Final Flashcards
(42 cards)
At what frequency do US waves travel through soft tissue?
1540 m/s
What are the three important properties of US?
Wavelength, wave frequency, acoustic velocity
What are the 4 interactions of US with tissues?
Absorption, reflection, scatter, refraction
What is absorption?
The strongest interaction between US and ST
Strongly contribute to beam attenuation during propagation
Increases as US frequency increases
What is reflection?
It occurs at the surface of a medium
Allows of image reconstruction
What is scatter?
Occurs in all directions from particles whose dimensions are smaller then the US wavelength
Causes a loss of wave intensity out of the main direction of the US beam
What is refraction?
When the US beam bend when it enters a medium of different wave velocity at non-normal incidence
When the US beam travels from an area of low sound velocity to an area of high sound velocity, the beam will —-
bend away from normal
When the US beam travels from an area of high sound velocity to an area of low sound velocity, the beam will —
bend toward normal
What is continous US
An older style of US
When the transducer will continously send out US waves
What is continous US
An older style of US
When the transducer will continuously send out US waves and would need a receiver to receive the reflected waves
What is pulsed US?
A new style of US
Usually 3-5 cycles in a length
Allows the transducer to receive the waves back and form an image
What is the piezoelectric effect?
The process of the US waves being reflected and scattered back to the transducer, which then is converted in electrical signals to create an image
What is the transducer?
The most important component of the US system
Produces US pulses and receives US echoes
How strong is a curvilinear transducer and what is it used for?
4MHz
Used for abdomen, pelvis, obstetric applications
How strong is a linear transducer and what is it used for?
7MHz
Used for vascular applications and superficial structures
How strong is a transvaginal and transrectal transducer?
8MHz
What is lateral resolution?
How close two objects can be perpendicular to the axis of the beam and still be detected as two distinct entities
What controls lateral resolution?
Beam width and shifting the focus on the US machine
What is axial resolution?
The ability to separate structures parallel to the US beam
Based on wavelength
What are the requirements of an US machine?
Uninterrupted power supply, processes to transform the acquired data into an image, a means to display the image, a hard drive to record the examination
What are the limitations of US in general?
Highly operator dependent
Bone and air cause the US wave to reflected
As US waves interact they lose energy as heat, degrading image quality that can render a non-diagnostic image
What is A mode
Amplitude mode
What is A mode used for?
Ophthalmology and was used to determine mid-line in the brain
