Physics Flashcards 1

Front 1

What is a transducer

Back 1

Any device that converts one form of energy to another

Front 2

Ultrasound transducers...

Back 2

Convert electric energy to acoustic energy and acoustic energy back to electric energy when recieving the echoes back from the body.

Usually use man made lead zirconate titanate (PZT) or barium titanate

Front 3

Piezoelectric Effect

Back 3

1. US machine sends electric signal to the transducer

2. Active element vibrates which sends a mechanical disturbance into the body

3. Medium begins to vibrate which sends echoes back to the transducer.

4. Active elemnt converts vibrations into electric impusles which gets sent to the machine to form images.

Front 4

Curie Point

Back 4

365 degrees. Makes the trasnsducers piezoelectric

Front 5

Damping Element

Back 5

Bonded to the back of the active element. Limits ringing of the crystal .

Front 6

Damping Element 2

Back 6

1.Shortens SPL and range resolution and pulse duration.

2. Improves image quality

3. Increases bandwidth

4. Decreases the Quality Factor (Q)

5. Decreases the transducers sensitivity to reflected echoes.

Front 7

Bandwidth

Back 7

Range of frequencies within the pulse

Front 8

Matching Layer

Back 8

1.Reduces reflections at transducer-tissue interface.

2. Usually 1/4 the wavelength of the ultrasound beam

Front 9

Matching Layer 2

Back 9

1. Used to reduce the impedence difference between the transducer and the element and the skin itself.

2. Helps send more US energy into the body rather than reflecting it because of the impedence difference. Gel also helps reduce the impedence difference.

Front 10

Impedence Range

Back 10

Highest- PZT (Element, transducer)

Mid- Matching Layer
Mid- Gel
Lowest- Skin

Front 11

Wire

Back 11

1.Connected to the transducer element to send the voltage to it or receive the voltage from it.

2.Wire sends an electric voltage to the transducer; this voltage deforms the crystal and causes it to vibrate.

Front 12

Case and Insulation

Back 12

Plastic or metal housing surrounding all of the transducer componets.

Prevents electrical noise from altering the transducer performance

Protects the transducer parts

Protects patients from electricl shock

Front 13

Resonant Frequency

Back 13

The operating frequency of a transducer.

Depends on:
1.Thickness of the crystal
2. Speed of sound in the crystal

Front 14

Frequency

Back 14

Directly related to speed of sound in the crystal.
-Higher speed=higher frequency
-Lower speed= lower frequency

Indirectly related to crystal thickness.
-Thinner crystal-higher frequency
-Thicker crystal-lower frequency.

Front 15

Bandwidth

Back 15

Difference between the highest and the lowest frequency in a pulse.

The shorter the pulse, the wider the bandwidth.

Front 16

Short Pulse Duration
(Shorter SPL, Better Axial Resolution)

Back 16

Wide Bandwidth
More Listening Time
Better Image
Wider Range of Frequencies

Front 17

Long Pulse Duration

Back 17

Narrow Bandwidth

Front 18

Advantages of Wide Bandwidth

Back 18

Fewer Cycles per pulse give longer listening time

Can recieve a wider range of frequencies

Lower Quality Factor and better images

Front 19

Disadvantage of Wide Bandwidth

Back 19

Decreased probe sensitivity

Element is not responsive to the returning sound waves.

Front 20

Quality Factor

Back 20

Another measure of frequency bandwidth

The ratio of the transducer frequency to its bandwidth

Higher quality factor transducers have narrower frequency bandwidths and poorer axial resolution (Poorer Image)

Front 21

Near Zone
(Fresnel Zone)

Back 21

Region between the transducer and the focus.

Determined by the size and operating frequency of the element.

Increases with increasing frequency,element size, or diameter squared

Larger crystal diameter, longer focal length

Higher frequency,longer focal length

Front 22

Focal Depth

Back 22

Larger the crystal diameter, the farther or deeper the beam focus

Smaller the crystal diameter, the shallower the focus or focal depth

Front 23

Far Zone
(Fraunhofer Zone)

Back 23

Region that lies beyond the distance of one near zone length

Place where the beam begins to diverge

Beam intensity tends to drop off here but it is also more homogeneous

Front 24

Beam Width Depends on:

Back 24

Frequency
Aperture (size of the source)
Distance from the transducer

Front 25

Frequency and Diameter

Back 25

Directly proportional to near zone length:
-increasing frequency or diameter increases near zone length

Inversely proportional to divergence:
-Smaller frequency or diameter, more divergence

Front 26

Diffraction

Back 26

When sound waves are produced by a small source they diverge or spread as sound propagates

Front 27

Huygen's Principle

Back 27

The tiny wavelets not only interfere, but combine to produce a sound beam with most of the energy transmitted along a main, central beam having the shape of an hourglass.

Front 28

Divergence

Back 28

Smaller Crystals have more divergent beams

larger Crystals have less divergent beams.

Front 29

PZT Crystals and Beams

Back 29

Larger Crystal Diameter=Less Divergence

Increased Propagation Speed=Increased Frequency

Decreased Frequency=Increased Divergence

Increased Frequency=Decreased Divergence

Smaller Crystal Diameter=More divergence

Front 30

Axial Resolution

Back 30

Comes from beam's axis

The minimum distance 2 structures are seperated from front to back, and still be distinguished as seperate by the ultrasound machine.

Parallel to the beam

Determined by the SPL.
Shorter SPL gives better Axial Resolution

Front 31

Lateral Resolution

Back 31

Best at the focus of the beam because diameter is smallest there

Improved by focusing

Determined by scan plane width or beam diameter

Front 32

Elevational Resolution

Back 32

Third Dimension

Thinnest Slice is better