review prof Flashcards
How many hertz is 5 MHz
5,000,000
How many milliliters are contain in a bucket filled with 3 liters of fluid?
3000
Sound must travel through a ________
medium
Sound is a _____________, _____________ wave
mechanical, longitudinal
the movements that propel a sound wave
compressions & rarefactions
In this type of wave the particles vibrate/move in a perpendicular direction to the direction of the wave
transverse wave
There are many types of waves in science. Waves that have ________ _________ are sound waves
acoustic variables
this function can be used to measure area of something (measure in cm² or ft²)
ellipse
areas of decreased pressure and density in a sound wave during movement
rarefactions
Sound cannot travel through a ___________
vacuum
units, used for volume
cm³, ft³
unit of measure for Pressure (which is an acoustic variable)
Pascals
the time it takes to complete a single cycle (determined by the sound source).
Period
This setting affects penetration and axial resolution
Frequency
True or False: Percent is a unit
False. Percent is from the Latin adverbial phrase per centum meaning “by the hundred.” It represents the portion of one hundred being considered (one-hundredth) and is not a unit.
In this type of wave the particles vibrate/move in a parallel direction to the direction of the wave
longitudinal wave
What is the range of frequencies found in audible sound?
20Hz-20000Hz
The difference between the average value and the maximum value of an acoustic variable. On a wave diagram, shown as the distance from the rest position to the crest (or trough)
Amplitude
unit for power
Watts
regions of higher density and pressure within a sound wave as it travels
compressions
The rate that work is performed or rate of energy transfer.
This is controlled by the sonographer and is a big factor in bioeffects.
Power
Formula (W/cm²): power divided by area
Intensity
sound waves with frequencies above 20,000 Hz
ultrasound
the number of occurrences within a given time period (usually 1 second)
Frequency
Conversion of sound to heat. Process of attenuation. Creates potential for a bioeffect.
Absorption
Decrease in amplitude and intensity, with distance, as a wave travels though a medium.
Attenuation
Concentration of mass within a volume
(also an acoustic variable)
Density
The amplitude of a wave changes as it moves through the body. What happens?
The amplitude decreases. Determined by the sound source initially, attenuation slowly breaks down the amplitude of the wave as it travels.
A logarithmic unit of sound intensity. the unit for sound.
Decibel
This factor decreases as sound propogates through the body. Intensity is proportional to the AMPLITUDE of the wave SQUARED.
Intensity
sound waves with frequencies below 20 Hz
infrasound
What are the typical values of frequency used by diagnostic ultrasound?
2MHz-15MHz
Relationship between power and amplitude is expressed as….
Power ∞ Amplitude²
(∞ means proportional)
What are the three acoustic variables?
pressure, density, and distance
How many liters are there in 40ml of fluid
0.040
One complete variation of an acoustic variable
Cycle
Time per cycle
Period
Traveling wave of acoustic variables
Sound
A device that converts one form of energy to another
Transducer
the interference that occurs when two waves combine to make a wave with a larger amplitude
Constructive interference
the interference that occurs when two waves combine to make a wave with a smaller amplitude. The waves that combine may be called “out-of-phase”
Destructive interference
The speed that sound waves travel through a medium. Unit- distance over time usually: m/s, mm/µs.
Propagation Speed
The length or distance of a single cycle. A cycle can be measured from any point on a wave to an identical point on the next wave. Determined by the sound source AND the medium.
wavelength
How to determine the wavelength?
Divide the propagation speed (1.54mm/microseconds ) by the frequency
The rate that sound travels through a medium
propagation speed
True or False. A wave of 5MHz and a wave of 3 MHz will both travel the same speed through the liver.
True! All sound, regardless of the frequency, travels at the same speed through an specific medium.
An increase in the stiffness of the medium will increase or decrease the propagation speed.
Increase (S=S)
If frequency increases, period
Decreases
If frequency increases, wavelength _______
Decreases
If the frequency of sound is doubled, what happens to the wavelength?
wavelength will be halved
In diagnostic imaging, short bursts, or pulses, of acoustic _____ are used to create anatomic images.
energy
The time from the start of a pulse to the end of that pulse. This is an inherent feature of the transducer and is not controlled by the sonographer.
Pulse Duration
The typical number of cycles used in clinical imaging is?
2-4
Pulse Repetition Period
The PRP includes the start of one pulse to the start of the next pulse (including the listening time).
When you increase the depth, which increases the Pulse Duration or the Pulse Repetition Period?
The PRP increases. Remember the PD is determined by the probe you select and doesn’t change during the scan.
While the technologist changes the depth they change the:
a. The listening time (PRP)
The sonographer changes only the listening time between pulses.
PRP is determined by the ____________
Depth
Pulse Repetition Frequency
the number of pulses that occur in 1 sec.
PRF is determined by the ____________
Depth
True or False: The sonographer can alter the PRF
True
Depth controls the PRP and that controls the PRF. This alters the Duty Factor as well.
What are the units for Duty Factor?
Duty Factor has no units.
What are the typical values for the PRF in clincal ultrasound?
1,000-10,000 Hz or 1-10 kHz
What type of ultrasound cannot be used to make anatomical images?
Continuous wave
What are typical Duty Factor values?
0.1% to 1%
Very little talking, LOTS of listening.
Formula:
____?_____= # of cycles x wavelength
Spatial Pulse Length
Spatial Pulse Length is determined by __?__
The Source and the Medium
Pulse Repetition Frequency is the reciprocal of ____
PRP
In soft tissue, every 13 microseconds of go-return time means the reflector is ____ in the body
1 centimeter
If an echo enters the body and returns to the transducer in 26 microseconds, how deep was the reflector?
2 cm
The frequency and the ______ are reciprocals
period
A _____ wave needs a medium to propagate
mechanical
A shorter period means a _____ _____
higher frequency
How big or loud a signal is
Amplitude
A change within the medium caused by a wave is called a ____________
variable
Acoustic Imepdance has units of
Rayls
Absorption is the conversion of energy from an acoustic wave to ____.
heat
The absence of a medium
Vacuum
The amount of refraction that occurs is decided by
Snell’s Law
The three mechanical wave interactions that occur within a medium which consititue/create attenuation are:
absorption
reflection
refraction
Normal Incidence
when a beam strikes an interface in a perpendicular direction
This type of scattering is increased or decreased depending on the wavelength
Rayleigh
What is the attenuation determined by? (2 answers)
path length
frequency of sound
Reflection off of smooth surfaces, such as mirrors or a calm body of water. Occurs when the wavelength is SMALL when compared to the surface irregularities.
specular reflection
A shorter pulse leads to a _________ bandwidth
wider
(good-we want that!)
What does the abbreviation SPTA mean?
spatial peak, temporal average
Why is SPTA important in ultrasound?
most important factor for thermal bioleffects
What are the units for intensity?
W/cm²
Define ‘Decibel’
A logarithmic or RELATIVE scale that demonstrate a RATIO of the final strength to the initial strength (word for word on boards)
A property of certain materials to CREATE A VOLTAGE when:
PRESSURE IS APPLIED or when the material is MECHANICALLY DEFORMED
Piezoelectric Effect
another name for piezoelectric materials
Ferroelectric Material
Man-made (synthetic) materials
barium titanate, lead metaniobate, lead titanate, LEAD ZIRCONATE TITANTE (PZT)
What is the significance of the Curie Point?
The Curie Point or Curie temperature is approximately 360 degrees Celsius. Heat sterilization reaches these temperatures and will DEPOLARIZE the transducer (PZT)
Define Sterilization
The COMPLETE destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation.
Define Disinfection
Applying a chemical agent to reduce or eliminate infectious organisms of an object such as a transducer. Anything that penetrates skin or a mucous membrane require sterilization.
What chemical do we use to disinfect transducers?
Cidex or GLUTERADEHYDE
How much of the incident US energy is reflected at at a soft-tissue boundary between biological tissues
(such as blood and muscle)
Typically, less than 1% of the incident US energy is reflected. There is a “conservation of energy” at a boundary.
How much sound is reflected at an air-tissue interface?
99%. Air-Tissue interfaces produce the greatest reflection of sound of any boundary!!
How much sound is reflected at an bone-tissue interface?
50%
For reflection of sound to occur at the boundary between two media, this must be present
Different acoustic impedances
The physics of refraction are described by ____________.
Snell’s Law
For refraction of sound to occur at the boundary between two media, this must be present
Oblique Incidence AND Different Propagation speeds.
A sound wave is created by a transducer, reflects off of an object and returns to the transducer. The depth of the reflector is 10 cm. The round trip time is 2 seconds. What is the speed of the sound in the medium?
Note the question did NOT say in soft tissue. Edelman makes a point that you must know the formula Speed=distance/time for the boards when not given ‘soft tissue’ as part of the question. Thus, the answer is 10 cm/s
A sound pulse is produced by a transducer and travels in an ultrasound phantom from the transducer to pin ‘D’. It travels from the transducer, to the pin, and back to the transducer in 130 microseconds. How deep is pin ‘D’?
10cm deep.
Note that an ultrasound phantom will have a propagation speed equivalent to soft tissue so the 13 microsecond rule applies.
What is the size of the crystal (PZT) element in a transducer?
1/2 a wavelength thick
Why do we check the transducer housing (case) for cracks?
Cracks can increase the risk of electrical shock.
So can a frayed or exposed wire.
What is the significance of the Matching Layer
has an acoustic impedance between the acoustic impedance of the active element and the skin
What is the significance of Acoustic Gel
Removes air from between skin and transducer face (matching layer)
AND
Increases the efficiency of sound transmission
_______ pulses create better images
short
Ideally the damping material controls the way we produce sound. We want:
________ pulse length and duration
________ sensitivity
________ bandwidth
________ Q factor
Ideally the damping material controls the way we produce sound. We want:
SHORT pulse length and duration
LOW sensitivity
WIDE bandwidth
LOW Q factor
Do Continuous wave transducers use damping?
NO. They don’t pulse so they do not need a damping material. Neither do therapeutic probes.
Define Bandwidth
The RANGE OF FREQUENCIES between the highest and the lowest frequency emitted from the transducer.
Which produces a wider bandwidth: Diagnostic Transducer or Therapeutic Transducers?
Diagnostic Transducers (because they use damping)
List all possible names of the main frequency emitted by the transducer (4)
center
resonant
primary
natural
What are the units for the Q factor?
None. No units.
The thickness of the crystal equals __ of the wavelength of sound in the crystal; thus, the thickness of the matching layer is ____ of the wavelength of sound in the matching layer.
The thickness of the CRYSTAL equals 1/2
thickness of the MATCHING LAYER is 1/4
When the PZT crystal is half as thick, the sound’s frequency is _______ as high.
twice
What is an advantage of a waterpath delay?
Improve visualization of superficial structures
(waterpath delay also known as “stand-off pad”)
