SPI review 2 Flashcards
attenuation coefficient and its units
the amount of attenuation per cm units dB/cm
attenuation cefficient is directly related to
frequency
attenuation coeff does not change when ________ changes
path length
in soft tissue attenuation coeff is approcimatley
1/2 the freqyency
mathmatical expression for attenuation coeff in soft tissue
0.5dB/cm/MHz
impedance
a number associated with a meduims resistance
calculated not measured
units are Rayls “Z”
acoustic impedance =
density x propagation speed
rayleigh scattering is =
freq to the 4th
oblique incidence
anything other than right angels
AKA normal incidence
perpendicular
orthogonal
right angel
ninety degrees
typical % of reflected intensity between soft tissue boundary
1%
% refelcted at air/tissue interface
99%
% reflected at bone/tissue interface
50%
refraction is
transmission with a bend
the physics of refraction is described by
snells law
refraction requirs _____ incidence
oblique (and diff speeds)
the angel of reflections is = to
the angle of incidence
which of the following best descrobes a refelction from a rough boundry?
non diffuse, absolute, rayleigh, smooth, non specular
non specular
the time of flight and and distance are ________ related
directly
range equation
distance to boundry = go return time x speed / 2
in soft tissue, every ____ of go return time means the reflector is ___ deeper in the body
13 micro sec
1cm
a property of certain material to create a voltage when pressure is applied or when the material is mechanically deformed
piezoelectric effect
materials deform or change shape when a voltage is applied to them
reverse piezoelectric effect
PZT AKA
ferroeclectric material
natural PZT
quartz, rochelle salts, tourmaline
man made PZT
barium titanate, lead metaniobate, lead titanate, lead zirconate titanate
temp PZT will depolarize at
360C* or 680F*
the complete destruction of all living microorganisms by heat, chemical agents, or radiation
sterilization
reduce infectious organisms
disinfection
thickness of PZT
1/2 wavelength thick
thickness of matching layer
1/4 wavelength thick
what is backing material made of
epoxy resin impregnated with tungsten
imaging transducer characteristics
damping
short pulse length and duration
low sensitivity
wide bankwidth
low Q factor
decreased output power
bandwidth
the range of frequencys from the highest to the lowest emitted from the transducer
bandwidth =
max freq - min freq
the process of _______ increases the range of freq in the bankwidth
backing material
main freq AKA
center
resonant
primary
natural freq
a unitless number representing the extent of damping
quality factor (Q factor)
the Q factor in typical imaging can be aprroximated by the number of _____ __ _______
cycles in the pulse
typical Q factor value
2-4
Q factor equation
Q = resonant freq/bandwidth
in pulsed wave transducers the main or center freq of the US pulsed transducer is determined by 2 characteristics of the crystal
thichness and prop speed
prop speed for PZT is approx
4-6mm/micro sec
in continouis wave trans the sound waves freq = the _______
freq of the voltage applied to the PZT by the machines electronics
when the PZT is 1/2 as thick the sounds freq is ____ __ _____
twice as high
the thinner the active element the _____ the freq
higher
the _________ the active materials prop speed the ________ the transducers freq
faster
higher
thin crystal and fast PZT =
higher freq
thick crystal and slow PZT =
lower freq
when a transducer is covered with gel on the inside, what can’t it come into contact with in order to make the image? gel, water, talcum powder, sterile liquid, lubricating gel
talcum powder
t or f
if the freq of the electrical excitation voltage of a pulsed wave transducer is 6MHz, the main or ceter freq of the transducer is 6MHz
F
the impedance of a transducers active element is 1,900,000Z and for the skin is 1,400,000Z what is an acceptable impedance for the matching layer? 1,200,000Z, 1,400,000Z, 1,726,000Z, 1,950,000Z
1,726,000Z
T or F
the damping material improves the systems longitudinal res
T
narrow beams create ______ images
better
for unfocused continuous wave disc transducers, at the end of the near zone the beam diameter is __ the ________ _______
1/2
transducer diameter
at 2 near zone lengths, the beam diameter is ____ to the _______ -________
=
transducer diameter
two factors that determine focal depth (distance from tranducer to the focal point)
transducer diameter
freq of ultrasound
beams with a deep focas have a _____ ______ at the focus
lower intensity
shallow focus
small diameter
low freq
deep focus
large diameter
high freq
divergence is determinded by
transducer diameter
freq of ultrasound
in the far field, beam is narrow ________ res is the best with large diameter and high freq
lateral
in the far field, beam is wide where _______ res is worse, with small diameter and low freq
lateral
less divergence
narrower beam in far field
larger diameter active element
high freq
improved lateral res in far field
more divergence
wider beam in far field
small diameter active element
low freq
degraded lateral res in far field
v shaped wave
diffraction pattern
aka
huygens wavelet
huygens wavelet caused by
produced by a tiny source near the size of a wavelength, the waves will diverge in hour glass or V shage as they propagate
what happens in a huygens wavelet
each tiny part of transducer is individual source of sound. V shape is result of constructive and destructive interference of the many sound wavelets emitted from numerous soud sources.
a sound beam is created by a round PZT with a diameter of 10mm. The focal depth of the sound beam is 8cm. What is the diamter of the sound beam at a depth of 8cm? 8cm, 3mm, 5mm, 4mm
5mm
a sound beam is created by round pzt with a diameter of 10mm. The focal depth of the sound beam is 8cm. What is the diameter of the sound beam at a depth of 16cm? same as the trans diameter, 3/4 the trans diameter, 1/2 the transducer diameter, 4mm
the same as the transducer diameter
the ability to image accurately, not merely quality
resolution
the ability to distinguish two structures that are close to each other, front to back, paralley to, or along the beams main axis
axial resolution
axial res AKA
L longitudinal
A axial
R range, radial
D depth
units for axial res
distance
shorter pulses create ______ LARD res
shorter
can sonographer change LARD res
no, need new trans
T or F
a short pulse means a short spatial pulse length or a short pulse duation
T
when the LARD res is low the image accuracy is ________
superior
LARD equation
LARRD = spatial pulse length/2
typical LARRD value
0.05-0.5mm
LARRD soft tissue Equation
LARRD=0.77x # cycles in pulse/freq
LARRD is best with
less ringing (fewer cycles in pulse)
higher freq (shorter wavelength)
the minimum distance that 2 structures are separated by side to side, perpendicular to the sound beam that produces 2 distinct echoes
lateral res
lateral res AKA
L Lateral
A Angular
T Transverse
A Azimuthal
units of LATA
length
lateral res is = to
the beam diameter
since the beam diameter varies with _____ LARA res also vaies with _____
depth
lata res is best at
the focus or one near zone length (focal depth from the transducer because the sound beam is narrowest at that point
when 2 side by side structures are closer together than the beams width
only one wide reflection is seen on the image
why is LATA not as good as LARRD
US pulses are wider than they are short
LATA res is = to
beam diameter
high freq sound improves
LARRD everywhere in the image and LATA in the far field only
focusing alters beam in what ways
narrower waist in the US beam
shallower focus
smaller focal zone
focusing is effective in
the near field and focal zone
two types of focusing
fixed aka conventional or mechanical
adjustable by electronics aka phases array
phases array meand
adjustable or multi focusing
3 methods of focusing
lens
curved pzt
electronic focusing
lens
external focusing, distal to pzt
curved pzt
internal focusing
electronic focusing
adjustable, phased array
multy focusing
fixed focus have _____ lateral res
poor
an operation that lateral res of a given depth be estimated
measure the largest dimension on the image size of a point reflector
the more cycles there are in a pulse, the ______ is the numerical value of range res
greater
