ARDMS - SPI Study

What would you do if you had aliasing in the pulsed wave?

1) drop baseline 2) increase scale 3) change to a lower transducer

A sound wave propagates fastest through which substance? Bone Muscle Fat or Gas

Bone

When using a 5 MHz transducer, in which tissue is the ultrasound wavelength the shortest?

Fat in this question Use wavelength equation speed over frequency

Which control allows adjustment for attenuation at specific depths?

Time gain compensation

Which technique results in a three dimensional image?

surface rendering

depth ambiguity

the inability to determine the depth of the reflector if the pulses are sent out too fast for them to be timed - can happen with increased prf

What determines the center frequency of a transducer?

thickness

Dynamic range

use compression

What is the Nyquist limit?

1/2 PRF

Which angle of isonation to blood flow produces the maximum doppler shift?

180 degrees

Which frequency is best to evaluate structures lying 1 to 2 cm from the transducer?

8 MHz - higher frequency

What is the Nyquist limit if a pulsed doppler instrument has a pulse repetition frequency of 16 khz?

8 khz - 1/2 prf

Temporal resolution:

Best with faster frame rate Best with shortest time to create image Worse with mult focal zone & deeper imaging Relates to frame rate & line density

When the focal point in a B mode image is electronically changed, which type of focusing is in use?

Dynamic

To which acoustic variable is penetration depth inversely related?

Frequency think about how far the ultrasound wave can penetrate or travel into the body

What does coded excitation improve?

Improves penetration, axial resolution, spatial resolution and contrast resolution

Large Diameter & High Frequency =

Less Divergence/Shallow focus

Small Diameter & Low Frequency =

More Divergence/Deep focus

Which factor determines the displayed depth of a reflector?

Propagation speed of the medium Where a reflector is displayed on the screen how deep

Which term describes the averaging together of scan lines from multiple angles to create one image?

Spatial compounding

Which condition must be present for refraction to occur?

a difference in tissue propagation speeds and oblique incidence

Coded excitation:

a way of processing the pulse to improve contrast resolution improves with axial and penetration allows multi frequency of bflow imaging reduces speckle

Which type of interaction between sound and tissue is most affected by the thermal index (TI)?

absorption

Which imaging mode requires two elements mounted side by side?

continuous wave doppler

What is the potential affect of increasing prf?

depth ambiguity

Spatial resolution:

determined by # of pixels in scan converter axial, lateral, elevational and contrast res. improves with fill in interpolation increases with decreased tx freq

elevational resolution

determined by the thickness of the imaging plane perpendicular to scan plane

Which technique the sharpness of high contrast boundaries?

edge enhancement

Which variable decreases when the number of acoustic lines per frame is increased without changing the maximum depth?

frame rate

PW positives

gate, angle correct, 1 crystal, depth of sample volume, pw only one that aliases

Thinner pzt crystals = inverse

high frequency

What is the most common cause of localized vertical nonuniformity in a real time b mode image?

improper time gain compensation

How does frequency compounding improve image quality?

improves dynamic range

frame rate

improves signal to noise ratio det. by speed of sound in medium and imaging depth adjustable by depth shallow has better higher frame rate lower line density

Attenuation

improves with tgc

Which factor reduces the likelihood of aliasing in pulsed wave spectral doppler?

increased Nyquist limit

What is a benefit of using contrast agents?

increased amplitude of the returning dopplers

Which action can improve axial resolution of a displayed image?

increasing the transducer frequency short spl damping

When a fluid is flowing at a slow and constant rate within a long tube having a uniform diameter, what is the nature of the flow?

laminar

doppler packet - aka ensemble length

large # and long ensemble lenghts = better velocity measurements sensitive to low flow reduces frame rate and temp resolution

What does coded excitation improve in addition to penetration?

lateral resolution

Thicker pzt crystals = inverse

low frequency

In an unfocused transducer, what defines the region between the transducer face and the point where the beam diverges?

near field

CW positives

no aliasing high sensitivity 2 crystals

Harmonics

non linear improves lat resolution - has strong beams elimnates near field artifacts eliminates grating lobes improves shadowing from calcifications

What is an advantage of using a pulsed wave doppler versus continuous wave doppler?

provides depth specificity

Which imaging mode requires a broadband transducer?

pulsed wave doppler

Which variable can cause an acoustic shadow artifact?

refraction

Which scenario will produce no doppler shift to the receiver?

source and receiver moving at the same speed and direction

Which technique utilizes frequency modulation of the transmitted pulse to improve signal to noise ratio?

spatial compounding