ultrasound transducers

Question 1

What can you do to improve contrast res 
increase sector width
decrease number of focal zones
use a 2D or matrix array 
use a phase array
used a curved array

Answer 1

use a 2D or matrix
they have both rows and columns, it allows electronic focusing in the out of plane dimension with resulting slice thickness thinner compared to 1D

Question 2

a method used to improve frame rates with multi zone electronic focusing is termed:
apodization
parallel procesing
f-number focusing
low q xducer
none of the above

Answer 2

parallel processing

aka coprocessing; frame rates can be improved by simultaneously acquiring data for multiple acoustic scan lines

Question 3

when increasing the number of transmit focal zones to improve spatial res, the trade off is:
lateral res vs axial res
spatial res vs contrast res
lateral res vs temporal res
contrast res vs frame rate
elevational res vs frame rate

Answer 3

lateral res vs temproal res
ea transmit focus requires a pulse/listen cycle; more focal zones decreases frame rate; temporal res is related to frame rate

Question 4

what type of res is affected by PD
lateral res
contrast res
temp res
axial res
elevational res

Answer 4

axial resolution

Question 5

what component of a PW xducer helps to reduce the SPL and improve axial res?
matching layer
lens
element
backing material
radiofreq shield

Answer 5

backing material

it reduces the length of time the crystal rings

Question 6

the matching layer b/w the pat element and the tissue is designed to:
insulate the pt from the hot element
reduce the vibration of the xducer
reduce acoustic imped mismatch b/w element and tissue
increase the reflection coefficient at xducer-skin interface
decrease SPL

Answer 6

REDUCE ACOUSTIC IMPEDANCE MISMATCH B/W ELEMENT AND TISSUE

there is a large acoustic impedance mismatch b/w crystal and tissue. This would result in large reflection with little energy transfer into body

Question 7

what type of xducer could you choose to produce a beam that is symmetrical about the beam axis
annular array
linear sequenced array
phased array
curved array
tightly curved array

Answer 7

annular array
its a round xducer where elements are arranged concentrically and creates a cone shaped beam that is symmetric in all dimensions

Question 8

what is an advantage of a single crystal or pure wave crystal xducer
lower freq at higher res
absence of aliasing with PW
higher frame rates
wide bandwidth
greater steering angles

Answer 8

wide bandwidth

Question 9

what is the optimal thickness for the matching layer
equal to thickness of crystal
1/4 wavelength
1/2 pulse length
2x transducer diameter
1/2 width of backing material

Answer 9

1/4 of a wavelength

Question 10

dynamic apodization is a method employed to:
focus beam at multiple depths on transmit
focus the beam at multiple depths on receive
reduce side lobes
reduce beam width in z axis
steer beam

Answer 10

reduce side lobes

Question 11

what is the purpose of curving the xducer elements or applying a lens over the elements
provide focusing in out of plane (elevational) direction
to reduce acoustic imped mismatch b/w crystal and skin
reduce crystal ringing and improve axial res
help reduce electronic interference
all of the above

Answer 11

provide focusing in the out-of-plane direction

Question 12

a wide bandwidth xducer w/ multiple transmit freq; which freq should you select for max penetration
3 MHz
3.5 MHz
4 MHz
5MHz
penetration not affected by freq

Answer 12

3 MHz

Question 13

with a standard 1D linear array, what type of res is affected most by electronic focusing and dynamic aperture

lateral res
contrast res
temp res 
axial res
elevational res

Answer 13

lateral res
lateral res is improved at depth by increasing transducer width or aperture size in an array; the larger the aperture the smaller the beam width at the focal point

Question 14

what type of xducer has the same measurement for elevational and lat res

convex linear array
phased linear array
annular array
sequential linear array
mech sector

Answer 14

annular array

Question 15

if the # of cycles in the transmitted PW is inc

axial res is degraded
lateral res is degraded
SPL becomes shorter
rate of attenuation is inc
penetration is decreased

Answer 15

axial res is degraded

axial res is proportional to pulse length. it degrades as pulse length inc

Question 16

the transducer you are using is an array assembly. what is the advantage?
xducer arrays pruduce pure, single freq beams
xducer arrays enable mech steering
xduce arrays produce long pulses for improved axial res
xducer arrays have greater dynamic range, = more shades of grey
xducer arrays enable electronic focusing and steering

Answer 16

xducer arrays enable electronic focusing and steering

arrays use multiple elements rather than a single to form the beam.

Question 17

axial res is improved with
inc bandwidth
shorter pulse length
shorter wavelength
b & c
all of the above

Answer 17

all of the above

Question 18

which of the following is not assoc. with a low-q transducer

wide bandwidth
multifreq selection
long pulse length
diagnostic pw u/s
loss of most energy in first few vibrations

Answer 18

long pulse length

xducers used for diagnostic u/s are low-q xducers. they have wide bandwidth which allow multi freq selection. they have short pulses for good axial res; the short pulse results in most of the energy within it is lost after first few vibrations

Question 19

you suspect that a bright spot on the b-mode is a calcification, but there is no postieror acoustic shadow.  how can you optimize your system to demonstrate a shadow distal?
move focal zone below hyper echoic focus
increase xducer freq
increase acoustic power output
increase dynamic range
decrease scan line density

Answer 19

increase xducer freq
if the sound beam is wider than the stone a shadow may not occur because tissue on either side will send back reflections for that depth

Question 20

what is a side lobe
uneven xducer element
accessory pulse used for electronic steering
sound beam emitted from the xducer that travels in a diff direction from main beam
nonlinear propagation of the sound beam
additional backing material on the xducer edge used to reduce lateral vibrations

Answer 20

sound beam emitted from the xducer that travels in a diff direction from the main beam

Question 21

inc which of the following will result in improved axial res?
PD
Pulse length
Freq
period
Focusing

Answer 21

freq

axial res is improved by reducing pulse length or PD

Question 22

what is the advantage of using multiple transmit focal zones?
inc lateral res
inc temporal res
inc elevation res
inc axial res
all of the above

Answer 22

inc lateral res

Question 23

which probe would provide best axial res to measure thickness of small structure?
5MHz linear array
7MHz linear array
10 MHz linear array
5 MHz curved arrray
5MHz phasyed array

Answer 23

10 MHz linear array

axial res improves with inc freq

Question 24

what is the f-number?
aperture multiplied by number of elements in xducer
number of xducer elements divided by fraunhofer zone
beam width 1 cm from xducer surface
focal length divided by aperture
focal length multiplied by number of elements in xducer

Answer 24

focal length divided by aperture

Question 25

which factor least influences axial res>
damping
freq
beam width
PD
pulse freq

Answer 25

beam width

beam width affects lateral res

Question 26

what disadvantage is related to the use of a tightly curved array?
axial res degrades w/ depth
field of view compromised
temp res compromised
lateral res degrades
elevation res compromised

Answer 26

later res degrades w/ depth

scan lines become spaced farther apart in far field compared to near field

Question 27

what res is most affected by mech. focus on a linear array xducer?
elevational res
lateral res
contrast res
temp res
axial res

Answer 27

elevational res;

determined by slice thickness; measure of beam width perpendicular to imaging plane