2.1 Ultrasound Physics Flashcards
1
Q
Ultrasound is:
A
mechanical energy (vibration) that travels through a medium (tissues)
2
Q
what is the unit of measurement for ultrasound?
A
Hz (the number of sound waves/second)
3
Q
medical ultrasound is in the range of:
A
2.5-15 MHz (Mega Hz)
4
Q
human hearing is in the range of:
A
20-20,000 Hz
5
Q
main physical property behind ultrasound:
A
the piezoelectric effect
6
Q
the piezoelectric effect
A
Property of certain materials to create voltage when mechanically deformed; * produced by passing an electrical current through a piezoelectrical crystal
7
Q
pulse repetition frequency
A
the number of pulses per unit of time
8
Q
amplitude
A
- The strength of the sound beam.
- The difference between the maximum value and the average
- NOT the difference between the maximum and minimum values of the wave.
9
Q
power
A
- Rate of work, ability to do work.
- Units: Watts
10
Q
Power ______ as the sound propagates through the body?
A
decreases
11
Q
Intensity
A
- Concentration of energy in a sound beam.
- Units: watts/cm2
12
Q
Intensity is _______ proportional to power.
A
directly
13
Q
compression
A
high pressure waves
14
Q
rarefraction
A
low pressure waves
15
Q
Zones: near
A
the region of a sound beam in which the beam diameter decreases as the distance from the transducer increases
16
Q
Zones: focal
A
the region where the beam diameter is most concentrated giving the greatest degree of focus
17
Q
Where is the BEST (sharpest) image obtained?
A
It depends on the transducer
18
Q
Zones: Far
A
the region where the beam diameter increases as the distance from the transducer increases
19
Q
absorption
A
loss of US energy due to its conversion to another form, such as heat or intracellular vibration
20
Q
acoustic impedance
A
the resistance to sound transmission through a medium
21
Q
attenuation
A
loss of sound energy when the wave travels through tissue due to absorption, reflection, and scattering of sound energy
22
Q
doppler effect
A
a change in sound frequency due to motion (i.e. flow) between a sound source and the receiver (target)
23
Q
doppler effect: change in sound frequency is said to be POSITIVE when…
A
the receiver is moving toward the source
24
Q
doppler effect: change in sound frequency is said to be NEGATIVE when…
A
the receiver is moving away from the source
25
echnogenicity
degree of brightness displayed in an ultrasound image
influenced by the amount of beam returning to the transducer (reflected) after it encounters a target structure
26
frequency
number of cycles/sec
INVERSE of wavelength
27
interface
boundary layer between tissue layers of different acoustic properties -- why we use gel
(i.e. change in medium from one type to another)
28
resolution
ability to distinguish 2 structures that lie close to each other
29
high resolution, two structures appear:
separate
30
low resolution, two structures appear:
like one
31
scattering
process by which ultrasound waves are force to deviate from reflection due to irregularities in the reflective surface
32
wavelength
distance between two consecutive peaks or troughs of a wave
33
period
the time required to complete a single cycle
34
unit of measurement for period:
time units—seconds, hours, milliseconds
35
the period is determined by:
the sound source (transducer)
36
frequency (repeat)
the number of cycles of acoustic variable that occur in one second
37
unit of measurement for frequency:
Hzf
38
Frequency and period are __________ related
inversely
39
frequency is determined by:
the sound source (transducer)
40
wavelength
length or distance of a single cycle
41
unit of measurement for wavelength
any length unit—meter, mm, micrometers
42
wavelength influences ___________ (hint: image quality)
resolution
43
wavelength is determined by:
the sound source (transducer)
44
propagation speed
the rate at which sound travels through a medium
45
unit of measurement for propagation speed:
m/s, mm/μs
46
propagation speed is determined by:
medium
47
by convention, the speed of sound through body tissues is:
1540 m/s
48
what determines how far US waves can travel?
the frequency of the transducer
49
the HIGHER the frequency, the ____ it can penetrate
LESS
50
the LOWER the frequency, the ______ it can penetrate
DEEPERA
51
Attenuation is _______ related to frequency
directly
52
what is the speed of sound through bone?
4000 m/s
53
what is the speed of sound through air? lung?
300; 500
54
The ___________ the frequency of the beam, the _________ resolution the image will have. But, the penetration into tissue will be _________.
HIGHER
MORE
LESS
55
Hyperechoic tissues appear _______ on the screen
bright
56
hypoechoic tissues appear _______ on the screen
opaque
57
the reason that frequency and tissue penetration are inversely proportional is because velocity through a medium is ___________
constant
58
So, if frequency increases or decreases, the wavelength must increase or decrease in the _____________ direction to maintain the constant velocity
OPPOSITE
59
most ultrasound waves are _______; therefore, they ______ enter the body.
reflected; never
60
what is gel used?
to prevent a large difference in impedance when ultrasound passes through two very different materials and causes the majority of US waves to be reflected
61
which transducer design is best used for vascular structures and small parts?
Linear
62
which transducer design is best used for cardiac, upper body, abdomen, and pelvis?
phased array
63
what is the curved array best used for?
abdominal, OB, renal, urologic
Ex: gastric ultrasound
64
which transducer design has a higher frequency, linear or curvilinear?
linear
65
which transducer design is better for looking at a smaller area and gauging depth, linear or curvilinear?
linear
66
this probe gives a wider angle of view:
curvilinear
67
hyperechoic structures that tend to appear white on screen and why?
bone; pleura (diaphragm), and tendons
reflects majority of sound waves
68
isoechoic structures that tend to appear in various shades of gray on screen and why?
most solid organs; thick fluid
allow some sound waves through but reflect others
69
another term for isoechoic
echogenic
70
hypoechoic structures appear black on screen and why?
fluid within a cyst, urine, blood
allow most sound waves through
71
how do veins and arteries appear on screen?
anechoic, round structures
72
distinguish how veins and arteries appear on screen:
veins are collapsible with increased pressure
arteries are pulsatile and non-compressible
73
how does fat and muscle appear on ultrasound?
hypoechoic background with hyperechoic streaks
74
how to distinguish fat and muscle on ultrasound
- fat is primarily superficial
- muscle tissue has a "different appearance" ...
75
how does bone appear on ultrasound?
hyperechoic and bright, with an acoustic shadow below
76
why does an acoustic shadow occur below bone?
due to the inability of ultrasound waves to penetrate the structures below
77
how do nerves appear in the supraclavicular area?
HYPOechoic and in bundles
(d/t nerve fibers within the nerve)
78
how do infraclavicular and lower extremity nerves appear on ultrasound? on long axis?
HYPERechoic
on long axis they appear speckled
79
distinguish supraclavicular from infraclavicular nerves:
supraclavicular = hypoechoic
infraclavicular = hyperechoic
80
how do tendons appear on ultrasound?
hyperechoic; but the "streaks" appear longer than the nerves
(this is due to the composition of the tendon's outer layer)
81
how do tendons appear on long axis view?
with internal hyperechoic lines
82
Short Axis AKA...
cross-sectional
83
Long Axis AKA...
longitudinal
84
what does PART stand for when it comes to image acquisition?
P: Pressure
A: Alignment
R: Rotation
T: Tilt
85
alignment
SLIDING of the transducer along the body part/surface being examined
86
rotation
TWISTING of the probe during examination
87
tilt
CHANGING THE ANGLE of the transducer while keeping it in place
88
which movement of the transducer is most useful to align the needle with the transducer beam?
ROTATION
89
which movement of the transducer is most useful in aligning the beam PERPENDICULAR to the target in order to improve image quality?
TILT
90
which movement of the transducer is most helpful in locating the target and needle?
ALIGNMENT
91
the three basic adjustments on the ultrasound machine settings are:
depth, gain, and focus
92
if the depth is set too high, the _________ and _______ of the target structure are decreased
definition; resolution
93
the depth should be set __________ (____ cm) the distance at which the structure is located
just below; 1-2 cm
94
what is the purpose of gain?
allows for compensating the attenuation of the signal as it travels deep into tissues
95
too low of gain will not allow for:
tissue differentiation
96
too high of gain will cause:
loss of resolution
97
the ideal gain setting is one that allows for:
tissue differentiation
98
the gain should be ________ as the distance to the probe increases
increased
99
increase gain = _______ image
decreased gain = _______ image
brighter; darker
100
focus
allows for the concentration of the beam to be at its sharpest when it reaches the area of interest
101
focus is based on the:
focal zone of the ultrasound beam
102
focal zone of the ultrasound beam
where the beam is at its narrowest (diameter) and density of the waves is highest
103
crossbeam
method by which the beams from the transducer form a cross-weave
(this allows for better definition and sharper images)
104
doppler or color flow allows for:
identification of blood vessels based on flow
105
doppler: red color typically indicates
flow TOWARDS the transducer
106
doppler: blue color typically indicates
flow AWAY from the transducer
107
in-plane needle insertion
refers to the needle being inserted and followed in the same plane as the ultrasound beam, AKA PARALLEL
108
out of plane needle insertion
needle is inserted perpendicular to the beam
109
which type of needle insertion allows for visualization of the entire needle during the procedure?
in plane
110
which type of needle insertion is a more difficult approach, since you can only see a portion of the needle shaft?
out of plane
111
what are the 3 basic ergonomic principles to maximize patient and provider comfort when using ultrasound?
patient positioning
equipment positioning
operator positioning
112
artifacts
false images or shadows that may confuse what you see
ex: acoustic, anatomic, optical illusion
113
acoustic shadows are caused by:
bone
114
acoustic enhancement is seen as:
shadows usually under blood vessels
115
tissue reverberation is caused by:
strongly reflective tissues such as the pleura, seen as an area of brightness under the structure
116
reverberation artifacts
caused by needles and other structures
117
air artifact is usually seen when (2):
1- the transducer loses contact with the skin
2- there is not enough conductive media
118
what are the most common sources of confusion that cause anatomic artifact?
tendons and nerves
119
how can the provider identify nerves?
nerve stimulator
120
blood vessels with thrombi can be confused with:
neural structures
121
enlarged lymph nodes can be mistaken for:
neural tissue, occluded vessels
122
how can edema cause artifact? (2)
1- may disfigure the appearance of anatomic structures, including nerves
2- may change the electrical thresholds, making the location of nerve tissue difficult
