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Flashcards in Final 1 Deck (52):
1

Axial resolution is

The minimum separation necessary to resolve reflectors along the scan line.

2

ultrasound transducers operate according to

the piezoelectric principle

3

in a single element transducer, additional beams not included in the ultrasound beam are called

side lobes

4

electric ______ applied to a transducer are converted to ultrasound

voltages

5

with phasing, the reception beam is ___ and dynamically_____

steered ; focused

6

a ___ impedance of the transducer element allows more energy to transmit into the patient

lower

7

vector image format is similar to that for convex array except that the transducer ___ is ____-

contact surface is smaller

8

the 3 aspects of imaging resolution are

contrast ; temporal ; and detail resolution

9

___ resolution relates more directly to transducers

detail

10

the spatial pulse length will increase ____ with ____

wavelength w/ # of cycles in pulse

11

vector array is a combination of ___ & ___ array operations

linear & phased

12

the useful range for most diagnostic range application is ___ mhz

2-15

13

What 3 things does phasing do?

focus the beam, improve image quality, steer the beam

14

the matching layer reduces_____

reflection of ultrasound at element

15

arrays have additional beams resulting from their multielement structure termed

grating lobes

16

the formation of a beam from an aperture is explained by ___-

Huygen's Principle

17

Near Zone length is determined by the size and the ___ of the element

operating frequency

18

at a distance of two near zone lengths, the beam diameter is __ to the transducer

equal to

19

ultrasound transducers convert __ energy into ___ energy & vice versa.

electric ; ultrasound

20

T/F: the near zone length decreases with an increase in frequency

false

21

arrays are operated in two ways called

sequencing and phasing

22

describe the far zone

lies beyond 1 near zone length, Fraunhofer zone, increase in beam width

23

the impedance of the matching layer is ____

an intermediate value between the transducer element and tissue

24

attenuation encompasses

absorption, scattering, reflection

25

impedance increases when __ increases

density, propagation speed

26

pulse duration increases with __ & ____.

period, # of cycles in pulse

27

impedance is equal to density (x) ___

propagation speed

28

in oblique incidence, the ___ & ___ angles are always equal.

incidence & reflection

29

intensity = the power of a wave divided by the ___ over which the power is spread

area

30

the average propagation speed in human soft tissue is

1.54 mm/ms

31

amplitude is the maximum variation that occurs in an acoustic _____

variable

32

best way to describe the role of ultrasound scattering in diagnostic imaging

it is responsible for the enhancement and allows us to see the tissue surfaces

33

w/o matching, the transducer has an impedance of __ times that of tissue

20

34

the brightness of the dot corresponds to the __ of the returning echo

strength

35

the location of each dot corresponds to the ____ of the echo to return

time

36

a ___ scan is shaped like a slice of pie

sector

37

vertical parallel scan lines are seen with which transducer format

linear array

38

Snell's law relates the ___ beam direction to the incident beam direction & the speeds of sound in 2 materials forming the interface

transmitted

39

regions of lower pressure and denisty are called _____

rarefactions

40

the method in which each pulse originates from the same starting point is termed a ___ image

sector

41

wavelength is the __ over which one cycle occurs

distance

42

CW sound is not described by

pulse duration

43

the fraction of time that pulsed ultrasound is on is called ___

duty factor

44

T/F: The higher the transducer frequency, the lower the Rayleigh scattering.

false

45

T/F: The shorter the pulse, the broader the bandwidth

true

46

the unit for impedance is _____

Rayl

47

sequenced, phased, and vector are types of ____

operations

48

the beam width @ any location depends on

wavelength, aperture, distance from the transducer

49

T/F: Attenuation increases with an increase in wavelength.

False

50

lateral resolution is equal to ____

beam diameter

51

diagnostic ultrasound transducers generate a ____ of sound into the body

pulse

52

Pulsed ultrasound consists of ___ separated by ___ of time

pulses ; gaps.