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Carnegie Physics Int

Introduction to the Physics of Ultrasound PPT

What is sound? a mechanical, longitudinal wave that travels in a straight line
What does sound require? a medium through which to travel
What is ultrasound? a mechanical, longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz.
Medical Ultrasound frequency: 2MHz to 16MHz
How is ultrasound produced? by passing an electrical current through a piezoelectrical crystal
True or false: The frequency affects the quality of the ultrasound image True
The HIGHER the frequency: the BETTER the resolution
The LOWER the frequency: the LESS the resolution
Does HIGHER or LOWER frequency penetrate better into the body? Lower.
How can one transducer replace several tranducers? By altering its transmit frequencies.
When a single transducer alters its transmit frequencies it is able to view: A range of superficial to deep structures.
The size, design, and frequency of a transducer are dependent upon what? The examination.
In Image formation the electrical signal does what? Produces 'dots' on the screen.
In image formation the brightness of the dots is proportional to: The strength of the Returning echoes.
In image formation the location of the dots is determined by: Travel time.
The velocity of ultrasound in tissue is assumed constant at: 1540m/sec.
What is the formula for determining the location of 'dots' in image formation? Distance = Velocity/Time.
What determines Acoustic Impedance (AI)? The density of the material in which sound is propagated.
What happens to impedance as materials become denser? Increases.
What causes reflections? The interface of different Acoustic Impedance's (AI's).
What causes signal reflection to increase? Larger differences between Acoustic Impedance's (densities).
What causes signal reflection to decrease? Smaller differences between Acoustic Impedance's (densities).
What happens to sound as it goes deeper into the body? Attenuation.
The largest difference in Acoustic Impedance's is: Solid-gas interface.
What are the interactions of Ultrasound with Tissue? Reflection, Refraction, Transmission, and Attenuation.
What forms the ultrasound image? Reflected echoes.
True or false: The angle of incidence > angle of reflection False.
What happens during transmission? Ultrasound waves continue deeper into the body. These waves will reflect from deeper tissue structures.
Define Attenuation? The deeper the wave travels in the body, the weaker it becomes.
What processes cause attenuation? Reflection, absorption, and refraction.
How do you compensate for signal attenuation as more tissue is penetrated? Adjust the gain based on depth.
Increasing the gain does what to an image? Makes it brighter.
Decreasing the gain does what to an image? Makes it darker.
What causes White Dots? Strong reflections.
Ultrasounds behavior within the diaphragm, tendons, and bone is considered what? Hyperechoic.
What causes Grey Dots? Weaker reflections.
Ultrasounds behavior within solid organs and thick fluid is considered what? Isoechoic.
What causes Black Dots? No reflections.
Ultrasounds behavior within cyst fluid, urine, or blood is considered what? Hypoechoic (echofree).
What determines how far ultrasound waves can travel? The frequency of the transducer.
What frequency of ultrasound travels (penetrates) the farthest? Low.
How is attenuation related to frequency? Directly.
Which frequency of ultrasound travels (penetrates) the least distance within the body? High.
Although you can't control the depth of the beam as it keeps going until attenuated, what can you control? The depth of displayed data.
How thick is the ultrasound beam profile? 1 mm.
Is an Ultrasound image 2 or 3 dimensional? 2.
What is the ultimate goal of any ultrasound system? To make like tissues look the same and unlike tissues look different.
What helps an ultrasound system achieve its ultimate goal? It resolving capability (resolution) and its processing power.
What are the different types of resolution? Axial/lateral, spatial, contrast, and temporal.
Which resolution specifies how close together two objects can be along the axis of the beam yet still be detected as two separate objects? Axial.
Which resolution has the ability to resolve two adjacent objects that are perpendicular to the beam axis as separate objects? Lateral.
Which resolution allows you to identify two very close reflectors as different? Spatial.
Which resolution grants the ability to accurately locate the position of moving structures at particular instants in time? Temporal.
Which resolution grants the ability to resolve two adjacent objects of similar intensity/reflective properties as separate objects? Contrast.
While axial resolution improves as frequency increases, what improves lateral resolution? Beamwidth.
What is another name for Spatial resolution? Detail.
Spatial resolution is the combination of what? Axial and Lateral resolutions.
Temporal resolution is also known as? Frame rate.
What is Contrast resolution dependant upon? Dynamic range.
What are some of Ultrasounds applications with regards to vessels? Assessment of position, size, patency.
What are some some of Ultrasounds applications? Visualization of nerves and soft tissue masses. Guided procedures in real time (Dynamic imaging). Central venous access. Nerve blocks.
Frequency is equal to: oscillations per second.
How is frequency expressed? Hertz (Hz).
what converts the returning ultrasound echo back into an electrical signal? the piezoelectric elements within the transducer.
What does the thickness of the piezoelectric crystal determine? The frequency of the scanhead (Thicker = lower, Thinner = higher)
Created by: ICVT2b