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What 2 variables determine the mediums properties?
Stiffness-resistance of a material to compression, and Density-concentration of mass per unit of volume
What is the rule of thumb regarding propagation speed?
Prop speed increase=Stiffness increase=Density decrease
Define Axial resolution.
The minimum reflector separation necessary to resolve reflectors ALONG a scan line
Define Lateral resolution.
The minimum reflector separation necessary to resolve reflectors ACROSS a scan line
The level at which signals are not transmitted through an ultrasound receiver is termed what?
Unit which imaging information is divided for storage and display in a digital instrument
Define dead zone.
Distance between the transducer face and the 1st rod, no image, area very close to the transducer
Define matching layer.
Material attached to the front of a transducer to reduce the reflections at the transducer element
Define damping material.
Material attached to the rear of the transducer to reduce the pulse duration
Define: Grating lobes?
Additional, weaker beams of sound traveling in directions different from the primary beam
Define: Slice thickness.
Also called sectional thickness, Echoes from adjacent tissues filling what should be anechoic
Describe the piezoelectric effect?
When electricity is applied the PZT elements converts the electricity into ultrasound pulses
What are the 3 mechanisms of action for ultrasonid bioeffects?
Heat-Intensity, Radiation force-Exposure time, and Cavitation-mechanical effect to tissue
WHat factor is the operating crystal dependant on?
Thickness of the element and the mediums prop speed
Define: Huygen's principle.
Each surface of multiple transducer, diffract producing small waves that join together and form one main energy sound beam
Why do we use coupling gel?
To provide a good sound path from the transducer to the skin, eliminating the thin layer of air that would reflect the sound
What type of format, beam steering, and beam focusing does the following have: Linear Array.
Rectangular image, Electronic focusing, Mechanical steering
What type of format, beam steering, and beam focusing does the following have: Curved Array.
Convex image, Electronic focusing, Mechanical steering
What type of format, beam steering, and beam focusing does the following have: Phased array.
Sector image, Electronic focusing and steering
What type of format, beam steering, and beam focusing does the following have: Annular array.
Sector image, Mechanical steering, Electronic focusing
What type of format, beam steering, and beam focusing does the following have: Single element.
Pie shape image, Mechanical focusing and steering; Lens mirror
All of the following may be used as units of amplitude except which: Millimeters, Degrees, Pascals, meters per second
What 2 conditions are necessary for refraction to occur at a boundary between two media?
Different prop speeds and oblique incidence
When red blood cells move away from a transducer, the frequency of the wave returned from the RBC is what?
Less than the emitted frequency
Which of the following parameters is determined by the medium: Wavelength, Freq, Period?
Wavelength and Spatial pulse length depend on the sound source and medium
Which of the following contributes most to total attenuation in soft tissue: Absorption, Reflection, Scattering?
Which of the following statements is true regarding axial resolution artifiacts: Higher quality images are associated with higher numbers, Axial resolution is reported in units of cm3, Numerically axial resolution equals 1/4 the pulse length, or Too few reflectors appear on the image?
Too few reflectors appear on the image
Which of the following is considered an acoustic variable: Freq, Period, Power, or Pressure?
What is the power intensity for the following: 0dB, -3dB, -6dB, -9dB?
0=100%, -3=1/2, -6=1/4, -9=1/8
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