Module 4 : Resolution

Question 1

resolution

Answer 1

• most important thing to consider

- 3 aspects

Question 2

3 aspects of resolution

Answer 2

• detail (spatial)
• contrast
• temporal

Question 3

detailed resolution types

Answer 3

• axial (y)
• lateral (x)
• elevational (z)

Question 4

axial resolution

Answer 4

• ability to separate reflectors along the path of the beam

- dependant of the SPL and is calculated by 1/2 SPL

Question 5

axial resolution equation

Answer 5

AR = 1/2 SPL

SPL decreases axial resolution improves

Question 6

high frequency probes + axial

Answer 6

• increased frequency = decreased wavelength = decreased SPL = increased AR

Question 7

wide bandwidth + axial

Answer 7

• wider bandwidth = shorter pulse = increased AR

Question 8

decreased wavelength + axial

Answer 8

• decreased wavelength = decreased SPL = increased AR

Question 9

increased dampening + axial

Answer 9

• increased dampening = decreased RD = decreased SPL = increased AR

Question 10

low Q factor + axial

Answer 10

• lower Q = increased AR

Question 11

axial resolution names

Answer 11

- LARD
\+ longitudinal 
\+ axial
\+ range
\+ depth

Question 12

lateral resolution

Answer 12

• ability to separate reflectors perpendicular to path of beam
• dependent on width of beam
• not constant with depth

Question 13

beam width and lateral resolution

Answer 13

• beam width decreases lateral resolution improves

Question 14

distance form probe + lateral

Answer 14

• beam shape changes with depth

- wider = worse lateral

Question 15

amount of focusing + lateral

Answer 15

• lateral resolution increases at the focus but worse everywhere else especially far field

Question 16

size of aperture + lateral

Answer 16

• shortens NZL so improves at focus but worse everywhere else

Question 17

NZL = lateral

Answer 17

• pushed deeper get better lateral resolution deeper

Question 18

higher frequency + lateral

Answer 18

• pushes near zone length deeper improving lateral resolution

Question 19

lateral resolution names

Answer 19

• LATA
• latera
• angular
• transverse
• azimuthal

Question 20

elevational resolution

Answer 20

• also known as slice thickness ability to separate reflectors perpendicular to image plane beam
• just like lateral resolution dependent on width of beam in Z axis
• fixed
• beam width in z axis decreases elevational resolution increases

Question 21

higher the frequency + elevational

Answer 21

• pushed near zone length not penetrating deeper but better resolution

Question 22

amount of focusing in z plane + elevational

Answer 22

• external mechanical focusing

- cannot be controlled but more focusing is better

Question 23

NZL + elevational plane

Answer 23

• longer = better

- shorter = worse

Question 24

distance from probe + elevational

Answer 24

• gets worse deeper without focusing

Question 25

contrast resolution

Answer 25

- ability to distinguish subtle differences in tissue gray scale - related to bit depth - higher bit depth more shade of gray more stuff to do with dynamic range

Question 26

temporal resolution

Answer 26

- ability to appreciate moving structures in real time - related to frame rate - frame rate increases temporal resolution increase

Question 27

temporal resolution formula

Answer 27

PRF = n x LPF x FR ``` n = number of foci LPF = lines per Frame FR = frame rate ```

Question 28

temporal resolution formula with penetration

Answer 28

penetration (cm) x n x LPF x FR = 77000 cm/s - 77000 used because it represents Hal the average speed of sound in soft tissue - if you exceed this you get range ambiguity

Question 29

depth of penetration + temporal

Answer 29

- have to go deeper takes longer for it to come back = less FR = less TR

Question 30

number of foci + temporal

Answer 30

- hard to look at more than one thing - have to add scan lines for every focus - decrease FR = decrease TR

Question 31

sector width + temporal

Answer 31

- sector down = less lines per scan = less FR = less TR

Question 32

number of lines per frame

Answer 32

- increase lines per Frame = decrease FR = decrease TR | - want not a lot of interpolation

Question 33

frame rate + temporal

Answer 33

- increase FR = increase TR