# Module 5 : Real-Time Considerations Flashcards

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1
Q

real time scanning

A
• real time scanning consists of multiple frames per second and each frame is made up of multiple scan lines
2
Q

real time scanning - limitation

A
• each scan line has to wait for all echoes to be received from selected depth prior to next pulse being sent out
• depth is limiting factor along with number of focuses
3
Q

frame rate

A
• number of times the sweep of sound is produced by the transducer (frames per second)
4
Q

frae rate and temporal resolution

A
• frame rate increases = temporal resolution increases
5
Q

temporal resolution

A
• gives us ability to image moving structs, overcome motion artifact
• survey quickly
6
Q

what frame rate can we detect flicker

A
• 15-20 fps
7
Q

frame rate in imaging

A
• 30-60 fps

- 120 scan lines

8
Q

factors affecting frame rate

A
• depth of field
• sector angle
• number of lines
• number of focal zones
9
Q

frame rate - depth

A
• higher frame rate = less depth

- lower frame rate = deeper depth

10
Q

frame rate - sector angle

A
• higher frame rate = narrower sector

- slower frame rate = wider sector

11
Q

frame rate - scan lines

A
• higher frame rate = less lines

- lower frame rate = more lines

12
Q

frame rate - unsimplified equation

A

depth (cm) x LPF x # of foci x FR = 77000cm/sec

• 77000 is 1/2 154000
13
Q

frame rate - simplified equation - RANGE AMBIGUITY

A

FR = 77000 cm/sec / LPF x depth x # of foci

14
Q

reciprocal of frame rate

A
• the time it takes to produce one frame

FR = 1/ T frame

15
Q

scan line density

A
• number of scan lines per degree or number of scan lines per centimeter
• 1 line/degree = good resolution
16
Q

low line density

A
• more interpolation
17
Q

high line density

A
• over writing occurs
18
Q

spatial resolution

A
• scan lines are and aspect of spatial resolution

- things that effect scan line density have and impact on the details of the image we see

19
Q

factors affecting spatial resolution

A
• number of scan lines
• number of focal zones
• size of sector
20
Q

cine loop

A
• system can store many frames into memory that can be reviewed after freezing
21
Q

RAM memory

A
• the cine loops are stored in RAM memory of machine (Random Access Memory)
• it is short term and is erased when we un freeze
22
Q

advantage to cine loop

A
• can improve efficiency of seeing tiny sturcuters missed during real time interrogations
23
Q

freeze frame

A
• continuous display of a single Fram in the memory on the monitor
• same image is read over and over and the raster display continuous to write image to display
• a CRT refreshes 30 frames per second even though image is frozen
• if machine stops writing phosphor stops glowing and image disappears
24
Q

side lobes

A
• secondary projections of ultrasound energy that radiate away from main beam
• limited to single disc mechanical probes and radial mode vibration is key contributor
25
Q

side lobes - issue

A
• can falsely place reflectors in the image as if they came from main beam
• because machine assumes all reflections come from centre beam
26
Q

side lobes - correction

A
• insulator ring is added to element to suppress the radial mode vibration
27
Q

grating lobes

A
• just like side lobes but are specific to array probes
• same assumption is made by machine with result being and artifact
• result of crosstalk between crystals
28
Q

grating lobes - correction

A
• apodizaiton

- sub dicing

29
Q

apodizaiton

A
• weakening voltages to outer crystals to reduce grating lobes
30
Q

sub dicing

A
• each element divide into smaller pieces or sub elements that will act as one crystal
• if cut to dimension of less than one wavelength the grating lobes will project at 90’ or greater
+ then transmitted into air between crystals so reduce effect go cross talk
31
Q

channels

A
• refers to number of elements in the array
32
Q

are more channels better

A
• more channels means more precise control over beam characteristics
+ like dynamic aperture