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Carnegie Physics

Phearless Physics PPT (Ultrasound Physics)

A sound wave travels through matter by: Compressing and rarefacting it.
What is sound? energy traveling through matter as a wave.
Different types of matter influence sound waves to travel at? different velocities or directions.
1 repetitive periodic oscillation is equal to what? 1 cycle
How is frequency measured? Number of cycles per second - Hertz (Hz)
What is the range of human hearing? 20 - 20,000 Hz
What is the range of Ultrasound? 20,000 Hz and greater
What is the range of Diagnostic Ultrasound? 2.5 to 10 MHz (Megahertz or millions hertz)
1 cycle in 1 second is equal to what? 1 Hz
What are the properties of high frequency ultrasound? (5-10 MHz), Greater resolution, Less Penetration. Useful for resolving shallow structures such as vascular, abscess, t/v gyn, testicular.
What are the properties of low frequency ultrasound? (2-3.5 MHz), Less resolution, Greater Penetration, Useful for resolving deeper structures such as the Aorta, t/a gyn, card, gb, renal.
What is a wavelength? The length of one complete cycle (a measurable distance).
What is Amplitude? The degree of a waves variance from the norm (the norm can be visualized as the straight-line plane a wave oscillates above and below)
How does a probe produce an image? By emitting a sound wave pulse and measuring the time it takes from the emission of that pulse until the time its echo returns.
How do waves travel? By displacing matter, expanding and compressing adjacent tissues.
What happens to an ultrasonic wave as it travels through the tissue it encounters? It is propagated, impeded, reflected, refracted, or attenuated.
What increases a sound waves propagation velocity? Stiffness
What decreases a sound waves propagation velocity? Density
What is the propagation velocity of ultrasound through bone? 4'080 m/sec
What is the propagation velocity of ultrasound through air? 330 m/sec
True or false: Sound travels faster through bone than through air. True
What is the average propagation velocity of ultrasound through soft tissue? 1,540 m/sec
Acoustic impedance of a material is the product of what? it's density and propagation velocity
Difference in acoustic impedance do what to ultrasound waves? create reflective interfaces that echo ultrasound back towards the probe.
How is sound reflected in a Homogeneous medium? It is not reflected.
What is an acoustic interface? Where tissues of different acoustic impedance meet.
When is almost all sound reflected? When two types of tissues with greatly different acoustic impedance come together (Bone/tissue or Air/tissue).
What is refraction? A change in direction of the sound wave as it passes from one tissue to a tissue of higher or lower sound velocity.
How can you minimize refraction? By scanning perpendicular to the interface that is causing it.
How does refraction adversely effect ultrasound scans? By distorting the depth reading of the probe.
What is reflection? The production of echoes at reflecting interfaces between tissues of differing physical properties.
When do Specular reflections occur? At large smooth interfaces (Reflects sound like a mirror).
When do Diffuse reflections occur? At small interfaces or nooks and crannies (may be smaller than the wavelength of the sound)
Give some examples of areas where a Specular reflection might occur? Diaphragm, Bladder wall.
in order for specular reflectors to return echoes to the probe how must the sound beam be aligned to the interface? Perpendicular.
What type of reflector produces the echoes that form the characteristic pattern of solid organs and other tissues? Diffuse.
As sound waves travel through a medium what happens to their intensity? Diminishes.
In ideal systems, sound pressure (amplitude) is only reduced by what? The spreading of waves.
In non ideal systems (real systems), sound pressure (amplitude) is also reduced by what? The scattering, reflection, and absorption.
The decrease in the intensity of sound pressure (loss of amplitude) is called what? Attenuation.
What are the main parts of an ultrasound scanner? Transmitter, transducer, receiver, processor, display, and storage.
How does a transmitter work? a piezoelectric crystal converts energy into sound waves and then receives sound waves and converts them back to energy.
How does a Continuous mode transducer work and what is it used for? It uses 2 crystals - 1 talks, 1 listens. it is used for doppler or therapeutic ultrasound.
How does a Pulsed mode transducer work and what is it used for? 1 crystals talks and then listens. it is used for diagnostic ultrasound.
How does a Receiver work? Sound waves hit and make voltage across a Piezoelectric crystal and the receiver detects and amplifies these voltages to compensate for attenuation.
What are the 2 types of Signal Amplification? TGC and Gain
What is TGC? Time Gain Compensation - Signal Amplification allows for the selective enhancement or suppression of sectors of the image such as enhancing deep tissue and suppressing superficial. (*think blinders)
What is Gain? Affects all parts of an image equally and is seen as a change in "brightness" of the images on the entire screen. (*Think Glasses)
What are the 2 types of displays? B-Mode and M-Mode
What is B-Mode? Real time, 2D gray scale display. Flip book - 15 to 60 images per second.
What is M-Mode? Echo amplitude and position of moving targets. Valves, vessels, chambers.
What is Echogenicity? The amount of energy reflected back from tissue interface.
What is Hyperechoic? Greatest intensity. White
What is Anechoic? No signal. Black
What is Hypoechoic? Intermediate. Shades of gray
What 3 terms describe the Echogenicity range of an image? Hyperechoic, Anechoic, and hypoechoic.
Image Resolution quality is dependent on which 6 things? Axial Resolution, Lateral Resolution, Focal Zone, Probe Selection, Frequency Selection, and Recognition of Artifacts
What is Axial Resolution? The ability to differentiate two objects along the long axis of the ultrasound beam. It is determined by the length of the pulse and the number of cycles in each pulse. Higher frequencies produce better resolution.
What is the maximum resolution distance of 2 objects when using a 5 MHz transducer? 1 mm
What is the maximum resolution distance of 2 objects when using a 10 MHz transducer? .5 mm
How big is the wavelength of a 5 MHz transducer? .308 mm
How big is the wavelength of a 10 MHz transducer? .15 mm
What is Lateral Resolution? The ability to differentiate objects along an axis perpendicular to the ultrasound beam.
What is Lateral Resolution dependent upon? The width of the ultrasound beam (which can be controlled by focusing the beam) and the distance between the objects.
True or false: with lateral resolution the ultrasound beam is made up of a strong individual beam. False. (Multiple individual beams. They are fused to appear as one beam. The distances between the single beams determines the resolution)
What is Acoustic Enhancement? The opposite of acoustic shadowing. Better ultrasound transmission allows enhancement of the ultrasound signal distal to that region.
What is Acoustic Shadowing? Occurs distal to any highly reflective or highly attenuating surface. Important diagnostic clue seen in a large number of medical conditions such as Biliary stones, Renal stones, and tissue Calcifications.
Failure to visualize the source of a shadow is usually caused by what? The object being outside the plane of the ultrasound beam. The shadow may be more prominent than the object causing it.
What is Lateral Cystic Shadowing? A type of refraction artifact and can be falsely interpreted as an acoustic shadow (similar to gallstone).
What is a Beam-Width Artifact? Gas bubbles in the duodenum which could simulate a gall stone. It DOES NOT assume a dependent posture and they DO NOT conform precisely to the walls of the gallbladder.
What is a Side Lobe Artifact? More than one ultrasound beam is generated at the transducer head and the beams other than the central axis beam are referred to as side lobes. Side lobes are of low intensity.
How can you obviate (prevent) Side Lobe Artifacts? By alternating the angle of the transducer head.
What is a Reverberation Artifact? There are several types and they are caused by the ehco bouncing back and forth between two or more highly reflective surfaces.
What do Reverberation Artifacts look like? On the monitor parallel bands of reverberation echoes are seen. This causes a "comet-tail" pattern.
What are some common reflective layers that can cause Reverberation Artifacts? The abdominal wall, gas, and foreign bodies.
What causes a Contact Artifact? Poor Probe-Patient Interface.
A probe can give shallow or detailed images depending on the? Frequency
How should you hold a probe to an organ wall being studied? Perpendicular to the organ wall.
An example of using knowledge of physical properties of tissues to help with positioning of probes during ultrasound: use bladder for acoustic window to ta.
What is the name for the general category of false readings you should be on the look out for when imaging? Artifacts
What should you remember to adjust to help your image? Adjust depth, tgc, and gain.
Created by: ICVT2b
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