Exam #1 Flashcards
Definition of Unrelated?
Two items that are not associated
Definition of Directly related/proportional?
When one item increases, the other increases
Definition of Inversely related/proportional?
When one item increases, the other decreases
Definition of Reciprocal relationship?
Special type of inverse relationship where the numbers when multiplied together equal 1
Definition of Transverse waves?
Particles move in a direction that is perpendicular to the direction that the wave moves or propagates
Definition of Longitudinal waves?
Particles move in the same direction that the wave propagates
Sound is a?
Mechanical wave aka longitudinal wave
Definition of Amplitude, units, typical value?
Bigness of a wave aka the difference between the maximum value and the average value of an acoustic variable
Units: Decibels (dB), Pascals, g/cm^3, cm, mm, um
Typical value: 1-3 MPa
Definition of Frequency, units, typical value?
The number of cycles that occur in one second
Units: cycles/second
Typical value: 2-15MHz
Definition of Period, units, typical value?
Time it takes a wave to go one complete cycle aka the start of one cycle to the start of the next
Units: microseconds, seconds, hours, days
Typical value: 0.06 to 0.5 us
Definition of Power, units, typical value?
Rate of energy transfer
Units: WATTS
Typical value: 0.004 to 0.09 WATTS
Definition of Intensity, units, typical value?
Concentration of energy in a sound beam
Units: watts/square centimeter (W/cm^3)
Typical Value: 0.01 - 300 W/cm^3
Definition of Wavelength, units, typical value?
The distance or length of one complete cycle
Units: mm, cm, M
Typical value: 0.1 - 0.8mm
Wavelength refers to?
Distance
Period refers to?
Time
Definition of Propagation Speed, units, typical value?
Rate at which a sound wave travels through a medium
Units: m/s
Typical value: 500 - 4000 m/s
Definition of Pressure and units?
Concentration of force in an area
Units: Pascals (Pa)
Definition of Density and units?
Concentration of mass in a volume
Units: kg/cm^3
Definition of Distance and units?
Measure of particle motion
Units: cm, mm, um
Definition of Pulse duration, units, typical value?
Actual time from the start of a pulse to the end of that pulse
Units: units of time (us)
Typical value: 0.3 to 2.0 us
Definition of Pulse Repetition Period and units?
Time from the start of one pulse to the start of the next
Units: ms (units of time)
Definition of Pulse Repetition Frequency, units, typical value?
Number of pulses that an ultrasound system transmit into the body each second
Units: Hz or per second
Typical value: 1,000 to 10,000 Hz or 1,000 - 10,000 pulses per second
Definition Duty factor, units, typical value?
The percentage or fraction of time that a system transmits a pulse
Units: none
Typical value: 0.2 to 0.5%
Definition Spatial pulse length, units, typical value?
Distance that a pulse occupies in space from the start to the end of a pulse
Units: mm (any unit length)
Typical value: 0.1 - 1.0 mm
Pulse duration deals with?
Time
Pulse length deals with?
Length
Wavelength and Frequency are?
Inversely related/proportional
Period and Frequency are?
Reciprocals and inversely related
Power and Amplitude are?
Directly proportional
When Intensity increases, power and amplitude?
Increase
Stiffness and Speed are?
Directly related
Density and Speed are?
Inversely related
Pulse Duration is ___ ____ to period?
Directly proportional
Pulse Duration is ______ ______ to frequency?
Inversely proportional
Spatial Pulse length is ____ ____ to wavelength?
Directly proportional
Spatial Pulse length is ____ ____ to frequency?
Inversely proportional
Pulse repetition period is ____ to period?
Unrelated
Pulse repetition period is only ____ to depth of view?
Related
Pulse repetition frequency and depth are?
Inversely related
Pulse repetition frequency is ____ to frequency?
Unrelated
Pulse repetition frequency is only ____ to image depth?
Related
PRP and PRF are?
Inversely related and have a reciprocal relationship
PRF and duty factor are?
Directly proportional
Duty factor is ___ ____ to image depth?
Inversely related
Distance and Attenuation are?
Directly related
Frequency and Attenuation are?
Directly related
Scattering is ____ ____ to Frequency?
Directly related
Absorption is ___ ___ to Frequency?
Directly related
How are normal incidences different from oblique incidents?
Normal incidence:
Sound beam strikes the boundary at exactly 90 degrees (perpendicular, orthogonal, right angle, 90 degrees)
Oblique incidence:
Occurs when incident sound beam strikes the boundary at any other angle than 90 degrees
Which parameter is the only parameter determined by BOTH the source and the medium?
Wavelength
Which parameter is only solely determined by the medium?
Speed
What is Attenuation?
As sound waves propagate through the body, they move from medium to medium creating weak reflections which are the basis for the images that we create as we scan
THE WEAKENING OF SOUND WAVES AS THEY TRAVEL may change direction
Aka the decrease in intensity, power, and amplitude determined by path length and frequency of sound
Definition of Reflection?
The portion of the wave energy that is redirected back to the transducer 2 types specular and diffuse
What is Scattering?
Random redirection of sound in many directions
What is Absorption?
Occurs when ultrasound energy is converted into another energy form such as heat
What is Refraction?
change in direction of wave propagation when traveling from one medium to another
only occurs if there is oblique incidence and different propagation speeds through 2 media
refraction is transmission with a bend
Pulse Repetition Period vs Pulse Repetition Frequency?
Pulse Repetition Period:
1 pulse duration + 1 listening time
Transmit time “on time” and Receive time “off time”
Pulse Repetition Frequency:
Extending or delaying the pulses being sent from the sound source
When depth increases?
PRP is longer and lower PRF
When depth decreases?
PRP is shorter and higher PRF
What is the speed of sound as it travels through a tissue? UNITS important
1540 km/s aka 1 mile per second
What is the difference between Constructive and Destructive waves?
Constructive interference: when several in-phase waves come together to form a single wave of greater amplitude than any of the original in-phase waves
Destructive interference: when a pair of out-of-phase waves come together and cancel out each other’s amplitude resulting in a single wave of lesser amplitude than either of the original out-of-phase waves
Label diagram of a wave:
- period
- wavelength
- frequency
- amplitude
Period is determined by?
The sound source only
Frequency is determined by?
The sound source only
Amplitude is determined by?
The sound source only
Power is determined by?
The sound source only
Intensity is determined by?
The sound source only
Wavelength is determined by?
BOTH the sound source and the medium
Propagation speed is determined by?
The medium only
Speed is determined by?
ONLY PARAMETER SOLELY DETERMINED BY THE MEDIUM
What is the difference between continuous wave ultrasound and pulsed wave ultrasound?
Continuous wave ultrasound:
transducer has 2 crystals one for sending one for receiving
it sends and receives at the same time
DOES NOT produce an image
Pulsed wave ultrasound:
one crystal that turns on and off (on to send and off to receive)
sends the sound in short bursts
consists of individual cycles that propagate as a single unit to CREATE an image
What is infrasound?
When frequency > 20 Hz below the threshold of human hearing
What is acoustic/audible sound?
Between 20 Hz and 20,000 Hz
What is ultrasound?
When frequency is higher than 20,000 Hz or 20 kHz
What is half value layer thickness?
Thin half-value:
high frequency sound
media with high attenuation rate such as lung and bone
Thick half-value:
low frequency sound
media with low attenuation rate such as water
What makes better quality images: higher frequency or lower frequency?
Higher frequency
