ultrasound physics ch. 10

resolution

ability to image accurately

resolution describes

image quality

axial/long resolution

ability to distinguish 2 structures that lie close together
-parallel to the sound beam

long/axial resolution units

mm, cm, any unit of distance

long/axial resolution equation

SPL/2

shorter pulses=

better axial resolution

axial resolution determined by

SPL

SPL is .5 mm; what is the axial resolution

.25mm

SPL= .5mm
axial resolution= .25mm
what if cysts were .20mm apart?

we would not be able to see them separate from each other

lower SPL number=

Better resolution

SPL=10mm
2 cysts will be "resolved" on the monitor if they are ______ apart

5mm

long resolution short pulse

Reflector separation is greater than ½ SPL, separate echoes produced, displayed accurately.

long resolution long pulse

-Reflector separation is less than half the SPL
-Echoes from 2 interfaces are not separated. Pulse length too long.

long/axial resolution also called

-longitudinal
-axial
-range
-radial
-depth
(LARRD)

long/axial resolution parallel to

main axis of sound beam

Can the sonographer adjust the axial resolution?

no because you can't adjust the SPL

axial resolution typically values

.1 to 1.0mm
-lower values=shorter pulses
-shorter pulses=better resolution

range resolution equation

.77 x #cycles in pulse / F

how do we create a short pulse

-less ringing of crystal
-fewer cycles
-increase F

Improve axial resolution by:

-Shorter SPL

-Shorter pulse duration

-Higher frequencies (shorter wavelength)

-Fewer cycles (less ringing) From damping

-Lower numerical values

T/F The higher the frequency within a pulse, the lower the numerical value of axial resolution and the better the resolution.

true

T/F An US system with a greater pulse length will generate the image with greater detail.

false

Which of the following transducers has the worst axial resolution?
A. 4 MHz; 4 cycles/pulse
B. 4 MHz; 2 cycles/pulse
C. 2 MHz; 2 cycles/pulse
D. 2 MHz; 4 cycles/pulse

D

lateral resolution

Minimum distance that two side by side structures (perpendicular to sound beam) can be apart and still create two distinct echoes.

lateral resolution equal to

beam width

lateral resolution units

mm, any unit of length

beam width and lateral resolution varies with

depth

lateral resolution is best at

the focus because beam is most narrow

4 terms for lateral resolution

-Lateral
-angular
-transverse
-azimuthal
(LATA)

T/F LATA resolution is better than LARRD

false

LATA resolution is NOT as good as LARRD because ultrasound pulses are wider than they are short.

Higher F TRX have _________ axial resolution and lateral resolution

better

higher F=

shorter pulses
higher LARRD
higher LATA
decreased divergence

focusing improves

lateral resolution

3 modes of focusing

-external focusing or fixed
-internal focusing
-phased array

external focusing or fixed

-lens attached to crystal
-FIXED; not adjustable

internal focusing

-curved PZT
-increase the curvature-increase degree of focus
-cannot change; fixed

phased array

-electronic focusing
-multi element transducers only
-adjustable

4 distinct changes when sound beam is focused:

1. Beam diameter narrows in near field and focal zone.
2. Decreased focal depth. (shortens near field)
3. Beam diameter beyond focal zone widens. (degraded Lat. Resolution in the far field)
4. Focal zone reduced.

Which of the following axial resolutions will give the finest detail?
A. 0.22 mm
B. 0.8 cm
C. 9.10 mm
D. 0.25 mm

A. .22mm

What happens when pressure is applied to a piezoelectric crystal?

emits electrical signal

Increasing which of the following will increase axial resolution:
A. Focusing
B. Period
C. Pulse duration
D. Frequency

D. frequency

Which transducer will provide the longest near zone length?
A. 3.5 MHz, 3mm diameter
B. 10 MHz, 4mm diameter
C. 7.5 MHz, 6mm diameter
D. 10 MHz, 6mm diameter
E. 7.5 MHz, 4 mm diameter

D

Another name for axial resolution:

range resolution

Focusing a sound beam will improve which type of resolution?

lateral

SPL divided by two =

axial resolution

_________frequency transducers have the best range resolution.

high

Which SPL would provide better resolution? How far apart would two structures need to be to create two echoes?
SPL: 6mm
SPL: 4mm
SPL: 2 mm

2mm; 1mm

B

Lateral resolution is represented by dots A or B?

A

axial resolution is represented by dots A or B?

5mm

azimuthal resolution at focus

axial resolution determined by

pulse length

lateral resolution determined by

beam width

axial resolution best with

short pulses
high F
few cycles

lateral resolution best with

narrowest beam

does axial resolution change?

same at all depths, does not change

does lateral resolution change?

changes with depth
best at focus

in the near field, axial resolution best with

shortest pulse

in the near field lateral resolution best with

smallest diameter crystal

in the far field, axial resolution best with

shortest pulse

in the far field, lateral resolution best with

largest diameter
highest F