Anatomy of a Scanner v2.0 Ultrasound Probe PDF

Ultrasound probe anatomy circa 1988 alogue probes – annular array send receive crystal Backing layer Crystal width = ½ ʎ Protective window (Fixed) e problems of unfocused ultrasound...

Ultrasound probe anatomy circa 1988 alogue probes – annular array send receive crystal Backing layer Crystal width = ½ ʎ Protective window (Fixed) e problems of unfocused ultrasound transducers… Fraunhofer Diffraction (Spherical Spreading) Diameter or radius of Fresnel Diffraction (Plane Wave) crystal aperture Crystal D probe Near Field λ Far Field r (NFD)Near Field Depth or Rayleigh distance 2 2 𝐷 𝑟 𝑁𝐹𝐷= 𝑜𝑟 4λ λ Pure analogue (AAA) Received by a electromagnetic Recorded onto Transmitted as (vibrational) and played back sound by an microphone, via a vibrational electromagnetic device (vibrational) speaker Why don’t we rely on analogue systems?  HUGE amounts of interference/noise  No ability to manipulate signal  Expensive, unreliable sometimes fragile components Ultrasound machine anatomy – electronic/digital beamfor sic (very basic) Transmit Transmit beam power former control Output to screen Transmit Post processing receive Receive Cine digitise Amplitude Image memory beam processing formation former Pre processing  Pre send controls ? Receive controls  Pre send controls ? Analogue processing Transmit beam former Receive controls  Pre send controls Focus Fan (Scan image width) Frequency Analogue processing Transmit beam former Receive controls The transmit beamformer produces the correct electrical signal to apply to the crystal array Transmit beam 1. It takes the preset electrical output from the machine, former 2. combines it with the user controls of the machine, 3. and forms the correct profile of electrical signals to excite the crystals in the probe array Electrical + User output of selection machine  Analogue processing The Digital analogue convertor(? Coordinator) (DAC) 4. coordinates the analogue response of the crystals within the probe to produce the correct beam of ultrasound Beam forms + User the selection transducer  Emley Moor Mast Or Mordor as many of us know it Time to transmit guys Not recommended for Gradescope EDIEs Back to probe anatomy…. Ultrasound probe anatomy Digital probes suppression production transmission Ultrasound insulation Backing layer Acoustic window P.Z.T Matching layer crystal array https://www.youtube.com/watch?v=lmy8J8n9wPU Ultrasound probe anatomy Digital probes suppression production transmission surrounding layers PZT advantages? it is efficient at converting electrical energy Backing layer to mechanical energy, and vice versa, Acoustic window relatively easy to machine or mould to any P.Z.T Matching layer crystal required shape or size. Disadvantages? array it has a characteristic acoustic impedance that is many times higher than that of the soft tissue resulting in vibrations which would continue long after the applied driving voltage had finished as the pressure wave bounced back and forth inside the crystal. Such ‘ringing’, as it is called, would result in an overly long pulse. And little useful sound transmission Ultrasound probe anatomy Digital probes suppression production transmission Backing layer This unwanted ‘ringing’ can be much reduced by having a backing (damping) layer behind the PZT, Backing layer Backing layer Acoustic window P.Z.T Matching layer crystal IDEALLY made of a material with array both high characteristic acoustic impedance and the ability to absorb ultrasound So to absorb reflected ultrasound and eradicate ringing BUT If the impedance of the backing layer were identical all the absorbed sound would be converted into heat and reduce the sensitivity of the probe and cause internal Ultrasound probe anatomy Digital probes suppression production transmission Backing layer So as a result Backing layer the practical compromise is, to have a Acoustic window P.Z.T Matching layer backing layer with impedance somewhat crystal lower than that of the PZT. This compromise impedance is chosen to give a useful array reduction in ringing without lowering sensitivity too much. The remaining ringing is removed by using matching layers, as discussed next. Ultrasound probe anatomy Digital probes suppression production transmission Matching layer As well as the ringing problem, without a matching layer only a small fraction of the wave’s power would be Backing layer transmitted to the patient resulting poor sensitivity. Acoustic window P.Z.T Matching layer In order to overcome this, at least one ‘impedance crystal matching layer’ is bonded to the front face of the PZT. array it should have an impedance equal to square root of the impedance of the crystal multiplied by the impedance of humans tissue, √ PZT x Tissue in ‘non-mathsy’ words halfway between the impedances of PZT and tissue And…. Ultrasound probe anatomy Digital probes suppression production transmission Matching layer should have a thickness equal to a quarter of a wavelength. Backing layer ??? Acoustic window P.Z.T Matching layer This is clever… crystal Scenario 1 array IF the sound is reflected off the front of the matching layer it will 180o out of phase with sound reflected from the back of the matching layer – it will cancel it out removing ringing signal Ultrasound probe anatomy Digital probes suppression production transmission Matching layer should have a thickness equal to a quarter of a wavelength. Backing layer ??? Acoustic window P.Z.T Matching layer This is clever… crystal Scenario 2 array IF the sound is reflected off the front of the matching layer but then also reflected off the back of the matching layer it will have advanced 180o back into phase with the next wave - amplifying transmitted signal Ultrasound probe anatomy Digital probes Acoustic window suppression production transmission A protective layer over the matching layer with an impedance between the matching layer and human tissue Backing layer Acoustic window P.Z.T Matching layer crystal array Ultrasound probe anatomy different probe types Array of crystals Ultrasound probe anatomy send = electrical current ltrasound probe anatomy Order of firing 1st last The crystal fire in a order and with a time delay that mean the signal will be in phase at the distance the user has selected as the focus Ultrasound probe anatomy = electrical current Beamforming Phased array 1 2 3 1 3 2 1 3 2 s how phased array probes work, how 3D scanning is achieved (& 4D is this in real t  Pre send controls Focus Fan (Scan image width) Frequency P P P Patient interaction’y bit covered before ltrasound probe anatomy Order of firing 1st last The crystal fire in a order and with a time delay that mean the signal will be in phase at the distance the user has selected as the focus  Pre send controls Focus Fan (Scan image width) Frequency P P P P Analogue processing P P receive beam former Pre digital receive controls Post receive controls Depth Gain &TGC Gain & TGC Post digital receive Image depth controls  Receiving beam former - function 1 amplification Takes the raw analogue electrical signals and 1. Auto Amplifies into usable output (some pre amp may happen before ADC) 2. User controls desired gain setting & TGC 3. T.EQ (registrars button) may be used to balance signal into useful range again User gain User TGC Original signal Auto gain T.EQ setting setting setting Function 2 - Analogue digital controller (ADC) Takes the raw analogue electrical signals and converts them to a digital output 15 Binary output 14 13 (e.g. 4 bit) 12 11 10 9 8 7 6 5 4 3 2 1 0 Time or depth increments Analogue digital controller (ADC) Takes the raw analogue electrical signals and converts them to a digital output 1111 15 1110 14 1101 13 12 3,7,12,10,7,7,14,14,1,2,10,12,4 1100 1011 11 1010 10 1001 9 1000 8 0011011111001010011101111110 0111 7 6 111000010010101011000100 0110 0101 5 0100 4 0011 3 0010 2 0001 1 0000 0 Time or depth increments P P P Coherent Demodulatio Coherent P P image former n/ compression image former Pre digital receive controls Post receive controls Depth P Gain &TGC Gain & TGC Post digital receive Image depth controls Coherent signal processing Once digitised the scanner then organises and processes incoherent signal from all the separate crystals into one coherent output signal, accounting for the differing phases and amplitude of the returning signals, rather like a orchestra tuning up before they begin to play Demodulation and Incoherent signal processing Once the signal is given coherence the process is then convert it into a signal that has a value independent of its phase or amplitude, so that in can be turned into a brightness output on a screen, this process is known as demodulation and produces an incoherent signal P P P P P P P P Pre digital receive controls Post receive controls Depth P Gain &TGC Gain & TGC Post digital receive Image depth controls P P P P P Scan Conversion Pre digital receive controls Post receive controls Depth P Gain &TGC Gain & TGC Post digital receive Image depth controls Scan conversion In a similar way to how the ADC converter takes the output from the transducer crystals the converter takes the output from the image former and converts it into a digital output suitable for the display 1111 15 1110 14 1101 13 1100 12 Binary 1011 11 output 1010 10 1001 9 (eg 4 1000 8 bit) = 15 0111 7 levels of 0110 6 output 0101 5 0100 4 0011 3 0010 2 0001 1 0000 0 Time or depth increments  Scan conversion In a similar way to how the ADC converter takes the output from the transducer crystals the converter takes the output from the image former and converts it into a digital output suitable for the display 1111 15 1110 14 1101 13 1100 12 1011 11 1010 10 1001 9 1000 8 0111 7 0110 6 0101 5 0100 4 0011 3 0010 2 0001 1 0000 0 Time or depth increments Scan conversion Taking each of those lines of scan and displaying them as part of an image P P P Cine P P memory Pre digital receive controls Post receive controls Depth P Gain &TGC Gain & TGC Post digital receive Image depth controls Cine memory But that’s not all…  Cine memory – not only does the machine store the image info it also stores the raw digital data 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01001 01001 01001 01001 01001 01001 01001 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01001 01001 01001 01001 01001 01001 01001 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01001 01001 01001 01001 01001 01001 01001 But that’s not all… P P P Post processing Cine P P memory Pre digital receive controls Post receive controls Depth P Gain &TGC Gain & TGC Post digital receive Image depth controls  Cine memory – which allows post processing control to happen 10001010101001010101 Gain? 10001010101001010101 10001010101001010101 10001010101001010101 Frame Averaging? 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 X2 ÷3 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01001 01001 01001 01001 01001 01001 01001 01001 Edge enhancement? 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 Take all signals > 1100 and x 1.5 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 10101001010101010101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01010100101010010101 01001 01001 01001 01001 01001 01001 01001 10001010101001010101 10001010101001010101 10001010101001010101 Dynamic range? 10001010101001010101 10001010101001010101 10001010101001010101 10001010101001010101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01011000101010100101 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 01010101010010101010 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 10101001010110100110 Increase number of ‘different 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10010110100101010010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10100101010100101010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101010101001100010 10101001010101010101 00101010101010100101 10101001010101010101 00101010101010100101 10101001010101010101 00101010101010100101 greys’ according to difference in 10101001010101010101 00101010101010100101 10101001010101010101 00101010101010100101 10101001010101010101 00101010101010100101 10101001010101010101 00101010101010100101 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01101001101001011010 01010100101010010101 01001 01010100101010010101 01001 01010100101010010101 01001 digital output 01010100101010010101 01001 01010100101010010101 01001 01010100101010010101 01001 01010100101010010101 01001 Any ? A valve amplifier – anyone spot the obvious ‘mistake’? And this one too