is inversely related to the frequency it produces so the thinner element should be the one that creates the higher frequency transducer a at 0.3 millimeters is thinner than 0.8 millimeters so again the answer is transducer a and if we plug in our numbers to our formula again look we have six millimeters per microsecond propagation speed on top divided by two multiplied by the thickness we're going to do the same thing for transducer b and we see that when we decrease the size of the element we are increasing the transducer frequency they are inversely related next in our transducer anatomy tour we are going to talk about the matching layer in section 8.2 so referring back to our image here we have the matching layer is the very front part of the transducer sits in between the pzt and the patient so the matching layer is going to be used to direct sound into the body by being an impedance between the element and the skin the matching layer is related to the transducer frequency so the matching layer is going to help to transmit the sound into the body by kind of being a middle impedance and that's going to be compared to the element and the skin the impedance value of a pct is more than 20 times that of skin and when we have that really large mismatch a lot of reflection is going to occur very little sound is actually going to make it into the body if we were just to place a pct crystal directly onto the skin i think we'd get something like 80 reflection and only 20 percent of the sound actually making it into the body to create those echoes so by putting the matching layer in between we are going to reduce that mismatch encouraging more sound to travel into the body so without that matching layer very little sound would actually make it into the body and to provide sufficient balance to the pzt the matching layer ends up being one quarter of the thickness of the wavelength so remember that pct is half of the wavelength matching layer is a quarter of the wavelength so that means that as the frequency increases the wavelength is going to decrease and when the wavelength decreases the thickness of the pzt and the thickness of the matching layer are also both going to decrease so thinner wavelengths mean thinner pct crystals than our matching layers so at the transducer face we have the pzt crystal and the matching layer sits in front of it now the matching layer in a lot of transducers is actually more than one layer things are going to be very very thin pieces of matching material that are going to equate to the quarter wavelength but each layer is meant to kind of act like a step down in impedance values to create an easier transition to the skin so we might see one two or three layers to that matching layer to step the impedance values down so the matching layer has a giant job to do to help get that sound directed into the body so we don't have too much reflection once the sound wave hits the skin but another thing that we're going to need in between the transducer and the skin is something called gel or the coupling medium the gel is water based so it shouldn't cause much if any attenuation and it's going to further reduce the impedance mismatch between the transducer and the skin the other thing the gel does is also eliminates the scattering that even a thin layer of air would cause in these images on the top one we see that we have an image being produced with no gel and then what it would look like with that gel present to summarize then in decreasing order of impedance is the pzt crystal which has a higher impedance than the matching layer matching layers which has a higher impedance than the gel which has a higher impedance than the skin remember we're trying to step down the impedances so we reduce the mismatch therefore encouraging more transmission of sound energy in to the body next up we're going to talk about backing material in section 8.3 the backing material sits behind the pzt crystal and in the body of the transducer the backing material in this image is represented by this yellow part vacuum material which is also known as dampening material is in direct contact with the pzt elements the vacuum material is often made of a resin which is going to be mixed with a metallic powder or filaments usually made of tungsten the backing material is going to keep the pzt material from ringing for too long by reducing the number of cycles in each pulse so recall that when we create a pulse there are going to be a number of cycles within that pulse and the fewer cycles that we have in the pulse is going to create better more detailed images and that's because the spatial pulse length or the spl increases with the more cycles that the pulse contains so if the pct crystal is allowed to ring it will add more cycles to a pulse and long sbls degrade the quality of the image therefore we want that backing material in our imaging transducers to keep the pulses short and improve our resolution when backing materials added to a transducer we want the acoustic impedance of the backing material to be very similar to the pzt impedance when you have similar impedances the sound is more likely to travel through it versus being reflected so if that backing material matches the impedance of the pct material then we are going to expect more transmission to occur through it therefore encouraging that sound energy to come into the backing material versus being expressed in a longer pulse so that backing material is going to help create very short pulses to match the impedance of the pct crystal most dampening material is made of an epoxy resin that has tungsten filaments throughout it now adding backing material to transducers does have some consequences but they're not all bad the first one is that it can decrease sensitivity meaning that it could cause the transducer to miss very low amplitude reflectors another consequence is that it can cause a wide bandwidth and thirdly it can cause a lower quality factor our first consequence told us that backing material decreases an ultrasound system's sensitivity sensitivity is the machine's ability to process and display weak echoes when sound waves come back to the transducer they've attenuated quite a bit so they are very weak they still need to interact with the pct material to create the electrical voltage that will become the image now that dampening material is going to shorten the pct element's reaction time in both transmission and reception so that means it's going to cause it to not contract and expand as long so those very weak echoes that are coming back are going to be even weaker due to the backing material and this might weaken them to the point that they're not even detectable anymore so here we have two transducers receiving echoes coming back so those receiving echoes are going to interact with the pct element and some of that sound energy gets directed into the backing material now if there's a lot of backing material that's kind of where it ends it's going to get stuck in there that voltage is never going to make it to the wire to make it back to the machine however if we have weaker echoes coming back into a transducer with just a little bit of backing material or no backing material that sound wave is going to interact with the pct element and a lot of that sound energy is still going to make it into the wire to go back to the machine so our dampening material reduces the sensitivity to those really weak echoes that are coming back because it's going to make it just a little bit weaker before the machine even gets the signal our second consequence is that backing material increases the transducer's bandwidth now the bandwidth is the range of useful frequencies that a device can operate at so many imaging transducers can operate at multiple frequencies and the bandwidth is the highest frequency minus the lowest frequency in this image we have how bandwidths are typically depicted in graphical form so we have kind of our operating frequency the frequency that the pct element likes to operate at where it kind of naturally resonates and then we have a frequency that's very low that the pct crystal can create and we have frequencies that are higher that the pzt crystal can create so we see that the bandwidth is the highest frequency minus the lowest frequency that a transducer can create so to calculate bandwidth we are going to take the maximum frequency and subtract the minimum frequency in this transducer on top here we see that we have transducer a which can produce frequencies up to 12 megahertz and down to three megahertz this transducer has a bandwidth of nine megahertz this is actually very wide it has a very wide range of frequencies that it can produce the resonant frequency which is also known as the operational frequency is typically the middle of that which for transducer a is around seven and a half megahertz compare these values then to transducer b which has a frequency range of five megahertz to three megahertz five minus three is a two megahertz bandwidth which would be considered narrow and that is because it has a low variation from its resonance frequency resonant frequency again is kind of the middle of the road of the frequencies that it can produce so for transducer b it is four megahertz when sound is created it can do one of two things we can let it ring freely or we can dampen it so if we allow sound to ring freely without any restriction it's going to ring at a very pure frequency think about plucking a guitar string or hitting a key on a piano if you just hit it you'll get the tone intended but if you dampen the sound or cause it so it can't resonate freely it's going to create other frequencies within it and that is one of the ideas behind bandwidth if we let the pct crystal ring for a long time without that dampening material it's going to create a very pure frequency if we put that backing material on there it's going to cause the pct crystal to not resonate as freely and when it does it's going to cause a lot of frequencies as its resonation is dampened another thing to consider when sound is created if we allow it to resonate freely without restriction it can create a sound wave that has a lot of cycles within it when we begin to dampen how the sound wave resonates it is going to shorten the amount of cycles created and both of these are side effects of having that dampening material there we're going to get dampened sound waves that are going to create more frequencies which create the bandwidth and we're going to see that the cycles are shortened we can kind of relate this to how a bell rings given the opportunity it could ding [Music] for a really long time if we put a little bit of dampening on we might get a little bit less ring might just be a ding and if we put a lot of dampening on we'll barely get her any ring at all we might hear something like dink i found my small replica of the liberty belt and thought i would try this to show you so let's take a listen see if you can tell which one has no dampening just a little bit of damping and the most dampening [Music] were you able to figure it out let's listen one more time these first two are going to be free ringing the second one has just a little bit of dampening and the last one has a lot so if we compare these sounds of the bell to our transducer when we bring the pzt crystals without dampening material they ring for a very long time at a pure frequency when we introduce that dampening material or somehow dampen how the pzt crystals resonate we are going to start to hear more of like a little click sound out of the pct crystals and that little click is going to hold a lot of frequencies thus creating a wider bandwidth so by adding that dampening material to the transducer we are achieving two improvements for ultrasound imaging we are creating a wide bandwidth and short pulses and for imaging transducers we see that wide bandwidths offer more flexibility we can use those higher frequencies in the bandwidth to create images on thinner patients or get more detailed images or we can then use those low frequencies within the bandwidth to create images on larger patients or we can use it for doppler because remember rayleigh scattering increases with higher frequencies so we want to use lower frequencies when we use doppler imaging in modern machines the machines are capable of using the frequencies on their own or it can combine all those frequencies within the bandwidth to create optimized parts of an image and as we've mentioned a few times fewer pulses are going to be good as well because they improve the detail resolution fewer pulses mean shorter spatial pulse lengths and the shorter the pulse length the more axial resolution that can be achieved and with improved axial resolution we see more detail so in our continuous wave transducers we typically do not put any backing material in them they are not imaging transducers we're not looking to increase any detail in our pictures because we can't get them anyway so continuous wave transducers typically don't have any vacuum material what we see then is that they ring at a very pure frequency they're going to have a lot and in continuous wave infinite cycles and this is going to create a very narrow bandwidth compare that then to a pulse wave transducer that has just a little bit of backing material we're going to see that the pulse still has a lot of cycles in it but it has a definite end because it is a pulsed wave this is going to create a wider bandwidth than a continuous wave transducer but it'll be narrower than a bandwidth with a transducer that has more backing material this is kind of like the middle bell ringing that we heard so this transducer is going to have poorer detail resolution because it has a little bit longer pulses than what we would want but it'll still be more sensitive to those returning echoes lastly we can compare all these to a pulse wave transducer that has a lot of backing material this backing material is basically going to cause the pzt crystals to create a click and within that click we are going to see very few cycles and multiple frequencies that multiple frequency creation makes for a wider bandwidth and the very short click and the fewer cycles results in a short spatial pulse length which creates superior detail and resolution so backing material is good for our images because it creates more frequencies higher bandwidth short cycles shorter spl better detail resolution the third consequence that we learned about is that back-end material will reduce the quality factor now the quality factor is a unitless number that is inversely related to bandwidth i want to point out that it is very important that when you are talking about quality factor you're talking about the quality of the tone produced by the transducer not the quality of the image so when we say something has a high q factor it means that it is a very pure tone not that it is producing a very good image in fact low q factor produce better ultrasound images let's take a look at examples showing how the q factor is inversely related to the bandwidth so when a wave has a high q factor it will have a narrow bandwidth and that means that there is less variation from its operating frequency so for example let's say we have taken a sample from a wave that has an operating frequency of 1.5 hertz and if this was our sampling we can see that there is a one hertz wave and a two hertz wave and this is going to create a very narrow bandwidth because we can take two the maximum frequency minus one the minimum frequency and see that the bandwidth is one hertz so this sound is actually very pure if we had an operating frequency of one and a half we're really only varying from the natural operating frequency by half a hertz either direction so we have a very pure sound to calculate the q factor for this wave we would want to use the formula for q factor which is the operating frequency of the wave divided by the bandwidth so for this wave we can calculate the q factor to be 1.5 and that is because we have 1.5 hertz the operating frequency divided by 1 hertz which gives us a q factor remember its unit list of 1.5 so the frequencies that are exhibited in this wave are very close to its operating frequency which means it has a very high q factor it's high quality tone because it is very close to being a very pure tone now let's compare that to a wave that has lots of frequencies within it so when we have low q factor it's usually due to a wide bandwidth and that means that there is more variation from its operating frequency so again here we have an example of a wave and let's say that this wave sample was taken from an operating frequency of three and a half hertz in this wave sample we can see it has a one hertz actually has two three four five and up to a six hertz that red wave in the middle so the bandwidth of this wave is very wide because we are going to take six the maximum minus one the minimum to calculate a five hertz bandwidth so this sound is not very pure it has a lot of other frequencies within it but we're still going to calculate the q factor and we're going to use that again using our formula being the operating frequency divided by the bandwidth and when we do that we can calculate the q factor for this wave to be 0.7 and that's because we took the operating frequency of 3.5 hertz and divided it by the bandwidth so we see that the frequencies that are within this wave are further from the operating frequency there's more of them and it means that it's going to have more tones and lower quality so to summarize the consequences of adding backing material which we typically find in our imaging or pulse wave transducers let's compare imaging transducers to continuous wave transducers in our imaging transducers we will see that we have short pulses dampened pulses because of that backing material with that backing material we are going to see wider bandwidth and lower q factors and because of all of this this type of transducer will have low sensitivity to returning echoes compare that then to the continuous wave transducer continuous wave transducers are typically going to have longer waves undampened waves there's going to be no backing material in them and because of that no backing material they're going to have very narrow bandwidths which create high q factor waves and create more sensitivity remember that calculating the bandwidth is as simple as taking the maximum frequency created by a transducer and subtracting the minimum frequency created by the transducer that gives you your bandwidth and then the q factor is calculated by taking the natural operating frequency of a transducer and dividing it by the bandwidth and this will remind us that q factor and bandwidth are inversely related moving on to section 8.4 we'll talk about the wire now the wire in this image is going to travel through the cord and through the backing material to attach directly to the pzt crystal in an ultrasound transducer the wire connects the element to the ultrasound system and each pzt element has its own wire so during transmission a voltage travels down the wire to the pct face where it will cause the pzt to deform and then the element to create the ultrasound wave in reception the wire is going to take the voltage produced from the pzt crystal by receiving that echo it's going to take the voltage and return it back to the machine for processing all the wires typically gather together at the base of the transducer and then run through the cord so if a transducer has 250 elements on it then 250 wires are running back through the cord and as we'll learn in a few units we need those individual wires because we are going to send electrical voltages in very specific patterns to the pzt elements to activate them in the way that we want so that is why each pct element is going to have its own wire we need to communicate with each pct crystal all those wires run through the cord it's really important that we take care of the wire where it attaches to the transducer and make sure that we don't run over the cord with the machine to finish up our transducer anatomy we'll take a brief look at the housing of the transducer the case of the transducer is the outer shell and it's typically going to be made of plastic or metal next in then we have the electrical shield and this is going to be a metal layer under the case this is going to help keep outside electrical interference from entering the transducer remember we do have voltages coming down those wires if we were to have some extra electrical information get into those wires then we could really affect how the wires are creating a voltage on the pct crystals can in turn produce electrical interference artifact in our images the next layer and then is the acoustic insulator and this is going to be a thin barrier of cork or rubber and the whole point of it is to separate the internal components of the transducer from the case and the electrical shield the point of the acoustic insulator is to absorb some of those vibrations that are coming back from the body during echoes so those extra vibrations are not creating new vibrations on the pzt crystal that might be interpreted as sound waves so the acoustic insulator absorbs those extra vibrations and keeps them from interfering with the true echoes that are returning the outer portion of the transducer should be inspected for cracks or damage before every use it's the housing that will protect the sonographer and the patient from electrical shock the case of our transducer typically has a notch on the outside and this will indicate which side of the transducer corresponds with the imaging sector so for example we've got a cardiac transducer here the notch is over here this notch indicates which side of the transducer face aligns with the probe orientation marker so this part of the transducer is making this part of the image same idea on this one we have the notch this is indicating then that this part of the transducer face will create this side of the image moving over our notches on our transducers correspond with the probe orientation marker you might notice on your transducer that there are other little notches and grooves on it as well these are to attach a biopsy needle bracket too so these this is the bracket and attaches into these little grooves on either side of the transducer and then you can put a needle in it to aid in the accuracy and repeatability of your biopsy and these little grooves and notches are actually very difficult to get gel out of so you want to make sure that you're double checking them to make sure that your transducer is nice and clean for your next patient and speaking of cleaning the transducer we need to make sure that we are cleaning the transducer after every patient typically that starts with using an approved wipe to clean off the gel and complete a low level disinfection low level disinfection is completely fine for the transducers that we use just across the body no open sores or anything just wipe them down with a cloth get all the extra gel off and then wipe them down with a disinfecting wipe any transducers that are inserted into a body cavity have been in contact with open wounds or have been used in a biopsy should undergo high level disinfection now high level disinfection is going to reduce the biological burden of microbes and viruses currently there are some fluid solutions like gluteraldehyde and orthophethylehyde or opa that are used to soak the transducer we've got a couple examples here of gus units these are going to be the units that hold the chemical solution you insert the transducer into them and soak them for a period of time this example of gus unit is used to soak most of our regular transducers that we use daily with our machines where this one is actually showing us how trans esophageal transducers once that are inserted into the esophagus are cleaned there's also another option that we can use for our daily use transducers and that is going to be called a trophon unit the trophon unit uses steamed hydrogen peroxide to clean the transducer due to increased regulations around the fluid soaking method of cleaning transducers tropons are actually gaining quite a bit of popularity but they are a little bit more expensive and they have been known to melt the glue that is used to make the transducers regardless of how you clean the transducer you should always store it to avoid contamination after a high level disinfection autoclaving which would result in sterilization of an item requires extremely high temperatures and that'll definitely melt the glue that is used to make the transducer so we typically don't sterilize our transducers but prefer to perform a high level disinfection we're worried again with autoclave that we might get to that curry point however most autoclave procedures only get up to about 250 degrees fahrenheit where curry point is more like 570 degrees so the event is still low but we don't want to risk it and we know that it's going to melt the glue so we try to avoid those high temperature sterilizing procedures if we need to use a transducer in a sterile procedure like a biopsy or like a surgery then we are going to cover them with a sterile probe cover use sterile coupling gel and then we will clean the transducer in that high level disinfection when we are done with the procedure and that brings us to the end of unit 8 transducer anatomy make sure to work through your workbook you'll get more practice with working with the formulas that we learned in this unit as well as understanding the implications of having backing material and being able to compare imaging transducers to continuous wave transducers you'll also be able to review those nerd check questions that are open-ended questions that you can use to help you study the material that's been presented