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Carnegie Physics Int
Introduction to the Physics of Ultrasound PPT
Question | Answer |
---|---|
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) |