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MIDS 139 (Core Exam) > Ch 5 Transducers + Phasing > Flashcards

Ch 5 Transducers + Phasing Flashcards

1
Q

What are mechanically steered probes?

A

-Single crystal attached to head of motor
-Motorized to steer to produce a sector image (slice of pie)
-No longer used + replaced by phased array probes

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2
Q

What is the pedof (blind probe) used for?

A

-For doppler imaging! A single crystal is split in half OR 2 crystals are used for CW (1 receiving, 1 listening)
-Does not create an image
-Used in cardiac + vascular to detect weak RBCs

(has a narrow bandwidth to increase sensitivity to detect the weak echoes)

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3
Q

List 3 advantages + 3 disadvantages to using the pedof probe?

A

Advantages:
-High sensitivity to detect weak RBC signals
-Cheap
-Small footprint to image b/w ribs + SSN

Disadvantages:
-No 2D image
-Manual steering
-Fixed focus

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4
Q

What is a frame?

A

A complete scan of the u/s beam

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5
Q

What is an array?

A

-Group of elements (crystals) that can be turned on/off through electronic switches
-Arranged in a straight or curved line

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6
Q

Electronic scanning is performed with what?

A

Arrays (group of elements/crystals)

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7
Q

List the 2 ways that arrays operate?

A

-Sequencing
-Phasing

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8
Q

What is 3D imaging?

A

Imaging in the elevational plane

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9
Q

What is the 2D array also called?

A

Matrix array

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10
Q

What are linear sequenced array probes?

A

-Straight line of rectangular elements
-Parallel scan lines produced by pulses originating at different points across the array
-Produces rectangular image

1 element = 1 wavelength width
Width of image = length of array

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11
Q

List examples of structures we would image with linear sequences array imaging?

A

Vascular, small parts, superficial scanning, MSK

(b/c this is a high frequency probe it gives us better resolution)

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12
Q

What are convex sequenced array probes?

A

-Aka curved/curvilinear array
-Has a curved line of elements
-Produces a sector image (slice of pie)
-Pulses travel out in different directions from different points

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13
Q

List examples of structures we would image with curved array imaging?

A

-Abdomen, OB, GYN
-Allows for large FOV

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14
Q

What is phasing?

A

-The process of exciting/stimulating individual crystals by small time differences (<1 us)
-Allows us to steer the beam in a specific direction

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15
Q

Which probes need phasing to steer the beam?

A

Sector array probes (cardiac probe)

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16
Q

List pros + cons of using the sector probe?

A

Pros:
-Ability to steer + focus beam by phasing in the lateral dimension
-Good temporal resolution, smaller FOV + less scan lines
-Small footprint (probe head) for scanning b/w ribs

Cons:
-Fixed elevation focus
-Resolution in far field is worse compared to in near field

17
Q

Explain the sector probe?

A

-64 to 128 crystals
-Small footprint creates sector (slice of pie) image
-Best for cardiac
-Narrow near field, large far field
-Low frequencies for adults, higher frequencies for pediatrics
-Steering + focusing done by phasing
-Does NOT use sequencing
-Scan lines originate from same starting point

18
Q

What is a vector array?

A

-Aka trapezoidal scanning
-Has extended FOV
-The “wings” (sides) of the image are steered by phasing, while the center of the image is sequenced

19
Q

Phasing can be applied to each element group in a linear sequenced array to do what 2 things?

A

-Steer pulses in various directions
-Initiate pulses at various starting points across the array

20
Q

Do greater curves (longer time delays) place the focus closer or farther to the probe?

A

Closer - shallower

21
Q

Do smaller curves (shorter time delays) place the focus closer or farther from the probe?

A

Farther - deeper

22
Q

List 2 ways we can change the focus in the lateral plane?

A

-By changing the applied delay profile for a shallower or deeper focus
-By changing the dynamic aperture (# of active crystals)

23
Q

Does a smaller NZL place the focus closer or farther?

A

Closer

24
Q

Does a larger NZL place the focus closer or farther?

A

Farther

25
Q

Is a smaller aperture (group of crystals) used with a short or long NZL?

A

Short

26
Q

Is a larger aperture (group of crystals) used with a short or long NZL?

A

Long

27
Q

What is dynamic focusing?

A

Continual changing of the reception focus to receive echoes from deeper locations

(think of how the focus always changes with a video camera)

28
Q

As the focus continues to change during echo reception with array probes, will the aperture increase or decrease to maintain a constant focal width?

A

Increase

29
Q

Do 1D or 2D array probes have a fixed elevation focus?

A

1D

30
Q

Electronic focusing eliminates the need for what?

A

A lens or curved elements

31
Q

How many rows of elements are needed so phasing can be applied to focus the 3D electronically?

A

At least 3 rows

32
Q

Manual focusing can be achieved in the 3D with what?

A

A lens or curved elements

33
Q

Explain 2D arrays?

A

-Are 2D b/c the elements are positioned in 2 dimensions
-Has the ability to steer + focus beam in 2 dimensions
-Has a hundred to thousands of elements
-Biplane imaging + 3D volume imaging facilitated

34
Q

What are invasive probes for?

A

-To enter vagina, rectum, esophagus or a blood vessel
-To get closer to anatomy of interest
-Is higher frequency which improves resolution

35
Q

What is grating/side lobe artifacts?

A

-Is created by weaker peripheral/side beams reflecting off a strong reflector
-It is additional weak beams from multi element probes
-U/s assumes the reflector came from the main beam + places the reflector laterally to the true one

(think of GB)

36
Q

How can grating/side lobes be reduced?

A

-Apodization (driving the elements with different voltages across the aperture)

-Elements in middle of the aperture have higher amplitude, whereas elements at the periphery have less amplitude

MIDS 139 (Core Exam) (16 decks)

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