Penny book Flashcards
What type of wave is sound
Mechanical and longitudinal
The frequency ranges for ultrasound are
20,000 hz or 20KHZ
The speed of sound in soft tissue is
1,540 m/s or 1.54 mm/us
Which of the following transducers fires the elements in groups
Linear sequenced array
The unit for wavelength is
mm
Enhancement is caused by
Passes through a weakly attenuated structure
The wavelength in a material having a prop speed of 1.5 mm/us employing a transducer frequency of 5.0 mhz is
.3 mm
An u.s transducer converts
Mechanical to electrical
Low attenuation to highest
Fat, muscle, bone, air
Prop speed lowest to highest
air, bone
If the frequency doubles what happens to the wavelength
decreases by one half
What happens to intesnsity if the ampliutude of the signal is halved
quartered
What would be used to decribe the percentage of the time the sound is on
Duty factor
A 3-db gain would indicate a increase in intensity by
2 times (doubling of intensity)
Ignoring the effects of attenuation the intensity of the us beam is usually greater of the focal zone because of
The smaller beam diameter
Attenuation denotes
Weakening of the strength of the beam as it travels. Typically from absorption, reflection, or scattering
What has the lowest intensity
SATA
What is the definition of the beam uniformity ratio
BUR = SP/SA. the spatial peak intensity divided by the spatial average intensity
Continuous wave doppler has a duty factor of
100% it is transmitted 100% of the time
The spatial pulse length is defined as the product of ____ and the number of _____ in a pulse
Wavelength and cycles
With phased array transducers, the transmitted sound beam is steered by
Varying the timing of pulses to the individual piezoelectric materials // phased array transducers operate by shocking the element with minute time differences in between
If the gain of an amplifier is 18 db, what is the new gain if the power is reduced by half
15 db // 18 db - 3db (half) = 15 db
Which of the following is true regarding SATA/SPTP
SPTP is always equal to or greater than SPTA
If the amplitude of a wave is increased threefold, the power will
Increase ninefold // Power is proportional to the amplitude squared.
Ultrasound attenuates an average of _____ db/cm of travel for each megahertz or frequency
0.7 db/cm
If the intensity transmission coefficient is 0.74, the intensity reflection coefficient will be
0.26// It has to equal 100
Acoustic impedance is defined as the product of
The speed of sound in tissue and density of tissue
Rayleigh scattering is an example of
A reflector whose size is smaller than the wavelength
Assuming normal incidence, if the medium 2 impedance is equal to medium 1 impedance
100% of the intensity will be transmitted because there will be no reflection since they are identical
What is the total attenuation of a 3.5 MHz pulse after passing through 2 cm of soft tissue
3.5 dB // (0.5 x 3.5) x 2
The thinner the piezoelectric element the
The higher the frequency
The uit for impedance
Rayls
A sound beam encounters an interface at a 90 degree angle. If the speed of sound in the first tissue is 1540 m.s and the speed of sound in the second tissue is 1450 m/s, which numbers most closely approx. the angle of beam transmission
90 degrees
ALARA stands for
As Low As Reasonably Achievable
A “dB” describes the
Ratio of 2 sound intensities
The correct equation for snells law
sin 0t= (c2/c1) x sin 01 / Describes refraction at an interface
The attenuation coefficient of sound in soft tissue can be defined by what equation
frequency/2
The intensity transmission coefficient is equal to
1 - intensity reflection coefficient
The rang equation explains
Distance to the reflector
The typical value for attentuation coefficient for 6 MHz ultrasound in soft tissue is
3 db/cm bc it is one half
What must be known to calculate distance to a reflector
Travel time and prop speed
Specular reflections occur when
The interface is larger than the wavelength
What is the reflected intensity from a boundary between two materials if the incident intensity is 1mW/cm2 and the impedences are 25 and 75
0.25 mW/cm2
The layer of material within the transducer which has a intermediate impedance between the transducer element and human tissue is know as the
Matching layer
What relates bandwidth to operating frequency
Quality factor
PZT effect can be best described as
Mechanical deformation that results from a high voltage applied to the face of the crystal that in turn generates a pressure wave
Most commonly found in transducers
Lead zirconate titanate
Diffraction refers to
Spreading out of the us beam
Prefered method for sterilizing us transducers is
Cold sterilization
A transducer with which frequency would have the thickest elements
2 MHZ (lowest number)
What is best defined as the ability to discriminate between two closely spaced reflectors
Spatial resolution
What is an effect of focusing
Improved lateral resolution
Bandwidth is
Range of frequencies produced by the transducer
What is the technique that permits “virtual palpation” of a lesion to determine the hardness or softness of tissue
Elastography
The acoustic impedance of the transducers matching layer is
Chosen to improve transmission into the body
If the amount of damping decreases, the bandwidth
Decreases
The region where the sound beam diameter is the smallest is referred to as the
Focus
The near-zone length is determined by
Transducer frequency and element diameter
A two-element continuous wave transducer is
only used for spectral doppler
A waves initial intensity is 2 mW/cm2. There is an increase of 10 dB. What is the final intensity
20 mW/cm2
What best describes a transducer that has multiple elements in a curved shape
Curvilinear
What is the name of the control that compensates for attenuation related to path length
TGCs / compensation is the same as TGC (time gain compensation)
The echoes are stored before final display by the
Computer memory
What portion of the u.s system drives the transducer
Pulser
What doppler mode uses the amplitude of the doppler shift in order to produce an image demonstrating flow in a vessel
Power doppler
How many different shades of gray can the human eye discern at one time
100
Most current u.s systems have ___ shades of gray
256
How many bits per pixel can be displayed with 4 bits of memory
2^4= 16
The spatial resolution capabilities of the system are primarily
Transducer
The echo intensity on a grayscale of 32 shades is represented by the binary number
100,000
Preprocessing of the info that is fed to the scan converter
Determines the assignment of echoes to predetermined gray levels
What grayscale systems typically use a means of signal dynamic range reduction
Compression / it is the opposite of dynamic range.
Area is expressed by what unit
cm2
If the frequency of a transducer is increased what will decrease
Wavelength
With tissue harmonic imaging there
Decreased artifacts in the near field
What is in the range of infrasound
15 Hz
What is in the range of audible sound
18 Khz
What can be changed by the operator
PRF because you adjust the depth
The time is takes for one cycle to occur
Period
The length of the pulse is the
Spatial pulse length
Assuming oblique angle of incidence, if the prop speed of medium 1 is greater than the prop speed of medium 2, what will the angle of transmission be?
Less than the angle of incidence // Medium 2 is transmission
A 5-mHz wave travels through 5 cm of soft tissue. If a 3.5 MHz transducer is selected instead, what happens to the prop speed of a medium
No change / Prop speed is only determined by the medium (stiffness and density)
The slowest prop speed is found in which medium
Air
What represents the strength of the beam
Intensity
What is the unit of pressure amplitude
Pascals (pa)
Unit of intensity is
W/cm2
What else changes with a change of amplitude
Output power
What will increase the acoustic exposure to the patient
Increasing output gain
What operator control adjusts the intensity of the transmitted pulse
Power
What happens to the power if the intensity is doubled
Doubles / they are directly related
The number of pulses that occur in 1 sec is
PRF
What is along the x-axis on a spectral doppler waveform
Time
What is the unit for spatial pulse length
m
What testing device is used to measure acoustic output (intensity) level
Hydrophone
What is the principle that states sound waves are the result of the interference of many wavelets produced at the face of the transducer
Huygens principle
When using tissue harmonic imaging, the frequency used is
Double the fundamental frequency
In B-mode imaging, amplitude is located on what axis of the image
z
What determines the radial resolution of a system
Spatial pulse length
The axial resolution can be improved by decreasing the ___ or increasing the ____
Number of cycles in a pulse, frequency
2 reflectors are 1.3 mm apart in a plane that is parallel to the beam. The spatial pulse length of the transducer is 2.6 mm. The 2 reflectors will
Will show up as two dots on the screen
In what zone does beam divergence occur
Fraunhofer zone (far zone)
The larger the aperture,
The longer the near zone
The ability to resolve two reflectors that lie parallel to the beam is ___ resolution of a system
Axial
The more focal zones used, the
worse the temporal resolution
In the most common type of transducers, the slice thickness plane is focused
Using a lens
If sound travels through a large quantity of water and then encounters a reflector, the reflector will appear to be
Too far away / If the prop speed is less than 1.54 mm/us
What is the maximum temp increase below which there should be no thermally induced biological effects
2 celsius
2 sound beams with different frequencies are traveling through soft tissue. Which beam will travel faster
Both will travel at the same speed / prop speed and frequency are unrelated
A video display that is limited to only black and white, with no other shades of gray is called
Bistable
The name for the smallest amount of digital storage
bit or binary digit
In the fresnel zone, the beam
the beam area decreases with distance from the transducer
Info that travels to the scan converter from the receiver is initially in what format?
Analog
What is true about color doppler
Each pixel can either be grayscale or color, it cannot be both
What preserves the pixel density when enlarging the image
Write magnification/ it enlarges the image before the image is stored in digital memory
Whats the relationship between amplitude and frequency
They have no relation
Whats the relationship between spatial pulse length and pulse duration
Directly related
What is true about axial resolution
It does not vary with depth
If the ____ is increased, the flow increases
Pressure differential
What law describes the relationshiop between flow and the pressure differential, viscosity, and length
Poiseuilles law
The most common type of flow found in the body
Laminar
