Chp 3 - Pulse-Echo Intrumentation Flashcards
How long does it take for sound to travel 1cm in soft tissue
13 us (1way)
What is apodization?
A technique used to vary the voltage to individual elements used to reduce grating lobes
What is the smallest unit of memory in a digital device?
a bit
What is the smallest compoenent of a 3D device?
a voxel
What is a byte
8 bits of memory
What is the difference between B mode comet tail and ring down?
Comet tail - is reverb from small reflectors
Ring down - is an artifact of reverb from gas/air
Where is amplitude mode used today?
in echocardiography and ophthalamogy
What is the range/distance equation
d = c x time /2
What is the assumed distance in soft tissue?
d = 0.77t
What is the main function of the beam former?
controls timing of the elements and apodization
What is coded excitation?
sends a series of encoded pulses to form one SL (instead of one pulse per SL)
What does the master synchronizer do?
part of the machine responsible for controlling the timing of the echoes
What is rectification?
turns negative voltages into positive voltages
What is the formula to determine the shades of grey?
2^n
n = number of bitd
What produces the step ladder appearance?
reverb
In a standard cathode ray tube used to display ultrasound images, what
are the charged particles that are emitted from a “gun” from the rear of
the tube?
Electrons
How does a cathode ray tube steer the charged particles emitted by
the electron so that they sweep across the front screen?
By using a magnetic field
How many fields are in a frame?
2
An increase in compression results in what happeneing to the DR?
Decreases
An advantage of coded excitation is improved:
signal to noise ratio
Additional reflectors on the screen (with an array transducer) that are
from extraneous sound waves off the primary axis of the beam are:
Grating lobes
When will a reflector be placed too close to the transducer than it should be?
when the sound beam goes through anything faster than 1540 m/s
When will a reflector be placed farther than it should to the transducer?
when the sound beak travels through anything slower than 1540 m/s
The part of the machine responsible for timing the reception of the
pulses to determine their location is the:
The master synchronizer
When does edge shadow occur?
when sound strikes a curved reflector (ex GB or carotid artery)
What is the difference between side lobe and grating lobe?
side lobe occurs with all transducers while grating lobe only occurs with linear transducers
How can you reduce grating lobes?
harmonics, subdicing, apodization
