Physics Chapters 5-6 Santanna Flashcards
Intensity may be reported in various ways with respect to
space and time
_____ is a key parameter with regard to bio effects
Intensity
_____ is being the most relevant to tissue heating
SPTA ( spatial peak temporal average)
_____ is greater than average
peak
What is the highest intensity?
SPTP (spatial peak temporal peak)
What is the lowest intensity?
SATA (spatial average temporal average)
positive decibels means intensity is getting
bigger
negative decibels means intensity is getting
smaller
What is the decrease in strength of a sound wave as it travels? What is the units?
attenuation, dB
True or false? The further sound travels, the weaker it gets or the move it attenuates
True
In soft tissue, ___ frequencies attenuate less.
lower
This is reflection from a smooth reflector, like a mirror. It returns in one direction.
specular reflection
What happens when propagating sound energy strikes a boundary between two media and some energy returns to the probe?
reflection
The reflection of sound back in the general direction of the probe but in a number of directions
diffuse reflection or backscatter
What is the distrubtion of sound randomly in all directions.
scattering
Does higher frequency scatter more?
YES
What is the equation for rayleigh scattering and the definition?
organized and omidirectional
rayleigh scattering is proptional to frequency^4
what is the amount of attenuation per centimeter is called? What are the units?
attenuation coefficient and dB/cm
attenuation coefficient is directly related to
frequency
The distance sound travels in a tissue that REDUCES the intensity of sound to one-half of its original value
the units are
half value layer thickness
cm
What does half value layer thickness depend upon?
the medium and frequency of sound
Thin half value means
higher frequency sound media with high attenuation rate
Thick half value means
low frequency sound media with low attenuation rate
What is calculated not measure? A number associated with a medium
Impedance
What is the units for impedance?
Rayls (Z)
A normal incidence
perpendicular
orthogonal
right angle
ninety degrees
anything other than a 90 degree angle
oblique incidence
Intensity of the sound wave prior to striking a boundary
incident intensity
the intensity after striking the boundary that turns around and reflects back to the probe
reflected intensity
the intensity that after striking the boundary continues on in the same direction
transmitted intensity
The % of the US intensity that bounces back when the sound strikes a boundary
Intensity Reflection Coeficient (IRC)
Is IRC and ITC unitless?
True
% of incident intensity that after striking the boundary continues on in the same direction
Intensity Trasmission Coefficent
What occurs if the two media at the boundary have different acoustic impendaces ?
reflection
Will transmission and reflection with oblique incidence occur?
It may or may not
Materials used for the matching layer of a transducer must have an impedance level between the
skin and PE element
What is the function of the damping material of an ultrasound transducer
reduces “ringing” of the PZT
A ____ MHz transducer will have the thinnest element
a. 2 mhz
b. 12 mhz
c. 5 mhz
12
A frequency of the transducer depends primarily on the
element thickness
While scanning soft tissue, the reflected wave returned to the transducer in 5usec. How far away is the reflector?
4 cm
Range equation is used to determine the
distance to the reflector
damping of the sound beam
reduces the SPL
What is defined as the range of frequencies contained in the US pulse.
bandwidth
The use of backing material would result in all the following expect:
a. wider bandwidth
b. lower quality images
c. decreased sensitivity
d. lower Q factor
b
if you change from a transducer with 20 mm crystal thickness to one with 40 mm thickness, the frequency of the sound produced will:
half
imaging probes have a ___ q factor and a ____ bandwidth
low and wide
as transducer frequency ____ the q factor ___
increases and increases
they are directly related
a larger bandwidth leads to
improved axial resolution
as the q factor increases the bandwidth
decreases/ narrows
What is time of flight?
time it takes for a pulse to travel to and from the transducer and the reflector
the time of flight and the distance the sound travels are ____ related
directly
what is a property of material to create a voltage when pressure is applied or when the material is mechanically deformed.
piezoelectric effect
Man made peizoelectric materials
lead zirconate titanate (PZT)
barium titanate
lead titanate
natural piezoelectric materials
quartz and tourmaline
What degrees can PZT be destroyed at?
360 C
680 F
this is why we can’t autoclave probes
what is the complete destruction of all living microorganisms by means of exposure to heat, chemicals, or radiation.
sterilization
using a chemical agent to reduce or eliminate infectious organisms on probes
disinfection
What is HLD?
higher level disinfecting (vaginal probes)
Can we use alcohol as a disinfectant?
NO
What transducer component protects the internal components from damage, and insulates the patient from electrical shock.
case
What is active element?
piezoelectric crystal that is also called PZT, ceramic, or crystals.
How thick is active element or PZT?
1/2 wavelength thick
Backing element/ Damping element is made of
epoxy resin impregnated with metal powder
When a emitted sound is dampened, what happens
it is short in duration and length
crystal damping enhances
axial resolution
where is the matching layer postioned
in front of the PZT at the face of the transducer
how thick is the matching layer
one-quater wavelength thick
does CW probes need backing/damping materials
NO
Impedences
PZT > Matching layer> gel> skin
what are imaging transducer characteristics
damping is effective
short pulse length and duration
low sensitivity
wide bandwidth
low q factor
decreased output power
no damping and narrow bandwidth
high q factor (CW)
damping and wide bandwidth
low q factor
characteristics of high frequency pw imaging transducers
thinner, PZT crystals
PZT with higher speeds
characteristics of low frequency pw imaging transducers
thicker PZT crystals
PZT with lower speeds
