Physics Boards Flashcards
(282 cards)
0
Q
Nyquist limit?
A
1/2 prf
1
Q
Near zone length?
A
6
2
Q
What determines the range of brilliancies within a displayed image?
A
Contrast
3
Q
A television image is made up of how many closely spaced horizantal lines?
A
525
4
Q
Bistable images , which only appear in black and white have what kind of contrast?
A
High
5
Q
What determines the brilliance of the displayed image?
A
Brightness = brilliance
6
Q
Greyscale imaging was first made possible with the use of what?
A
Scan Converters
7
Q
What does the scan converter do?
A
Ultrasound info is obtained from pulses emitted by a transducer that penetrates into the body. Multiple penetrations, or spokes, are needed for each two dimensional image. However television displays video infromation as 525 interlaced , horizantal lines divided into two fields. THE SCAN CONVERTER TRANSLATES THE INFORMATION FROM THE SPOKE FORMAT INTO VIDEO FORMAT.
8
Q
The process of storage of information into the scan converter is called what ?
A
Writing. Image is then read from the scan converter for display on the CRT
9
Q
What are analog #’s?
A
Real world numbers that are found in our everyday lives
10
Q
What are digital numbers?
A
associated with a computer device
11
Q
What is Spacial Resolution?
A
Image detail
12
Q
What are the four limitations of analog scan converters?
A
image fade
image flicker
instability
deterioration
13
Q
Digital scan converters use computer technology to convert images into numbers using a process called?
A
digitizing
14
Q
What is a pixel?
A
The smallest building block of a digital picture?
15
Q
What is the number of picture elements per inch?
A
Pixel density
16
Q
Higher pixel density is achieved what?
A
smaller pixels
17
Q
Spacial resolution is improved with high or low pixel density?
A
High
18
Q
Low pixel density = ?
A
Larger pixels
19
Q
What is the smallest amount of computer memory?
A
Bit 0’s and 1’s
20
Q
What is a byte?
A
A group of 8 bits of computer memory
10011111
A word of computer memory is made up of 2 bytes or 16 bits
21
Q
More shades of grey appear on an image with more what?
A
More bits per pixel.
22
Q
Images that have many shades of grey have superior what?
A
Contrast resolution
23
Q
More shades of grey = ?
A
IMPROVED CONTRAST RESOLUTION
MORE BITS PER PIXEL
24
How do you determine the number of shades of grey there are in an image?
Multiply 2 by itself the same number of times as there are bits
2 to the (number of bits) power)
25
How many possible shades of grey are displayed with 5 bits of memory?
32
mulitpling 2 by itself 5 times yield 32
2x2x2x2x2 = 32
26
Any processing of the reflected signals before storage is called what?
pre-processing.Pre processing alters the image data forever and cannot be reversed or "un-done".
27
What is the manipulation of an image after storage in the scan converter, a process that can be reversed or applied to a frozen image?
Post Processing
28
Read magnification occurs during what stage of processing?
Post processing. It can be catorigized by the number of pixels or scan lines in the magnified image is the same as the original image. MAGGING AFTER YOU HAVE ALREADY AQUIRED.
29
Write magnification occurs during what processing stage?
pre processing. It is applied during data aquisition. Mag'ing DURING SCANNING
30
Harmonic imaging = ?
2 x fundamental frequency
31
Contrast harmonics are created because of uneven changes in the size of the bubble when exposed to a sound beam of adequate strength. What is this called?
resonance
32
The amount of contrast harmonics produced may be estimated by a number called what?
Mechanical Index
33
The mechanical index depends on what ?
frequency of transmitted sound
| pressure of the sound wave
34
Harmonic production (as well as the mechanical index) increases with :
more pressure
| lower frequency
35
what is the frequency used in ultrasound?
2 to 4mz
36
low MI =
less than .1
high frequency sound
low beam strength
37
medium mi(high mi)=?
.1 - 1.0 mi
resonance
low frequency
38
highest mi =
greater than 1
bubble disruption
lowest frequency
39
What are the 2 characteristics of contrast agents?
the nature of the outer shell
| the gas that fills the microbubble
40
When are tissue harmonics created?
During transmission
41
Beams that are least likely to create artifacts are most likely to create what?
harmonics
42
What causes the strongest harmonic signal?
Contrast harmonics because bubble diruption creates the strongest harmonic signal.
43
sound in compression travels ______ than sound in rarefaction
faster
44
Volume of blood moving at a particular time?
flow
45
When exposed to the high pressure component of a sound wave, a microbubble will ________.
shrink
46
In phasic flow, blood accelerates and decelerates from what?
Respiration
47
Phasic flow appears in _________ circulation.
venous
48
Pulsitile flow occurs in _________ circulation.
arterial
49
Steady flow occurs when?
In venous circulation when an individual stops breathing for a moment. (decrease in venous return)
50
What exist when the flow streamlines are aligned and parallel and blood travels at individual speeds?
Laminar Flow
51
What are the 2 forms of laminar flow?
Plug Flow
| Parabolic Flow
52
What occurs when all of the layers and blood cells travel at the same velocity?
plug flow
53
What kind of flow is it when the velocity is highest in the center of the lumen and gradually decreases to its minimum at the vessle wall? Has a bullet shaped profile?
Parabolic Flow
54
What predicts whether flow is laminar or turbulant?
Reynold's number
55
What is characterized by chaotic flow patterns in many different directions and at many different speeds?
turbulent flow
56
Sound associated with a turbulent flow is called what?
murmur or a bruit
57
Tissue vibration associated with turbulence is called what? It can also be described as a palpable murmer?
a thrill
58
How does blood flow from one location to another?
energy gradient
59
A form of potential or stored energy. It has the ability to perform work
pressure energy
60
THis type of energy is a form of stored;potential energy and is associated with an elevated object
Gravitational energy
61
A narrowing of the lumen of the vessel
Stenosis
62
Pressure Gradient = ?
Flow x Resistnace
| Pressure gradient increases when either the flow increases or resistance increases
63
Voltage = ?
current x resistance
64
What is the typical resistance of veins?
low resistance
65
The shape of a vein during normal function is:
flattened or hourglass shaped
66
As more pressure occurs within the vein, what happens to the shape?(during excercise when venous flow increases)
Becomes more circular
67
The pressure acting to expand the veins is known as what?
transmural pressure
68
What is related to the weight of blood pressing on a vessel measured at a height above or below the heart?
hydrostatic pressure
69
The significance of hydrostatic pressure in clinical medicine is demonstrated when?
When taking a patients blood pressure.
70
Blood pressure is accurately assessed when the measurement is made at what location?
at the same level of the heart. Blood pressure will obviosley be WAY too high at levels below the heart and WAY to low at levels above the heart.
71
When a patient is supine, what is the hydrostatic pressure?
0. All parts are at the same level of the heart
72
During inspiration, the diaphragm moves downward, the chest cavity expands. This creates what kind of pressure in the chest?
negative
73
Negative thoracic pressure (inspiration), produces a suction that does what to the venous return towards the heart?
Increases
74
During expiration, the diaphram moves upward which increases the thoracic pressure in the chest. Expiration does what to the venous return to the heart?
Decreases
75
During inspiration, the abdominal compression increases abdominal pressure which does what to the venous flow in the legs?
Decrease.
| It increases with expiration(flow to the legs)
76
Doppler shift is also called what?
doppler frequency
77
The frequency does not change when the distance between the sound source and the receiver remains _______.
constant
78
Frequency changes as a result of what?
Relative motion between the source and the reciever
79
What principle is used to measure red blood cell velocities?
Doppler principle
80
What is the doppler shift?
The low frequency that rides on top of the much higher transducer's transmitted frequency
81
The process of extracting the low doppler frequency from the higher transducer frequency.
demodulation
82
What is the formula for doppler shift?
Doppler Shift = reflected frequency - transmitted frequency
If the doppler shift is a positive number, that obviously means there is a positive shift.
Transmitted frequency - 5,000,000
Reflected Frequency - 5,003,000
shift = + 3,000
83
When RBC's move toward the transducer, the doppler shift is _____, that is , the reflected frequency is _______ than the transmitted frequency.
positive; higher
84
What is the equation for Doppler Shift?(elongated)
Doppler shift= 2 x speed of blood x transducer frequency x Cos 0
_______________________________________
propagation speed of blood
85
My grandsons bag of marbles contain 30 marbles, If he decrease his bag by a factor of three, how many marbles does he have?
```
10.
30/3 = 3
# at first divided by the factor
```
86
Simplify the expression 10 to the -3 power?
.001
-3 is milli which is thousandths
```
.1 = tenths
.01= hundreths
.001= thousanths
```
87
Simplify the expression 10 to the 3rd power
```
1000
+3 is thousands
10=1 take 1 and move it three to the right and you get thousand
+1 = tens
+2= hundreds
+3 = thousands
```
88
What is the reciprocal for the prefix milli? 10 to the -3?
kilo
89
.00875 equals what in notation?
8.75 x 10 -3 power
90
Density is defined as ?
mass per unit volume
91
What are the acoustic variables?
density
motion/distance
pressure
temperature
92
A sound wave is a traveling variation in quantities called:
acoustic variables
93
With longitudinal waves , particles oscillate ______ to the direction of the sound beam?
parallel
94
If the amplitude is doubled, what happens to the intensity?
Increased by a factor of 4
95
Bulk modulus refers to which of the following quantities?
stiffness
96
Arrange the following media in order in terms of propogation speed from lowest to highest
bone, muscle, air , fat
air - fat - muscle - bone
97
What is the formula for wave lenght?
Propogation speed / frequency
98
Pulse duration =?
```
# of cycles x period
0r
```
of cycles / frequency
99
Spacial pulse length= ?
of cycles x wavelength
or
of cycles / frequency
100
Common SPTA intensities are greater or less than 720 mW/cm?
less than 720 mW/cm 2
101
If the intensity transmission coefficent is .74, what is the reflection coefficient?
.26
102
The advantage of a 256x256 image format compared to a 64x64 image format is = ?
more pixels = greater spatial res/detail
103
Elastography is an ultrasound imaging mode that depicts tissue _______.
stiffness
104
A bistable picture is represented by only two shades , black and white, and requires _________bits.
1
2 to the x power(number of bits) = 2 shades(black and white)
2 to the 1 power will give you 2
105
The ability of grey scale display to distinguish between echoes of slightly different intensities is called _________
contrast resolution
106
PACS?
Picture Archiving and Communications System
107
The averaging of sequential frames together to provide a smoother image appearance is called __________.
persistence
108
In which excitation technique do ensembles or trains of pulses drive the transducer to generate a single scan line?
coded excitation
109
What is the purpose of write zoom?
Improve spacial resolution of the displayed image
110
How many pixels compose an image in which the matrix is described as 500 rows and 500 columns?
250,000
111
What is the Reynolds number that predicts when turbulence will occur?
2000
112
What is the auscultatory consequence of turbulent flow?
bruit
113
What is neccesary in order for blood to flow?
pressure gradient
114
What of flow is occurring when the average flow velocity is 1/2 the maximum velocity in the center of the vessel?
parabolic flow
115
What is another term for gravitational potential energy?
hydrostatic pressure
116
What is the definition of volumetric flow?
amount of fluid moving past a reference point in time
117
What type of arterial flow demonstrates a constant velocity across an entire vessel?
plug flow
118
The pressure difference between the inside of the vein and the tissue outside is known as:
transmural flow
119
In order to maintain flow, if the area of a vessel increases, what must happen to the velocity of the flow?
it must decrease
120
What indicates turbulent flow?
Reynolds number
121
When sound travels faster through compressed tissue than it does through expanded tissue, the type of propagation speed present is __________.
non - linear
122
Where is harmonic energy located?
near field or center of the beam
123
What is the ability of a test to predict disease?
sensitivity
124
Test objects evaluate?
detail resolution
125
What does development of a quality assurance program ensure?
image consistency
126
What assessment does a quality assurance provide?
image quality
127
The ability to place reflections in their proper position no matter the imaging orientation describes :
registration
128
The ability of a test to predict absence of disease?
specificty
129
What describes the mechanistic approach to the study of bioeffects?
cause-effect
130
What does 3 db mean?
1/2 the original intensity
131
What is the formula for duty factor?
Pulse duration/ PRP
132
What is intensity?(formula?)
amplitude squared
133
If the amplitude of a sound wave is increased threefold, the intensity will:
increase 9 fold
134
An echo from which reflector is most dependent on the angle of incidence?
specular reflector
135
If the propagation speed through the second medium is less than the first medium, the transmission angle is ______ than the incident angle.
less
136
What is normal incidence?
= to 90 degrees
137
What is the Reynolds number for laminar flow?
less than 1500
138
What is the Reynolds number for Turbulent flow?
Greater than 2000
139
What is inertia?
tendency of fluid to resist changes in its velocity
140
Inertial energy loss occurs during three events:
1. pulsatile
2. phasic
3. stenotic
141
If resistance increases, volumetric flow will _______.
increase
142
Energy is neither created nor destroyed as it flows through a vessel. This is known as:
continuity rule
143
When venous flow in the legs decreases, venous flow to the heart _______.
increases
144
Another name for RBC's is :
erythrocytes
145
Hydrostatic pressure is related to the weight of blood measured where?
At a height above or below the right atrium
146
What determines the shape of a vein?
transmural pressure
147
The typical hematocrit % is
45%
148
What is the simplified law of hemodynamics?
Pressure Gradient= volumetric flow * Resistance
149
What causes an increase in pressure gradient?
Flow increase and resistance increase
150
Hydrostatic Pressure = pgh
p=density
g=?
h=?
```
g = gravitational pressure
h= height of column of blood
```
151
Where is hydrostatic pressure most accurate?
right atrium
152
At locations below the heart, hydrostatic pressure is:
positive
153
What is the cardiac flow rate?
5000ml/min
154
What is the formula for doppler shift?
F dop = F (recieved) - Frequency (transmitted)
155
What is the doppler equation?
Fdop = 2 ( V rbc's * Frequency * Cos 0
__________________________
c(propoagtion speed of tissue-1.54)
156
Doppler frequencies indicate speed or velocity?
velocity
velocity is defined by magnitude and direction
speed is strictly magnitude
157
When an angle exist between the direction of flow and the sound beam, the neasured velocity is ________ than the true velocity.
less
158
measured velocity = true velocity * ________.
cos0
159
Phasic flow appears in _________ circulation.
venous
160
Pulsitile flow occurs in _________ circulation.
arterial
161
Steady flow occurs when?
In venous circulation when an individual stops breathing for a moment. (decrease in venous return)
162
What exist when the flow streamlines are aligned and parallel and blood travels at individual speeds?
Laminar Flow
163
What are the 2 forms of laminar flow?
Plug Flow
| Parabolic Flow
164
What is the cosine of 0 degrees?
+1
164
What is the cosine of 180 degrees?
-1
165
What is the cosine of 60 degrees?
.5
| The cosine of 60 degrees is .5 ; therefore the measured velocity at 60 degrees is 1/2 the actual velocity
166
If red blood cells travel at 2m/s and at a 60 degree angle to the sound beam, what will the doppler report?
1 m/s
167
What is the cosine of a 30 and 45 degree angle?
.87 and .71
168
What dose non directional doppler or non coherent predict?
The pressence of blood velocity and NOT the direction
169
What does Bidirectional doppler detect?
Distinguishes the direction of flow toward or away from the transducer
170
What is phase quadrature or quadrature detection?
A signal processing technique for bidirectional doppler
171
What is the main disadvantage of CW?
range ambiguity-NO SPECIFICITY
172
How many crystals does a PW doppler take?
```
1 crystal
dampened PZT
low Qfactor
Wide BW
Lower sensitivity
```
173
How many crystals for a CW doppler?
```
2
undampened PZT
High Q factor
Narrow Bandwidth
High sensitivity
```
174
What creates aliasing?
HIGH FREQUENCY TRANSDUCERS
HIGHER BLOOD VELOCITIES
DEEP GATE - DEEPER IMAGING = LOW PRF
175
What are the 5 techniques that are used to avoid aliasing artifact?
1. Adjust the scale to its maximum
2. Select a lower frequency transducer
3. Select a new ultrasonic view with a shallower sample volume.
4. Use continuous wave doppler
5. adjust the baseline
176
Simultaneous anatomic imaging as seen in CW(one crystal listens and one recieves) is called:
duplex imaging
177
What is the greatest advantage of pulse doppler?
range resolution aka
range specificty
freedom from range ambiguity artifact
178
What is variance mode on a color map?
distinguishes laminar flow from turbulent flow
laminar flow is on the (L) Left -and-
turbulent flow is on the right
179
What does the black area in the center of a color doppler represent?
0 doppler shift
180
What is power doppler?
Determines the presence of flow only
181
With color doppler, multiple pulses are used to accuratley determine blood cell velocities. Theses multiple pulses are called:
packets or ensemble
182
Low frequency doppler shifts that are usually located at the baseline are called
clutter
| with color its called ghosting artifact
183
What is a special form of mirror image artifact that appears as an identical image both above and below the baseline?
crosstalk
184
What is performed to assess the mean velocity of color doppler?
autocorrelation
185
What tool breaks complex signals into its basic building blocks and identifies individual velocities which make up the reflected doppler signal?
Spectral analysis
2 forms:
1. FFT - cw and pw
2. Autocorrelation - color doppler
186
THe region between the baseline and the spectrum is:
the spectral window
187
A wider range of velocities and doppler shifts within the sample volume is a situation known as :
spectral broadening
188
What is a quantitive , doppler derived measurement of the vascular resistance of a segment of the arterial system?
Resistive index
189
which is the horizontal axis?
x axis
190
what does the z axis represent?
brightness
191
What does it mean to INCREASE by a factor of two or three?
To multiply by 2 or multiply by 3
192
What does it mean to decrease by a factor of 2 or 3?
divide by 2 or divide by 3
193
What is the formula for perimeter of a circle(circumfrence)?
c= pie x diameter
or
c = pie(2 x Radius)
194
What is the formula for area of a square or rectangle?
area = lenght x width
195
What are the units for perimeter?e
meter
196
What are the units for area?
meters squared
197
What are the units for volume?
The units for volume are meters cubed
198
What is the formula for area of a circle?
A= pie x radius squared
199
What is the formula for volume of a square or a rectangle?
volume = length x height x width
200
Sound waves are what kind of waves?
mechanical
201
Longitudinal waves propogate by a series of particle ________ and __________
compression and rarefaction
202
What are acoustic variables?
```
physical quantities that change as sound travels through the medium:
pressure
density
temerature
distance - particle motion
```
203
What is pressure?
pressure is the concentration of force or force per area
204
What is density and what is the formula?
Density is the concentration of mass per volume
density = mass/volume
205
What are the 7 acoustic parameters?
```
Wavelenght
Amplitude
Power
Propogation Speed
Period
Intensity
Frequency
```
206
What is interference?
Waves that are at the same location at the same time.
207
What is constructive interference?
Constructive interference occurs between in phase waves and results in a LARGER amplitude of a new wave.
208
What is the definition of period?
Time to complete one cycle
| Time from the start of one cycle to the next
209
What is the definition of frequency?
The frequency is known as the number of events for a specified duration of time
210
What is the diagnostic ultrasound range ?
1 MHZ - 15 MHZ
211
What are the frequencies for therapeutic ultrasound?
.5 MHZ - 3 MHZ
212
What are the 3 bigness parameters?
Amplitude
Power
Intensity
213
What is the definition of Amplitude?
Max variation that occurs in an acoustic variable.
| The difference between the mean and the maxima or the the mean and the minima
214
What determines Amplitude? Amplitude can be measured in ANY of the acoustic variables-
volts - pascals - decibels - distance
```
Initially, its the sound source. As the beam transmits through tissue, the amplitude will decrease and this is known as attenuation.
Other names for amplitude include:
acoustic amplitue
acoustic intensity
output power
```
215
What is the definition of power?
Power is known as the rate at which work is performed. It is measured in units of watts.
Determined by the sound source initially , and then by the medium through attenuation.
216
What happens to power if the amplitude is decreased by a factor of 3?
~Power = amplitude squared
amplitude = 1/3
since its squared: 1/3 x 1/3 = 1/9!
217
What happens to power if the amplitude is tripled?
power = amplitude squared
amplitude = 3
3 x 3 = 9 fold
218
What is the formula for intensity?
intensity = power/area
| intensity is porportional to the amplitude squared
219
What is the definition of wavelenght?
length or distance of one cycle
| Determined initially by the sound source, then the medium through attenuation
220
What is the definition of intensity?
Concentration of energy in a sound beam.
Determined initially by the sound source only , then affected
by the medium through a process called attenuation
221
What is the formula for wavelenght?
WL = prop speed/ frequency
222
What is elasticity?
Ability of a solid object to return to its original shape after distortion by a force
223
What is compressibility?
Measure of how much the volume of a material changes for a given distorting force
224
What is stiffness?
Ability of an object to resist compression.(inverse to compressibility and elasticity).
225
Sound travels faster in _______ and slower in _________.
```
faster in solids and slower in gasses
.3 air
.5 lung
1.54 soft tissue
3.5 - 4 bone
```
226
What does a high bulk modulus mean?
Not compressible or Stiff / inelastic
227
An increase in stiffness = an increase in ________.(hint s = s)
Speed.
| An increase in density = a decrease in speed
228
What has the greatest affect on propagation speed of a medium?
stiffness or compressibility
229
What determines the three bigness parameters and are they adjustable by the sonographer?
Initially determined by the sound source and then decreased by attenuation. They are ALL adjustable by the sonographer.
230
Wavelength is the only parameter that is determined by the _________ and the _______.
sound source
| medium
231
What is the main advantage of Pulsed Wave ultrasound?
range resolution
232
What is the formula for pulse duration? What is pulse duration?
of cylces x period
```
# of cycles / frequency
Pulse duration is the TIME from the start of one pulse to the end of the same pulse. It is the actual time that a pulse is on.
```
233
What is the equation for duty factor?
PD/ PRP x 100
| Duty factor is a percentage
234
What is duty factor?
% of time that sound is transmitting. -
| determined by the sonographer by adjusting the depth of view
235
Is Pulse duration and Spacial Pulse length adjustable by the sonographer?
NO!!!!
236
What does shorter SPL give you as far as resolution?
Better axial resolution/detail resolution
237
How does the sonographer adjust the duty factor?
adjusting the imaging depth. Since duty factor= pd/prp,
increasing the imaging depth, which would mean an increase in prp, would essentialy decrease the duty factor
Duty Factor = PRF
when prf increases, the duty factor increases
238
What is the definition of PRF?
The number of pulses that are sent into the body in one second
239
What does the term temporal mean?
Refers to all time; transmit and recieve
240
What does the term pulsed refer to?
refers TO THE AVERAGE INTENSITY FOR THE PULSE DURATION ONLY
241
What is spacial peak intensity?
The beams intensity at the location where it is maximum.
242
What is the spatial avg intensity? hint: cross sectional area.
The average intensity across the beam's entire cross sectional area. Think of spacial as "in space" or " area".
243
What is the temporal peak intensity?
The point in time where the beam is at its maximum intensity
244
What is I max?
The average intensity during the most intense half cycle. The half cycle is "half" of one full cycle in a wave. Basically it is the avg of the max amplitude.
245
What is the Pulse Average?
The average of intensities during the pulse duration or TRANSMIT TIME
246
What is the temporal avg?
The average intensity during the entire pulse repetition period; which is from the beginning of one pulse to the beginning of the next pulse. This is the only intensity measured at BOTH THRANSMIT AND RECEIVE TIMES!
247
What is the duty factor of pulsed ultrasound? The percentage of time an actual pulse is being sent out?
.2%
| 99.8% of the time is when the system is listening and silent and the intensity is 0
248
What are the units for intensity? hint: formula for intensity
Watts/ cm squared
intensity = power/area
or
watts / cm squared
249
The different measurment of intensities is important in the study of ___________. Why do we care about how intense a beam is?
bioeffects
250
Which intensity is the most relevant with respect to tissue heating?
SPTA
Spacial Peak Temporal Average
The average of the TRANSMIT AND RECIEVE TIME
251
What does the beam uniformity coefficient or the SP/SA factor describe?
The spread of a beam in space. The SP/SA factor is unitless with a value of 1 or greater
252
When are the ALL the pulse average's and temporal averages the SAME?
So everything ending with PA or TA equal the same?
SPTA= SPPA AND SATA = SAPA?
During CW because the beam is always on
253
What is the logarithm of 1000? hint: count the numbers of zero for log
3
254
What quantifies relative change of the strength of a sound beam?
decibel or decibel notation
| "the signal strength has doubled" or is "now 1/10"
255
What is the meaning of a 6db change?
3db means the intensity doubled so a 6db change = INTENSITY QUADRUPLED
256
When a waves intensity doubles, what is the relative change in decibel notation?
+3 db
257
When the intensity increases 10 fold, what is the relative change in decibel notation?
+10 db
258
A sound beam had increased from its initial intensity by a factor of 100. How is this described in decimal notation?
Well,
10 x 10 = 100
an increase 10 fold = +10db
10db + 10db = 20db
20db
259
A sound beam has decreased to 1/100 of its initial intensity. How is this described in decimal notation?
1/100 = 1/10 x 1/10
1/10 in decimal notation = -10db
- 10db + -10db = -20db
- 20db
260
What is the method of describing the extent to which a signal can vary and still be processed acuratley?
dynamic range
261
What is the formula for volumetric flow rate?
Q(flow) = P(pressure) x pie x radius to the 4th
___________________________
8 x lenght of vessel x viscosity
262
When does steady flow occur?
in the venous system when the individual stops breathing for a moment
263
What does path lenght and frequency of sound determine?
attenuation
1. the further sound travels, the greater the attenuation and the weaker the beam becomes
2. the HIGHER the frequency, the greater the attenuation
264
Reflection,scattering and absorbtion contribute to:
attenuation
265
Most interfaces are not smooth, but have some irregularities. When a wave reflects off an irregular surface, it radiates in more than one direction. This is called what?
diffuse reflection
266
What has more scatter, more attenuation, and does not create harmonic imaging?
high frequency sound
267
What is the form of scattering when the structure's dimensions are much smaller than the beam's wavelength and the scattering is redirected equally in all directions?
Rayleigh scattering
268
When the boundry is smooth, the sound is reflected in only one direction in an organized manner?
specular
269
Scattering is directly related to what?
frequency
270
What is the formula for TOTAL attenuation?
total attenuation = attenuation coefficient x distance
271
What is the formula for the ATTENUATION COEFFICIENT?
atten coef = 1/2 the frequency in soft tissue
272
What is impedance and what is the formula?
Impedence is the acoustic resistance to sound in a tissue. The formula is:
density of medium x speed
273
Define sensitivity of a diagnostic test?
| How is it calculated?
Sensitivity measures how sensitive the test is in identifying the presence of disease or the probability that a test will be positive when the patient actually has the disease.
True Positive
__________
true positive + false negative
274
Define specificity?
Specificity measures "how specific" the test is in RULING OUT disease.
true negative
___________
true negative + false positive
275
Define the positive predictive value
Positive predictive value test is defined as the probability that the disease is present when the result of the diagnostic test is positive.
This is different than sensitivity, because it has to do with "testing" and EVERYTHING IS POSITIVE
TRue positive
__________
true positive + false positive
276
Define the negative predicitve value.
Negative predictive value is defined as the probability that the disease is not present when the result of the diagnostic test is negative. EVERYTHING IS NEGATIVE:
true neg
________
true negative + false negative
277
Define accuracy
porportion of test that yielded the correct results
278
While performing an ultrasound exam with a 3-MHZ transducer,the sonographer activates the harmonic mode. What is the fundamental frequency?
3 MHZ.
| The fundamental frequency is defined as the frequency of sound wave transmitted by the transducer.
279
Which intensity is best used with respect to bioeffects?
SPTA
| Spacial Peak Temporal Average
280
What is the mechanical index?
number related to the possibility that cavitation will occur.
