9848 Lecture Notes - Lecture 6: Medical Ultrasound, Electric Potential, Lincoln Near-Earth Asteroid Research
19 Jun 2018
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Introduction to Ultrasound Continued
Objective 4
Basic Technological Implementation of Ultrasound
- Pulse Echo Method
- Information from the Echoes
Pulses of echoes
•Wherever there is uniformity in the material then these sound pulses just travel FORWARD
deeper into the material.
•HOWEVER, where there are DIFFERENCES in material - due to STRUCTURE or density
changes in the material then the BOUNDARY between these two different regions acts as a
REFLECTOR
•SOME of the pulse energy gets reflected BACK to the transducer probe
•This reflected pulse energy is what we call an ECHO. An echo is ALSO a PULSE of sound, but it
moves opposite to the initial generated sound pulse we made.
•The rest of the energy of the sound pulse (now decreased) continues forward and ‘deeper’
The pulse echo method
•ALL medical ultrasound technology relies on the RECEPTION of the ECHOES.
•This is sometimes called the ‘PULSE-ECHO’ method
The probes job is two fold
•It must first GENERATE an ultrasound pulse AND it must then be ‘ready’ to RECEIVE an
ultrasound echo-pulse
•The crystal inside the transducer-probe upon being ‘hit’ by the echo-pulse of energy
VIBRATES
•The PIEZO ELECTRIC effects occurs
The crystal forms an electric potential (voltage) across it
This is a pulse of electrical energy and is a SIGNAL
•This voltage signal is then used by the electronic circuitry in various ways to extract
information and make images
Pulse echo ‘Ranging”
•It can be calculated where the echo ‘comes from’
By knowing the time at which we sent out the initial sound pulse, and the time when we
received the echo
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Then we can calculate the depth that the echo came from
Or -rather - this calculation is inbuilt into the electronics !!
•Clearly ECHOES from DEEPER boundaries take longer to arrive back at the probe
•The circuitry must be capable of coping with MANY echoes all arriving back at the probe,
separated by small intervals of time.
Echo size
•The amount of ENERGY that an echo has is also IMPORTANT
•The larger the energy, then the larger the VOLTAGE signal caused.
•We can convert this (usually) into a STORED NUMBER inside the computerized digital
memory.
•Each stored number is assigned a brightness value on a TV screen monitor.
•The bigger the stored number, the BRIGHTER value on the TV screen.
Different lines of sight
•Taking a simple modern LINEAR probe. This consists of many crystals placed next to each
other.
•Each acts like a ‘rifle’ sending its own ‘bullet’ of sound (a pulse) into the material.
•Each crystal also receives echoes from its line of sight.
In this way hundreds of tiny crystals mean many lines of information.
•By knowing which crystals received which echo then every echo now has THREE pieces of
information
2 Dimensional Real Time Ultrasound (2DRT)
•Each echo is known to have an x coordinate (because we know which crystal was used along
the probe).
•Each echo also has a y coordinate. This is the DEPTH where the echo came from that was
calculated.
•Each echo has a VALUE (size) and larger values have larger stored numbers.
•All this means that we can construct an IMAGE where we display a POINT (x,y) on a TV
screen and it has a brightness dictated by the size of the echo from that point.
•There will be points that are less bright than others and some brighter than others.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Pulses of echoes: wherever there is uniformity in the material then these sound pulses just travel forward deeper into the material. However, where there are differences in material - due to structure or density changes in the material then the boundary between these two different regions acts as a. Some of the pulse energy gets reflected back to the transducer probe. This reflected pulse energy is what we call an echo. An echo is also a pulse of sound, but it moves opposite to the initial generated sound pulse we made. The rest of the energy of the sound pulse (now decreased) continues forward and deeper". All medical ultrasound technology relies on the reception of the echoes. It must first generate an ultrasound pulse and it must then be ready" to receive an ultrasound echo-pulse. The crystal inside the transducer-probe upon being hit" by the echo-pulse of energy. The crystal forms an electric potential (voltage) across it.
